NL8001845A - METHOD FOR THE MANUFACTURE OF ANISOTROPE MEMBRANES AND MEMBRANES MADE THEREFORE - Google Patents

Description

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Methods for the production of anisotropic membranes as well as membranes thus manufactured.

The invention relates to processes for the production of anisotropic membranes, in particular hollow fiber membranes. Particularly attractive sides of the invention are processes for the manufacture of polysulfone hollow fiber membranes suitable for the separation of gases, wherein the material of the hollow fiber membrane effects separation by selective permeation and anisotropic polysulfone hollow fiber membranes.

The suitability of using membranes for the separation of fluids compared to other separation methods such as absorption, adsorption and liquefaction often depends on the cost of the equipment and its use including energy consumption, the degree of selectivity of the separation desired, the total pressure losses caused by the equipment for performing the separation method that may be allowed, the useful life of such equipment, and the size and ease of use of such equipment. Therefore, membranes are desired which provide the desired separation selectivity, flow and strength. In addition, in order to be industrially attractive on an economic basis, the membranes should preferably be able to be manufactured in large quantities while obtaining reliable product quality and they can be easily and relatively cheaply arranged in a permeator. Particularly suitable membranes are one-piece anisotropic hollow fiber membranes, which have a relatively thin layer (often referred to as separating layer, boundary layer or active layer) which forms one piece with a porous structure, which supports the separating layer and little or no resistance to the passage of f louda. To form these unitary anisotropic membranes, a unitary membrane structure must be prepared containing diametrically opposed structures. The separating layer must be shaped to be thin and have little or no pores or other defects. On the other hand, the conditions under which the unitary anisotropic membrane is manufactured must also provide a support structure which is very open so that it has little resistance to the flow of volume.

Membranes are made in film and in hollow fiber form. Many proposals have been made with regard to the production of single-forming anisotropic membranes in film form. Generally, anisotropic film membranes are prepared by pouring a solution of the polymer to form a membrane in a solvent on a surface, e.g. a polished glass surface. The polymer can be coagulated, at least in part, in the air or in a gas or vapor environment, and then it is usually immersed in a liquid coagulant. There is considerable flexibility in the manufacture of anisotropic film membranes. Since the polymer solution is supported, the membrane precursor structure, e.g. not to be self-supporting, at least until after coagulation is complete. Also, because one surface of the molded membrane is in contact with the support, each side of the membrane can be subjected to different coagulation conditions, making it possible to obtain essentially different structures on both surfaces of the membrane. Therefore, membranes 30 can be obtained with a relatively thin layer, which have virtually no pores on one surface of the film membrane, while the rest of the membrane is relatively porous. In addition, since the film membrane precursor is supported, the coagulation conditions, including the coagulation times, can be varied considerably to obtain the desired film membrane structure.

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However, in some instances, film membranes may not be as attractive as other gas separation equipment due to the need to support film membranes to withstand operating conditions and the overall complexity of the equipment containing film membranes. Membranes in the hollow fiber configuration can avoid some shortcomings of film membranes for many separation operations.

The hollow fibers are generally self-supporting, even under operating conditions, and can provide a greater amount of membrane surface area per unit volume of the separation equipment than that provided by membrane films. Therefore, separation equipment containing hollow fibers can be attractive from the viewpoint of ease, size and reduced complexity of their design.

Many more different considerations play a role in the manufacture of a film membrane than is the case in the manufacture of a hollow fiber membrane. For example, e.g. no solid support, or intermediate surface are provided in a method of spinning a hollow fiber membrane. In addition, in spinning methods, the polymer solution must be sufficiently viscous to provide a self-supporting extrudate before and during the coagulation, and the coagulation must be carried out itself after the extrusion, such that the hollow fiber membrane is not adversely affected.

Methods of manufacturing unitary anisotropic membranes must not only meet the criteria for manufacturing unitary anisotropic hollow fiber membranes, but must also be compatible with hollow fiber spinning capability. Hence, there are many barriers to the techniques available to manufacture unitary anisotropic hollow fiber membranes. Usually, in hollow fiber membrane spinning methods, a solution of the polymer to form the hollow fiber membrane in a solution is extruded through a spinneret suitable for forming a hollow fiber structure, and a gas or liquid is introduced into the bore of the hollow fiber extrudate so that the hollow fiber 800 1 8 45 configuration can be maintained. The hollow fiber extrudate must be quickly coagulated, e.g. by contact with a non-solvent for the polymer, so that the hollow fiber configuration can be maintained. The hollow fiber spinning process contains many variables that can affect the structure or morphology of the hollow fiber membrane, such as the conditions of the polymer solution when extruding from the spinneret, the nature of the fluid entering the bore of the hollow fiber membrane extrudate maintained, the environment to which the exterior of the hollow fiber extrudate is subjected, the rate of coagulation of the polymer in the hollow fiber extrudate and the like. Since the hollow fiber formation process relies on coagulation of polymer from a polymer solution, the nature of the polymer solvent can have a great influence on determining the morphology of the hollow fiber membrane and its separation properties.

The solvent must have many properties to be suitable for the production of anisotropic membranes (in particular anisotropic hollow fiber membranes). The solvent (or solvent containing a liquid carrier) must be e.g. be able to dissolve the polymer to form the hollow fiber membrane, but still allow the polymer to coagulate easily to form the anisotropic structure. In addition, if hollow fiber membranes are desired, the solvent (or a liquid carrier-containing solvent) must provide the ability to prepare a polymer solution of suitable viscosity to form the hollow fiber membrane and it is advantageous if these viscosities can be obtained without using exceptionally high polymer concentrations in the solution. Since suitable hollow fiber membranes are often obtained when the extrudate undergoes a significant drop in temperature when dispensing from the spinneret, the liquid carrier should provide suitable hollow fiber viscosities for operating at elevated temperatures, because elevated temperatures provide the appreciable temperature drop facilitates. The solvent 80 0 1 8 45 • f y 5 \ or any other component of the liquid carrier should not undergo degradation at such elevated temperature.

The solvent should be miscible with non-solvent used to promote coagulation of the polymer and be capable of being removed, e.g. by washing, from the coagulated structure, so that the membrane is not excessively softened and thereby weakened by the solvent. In addition, the solvent (or a liquid carrier-containing solvent) should not exhibit excessive heat of dilution in the non-solvent used to promote coagulation of the polymer.

In order for a method to be attractive for the production of commercial quantities of membranes, it is also desirable that the method be safe and economical. Therefore, the solvent 15 should not be excessively toxic and preferably has a very low vapor pressure to minimize the risk of inhalation and / or air pollution. Moreover, with a solvent with a very low vapor pressure, the risk of explosion and fire is also minimized. In addition, waste-20 materials from the spinning process must be able to be discarded or recycled economically and safely.

Since the solvent is only a constituent used in spinning, other constituents, such as fluid in the bore of the hollow fiber extrudate, non-solvent that aids in coagulation, must be solvent-removing washings hollow fiber membranes and the like are also economical and safe. So far proposals have been made to e.g. gasoline, kerosene or other hydrocarbon materials to be used in spinning, either as coagulants or to aid in drying, as described in U.S. Patent 4,127 * 625

Such materials clearly cause toxicity and fire risks as well as disposal problems. In addition, in the amounts necessary to e.g. coagulation, scrubbing and the like, the cost of the hydrocarbon materials is a factor in the spinning process economy. Therefore, it is desirable to use very safe, readily available materials, such as water, where it is needed in the spinning process, especially as a non-solvent to aid in coagulation and washing to remove solvent from the hollow fiber membrane. The ability to use water depends, of course, to a great extent on the properties of the solvent to water, i.e., water solubility, heat of dilution in water, stability in water and the like.

In accordance with the invention, there are provided methods for the manufacture of anisotropic membranes using certain beneficial solvents. The methods of the invention can provide anisotropic membranes that have a very thin separating layer with relatively few pores in an underlying region with an open cell structure, which has little resistance to fluid flow. These membranes can be particularly attractive for gas separations. In addition, the polymers that can be used in accordance with the invention to provide membranes include polysulfones that have the desired strength and chemical resistance as well as the desired permeation properties expressed in permeate flow and selectivity. The methods of the invention can successfully use water as a non-solvent to assist in coagulation of the polymer and to wash solvent from the membranes. In addition, the solvents have a. low vapor pressure, do not cause excessive risk of explosion or fire and can be discarded or recycled economically and safely.

In accordance with the invention, an anisotropic membrane is made from a solution of membrane-forming polymer and a liquid carrier, which consists of an N-acylated heterocyclic solvent of formula 1, wherein X is a group -CHg-, -N (R ') - or - 0-; R is hydrogen, a methyl or ethyl group, and R 'is hydrogen or a methyl group. The polymer solution is provided in the form of a precursor and is then coagulated in a liquid coagulant containing water to form the anisotropic membrane. The anisotropic membrane can be a film or, preferably, a hollow fiber. Typical N-acylated heterocyclic solvents are 1-formyl-piperidine, 1-acetylpiperidine, 1-formyl morpholine and 1-acetyl morpholine. A preferred ... N-acylated heterocyclic solvent 5 consists of 1-formylpiperidine. In the brochure "1-Formylpiperidine" from Reilly Tar & Chemical Corporation, it is stated that 1-formyl-piperidine a kpt. of about 222 ° C, a vapor pressure of 0.111 mm of mercury at 25 ° C, a self-ignition point of 102 ° C and an LD 3 (oral rat) of 0.88 g / kg body weight.

In the methods of the invention which relate to the manufacture of hollow fiber membranes, the polymer solution has a suitable temperature to essentially keep the fiber-forming polymer in solution and provide the polymer solution at a fiber-forming viscosity prior to extruding the hollow fiber precursor. . The polymer solution is extruded through a ring spinneret to form a hollow fiber precursor. A fluid is injected into the bore of the hollow fiber precursor as it is extruded from the spinneret at a rate sufficient to keep the bore of the hollow fiber precursor open. The injection fluid is preferably very miscible with the liquid carrier and therefore often consists of water. The hollow fiber precursor is then contacted with the liquid coagulant, which is a non-solvent for the polymer in the polymer solution. The liquid coagulant is preferably very miscible with the liquid carrier and the injection fluid. Usually the temperature of the liquid coagulant is low enough that the polymer solution at that temperature is very viscous and may even be a gel. The contact of the hollow fiber precursor with the liquid coagulant lasts long enough to substantially coagulate the polymer in the hollow fiber precursor under the conditions of the liquid coagulant and thereby provide a hollow fiber. The hollow fiber is then washed, ie contacted with a non-solvent containing water, to extract from the polymer, which is miscible with the liquid carrier, the content of 80 0 1 8 45 8 of liquid carrier in the hollow fiber to less than 5% by weight, based on the weight of the polymer in the hollow fiber. The washed hollow fiber can then be dried at a temperature at which the selectivity or flow exhibited by the hollow fiber is not undesirably affected.

In accordance with the invention, the hollow fiber membranes preferably have a substantially circular cross section with circular concentric bores. In many instances, the hollow fiber membrane can be circular and concentric within the tolerances of the machining required to produce suitable spinnerets. The outer diameter of the hollow fiber membrane can vary widely, e.g. from 100 or 150 to 1000 or more um. Often the outside diameter of the hollow fiber membrane is 200 or 300 to 100 µm.

The ratio of the thickness of the wall to the outside diameter of the hollow fiber membrane can also vary greatly depending on the required slack pressure to be applied for a given separation operation. Since the cellular support is open, an increase in wall thickness cannot lead to an excessive reduction in flow through the membrane wall. Characteristic ratios of the thickness to the outer diameter are 0.1 or 0.15 to 0.005, usually from 0.15 to 0.005.

The hollow volume of the hollow fiber membranes, i.e. the areas within the wall of the hollow fiber membrane in which no material of the hollow fiber membrane is contained, is substantial. The hollow volume can be determined by a density equation with a volume of the bulk polymer (or other material of the hollow fiber) corresponding to a hollow fiber 30 having essentially the same external physical dimensions and configurations as the wall of the hollow fiber membrane. Since the cellular support of the hollow fibers is open, relatively small hollow volumes can be obtained for anisotropic hollow fiber membranes without excessively low permeate flow.

Often the hollow volume is at least 30 to 35> e.g. at least UO, usually more than ^ 5 or 50 vol. #, and can go up to 65 800 1 8 45% Λ 9 or 70 or even more vol. 5¾.

The liquid carrier may consist essentially of the solvent or the solvent may be mixed with one or more other ingredients to provide the liquid carrier. The other ingredients may be solid or liquid at room temperature, but are dissolved in the liquid carrier. In many cases, especially when the precursor has been exposed to the atmosphere prior to coagulation of the polymer, it is preferred that the liquid carrier (including optional diluent) be substantially non-volatile, e.g.

The liquid carrier preferably has essentially no component (solvent or diluent) with a vapor pressure of more than 0.8, more preferably 0.6 at, at the temperature at which the polymer solution is extruded. However, when a volatile component is used in the liquid carrier, the precursor is exposed to an atmosphere prior to contacting with a liquid coagulant, and the atmosphere to which the precursor is exposed may advantageously contain significant amounts of a such a volatile component in order to delay the loss of the precursor component. Gaseous components are generally avoided but may be of use, especially when the precursor is immediately contacted with the liquid coagulant. The ingredients are preferably compatible with the solvent and the liquid coagulant. Often the other ingredients are very soluble in the N-acylated heterocyclic solvent, e.g. at least 50, preferably 100 parts by weight can be dissolved in 100 parts by weight of the N-acylated heterocyclic solvent at room temperature (about 25 ° C) and the other ingredients are preferably miscible in all proportions with the N-acylated heterocyclic solvent and the liquid coagulant.

Ingredients other than the N-acylated heterocyclic solvents that may be useful in the liquid carrier are solvents such as dimethylacetamide, dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide; viscosity modifiers, 80 0 1 8 45 10 such as isopropylamine; surface active agents; plasticizers and the like. A particularly useful component for the liquid carrier is a diluent, which can be a solvent or non-solvent for the polymer. Preferably, the acylated heterocyclic solvent constitutes at least 50, more preferably at least βθ wt% of the liquid carrier.

The use of diluents can provide particularly attractive liquid carriers to provide certain solvent actions with the individual polymer molecules, so that often the polymer can be coagulated or solidified from the polymer solution with little or no change in energy. According to our theory, the behavior of the polymer molecules in solution is influenced not only by the interaction between the polymer molecules, but also by the influence of the solvent (and liquid carrier) on the polymer molecule.

According to the theory as described by Flory, Principles of Polymer Chemistry (1953) »chapter XIV, pp. 595-639» the molecular dimension of the polymer in a given solvent-polymer system remains at a certain temperature, without disturbance of the intramolecular interactions . As the temperature increases from this particular temperature (theta temperature), the polymer swells in the solution. The greater the "swelling" of the polymer molecule at a reference temperature, the better is the solvent for the polymer at that reference temperature. When the temperature is raised from theta temperature, a polymer molecule with molecular weight. infinite stiffening or precipitation, i.e., the intramolecular forces of the polymer molecule are greater than the forces between the solvent and the polymer molecule.

A meaningful assessment of a liquid carrier polymer system can be made by viscosity measurements on a very dilute solution of the polymer in the liquid carrier in order to determine the intrinsic viscosity (the ability of the polymer to increase the viscosity of a solution) ( e.g.

