Molecular sieve membrane and its preparation method, system and method for producing isoprene from isopentane

Abstract

The present invention provides a molecular sieve membrane and a preparation method thereof, as well as a system and method for producing isoprene from isopentane. The preparation method of the molecular sieve membrane comprises: placing a porous carrier in a treatment solution containing an organic polymer for pretreatment; then using a secondary growth method to grow the molecular sieve membrane on the pretreated porous carrier; wherein the organic polymer comprises one or more of an acrylic ester polymer, a vinyl ester polymer, a vinyl alcohol polymer, and a polyimide polymer. Pretreating the porous carrier with a treatment solution containing an organic polymer can effectively improve the separation performance of the molecular sieve membrane. In the process of producing isoprene from isopentane, the molecular sieve membrane is used to selectively remove the hydrogen generated in the reaction, thereby increasing the conversion rate of isopentane and simultaneously increasing the selectivity and yield of the product isoprene, thereby achieving a one-step, efficient production of isoprene from isopentane.

Description

Technical Field

[0001] The present invention belongs to the field of fine technology, and specifically relates to a molecular sieve membrane and a preparation method thereof, and a system and method for preparing isoprene from isopentane in one step. Background Art

[0002] Isoprene, also known as 2-methyl-1,3-butadiene, is a typical material with conjugated double bond structure, and is an important monomer of synthetic rubber. Along with the continuous improvement of my country's industrial level, the demand for rubber is improved year by year, and the natural rubber output by rubber tree is limited, and is affected by conditions such as weather, temperature, humidity, pests and diseases. Therefore, industrial synthetic isoprene rubber is a potential pathway for replacing natural rubber. Thermoplastic elastic rubber is prepared by isoprene, has the advantages of high temperature resistance, good sealing, physical and mechanical strength height, and can be used as the raw material of products such as hot melt adhesive, pressure-sensitive adhesive. In addition, isoprene is widely used in the synthesis of intermediates (such as carotene and vitamins) of medicine, pesticides and spices.

[0003] In production and life, a large amount of C s Alkanes have low economic value and currently have limited utilization. Therefore, producing high-value-added isoprene from inexpensive isopentane is a promising utilization strategy. Currently, the traditional method for producing isoprene from isopentane is a two-step dehydrogenation process. First, isopentane undergoes a first-step dehydrogenation reaction to produce isopentene, which is then dehydrogenated in a second step to produce the final product, isoprene. This method is technically mature, but it is complex, requires significant investment, and consumes high energy.

[0004] Membrane catalytic reactors are a new catalytic reaction technology developed in recent years with broad application prospects. They can simultaneously complete the catalytic reaction and product separation processes, thereby realizing an integrated catalysis-reaction-separation process. Membrane reactors are not simply a combination of reactor and membrane components in the process flow, but rather a coupling of the two. While achieving the reaction, they selectively remove the reaction products, promoting the reaction equilibrium to shift toward the positive direction, thereby achieving the goal of improving reaction conversion rate and product selectivity. By integrating reaction and separation, membrane reactors improve the process flow, simplify the subsequent product separation process, increase production efficiency, and effectively reduce production costs.

[0005] Molecular sieve membranes, a popular emerging inorganic material in recent years, have garnered widespread attention in fields such as gas and solvent separation due to their uniform pore size and regular structure. Furthermore, their excellent thermal and chemical stability make them suitable as separation media in membrane reactors. Providing a molecular sieve membrane suitable for the production of isoprene from isopentane to improve isoprene production efficiency is a pressing issue. Summary of the Invention

[0006] In order to solve all or part of the above technical problems, the present invention provides the following technical solutions:

[0007] One of the objects of the present invention is to provide a method for preparing a molecular sieve membrane, comprising:

[0008] placing the porous support in a treatment solution containing an organic polymer for pretreatment;

[0009] Then, a secondary growth method is used to grow a molecular sieve membrane on the pretreated porous support;

[0010] The organic polymer includes one or more of acrylic polymers, vinyl ester polymers, vinyl alcohol polymers, and polyimide polymers.

