WO2011161214A1 - Process for removing c2+ hydrocarbons from natural gas or gas which accompanies mineral oil using membranes - Google Patents

Abstract

The invention relates to a process for removing C₂₊ hydrocarbons from natural gas or gas which accompanies mineral oil using membranes. This involves passing a feed gas under a pressure of 2 to 500 bar within a temperature range from -30°C to +60°C through a membrane composed of a porous inorganic material or an organic polymer. The C₂₊ gas permeates through the membrane as a preferred adsorbate or condensate and accumulates in the permeate space as a result of an increase in the amount controlled by the membrane to 1.5 times to 50 times the level in relation to the feed side. The condensate of C₂₊ hydrocarbons which results from the temperature going below the dew point is drawn off from the permeate side within the temperature range from -70°C to +50°C at a pressure of 1 to 360 bar. The separation is effected under practically relevant pressure conditions without energy-intensive expansion or cooling and with improved separation performances. The process can be used advantageously in relatively small mineral oil fields with a reduced level of process technology complexity. The use of natural gas in accordance with its delivery pressure is particularly advantageous.

Description

Process for the separation of C ₂₊ hydrocarbons from natural gas or associated petroleum gas using membranes

The invention relates to a process for the separation of C ₂₊ hydrocarbons from natural gas or associated petroleum gas using membranes. State of the art

 Natural gas is a mixture of various hydrocarbons (HC) in a clearly fluctuating composition. The composition of natural gas and associated gas depends on the geographical location, type and depth of the deposit. In addition to "dry" natural gases, which contain almost only methane and little other light hydrocarbons, other, "wet" natural gases (such as associated gas) occur in which considerable amounts of easily liquefied hydrocarbons (propane, butane, pentane) and higher saturated hydrocarbons (HKW) are present. In addition, the natural gases can still contain very different amounts of nitrogen, carbon dioxide and sulfur, especially in the form of hydrogen sulfide. Natural gas is usually saturated with water during production.

 When transporting the gas, changes in physicochemical parameters, such as temperature and pressure, can cause condensates that lead to malfunctions and system failures in the system or at the end customer. This incoming gas liquefaction is caused by falling below the hydrocarbon dew point. The hydrocarbon dewpoint is defined as the saturation point of a hydrocarbon in a hydrocarbon mixture. When the dew point is reached, condensation sets in. Lowering the temperature may cause the dew point to be reached. A possible cause of gas cooling, in addition to external temperature influences, is the Joule-Thomson effect with pressure reduction of the gas. Before the grid feed, which is characterized by the expansion of gases, it is therefore usually necessary to go through the following preparatory steps:

 Separation of free liquid (condensate separation)

Desulphurization, removal of C0 ₂

 Setting the steam dew point (gas drying)

- Setting the hydrocarbon dew point

In addition to the technological need for hydrocarbon separation from natural gas, the extraction of so-called liquid gases with C _{3+ is} of importance for applications as liquid energy sources. In addition, C ₂₊ fractions are of interest as starting materials. point of large chemical derivatives. The hydrocarbon removal is not only located at the production fields, but is also necessary for underground gas storage (UGS), if former oil or gas deposits are used as a storage structure (UGS Fronhofen).

 Established methods for dew point adjustment are freezing condensation, absorption and adsorption. The state of the art for removing hydrocarbons is the freezing of the natural gas produced. Remove the temperature-liquid separators next to

Hydrocarbons, water and glycols and are operated at temperatures from -25 ° C to -30 ° C. Two methods of cryogenic extraction, low-temperature separation (LTS) and cold frac technology in gas processing are used. In the case of low-temperature separation, cooling takes place exclusively by means of a pressure release (Joule-Thomson effect), while cold-frac requires external cooling.

 LTS systems require a sufficient outlet pressure of the gas. Natural gas cools with pressure reduction by approx. 0.4 K per bar (Joule-Thomson effect). This property of the gas is exploited to separate water and higher hydrocarbons. The cooling is greater with the same overpressure, the lower the

Output temperature of the gas is. Therefore, it may be necessary to precool the gas prior to expansion cooling (Groningen gas field). If the pressure loss permitted for the gas flow is small, an LTS is no longer physically possible. In the latter case, external cold must be supplied. Since such cold-frac systems are very energy-intensive, the ambient temperature can already be considered economic k.o. Criterion. With increasing ambient temperatures, these systems become economically inefficient in a specific case.

 Hydrocarbons obtained from LTS or cold-frac processes are further worked up in rewarding quantities in refineries or at low levels

flared. Solid adsorbents are also used for hydrocarbon removal and returned to the conditioning cycle after thermal regeneration. Natural gases can be freed of C ₅ and C ₆ hydrocarbons by adsorption on activated carbon. From associated gas can be condensed by utilizing the condensation behavior by compression to 25 to 30 bar hydrocarbons. However, this method is not sufficient at gas temperatures> 0 ° C, for example to meet the GERG requirements with respect to the HC dew point. Thus, further treatment steps of the gaseous phase (eg deep-freeze condensation) are necessary.

 In US 4,203,742 the complex distillation of the individual components is

Natural gas or natural gas mixtures described. There is a stepwise decomposition, the fractions C ₃ , C ₄ and C ₅ are obtained.

 By using cooling condensation, for example, a method for

Production of liquefied natural gas from pressurized natural gases, for example in DE OS 28 20 212 described. The underlying cooling method is extended in DE 44 40 401 A1 by a technological solution for optimizing the refrigeration budget. In general, however, a cooling process for the recovery of liquid gas components consisting of C _{2+ is} considered to be energy-intensive and therefore disadvantageous.

