DE102010030485A1 - Process for the separation of C2 + hydrocarbons from natural gas or associated petroleum gas using membranes - Google Patents

Abstract

The invention relates to a process for the separation of C2 + hydrocarbons from natural gas or associated petroleum gas using membranes. A feed gas is passed under a pressure of 2 to 500 bar in a temperature range from –30 ° C to + 60 ° C over a membrane made of a porous inorganic material or an organic polymer. The permeating C2 + gas condenses by falling below the dew point inside the membrane, is enriched outside the membrane to at least 1.5 times the feed side, and the condensate from C2 + hydrocarbons is at a pressure of 1 to 360 bar in the temperature range from - Subtracted 70 ° C to + 50 ° C from the permeate side. The separation takes place under practice-relevant pressure conditions without energy-consuming relaxation or cooling and with improved separation performance.

Description

The invention relates to a process for the separation of C ₂₊ hydrocarbons from natural gas or associated gas with the use of 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, there are other, "wet" natural gases (such as associated petroleum gas) 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.

• – Abtrennung freier Flüssigkeit (Kondensatabscheidung)
• – Entschwefelung, Entfernung von CO₂
• – Einstellung des Wasserdampftaupunktes (Gastrocknung)
• – Einstellung des Kohlenwasserstofftaupunktes

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 relaxation of gases, therefore, the following reprocessing steps must generally be carried out:

• - Separation of free liquid (condensate separation)
• - desulfurization, removal of CO 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 a starting point for large-scale chemical products.

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. Apart from hydrocarbons, the temperature / liquid separators remove water and glycols and are operated at temperatures of -25 ° C to -30 ° C.

• – Low-Temperature Separation (LTS) und die
• – Cold-Frac-Technologie

There are two methods of cryogenic extraction, the

• - Low-Temperature Separation (LTS) and the
• - Cold Frac technology

Used in gas processing. In the case of low-temperature separation, the 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. Ergas 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.

In this case, the cooling is greater with the same overpressure, the lower the starting temperature of the gas. 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 regarded as an economic co-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 flared off at low volumes.

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 25-30 bar hydrocarbons. However, this method is not sufficient for gas temperatures> 0 ° C to z. B. to meet the GERG requirements regarding the HC dew point. Thus, further treatment steps of the gaseous phase (eg deep-freeze condensation) are necessary.

In US 4203742 the complex distillation of the individual components from natural gas or natural gas mixtures is 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 obtaining liquefied natural gas from pressurized natural gases, for example, in DE OS 2820212 described. The underlying cooling process is in DE 4440401 A1 expanded by a technological solution to optimize the refrigeration budget.

In general, however, a cooling process for recovering liquid gas components consisting of C ₂₊ is considered to be energy-intensive and therefore disadvantageous.

DE 3445961 A1 uses the Joule-Thomson effect to cool off pressurized gases via 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 enrichment of hydrocarbons are known in the art. However, these methods 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, wherein a further liquefaction of the previously adsorbed species is accompanied by a compression work.

In the WO 94/01209 describes the synthesis of dense ZSM-5 layers and their use in the selective adsorption of hydrocarbons up to an applied feed pressure of 100 kPa. In this method, however, the prior execution of a condensation with simultaneous cooling to temperatures ≥ 0 ° C is required.

In the in DE 10 2004 001 974 A1 described invention preferably flow the molecules with smaller diameters through the membrane, for. B. 1-butene is enriched in permeate while 2-butenes are retained. This separation method is unfavorable for the conditioning of natural gas and associated gas, since the majority of the hydrocarbon mixture - methane - would have to pass through the membrane, which is technically difficult to achieve.

In the patent DE 693 26 254 T2 It is described that it is possible to separate butane from methane by means of supported MFI membranes, whereby adsorption increases the higher hydrocarbon in the permeate. Porous metal carriers were used as well as ZSM-5 zeolites as selective layer, which in contrast to silicalite are more aluminous and therefore more hydrophilic. The permeation tests were carried out using a sweep gas on the permeate side at practical pressures of ≤ 100 kPa.

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] on MFI membranes the separation of natural gas components at 1-4 bar and pressure differences up to 3 bar described. Here and as with all previously described separations of natural gas and associated gas components according to the adsorption method is the Separation preferred by the so-called surface diffusion, which has so far deteriorated after increasing the feed pressure and the differential pressures between feed and permeate.

All known developments is 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. Either a costly compaction would be required to obtain liquid components, or permeates obtained in a cascade separation would have to be further enriched in higher HC. 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 use of complex processes, such as cooling and compression.