35 at 25 ° C or remain consistent, although other temperatures can also be used as long as it is consistently used) 800 1 8 45 11 and the intrinsic viscosity of the polymer at the theta temperature (intrinsic theta viscosity). The ratio of the intrinsic viscosity to the intrinsic theta viscosity (hereinafter referred to as "intrinsic viscosity ratio") is indicative of the action of the solvent (liquid carrier) on the polymer molecules. The intrinsic viscosity for a given liquid carrier polymer system is obtained for determining the viscosity of the polymer system ('Tj) at a number of differently diluted polymer concentrations. The viscosity of the liquid carrier (I) Q) is also determined at the same temperature. The ratio of η: ηο is the relative viscosity and plotting a natural logarithm of the relative viscosity divided by the polymer concentration against the polymer concentration yields the intrinsic viscosity when extrapolating to a polymer concentration of zero. The diluted polymer solutions used are suitably selected to provide relative viscosities from about 1.1 to 2.5. In order to determine the intrinsic viscosity of the polymer at the theta temperature, various techniques can be used, as described by Flory, supra, pages 612-622. The intrinsic viscosity of the polymer in a theta solvent at the theta temperature can be e.g. are determined by viscosity measurements as described above. Theta solvents and theta temperatures for many polymers can be found in the literature, see e.g.

25 Brandrup, et al., Polymer Handbook. 2nd Ed. (1975), pp. IV-157 to IV-173. If necessary, theta solvents and temperatures can be determined by any of the techniques or described by Brandrup et al. On pages IV-157 to IV-159 · The temperature of the polymer solution during the viscosity determination should be maintained as accurately as possible at the theta temperature since the intrinsic viscosity of many polymer solutions changes rapidly at temperatures close to the theta temperature. Instead, the intrinsic theta viscosity can be estimated using a light scattering technique to determine the second transition coefficient of the polymer in a solvent at different temperatures. A suitable method is described 80 0 1 8 45 12 by Kaye in "Low Angle Laser Light Scattering", Analytical Chemistry, 1 * 5 (1973), Liz. 221 - 225 and is based on determining the amount of light scattering from a laser beam passed through the polymer solution at different temperatures. See e.g. Stacy, Light Scattering in Physical Chemistry (195 ^), biz. 117 ff, for a description of the relationship between light scattering and the second transition coefficient. Care should be taken to remove all solids from the polymer solution e.g. by filtration, which can affect the light scattering data. The intrinsic viscosity of the polymer is obtained at any temperature, the second transition coefficient being determined, and an expansion of the intrinsic viscosities and second transition coefficients can be performed and extrapolated to the point where the second transition coefficient is zero. The intrinsic viscosity on this pmit is the intrinsic theta viscosity. The method for determining the intrinsic theta viscosity is an approximation. However, such an approach may still be useful in providing a suitable polymer-liquid support system 20 for use in accordance with the invention for manufacturing a hollow fiber membrane from a polymer. In general, suitable polymers in the liquid carriers of the invention provide dilute solutions exhibiting an "intrinsic viscosity ratio" of 1.05-1.7, e.g. 1.05 - 1.5 and usually 1.1 - 1.5.

The second transition coefficient of the liquid carrier / polymer system can similarly be used to determine suitable liquid carrier / polymer systems. The second transition coefficient exhibited by many useful liquid carrier / polymer systems is often below 15, e.g. below 12, such as below 10 mol.cm ^ / g ^ (multiplied by 10 ^) (at 25 ° C). The second transition coefficient for the liquid carrier / polymer systems often exceeds 0.5, e.g. above 1 and sometimes above 3, e.g. 3 and 8 mol.cm ^ / g ^ (multiplied by 10 ^) (at 25 ° C).

Another useful method for determining liquid support / polymer systems that may be suitable for providing hollow fiber membranes according to the method of the invention is the interaction parameter described by Blanks et al in "Solubility of Styrene -Acrylonitrile Copolymers, "Structure-Solubility Relationships in Polymers, ed. Harris et al.

5 {1977) biz · 111 - 122. The interaction parameter (A ^) can be represented by:

Aip = (V / RT) («f, -S) 2 + 0.25 ^ (^ - S) 2 + (J -S) 2J

12 n d, p d, s p, p p, s h, p h, g 3

10 wherein V is the mol volume of the solvent in cm / mol; R

m is the gas constant (12 cal / ° K.mol); T is the temperature in K; tf, and the (London) dispersion force component of the d, d, "p" s "1 solubility parameter, (cal / cnr) 5 of the polymer and the solvent, respectively; <f and -f are the polar bond P * p P, s 3 1 terms of the solubility parameter (cal / cnr) 5 of the polymer and the solvent, respectively; and £, and

N

i are the hydrogen bonding terms of the solubility n, s O 1 20 parameter (cal / cnr) 2, of the polymer and the solvent, respectively. The total solubility parameter («5 ^) can be defined as: i 2.J 2 + i 2 + i 2.

T d p h 25 Solubility parameters are suitably used to characterize liquid carriers and solutes and values for solubility parameters and components are often found in the literature, see e.g. Shaw, "Studies of Polymer-Polymer Solubility Using a Two Dimensional Solubility Parameter Approach," 30 J. of Applied Polymer Science. 18, biz. hh9 - h72 (197 * 0 »and Brandrup, et al., The Polymer Handbook, 2nd ed. biz. IV-337 to TV-359 (which also describes experimental techniques for obtaining solubility parameters and components). The components of the solubility parameter which are used to calculate the interaction parameter for a liquid carrier containing more than one constituent can be estimated on a volume fraction average basis, this estimate is an approximation, because in many cases the volume of the components of the liquid carrier are not additive Often 5, the exchange parameter at 20 - 30 ° C of the polymer and the liquid carrier is less than 0.5, eg less than 0.3. The exchange parameter is generally at least 0 , 01, preferably at least 0.02, eg at least 0.05 ·

Also, the liquid carrier preferably has a solubility parameter that is approximately equal to (i.e. within 5 or 10% of) the solubility parameter of the polymer or more. In many instances, at least one of the polar bond term and the hydrogen bond term of the solubility parameter, and sometimes both, is greater (i.e., no more than) 0.5 e.g. more than 0.3 (cal / 15 cnr) 2, below the corresponding term for the polymer. Suitable membranes can be made from polymer solutions in which the addition of liquid coagulant, even in very small amounts, does not significantly improve the solvent's ability to dissolve the polymer. Often the polymer bond term and the hydrogen bond term of the liquid carrier solubility parameter are each greater than the corresponding terms of the polymer solubility parameter.

Often the surface tension of the liquid carrier 25 is within 10, e.g. 5 or 7, dynes / cm of the surface tension of the polymer at room temperature (25 ° C). Generally, when the liquid carrier / polymer system in a dilute polymer solution exhibits a suitable "intrinsic viscosity ratio", second transition coefficient and interaction parameter, it exhibits a surface tension close to the surface tension of the polymer. Often useful liquid carriers exhibit a surface tension at room temperature (25 ° C) of less than 3-5 dynes / cm above the surface tension of the polymer. Surface 35 stresses for polymers can be determined experimentally by any conventional method and one of these methods is described by Tanny in J. of Applied Polymer Science, vol. 18, pp. 2153-2151 * (1971 *).

Frequently, the liquid carriers used in the process of the invention contain a diluent 5 which is a non-solvent for the polymer. Non-solvents are generally characterized in that they exhibit little ability to dissolve polymer, e.g., the polymer solubility is less than 10, such as less than 2, and often less than 0.5g / 100ml of non-solvent. The non-solvent preferably exhibits little or no swelling action on the polymer. The non-solvent, when added in sufficient amount, is usually capable of effecting a phase separation of the polymer solution. Preferably, the non-solvent is not added in an amount such that the polymer solution 15 is excessively unstable under the processing conditions prior to precursor formation. Often the amount of non-solvent in the liquid carrier is at least 2, e.g. at least 5 parts per 100 parts by weight of liquid carrier.

Suitable non-solvents can be the liquid coagulant or one or more components of the liquid coagulant. Some desirable solvents can keep the polymer in solution in the presence of at least 5 e.g. at least 10% by weight of the liquid coagulant, based on the weight of the solvent (e.g., at 25 ° C). Preferably, however, the addition of relatively small amounts of liquid coagulant to a solution of the polymer and the liquid carrier results in phase separation or solidification of the polymer solution.

Typical diluents including non-solvents are formamide, acetamide, ethylene glycol, water, trimethylamine, triethylamine, isopropylamine, isopropanol, methanol, nitromethane, 2-pyrrolidone, acetic acid, formic acid, aqueous ammonia, methyl ethyl ketone, acetone, glycerol. Low molecular weight inorganic salts such as lithium chloride, lithium 35 bromide, zinc chloride, magnesium perchlorate and lithium nitrate can also be used in the liquid carrier.

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A sufficient amount of polymer is present in the polymer solution to allow the precursor to be formed. Therefore, to prepare a hollow fiber membrane, the polymer concentration is sufficient such that the polymer solution has a fiber-forming viscosity at the temperature of the polymer solution when it is formed (i.e., extruded) into a hollow fiber precursor. Excessively low viscosities can lead to breakage of the hollow fiber precursor and the inability to maintain the desired hollow fiber configuration. High viscosities are desirable, but excessively high viscosities may be undesirable because of the pressures required to extrude the polymer solution. Often the viscosity of the polymer solution to be extruded is at least 5000, often at least 10,000 cp, and may even be as high as 500,000 or 1,000,000 cp at the extruding temperature. Many attractive hollow fiber membranes are manufactured using polymer solution viscosities at the extruding temperature in a range of 10,000-500,000 cp. In some cases, sufficient polymer may be present in the polymer solution that at the temperature of the liquid coagulant, the polymer solution obtains an essentially non-flowing structure, e.g. becomes particularly viscous or undergoes a physical change, e.g. forms a gel (ie, an elastic structure, in which at least a portion of the polymer is insoluble in the liquid carrier and liquid carrier is trapped in the cavities) or results in a phase separation.

The polymer concentration of the polymer solution is suitably high enough to ensure that the membrane contains enough polymer to provide the desired high strength of the membrane. When the polymer concentration of the polymer solution is low, large cavities, including large cells and macro-cavities, can occur in the membrane wall, resulting in a low strength wall structure. At higher polymer concentrations, the hollow fiber wall formed is generally dense and macro-cavities are generally less common, so that the hollow fiber membrane can exhibit greater strength.

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Macro cavities are large cavities with a main dimension of more than 3 µm. Preferably, a sufficiently high polymer concentration is used that little or no macro-cavities are formed under the coagulation conditions. Since the invention can successfully provide an open cellular structure in the membrane wall, the increase in polymer density can be achieved with little or no reduction in flow through the matrix of the membrane wall. The maximum polymer concentrations that can be used in the polymer solution are generally determined on a practical basis by the ability of conventional equipment to form membranes from highly viscous polymer solutions. The maximum preferred concentrations of polymer in the polymer solution will also depend on the nature of the polymer and the liquid carrier. In polymer with 15 low molecular weight. can e.g. higher polymer concentrations are preferred for use than is the case for high molecular weight polymers. Often times, the polymer concentration is at least 25% by weight, based on the polymer solution. Polymer concentrations of up to 5 or 50% by weight may be useful in some cases. Polymer concentrations of 28 or 30 to 38 or 40% by weight are desirable in most cases.

Often the viscosities of the polymer solutions used in accordance with the invention are of relatively high activation energy. An activation energy is a relationship between temperature and viscosity and this relationship can be represented as:, E / RT η * A, e where η is the viscosity of the polymer solution, E is the activation energy, R is the gas constant (about 2 cal / ° K, mol) is 30 and T is the temperature (° K). See Art, et al., Fifth

International Symposium on Fresh Water from the Sea, vol. h (1976). The slope of a plot of the logarithm of the viscosity (in poise) against the reciprocal absolute temperature (° K ~) is generally linear and from that slope the activation energy 35 (cal / mol) can be read approximately. Often the activation energy is at least 8 kcal / mol, e.g. 8.5 - 15, such as 800 1 8 45 18 9 - 12, usually 9.5 - 12 kcal / mol. Usually, the desired liquid carriers containing a non-solvent as a diluent take the activation energy. at an increased concentration of the non-solvent.

The polymer solution can be prepared in any suitable manner, e.g. the liquid carrier can be added to the polymer, the polymer can be added to the liquid carrier, or the polymer and the liquid carrier can be combined simultaneously. The liquid carrier, when it consists of more than one component, can of course be mixed with the polymer on a component after component basis. When the liquid carrier e.g. consisting of a solvent and a non-solvent, the polymer can be successfully mixed with the solvent prior to the addition of the non-solvent. When the non-solvent is added after dissolving the polymer and the solvent, the non-solvent is generally added slowly so that the local areas of elevated non-solvent concentrations are minimized in order to coagulate or precipitate avoid the polymer in such local areas. Elevated temperatures can be used to facilitate mixing of the polymer and the liquid carrier. However, the temperature should not be so high as to adversely affect one or more of the components of the solution to be formed. The time required to complete the mixing to obtain a polymer solution can vary widely depending on the dissolution rate of the ingredients, the temperature, the efficiency of the mixing equipment, the viscosity of the polymer solution to be prepared and the like.

It is desirable to continue mixing the polymer solution until a substantially uniform composition is obtained throughout the polymer solution. Any suitable mixing equipment can be used in preparing polymer solutions suitable for use in accordance with the invention.

Preferably, the mixing equipment does not cause excessive air entrapment in the polymer solution in order to facilitate any subsequent degassing of the polymer solution. Often "components of the polymer solution have significant volatility under the mixing conditions. These volatiles may cause excessive risk from the standpoint of fire and health hazard, and the loss of volatiles will also lead to alteration of the polymer solution composition. Therefore, in most cases the mixing of Hetj polymer and the liquid carrier is carried out in a closed vessel. An inert atmosphere can be provided in such closed vessels. The polymer solution components may be adversely affected when exposed to atmospheric conditions ( eg with air present). The total pressure of the atmosphere in the mixing vessel is preferably relatively low in order to minimize any dissolution or entrapment of the inert atmosphere in the polymer solution during the formation of the polymer solution. Wed. a pressure lower than 2 or 3 at is absolutely used.

Often the polymer solution contains trapped or dissolved gases, and these gases can lead to the formation of anomalies, e.g. macro-cavities, in the membranes. Therefore, it is generally desirable to subject the polymer solution to a degassing operation. Preferably, the polymer solution is substantially free of entrapped or dissolved gases prior to extruding the hollow fiber precursor. Any suitable degassing equipment and any suitable degassing conditions can be used to achieve the desired degassing. Sufficient degassing can e.g. are obtained by keeping the polymer solution in a closed vessel for a period of time sufficient to allow the entrapped or dissolved gases to escape from the polymer solution, conventional degassing equipment such as "J" tubes, centrifugal degassers, ultrasonic degassers and the like can be used in degassing the polymer solution. Since many of the polymer solutions usable in accordance with the invention have a relatively high viscosity, the polymer solution 800 in the degasser can be at an elevated temperature in order to reduce its viscosity and thereby release the entrapped or dissolved gases. At elevated temperatures at which the polymer solution can be treated and the length of time the polymer solution is at such an elevated temperature should not be so excessive as to cause adverse effects on the polymer solution or its components. Degassing can be performed at relatively low absolute pressure (i.e., vacuum) or at such higher pressure that, e.g. excessive volatilization of one of the components of the polymer solution is prevented. The pressure should not be so high as to lead to excessive dissolution or redissolving of atmospheric gases in the degasser.