 DE 34 45 961 A1 makes use of the Joule-Thomson effect for cooling from below

Pressure gases over their relaxation. This method proves to be disadvantageous for gases with a low delivery pressure or for technologically necessary compaction.

By preferred adsorption on porous materials, low-energy methods for enriching C ₂₊ hydrocarbons are known to the person skilled in the art. However, these processes are also energy-intensive by so-called pressure-swing processes. Thus, in order to obtain the adsorbed components, it is often necessary to work in a vacuum, with further liquefaction of the previously adsorbed species being accompanied by compression work.

A further development is the synthesis of crack-free, porous material layers, which can selectively separate C ₂₊ from the main fraction. The separation of C ₂₊ from the gas mixture takes place on account of the substance-specific adsorption capacity of the porous layer and a physical driving force, such as pressure and concentration differences on both sides of the membrane.

 WO 94/01209 discloses the synthesis of dense ZSM-5 layers and their use in selective adsorption, among others. from hydrocarbons to an applied one

Feed pressure of 100 kPa described.

 In the patent DE 693 26 254 T2 it is described that it is possible to separate butane from methane by means of carrier-supported MFI membranes, which is enriched by adsorption of the higher hydrocarbon in the permeate. The permeation tests were carried out using a sweep gas on the permeate side at pressures of <100 kPa, which are unrealistic in practice.

 Further separations of hydrocarbons and comparable components on organic porous membranes have been described. For example, was through

Santamaria et al. [M. Arruebo et al., Separation and Purification Technology 25 (2001) 275-286] described on MFI membranes the separation of natural gas components at 1 to 4 bar and pressure differences up to 3 bar. Here and as with all previously described separations of natural gas and Erdölbegleitgas components according to the adsorption, the separation is carried out by the so-called surface diffusion, which has so far deteriorated after increasing the feed pressure and the differential pressures between the feed and permeate.

All known developments are based on the problem that a mixture of various gaseous hydrocarbons is obtained as permeate, which usually contain methane as the main component. The separation efficiency of membranes is therefore usually insufficient to use the gas fraction obtained as a liquefied gas. It should either a costly compaction to obtain liquid components, or it would have to be enriched in a cascade separation Permeate further enriched with higher KW. These methods are complex in terms of apparatus or associated with high operating costs.

Object of the invention

The object of the invention is a simple and cost-effective separation of C ₂ + liquid-gas components from natural gas and associated gas using porous membranes with concomitant condensation of higher hydrocarbons without exclusive utilization of complex processes, such as cooling and compression. Another object is the separation of the C ₂₊ liquid gas components at realistic pressures occurring in practice of higher than 1 bar, in particular higher than 5 bar.

Another object is to provide a separation process in which C ₂ + gases are liquid as a permeate without additional technical measures.

Summary of the invention

The invention is that a starting gas mixture, which may be a natural gas or a Erdölbegleitgas and is referred to herein as "feed gas", at the delivery pressure of these gases, which is in the range of 2 to 500 bar, and adjusting itself after the promotion Temperature, which is in the range of -30 ° C to +60 ° C, is passed over a membrane, wherein the higher hydrocarbons from C ₂ pass through the membrane, thereby by concentration below the dew point and condensed in the permeate space are removed Detailed Description of invention

According to the invention C ₂ + hydrocarbons are separated from a natural gas or associated gas by a feed gas comprising 0.5 to 35 mol% of gaseous C ₂ + - hydrocarbons under a pressure of 2 to 500 bar in a temperature range from - 30 ° C to + 60 ° C is passed over a membrane of a porous inorganic material or an organic polymer, wherein the inorganic membrane has pore openings to the permeate side of the membrane from 0.5 to 10 nm or the polymeric membrane has higher selectivities to C ₂₊ hydrocarbons than to Has methane and the permeating C ₂₊ gas is condensed within the membrane and permeatseitig and enriched on the permeate side by Stoffmengenerhöhung to at least 1.5 times in relation to the feed side and is condensed by dew point undershooting, and the condensate of C ₂₊ -Koh- Hydrocarbons at a pressure of 1 to 360 bar in the temperature range of -70 ° C to + 50 ° C deducted from the permeate side en, wherein the pressure difference between the feed and permeate side is 1 to 140 bar and wherein no purge gases are used. The pressure on the feed side is in the range of 2 to 500 bar and corresponds to the delivery pressure of the feed gas. An essential feature of the invention is that the extracted natural gas or associated gas does not have to be subjected to additional pressure change steps. Since the extracted gases are produced with different pressure depending on the location and these pressures are regularly in the range of 2 to 500 bar, the feed gas can be passed unchanged at this pressure across the membrane.

 Since the natural gas treatment is usually pre-stressed to 70 to 80 bar, it is also an advantageous embodiment of the invention to use feed gases in the pressure range from 70 to 80 bar. Preferred pressure ranges are therefore 30 to 200 bar, in particular 30 to 85 bar.

From the feed side, the portion of the gas containing C ₂ + hydrocarbons passes through the membrane to the permeate side. This results in a pressure reduction to the feed side of 1 to 140 bar by building a corresponding back pressure on the permeate side. For example, a pressure of 200 bar is reduced to 70 bar, a pressure of 70 bar to 30 bar or a pressure of 30 bar to 20 bar or a pressure of 20 bar to 1 bar. The desired pressure on the permeate side depends inter alia on the course of the phase envelopes (see FIG. 1 a).