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 3-500 bar, and in which adjusts to the promotion Temperature, which is in the range of -30 ° C to + 60 ° C, is passed over a membrane, the higher hydrocarbons from C ₂ pass through the membrane and then condensed.

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 of 0.5 to 0.8 nm or the polymeric membrane has higher selectivities to C ₂₊ hydrocarbons to methane and the permeating C ₂₊ gas is condensed inside and outside the membrane and is 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₊ Hydrocarbons is withdrawn at a pressure of 1 to 360 bar in the temperature range of -70 ° C to 50 ° C from the permeate side , wherein the pressure difference between the feed and permeate side is 1-140 bar and wherein no purge gases are used.

The pressure 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 subsidized 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 70-80 bar, it is also an advantageous embodiment of the invention to use feed gases in the pressure range 70-80 bar. Preferred pressure ranges are therefore 30 to 200 bar, in particular 30-85 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 envelope (see ).

Particularly advantageous are higher feed pressures in the range of 30 to 200 bar, in particular 70-200 bar with high methane content. As a result, z. B. win n-butane better than liquid component.

Based on the pT dew point curves, the respective process parameters for different gas mixtures to be worked up are to be predicted. The pT dew point curves can be determined experimentally for individual gas mixtures or are modelable, as in 1 shown on different gas mixtures.

The pressure on the permeate side is 1 to 80 bar, preferably 10 to 70 bar, in particular 30 to 70 bar.

The proportion of gaseous C ₂₊ hydrocarbons in the feed gas is very different according to the delivery conditions of various deposits of natural gas or according to the amounts present in Erdölbeleitgas and may be in the range of 0.5-35 mol%. For use in the present process 0.5-30 mol% are preferred, preferably 0.5-25 mol%, in particular 0.5-20 mol%. Other preferred ranges are 0.5-10 mole%, especially 0.5-5 mole%.

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

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 condensate is then withdrawn continuously or discontinuously from the permeate space. The enrichment on the permeate side of the membrane corresponds to a Stoffmengenerhöhung to at least 1.5 times, preferably 1.5 to 50-fold, especially 3- to 40-fold compared to the amount of material on the feed side.

The dew point is the transition of a, in the present case, higher hydrocarbon, from the gaseous to the liquid state. 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, the increase in the amount of C ₂₊ hydrocarbon substances is necessary with decreasing pressure and at a constant temperature in order to observe a condensation (see 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. On the membrane, the proportion of the higher hydrocarbon is enriched by adsorption, so that takes place in the permeate an increase in the proportion of C ₂₊ hydrocarbons compared to the feed. Pressure and concentration ratios are chosen 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.

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 permeatseitige enrichment of 40.4 mol% n-butane as a 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 the 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 by dew point undershooting additionally contributes. 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 by a downstream membrane after the permeate space 1 is possible. For example, by a first membrane stage C ₂₊ Shares of 2.7 mol% enriched to 9.4 mol%, the enrichment of C is achieved by a second downstream stage membrane fraction ₂₊ 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 ₅ fraction can be selectively obtained on membrane 1, after which, after further supply of the gaseous permeate stream to a membrane stage 2, by dropping below the dew point of the C ₅ fraction, a C _5,6 mixture can be withdrawn liquid. On a third membrane analogous arrangement C _4,5,6 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 is carried out on inorganic porous membranes or polymer membranes without the aid of flushing gases at elevated, practice-relevant pressure conditions (p> 2 bar) and improved separation performance in comparison to low-pressure applications. As a result, the energy consumption is significantly reduced compared to known methods.

Another advantage 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 be used to remove higher hydrocarbons from the previously unobstructed or hardly used associated petroleum gas.

Particularly advantageous for the process according to the invention are porous membranes of inorganic materials. Their particular advantages are their high chemical resistance, pressure and pressure swing resistance and thermal stability. A prerequisite for a selective separation is a uniform pore size of the inorganic membrane material in the molecular size of the components to be separated. Therefore, zeolite membranes are suitable because they have an inherent, defined pore system. The hydrophobic silicalite or low-aluminum ZSM-5 from the group of MFI zeolites is particularly suitable for the separation of non-polar components from natural gases.

The use of membranes promises analogously a preferred adsorption of the higher hydrocarbons in the membrane layer, wherein a higher chemical potential on the feed side to the permeate side, a mass transfer of the adsorbed species in 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 zeolite-based materials do not exhibit the disadvantages of polymer membranes and allow 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.

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 separated separately, 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 in DE 103 04 322 A1 described. 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.