[0011] The applicant has discovered that pre-treating the porous carrier with the above-mentioned organic polymer can optimize the growth process of the molecular sieve membrane, achieve good bonding between the molecular sieve membrane and the porous carrier, and thus improve the separation performance of the molecular sieve membrane.

[0012] In some preferred embodiments, the organic polymer includes a methyl acrylate polymer.

[0013] In some preferred embodiments, the organic polymer includes one or a combination of polymethyl methacrylate, polyvinyl alcohol, polyethyleneimine, and polyvinyl acetate.

[0014] In some embodiments, the organic polymer is dissolved in an organic solvent to prepare the treatment solution, and the organic solvent includes one or more of an alcohol solvent, a ketone solvent, and a carboxylic acid solvent.

[0015] In some preferred embodiments, the organic solvent includes a ketone solvent. More preferably, the organic solvent includes acetone.

[0016] In some embodiments, the mass concentration of the organic polymer in the treatment solution is 0.01% to 0.50%.

[0017] In some embodiments, the porous carrier is made of porous alumina, mullite, silica, or zirconia, preferably porous alumina.

[0018] In some embodiments, the pretreatment specifically includes: soaking the porous carrier in the treatment solution for 0 to 0.5 hours, taking it out after soaking, and then heat treating it at a temperature of 100° C. to 200° C. to complete the pretreatment.

[0019] In some embodiments, the secondary growth method includes: loading the seed crystals on the surface of the pretreated porous carrier, and then high-temperature treating it at a temperature of 500°C to 1000°C for 0.5 to 2.0 hours. After the high-temperature treatment is completed, the porous carrier loaded with the seed crystals is placed in a membrane-forming mother solution to grow the molecular sieve membrane.

[0020] In some embodiments, the method of loading the seed crystals on the surface of the pretreated porous carrier includes any one of vacuum filtration, dip coating, spin coating, friction coating, and interfacial coating.

[0021] The seed crystal and film-forming mother solution may be any seed crystal and film-forming mother solution used in the secondary growth method in the prior art, and the present invention does not make any special limitation thereto.

[0022] A second object of the present invention is to provide a molecular sieve membrane obtained according to the preparation method in any of the above technical solutions.

[0023] In some embodiments, the type of the molecular sieve membrane is LTA molecular sieve membrane, MFI molecular sieve membrane, FAU molecular sieve membrane, BEA molecular sieve membrane, CHA molecular sieve membrane, SOD molecular sieve membrane, MOR molecular sieve membrane or DDR molecular sieve membrane.

[0024] A third object of the present invention is to provide the use of the molecular sieve membrane in any of the above technical solutions in the preparation of isoprene from isopentane.

[0025] A fourth object of the present invention is to provide a molecular sieve membrane reactor, comprising the molecular sieve membrane described in any one of the above technical solutions.

[0026] A fifth object of the present invention is to provide a system for producing isoprene from isopentane in one step, comprising:

[0027] A feeding mechanism, used for providing a reaction raw material containing isopentane;

[0028] a preheater, the preheater being in communication with the feed mechanism via a pipeline and being at least configured to gasify the isopentane provided by the feed mechanism;

[0029] The molecular sieve membrane reactor described in any of the above technical solutions is connected to the preheater through a pipeline, and the isopentane vaporized by the preheater reacts in the molecular sieve membrane reactor and separation of the product isoprene and hydrogen is achieved.

[0030] In some embodiments, the molecular sieve membrane reactor includes a shell having a hollow cavity, a feed pipe and a first discharge pipe are provided on the shell, and the feed pipe is connected to the preheater;

[0031] The molecular sieve membrane described in any of the above technical solutions is sealed and installed in the hollow cavity of the shell to separate the hollow cavity into a first cavity and a second cavity, the first cavity is filled with a catalyst, and the second cavity is connected to the second discharge pipe;

[0032] The vaporized isopentane enters the first cavity through the feed pipe and contacts the catalyst therein to react. The isoprene produced by the reaction flows out through the first discharge pipe. The hydrogen produced by the reaction passes through the molecular sieve membrane into the second cavity and flows out through the second discharge pipe.