 Particularly advantageous are higher feed pressures in the range of 30 to 200 bar, in particular 70 to 200 bar at high methane content. This allows e.g. n-butane better than liquid component gain.

 Based on the p-T dew point curves, the respective process parameters for different gas mixtures to be worked up are to be predefined. The p-T dew point curves can be determined experimentally for individual gas mixtures or are modelable, as shown in Fig. 1 at various gas mixtures.

In addition, as shown in Fig. 2, a dew point curve is established depending on the methane content. On the basis of this behavior, the condensation of the C ₂₊ alkanes can be derived and adjusted on the process side. If, for example, an alkane mixture with 80% methane content at 30 bar and this is passed through a C ₂ + -selective membrane, the driving force is a pressure drop to the permeate space to 20 bar, reduced in the permeate space by the separation efficiency of an MFI membrane of methane to 45%. The increase in the amount of C ₂₊ constituents is thus accompanied by a liquefaction of this fraction. In the permeate space condensed gas can be separated.

 The pressure on the permeate side is 1 to 360 bar, preferably 10 to 70 bar, in particular 30 to 70 bar.

The proportion of gaseous C ₂₊ hydrocarbons in the feed gas is according to the

Delivery conditions of various deposits of natural gas or according to the existing Erdölbeleitgas amounts very different and may be in the range of 0.5 to 35 mol%. For use in the present process, 0.5 to 30 mol% are preferred. zugt, advantageously 0.5 to 25 mol%, in particular 0.5 to 20 mol%. Further preferred ranges are 0.5 to 10 mol%, especially 0.5 to 5 mol%.

The term "C ₂ + hydrocarbons" covers C ₂ - C ₈ hydrocarbons, essentially ethane, propane and n- or iso-butane, with higher hydrocarbons of C ₅ to C ₈ and also present only in small proportions For example, North Sea natural gas contains only about 0.3 to 1.4 mol% higher C ₅ - C ₈ -KW, while Kazakh natural gas contains about 2.5 mol% thereof, while Kazakh crude oil contains only about 0.8 Mol% C ₄ - C ₈ - KW.

The C ₂₊ hydrocarbons are preferably selected from C ₂ -C ₅ hydrocarbons. In particular, these are propane, n-butane, i-butane and mixtures thereof.

Very particularly preferred is the recovery of C ₄ hydrocarbons according to the present method.

By means of the membranes used, the C ₂₊ hydrocarbons are enriched in the permeate space and condense after falling below the respective dew point of the individual hydrocarbon. The enrichment achieved by the membrane or increase in the amount of material leads, for example, from a gas mixture of 90% methane / 10% butane in the feed to a mixture in the permeate with butane contents of, for example, 40 to 50 mol%. Due to the increased amount of butane in the permeate and a sufficiently high pressure on the permeate side, the permeate precipitates as condensate, since the dew point is exceeded. In order to allow the mass flow and the condensation, there must be a pressure difference from feed side to permeate side of the membrane, usually at least 1 bar, advantageously at least 5 bar, in particular at least 10 bar and more. The condensate is then withdrawn continuously or discontinuously from the permeate space. The enrichment on the permeate side of the membrane corresponds to an increase in the amount of material to at least 1.5 times, preferably 1.5 to 50 times, in particular 3 to 40 times, the amount of substance on the feed side Increasing the proportion of the higher alkane, for example, C ₄ in% by volume in the permeate over the original fraction in the feed.

At the dew point, the transition of one, in this case higher carbon hydrogen, from the gaseous to the liquid state takes place. The dew point of hydrocarbons depends on the temperature, pressure, type of hydrocarbon (number of carbon atoms) and the composition of the hydrocarbon mixture. Up to a certain pressure range, increasing the amount of C ₂₊ -hydrocarbons is necessary with decreasing pressure and at a constant temperature in order to observe a condensation (see FIG. 2). A similar curve results at constant pressure and rising temperature.

Preferably, a pressure difference between the feed and permeate space to allow increased flow, so that large mass flows can be handled. At the membrane, the proportion of the higher hydrocarbon is enriched by adsorption, so that In the permeate space an increase in the proportion of C ₂₊ hydrocarbons compared to the feed takes place. Pressure and concentration ratios are selected in the process so that the dew point curve is exceeded and C ₂ + hydrocarbons condense in the permeate space and can be withdrawn as a liquid.

 The separation efficiency is thus increased by a higher feed pressure and a higher

Pressure difference between the feed and permeate side of the membrane, preferably by entering thereby condensation of C ₂ + hydrocarbons.

 Already at 10 bar feed pressure and 1 bar permeate pressure and a feed-side loading of 9.4 mol% of butane in methane at 25 ° C, for example, a permeate side enrichment of 40.4 mol% n-butane as condensate.

 The pressure difference between the feed side and permeate side is preferably 5 to 60 bar, in particular 10 to 40 bar. Feed side of the membrane is the side to which the feed gas is supplied. Permeate side of the membrane is the side from which the permeate or condensate is derived.

 The temperature of the feed gas generally corresponds to the conveying temperature and can therefore vary within wide limits, for example between -30 ° C and +60 ° C. The temperature on permeate side of the membrane is advantageously in the range of -70 ° C to +50 ° C, with a lower temperature on the permeate side to the Stoffmengenerhöhung additionally contributes by dew point. The temperature reduction can be due to the process by relaxation or, taking into account a positive energy balance, by external cooling. Likewise, taking into account a positive energy balance, a pre-compression of the feed stream. However, this is not preferred.