In the DE 101 07 539 A1 describes the formation of a composite membrane on a ceramic, porous support material on which a mesoporous zeolite layer is deposited, subsequently producing the closed zeolite layer on / in the surface thereof 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, CIT-1, DAF-1, stilbite, beta, bogsite, EMC-2, STA-1, terranovite and theta-1.

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

For higher pressures in the range of 20 to 140 bar, zeolites with pore openings of 0.7-0.8 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 in particular by an increased flux.

Preferably, the zeolites are coated on a porous corundum layer, optionally on an intermediate porous zeolite support layer which acts as a seed and growth layer of the zeolite membrane. The application of the later microporous zeolite layer can be carried out by in situ crystallization or by grinding a microporous similar zeolite to particle sizes of> 1 micron, applying the particles to the corundum support material 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. In addition to support materials made of metal composite membranes are mainly produced on corundum carriers, as they are cheaper to produce and membrane and support are 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 subsequent 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 TiO _{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.

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

The intermediate layer is heat treated to further improve the adhesion and burnout of any organic suspending and binding agents, choosing a temperature below the phase transition of the silicalite. 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 can vary depending on the synthesis method, the reagents used, the physical synthesis parameters and the desired membrane properties with respect to selectivity and flux. 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, with SDA for the structure-directing agents, also termed template, stands. For example, SDA can be tripropylammonium hydroxide or tripropylammonium bromide or a mixture of both.

To realize technically relevant flows through the membrane, the synthesis composition, especially the template content and water content, was optimized (Example 2). Templat portions of from 0.01 to 1.2 mol and water fractions 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 SiO ₂ source used, the pH of the synthesis solution should be adjusted to 10 to 14, preferably between 11.0 and 12.5. As a silica source to disperse SiO ₂ are suitable, tetraethylorthosilicate (TEOS) and kollodidales SiO ₂ 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 aim of the seal is to prevent zeolite growth on the desorption side.

The synthesis can be carried out under autogenous pressure, under normal pressure, standing or flowing, for 3-120 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 calcining is carried out at a heating rate of 0.3 to 5.0 K / min, preferably 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. At low feed pressures and applied pressure differences between permeate and feed, only low leakage currents are measured (less than 0.1% of the total flow).

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

The membranes must be meso- and macroscopically dense, allow no leakage flow and thus allow only adsorptive processes on the surface, with the mass transfer thus proceeding 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 that allow high permeate flows due to their low layer thicknesses. The thickness of the separating layer is 5 to 200 μm. The thickness of the separating layer is preferably less than 50 μm, more preferably less than 20 μm, in particular 5-20 nm.

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

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

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

1a pT dew point curves for predetermining the respective process parameters - Example A

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

2 Phase behavior as a function of methane content and pressure in the case of condensation of C ₂₊ -KW; Adjustment via membrane diffusion

3 Cascade separation - schematic sequence

4 schematic representation of the layer structure of a membrane

In 1a pT dew point curves are shown for the prediction of 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 8th 6 4 Propane [%] 20.9 19.9 14.6 11.6 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%.

In 1b pT dew point curves are shown for predetermining the respective process parameters for the following example B (all percentages are mol%). B Methane [%] 90 86 82 78 74 70 Ethane [%] 4 6 8th 9 11 12 Propane [%] 2.9 3.9 4.9 5.9 6.9 8th 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 2 the possibility of liquefying C ₂₊ components from a hydrocarbon mixture with 90% methane, 4% ethane, 2.9% propane, 1.4% butane and the balance of N ₂ at a constant temperature of -3 ° C is shown ,

In this case, the methane concentration of the feed is located on the right side of the curve (gas region), whereas by passing through the latter under pressure reduction the permeate space is characterized by a methane concentration on the left side of the curve (gas-liquid region).

The reduction in methane and the increase in C ₂₊ -KW are according to the following table: Methane [%] 90 86 82 78 74 70 Ethane [%] 4 6 8th 9 11 12 Propane [%] 2.9 3.9 4.9 5.9 6.9 8th Butane [%] 1.4 2.4 3.4 5.4 6.4 8.4 nitrogen rest

In 3 schematically a cascade separation is shown, wherein for further enrichment of the C ₂₊ fraction, a concentration of C ₂₊ fraction over the permeate space downstream membranes takes place.

4 shows the construction of a zeolite separator as a membrane with the individual layers.

option A

MFI release layer 1 (above) after composition of 100 moles SiO 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 O, below MF layer 2 made of MFI, including a corundum MF sheet 3, including the corundum support layer 4.

Variant B

MFI release layer 1 (above) after composition of 100 moles SiO ₂ : 0.169 moles Al ₂ O ₃ : 0.6 moles TPABr: 0.0 moles TPAOH: 3.3 moles Na ₂ O: 2000 moles 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. In addition, the carriers have a microfiltration layer of α-corundum provided by the manufacturer with an average pore size of 200 nm. The ends were sealed with glass solder.