Generally, degassing is preferably conducted at an absolute pressure below 2 at, and most often, degassing is conducted at reduced pressure. The degassing can be carried out in a closed vessel. An inert atmosphere can be used during the degassing operation.

The degassed polymer solution can then be used to form the membrane precursor. When transporting the polymer solution, it is preferred that the tubes and pumping equipment be designed so that gas (e.g. air) does not leak into the transport system and pass into the polymer solution. The polymer solution may contain solid impurities, such as substance, polymeric oligomers and the like, which adversely affect the membrane. The polymer solution is therefore often filtered before entering the spinneret. Preferably, the filtration is sufficient to remove virtually any solid particles larger than e.g. 50 µm in height 30 and often virtually all particles larger than 0.5 µm in largest size and are removed by filtration. Elevated temperatures can be used to provide transportation and filtering of the \. polymer solution. However, such elevated temperatures should not be so high as to lead to any deleterious influence on the polymer solution or its components.

800 1 8 45 «. 21

Often water forms a major amount of the liquid coagulant sufficient to provide a suitable strong non-solvent to effect the polymer coagulation. The liquid coagulant may e.g. at least 50, such as at least 75 and usually at least 85% by weight of water. It is advantageous if the liquid coagulant does not cause any significant swelling of the polymer.

Since water often constitutes a major amount of the liquid coagulant, the polymer preferably exhibits little or no swelling in water. Desirably, the composition of the liquid coagulant is such that the heat of dilution of the liquid carrier in the liquid coagulant is greater than -3.5, e.g. more than -3 »e.g. greater than -2.5, and often greater than -2 kcal / mol.

The absolute value of the heat of dilution of the liquid carrier in the liquid coagulant is often less than 3 kcal / mol. In many cases, the heat of dilution is in the range of -0.5 to -2 kcal / mol. The dilution heat can be determined using any conventional method and is generally determined at 25 ° C.

The liquid coagulant, especially in the manufacture of continuous fiber hollow fiber membranes, contains a liquid carrier which is removed from the precursor. The liquid carrier can degrade the non-solvent strength of the liquid coagulant. The liquid coagulant is therefore preferably replaced by fresh or recycled liquid coagulant containing little or no liquid carrier. Often the concentration of the liquid carrier in the liquid coagulant is less than 10, preferably less than 5, such as less than 2% by weight.

The liquid coagulant may contain additional ingredients such as surfactants, materials that increase or enhance the non-solvent strength of the liquid coagulant relative to the polymer, materials that promote the solubility of the liquid carrier ingredients in the liquid coagulant, materials which reduce the heat of dilution of the liquid carrier in the liquid coagulant, freezing point depressants and the like. Common additional ingredients for the liquid coagulants which can be used in the manufacture of the membranes are low molecular weight alcohols such as methanol, isopropanol, salts such as sodium chloride, sodium nitrate, lithium chloride, organic acids such as formic acid and acetic acid and the like.

The liquid coagulant is preferably kept at a temperature at which the polymer solution is virtually non-flowing. Although suitable temperatures are generally low, some polymer solutions may be substantially non-fluid at room temperature or higher. Therefore, liquid coagulation temperatures of up to about 90 ° C or higher can sometimes be used. Often, however, the temperature of the coagulant is below 35 ° C and highly desirable membranes are often made using a temperature of the liquid coagulant below 20 ° C, e.g. below 10 ° C. Usually their temperature is conveniently above 0 ° C, e.g.

20 in the range of 0-10 ° C. However, with suitable co-equipment and the presence of freezing point depressants in the liquid coagulant, temperatures of -15 ° C or less can be obtained.

The residence time of the precursor in the liquid coagulant should be sufficient to ensure that the amount of coagulation at the temperature of the liquid coagulant provides sufficient strength to the membrane for further processing. It is often desired that coagulation of the polymer in the precursor takes place within a few seconds so that the dimensions of the equipment for the coagulation stage are not excessively large. Since the exterior of e.g. the hollow fiber precursor is in direct contact with the liquid coagulant, it is generally coagulated almost immediately. In some instances, almost complete coagulation of the polymer in the precursor under the conditions of the liquid coagulant can occur almost immediately. More often, however, the precursor shows an observable transition in the liquid coagulant from a clear or translucent structure to an opaque structure. This transition can be gradual, and sometimes the course of the transition can be observed. The time for this transition under the conditions of the liquid coagulant can vary widely, but in many cases it is less than 0.001, e.g. 0.01 to 1 and often 0.02 to 0.5 sec.

In general, even after coagulation of the precursor, the membrane still contains significant amounts of liquid carrier, which may adversely affect its strength properties and may even cause coagulated polymer to be redissolved. It is therefore most convenient that the membrane be subjected to at least one washing step for further removal of liquid carrier. Often the membrane washing is carried out under substantially the same conditions (e.g. temperature) as in which the coagulation takes place. The temperature used for washing often relies on the strength of the liquid carrier-containing membrane, the useful temperature range to which the washing liquid can be subjected, and the ease of obtaining the washing liquid at such a temperature. In general, temperatures during washing should be avoided which could lead to unwanted annealing of the membrane surface. Often the temperature of the wash is in the range of 0 - 50 ° C, preferably 0 - 35 ° C. Especially when the liquid carrier and the liquid coagulant are miscible with water, suitable water is used as the washing liquid. The washing liquid can contain 30 additives, in order to e.g. promote the removal of the liquid carrier. When e.g. If water is used as a washing liquid, a water-miscible organic material (e.g., methanol or isopropanol) can help facilitate the removal of the liquid carrier.

Frequently, the liquid support content of the membrane can be easily reduced to less than 20 wt.% Of liquid 80 0 1 8 45 2b support (e.g., by passing the hollow fiber through a washing liquid for 2-5 min.). The reduction of the liquid carrier content of the membrane to desired low levels, e.g. less than 5 and sometimes less than 2% by weight of liquid carrier, however, 5 may require relatively long additional washing. This additional wash often takes at least 3 hours and can even take up to 20 or more days. The additional washing can be accomplished by continuously (rinsing) washing liquid containing little or no liquid carrier over the membrane or by soaking or storing in washing liquid. Generally, a combination of rinsing and storage is used to remove the liquid carrier from the membrane. When the membranes are stored in washing liquid, a periodic replacement of washing liquid can be advantageous if the concentration of liquid carrier in the washing liquid becomes undesirably high. Although the membranes can be stored in the washing liquid for periods of more than 20 days, usually only few additional amounts of liquid carrier are removed from the membranes after such a long storage period. Usually, the washing of the membranes 20 is continued until the liquid carrier content of the membrane is less than U-5% by weight of the membrane.

The membranes are dried after washing in order to remove the washing liquid. The presence of liquid in the anisotropic membranes can reduce the flow of groups, e.g. greatly reduces gases permeating through the membrane, and is therefore generally undesirable. Convenient drying can be accomplished by exposure to a gaseous atmosphere. Usually air is a suitable gaseous atmosphere. Usable drying conditions can vary within wide limits. Suitable drying conditions can e.g. temperatures are from -15 ° C to below 90 ° C or higher and relative humidities in the range 0-95, e.g. 5 - 60%. Often the temperature ranges from 0 - 80 ° C at an absolute humidity of less than 20 or 30, e.g. 5-15g / m2. In many cases, the drying of membranes under the prevailing laboratory conditions, e.g.

20 - 25 ° C and Uo - 60% relative humidity, acceptable.

800 1 8 45 25

Materials useful for the preparation of anisotropic membranes can be organic polymers or organic polymers mixed with inorganic substances, e.g. fillers, reinforcing agents and the like.

The method according to the invention can thus be used successfully in the manufacture of metal hollow fiber membranes in accordance with the teachings of US patent 1 *. 175 · 153 · Suitable polymers are soluble in the N-acylated heterocyclic solvents used according to the method of the invention. Desirably, at least 50 and preferably at least 100 parts by weight of polymer can be dissolved in 100 parts by weight of the N-acylated heterocyclic solvent (at 25 ° C) and most commonly the N-acylated heterocyclic solvent and the polymer are 15 proportions miscible. Even though the N-acylated heterocyclic solvent is a good solvent for the polymer and is miscible with the liquid coagulant, the polymer may still not be acceptable for membrane production if the solvent cannot be easily removed from the membrane after coagulate. When the polymer retains the solvent, the polymer structure of the membrane can be weakened to result in excessive compaction of the anisotropic structure, which leads to an undesirable decrease in the permeability of the membrane to permeating groups, e.g. gasses. In addition, when excessive amounts of solvent remain even after drying, the resulting membrane may not have sufficient structural strength to withstand the separation conditions.

Often the "intrinsic viscosity ratio" for suitable polymers in dilute solution in the N-acylated heterocyclic solvent is at least 1.05, preferably at least 1.3. Often the "intrinsic viscosity ratio" is up to 2, e.g. 1.3 - 1.75 or even 1.5 - 1.75

Often the second transition coefficient for polymer solutions containing a suitable polymer in the N-acylated heterocyclic solvent is below 20, e.g. below 8 0 0 1 8 45 2 6 15 mol.cm ^ / g2 (multiplied by 10 ^) (at 25 ° C). In many cases, the second transition coefficient is at least 3 2 0.5 »e.g. at least 1, or even at least 3 mol.cm / g (multiply by 10U) (at 25 ° C). Often the interaction parameter of suitable polymers with the N-acylated heterocyclic solvent at 20-30 ° C is less than 0.5, such as less than 0.3, and usually at least 0.005, such as at least 0.01 and sometimes at least 0, 02.

In general, it is preferred that the polymer 10 be substantially non-crystalline, e.g. less than 25% w / w, and thick since less than 1 or 2% is crystalline, because crystalline polymers usually exhibit a low permeability coefficient. However, polymers containing significant crystallinity may sometimes be desirable. Also, the polymer is often nonionic to promote the preparation of anisotropic membranes.

The polymeric material is preferably selected on the basis of its separating power, ie its ability to provide the desired separating selectivity at an appropriate permeate amperage and chemical resistance, particularly with respect to the fluid stream components desired to be treated. using the membrane.

The polymer should have a molecular weight. possess sufficient for e.g. the formation of hollow fibers. Generally, for a particular type of polymer, the longer the polymer chain, the greater the tensile strength exhibited by the polymer and the glass transition temperature of the polymer. These increases in physical properties with increasing molecular weight can often be accomplished with little or no change in the polymer's separation properties. For example, the anisotropic membrane can, by providing polymers of high molecular weight.

made stronger and is more resistant to the components of supplied streams which may adversely affect the polymer. Increased molecular weight. however, polymer generally results in an increase in the viscosity of the polymer solutions to form the precursor. It is therefore often desirable to use a polymer with an 8 0 018 45

2T

narrow molecular weight distribution, so that the polymer exhibits high strength properties without excessive viscosity increase. With a wide distribution of molecular weight. the polymer e.g. a significant amount of low molecular weight polymer molecules. but cause a high solution viscosity due to the presence of polymer molecules with considerably higher molecular weight. A suitable way to obtain the molecular weight. distribution of a polymer consists of the ratio of the average mole. wt. of the polymer by weight 10 to the numerical average molecular weight. of the polymer. The higher ratios indicate that the mole wt. distribution is wider. Often the ratio is less than 3.

The strength of the polymer should be sufficient to prevent damage to the separating layer during foreseeable handling and transportation operations when manufacturing the membrane, manufacturing a permeator containing the membrane, and installing and using the permeator. the polymer exhibit sufficient strength to withstand the operating conditions of the gas separation. The strength of the polymer can be expressed based on e.g. tensile strength, Young's modulus or the like. While these mechanical properties may each affect the overall strength of the membrane, an indication of whether the polymer has sufficient strength from considering tensile strength of the polymer can often be obtained. In general, suitable polymers for membranes have a tensile strength of at least 350, such as at least 400, and preferably at least 500, such as at least 600 kg / cm. The tensile strength can be as high as possible, but few polymers that are favorable as membrane materials

O

30 eels have a tensile strength above 2000 kg / cm. The strength of a polymer can be adversely affected by materials that e.g. dissolve, plasticize or swell the polymer. Often many suitable polymers for membrane separations are dissolved, plasticized or swollen or otherwise adversely affected by one or more materials. In some cases, industrial flows, e.g. gas streams to be treated using 800 1 8 45 28 of the separation membranes, one or more components, which adversely affect the membrane material. By using a high strength membrane material, a reduction in the strength of the material due to the presence of such deleterious components in the blends supplied is permissible, because the attenuated membrane is still resistant to the separation operating conditions.

The selective permeation of many fluids, including 10 gases, in many polymers has been described. In these described permeations, the separation mechanism apparently relies on an interaction with the material of the membrane. Therefore, high finishing separations can be obtained by using different polymers. Polyacrylo-15 nitrile makes it e.g. possible to permeate nitrogen 10 times faster than methane, while in a polysulfone membrane, methane can permeate slightly faster than nitrogen. The literature is full of information regarding the permeation properties of polymers. See e.g. Hwang, et al., "Gas Transfer 20 Coefficients in Membranes", Separation Science, vol. 9 »p.

U61 - U78 (197 ^) and Brandrup et al., Polymer Handbook, 2nd ed. Section III (1975) The suitability of a polymer for e.g. gas separation can be easily determined using e.g. conventional techniques for determining permeability constants, permeabilities and separation factors, as described by Hwang et al., in Techniques of Chemistry, vol. VII, Membranes in Separations (1975) chapter 12, p.

296 - 322.

Typical polymers suitable for making one-piece anisotropic membranes are e.g.

substituted and unsubstituted polymers such as polysulfones; polystyrenes, including styrene-containing copolymers such as acrylonitrile-styrene copolymers and styrene-vinylbenzyl halide copolymers, polycarbonates, cellulosic polymers such as cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose; polyamides and polyimides, including aryl polyamides and aryl polyimides; polyethers, polyacetal, polyarylene oxides, such as polyphenylene oxide and polyxylylene oxide; polyester amide diisocyanate; polyurethanes, polyesters (including polyarylates), such as polyethylene terephthalate, polyalkyl methacrylate, polyalkyl acrylate, polyphenylene terephthalate; polysulfides; polymers from monomers with alpha-ethylenically unsaturated bond other than polyvinyls mentioned above, e.g. polyvinyl chloride, polyvinyl fluoride, polyvinylidene chloride, polyvinylidene-10 fluoride, polyvinyl alcohol, polyvinyl esters, such as polyvinyl acetate and polyvinyl propionate, polyvinylpyridines, polyvinyl pyrrolidones, polyvinyl ethers, polyvinyl ketones, polyvinyl aldehydes, such as polyvinyl aldehydes, such as polyallyls; Polybenzobenzimidazoles, polyhydrazides, polyoxadiazoles, poly triazoles, polybenzimidazole; polycarbodiimides; polyphosphazines, and interpolymers including block interpolymers containing repeating units of the aforementioned, such as terpolymers of aerylonitrile-vinyl bromide sodium salt of 20 p-sulfophenylmethallyl ethers, and graft polymers and mixtures containing any of the above. Typical substituents that provide substituted polymers are halogens such as fluorine, chlorine and bromine, hydroxy groups; short chain alkyl groups; short chain alkoxy groups; monocyclic aryl and short chain acyl groups.

