DE102010009542A1 - Process for the separation of natural gas or petroleum gas components from inorganic porous membranes - Google Patents

Abstract

The process is particularly relevant for the processing of natural gas and associated petroleum gases. With the method described, it is possible to separate hydrocarbons from one another at pressures relevant to practice, without the use of sweep gas on the permeate side. The invention is based on the technical problem of developing a method for separating natural gas or associated petroleum gas components on inorganic porous membranes with which higher hydrocarbons can be effectively separated continuously at high gas throughputs without complex cooling of the gases. The object is achieved by a method which is characterized by the following features: a) feed pressures greater than 5 bar are used, the pressure on the permeate side being lower than on the feed side. b) a pressure-mediated, increased condensation of the higher hydrocarbons at the pores of the membrane is used to increase the separation capacity c) mesoscopically and macroscopically dense inorganic membranes with microchannels with pore sizes in the area of the hydrocarbons to be separated are used. d) the process temperature is selected so that the pressure-mediated, increased condensation of the higher hydrocarbons in the pores of the interface is ensured.

Description

Field of application of the invention

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 expensive expansion and cooling using membrane technology. The separation itself is carried out on advanced, inorganic porous membranes without the aid of purge gases at elevated, practice-relevant pressure conditions (p> 5 bar) and improved separation performance in comparison to low pressure applications. By means of the developed method it is also possible to use smaller natural gas fields, because by means of the membrane technology a flexible, procedurally less expensive procedure for the removal of higher hydrocarbons from the raw gas is available. In addition, the developed process can find application for the removal of higher hydrocarbons from the hitherto little or no use of associated petroleum gas or other hydrocarbon mixtures.

State of the art

Natural gases have at their source sometimes considerable amounts of undesirable higher hydrocarbons (HKW), which must be removed before transport from the pump to the consumer in order to avoid malfunctioning by formation of gas hydrates. Crude oil gases still have significantly higher amounts of HKW, which is why these are currently hardly used.

A common treatment method of natural gas is currently the adsorptive drying by means of glycol and the removal of higher hydrocarbons by deep-freeze condensation. The deep-freeze condensation is a process and energy-consuming process that causes a compression of the delivered gas after the relaxation. Partly in addition, a pre-cooling of the gas stream is required.

In the article "Gas conditioning by means of permeable membranes" by G. HINNERS in ERDÖL ERDGAS KOHLE 120th ed. 2004, Issue 2 the trial of polymer-based membranes for the separation of HKW from natural gases under elevated pressure conditions is described. These show the disadvantage that they swell due to the higher hydrocarbons contained in the gas stream, whereby the selectivity decreases.

Membranes of inorganic-non-metallic materials do not have this defect. Further 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 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.

So describes WO 94/01209 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 DE 695 33 513 T2 is reported by the principle separation of various so-called feedstocks, which may also consist of hydrocarbons, such as those found in natural gas. However, the separation principle of molecular diffusion (p _feed = p _permeate ) is assumed. Also treated DE 696 30 570 T2 the possibility of hydrocarbon separation by means of pervaporation. Separation by pressure-mediated and non-diffusive preferred adsorption is not described.

DE 10 2004 001 974 A1 the possibility of olefin separation under elevated pressure conditions is described. It describes the separation of close-boiling mixtures by molecular radii. Although feed-side pressures of 1 to 100 bar and a permeate-side pressure of 0.01 to 10 bar are reported here, the separation principle is conversely the same as that of the invention. 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 the 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 patent DE 693 26 254 T2 it is described that it is possible to separate butanes from methane by means of supported MFI membranes, whereby adsorption increases the higher hydrocarbon in the permeate is enriched. 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 pressures far below 5 bar.

Further separations of hydrocarbons and comparable components on inorganic 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 in all previously described separations of natural gas and Erdölbegleitgas components according to the adsorption method, the separation is preferably carried out by the so-called surface diffusion, which has so far deteriorated after increasing the feed pressure and the differential pressures between feed and permeate.

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 Fonts 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 patent 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 published patent application DE 101 07 539 A1 describes the production of a composite membrane on a ceramic, porous support material, on which a mesoporous zeolite layer is deposited, wherein subsequently the closed zeolite layer is formed on / in the surface thereof by hydrothermal synthesis. No details are given on this mesoporous intermediate layer and the hydrothermal synthesis.

Inventive solution

The starting point of the present invention is that with an increase in the feed pressure to 5 bar and constant or adjusted permeate pressures always a reduction in the separation performance of the membranes was observed in the potential use for the decomposition of natural gas and associated gas in the respective individual components. This justifies the more theoretical applications of inorganic membranes for the separation of natural gas and associated gas components. There was no evidence of separation by means of the layers produced under practical conditions at elevated pressure conditions. The invention has for its object to develop a process for the separation of natural gas or Erdölbegleitgas components of inorganic porous membranes, can be separated with the higher hydrocarbons effectively without complex cooling of the gases continuously with high gas flow rates.