For the mesoporous zeolite layer, a silicalite having a Si / Al molar ratio> 500 is reduced to a fineness of d ₁₀ = 0.25, d ₅₀ = 0.43 and d ₉₀ = 0 by means of a stirred ball mill with deionized water as a dispersing agent without any other additives. Milled 80 microns. By means of a 5% suspension of the ground silicalite to which a binder has been added, the corundum carriers are coated by slip casting. It forms after a life of 5 min under the given conditions, a layer thickness of 25 microns.

Prior to the synthesis, the corundum support coated in the interior with milled silicalite crystals is heat-treated at 700 ° C. for 1 h.

The synthesis solution for forming a closed film on the mesoporous silicalite layer has a composition of 100 moles SiO 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 O (electron microscopy ) on. An average layer thickness of 40-75 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 moles of SiO ₂ : 0.169 mol Al ₂ O ₃ : 0.6 mol TPABr: 0.0 mol TPAOH: 3.3 mol Na ₂ O: 2000 mol H ₂ O (electron microscopy ) produced. An average layer thickness of 17-23 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 the silicon source Levasil ^® 300 serves / 30%, containing a small amount of Al ₂ O _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.

Example 2 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 separation tubes with an internal separating layer are characterized by (vani) layer 4: Al ₂ O ₃ support body (about 1.5 mm), layer 3: Al ₂ O ₃ microfiltration layer (about 40 μm), layer 2 : MFI seed layer (about 30 μm), layer 1: MFI separating layer (about 30 μm). 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 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. _Feed in cash P _Peat in cash Temperature in ° C liquid C ₂₊ fraction in l / (h · m ² ) 20 1 50 0.00 20 1 25 0.00 20 1 0 0.00 20 1 -25 0.27 30 20 50 0.00 30 20 25 0.32 30 20 0 0.57 30 20 -25 0.69 70 30 50 2.04 70 30 25 2.54 70 30 0 2.91 70 30 -25 3.21 200 70 50 3.92 200 70 25 4.53 200 70 0 4.99 200 70 -25 5.21

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• US 4203742 [0015]
• DE 2820212 A [0016]
• DE 4440401 A1 [0016]
• DE 3445961 A1 [0018]
• WO 94/01209 [0020]
• DE 102004001974 A1 [0021]
• DE 69326254 T2 [0022]
• DE 1020040001974 A1 [0055]
• DE 10027685 B4 [0055]
• DE 10304322 A1 [0055]
• DE 10107539 A1 [0056]

Cited non-patent literature

• Santamaria et al. [M. Arruebo et al., Separation and Purification Technology 25 (2001) 275-286] [0023]

Claims (9)

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 from 0.5 to 0.8 nm or the polymeric membrane to higher selectivities 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, and the condensate of C ₂₊ hydrocarbons at a pressure of 1 to 360 bar in the temperature range from -70 ° C to + 50 ° C. is deducted from the permeate side, wherein the pressure difference between the feed and permeate side is 1-140 bar and wherein no purge gases are used. A method according to claim 1, characterized in that the feed gas comprises 0.5-30 mol%, in particular 0.5-25 mol%, especially 0.5-20 mol% of gaseous C ₂₊ hydrocarbons. Method according to one of claims 1 or 2, characterized in that the pressure of the feed gas is in the range of 30-200 bar, in particular 30-85 bar. Method according to one of claims 1 to 3, characterized in that the pressure difference between the feed and permeate side is 5 to 60 bar. Process according to one of Claims 1 to 4, characterized in that the increase in the amount of material from the feed side to the permeate side of the membrane is in the range of 1.5 to 100 times, in particular 3 to 40 times, based on the molar concentration. Method according to one of claims 1 to 5, characterized in that the porous inorganic material is a zeolite membrane having an Si: Al ratio of 50 to 700, preferably 150 to 450. Process according to any one of claims 1-5, characterized in that the zeolite is chosen from ZSM-5, CIT-1, DAF-1, Stilbite, Beta, Boggsite, EMC-2, STA-1, Terranovaite and Theta-1. Method according to one of claims 1 to 7, characterized in that non-condensed C ₂₊ -hydrocarbon gas is discharged from the permeate side and fed as a new feed to another membrane and this measure is repeated one or more times as a cascade separation. Method according to one of claims 1 to 8, characterized in that the C ₂₊ hydrocarbons C ₂ -C ₅ hydrocarbons, in particular n-propane, i-propane, n-butane and i-butane.

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