[0033] In some embodiments, the system further includes a purge gas supply mechanism, and a purge gas pipeline connected to the purge gas supply mechanism is provided on the shell. The purge gas provided by the purge gas supply mechanism enters the second cavity through the purge gas pipeline to purge the hydrogen entering the second cavity and flow out from the second discharge pipeline.

[0034] In some embodiments, a blocking member is installed in the first cavity near the feed pipe and the first discharge pipe to prevent the catalyst from being lost.

[0035] Furthermore, the blocking member may be quartz wool, or other blocking members that have the function of blocking catalysts and are breathable.

[0036] A sixth object of the present invention is to provide a method for producing isoprene from isopentane in one step, using the system described in any one of the above technical solutions, comprising:

[0037] A mixed gas containing isopentane and an inert carrier gas is introduced into the molecular sieve membrane reactor, and the isopentane contacts the catalyst therein to undergo a dehydrogenation reaction to generate isoprene and hydrogen; wherein the generated hydrogen permeates the molecular sieve membrane to separate from the isoprene.

[0038] In some embodiments, the active components of the catalyst include one or more of Pt, Sn, Zn, Re, Co, Cu, Fe, Ga, Mn, Na, K, and Mg, and the carrier of the catalyst includes one or more of alumina, magnesium aluminum spinel, MFI molecular sieve, Beta molecular sieve, and silica.

[0039] In some embodiments, the mass ratio of the active component to the carrier in the catalyst is 0.01 to 10%, preferably 0.1 to 2%, and more preferably 0.1 to 1%.

[0040] In some embodiments, the catalyst is loaded inside the molecular sieve membrane reactor in the form of any one or more of stacking filling, in-situ growth, vacuum impregnation, magnetron sputtering, physical vapor deposition, chemical vapor deposition, and atomic layer deposition.

[0041] In some embodiments, the inert carrier gas includes at least one of nitrogen, argon, helium, and neon.

[0042] In some embodiments, in the method, the feed mass space velocity of isopentane is 1 to 100 h -1 In some preferred embodiments, the feed mass space velocity of isopentane is 1 to 10 h -1 .

[0043] In some embodiments, the reaction temperature of the dehydrogenation reaction is 300-600°C. In some preferred embodiments, the reaction temperature of the dehydrogenation reaction is 400-500°C, more preferably 400-450°C.

[0044] In some embodiments, the pressure difference across the molecular sieve membrane of the molecular sieve membrane reactor is controlled to be 0.1-10 MPa. In some preferred embodiments, the pressure difference across the molecular sieve membrane is 0.1-2 MPa, more preferably 0.1-0.2 MPa.

[0045] In some embodiments, the method further includes: using a purge gas to purge the hydrogen that has passed through the molecular sieve membrane to accelerate the discharge of the hydrogen.

[0046] In some embodiments, the purge gas includes at least one of nitrogen, argon, helium, and neon.

[0047] Compared with the prior art, the present invention has at least the following beneficial effects:

[0048] The present invention uses a pretreatment liquid containing an organic polymer to pretreat the porous carrier to enhance the interaction between the molecular sieve membrane and the porous carrier, so that the molecular sieve membrane can be well combined with the porous carrier during the growth process, optimize the growth process of the molecular sieve membrane, and thus improve the separation performance of the molecular sieve membrane;

[0049] The prepared molecular sieve membrane is suitable for the reaction of producing isoprene from isopentane. The dehydrogenation reaction of the isopentane raw material is carried out in the molecular sieve membrane reactor. The molecular sieve membrane selectively removes the hydrogen produced by the reaction, effectively improving the conversion rate of isopentane and significantly improving the selectivity and yield of the isoprene product. This realizes the one-step method for the efficient preparation of isoprene from isopentane, overcoming the shortcomings of the original two-step dehydrogenation method for isopentane, such as complex process, large investment, cumbersome product separation and high energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0051] Figure 1 1 is a schematic diagram of a system for producing isoprene from isopentane in one step according to an embodiment of the present invention;

[0052] Figure 2 Schematic diagram of the structure of a molecular sieve membrane reactor in one embodiment of the present invention. DETAILED DESCRIPTION

[0053] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching those skilled in the art to employ the present invention in various ways in virtually any appropriate detailed embodiment.