 Uncondensed permeate, which mainly contains methane, can be recycled to the feed, optionally after prior densification. However, the process can be conducted so that retentate and gaseous permeate are chemically identical. Furthermore, it is possible to remove two different gaseous hydrocarbon mixtures from the permeate or retentate space.

A further optimization of the method according to the invention can be carried out by a cascade-like succession of different types of membranes and different pressure ratios. Depending on the pressure, membranes with different pore openings and / or different zeolites or zeolites and organic membranes are arranged one after the other. Thus, a further concentration of the C ₂₊ fraction through a downstream membrane after the permeate space 1 is possible. For example, by a first membrane stage C ₂ + Shares of 2.7 mol% to 9.4 mol% enriched, the enrichment of C is achieved by a second downstream stage membrane ₂₊ fraction to 40.4%, which falls below the dew point condensation takes place.

Another advantage of a cascade separation is the targeted fractional separation of liquid hydrocarbons. Thus, for example, the C ₆ fraction can be selectively obtained on membrane 1, after which, after further supply of the gaseous permeate stream to a Membrane stage 2 by falling below the dew point of the C ₅ fraction, a C _{5 6} mixture can be withdrawn liquid. On a third membrane analogous arrangement C4, ₅ , 6 mixtures are obtained, etc

 The process according to the invention is characterized by the continuous separation of higher hydrocarbons from natural gas and associated gas without the need for energy-intensive expansion and cooling using membrane technology. The separation itself takes place on inorganic porous membranes or polymer membranes without the aid of purge gases at elevated, practice-relevant pressure conditions (p> 1 bar) and improved separation performance in comparison to low-pressure applications. As a result, the energy requirement is significantly reduced compared to known methods.

Further advantageous over known methods is the fact that not all the gas permeates, but preferably the condensable components in the form of C ₂ + hydrocarbons. This achieves a significant increase in performance.

 By means of the method according to the invention, it is possible to use smaller natural gas fields, since by means of membrane technology, a flexible, less complicated process technology for removing higher hydrocarbons from the raw gas is available. In addition, the method can also find the method for removing higher hydrocarbons from the previously unused or hardly used associated petroleum gas, which is usually flared off.

Particularly advantageous for the process according to the invention are porous membranes of inorganic materials. Their special advantages are their high chemical resistance, pressure and pressure swing resistance as well as thermal stability. A prerequisite for a selective separation is a uniform pore size of the inorganic membrane material. Based on the applied feed pressure, the pore size of the membrane is determined. If the pore size is not in the molecular size of the components to be separated, at least condensation of the C ₂₊ fraction must take place in the pores of the membrane. Therefore, membranes of zeolite are suitable, since they have an inherent, defined pore system, but also membranes with narrowly distributed pore sizes based on silica or carbon in the pore size range of 0.5 to 10 nm; preferably 0.5 to 5 nm; especially 0.5 to 2 nm. Another preferred range are 0.5 to 0.8 nm. Especially for the separation of non-polar components from natural gases is the hydrophobic silicalite or low-aluminum ZSM-5 from the group of MFI zeolites.

The use of membranes promises in an analogous manner a preferred adsorption of the higher hydrocarbons in the membrane layer, wherein a higher chemical potential on the feed side to the permeate side mass transport of the adsorbed species into the permeate occurs. This method can be evaluated as low in energy. The permeate defined is the gas flow passing through the membrane. The feed is defined as the gas flow to the membrane module input. The retentate is defined as the gas flow that does not pass through the membrane to the membrane module outlet. Porous inorganic materials based on zeolites do not show the

Disadvantages of polymer membranes and allow a comparable separation of hydrocarbons. Among them, the MFI zeolites have inner-crystalline pores or channels in the order of the hydrocarbons to be separated.

 As membranes of the invention are preferably used inorganic

 Membranes with microchannels and pore sizes in the range of the molecular size of the hydrocarbons to be separated. Preference is given to zeolites having defined pore dimensions.

 A preferred membrane is thus the above-described membrane according to the invention having pore openings of 0.5 to 0.8 nm. In a further embodiment, porous inorganic membranes having pore sizes of up to 10 nm, in particular 1 to 10 nm, in which pore condensation occurs in the pores are preferred if higher pressures of eg 70 or 50 bar can be reduced to pressures of 30 or 20 bar, depending on the molecular composition.

 The zeolite membranes on porous supports can be prepared in various ways. Common is in situ crystallization directly on the support, or seed-based synthesis for more oriented, uniform growth.

 Seed crystals are usually prepared and deposited separately for this purpose, see DE 10 2004 0001 974 A1 / DE 100 27 685 B4, or a seed layer is produced directly on the support during a separate synthesis step, as described in DE 103 04 322 A1. Subsequently, the formation of a continuous synthesis layer out of a dilute solution, which is mainly to support crystal growth. Both methods are very process-intensive.

 DE 101 07 539 A1 describes the production of a composite membrane on a ceramic, porous support material on which a mesoporous material is deposited

 Zeolite layer is deposited, wherein subsequently the closed zeolite layer is formed on / in the surface by hydrothermal synthesis. No details are given on this mesoporous intermediate layer and the hydrothermal synthesis.

 Advantageous membranes of the invention are zeolites of the following types: ZSM-

5, FAU, MFI, CIT-1, DAF-1, Stilbite, Beta, Boggsite, EMC-2, STA-1, Terranovaite and Theta-1.

 Zeolites with pore openings of 0.5 to 0.6 nm, which are particularly suitable for pressures in the range of 1 to 140 bar, are ZSM-5, FAU, MFI, CIT-1, DAF-1 and Stilbit.

