JP2000061279A - Method for controlling structure of cellulosic separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for arbitrarily controlling the structure of a cellulosic separation membrane in the range from a uniform dense structure to a skin-core structure by using the same solidifying bath when the chemically stable separation membrane less in the adsorption of org. substances is produced. SOLUTION: When a cellulosic separation membrane is produced from a cupro-ammonium cellulose soln., an aq. soln. of a potassium salt is used as a solidifying bath and the structure of the separation membrane is arbitrarily controlled over the range from a uniform dense structure to a skin-core structure by varying at least one selected from the temp. and concn. of the solidifying bath and solidification time. The temp. of the bath ranges from 0 to 100 deg.C and the concn. ranges from 3 to 50 wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to cellulose used for separating low to medium molecular weight organic substances in medical fields such as hemodialysis, concentration / purification in food / fermentation / pharmaceutical fields, and water treatment fields. The present invention relates to a method for manufacturing a separation membrane.

[0002]

2. Description of the Related Art Membranes are used in hemodialysis, food / pharmaceutical concentration / purification, battery separators, gas separation, and in recent years, water purification technology using membranes has progressed due to deterioration of water source water quality. It covers a wide range of fields. With the spread of the above applications, the optimum structure, permeation / separation performance, and durability required for the membrane have become extremely wide-ranging.

As a material of such a separation membrane, for example, polysulfone type, polyethylene type, cellulose type, cellulose derivative type, polyamide type, polyimide type, polyacrylonitrile type, polyvinyl fluoride type, polyvinyl alcohol type polymer and the like are used. There is. When using a membrane in an aqueous solution system, for example, in a polysulfone membrane,
Although it is excellent in heat resistance and solvent resistance, it is a hydrophobic material, so the organic substances in the aqueous solution to be treated are adsorbed on the membrane surface and inside the pores, and the filtration rate due to membrane contamination and clogging becomes rapid. There was a problem that it is easy to cause a drop. To this end, JP-A-53-13679 and JP-A-59-196321.
There has been proposed a hydrophilization treatment method in which a sulfonic acid group (hydrophilic group) is introduced, as shown in Japanese Patent Publication No.

On the other hand, a reverse osmosis composite membrane composed of a polyamide-based polymer as disclosed in Japanese Patent Publication No. 55-147106 is mainly used for desalination of seawater or for water treatment, and is mainly used for removing salts from an aqueous solution or harmful. For the purpose of removing low molecular weight organic substances,
It has been used recently. However, contamination of the membrane is likely to occur due to the adsorption of cations and the adsorption of organic substances, and as a result, the flow rate is reduced and the material permeation performance is changed due to the clogging of pores. Therefore, a chemical cleaning process is required in the film processing process, resulting in a high processing cost. In addition, there is a problem in that it is easily decomposed by an oxidizing agent such as chlorine for disinfection in tap water and is chemically stable.

On the other hand, a separation membrane using a cellulosic polymer is a hydrophilic material, so that it is less likely to adsorb organic substances such as plasma and protein, and the decrease in membrane permeation rate over time is small. Is widely used as. Further, even when it is used for concentration / purification of foods / pharmaceuticals, it is desired that the hydrophilic material has a small adsorption (organic adsorption) of a useful protein component having physiological activity on the membrane surface. Also in the water treatment field, it is desired that the hydrophilic material has a small adsorption of ions and organic substances contained in the water to be treated and a small decrease in the membrane flow rate.