[0054] Example 1

[0055] This embodiment provides a method for preparing an MFI molecular sieve membrane:

[0056] Dissolving polymethyl methacrylate (PMMA) in an acetone solution to prepare a treatment solution with a mass concentration of 0.01%; placing a porous support made of α-Al2O3 in the treatment solution and soaking it for 5 minutes. After soaking, the support was taken out and dried at 200°C to obtain a pretreated porous support;

[0057] The MFI molecular sieve membrane is grown on the above-mentioned porous support using a secondary growth method, specifically as follows:

[0058] The MFI seed crystals were loaded onto a pretreated porous carrier by vacuum filtration and then subjected to high-temperature treatment at 600°C for 60 minutes. The treated carrier was placed in a membrane-forming mother liquor composed of tetrapropylammonium hydroxide, tetraethyl silicate and water in a ratio of 0.15:1:90, and hydrothermally synthesized at 160°C for 24 hours to grow an MFI molecular sieve membrane.

[0059] This embodiment provides a molecular sieve membrane reactor containing the MFI type molecular sieve membrane prepared as described above, such as Figure 2As shown, the above-mentioned MFI type molecular sieve membrane grows on the inner wall of the hollow tubular α-Al2O3 carrier to form a tubular MFI type molecular sieve membrane; the molecular sieve membrane reactor includes a shell with a hollow cavity, on which a feed pipe 15, a first discharge pipe 22, a purge gas pipe 21 and a second discharge pipe 23 are opened; the molecular sieve membrane is placed in the hollow cavity of the shell, and the two ends of the tubular molecular sieve membrane are against the inner wall of the shell to separate the hollow cavity into a first cavity 16 and a second cavity 24, and in the second cavity 24, near the place where the tubular molecular sieve membrane is against the shell, a graphite sealing ring 19 is also provided to ensure that the first cavity 16 and the second cavity 24 are sealed and separated; the first cavity 16 is filled with a catalyst 18, and quartz wool 17 is provided near the feed pipe 15 and the first discharge pipe 22. The quartz wool 17 is used to prevent the catalyst 18 from losing from the feed pipe 15 and / or the first discharge pipe 22.

[0060] like Figure 1 As shown, this embodiment provides a system for producing isoprene from isopentane in one step. The system includes a feed mechanism 5, a preheater 6, a molecular sieve membrane reactor 7 having the MFI molecular sieve membrane prepared above, an inert carrier gas delivery circuit, and a purge gas supply mechanism. The feed mechanism 5 delivers the raw material isopentane via pipeline 4 into the preheater 6 for vaporization. The inert carrier gas delivery circuit includes a pipeline 1 connected to the preheater 6, a mass flow controller 2, and a ball valve 3. The inert carrier gas enters the preheater 6 via pipeline 1 and mixes with the vaporized isopentane to form a mixed gas. The mixed gas undergoes a dehydrogenation reaction in the molecular sieve membrane reactor 7.