 For higher pressures in the range of 20 to 140 bar, zeolites with pore openings of 0.7 to 0.8 nm such as Beta, Boggsite, EMC-2, STA-1 and Terranovaite and Theta-1 are suitable. These zeolites, which are processed as membranes, are characterized by an increased flow.

In addition, amorphous, inorganic membranes, for example based on SiO ₂ or carbon, with pore sizes in the range of 0.5 to 10 nm and narrow pore size Size distribution at feed pressures, which lead to the condensation of C ₂₊ alkanes in the pores of the membranes, also suitable.

Preferably, the zeolites are coated on a porous corundum layer, optionally on an intervening porous zeolite support layer, which acts as a seed and growth layer of the zeolite membrane. The application of the later microporous zeolite can be performed by / ^'ns / iii crystallization or by grinding a microporous similar zeolite to a particle size of less than 1 μηη, coating the particles onto the Korundträgermaterial and hydrothermal treatment for adhesion to the dense membrane layer. In this case, a suitable microporous zeolite layer forms on one side of the membrane.

 To ensure sufficient stability of the membrane, it is synthesized on a porous support. It is mainly composite membranes produced on corundum carriers, since they are cheaper to produce and membrane and support are more similar in their chemical composition and their thermal expansion behavior ago. Other carrier materials, such as porous glasses or porous metals, are also suitable.

Membranes with the required properties are easy to prepare if the synthesis approach is simplified by replacing the difficult-to-produce seed layer by applying a ground slurry of the composition of the later membrane layer. For example, an MFI layer applied as a nucleation layer promotes uniform, secondary growth from a synthesis solution. This layer also constitutes a barrier layer, as a result of which the synthesis solution does not enter the porous corundum support. Both lead to a reduction of the manufacturing costs, since interlayer (s) among other things of Ti0 _{2 are} not required and a complex seed coating omitted from preceding publications. In addition, there are advantages of a technological nature when using diluted synthesis solutions.

 Preferably, the material for the mesoporous layer is prepared by milling commercial zeolite material to a fineness <1 μm, preferably <500 nm. The advantage of ground particles consists in the very good gearing with the macroporous or mesoporous carrier material and in a mechanical stabilization of the membrane.

 The formation of the porous Silikalithschicht takes place in a preferred manner by Schlickergießen. For metal-supported membranes, electrophoretic deposition of the particles is also possible.

 The intermediate layer is used to further improve the adhesion and the

Burning out any organic suspension and binder heat treated, wherein a temperature below the phase transformation of the silicalite is selected. Preferably, the selected temperature of this temperature treatment is between 400 ° C and 800 ° C, more preferably between 500 and 700 ° C. By way of example, the silicon / aluminum molar ratio of the secondary growth step synthesis solution for the MFI is> 2.5, preferably> 75. Higher proportions of aluminum result in a more hydrophilic behavior and are therefore disadvantageous for the separation of nonpolar mixtures.

 The composition of the silicalite synthesis solution may vary depending on

Synthesis method, the reagents used, the physical synthesis parameters and the desired membrane properties with respect to selectivity and flow vary. Synthesis compositions in the range of 100 mol of SiO ₂ : 0-35 mol of SDA: 0-50 mol of NaOH: 0-17 mol of Al ₂ O ₃ and 1 000- 100 000 mol of H ₂ O are possible, SDA being used for the structure-directing agents, also called template stands. SDA can be for example

 Tripropylammonium hydroxide or Tripropylammonimbromid or a mixture of both.

 For the realization of technically relevant flows through the membrane, the

Synthesis composition, especially the template content and water content, optimized

(Example 2). Templat portions of from 0.01 to 1.2 mol and water contents of from 4,000 to 40,000 mol per 100 mol of SiO ₂ in the synthesis batch are preferred for increasing the fluxes.

Depending on the Si0 ₂ source used, the pH of the synthesis solution should be adjusted to 10 to 14, preferably between 1100 and 12.5. Dispersible Si0 ₂ , tetraethyl orthosilicate (TEOS) and colloidal Si0 ₂ , such as LUDOX ^® or

LEVASIL ^®

 The support provided with the mesoporous silicalite layer is prepared prior to the synthesis such that the synthesis solution only comes into contact with the membrane side. For this purpose, for example, in an inner coating tubular support the outside be sealed with Teflon tape or wax. In the case of external coating, sealing with Teflon caps can prevent access to the interior. The goal of the seal is to be one

To prevent zeolite growth on the desorption side.

 The synthesis can be carried out under autogenous pressure, under atmospheric pressure, standing or flowing, for 3 to 120 h. Preferably, the synthesis is carried out under autogenous pressure at temperatures of 140 ° C to 200 ° C and 12 to 72 hours, more preferably between 160 ° C and 180 ° C and 16 to 48 hours.

 After synthesis, the supports with the synthesized membrane are rinsed in deionized water until unreacted synthetic components are removed from the pores. In general, this is the case when the pH of the wash water after repeated changes of the same at a pH of 7.

 The carriers are then gently dried. This can be done under room air conditions or after slow heating in a drying oven at 60 ° C.

After drying, the removal of structure-directing templations takes place, since these are located in the zeolite pores and would thus prevent access of the gases to be separated. The calcination is carried out at a heating rate of 0.3 to 5.0 K / min, before- at 1, 0 K / min at 400 to 550 ° C for 3 to 24 h, more preferably at 420 to 580 ° C with 5 to 12 h, performed.