A class of polymers that can be attractive for many gas separations are copolymers of styrene and acrylonitrile or terpolymers containing styrene and acrylonitrile. Often the styrene forms up to 70 or 70 moles, e.g. 10 - 50 moles # of the total monomer and the polymer. The acrylonitrile monomer suitably forms at least 20, e.g. 20-90 and often 30-80 moles # of the polymer. Other monomers that can be used in addition to styrene and acrylonitrile to provide e.g. terpolymers are ethylenically unsaturated monomers such as butene, butadiene, methyl acrylate, methyl methacrylate and maleic anhydride. Other monomers that can be used are e.g. vinyl chloride. The copolymers or terpolymers of styrene and acrylonitrile often have an average molecular weight. on a weight basis of at least 25,000 or 50,000, such as 75,000 - 500,000 or more.

One of the preferred polymers for anisotropic membranes is polysulfone because of its strength, chemical resistance and relatively good gas separation properties. Characteristic polysulfones are characterized by having a polymer-backbone consisting of the repeating structural unit of formula 2, wherein and R 4 are each independently an aliphatic or aromatic hydrocarbyl-containing group, e.g. 1 - kO carbon atoms, in which the sulfon of the sulfonyl group is bound to aliphatic or aromatic carbon atoms and the polysulfone 15 has an average molecular weight. suitable for film or fiber formation, often at least 8000 or 10,000. When the polysulfone is not cross-linked, the molecular weight is. of the polysulfone generally less than 500,000 and often less than 100,000. The repeating units can be linked, ie Rj and Rj can be linked by carbon-carbon bonds or by different linking groups such as -0-, -S-, -CH (0) -, -CH (0) -NH- -NH-C (0) -NH-, -O-C (0) -.

Particularly suitable polysulfones are the polysulfones in which at least one of the groups R1 and Rg contain an aromatic hydrocarbyl-containing group and the sulfonyl group is bound to at least one aromatic carbon atom. Conventional aromatic hydrocarbyl-containing groups are phenylene and substituted phenylene groups, diphenyl and substituted diphenyl groups, di-phenylmethane and substituted diphenylmethane-30 groups having a nucleus of formula 3, substituted and unsubstituted diphenyl ethers of formula b, wherein X is oxygen or sulfur. In the diphenylmethane and diphenyl ether groups shown, R 1 - R 12 are substituents which are independently a group of formula 5, wherein X 1 and X 2 are independently hydrogen or halogen (eg fluorine, chlorine or bromine), p is 0 or a whole number, e.g. 1 - 6, and Z is hydrogen, halogen (eg fluorine, 800 1 8 45 31 chlorine or bromine), - (Y) - ^ ^ (where q is equal to 0 or 1, Y is a group -0-, -S-, -SS-, —0C (0) - or -C (0) - and is hydrogen, a substituted or unsubstituted alkyl group of 1 to 8 carbon atoms or a substituted or unsubstituted aryl group (eg monocyclic or bicyclic with 6- 15 carbon atoms), a heterocyclic group, wherein the heteroatom is at least one nitrogen, oxygen or sulfur atom and is monocyclic or bicyclic with 5-15 ring atoms, sulfato and sulfono, especially short chain alkyl containing mono-10 cyclic or bicyclic aryl sulfato or sulfono, phosphorus containing groups such as phosphino and phosphato and phosphono, especially short chain alkyl containing or monocyclic or bicyclic aryl containing phosphato or phosphono, amine including primary, secondary, tertiary or quaternary amines, often with short chain alkyl or monocyclic or bicyclic The aryl groups are isothioureyl, thioureyl, guanidyl, trialkylsilyl, trialkylstannyl, trialkyl plumbyl, dialkylstibinyl. Often the substituents on the phenylene groups of the diphenylmethane and diphenyl ether groups provided by at least one of the groups R 1 - R 5 and R 1 - R 2 are hydrogen. The polysulfones with aromatic hydrocarbyl-containing groups generally have good heat stability, are resistant to chemical attack, and have an excellent combination of toughness and flexibility.

Suitable polysulfones are commercially available under the trade name such as "P-1700" and "P-3500" from Union Carbide, both commercially available products being diphenylmethane-derived polysulfones (especially derived from bisphenol A) with a linear chain of formula 6, wherein n, which indicates the degree of polymerization, is 50 - 80. These commercially available bisphenol A-derived polysulfones sometimes contain a crystallized fraction, which is believed to be an oligomer. Polysulfone solvents such as dimethylformamide and diemthylacetamide allow this crystallized fraction to be withdrawn from the solution and may even increase in crystal size and fraction. This crystallized fraction can lead to an increase in the difficulty of obtaining desired anisotropic hollow fiber membranes. The N-acylated heterocyclic solvents used in the process of the invention have been found to provide solutions containing these polysulfone polymers containing very little or no fraction of these crystals. In addition, the polymer solutions exhibit good stability against excessive crystal formation; therefore, the polymer solution can be stored even before use. This stability provides sufficient polymer solution life to cause sufficient degassing.

With respect to polysulfone polymer, e.g. P-3500, Table A provides a list of solvents and diluents attractive for making membranes, especially hollow fiber membranes according to the method of the invention.

Table A

General formulation Preferred formulation liquid carrier liquid carrier in parts by weight. parts by weight.

20 - -

Diluent 1-Formyl Dilute 1-Formyl Dilute piperidine ning piperidine ning _ agent _ agent

None 100 0 100 0

Formamide 85-98 2-15 87-95 5-13 25 Ethylene Glycol 65-98 2-35 75-95 5-25

Water 90-98 2-10 95-98 2-5

The methods of the invention are particularly advantageous for manufacturing hollow fiber membranes. With respect to this aspect of the invention, the solution 30 is extruded through a spinneret to form a hollow fiber precursor. Although any suitable hollow fiber spinneret can be used to manufacture the hollow fibers of the invention, it is preferred that the spinneret of the tube be in the opening type. Tube in orifice type spinnerets are characterized in that they have a ring surrounding an inwardly positioned injection tube. Most desirably, the injection tube is located concentrically within the opening in such a way that substantially the same amount of polymer solution is extruded at all points of the annular opening and the resulting hollow fiber precursor has a substantially uniform wall thickness. In most tube-type spinnerets, the polymer solution enters a cavity behind the annular opening to assist in the distribution of the polymer solution over the annular opening. Sometimes at least U and preferably at least 10 polymer solution ports are provided, and are most preferably equidistant from each other.

When spinning some polymer solutions, it may be desirable to keep the polymer solution at elevated temperature to provide desired spinning conditions.

Under such circumstances, it is desirable to provide a heater to maintain the spinneret at the desired extrusion temperature. Suitable heating means are electric or fluid heating mantles, embedded electric heating coils and the like. Because the residence time of the polymer solution in the spinneret is relatively short, the polymer solution is often heated at or near the desired extrusion temperature prior to entering the spinneret. Often the temperature of the polymer solution in the spinneret is at least 20 ° C, but it is preferably not at such a high temperature that the polymer solution is undesirably impaired during the residence time of the polymer solution at that temperature. Often the polymer solution in the spinneret has a temperature in the range of 20 -90 ° C, e.g. 25-80 ° C.

The size of the spinneret will vary depending on the desired internal and external diameter of the desired hollow fiber membrane. A class of spinnerets has an opening diameter (outer diameter) of 300-1000 µm and an inner opening diameter (often the outer diameter of the injection tube) of 100-500 µm with an injection capillary in the injection tube. The diameter of the injection capillary can vary 800 1 8 45 3k within the limits imposed by the injection tube. The injection tube is usually positioned relative to the plane of the spinneret opening. Typically, spinnerets are described by a configuration of the entrance of the annular opening and the length to width ratio of the annular opening portion of the spinneret. The entry configuration of the annular opening portion of the spinneret may be sudden, ie at an angle of more than 80 ° with the direction of flow of the polymer solution into the annular portion of the spinneret, or may be inclined with the annular portion of the spinneret, sl st below a slope of less than 80 ° C, e.g. 75 ° - 30 °, relative to the direction of the polymer solution flow through the annular spinneret. The ratio of the length over which the annular portion extends from the surface of the spinneret to the width of the annular opening at the spinneret surface can vary within wide limits; however, the length of the annular portion of the spinneret should not be so great that an undesirable pressure drop occurs as the polymer solution passes through the spinneret. Often these ratios range from 0.7 to 2.5, e.g. 1 - 2.

The dimensions of the hollow fiber precursor hang e.g. depending on the dimensions of the spinneret, the flow rate of the polymer solution through the spinneret, the jet elongation on the hollow fiber precursor, and the velocity and pressure of the fluid injected into the bore of the hollow fiber precursor. The flow rate of the polymer solution through the spinneret can vary within wide limits depending on the take-up speed of the hollow fiber.

However, the flow rate should not be so great as to cause a breakdown of the hollow fiber precursor. Spin operations are often made because the dimensions of the hollow fiber can vary widely, e.g. from 100 or 150 µm to 1000 or more µm outer diameter and the length of the hollow fiber formed at unit of time (spinning speed or take-up speed) can also vary widely, eg from 5 - 100 m / min (although higher Spin speeds can be used provided that the fiber is not excessively stretched and sufficient residence time was provided 80 0 1 8 45 Λ * 35 in subsequent dyeing steps), often described on the basis of jet elongation. the ratio of (i) the number of cm 2 / min polymer solution extruded through the spinneret divided by the cross-sectional area of the annular extruding region in cm to (ii) length in cm of this hollow fiber precursor that is extruded per min (eg the recording speed) The spin elongation is often 0.6 to 2, eg 0.7 to 1.8, preferably 0.75 to 1.5.

An injection fluid is introduced into the bore of a hollow fiber precursor in an amount sufficient to keep the bore of the hollow fiber precursor open. The injection fluid may be gaseous or is preferably liquid under the hollow fiber spinning conditions. The injection liquid should be miscible (and preferably miscible in all proportions) with the liquid coagulant and with the liquid carrier. Often the injection fluid is a non-solvent for the polymer. In many instances, the injection fluid need not be a strong non-solvent for the polymer. The injection fluid may contain one or more components and often contains at least one component of the liquid coagulant in order to promote the miscibility of the injection fluid with the liquid coagulant. Therefore, the injection fluid often contains water.

Often the injection fluid also contains a solvent or weak solvent for the polymer. The temperature of the injection fluid generally approaches the temperature of the polymer solution being extruded and the temperature of the spinneret because of the heat transfer through the wall of the injection capillary 30 which has been introduced into the spinneret. However, with appropriate insulation or other means to minimize heat transfer through the injection fluid in the spinneret or the use of an injection fluid cooled before being fed to the spinneret, the injection fluid may be significantly colder than the polymer solution temperature which is extruded. The velocity and pressure of the injection fluid fed into the bore of the 800 hollow fiber precursor should be insufficient to lead to any detrimental effect on the resolution or structure of the hollow fiber membrane. Often the velocity and pressure of the injection fluid is such that the ratio of the inner diameter of the hollow fiber to the outer opening diameter of the spinneret is less than 2.5, and preferably this ratio is between 0.5 and 1, 5 or 2.

The spinneret may be below the level of the liquid coagulant (wet jet) or preferably above the liquid coagulant (dry jet). When the dry jet spinning technique is used, it is preferred that the components of the liquid carrier be substantially non-volatile. The distance above the liquid coagulant on which the spinneret (hole) is arranged can vary considerably without the perceptible influence on the properties on the hollow fiber membrane. The spinneret is often arranged at 20 or 30 cm. Desired hollow fibers can be made when the surface of the spinneret is within 0.5 cm of the liquid coagulant. For convenience, the spinneret is often positioned within 0.5 - 15 cm of the liquid coagulant. The dry jet spinning technique is also preferred for convenience when the polymer solution is to be extruded at elevated temperature and the coagulation fluid is kept at a temperature that is significantly lower (eg at least 25 ° C, such as at least 30 ° C, below temperature of the polymer solution is maintained during extrusion.

The methods of the invention are particularly advantageous for producing anieotropic hollow fiber membranes from polysulfone, especially polysulfones containing diphenylmethane (including substituted diphenylmethane) and diphenyl ether (including substituted diphenyl ether) groups.

The polysulfone hollow fiber membranes of the invention exhibit several important structural features which allow combining desired strength properties with favorable fluid separation properties. The polysulfone membranes 800 1 8 45 37 according to the invention can be particularly attractive for carrying out gas separations.

A dry, fully-forming anisotropic hollow fiber membrane of polysulfone according to the invention has a wall with a thin outer skin on an open cellular support. The outer skin contains little or no pores (i.e., continuous channels for fluid flow through the outer skin). The cells in the cellular hollow fiber wall support are preferably relatively small in all dimensions. Desirably, the cellular support contains substantially no macro-cavities with a maximum length to maximum width ratio of greater than 10, preferably greater than 5. The preferred polysulfone hollow fiber membranes of the invention contain virtually no macro-cavities.

A hollow fiber membrane for gas separations is often judged on the basis of its gas separation characteristics, i.e. its selectivity for permeating a gas compared to at least one other gas from the gas mixture and the flow of the selectively permeated gas through the membrane wall as well as its strength. These properties depend on the chemical and physical nature of the material of the hollow fiber as well as the structure of the hollow fiber. Since morphological structures, which play an important role in determining the gas separation characteristics of the hollow fiber membrane, may have dimensions of the order of tens of angromromes, such structures cannot be observed visually even using the best optical microscope techniques available to be. Such small structures are therefore called "submicroscopic" structures.

The combination of microscopic techniques (especially without scanning electron microscopy and passage electron microscopy) and observable behaviors for characterizing agitator base hollow fiber membrane structures and a submicroscopic base can be very useful. A particularly useful microscope technique for characterizing hollow fiber membrane structures is scanning electron microscopy. To better understand the use of scanning electron microscopy for describing 800 hollow fiber membranes according to the invention, reference is made to the accompanying drawings.

Fig. 1 and FIG. 2 are scanning electron micrographs of all fiber membranes in which FIGS. 1a-1c show a hollow fiber membrane made from a polymer solution containing 32 wt% polysulfone (P-3500), 7 wt% formamide and 61 wt% Contains $ 1-formylpiperidine. Fig. 1a shows the cross section of the hollow fiber at 300x magnification. Fig. 1b shows a portion of the section of the hollow fiber at the outer edge 10 of the hollow fiber and has a magnification of 20,000 x.

Fig. 1c shows the structure of the cross section of the hollow fiber in an area approximately in the middle of the wall of the fiber and is a magnification of 20,000x.

Fig. 2 shows a cross section of a hollow fiber membrane 15 made of a polymer solution containing 36 wt% polysulfone (P-3500) and wt% 1-formylpiperidine, and is 300x magnification.