From the above, a membrane using a cellulosic polymer for the purpose of separation in an aqueous solution is promising, and a new membrane for real-time production of a membrane having a desired optimum structure and permeation / separation performance according to requirements. Technology is needed. Conventionally, as a method for producing a membrane for hemodialysis, a method for producing a hollow fiber membrane for dialysis from a copper ammonia cellulose solution using an aqueous sodium hydroxide solution (JP-B-50-40).
No. 168). Results of chemical structure change of copper-ammonium-cellulose complex during coagulation (Ikuya Miyamoto, Toshihiko Matsui, Masatoshi Saito, Kunihiko Okajima, Japan Textile Machinery Society, Vol.49,
No. 12, p. 45-52 (1996)), a normanated gel was formed, but the cross-sectional structure of the film obtained after the regeneration treatment was a uniform and dense structure. Further, JP-A-49
As described in JP-A-134920, the concentration of sodium hydroxide aqueous solution is in the range of 5 to 15% by weight, and a uniform and dense structure can be obtained. At 5% by weight or less, almost no solidification occurs, and at 15% by weight or more, skin
Although hollow fibers having a core structure are likely to be formed, the degree of formation of the skin / core structure is insufficient, and the water permeability is rather deteriorated. Further, in the manufacturing process, there is a problem of danger to human body (chemical damage, etc.) when exposed to liquid due to corrosive property of sodium hydroxide itself. In addition, when a film-like film is formed by using an aqueous solution of sodium hydroxide as a coagulant, after the regeneration treatment, the shrinkage in the plane of the film is large and the film size cannot be maintained. When composited by a method that does not involve stretching such as coating on a non-woven fabric, paper, hollow fiber membrane, etc.), the above-mentioned problem is also problematic in that the shape retention of the final molded product is poor.

Further, from a copper ammonia cellulose solution,
A method for producing a hollow fiber membrane for dialysis using an aqueous solution of sulfuric acid (Japanese Patent Publication No. 55-1363, JP-A No. 2-135130) is disclosed, and the membrane cross section has a portion close to the outer surface of the hollow fiber as an inner surface / intermediate portion. The structure was more dense (gradient structure) than the part close to the part. Conventionally, as a technique for producing a molded body such as a fiber or a hollow fiber membrane from a copper ammonia cellulose solution, any solution that does not dissolve copper ammonia cellulose can be used as a coagulation bath. The prior art also lists a number of coagulants. However, what is specifically shown as an example is limited to water and the above-mentioned sodium hydroxide and sulfuric acid, and other coagulants are merely examples. Other coagulants could not be used in practice due to reasons such as economic efficiency, work environment problems, and ease of recovery.

In the conventional manufacturing method, when controlling the cross-sectional structure of the membrane to have a uniform and dense structure or a gradient structure, it is necessary to change the coagulant species as described above, and at the same time the water permeability which can be reached is achieved. There was a limit. Therefore, depending on the required specifications of the membrane, it is necessary to fundamentally change the manufacturing equipment, which requires resources for capital investment.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a method for producing a cellulose separation membrane that is chemically stable and has a small amount of adsorbed organic substances. It is an object to provide a method for arbitrarily controlling the structure of a separation membrane in the range.

[0010]

Means for Solving the Problems As a result of intensive studies made by the present inventors, in the production of a cellulose separation membrane from a copper ammonia cellulose solution, the structure of the separation membrane is controlled by using an aqueous solution of calcium salt as a coagulation bath. The inventors have found that they can be achieved and have completed the present invention.

That is, according to the present invention, (1) at the time of producing a cellulose separation membrane from a copper ammonia cellulose solution, an aqueous solution of calcium salt is used as a coagulation bath, and at least one selected from the temperature, concentration and coagulation time of the coagulation bath. A method for controlling a cellulose separation membrane structure, characterized in that a cellulose separation membrane having a desired structure is obtained over a range from a uniform dense structure to a skin / core structure by changing the species.
(2) The method for controlling the structure of a cellulose separation membrane according to claim 1, wherein the temperature range of the coagulation bath is 0 to 100 ° C, and (3) the concentration range of the coagulation bath is 3 to 50% by weight. A method for controlling a separation membrane structure is provided.

The present invention will be described in detail below. In the present invention, the method for producing a cellulose separation membrane can be applied to an existing film forming process, and a copper ammonia cellulose solution is cast,
Or after extruding from the spinneret having an annular discharge port,
Molded by coagulation, regeneration and washing process. The form of the cellulose separation membrane may be any of film, tube, and hollow fiber. Further, drafting or stretching can be applied to the above-mentioned solidification and regeneration steps, as is done in a general-purpose process. Furthermore, a composite film obtained by forming a film on a porous support made of the same material or another material can be molded.

The cellulose concentration of the copper ammonia cellulose solution is in the range of 4.0 to 12.0% by weight, preferably 4.0 to 10.0% by weight. 4.0% by weight
If it is less than the above range, a brittle structure that cannot hold the molded body may be formed and mechanical properties may become insufficient. When it exceeds 12.0% by weight, it is difficult to adjust the solution, and the viscosity of the solution is so high that the operation during casting or extrusion from the spinneret becomes difficult. However, when forming a composite film obtained by forming a film on a porous support, the cellulose concentration is 1.0
It is possible even from a low concentration of about wt%.