 It has been found that the membranes prepared according to the above-mentioned process steps are extremely stable and essentially pressure-stable for the process presented here. There are at high feed pressures and applied pressure differences between

Permeate and feed only measured low leakage currents (less than 0.1% to total flux).

A zeolite membrane thus advantageously consists of the layers macroporous corundum layer, mesoporous zeolite carrier layer, microporous zeolite layer of the same zeolite as in the zeolite carrier layer, the zeolite for the mesoporous zeolite carrier layer ground to a particle size of less than 1 μηη and treated hydrothermally is. In the same way, this structure can also be done for a membrane made of Si0 ₂ - or carbon.

For feed gases with higher proportions of H ₂ S, C0 ₂ or water, it is advantageous to work with aluminum-poor zeolites whose Si: Al ratio is between 50 and 700, preferably 150 to 450, in particular> 250. Aluminum-free zeolites may also be used as silicalite are used.

 The membranes must not allow any leakage flow and thus allow only adsorptive processes on the surface, whereby the mass transport thus proceeds only through the inter-crystalline pore system. A transport between the crystallites of the porous inorganic layer must not take place or only to a very small extent due to the applied pressures. Advantageous for the separation process are membranes which allow high permeate fluxes due to their low layer thicknesses. The thickness of the separating layer is 5 to 200 μηη. The thickness of the separating layer is preferably from 10 to 80 .mu.m, more preferably less than 50 .mu.m, more preferably from 10 to 50 .mu.m, more preferably less than 20 .mu.m, in particular from 15 to 30 .mu.m.

 Furthermore, u.a. suitable polymer membranes, preferably separated by the solution-diffusion mechanism. These include e.g. rubbery polymers, silicone rubber, polyamides, polyethers, polyamide-polyether block copolymers.

Other examples of polymer membranes include poly (4-methyl-2-pentyne) (PMP) or PMP filled with Si0 ₂ nanoparticles. Examples of silicon-containing polymer membranes are those of polyoctylmethylsiloxane (POMS), polytrimethylsilylpropyne (PTMSP), polydimethylsiloxane (PDMS) or polytriisopropylsilylphenylacetylene.

 However, polymer membranes are not preferred because of their swelling behavior in the presence of higher hydrocarbons and hence decreasing selectivity.

 The invention will be explained in more detail by examples. In the accompanying drawing mean

 Fig. 1 a p-T dew point curves for the predetermination of the respective process parameters

Example A 1 b pT dew point curves in predetermination of the respective process parameters - Example B

 Fig. 2 phase behavior as a function of methane content and pressure at

Condensation of C ₂₊ -KW

 Fig. 3 cascade separation - schematic sequence

 Fig. 4 is a schematic representation of the layer structure of a membrane

FIG. 1 a shows p-T dew point curves for predetermining the respective process parameters for the following example A (all percentages are mol%).

 A

 Methane [%] 61, 7 63.7 70 75 80 85 90

Ethane [%] 16 15 12 10 8 6 4

Propane [%] 20.9 19.9 14.6 1 1, 6 9.7 6.8 3.9

Butane [%] 0.57 0.57 0.37 0.37 0.27 0, 17 0.07

 The curves show from left to right the following initial concentrations of methane: 90%, 85%, 80%; 75%, 70%, 63.7%, 61, 7%.

 FIG. 1 b shows p-T dew point curves for the predetermination of the respective process parameters for Example B below (all percentages are mol%).

 B

 Methane [%] 90 86 82 78 74 70

Ethane [%] 4 6 8 9 11 12

Propane [%] 2.9 3.9 4.9 5.9 6.9 8

Butane [%] 1, 4 2.4 3.4 5.4 6.4 8.4

Nitrogen rest

 The curves show from left to right the following initial concentrations of methane: 90%, 86%, 82%, 78%, 74%, 70%.

In Fig. 2, the possibility for liquefying C ₂₊ components from a hydrocarbon mixture at a constant temperature of -3 ° C is shown.

 The feed is located on the right side of the curve in the single-phase region (gas region), whereas when passing through this curve, through membrane-mediated reduction of the methane concentration, the permeate is characterized by a two-phase region on the left side of the curve (gas-liquid region). ,

In general, this is first to be determined with reference to FIGS. 1 a, 1 b and 2 for each gas mixture present in order to make a suitable statement for a diaphragm-controlled dew point adjustment. If, for example, the gas from FIG. 1 b is cooled from 20 ° C. to -40 ° C. with 70% methane at a constant 10 bar, higher alkanes precipitate. This is not possible for the gas with 90% methane content. In the simplified case of FIG. 2, this phase behavior is relevant to the process for changes in pressure. The permeate pressure must be adjusted so that condensation of the higher alkane still occurs, while the membrane enriches the higher alkane in the permeate space in percent. are both parameters set correctly in terms of process engineering, the higher alkane can condense.

In Fig. 3, a cascade separation is shown schematically, wherein for further enrichment of the C ₂₊ fraction, a concentration of C ₂₊ fraction over the

Permeatraum downstream membranes takes place.

 Fig. 4 shows the structure of a zeolite separating body as a membrane with the individual layers.

 option A

MFI separation layer 1 (top) after the composition of 100 moles of Si0 ₂ : 0, 169 moles Al ₂ O ₃ : 3.3 moles TPABr: 3.3 moles TPAOH: 3.3 moles Na ₂ 0: 2000 moles H ₂ 0 including MF layer 2 of MFI, including a corundum MF layer 3, including the corundum support layer 4.