[0061] Specifically, such as Figure 2As shown, the MFI type molecular sieve membrane in this embodiment grows on the inner wall of the hollow tubular α-Al2O3 carrier to form a tubular MFI type molecular sieve membrane; the molecular sieve membrane reactor 7 includes a shell with a hollow cavity, on which a feed pipe 15, a first discharge pipe 22, a purge gas pipe 21 and a second discharge pipe 23 are provided; the molecular sieve membrane is placed in the hollow cavity of the shell, and the two ends of the tubular molecular sieve membrane are abutted against the inner wall of the shell to separate the hollow cavity into a first cavity 16 and a second cavity 24, and in the second cavity 24, near the abutment between the tubular molecular sieve membrane and the shell, a graphite sealing ring 19 is further provided to ensure that the first cavity 16 and the second cavity 24 are sealed and separated; the first cavity 16 is filled with a catalyst 18, and quartz wool 17 is provided near the feed pipe 15 and the first discharge pipe 22. The quartz wool 17 is used to prevent the catalyst 18 from losing from the feed pipe 15 and / or the first discharge pipe 22. The mixed gas in the preheater 6 enters the first cavity 16 through the feed pipe 15, contacts the catalyst filled therein, and undergoes a dehydrogenation reaction to produce isoprene and hydrogen. The produced isoprene flows out from the first discharge pipe 22, and the produced hydrogen permeates the molecular sieve membrane 20 into the second cavity 24 and flows out from the second discharge pipe 23, thereby achieving separation of isoprene and hydrogen. In addition, in order to improve the separation efficiency, the present embodiment is provided with a purge gas supply mechanism to improve the dehydrogenation efficiency. The purge gas supply mechanism includes a pipeline 10, a mass flow controller 11, and a ball valve 12. The pipeline 10 is connected to the purge gas pipeline 21 of the molecular sieve membrane reactor 7. The purge gas supply mechanism introduces a purge gas into the second cavity (24) through the pipeline 10 and the purge gas pipeline (21) to drive the hydrogen in the second cavity (24) to flow out from the second discharge pipe (23).

[0062] The target product isoprene flows into the downstream mechanism through the first discharge pipe 22. As needed, back pressure valves 9, 13, a pressure gauge 8, etc. can also be set on the pipeline 14 connected to the first discharge pipe 22.

[0063] The feeding mechanism 5 in this embodiment is a high-pressure feeding pump. Of course, other raw material supply mechanisms can also be used.

[0064] This embodiment provides a method for preparing isoprene from isopentane in one step. The system provided in this embodiment is used, and 0.5 g of Pt-Sn / γ-Al2O3 catalyst is filled into the tubular carrier of the molecular sieve membrane reactor. The inner ends of the membrane tube are blocked by quartz wool to prevent the loss of the catalyst. The temperature of the molecular sieve membrane reactor is raised to 450°C, and the isopentane as a reactant is transported into a preheater by a high-pressure constant flow pump and fully mixed with nitrogen before entering the molecular sieve membrane reactor. The mixed gas composition is 80% nitrogen and 20% isopentane gas, and the total flow rate is controlled at 50 mL / min, wherein the feed mass flow rate of isopentane is 2.0 h -1The pressure inside the molecular sieve membrane (i.e., first cavity 16) was controlled at approximately 100 kPa, and the permeate side was purged with nitrogen at a constant flow rate of 20 mL / min. Under these reaction conditions, the isopentane conversion was 49.6%, the isoprene selectivity in the product was 48.2%, and the yield was 23.9%.

[0065] Example 2

[0066] The only difference between Example 2 and Example 1 is that the α-Al 2 O 3 carrier is pretreated with a 0.2% polyvinyl alcohol (PVA) acetone solution. The rest of the steps are the same as in Example 1 to prepare an MFI type molecular sieve membrane.

[0067] The molecular sieve membrane in the system of Example 1 was replaced with the molecular sieve membrane prepared in this example, and the isopentane-one-step isoprene reaction was carried out. 0.5 g of Pt-Sn / γ-Al2O3 catalyst was filled into the tubular carrier of the molecular sieve membrane reactor, and the inner ends of the membrane tube were blocked by quartz wool to prevent the loss of the catalyst. The temperature of the molecular sieve membrane reactor was raised to 450°C, and the isopentane as the reactant was transported into the preheater by a high-pressure constant flow pump and fully mixed with nitrogen before entering the molecular sieve membrane reactor. The mixed gas composition was 80% nitrogen and 20% isopentane gas, and the total flow rate was controlled at 50 mL / min, of which the feed mass flow rate of isopentane was 2.0 h -1 The pressure inside the molecular sieve membrane (i.e., first cavity 16) was controlled at approximately 100 kPa, and the permeate side was purged with nitrogen at a constant flow rate of 20 mL / min. Under these reaction conditions, the isopentane conversion was 45.0%, the isoprene selectivity in the product was 44.8%, and the yield was 20.2%.