According to the technical problem is solved by the method characterized in the main claim. It comes in the membranes used in pressure increase of the applied feed surprisingly pressure-mediated, increased adsorption and condensation of each higher hydrocarbon from the present hydrocarbon mixture and in the pores of the membrane and by an applied pressure difference between the feed and permeate to increase the flow through the membrane. Thus, the separation of the respective higher hydrocarbon is favored according to the invention technically. This procedurally advantageous effect is only favorable at sufficiently high absolute pressures of the hydrocarbon mixture on the inorganic porous separating layer.

Pressure-mediated is defined as the separation performance of the membrane due to the applied gas pressure of the feed compared to low-pressure applications. As practical pressures, pressures> 5 bar are defined. As low pressure are defined pressures <5 bar. 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.

This behavior can only be exploited on meso- and macroscopically dense membranes without leakage flow. The necessary membranes were obtained with a prior art improved manufacturing process. The natural gas or associated petroleum gas or mixtures of natural gas or petroleum gas containing components are pressurized to these inorganic porous membranes given so that preferably each higher alkane can be condensed on the inorganic porous layer to a greater extent than in low-pressure applications and separated from the feed.

Particularly preferred materials of the inorganic porous layer, here called membrane, are densely grown crystallites based on zeolitic structure types, particularly preferably MFI, FAU, LTA, MOR, FER, MEL, BEA; ITR and KFI and here particularly preferably the MFI structure with silicalite membranes without Al content or MFI membranes with an aluminum content and here particularly preferably ZSM-5 with NanAlnSi96-nO192 · 16H2O (0 <n <27) patented by the Mobil Oil Company , 1975. Particularly preferred in MFI membranes with aluminum contents are Si / Al contents of greater than 75.

The membranes should be meso-and macroscopically dense and thus allow only adsorptive processes on the surface, whereby the mass transfer thus proceeds only through the intracrystalline 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 flows due to their small layer thickness. The thickness of the separating layer is therefore preferably less than 50 μm, more preferably less than 20 μm.

The separation of natural gas or Erdölbegleitgaskomponenten takes place in the simplest case by an applied feed pressure> 5 bar and a differential pressure between the feed and permeate side (drawing 1, Example 1). The feed pressure may be different from that which is optimal for the membrane process and due to other technological processes. The permeate pressure adjusts depending on the permeate flow and can be lowered by pumps / compressors. A further development of the method further includes the selective separation by means of a modular, cascade separation plant, wherein preferably each of the highest hydrocarbon passes through the membrane and is separated from the feed. The retentate has over the input composition, the feed, a depleted in these components composition. The resulting retentate passes through another separation unit, which in turn separates the highest alkane contained in this mixture. This process is repeated until the original mixture of the natural gas or associated gas has been separated into its individual components.

The feed pressure in this process must always be within the range of pressure-mediating condensation. The highest alkane is defined as the hydrocarbon with the longest C-C carbon compound.

From the permeate can be done by compression or cooling, the separation of hydrocarbons. When compressing the permeate there is the possibility of recycling the remaining gaseous hydrocarbon mixture in the feed stream of the membrane reactor with the aim of Gesamtamtstofflichen use.

The enrichment of the respective higher alkane and the associated preferred mass transport is evidently preferably carried out by increased condensation of the higher hydrocarbons in the pores. This can be seen for example from a mixture of methane / n-butane with only 0.3% n-hexane. Here, n-hexane is first separated at the membrane at elevated pressures from the inorganic porous membrane, methane and n-butane remain in the retentate. If the n-hexane is separated, the separation of n-butane is carried out in a subsequent separation step on a downstream membrane (Figure 2, Example 1 and 3). This effect is observed at elevated feed pressures, preferably at p _Feed > 5 bar. The process conditions and membrane geometry can be varied so that either individual hydrocarbons are selectively separated or hydrocarbon mixtures are produced in the permeate.

By applying high feed pressures, it is possible to use pressure differences between the feed and permeate side without applying a vacuum to the permeate side. Thus, a general flux increase and thus permeate yields for technical applications are possible. With this method can also be dispensed with the use of sweep gas on the permeate side. There are several possibilities of permeate treatment available, in particular the compression. Depending on the overall technological process, the permeate can be recirculated uncompressed or compressed into the feed stream. The uncompressed recirculation makes sense if a compressor with subsequent condensate separation is already installed in the feed upstream 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, since these are cheaper to produce and membrane and support of their chemical Composition and their thermal expansion behavior ago are similar. 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, electrophoretic 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 regard 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 h, more preferably between 160 and 180 ° C and 16 to 48 h.

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).