 Variant B

MFI separation layer 1 (above) after the composition of 100 moles of SiO ₂ : 0, 169 moles of Al ₂ O ₃ : 0.6 moles of TPABr: 0.0 moles of TPAOH: 3.3 moles of Na ₂ O: 2000 moles of H ₂ O, below MF layer 2 made of MFI, including corundum MF layer 3, including corundum support layer 4.

 Example 1 Synthesis of the membrane unit

 To produce the Silikalithmembranen for gas separation, in particular for the separation of higher hydrocarbons of methane, Korundmonokanäle be used with an outer diameter of 10 mm, an inner diameter of 7 mm and a length of 125 mm. The carriers also have inside a microfiltration layer of corundum provided by the manufacturer with an average pore width of 200 nm. The ends are sealed with glass solder.

For the mesoporous zeolite layer, a silicalite having a Si / Al molar ratio> 500 is reduced to a fineness of di ₀ = 0.25, d ₅ o = 0.43 and d ₉₀ = 0 by means of an agitating ball mill with deionized water as a dispersing agent without any other additives , 80 μηη ground. By means of a 5% suspension of the ground silicalite containing a binder, e.g. As polydiallyldimethylammonium chloride is added, the corundum carriers are coated by Schlickergießen. It forms after a lifetime of 5 min under the given conditions, a layer thickness of 25 μηη.

 Prior to the synthesis, the inside is coated with ground silicalite crystals

Corundum carrier at 700 ° C for 1 h temperature treated.

The synthesis solution for forming a closed film on the mesoporous silicalite layer has a composition of 100 moles Si0 ₂ : 0.169 moles Al ₂ O ₃ : 3.3 moles TPABr: 3.3 moles TPAOH: 3.3 moles Na ₂ O: 2000 moles H ₂ 0 on. An average layer thickness of 40 to 75 μm is observed. The flow behavior of a membrane after this synthesis is 4.7 ml / min at a pressure difference on the feed and permeate side of 1 bar.

Another membrane with a closed, but thinner film, according to the synthesis approach of 100 mol Si0 ₂ : 0, 169 mol Al ₂ 0 ₃ : 0.6 mol TPABr: 0.0 mol TPAOH: 3.3 Mol Na ₂ 0: 2000 mol H ₂ O (electron microscopy - Figure 2). An average layer thickness of 17 to 23 μm is observed. The flow behavior of a membrane after this synthesis is 18.5 ml / min at a pressure difference on the feed and permeate side of 1 bar.

As silicon source Levasil ^® 300/30%, which contains a small amount of Al ₂ 0 ₃ .

Thus, the Si / Al mole ratio was 300. TPABr is tetrapropylammonium bromide, TPAOH is tetrapropylammonium hydroxide. The water used is deionized water. Before the synthesis, the carriers are wrapped with Teflon tape.

 The hydrothermal synthesis is carried out in an autoclave at 180 ° C for 24 h. After synthesis, the Teflon tape is removed and the membranes are rinsed in deionized water. After a space drying of 3 days, the calcination is carried out at 450 ° C for 5 h.

Examples 2 to 17 Separation of C ₂₊ hydrocarbons by dew point undershooting

The separating bodies obtained from Example 1 are characterized by their asymmetric structure. Here, a layered structure is characteristic. In the present case, ceramic separating tubes with an internal separating layer are characterized by (from outside to inside) layer 4: Al ₂ O ₃ support body (about 1.5 mm), layer 3: Al ₂ O ₃ microfiltration layer (approx. 40 μηη), layer 2: MFI seed layer (about 30 μηη), layer 1: MFI separation layer (about 30 μηη). The membranes are tested for their permeation behavior under different conditions. These are mounted in a stainless steel module, with a seal to the permeate space. To perform permeation tests at different temperatures, the module is heated or cooled. According to an application under practical conditions prevails on the permeate side during the measurement always lower pressure than on the feed side. The pressure on the feed side is adjusted to the test values by means of a back pressure regulator. The retentate flow was kept constant during the measurement by adjusting the feed flow to the permeate flow. Retentate is analyzed by GC analysis. Permeate is also analyzed by GC analysis and the condensed hydrocarbon fraction determined volumetrically. This results in different proportions of liquefiable C ₂₊ components in the permeate space as a function of temperature, pressure (feed), pressure (permeate) and methane content based on the total hydrocarbon mixture. The following Table 1 gives some of these test results as an example for a natural gas separation with 9% C ₂₊ components (main component butane with 4.7%, otherwise propane 2.7%, ethane 1, 6%).

Table 1

4 20 1 0 0,00

4 20 1 0 0.00

 5 20 1 -25 0.27

 6 30 20 50 0.00

 7 30 20 25 0.32

 8 30 20 0 0.57

 9 30 20 -25 0.69

 10 70 30 50 2.04

 1 1 70 30 25 2.54

 12 70 30 0 2.91

 13 70 30 -25 3.21

 14 200 70 50 3.92

 15 200 70 25 4.53

 16 200 70 0 4.99

 17 200 70 -25 5.21

Examples 18 to 28

 In a manner comparable to Example 2, a pressure-difference-dependent accumulation of n-butane from a methane / n-butane mixture in the permeate space was found (Table 2).

26 27,1 72,9 95,0 5,0

26 27.1 72.9 95.0 5.0

 30 50

 19.8 80.2 90.0 10.0

 27 25.2 74.8 95.0 5.0

 30 60

 18.2 81, 8 90.0 10.0

 28 26.9 73.1 95.0 5.0

 30 70

 21, 3 78.7 90.0 10.0

From Table 2, the Stoffmengenerhöhung C ₄ in the permeate over the feed fraction can be clearly seen. If the pressure in the permeate space is sufficiently high, n-butane accumulates in liquid form.