[0068] Example 3

[0069] The only difference between Example 3 and Example 1 is that 0.1% polyethyleneimine acetone solution is used to pretreat the α-Al 2 O 3 carrier. The rest of the process is the same as that of Example 1 to prepare an MFI type molecular sieve membrane.

[0070] The molecular sieve membrane in the system of Example 1 was replaced with the molecular sieve membrane prepared in this example, and the isopentane-one-step isoprene reaction was carried out. 0.5 g of Pt-Sn / γ-Al2O3 catalyst was filled into the tubular carrier of the molecular sieve membrane reactor, and the inner ends of the membrane tube were blocked by quartz wool to prevent the loss of the catalyst. The temperature of the molecular sieve membrane reactor was raised to 450°C, and the isopentane as the reactant was transported into the preheater by a high-pressure constant flow pump and fully mixed with nitrogen before entering the molecular sieve membrane reactor. The mixed gas composition was 80% nitrogen and 20% isopentane gas, and the total flow rate was controlled at 50 mL / min, of which the feed mass flow rate of isopentane was 2.0 h -1The pressure inside the molecular sieve membrane (i.e., first cavity 16) was controlled at approximately 100 kPa, and the permeate side was purged with nitrogen at a constant flow rate of 20 mL / min. Under these reaction conditions, the isopentane conversion was 42.3%, the isoprene selectivity in the product was 45.0%, and the yield was 19.0%.

[0071] Example 4

[0072] The only difference between Example 4 and Example 1 is that the carrier is treated with a 0.5% polyvinyl acetate (PVAC) acetone solution. The rest of the steps are the same as in Example 1 to prepare an MFI molecular sieve membrane.

[0073] The molecular sieve membrane in the system of Example 1 was replaced with the molecular sieve membrane prepared in this example, and the isopentane-one-step isoprene reaction was carried out. 0.5 g of Pt-Sn / γ-Al2O3 catalyst was filled into the tubular carrier of the molecular sieve membrane reactor, and the inner ends of the membrane tube were blocked by quartz wool to prevent the loss of the catalyst. The temperature of the molecular sieve membrane reactor was raised to 400°C, and the isopentane as the reactant was transported into the preheater by a high-pressure constant flow pump and fully mixed with nitrogen before entering the molecular sieve membrane reactor. The mixed gas composition was 80% nitrogen and 20% isopentane gas, and the total flow rate was controlled at 50 mL / min, of which the feed mass flow rate of isopentane was 1.0 h -1 The pressure inside the molecular sieve membrane (i.e., first cavity 16) was controlled at approximately 100 kPa, and the permeate side was purged with nitrogen at a constant flow rate of 20 mL / min. Under these reaction conditions, the isopentane conversion was 42.8%, the isoprene selectivity in the product was 44.6%, and the yield was 19.1%.

[0074] Comparative Example 1

[0075] The only difference between Comparative Example 1 and Example 1 is that, when preparing the MFI molecular sieve membrane, pure water is used to treat it, that is, no pretreatment is performed, and the rest is the same as in Example 1.

[0076] The isopentane conversion rate was 38.7%, the isoprene selectivity in the product was 42.0%, and the yield was 16.3%.

[0077] Comparative Example 2

[0078] The isopentane dehydrogenation reaction in this comparative example was carried out in a fixed-bed reactor: the difference from Example 1 was that a quartz tube was used instead of the molecular sieve membrane tube in the membrane reactor assembly, 0.5 g of Pt-Sn / γ-Al2O3 catalyst was filled into the quartz tube, both ends of the tube were plugged with quartz wool, and the temperature was raised to 400°C. The raw gas mixed uniformly during the preheating period was introduced. The mixed gas composition was 80% nitrogen and 20% isopentane gas. The total flow rate was controlled at 50 mL / min, of which the feed mass flow rate of isopentane was 1.0 h-1, and the pressure inside the quartz tube was 100 kPa. Under these reaction conditions, the isopentane conversion rate was 23.2%, the isoprene selectivity in the product was 7.8%, and the isoprene yield was 1.8%.