The invention will be explained in more detail with reference to the following examples.

example 1

Pressure-mediated, enhanced adsorption of the higher hydrocarbon

The membranes were tested for their permeation behavior under different conditions. For this purpose, they were mounted in a stainless steel module, with a seal by means of O-rings took place to Permeatraum. To perform permeation tests at various temperatures, the module was heated. According to an application under practical conditions prevailed on the permeate side during the measurement always lower pressure than on the feed side. The pressure on the feed side was set 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.

The results of the measurements are shown in the following tables:

Test 1 - Influence of differential pressure at constant permeate pressure

The influence of the separation properties is also dependent on the differential pressure of the temperature and the mixing ratio. (Table 1)

Test 2 - Influence of a higher alkane on the separation efficiency of methane / propane / n-butane and depletion of the higher alkane on the example of n-hexane

If various alkanes are present in an alkane mixture in their condensation, the highest alkane is preferably first removed. In a mixture of methane / propane / n-butane / n-hexane, therefore, the n-hexane is preferably first separated off. The separation of the components methane / propane / n-butane is very low in this case, but can be carried out after separation of the higher alkane, here n-hexane, analogous to the separation 1 with higher separation factors. The separation factor is defined as the ratio of the concentrations of the higher alkane in the permeate to the retentate. (Table 2) Table 1 Influence of the separation properties with increase of the feed pressure at constant maintained permeate pressure of 1.4 bar

Example 2

Synthesis of the membrane unit

To produce the silicalite membranes for gas separation, in particular for the separation of higher hydrocarbons from methane, corundum mono channels were used with an outer diameter of 10 mm, an inner diameter of 7 mm and a length of 125 mm. The carriers also contained a manufacturer-provided microfiltration layer of α-corundum 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 was 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 had been added, the corundum carriers were coated by slip casting. It formed after a life of 5 min under the given conditions, a layer thickness of 25 microns.

Prior to the synthesis, the corundum support coated inside with milled silicalite crystals was heat treated at 700 ° C for 1 h.

The synthesis solution for forming a closed film on the mesoporous silicalite layer had 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 - drawing 4). An average layer thickness of 40-75 μm was 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, was based on the synthesis of 100 mol 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 - drawing 5). An average layer thickness of 17-23 μm was 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.

Levasil served as a silicon source 300/30%, which contains 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 was deionized water. Before the synthesis, the carriers were wrapped with Teflon tape.

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

LIST OF REFERENCE NUMBERS

Description of the drawings

Drawing 4

Scanning electron micrograph:

• MFI separation layer (top) 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, including MF Layer of MFI, including corundum MF layer, including corundum support layer

Drawing 5

Scanning electron micrograph:

• MFI separation layer (top) 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 of MFI, including corundum MF layer, including corundum support layer

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 94/01209 [0006]
• DE 69533513 T2 [0007]
• DE 69630570 T2 [0007]
• DE 102004001974 A1 [0008, 0008]
• DE 69326254 T2 [0009]
• DE 1020040001974 A1 [0012]
• DE 10027685 B4 [0012]
• DE 10304322 A1 [0012]
• DE 10107539 A1 [0013]

Cited non-patent literature

• "Gas conditioning by means of permeable membranes" by G. HINNERS in ERDÖL ERDGAS KOHLE 120. Jg. 2004, No. 2 [0004]
• Santamaria et al. [M. Arruebo et al., Separation and Purification Technology 25 (2001) 275-286] [0010]

Claims (7)

Process for the separation of natural gas or associated petroleum gas components on inorganic porous membranes, characterized by the following features: a) it is operated with feed pressures greater than 5 bar, wherein the pressure on the permeate side is lower than on the feed side b) to increase the separation efficiency, a pressure-mediated, increased condensation of the higher hydrocarbons is used at the pores of the membrane c) meso and macroscopically dense inorganic membranes with micro channels with pore widths in the range of the hydrocarbons to be separated off are used. d) the process temperature is chosen so that the pressure-mediated, increased condensation of the higher hydrocarbons is ensured in the pores of the separation layer. A method according to claim 1, characterized in that the cascaded, staggered separation from the highest to the lowest hydrocarbon from the retentate takes place on successively connected membranes. A method according to claim 1, characterized in that the separation of hydrocarbons takes place from the permeate by cooling. A method according to claim 1, characterized in that the separation of hydrocarbons from the permeate by compression takes place and the remaining gaseous hydrocarbon mixture is recycled to the feed stream of the membrane reactor. A method according to claim 1, characterized in that working at process temperatures of <150 ° C. A method according to claim 1, characterized in that inorganic membranes are used, which have been obtained by synthesis of zeolites on a mesoporous zeolite support layer, wherein zeolites of the same or similar composition as the zeolites of the support layer ground to a particle size> 1 micron, 0, 5 to 30 microns thick applied to the carrier layer and subjected to a hydrothermal treatment. Process according to Claims 1 and 6, characterized in that inorganic membranes of silicalite with MFI structure are used.

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