Examples of hollow fiber membranes (as shown in the drawings) for examination the scanning electron microscopy 20 can be conveniently prepared by thoroughly drying the hollow fiber, dipping the hollow fiber in hexane and immediately placing the hollow fiber in liquid nitrogen so that the hollow fiber can be broken. After a clean break of the hollow fiber is obtained, the sample can be set up and then sputter coated with a gold and palladium mixture (using, for example, a Hummer II sputter coating apparatus). The coating method usually results in a 50-75 S coating applied to the hollow fiber sample. Therefore, the dimensions of very small details can be covered by the coating.

As can be seen in particular from Figure 1, the structure of the hollow fiber membranes is characterized by a relatively dense structure near the exterior surface with an open cell structure located beneath it. An increase in the size of the cells in the hollow fiber wall is noticeable as the distance from the external surface increases, to 800, generally a maximum size in a center region in the hollow fiber wall. The predominant structure of the cells in the central region of the section of the hollow fiber wall appears to consist of interconnected cells (cells with open passage 5 for gas flow in neighboring cells), i.e. an open cell structure. However, this interconnection between cells cannot be visually observed when the cells are very small, e.g. less than 0.1 µm in the largest dimension. This open cell structure allows fluid to easily pass through the hollow fiber wall, not a minimum of resistance. It is advantageous if the outer wall (and inner wall if present) forms the major part of the resistance to the flow of liquid through the membrane wall.

The dimensions of the cells, especially larger cells, which often occur in the middle region of the hollow fiber wall, can often be estimated using e.g. scanning electron microscopic techniques. In estimating the size and configuration of the cells, the observable passages between individual cells are considered to be broken in the cell wall and therefore the dimensions of the cells do not extend beyond these passages. Another feature of the cells, which may be important in assessing the strength of the membrane, is the thickness of the cell wall material, thereby forming the larger cells in the hollow fiber membrane wall. These estimates can be made by visually assessing photos of the cell structure or by using available computer scanning techniques, such as image analyzers to inspect and analyze the photo. Suitable image analyzers are image analyzers suitable for the analysis of conventional textile fibers, such as the Quantimet 720-2 image analyzer (trademark of Quantimet, Munsey, New York).

The configuration of the cells, especially in the larger cells, which often occur in the middle region of the hollow fiber wall, can vary widely. A convenient way to characterize the configuration of the cell is to divide the cross-sectional cell area by the square of the 800 circumference of the cell over that cross-section, thereby obtaining a configuration ratio. For example, the configuration ratio of a perfect circle is about 0.8, for square it is 0.06, and for a bar 0.01 or less. When the configuration ratio is in the range of 0.03 - 0.0 * 1, the cross section of the cells is often roughly a polygon in appearance. Such analyzes can be performed by visual inspection of photos of the cell structure of the hollow fiber wall or by using an image analyzer to inspect the photos. The configuration ratio can be suitably determined by analyzing any segment of the hollow fiber wall cross section, this segment containing cells large enough to be inspected and free from macro-cavities.

The area of a screened segment, to be representative, should generally be at least 25 µm (e.g., a segment with a minimum size of at least 5 µm). In many desirable hollow fiber membranes according to the invention, the average configuration ratio is at least 0.025 and in many cases at least 0.03 and even at least 0.035. Preferably segments of the hollow fiber cross section containing large cells (except macro-cavities) an average configuration ratio of at least 0.03 »eg at least 0.035

When the cell dimensions in a segment of a cross section of the hollow fiber wall are greater than 0.1, e.g. greater than 0.2 µm, analyzes of photos of cell structures such as e.g. observed by scanning electron microscopy, are successfully used to determine the ratio of average wall thickness to average cell cross-sectional area. Generally, the hollow fiber is the stronger the greater the ratio of the thickness of the polymer supporting the cell to the cross-sectional area of the cell. Often this ratio, especially for the largest cells in the hollow fiber membrane cross section, is at least 0.05, such as about 1 and sometimes even 2 - 20 cm 2. When analyzing photos of smaller cells and smaller wall thicknesses of scanning electrons - 800 1 8 45

In microscopic images, the thickness of the reflective coating may become significant and should be taken into account. Often at least the majority of the cells that can be seen in such pictures also have detectable passages that communicate with neighboring cells.

Preferably, most of the volume of the wall (determined by cross-sectional area) of the hollow fibers consists of cells with an average head size of less than 2 µm. Often at least 75 vol. #, E.g. at least 90 vol. # 10 of the wall from cells having a main size of less than 2 µm, preferably less than 1.5 µm, e.g. less than 1 µm. Some favorable favorable hollow fiber membranes have virtually no cells with a main size of more than 2 or 1.5 µm. As mentioned previously, the size of cells in the wall of the hollow fiber membranes usually varies considerably from a size too small to be determined by scanning electron microscopy to cells with a size of 2 µm or more. In some hollow fibers according to the invention, the predominant major dimensions of the larger cells in the hollow fiber membrane wall are less than 0.75 µm and in some cases almost all cells in the region of the largest cells in the hollow fiber membrane wall have a main size of 0 .1-0.7 .mu.m. Often this region of the largest cells forms at least 30 vol. #, Such as at least 50 vol. #, E.g. up to 50 or 75 vol. # 25 of the hollow fiber wall. Often desirable hollow fiber membranes have an average head size of peeling that is relatively even regardless of the segment (e.g., from 2 ...

at least 25 µm m surface with a minimum size of at least 5 µm) observed in at least most of the volume (e.g. at least 75 vol. #) of the hollow fiber wall.

In some instances, hollow fiber membranes may exhibit sufficient collapse resistance even though macro-cavities may be present. Macro cavities, if they exist in the hollow fiber, can differ greatly in shape and location in the hollow fiber wall. Macro cavities that closely approximate the shape of a circle can generally be admitted to a greater extent 800 1 8 45 k2 without unduly reducing the collapse resistance than long finger-shaped macro cavities. When macro cavities occur, it is desirable that they occur only in the thickness of the hollow fiber membrane from the inner wall 5 to 0.5 or 0.75 times the distance to the outer wall. Preferably, the hollow fiber membrane contains practically no macro-cavities with a maximum length to maximum width ratio of more than 10, e.g. The main size of the macrocavities is preferably less than 0.1 *, e.g. less than 0.3 times the thickness of the hollow fiber wall. Scanning electron microscopy can sometimes be useful for examining the porosity of the inner (bore side) skin of the hollow fiber membrane. Preferably, the inner skin is highly porous to allow the permeation of gases to pass through the bore of the hollow fiber with little resistance.

A useful microscopic technique for estimating particularly small structural properties, e.g. porosity of the external surface (and possibly the internal surface) of the hollow fiber membranes is the surface repeat technique. In this technique, a metal coating, e.g. a platinum coating is applied and then the polymeric hollow fiber is dissolved from the metal coating. The metal coating is then analyzed using continuous electron microscopy, e.g. at magnifications of 50,000 times or greater, in order to determine the surface features of the hollow fiber, which are repeated through the metal coating. Generally, the most preferred hollow fiber membranes of the invention provide smooth surface repetitions of the external surface that exhibit virtually no anomalies or irregularities (which could be pores) of greater than 100, often greater than 75 or even 50 & .

A particularly valuable analytical tool for kinetic assessment of hollow fiber membranes is the permeability of gases through the membrane. The permeability of a given gas through a membrane of a given thickness is the gas volume that passes through the membrane at standard temperature and pressure (STP) per unit area of the membrane per time unit 800 1 8 45 1 + 3 unit per unit of the partial differential pressure. One method for reporting permeabilities. Is: .enr (STP) per cm membrane surface per sec. for a partial pressure difference of 3 2 1 cm Hg across the membrane (cm / cm sec. cm Hg). Unless otherwise stated, all permeabilities herein are stated at standard temperature. and pressures are measured using pure gases. The permeabilities are reported in gas permeation units R & O (GPU) which are cm-5 (STP) / cm.sec.cm Hg x 10; therefore 1 GPU is equal to 1 x 10 cm (STF) / cm.sec.cm Hg. Several of the many available techniques for determining permeability and permeability constants (eg, the volume of gas (STP) passing through a given thickness of the membrane material per unit area per unit time per pressure differential unit over the thickness) reported by Hwang et al., Techniques 15 of Chemistry> vol. VII, Membranes in Separations, John Wiley &

Sons, 19759 chapter 12, pages 296 - 322. The permeability of a given gas represents permeation of the gas through the membrane regardless of the mechanism through which the gas passes through the membrane.

A useful kinetic relationship, which indicates the freedom of pores in the separating or boundary layer, and the size range of the pores in the boundary layer, consists in determining the ability of the membrane to gas with different moles. wt. to be separated, e.g. gases with low molecular weight, with markedly different molecular weight. Suitable pairs of gas for this analysis often contain one mol. hydrogen or helium and one mole. nitrogen, carbon monoxide or carbon dioxide. Preferably, the gas has a higher molecular weight. of the selected gas pair, a permeability constant (ie, the intrinsic permeability constant) of the polysulfone that is at least 10 times less than the intrinsic permeability constant of the lower molecular weight gas. in the polysulfone. The analysis can conveniently be performed at room temperature (e.g., at 25 ° C) and a pressure of 7f, 8 at absolute on the outside of the hollow fiber membrane and 1 at absolute on the bore side of the hollow fiber membrane. The polysulfone hollow fiber membranes according to the invention exhibit a permeability ratio of (i) the permeability of the gas with lower molecular weight for at least one 800 1 8 45 uu pair of gases. (P / l) ^, divided by the permeability of the higher molecular weight gas. (P / l) ^, until (ii) the square root of the molecular weight. of the gas with lower molecular weight, 5 λ / ΜΝτ »divided by the square root of the molecular weight. of the gas with a higher molecular weight, vM2, of at least 6, often at least 7.5. The theoretical maximum permeability ratio is the ratio of the intrinsic separation factor for the gas pair to the quotient of the square root of the molecular weight.

10 of the gas with lower molecular weight. divided by the square root of the molecular weight. of the gas with higher molecular weight.

As used herein, an intrinsic separation factor is the separation factor for a material that does not contain channels for gas flow through the material and is the highest attainable separation factor for the material. Such a material can be referred to as continuous or non-porous. The intrinsic separation factor of a material can be estimated by measuring the separation factor of a compact membrane from the material. However, various difficulties may arise in determining an intrinsic separation factor including imperfections that arise in the manufacture of the compact membrane, such as the presence of pores, the presence of fines in the compact membrane, undefined molecular order due to variations during membrane manufacture and the like. Therefore, the measured intrinsic separation factor may be different from the actual intrinsic separation factor. Therefore, a "measured intrinsic separation factor" as used herein refers to the separation factor of a dry compact membrane of the material.

Another useful method of characterizing hollow fiber membranes on a kinetic basis is to determine the permeabilities of a few low molecular weight gases. with about the same molecular weight, but one of which has a permeability constant in the polysulfone of at least 5%, preferably at least 10 times more than that of the other gas. Characteristic 80 0 1 8 45 gas pairs which have approximately the same molecular weight. possessing but significantly different permeability constants for many polysulfones suitable for hollow fiber membranes are ammonia and methane; carbon dioxide and propane. This relationship can be expressed as the quotient of a difference of the permeability of the easy permeating gas (P / l) ^, and the permeability of the less easily permeating gas (P / l) divided by (P / l) times the permeability constant of the less readily permeating gas, Pg, divided by the permeability constant of the more easily passing gas PF: Γ "] - (P / 1) F - (P / l) g Pg

(p / ^ s J

In many cases, this ratio is at least 0.001, such as at least 0.01 and preferably at least 0.02. This relationship is indicative of the material of the hollow fiber membrane that accomplishes at least a portion of the separation.

Another useful kinetic analysis of the hollow fiber membrane consists of the ratio of the permeability of the gas to the permeability constant of the polysulfone for the gas: (P / l)

P

The gas used to determine this relationship, which preferably readily permeates through the membrane, is e.g.

Hydrogen, helium, ammonia or the like. Often this k. A ratio of at least 5 x 10, such as at least 1 x 10, preferably at least 2 x 10 to 1 x 10 °, such as 1 x 1 to 0.6 x 10 cm. This relationship indicates a low resistance to gas flow through the hollow fiber membrane structure and thus the high permeabilities of the desired permeating gas which can be obtained.

The structure of the hollow fiber membranes of the invention can also be deduced from other kinetic observations. E.g. Dried hollow fiber membranes exhibit very little liquid water permeability due to the presence of little 800 pores or no pores in the separating or boundary layer. The water permeability is often less than 0.5 x 10 * ^ or even less than 0.2 x 10 “^, such as less than 0.1 x 10“ ^ and sometimes less than 0.01 x 10 ”cm- 3 (liquid) / cm sec sec cm Hg, even after 1+ days of soaking in water at room temperature (25 ° C). The determination of the water permeability can conveniently be performed at room temperature at a pressure drop of 3 ¾ at the supply side to the permeate side of the membrane at an absolute pressure of 1 +, ¾ at the supply side. Often the maximum pore size is less than 250 2 and often less than 150, eg less than 100 2.

One method of determining the size and openness of the cellular support is to subject the hollow fiber membrane to the usual Brunauer, Emmett and Teller (BET) adsorption analysis to determine surface areas. In a BET analysis, a monolayer of a gas, e.g. nitrogen, adsorbing on the available inner surface of the hollow fiber and the amount of gas adsorbed is determined and assumed to be proportional to the available surface. In the BET analytical technique described herein, the analysis is performed such that the inner surface of cells that are not open does not contribute significantly to determining the available surface. Smaller cells provide more surface area per g of polymer than larger cells.

Therefore, a BET analysis provides an indication of the openness of cells that are too small to be visualized with e.g. scanning electron microscopy. Many hollow fiber membranes according to the invention have a surface area as determined by the BET method of at least 18 or 20 and preferably at least 22 m / g. At very high BET certain surfaces, e.g.

50 or 70 m / g, the hollow fiber is often observed to have a fibrillated structure rather than a cellular structure. Fibrillary structures can sometimes be relatively weak compared to cellular structures. Usually, the hollow fiber membrane inner surface, determined by a BET analysis, ranges from 18 or 22 to 30 m / g. Hollow fibers which have an 800 1 8 45 hr predominantly closed cell structure often exhibit BET surface area of less than 18 or 20 m / g. Another useful method for determining surface areas determined by BET analysis is expressed in area per 5 volume unit of hollow fiber wall. Often desired hollow fiber membranes according to the invention have a surface, determined by BET analysis, of 10 - 30, such as 10 - 20 m 2 / cm 3, hollow fiber wall volume.