[0079] Table 1 Relevant reaction conditions and effects of the embodiments of the present invention and comparative examples

[0080]

[0081] As can be seen from Table 1, compared with conventional fixed-bed reactors, the method provided by the present invention effectively improves the conversion rate of the isopentane feedstock and significantly enhances the selectivity and yield of the isoprene product by selectively removing hydrogen generated by the dehydrogenation reaction in a molecular sieve membrane reactor. Furthermore, pretreating the porous support with a treatment solution containing an organic polymer effectively increases the conversion rate of isopentane and the yield of isoprene. This invention achieves a one-step, efficient production of isoprene from isopentane, improving production efficiency and effectively reducing production costs.

[0082] The various aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and are not intended to limit the present invention, the scope of which is defined solely by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0083] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments using other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0084] Although the present invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and / or additions may be made and that substantial equivalents may be substituted for the elements of the embodiments without departing from the spirit and scope of the present invention. Additionally, many modifications may be made to adapt specific circumstances or materials to the teachings of the present invention without departing from the scope of the present invention. Therefore, it is not intended herein to limit the present invention to the disclosed specific embodiments for carrying out the present invention, but rather to include all embodiments within the scope of the appended claims. Furthermore, unless specifically stated, any use of the terms first, second, etc. does not indicate any order or importance, but rather uses the terms first, second, etc. to distinguish one element from another.

Claims

1. A method for preparing a molecular sieve membrane, characterized in that: include: Pretreating the molecular sieve membrane comprises: soaking the porous support in a treatment solution containing an organic polymer for 0.5 min to 0.5 h, and then heat treating the porous support at a temperature of 100° C. to 200° C.; wherein the mass concentration of the organic polymer in the treatment solution is 0.01% to 0.50%, and the organic polymer is selected from one or a combination of polymethyl methacrylate, polyvinyl alcohol, polyethyleneimine, and polyvinyl acetate; Then, a secondary growth method is adopted to grow a molecular sieve membrane on the pretreated porous support.

2. The preparation method according to claim 1, wherein: The organic polymer is dissolved in an organic solvent to prepare the treatment liquid, and the organic solvent includes one or more of an alcohol solvent, a ketone solvent, and a carboxylic acid solvent.

3. The preparation method according to claim 2, wherein: The organic solvent includes a ketone solvent.

4. The preparation method according to claim 3, wherein: The organic solvent includes acetone.

5. The preparation method according to claim 1, wherein: The porous carrier is porous alumina, mullite, silica or zirconia.

6. The preparation method according to claim 5, characterized in that: The porous carrier is porous alumina.

7. The preparation method according to claim 1, wherein The secondary growth method includes: loading seed crystals on the surface of the pretreated porous carrier, and then high-temperature treating the porous carrier at a temperature of 500°C to 1000°C for 0.5 to 2.0 hours. After the high-temperature treatment is completed, the porous carrier loaded with seed crystals is placed in a film-forming mother solution to grow a molecular sieve membrane.

8. The molecular sieve membrane obtained by the preparation method according to any one of claims 1 to 7.

9. The molecular sieve membrane according to claim 8, characterized in that The type of the molecular sieve membrane is LTA molecular sieve membrane, MFI molecular sieve membrane, FAU molecular sieve membrane, BEA molecular sieve membrane, CHA molecular sieve membrane, SOD molecular sieve membrane, MOR molecular sieve membrane or DDR molecular sieve membrane.

10. Use of the molecular sieve membrane according to claim 8 or 9 in the preparation of isoprene from isopentane.

11. A molecular sieve membrane reactor, characterized in that: Comprising the molecular sieve membrane according to claim 8 or 9.