The degree of polymerization of cellulose molecules is 600 to
A range of 2000 is desirable. If it is less than 600, the structure becomes brittle and the mechanical properties may be insufficient. If it exceeds 2000, it becomes difficult to prepare a copper-ammonia cellulose solution. The copper ammonia cellulose solution may be prepared by a conventionally known method. It is possible to purify linter, which is a cellulose raw material, and dissolve the purified linter in a copper ammonia solution to obtain a copper ammonia cellulose solution.

In the present invention, it is necessary to use an aqueous solution of calcium salt for the coagulation bath. As the calcium salt, one that can be dissolved in water, such as calcium acetate, calcium chloride, or calcium bromide, is used. Of these, calcium chloride is preferred. Further, the concentration of the calcium salt aqueous solution used as a coagulant may be in a concentration range that can be dissolved in water,
It is preferably 3 to 50% by weight. The calcium salt aqueous solution is brought into contact with the copper ammonia cellulose solution to gel the copper ammonia cellulose solution, and then decopperization / ammonia treatment from the gel by the regenerant,
A dense layer can be formed by regenerating cellulose. The higher the coagulation bath concentration, the faster the gelation rate and the denser the film. If it is less than 3% by weight, the gelling ability of calcium salt is weak and a dense layer cannot be formed. When it exceeds 50% by weight, the salt concentration in the coagulation bath is high and the subsequent recovery process is not easy. More preferably, it is in the concentration range of 5 to 30% by weight.

The temperature range of the coagulation bath is a temperature range of 0 to 100 ° C. in order to form a dense layer on the contact surface side of the coagulating liquid. If it is lower than 0 ° C, the solubility in water becomes poor. Since the calcium salt compound can be dissolved and the temperature can be easily controlled, the range of 10 to 80 ° C is preferable. The higher the coagulation bath temperature, the faster the gelation rate and the more dense the layer can be formed.

The solidification time is preferably in the range of 0.2 seconds to 60 minutes. The longer the coagulation time is, the more the gelation penetrates inside from the contact surface with the coagulant, and the thicker the dense layer can be. After 60 minutes, the structure in which gelation can be completely permeated through the entire film thickness does not change thereafter. Moreover, it takes too much time and is not industrial. More preferably, it is in the range of 10 seconds to 30 minutes.

The degree of formation (thickness) of the dense layer inside the film can be arbitrarily controlled by changing one, two, or three of the above-mentioned temperature / time during coagulation and coagulation bath concentration. it can. Film forming process and desired film structure,
The above setting range and combination can be changed according to the physical properties.

As the regenerant, an aqueous acid solution such as sulfuric acid or hydrochloric acid or an aqueous ammonium salt solution such as ammonium sulfate, ammonium chloride or ammonium acetate is used. The concentration of the regenerant is preferably 1 to 50% by weight. If it exceeds 50% by weight, the cellulose may be decomposed by the aqueous acid solution. If it is less than 1% by weight, regeneration is not sufficiently performed.

Further, by the water washing step, the excess solvent can be sufficiently washed off to provide the membrane. The thickness of the cellulose separation membrane cannot be specified unconditionally depending on the required characteristics of the membrane, but is usually in the range of 1 to 500 μm. In order to improve the water permeability, it is better to make the film thickness thinner, and in order to improve the mechanical strength characteristics even if the water permeability property is low, the film thickness is better. In the case of coating on a porous support to form a composite, the thickness of the cellulose separation membrane layer itself can be further reduced to 1 μm or less for the latter purpose.

The membrane of the present invention is further impregnated with a pore size-retaining agent such as glycerin, ethylene glycol, or polyethylene glycol disclosed in JP-A-3-8422, followed by heating and drying, or by using acetone, methanol, or the like. A dry film can be obtained by a method of drying after replacing water with an organic solvent. Further, it can be assembled in a known module shape. The module shape may be any of flat membrane laminated type, flat membrane folded type, tubular coil type, hollow fiber type and the like.