The structures of the polysulfone hollow fiber membranes according to the invention allow the hollow fibers to withstand large pressure differences from the outside to the bore of the hollow fiber membrane, that is, the hollow fiber membranes have a high collapse pressure. Therefore, the hollow fiber membrane can have a relatively low ratio of thickness (wall) to external diameter while still maintaining a desired structural strength and thereby providing a favorable bore diameter size to minimize the pressure drop for gases passing through the bore possible. The collapse strength against external pressure of a pipe with a foamed wall structure 20 depends on the strength of the material of the pipe, the wall thickness of the pipe, the nature of the foamed wall structure, the outside diameter of the pipe, the density of the foam and the uniformity of the hollow fiber configuration (ie whether the configuration inside and outside are concentric and circular-shaped). Generally, the collapse pressure of the hollow fiber membranes of the invention has an approximate relationship to the strength of the hollow fiber material and the wall thickness divided by the outside diameter of the hollow fiber (t / D). This approximate relationship can be expressed as the tensile strength of the material of the hollow fiber and the third power of the ratio of the wall thickness to the external diameter. Such dressings may exist with respect to other strength properties of the hollow fiber material, such as the modulus of elasticity and the like. Frequently, the hollow fiber membranes of the invention exhibit a collapse 2 t 3 pressure (kg / cm) of more than k Tg (-), wherein Tg tensile strength 800 1 8 45 1 + 3 at the elastic limit (or at break) if appropriate) in 2 kg / cm. More suitable hollow fiber membranes according to the invention t 3 also exhibit a collapse pressure greater than 10 (φ) (Tg) (-) where φ is the volume fraction of the material of the hollow fiber membrane in the wall of the hollow fiber membrane. The volume fraction of the material of the hollow fiber membrane (φ) is therefore 1 min the amount of hollow volume (vol.%) / 100.

Anisotropic membranes can be manufactured according to the method according to the invention to minimize the separation or boundary layer thickness. Often the tendency to form pores in the membranes is increased as the boundary layer becomes thinner. In accordance with U.S. Pat. Nos. 71 + 2,159 of November 15, 1976 and 832.1 + 81 of September 13, 1977, a coating can be obtained in inclusive contact with a gas-separating membrane containing pores to increase the selectivity of the separation exhibiting the gas-separating membrane, wherein the coating material does not significantly affect the separation. Usually suitable membranes for coating according to the above-mentioned US patent applications have a permeability ratio as defined above of at least 6.5, often at least 7.5. In many cases, the uncoated membranes most suitable for coating have a permeability ratio of less than 1 + 0, such as less than 20 or 25. The ratio of the permeability of a gas (preferably a gas that readily permeates through the membrane material) to the permeability constant of the membrane material for the gas is at least 1 x 10 ^, preferably at least 2 x 105 to e.g. 1 x 106 cm "1. For example, it is beneficial when polysulfone (eg P-3500) hollow fiber membranes (and many other hollow fiber membranes) for coating exhibit a hydrogen flow of 100 - 1200 GPU or more and a hydrogen permeability ratio to show methane permeability from 1.5-2 to 10, eg 2-7

In many cases, the separation selectivity for at least one pair of gases after coating the membrane is at least 1 + 0 $, e.g. at least 50% of that of a substantially non-porous membrane of the same material, i.e., a non-porous membrane through which the gases essentially pass only through interaction with the material of the membrane. The selectivity of the separation of the coated membrane can be at least 35%, e.g.

5 are at least 50 or 100 # greater than the separation selectivity for the pair of gases which can be provided by the material of the coating when it is in the form of a substantially non-porous membrane. In addition, after coating, the current obtainable using the coated membrane is not excessively reduced, e.g. is the ratio of the permeability of a gas to the permeability constant of the material. . . . 1+ of the membrane preferably at least 5 x 10, more preferably at least 1 x 10 cm.

Particularly favorable coating materials for increasing the selectivity of the separation of the membranes do not cause excessive reduction of the permeation rate (flow) of the gas or gases which it is desired to permeate through the membrane wall. Often the materials for the coatings have relatively high permeability constants. The coating material should be able to provide enclosed contact with the outer surface of the membrane. After application, e.g. be sufficiently wet and adhere to the hollow fiber to ensure enclosed contact occurs.

The wetting properties of the material of the coating 25 can be easily determined by contacting the material of the coating, either as such or in a solvent, with the material of the membrane. In addition, based on estimates of the mean pore diameter in the separation thickness of the membrane, materials for the coating 30 of appropriate molecular size can be selected. When the molecular size of the coating material is too large to be absorbed by the pores, the material may not be suitable for providing containment contact. On the other hand, when the molecular size of the material for the coating is too small, it can be drawn through the pores of the membrane during the coating and / or separation operations. When the pores are of a wide variety of sizes, it may be desirable to use a polymerizable material as the coating material, which is polymerized after application to the membrane, or to use two or more coating materials of 5 different molecular sizes, e.g. by applying the materials of the coating in order of their increasing molecular size.

The coating materials may consist of natural or synthetic materials and are often polymers and suitably exhibit the desired properties for providing impermeable contact with the membrane. Synthetics include both addition and condensation polymers. Characteristic of the useful materials that can form the coating in polymers which are substituted or unsubstituted and which are solid or liquid under gas separation conditions and include synthetic rubbers, natural rubbers, liquids of relatively high molecular weight. and / or high-boiling; organic prepolymers, silicone silicone polymers, silicone silanes, polyurethanes, polyepichlorohydrin, polyamines, polyimines, polyamides, acrylonitrile containing copolymers such as polychlorinated acrylonitrile copolymers; polyesters including polylactoms and polyarylates, e.g. polyalkyl acrylates and polyalkyl methacrylates, wherein the alkyl groups e.g. 1-8 carbon atoms, polysebacates, polysuccinates and alkyd resins, terpinoid resins, linseed oil, cellulose polymers, polysulfones, especially aliphatic groups containing polysulfones, polyalkylene glycols such as polyethylene glycol, polypropylene glycol; polyalkylene polysulfates, polypyrrolidones, polymers from monomers with oC-ethylenically unsaturated groups, such as polyolefins, e.g.

Polyethylene, polypropylene, polybutadiene, poly (2,3-dichlorobutadiene), polyisoprene, polychloroprene, polystyrene including polystyrene copolymers, e.g. styrene-butadiene copolymer, polyvinyls, such as polyvinyl alcohols, polyvinyl aldehydes (e.g. polyvinyl formal and polyvinyl butyral, polyvinyl ketones, e.g.

Polymethyl vinyl ketone, poly vinyl esters, e.g. polyvinyl benzoate, polyvinyl halides, e.g. polyvinyl bromide, polyvinylidene-800 1 8 45 51 halides, polyvinylidene carbonate, poly N-vinyl maleimide, poly (1,5-cyclooctadiene), polymethylisopropenyl ketone, fluorinated ethylene copolymer, polyarylene oxides, e.g. poly-xylylene oxide, polycarbonates, polyphosphates, e.g. polyethylene-methylphosphate and the like and any interpolymers containing block interpolymers having repeating units of the above groups and graft copolymers and mixtures containing any of the above groups. The polymers may or may not be polymerized after application to the membrane.

Polysiloxanes are particularly useful materials for coatings. Typical polysiloxanes may contain aliphatic or aromatic groups and often contain repeated units of 1 to 20 carbon atoms. The molecular weight. of the polysiloxanes can vary within wide limits, but is generally at least 1000. Often the polysiloxanes have a molecular weight. from 1,000-300,000 or more when applied to the membrane. Common aliphatic and aromatic polysiloxanes are the poly (monosubstituted and disubstituted siloxanes), e.g. wherein the substituents are short chain aliphatic groups, such as a short chain alkyl group, including cycloalkyl, especially methyl, ethyl and propyl, or a short chain alkoxy group, an aryl group including mono- or bicyclic aryl, such as diphenylene naphthalene; short chain mono- and bicyclic aryloxy groups, acyl groups including short chain aliphatic and short chain aromatic acyl groups. The aliphatic and aromatic substituents can be substituted, e.g. by halogens, such as fluorine, chlorine or bromine, hydroxy groups, short chain alkyl groups, short chain alkoxy groups, short chain acyl groups, glycidyl groups, amino-30 groups and vinyl groups. The silicone can be cross-linked in the presence of a cross-linking agent around a silicone rubber

. I

and the polysiloxane may be a copolymer with a cross-linkable comonomer such as -methylstyrene to promote cross-linking. Typical catalysts that promote cross-linking are organic and inorganic peroxides.

Cross-linking can take place prior to applying the polysiloxane to the membrane, but preferably the polysiloxane is cross-linked after it has been applied to the membrane. Often the polysiloxane has a molecular weight. from 1000-100,000 or more prior to cross-linking. Particularly favorable poly-siloxanes are polydimethylsiloxane, polyhydrogenmethylsiloxane, polyphenylmethylsiloxane, polyfluoropropylmethylsiloxane, copolymer of cC-methylstyrene and dimethylsiloxane and post-cured polydimethylsiloxane-containing silicone rubber with a mole. wt. from 1000 - 50,000 or more prior to cross-linking. Some polysiloxanes wet the material of the hollow fiber enough to provide as much entrapment contact as desired. Dissolving or dispersing the polysiloxane in a solvent, which does not affect the material of the membrane, may facilitate the obtaining of entrapment contact.

Suitable solvents are usually liquid alkanes, e.g. pentane, isopentane, cyclohexane, aliphatic alcohols, e.g. methanol, some halogenated alkanes and dialkyl ethers, dialkyl ethers and the like as well as mixtures thereof.

The coating may be in the form of a substantially continuous membrane, i.e. an essentially non-porous membrane, in contact with the anisotropic membrane, or the coating may be discontinuous or discontinuous.

Preferably, the coating is not so thick as to adversely affect the behavior of the membrane, e.g. by causing an excessive decrease in flow or by causing such resistance to the gas flow that the separation factor of the coated membrane is essentially that of the coating. The coating often has an average thickness of at most 50 µm. When the coating is interrupted, there may of course be areas in which there is no coating material. The coating can often have an average thickness in the range of 0.0001 - 50 µm. In some cases, the average thickness of the coating is less than 1 µm and may even be less than 5000 µm. The cover layer can consist of a layer or at least two separate layers, which may or may not consist of the same material. The coating can be applied in any suitable 800 1 8 45 V * 53 manner, e.g. by a coating operation such as spraying, brushing, dipping into an essentially liquid substance containing the coating material or the like. The coating material is preferably present in an essentially liquid material upon application and may be in a solution using a solvent for the coating material, which is essentially a non-solvent for the coating material. membrane. It is convenient to apply the coating after the membranes have been assembled for later installation in a permeator, or even after installation in the permeator, in order to minimize handling of the coated membrane.

It is often possible to treat the outer surface of a membrane with a densifier, e.g. a plasticizer, swelling agent, non-solvent or a solvent (preferably a weak solvent) for the material of the anisotropic membrane in order to compact the outer surface of the membrane. The choice of a suitable compaction agent depends on the polymer of the membrane. Compounds which can be used are liquids and gases such as ammonia, hydrogen sulphide, acetone, methyl ethyl ketone, methanol, isopentane, cyclohexane, hexane, isopropanol, dilute mixtures of the polymer solvents (eg toluene, benzene, methylene chloride) in non- solvents for the polymer and the like.

The treatment can be carried out before or after the membrane has dried and can be carried out over a wide temperature range. Temperatures from 0 ° - 50 ° C, usually 10 - 35 ° C, are usually used. Treatment of the membrane with a densifier prior to coating to increase selectivity may be advantageous in some cases.

The membranes according to the invention are widely applicable in gas separation operations, in particular the separation of low molecular weight gases, by interaction of the permeating gases with the material of the membrane. Gaseous mixtures which can be used in gas separation operations consist of gaseous substances, or substances which are usually liquid or solid, but which form a vapor at the temperature at which the separation is carried out. Typical gas separation operations that are desired are separations of e.g. oxygen from nitrogen, hydrogen from at least one of the following gases: carbon monoxide, carbon dioxide, helium, nitrogen, oxygen, argon, hydrogen sulfide, nitrogen trioxide, ammonia, and hydrocarbon of 1 to 5 carbon atoms, especially methane, ethane and ethylene; ammonia with at least one of the following gases: hydrogen, nitrogen, argon, and hydrocarbon having 1 to 5 carbon atoms, e.g. methane, carbon dioxide with at least one of the following gases: carbon monoxide and hydrocarbon with 1 to 5 carbon atoms, e.g. methane; hydrocarbon helium with 1 to 5 carbon atoms, e.g., methane, hydrocarbon sulfur with 1 to 5 carbon atoms, e.g. methane, ethane or ethylene; and carbon monoxide with at least one of the following gases: hydrogen, helium, nitrogen or hydrocarbon of 1 to 5 carbon atoms. It is emphasized that membranes according to the invention can find a beneficial application when used in separation operations when a different gas mixture is used.

The examples below serve to illustrate the invention. All parts and percentages of gases are by volume and all parts and percentages of liquids are by weight unless otherwise stated. All gas permeabilities are determined using nearly pure gases with an outside pressure of 70 at absolute and 1 at the bore side of the hollow fiber membrane unless otherwise stated.

Example I

32 parts of polysulfone (P-3500) and 68 parts of a liquid carrier consisting of 90 parts of 1-formylpiperidine and 30 parts of formamide (reagent grade) are placed in a heated cap mixer containing dry nitrogen located. Before filling into the dop mixer, the polysulfone polymer is dried at 125 ° C for 5-7 days under vacuum (e.g., at an absolute pressure of less than 10 or 20 mm Hg). The formylpiperidine has a moisture content of 0.1 + 5 g / 100 ml and the formamide 0.15 g / 100 ml. The exposure of formamide to air 800 1 8 45 55 during filling of the heated doping mixer is minimized in order to avoid degradation of the formamide. In the heated dopant mixer, the polymer solution is kept at 80-100 ° C for sufficient time to completely dissolve the polysulfone 5 (residence times of 8 hours are generally used). The polymer solution is transferred to an air vent containing dry nitrogen gas, which is heated to 80 ° C. The air vent contains a cone-shaped separation with a bowl in the apex of the separation. The polymer solution is fed into the bowl under the mirror of the polymer solution in the bowl when fed to the working tank and the polymer solution flows over the rim of the bowl and along the conical separation in the form of a thin film. The polymer solution runs from the bottom edge of the conical separation onto a wire mesh leading to the polymer solution in the air vent.

A recirculation flow of the polymer solution into the air vent is maintained during venting. The air vent is kept at an absolute pressure of 250 - 350 mm Hg. Satisfactory degassing can also be obtained using substantially atmospheric pressure in the vent. Suitable deaeration is generally obtained in a deaerator residence time of less than 7 hours.

The vented polymer solution is pumped through a Zenith type H pump at a rate of 8.6g / min. to an orifice type spinneret tube with an opening diameter of 533 µm, an outer diameter of the injection tube of 203 µm and an injection capillary diameter of 127 µm. The spinneret has five equidistant polymer solution access ports located behind the annular extruder region and is maintained at a temperature of 50 - 50 ° C using an external electric heating jacket, and the temperature of the polymer solution is in the near this temperature. Deionized room temperature water (20-25 ° C) is fed to the spinneret at a rate of 1.2 ml / min. During the residence in the spinneret, the deionized water is heated by heat transfer. The spinneret is located 10.2 cm above the coagulation 800 1 8 45 5 6 bath. The hollow fiber precursor is extruded at a speed of 2,7 2.7 m / min.

The hollow fiber precursor runs down from the spin cap into an elongated coagulation bath. The coagulation bath contains mainly tap water and sufficient fresh tap water is added and coagulation bath liquid (liquid coagulant) purified to reduce the concentration of 1-formylpiperidine in the coagulation bath to less than 1 wt%. to keep. The liquid coagulant is kept at a temperature of 2 - U ° C. The hollow fiber precursor runs vertically down into the liquid coagulant a distance of 7-8 cm, then passes over a guide to a slightly upward sloping path through the liquid coagulant and then out of the coagulant bath. The distance over which immersion in the coagulation bath 15 takes place is 1.1 m.