Examples 29 to 36 Separation of C ₂₊ hydrocarbons by dew point under FAU zeolite membranes

The FAU membrane was tested analogously to Example 2. The following Table 3 gives some of these test results as an example for a natural gas separation with 9% C ₂₊ components (main component butane with 4.7%, otherwise propane 2.7%, ethane 1, 6%) again.

Table 3

Beispiele 37 bis 44 Abtrennung von C₂₊-Kohlenwasserstoffen durch Taupunkt- unterschreitung einer Silikamembran mit einer Porengröße von 1 nm

Examples 37 to 44 separation of C ₂₊ hydrocarbons by dew point below a silica membrane with a pore size of 1 nm

The testing of the silica membrane with a pore size of 1 nm was carried out analogously to Example 2. The following Table 4 gives some of these test results as an example for a natural gas separation with 9% C ₂₊ components (main component butane with 4.7%, otherwise propane 2.7% , Ethane 1, 6%) again.

Table 4

in bar in bar in °C Fraktion in l/(h^*m²)

in bar in ° C fraction in l / (h ^* m ² )

37 20 1 0 0

 38 20 1 -25 0.84

 39 30 20 25 1, 44

 40 30 20 0 2.48

 41 30 20 -25 3.15

 42 70 30 25 7.67

 43 70 30 0 12.02

44 70 30 -25 18.78

Examples 45 to 52 Separation of C ₂₊ hydrocarbons by dew point below a silica membrane with a pore size of 2 nm

The testing of the silica membrane with a pore size of 2 nm was carried out analogously to Example 2. The following Table 5 gives some of these test results as an example for a natural gas separation with 9% C ₂₊ components (main component butane with 4.7%, otherwise propane 2.7%). , Ethane 1, 6%) again.

Table 5

Claims

Claims 1. A process for the separation of C ₂₊ hydrocarbons from natural gas or associated petroleum gas to membranes, characterized in that a feed gas comprising 0.5 to 35 mol% of gaseous C ₂ + hydrocarbons under a pressure of 2 to 500 bar in a temperature range of -30 ° C to +60 ° C is passed over a membrane of a porous inorganic material or an organic polymer, wherein the inorganic membrane has pore openings to the permeate side of the membrane of 0.5 to 10 nm or the polymeric membrane has higher selectivities to C _{2 +} Hydrocarbons as to methane and the permeating C ₂ + gas is condensed within the membrane and is enriched outside the membrane on the permeate side by Stoffmengenerhöhung to at least 1, 5 times in relation to the feed side and is condensed by dew point below, and the condensate C ₂₊ hydrocarbons at a pressure of 1 to 360 bar in the temperature range from -70 ° C to + 50 ° C vo n the permeate side is withdrawn, wherein the pressure difference between the feed and permeate side is 1 to 140 bar and wherein no purge gases are used. 2. The method of claim 1, wherein the feed gas comprises 0.5 to 30 mol% of gaseous C ₂₊ hydrocarbons. 3. Process according to claim 1, wherein the feed gas comprises 0.5 to 20 mol% of gaseous C ₂₊ -hydrocarbons. 4. The method according to any one of claims 1 to 3, wherein the pressure of the feed gas is in the range of 30 to 200 bar. 5. The method according to any one of claims 1 to 4, wherein the pressure of the feed gas is in the range of 30 to 85 bar. 6. The method according to any one of claims 1 to 5, wherein the pressure difference between the feed and permeate side is 5 to 60 bar. 7. The method according to any one of claims 1 to 6, wherein the pressure difference between the feed and permeate side is 10 to 40 bar. 8. The method according to any one of claims 1 to 7, wherein the Stoffmengenerhöhung from the feed side to the permeate side of the membrane in the range of 1, 5 to 100 times, based on the molar concentration. 9. The method according to any one of claims 1 to 8, wherein the porous inorganic material is an aluminosilicate-based zeolite membrane, preferably having a Si: Al ratio of 50 to 700, preferably 150 to 450. A process according to any one of claims 1 to 9, wherein the zeolite membrane is selected from ZSM-5, MFI, FAU, CIT-1, DAF-1, Stilbite, Beta, Boggsite, EMC-2, STA-1, Terranovaite and theta-1. 1 1. The method according to any one of claims 1 to 10, wherein the zeolite membrane of the layers macroporous corundum layer, mesoporous zeolite support layer, microporous zeolite layer of the same zeolite as in the zeolite support layer, wherein the zeolite for the mesoporous zeolite support layer is ground to a particle size of less than 1 μηη and treated hydrothermally. 12. The method according to any one of claims 1 to 1 1, wherein the pore openings of the microporous layer is in the range of 0.5 to 0.8 nm. 13. The method according to any one of claims 1 to 12, wherein the layer thickness is in the range of 10 to 80 μηη. 14. The method according to any one of claims 1 to 13, wherein the pore openings are in the range of 1 to 10 nm. 15. The method according to any one of claims 1 to 14, wherein non-condensed C ₂ + hydrocarbon gas is removed from the permeate side and fed as a new feed membrane another and this measure is repeated one or more times as cascade separation. 16. The method according to any one of claims 1 to 15, wherein the C ₂ + hydrocarbons are selected from C ₂ - C ₅ hydrocarbons and mixtures thereof. A process according to any one of claims 1 to 16, wherein the dew point undershoot for each hydrocarbon to be separated is controlled depending on its molar amount, temperature and pressure on the permeate side of the membrane.