The uniform and dense structure in the present invention means a structure in which the average pore diameter of substantial pores is in the range of 1 nm to 500 nm. The skin-core structure is a dense structure having an average pore diameter of 1 nm to 500 nm near the surface and a non-uniform structure having a coarse portion having an average pore diameter significantly larger than the dense structure inside. Say. skin·
The core structure may have an inclined structure (gradient structure) in which the pore diameter gradually increases from the vicinity of the front surface portion toward the inside and the back surface portion. The larger the thickness ratio of the dense layer, the higher the strength of the separation membrane.

In the method for producing a cellulose separation membrane according to the present invention, the structure of the separation membrane can be controlled in the range from the uniform dense structure to the skin-core structure by controlling the thickness of the dense layer to an arbitrary value, and further the water content can be controlled. The permeation rate and the permeability of the substance can be controlled. For example, the cellulose separation membrane produced by the present invention shows selective separation of harmful organochlorine compounds in an aqueous solution, which is an environmental problem, and separability of low molecular weight to medium molecular weight organic matter, and nanofiltration, It can be used as a membrane for ultrafiltration and dialysis.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. The structures of the membranes used in the examples and comparative examples and the method of measuring the permeation performance are as follows. (1) Structure measurement of film cross section The undried film immediately after the production was freeze-fractured and then freeze-dried, and the cross section was observed with a scanning electron microscope (SEM) (S-800 manufactured by Hitachi, Ltd.). The dense layer thickness ratio is
It was calculated from the electron micrograph by the following formula (1). Dense layer thickness ratio (−) = Dense layer thickness (μm) / Total thickness (μm) (1) (2) Permeation performance measurement Chloroform at a concentration of 10 mg / ml (molecular weight: 119.
2) The aqueous solution was treated at a pressure of 1 kgf / cm ² , and the concentrations of the solution that had passed through the membrane and the solution before the treatment were measured by gas chromatography using a headspace method (manufactured by Shimadzu Corporation G
C / MSQP5000). VB ₁₂ (Molecular weight:
1357) was dissolved in water to a concentration of 20 mg / ml, and the concentration of the solution that passed through the membrane and the solution before treatment was measured at a wavelength of 3
The measurement was carried out by measuring the absorbance at 60 nm. Concentration Co before treatment
(Mg / ml), the concentration of the liquid passing through the membrane Cf (mg / m
The rejection rate (%) from 1) was calculated from the following equation (2). Rejection rate = (1-Cf / Co) × 100 (2) Further, the water permeation rate is 1 kgf at the membrane area Sm ²
/ Cm ² (ΔP) at 25 ℃ aqueous solution, time t
The amount Vml of liquid that passed through the membrane per minute was measured. The water permeability UFR (ml / m ² · hr · mmHg) was calculated from the following equation (3). UFR = V × 60 / (t × S × ΔP × 735.7) (3)

[0025]

Examples 1 to 4 A cellulose solution prepared by dissolving 10% by weight of cellulose linter in a copper ammonia solution was cast on a glass plate to a thickness of 250 μm. Then 1
In a 10 wt% concentration calcium chloride aqueous solution at 0 ° C.,
It was immersed for 1, 2, 5 and 30 minutes to solidify. Then 20
It was immersed in a 2 wt% sulfuric acid aqueous solution at 0 ° C. for 10 minutes for regeneration, and then washed with water. The films obtained by solidifying for 1, 2, 5, 30 minutes are referred to as Examples 1, 2, 3, 4 respectively. The film was cut out, the water permeability was measured, and freeze cutting was performed, followed by vacuum drying, and the cross section was observed with an electron microscope. The measurement results are shown in Table 1. The cross-sectional structure and physical properties could be easily controlled simply by changing the solidification time.

[0026]

Examples 5 to 7 A cellulose solution prepared by dissolving 10% by weight of cellulose linter in a copper ammonia solution was cast on a glass plate to a thickness of 250 μm. Then 25
It was immersed in an aqueous solution of calcium chloride having a concentration of 10% by weight at 0.5 ° C. for 0.5 minutes, 2 minutes, and 30 minutes to solidify. afterwards,
It was regenerated by immersing it in a 2% by weight sulfuric acid aqueous solution at 20 ° C. for 10 minutes and then washed with water. The films obtained by coagulating for 0.5, 2 and 30 minutes are referred to as Examples 5, 6 and 7, respectively. The film was cut out, the water permeability was measured, and after freeze fracture, vacuum drying was performed, and the cross section was observed with an electron microscope. The measurement results are shown in Table 2. The cross-sectional structure and physical properties could be easily controlled simply by changing the solidification time.