The hollow fiber from the coagulation bath is then washed with tap water in three consecutive godet baths. In the first godet bath the hollow fiber is immersed over a distance of 7.3 m. The first godet bath is kept at a temperature of 20 2 - U ° C and the concentration of 1-phenylpiperidine in the bath is kept below 3% by weight. by adding fresh water and purifying the washing medium. The second and third god baths are at room temperature (e.g., 15-25 ° C, depending on the tap water temperature and laboratory temperature) and fresh water is continuously added to the godet baths. The wet hollow fiber has an outside diameter of 10 µm and an inside diameter of 155 µm.

While the hollow fiber is still wet by water, it is wound onto a bobbin with as little tension as possible using a Leesona winder 30. The bobbin contains 300 m of hollow fiber and the thickness of the hollow fiber wound on the bobbin is less than 2 cm. The bobbin is placed in a vessel with tap water and tap water is added and removed from the vessel for 2 hours at a rate of U-5 1 / hour per bobbin at the temperature of the tap water (10-20 ° C). The bobbin is then stored for 7 days in the vessel containing tap water at room temperature 800 1 8 45 -t 1 57 (20-25 ° C). After storage, the hollow fiber while still wet is wound on a strand former to form strands of hollow fiber with a length of 3 m. Winding of the hollow fiber on the strand former is carried out with the minimum tension required for winding to be carried out. The strands of hollow fiber are hung vertically with the bores of the hollow fiber open at the bottom and allowed to dry for at least three days at prevailing laboratory conditions (20-25 ° C and 50% relative humidity). The dried hollow fiber has an outside diameter of 390 µm and an inside diameter of 10 µm and appears under scanning electron microscopy to resemble the hollow fiber as shown in Fig. 1.

Test loops of 10 hollow fibers each with a length of 15 cm are manufactured. At one end, the test loop 15 is embedded in a tubular sheet through which the bores of the hollow fibers communicate. The other end is plugged.

The bores of the hollow fibers in each test loop are placed under vacuum (50 - 100 mm Hg absolute) for 10 min. Each test loop is dipped in a coating solution of 2% by weight of anhydrous polydimethylsiloxane (Sylgard 184, Dow Corning Corp.). ) in isopentane while maintaining the vacuum for 10 minutes and then removing it from the coating solution. The vacuum is maintained for 10 minutes after the test loop is removed from the coating solution and the test loops are dried at ambient laboratory conditions (20-25 ° C, hQ-50% relative humidity). The permeabilities of the test loops for hydrogen and methane are determined using substantially pure gases at the prevailing laboratory temperature (20 - 25 ° C) with the outside feed surface side (outside) of the hollow fibers under a pressure of 70 at absolute and the bore side of the hollow fiber at 1 at is absolute. The measured permeabilities generally vary slightly from one test loop to another and some variations may result from leakage into the tubing sheet, damage to the hollow fiber from handling or the like. The average hydrogen permeability often ranges from 75-150 GPU (1 x 10 cm3 (STP) / cm2.sec.cm Hg) and the average 800 1 8 45 58 methane permeability often ranges from 1-2 GPU. The ratio of the permeabilities (separation factor) for hydrogen to methane is often 50-60. The pressure at which the hollow fiber fails is determined to be more than 110 kg / cm @ -1.

Example II

A degassed polymer solution containing 32 wt% polysulfone P-3500 and a liquid carrier consisting of 1-formylpiperidine and formamide is spun through a spinneret (jet) of the type described in Example I into a hollow fiber-10 membrane according to the method given in Table B. The polymer solution (dope) temperature for the barrels 885-1, 533-1-T and 537-1 is not measured directly and may be 60 - 70 ° C. Deionized water is used as an injection liquid and is provided at a rate sufficient to maintain the internal diameter of the hollow fiber. The coagulation bath contains water and the concentration of 1-formyl-piperidine in the coagulation bath is kept below 1 wt% by purification. The hollow fiber is immersed in the coagulation bath over a distance of 1 m. The residence time of the hollow fiber in each of the three wash baths (first, second and third god bath) is as follows:

Spinning speed, residence time in each m / min. wash bath, in sec.

30.5 56.9

25 36.6 VT, U

38.1 1 + 5.5 1 + 2.7 1 + 0.6

The hollow fiber is wound on a bobbin while still damp and the bobbin is washed in cold running tap water for 16-2L + hours, then stored in a bucket filled with water for 7 days. The hollow fiber is then

dried under prevailing laboratory conditions (22-25 ° C

and 1 + 0 - 60% relative humidity) and formed into test loops, coated and examined in the manner described in Example I, 35 except that a 1 wt% Sylgard 181+ solution is used and 20 hollow fibers are used in the trial loop. The observed behavior of the hollow fiber is shown in Table C.

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Example III

The method of Example II is repeated except for the following. The degassed polymer solution consists essentially of 35% by weight polysulfone P-3500 and 6J +% by weight 1-formylpiperidine, the spin-5 cap has an outside diameter of 533 µm, an inside diameter of 203 µm and an injection capillary diameter 127 µm. The spinneret is located 10.2 cm above the liquid level in the coagulation bath, the polymer solution feed rate to

O

the spinneret is 11.8 cm / min. and the spinning speed is 10 U2.7 m / min. The temperature of the polymer solution extruded from the spinneret is 5 ° C. The coagulation bath has a temperature of 1 - 2 ° C; the first god bath, 1 - 2 ° C and the second and third god bath, 20 ° C. The residence time of the hollow fiber in each of the godet baths is 1 + 0.6 sec. The hollow fiber has an outer diameter of 6 µm and an inner diameter of 166 µm prior to drying. A scanning electron microscope photograph of a dried hollow fiber according to this example is shown in Fig. 2. The collapse pressure of this hollow fiber o is 170 kg / cm. The hollow fiber is formed into test loops, coated (except that a 2% by weight Sylgard 18U solution is used) and tested in the manner described in Example 1. The hydrogen and methane permeabilities of the uncoated hollow fiber are respectively. 39 GPU and 2.1 GPU. A hollow fiber prepared in such a manner, except that the temperature of the coagulation bath is 5 ° C, has an internal diameter (wet) of 170 µm and 2 exhibits a collapse pressure of 100 - 150 kg / cm and after coating and in test loops a hydrogen permeability of 100 GPU and a methane permeability of 3.3 GPU.

Example IV

The method of Example II is virtually repeated, subject to the exceptions below. A degassed polymer solution of 36 wt% polysulfone P-3500 and wt% of a mixture of 87 wt%. parts of 1-formylpiperidine and 13 parts of formamide are spun at a temperature of 52 ° C through a spinneret with an outer diameter of ^ 57 µm, an inner diameter of 127 µm, and an injection capillary diameter of 76 µm um at a speed of 800 1 8 45 62 o 5 cm / min. The spinneret is placed 10.2 cm above the liquid level in the coagulation bath. The spinning speed is 30.5 m / min.

The coagulation bath and first god bath are at 3 ° C and the second and third god bath are at room temperature. The residence time in each of the three godet baths is 56.9 sec. The hollow fiber is stored in water in a storage bucket for 1.2 and 24 days instead of 7 days and samples of the hollow fibers are analyzed for hydrogen and methane permeability, collapse pressure and solvent content after each of the storage periods. The hydrogen and methane permeability of a test loop containing the sample of the uncoated hollow fiber are determined for the hollow fiber stored for 1 day with an external pressure of 7.8 at absolute and a bore pressure of 4.4 at absolute and for the coated hollow fibers which resp. 1, 2 and 24 days are stored using an external pressure of 70 at absolute and a drilling pressure of 1 at absolute. The hollow fiber in the dry state has an outside diameter of 456 µm and an inside diameter of 188 µm. The results are recorded in Table D.

Table D

20 Days in storage bucket 1 2 2k

Uncoated Hg 457 permeability, GPU Uncoated CH ^ 167

permeability, GPU

25 Coated Hg 93 102 114

permeability, GPU

Coated CH ^ 2.8 3.3 1.9

permeability, GPU

Burst pressure, 140 140 170 2 30 kg / cm 1-formylpiperidine in 2.25 1.46 0.95

fiber, wt

8001845 63

Example V

The method of Example IV is essentially repeated except that the spin speed is U5.7 m / min. and the residence time in each of the godet baths is 38 sec. is. In a loop, a chimney 5 is placed between the spinneret and the liquid level in the coagulating bath, such that a saturated atmosphere exists in the chimney. The spinneret is placed 10.2 cm above the liquid level in the coagulation bath. Another loop is performed, which is almost identical except that no chimney is used and the spinneret is placed 5 cm above the liquid level in the coagulation bath. Hollow fiber samples are formed into test loops, coated, and their hydrogen and methane permeability is determined after 1 day of storage in water. The results are as follows: 15 Chimney Without chimney H2 permeability, GPU 129 123 CH ^ permeability, GPU 1.5 1.3

External centerline, 370 µm

Internal diameter, µm 171 165 20

Example VI

The method of Example II is essentially repeated, subject to the exceptions below. A degassed polymer solution consisting of 38 wt% polysulfone P-3500 and 62 wt% liquid carrier of 87 parts of 1-formylpiperidine and 13 parts of formamide is spun through a spinneret having an external diameter at 70 ° C. of 635 µm, an internal diameter of 228 µm and an injection capillary diameter of 152 µm at a rate of 6 cm / min. The spinneret is placed 2.5 cm above the liquid level of the coagulation bath and the spinning speed is 30.5 m / min. The coagulation bath and the first god bath are at 3 ° C and the second and third god bath are at room temperature. The residence times of the hollow fiber in each of the three godet baths is 56.9 sec. The coagulation bath contains 7.5 wt. Acetic acid.

The dried hollow fibers have an outer diameter of yum and an inner diameter of 171 µm. The hollow fiber 800 1 8 45 6k0 exhibits a collapse pressure of 180 kg / cif. Samples of the hollow fiber are processed into test loops and hydrogen and methane permeability are determined both before and after coating. (The uncoated permeabilities are determined at an external pressure 5 of 7.8 at absolute and a bore pressure of 1 at absolute). . The results are as follows:

Uncoated Covered

Hg permeability, GPU U09 136 CHj permeability, GPU 107 2.1 10

Example VII

The method of Example VI is essentially repeated except that the spinneret has an outside diameter of h-83 µm, an inside diameter of 152 µm and an injection capillary diameter of 76 µm and the hollow fibers are stored in a bucket under different conditions as listed in Table E.

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Example VIII

The method of Example II is essentially repeated, subject to the changes below. The polymer solution contains 32 parts by weight of polysulfone P-3500 and 68 parts by weight of a liquid carrier of 85 parts by weight of 1-formylpiperidine and 15 parts by weight of ethylene glycol and is spun at 70 ° C through a spinneret with an external diameter of 635 µm, an internal diameter of 229 µm and an injection capillary diameter of 152 µm at a rate of 7.2 µm / min. The spin speed is 1 + 2.7 m / min.

The spinneret is located 10.2 cm from the liquid level in the coagulation bath. The coagulation bath and the first god bath are at 3 ° C and the second and third god bath are at room temperature.

The residence time of the hollow fiber in each of the three godet baths is 0.6 sec. The outside diameter of the hollow fiber is 1 + 56 µm and the inside diameter is 205 µm.

The hydrogen permeability of the coated hollow fiber is 6k GPU and the carbon monoxide permeability is 0.65 GPU.

Example IX

The method of Example II is essentially repeated, except for the changes below. The polymer solution contains 32 parts by weight of polysulfone P-3500 and 68 parts by weight of liquid carrier with 90 parts of 1-formylpiperidine, 5 parts of ethylene glycol and 5 parts of water.

The polymer solution is spun at 65-70 ° C through a spinneret with an outer diameter of 508 µm, an inner diameter of 152 µm and an injection capillary diameter of 102 µm. The spin speed is i + 3.5 m / min. The spinneret is 17 cm from the liquid level in the coagulation bath. The coagulation bath and the first god bath are at 5 ° C and the second and third god bath are at room temperature. The residence time of the hollow fiber in each of the three godet baths is 38 sec. The outside diameter of the hollow fiber is 1 + 50 µm and the inside diameter is 236 µm. The hydrogen permeability of the coated hollow fiber is 100 GPU and the carbon monoxide permeability is 2.3 GPU. The permeabilities are determined using a gas mixture of 25 moles hydrogen and 75 moles carbon monoxide using an external pressure of 150 cm Hg 800 1 8 45 67 absolute and laboratory vacuum on the bore side of the hollow fibers.

Example X.

The method of Example II is essentially repeated, subject to the changes below. The polymer solution is prepared from 32 parts by weight polysulfone P-35QO and 68 parts by weight liquid carrier containing 80 parts by weight of 1-formylpiperidine, 10 parts by weight of ethylene glycol and 10. parts of acetone. The concentration of the acetone is not determined after degassing. The polymer solution is spun at 80 ° C through a spinneret with an outer diameter of 635 µm, an inner diameter of 228 µm and an injection capillary diameter of 152 µm. The spinning speed is 26.2 m / min. The spinneret is 20.3 cm above the liquid level in the coagulation bath.

The coagulation bath and the first god bath are at 0 ° C and the second and third god bath are at 1h ° C. The residence time of the hollow fiber in each of the three godet baths is 66 sec. The bore of the hollow fiber is off-center and the outside diameter of the hollow fiber (wet) is 3 ^ -2 µm and the inside diameter 165 um. The hydrogen permeability of the uncoated hollow fiber is 225 GPU and after coating 82 GPU and the methane permeability of the uncoated hollow fiber is 50 GPU and after coating 1.6 GPU.

Example XI

The method of Example II is essentially repeated, subject to the changes below. The polymer solution contains

50% by weight of polysulfone P-1700 (a low molecular weight polysulfone, but otherwise similar to P-3500, from Union Carbide Company) and 60% by weight of a liquid carrier with 87 parts by weight of 1-formyl piperidine and 13 parts of formamide. The polymer solution is spun at 3G 70 ° C through a spinneret with an outside diameter of 635 µm, an inside diameter of 229 µm and an injection capillary diameter of 152 µm at a speed of 9 cm / min.

The spinneret is located 7 * 6 cm above the liquid level in the coagulation bath. The spinning speed is 30.5 m / min. The coagulating bath and the first god bath are at U ° C and the second and third god bath are at room temperature. The residence time of the 800 hollow fiber in each of the three godet baths is 56.9 sec. The outside diameter of the hollow fiber is 39 µm and the inside diameter is 15 µm. The collapse pressure of the hollow fiber is 175 kg / cm. Samples of the hollow fibers 5 are stored in water for 7, 22 or 23 days, dried and assembled into test loops. The test loops are treated in different ways. Some test loops are rinsed with isopentane prior to coating. In this method, the bores of the hollow fibers are subjected to a vacuum for ΊΟ 10 min, immersed in isopentane at room temperature (22 -25 ° C) for 10 min while maintaining the vacuum on the bore side of the hollow fibers, and then removed from the isopentane while maintaining the vacuum for an additional 10 min. Test loops (coated and uncoated) are also suspended in a closed vessel with gaseous ammonia at room temperature and a pressure of 18 kg / cm.