12. A system for producing isoprene from isopentane in one step, characterized in that: include: A feeding mechanism (5) for providing a reaction raw material containing isopentane; a preheater (6), the preheater (6) being in communication with the feed mechanism (5) via a pipeline and being used at least to gasify the isopentane provided by the feed mechanism (5); The molecular sieve membrane reactor (7) according to claim 11 is connected to the preheater (6) through a pipeline, and the isopentane vaporized by the preheater (6) reacts in the molecular sieve membrane reactor (7) and separation of the product isoprene and hydrogen is achieved.

13. The system according to claim 12, characterized in that: The molecular sieve membrane reactor (7) comprises a shell having a hollow cavity, a feed pipe (15) and a first discharge pipe (22) are provided on the shell, and the feed pipe (15) is connected to the preheater (6); The molecular sieve membrane (20) is sealed and installed in the hollow cavity of the shell to separate the hollow cavity into a first cavity (16) and a second cavity (24); the first cavity (16) is filled with a catalyst (18), and the second cavity (24) is connected to a second discharge pipe (23); The vaporized isopentane enters the first cavity (16) through the feed pipe (15) and contacts the catalyst (18) therein to react. The isoprene produced by the reaction flows out through the first discharge pipe (22). The hydrogen produced by the reaction passes through the molecular sieve membrane (20) into the second cavity and flows out through the second discharge pipe (23).

14. The system according to claim 13, wherein: The system further comprises a purge gas supply mechanism, wherein a purge gas pipeline (21) connected to the purge gas supply mechanism is provided on the housing, and purge gas provided by the purge gas supply mechanism enters the second cavity (24) through the purge gas pipeline (21) to purge hydrogen entering the second cavity (24) and flowing out from the second discharge pipe (23).

15. The system according to claim 13, wherein: Blocking members are installed in the first cavity (16) near the feed pipe (15) and the first discharge pipe (22) to prevent the catalyst (18) from being lost.

16. A method for preparing isoprene from isopentane in one step, characterized in that: The system according to any one of claims 12 to 15, comprising: A mixed gas containing isopentane and an inert carrier gas is introduced into the molecular sieve membrane reactor, and the isopentane contacts the catalyst therein to undergo a dehydrogenation reaction to generate isoprene and hydrogen; wherein the generated hydrogen permeates the molecular sieve membrane to separate from the isoprene.

17. The method according to claim 16, wherein: The active components of the catalyst include one or more of Pt, Sn, Zn, Re, Co, Cu, Fe, Ga, Mn, Na, K, and Mg, and the carrier of the catalyst includes one or more of alumina, magnesium aluminum spinel, MFI molecular sieve, Beta molecular sieve, and silica.

18. The method according to claim 16, wherein: In the catalyst, the mass ratio of the active component to the carrier is 0.01-10%.

19. The method according to claim 18, wherein: In the catalyst, the mass ratio of the active component to the carrier is 0.1% to 2%.

20. The method according to claim 19, wherein: In the catalyst, the mass ratio of the active component to the carrier is 0.1-1%.

21. The method according to claim 16, wherein: The feed mass space velocity of isopentane is 1 to 100 h -1 .

22. The method according to claim 21, characterized in that: The feed mass space velocity of isopentane is 1~10 h -1 .

23. The method according to claim 16, wherein: The reaction temperature of the dehydrogenation reaction is 300-600°C.

24. The method according to claim 23, wherein: The reaction temperature of the dehydrogenation reaction is 400-500°C.

25. The method according to claim 24, wherein: The reaction temperature of the dehydrogenation reaction is 400-450°C.

26. The method according to claim 16, wherein: The pressure difference on both sides of the molecular sieve membrane of the molecular sieve membrane reactor is controlled to be 0.1~10 MPa.

27. The method according to claim 26, wherein: The pressure difference on both sides of the molecular sieve membrane of the molecular sieve membrane reactor is controlled to be 0.1~2 MPa.

28. The method according to claim 27, wherein: The pressure difference on both sides of the molecular sieve membrane of the molecular sieve membrane reactor is controlled to be 0.1-0.2 MPa.

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