[0027]

Example 8 A cellulose solution prepared by dissolving 10% by weight of cellulose linter in a copper ammonia solution was cast on a glass plate to a thickness of 250 μm. After that, it was immersed in a 10 wt% concentration calcium chloride aqueous solution at 40 ° C. for 2 minutes to be solidified. Then, it was immersed in a 2% by weight sulfuric acid aqueous solution at 20 ° C. for 10 minutes for regeneration, and then washed with water. The film was cut out, the water permeability was measured, and freeze cutting was performed, followed by vacuum drying, and the cross section was observed with an electron microscope. The measurement results are shown in Table 2.

[0028]

Example 9 A cellulose solution prepared by dissolving 10% by weight of cellulose linter in a copper ammonia solution was cast on a glass plate to a thickness of 250 μm. Then, it was immersed in an aqueous calcium chloride solution having a concentration of 30% by weight at 25 ° C. for 2 minutes to be solidified. Then, it was immersed in a 2% by weight sulfuric acid aqueous solution at 20 ° C. for 10 minutes for regeneration, and then washed with water. The film was cut out, the water permeability was measured, and freeze cutting was performed, followed by vacuum drying, and the cross section was observed with an electron microscope. The measurement results are shown in Table 2.

[0029]

Comparative Examples 1 to 4 A cellulose solution prepared by dissolving 10% by weight of cellulose linter in a copper ammonia solution was cast on a glass plate to a thickness of 250 μm. Then 2
In a 10% strength by weight aqueous sodium hydroxide solution at 5 ° C,
It was immersed for 1, 2, 5 and 30 minutes to solidify. Then 20
It was immersed in a 2 wt% sulfuric acid aqueous solution at 0 ° C. for 10 minutes for regeneration, and then washed with water. Those having coagulation times of 1, 2, 5, and 30 minutes are referred to as Comparative Examples 1, 2, 3, and 4, respectively. The film was cut out, the water permeability was measured, and freeze cutting was performed, followed by vacuum drying, and the cross section was observed with an electron microscope. The measurement results are shown in Table 2. All of Comparative Examples 1 to 4 had a uniform and dense structure, and the cross-sectional structure could not be changed.

[0030]

Comparative Examples 5 to 8 A cellulose solution in which 10% by weight of cellulose linter was dissolved in a copper ammonia solution was cast on a glass plate to a thickness of 250 μm. Then 25
It was immersed in an aqueous solution of sulfuric acid having a concentration of 5, 10, 20, 30% by weight at 0 ° C. for 1 minute to be solidified. Then, it was immersed in a 2% by weight sulfuric acid aqueous solution at 20 ° C. for 10 minutes for regeneration, and then washed with water. Films coagulated with 5, 10, 20, 30 wt% sulfuric acid aqueous solutions are referred to as Comparative Examples 5, 6, 7, and 8, respectively.
The film was cut out, the water permeability was measured, and freeze cutting was performed, followed by vacuum drying, and the cross section was observed with an electron microscope. The measurement results are shown in Table 2. Comparative Examples 5 to 8 all had a skin-core structure, and the cross-sectional structure could not be changed.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

According to the method of the present invention, in the production of a cellulose separation membrane, the same coagulant is used, the water permeability is wide, and the structure of the separation membrane is arbitrarily selected in the range from a uniform dense structure to a skin-core structure. Can be controlled.

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Claims (3)

[Claims] 1. When producing a cellulose separation membrane from a cuprammonium cellulose solution, an aqueous solution of a calcium salt is used as a coagulation bath, and at least one selected from the temperature, concentration and coagulation time of the coagulation bath is uniformly used. A method for controlling a cellulose separation membrane structure, which comprises obtaining a cellulose separation membrane having a desired structure from a dense structure to a skin / core structure. 2. The method for controlling a cellulose separation membrane structure according to claim 1, wherein the temperature range of the coagulation bath is 0 to 100 ° C. 3. The method for controlling a cellulose separation membrane structure according to claim 1, wherein the concentration range of the coagulation bath is 3 to 50% by weight.