Both coated and uncoated hollow fibers are subjected to this ammonia treatment. The permeabilities of the hollow fiber for hydrogen and methane are determined by different external pressures. The pressure on the bore side is 1 at absolute. The results are shown in Table F.

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Example XII

The method of Example II is essentially repeated except for the following changes. The polymer solution contains 3¼% by weight of polysulfone P-3500 and 66% by weight of a liquid carrier 5 consisting of a mixture of nearly 2g of anhydrous lithium chloride per 1000 ml of solution with 1-formylpiperidine. The polymer solution is spun at 70-80 ° C through a spinneret with an outer diameter of 635 µm and an inner diameter of 228 µm and an injection capillary diameter of 152 µm. The spinneret 10 is located 3.5 cm above the liquid level in the coagulation bath. The spinning speed is 20 m / min. The coagulation bath is at 5 ° C, the first god bath is at 5 ° C and the second and third god bath are at room temperature. The residence time in each of the three godet baths is 86 sec. The outside diameter of the hollow fiber is 685 µm, and the inside diameter is 380 µm. The permeabilities are determined according to the method described in Example IX. The coated hydrogen permeability is 80 GPU and the coated carbon monoxide permeability is 2.9 GPU. The hollow fiber has a fine, knot-like structure, as observed from scanning electron microscope photographs, and has an internal surface area of 75 m / g when using a BET analysis.

Example XIII

The method of Example II is essentially repeated, except for the following deviations. The degassed polymer solution contained 32% by weight poly (phenylene ether) sulfone obtained from ICI, Ltd., and 68% by weight of a liquid carrier consisting of 90% by weight of 1-formylpiperidine and 10% by weight of formamide. The spinneret dimensions are outside diameter 533 µm, inside diameter 203 µm 30 and injection capillary diameter 13 µm. The polymer solution speed through the spinneret is 7.1 cm / min. and the take-up speed is k2tk m / min. The coagulation and first wash bath are at 1 - 2 ° C and the second and third wash bath are at 19 ° C. The polymer solution temperature is approximately in the range of +35 -55 ° C and the dimensions of the hollow fiber membranes for drying are outer diameter U35 µm and inner diameter 150 µm; 800 1 8 45 71 a sample, however, has an oval bore configuration.

The observed behaviors of the hollow fiber membranes are shown in Table G.

Table G

5 Loop no. Dope temperature ° C Permeabilities, GPU * (approx.) Uncoated (7.3) Coated (68) H2 0¾ H2 0¾ 1 55 325 120 In 1.3 2 50 1 * 00 11 * 0 1 * 7 1.0 10 3 1 * 0 170 50 35 0.3 * All permeabilities are determined with a bore side pressure of 1 at absolute. The outside print in at absolute is stated in brackets.

Example XIV

The method of Example II is essentially repeated, subject to the following deviations. The degassed polymer solution contains 32% by weight polysulfone (P-3500) and 68% by weight of a liquid carrier consisting of 90% by weight of 1-acetylpiperidine and 10% by weight of formamide. The spinneret dimensions are an outer diameter of 581 µm, an inner diameter of 178 µm and injection capillary diameter of 101 µm. The spinneret is 5 cm above the level of the liquid coagulant and has a temperature of 57 ° C. The recording speed is 1 * 2.1 * m / min. . The coagulation and first wash bath are at a temperature of 2 ° C and the second and third wash bath are at a temperature of 16 ° C. Further details are provided in Table H.

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Example XV

A hollow fiber is prepared according to the method described for loop No. 533-1 in Example II, except that the hollow fiber was stored in water for 7 days.

5 Samples of the hollow fiber are dried in a temperature and humidity setting environment (air) under various conditions and then processed into a test loop.

The hydrogen and methane permeability of coated and uncoated hollow fiber are determined. The results are reported in Table J.

80 0 1 8 45

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Example XVI

The method of Example I is essentially repeated except for the changes below. The polysulfone is dried at atmospheric pressure under a powered dry air atmosphere for 2 days. The deaeration of the polymer solution is carried out under atmospheric pressure under dry air. The polymer solution is extruded through the spinneret at a rate of 8.1 cm / min. and the take-up speed is H 2, H m / min. The outside diameter of the wet hollow fiber is 50 µm and the inside diameter is 155 µm. When the strands of hollow fibers are hung up to dry, the hollow fibers continue to form a loop, i.e. they do not open at the bottom.

The dried hollow fiber membranes have an outside diameter of 100 µm and an inside diameter of 100 µm.

Example XVII

The method of Example XII is essentially repeated except for the changes below. The polymer solution contains 3U by weight of a suspension polymerized copolymer of 33% by weight of acrylonitrile and 67% by weight of styrene in 66% by weight of a liquid carrier containing 75% by weight of 1-formylpiperidine and 25% by weight of formamide . The spinneret is 0.6 cm above the level of the liquid coagulant and the take-up speed is 13 - 1 U m / min. The coagulation bath and the first wash bath are at 2 - 3 ° C and the second and third wash bath are at 17 ° C. The hollow fibers 25 are dried and dipped in methanol or pentane and then exposed to form vapor at low partial pressure. The hollow fiber membranes are then coated with a solution of 3% by weight Sylgard in pentane. The coated hydrogen permeability is 20 - Ho GPU and the separation factor for hydrogen versus carbon monoxide is 20 - kO.

Example XVIII

The method of Example XII is essentially repeated except for the changes below. The polymer solution contains 30% by weight of a methyl brominated poly (phenylene oxide) (about 35-5% by weight brominated) in 70% by weight of 1-formylpiperidine. The spinneret is 2.6 cm above the level of the liquid coagulant 80 0 1 8 45 76 and the take-up speed is 13 - 1 ^ m / min. The coagulant and first wash bath are at k6 - U8 ° C and the second and third wash baths are at 1U ° C. After coating, the hollow fiber membranes exhibit a hydrogen permeability of 90 - 100 GPU and a hydrogen to carbon monoxide separation factor of 13 800 1 8 45

Claims (34)

1. A method of manufacturing an anisotropic membrane in which a polymer solution of a membrane-forming polymer in a liquid carrier containing solvent for the membrane-forming polymer is provided in the form of a precursor and then coagulated in a liquid coagulant containing water contains, characterized in that a liquid carrier is used containing N-acylated heterocyclic solvent of formula 1, wherein X is a group -CHg-, N (R *) -, 10 or -0-, R hydrogen, a methyl or is ethyl group and R 'is hydrogen or methyl group. 2. Process according to claim 1, characterized in that an anisotropic hollow fiber membrane is produced, by a. Extruding the polymer solution through an annular spinneret in order to form a hollow fiber precursor and keeping this polymer solution at a temperature sufficient during extrusion. is to keep the polymer almost completely in solution, b. inject a fluid into the bore of the hollow fiber precursor as it is extruded from a spinneret, the injection fluid being miscible with the liquid carrier and injected at a rate such that the bore of the hollow fiber precursor remains open; c. contacting the exterior of the hollow fiber precursor with the liquid coagulant, the liquid coagulant essentially consisting of water and containing less than 5% by weight of liquid carrier, the liquid coagulant being miscible with the liquid carrier and the injection fluid and the contact is sufficient to coagulate polymer in the hollow fiber precursor under conditions of the liquid coagulant to obtain a hollow fiber, and d. the hollow fiber washes with a non-solvent for the polymer in order to reduce the liquid carrier content in the hollow fiber to less than 5% by weight, based on the weight of the polymer in the hollow fiber. 80 0 1 8 45 Process according to claim 1 or 2, characterized in that the N-acylated heterocyclic solvent consists of at least one of the following compounds: 1-formylpiperidine, 1-acetylpiperidine, 1-formylmorpholine or 1-acetylmorpholine. Process according to one or more of the preceding claims, characterized in that, with respect to the polymer, the liquid carrier and the polymer system has a second transition coefficient of at most 15 x 10 .mu.m / cmfVg2 at 25 ° C. 5. Process according to one or more of the preceding claims, characterized in that a liquid carrier is used with a heat of dilution at 25 ° C in the liquid coagulant of more than -3.5 kcal / mol, 6. Process according to one or more of the preceding claims, characterized in that a polymer is used consisting wholly or partly of polysulfone. 7. Process according to claim 6, characterized in that a polysulfone consisting wholly or partly of a polysulfone with repeated structural unit of formula 2 is used, wherein R 1 and R 2 each independently have an aliphatic or aromatic hydrocarbon-containing group with 1 - Uo are carbon atoms and the sulfonyl group is attached to an aliphatic or aromatic carbon atom. 8. Process according to claim 7, characterized in that a compound of formula 2 is used in which at least one of the groups R 1 and R 5 contains an aromatic hydrocarbon-containing group. 9. Process according to claim 7, characterized in that a polysulfone with a structure of formula 6 is used, in which n equals 50-80. Process according to one or more of the preceding claims, characterized in that a liquid carrier containing non-solvent is used. 11. Method according to one or more of the preceding claims, characterized in that the washed hollow fiber 35 is dried at a temperature which does not have an undue adverse effect on the hollow fiber membrane. 800 1 8 45 12. Process according to one or more of the preceding claims, characterized in that a liquid coagulant containing at least 75% by weight of water is used. 13. Process according to one or more of the preceding claims, characterized in that the liquid coagulant is used at a temperature of at least -15 ° C to below 20 ° C. 11 *. Process according to claim 13, characterized in that the temperature of the liquid coagulant is kept at 0 - 10 ° C. Method according to one or more of the preceding claims, characterized in that the annular spinneret is placed above the surface of the liquid coagulant. 16. Process according to one or more of the preceding claims, characterized in that a polymer solution is used which contains at least 25% by weight of polymer. Process according to one or more of the preceding claims, characterized in that a polymer solution is used containing 28 - 1 * 0% by weight of polymer. Process according to one or more of the preceding claims, characterized in that a polymer solution is used with a viscosity at the extruding temperature of 10,000-500,000 cp. 19. Process according to one or more of the preceding claims, characterized in that a liquid carrier is used which contains non-solvent, the non-solvent containing at least one of the following compounds: formamide, ethylene glycol or water. 20. Anisotropic membrane obtained by the method according to one or more of the preceding claims. 21. A dry, integral anisotropic hollow fiber membrane for the separation of at least one gas from a gaseous mixture, provided with a homogeneously formed, thin external separating layer on an open cellular support and containing polysulfone, in which the majority of the volume of the hollow fiber membrane wall consists of cells with an average main size of less than 2 µm and the open cellular support contains practically no macro-cavities with a main size of more than 3 µm and a ratio of maximum length to maximum width of more than 10, the hollow fiber membrane exhibiting a ratio of 5 permeability of at least one of the gases hydrogen, helium and ammonia to the permeability constant of the material of the hollow fiber membrane for that gas of at least 5 x 10 ^ cm-1; a permeability ratio of (i) the permeability of a gas with a lower molecular weight. divided by the permeability of a gas with a higher molecular weight. to (ii) the square root of the molecular weight. of the gas with lower molecular weight. divided by the square root of the molecular weight. of the gas with higher molecular weight, of at least 6, in which the gas with lower molecular weight. consists of hydrogen or helium and the gas with higher molecular weight. consisting of nitrogen, carbon monoxide or carbon dioxide and has a permeability constant in the polysulfone which is at least 10 times less than the permeability constant of the gas of lower molecular weight. in that material, and a collapse pressure of at least lt (Tg) (t / D), where Tg is the tensile strength of the polysulfone, t the wall thickness is 20 and D is the outside diameter of the hollow fiber membrane. Polysulfone hollow fiber membrane according to claim 21, characterized in that it does not contain macro-cavities. 23. Hollow fiber membrane according to claim 21 or 22, characterized in that at least 90 vol. # Of the wall of the hollow fiber membrane consists of cells with a main cross-section of less than 2 µm, 2k. Hollow fiber membrane according to one or more of Claims 21 to 23, characterized in that at least 90 vol. # Of the wall of the hollow fiber membrane consists of cells with a main size of less than 1 µm, Hollow fiber membrane according to one or more of claims 21-2h, characterized in that the main configuration ratio of segments of the wall of the hollow fiber membrane containing cells having the largest average main size and no macro-cavities, at least 0, 03. 800 1 8 45 Λ - ft " Hollow fiber membrane according to one or more of claims 21 to 25, characterized in that the wall of the hollow fiber membrane contains cells with a main size of more than 0.2 / um and the ratio of average wall thickness to an average of 5 cell cross-sections. surface of the largest cells is at least 1 cm. Hollow fiber membrane according to one or more of claims 21 to 26, characterized in that the hollow volume of the wall of the hollow fiber membrane is at least 1 * 0 vol. To 10 70 vol. #. Hollow fiber membrane according to one or more of claims 21 to 27, characterized in that the hollow volume of the wall of the hollow fiber membrane is more than 1 * 5% by volume to 65% by volume. 29. Hollow fiber membrane according to one or more of claims 21 to 28, characterized in that the collapse pressure of the O hollow fiber membrane is greater than 10 (<j>) (Tg) (t / D), wherein <j> is the volume fraction of the hollow fiber membrane material in the wall of the hollow fiber membrane. Hollow fiber membrane according to one or more of claims 21 to 29, characterized in that it has a relationship of (i) the fracture of the difference between the permeabilities of a readily permeable gas and a less readily permeable gas, divided by the permeability of the less readily permeating gas multiplied by (ii) the ratio of the permeability constant of the less readily permeating gas to the permeability constant of the easy permeating gas, of at least 0.01, wherein the easy permeating gas has a permeability constant at least 30 times greater than the permeability constant of the less readily permeable gas and readily permeable gas and less readily permeable gas about the same molecular weight. to own. Hollow fiber membrane according to one or more of claims 21 to 30, characterized in that the thickness of the outer skin is less than 1000 8. 800 1 8 45 Hollow fiber membrane according to one or more of claims 21 to 31, characterized in that the outer skin is less than 500 2. 33. Hollow fiber membrane according to one or more of claims 21 to 32, characterized in that the permeability ratio is at least 7.5. 31 *. Hollow fiber membrane according to one or more of claims 21 to 33, characterized in that it has a maximum pore size of less than 150 µ. 35. The hollow fiber membrane according to one or more of claims 21 to 31 *, characterized in that the polysulfone is formed by a polysulfone of the repeated structural unit of formula 2, wherein and R 2 are independently aliphatic or aromatic hydrocarbon containing group having 1 - 1 * 0 is 15 carbon atoms and the sulfonyl group is bonded to an aliphatic; or aromatic carbon atom. Hollow fiber membrane according to one or more of claims 21 to 35, characterized in that at least one of the groups R 1 and R 5 contains an aromatic hydrocarbon-containing group 20. Hollow fiber membrane according to one or more of claims 21 to 36, characterized in that the polysulfone is formed by a polysulfone of the structure of formula 6, wherein n equals 50 - 80. Hollow fiber membrane according to one or more of Claims 21 to 37, characterized in that the material of the hollow fiber membrane has a tensile strength of at least 350 kg / cm. 39. A method of manufacturing an anisotropic membrane, as described herein. 30 1 * 0. Hollow fiber membrane, as described herein. 800 1 8 45