Molecular sieve membrane and preparation method therefor, and system and method for preparing isoprene from isopentane

Abstract

Provided are a molecular sieve membrane and a preparation method therefor, and a system and method for preparing isoprene from isopentane. The preparation method comprises: placing a porous carrier in a treatment solution containing an organic polymer, so as to perform pretreatment; and then growing a molecular sieve membrane on the pretreated porous carrier by using a secondary growth method, wherein the used organic polymer comprises one or more of an acrylate polymer, a vinyl ester polymer, a vinyl alcohol polymer, and a polyimide polymer. The pretreatment can effectively improve the separation performance of the molecular sieve membrane, and in the process of preparing isoprene from isopentane, hydrogen generated by reaction is selectively removed by using the prepared molecular sieve membrane, so that the conversion rate of isopentane can be increased, moreover, the selectivity and yield of product isoprene are improved, and one-step efficient preparation of isoprene from isopentane is realized.

Description

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

[0001] This application is based on and claims priority to the Chinese patent application with application number 2024100540959 filed on January 12, 2024, and invention name “Molecular sieve membrane and its preparation method, system and method for producing isoprene from isopentane”. Technical Field

[0002] The present application belongs to the field of fine chemical technology, and specifically relates to a molecular sieve membrane and a preparation method thereof, and a system and method for producing isoprene from isopentane in one step. Background Art

[0003] 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.

[0004] In production and daily life, the large amount of C5 alkanes produced by oil refining plants has low economic value and currently has 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 of dehydrogenation to produce isopentene, which is then subjected to a second step of dehydrogenation to obtain the final product, isoprene. This method is technically mature, but the process is complex, requires high investment, and consumes a lot of energy.

[0005] 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.

[0006] 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.

[0007] Summary of the Invention

[0008] The main purpose of this application is to provide a molecular sieve membrane and a preparation method thereof, and a system and method for producing isoprene from isopentane to overcome the deficiencies in the prior art.

[0009] To achieve the aforementioned invention objectives, the technical solutions adopted in this application include:

[0010] In a first aspect, the present application provides a method for preparing a molecular sieve membrane, comprising:

[0011] placing the porous support in a treatment solution containing an organic polymer for pretreatment;

[0012] Then, a secondary growth method is used to grow a molecular sieve membrane on the pretreated porous support;

[0013] The organic polymer includes one or more of acrylic polymers, vinyl ester polymers, vinyl alcohol polymers, and polyimide polymers.

[0014] In a second aspect, the present application provides a molecular sieve membrane obtained according to the above preparation method.

[0015] In a third aspect, the present application provides the use of the molecular sieve membrane in the production of isoprene from isopentane.

[0016] In a fourth aspect, the present application provides a molecular sieve membrane reactor, comprising the molecular sieve membrane described in the present application.

[0017] In a fifth aspect, the present application provides a system for producing isoprene from isopentane in one step, comprising:

[0018] A feeding mechanism, used for providing a reaction raw material containing isopentane;

[0019] 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;

[0020] The molecular sieve membrane reactor described in the present application 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.

[0021] In a sixth aspect, the present application provides a method for producing isoprene from isopentane in one step, using the system described in the present application, comprising: passing a mixed gas containing isopentane and an inert carrier gas into the molecular sieve membrane reactor, wherein the isopentane contacts the catalyst therein to undergo a dehydrogenation reaction to generate isoprene and hydrogen; wherein the generated hydrogen passes through the molecular sieve membrane to be separated from the isoprene.

[0022] Compared with the prior art, the advantages of this application include:

[0023] (1) The present application uses a pretreatment liquid containing an organic polymer to pretreat the porous support to enhance the interaction between the molecular sieve membrane and the porous support, so that the molecular sieve membrane can be well combined with the porous support during the growth process, thereby optimizing the growth process of the molecular sieve membrane and improving the separation performance of the molecular sieve membrane;

[0024] (2) The prepared zeolite membrane is suitable for the reaction of producing isoprene from isopentane. The dehydrogenation reaction of the isopentane raw material is carried out in the zeolite membrane reactor. The hydrogen produced by the reaction is selectively removed by the zeolite membrane, which effectively improves the conversion rate of isopentane and significantly improves the selectivity and yield of the isoprene product. The one-step method for the efficient preparation of isoprene from isopentane is realized, overcoming the shortcomings of the original two-step dehydrogenation process of isopentane, such as complex process, large investment, cumbersome product separation and high energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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 paying any creative work.

[0026] FIG1 is a schematic diagram of a system for producing isoprene from isopentane in one step according to an embodiment of the present application;

[0027] FIG2 is a schematic structural diagram of a molecular sieve membrane reactor in one embodiment of the present application. DETAILED DESCRIPTION

[0028] In view of the problems existing in the above-mentioned prior art, the inventors of this case proposed this technical solution after long-term research and a large number of experiments. The technical solution, its implementation process and principles will be further explained below.

[0029] As one aspect of the technical solution of the present application, the present application provides a method for preparing a molecular sieve membrane, comprising:

[0030] placing the porous support in a treatment solution containing an organic polymer for pretreatment;

[0031] Then, a secondary growth method is used to grow a molecular sieve membrane on the pretreated porous support;

[0032] The organic polymer includes one or more of acrylic polymers, vinyl ester polymers, vinyl alcohol polymers, and polyimide polymers.

[0033] 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.

[0034] In some preferred embodiments, the organic polymer includes a methyl acrylate polymer.

[0035] In some preferred embodiments, the organic polymer includes one or a combination of polymethyl methacrylate, polyvinyl alcohol, polyethyleneimine, and polyvinyl acetate.

[0036] 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.

[0037] In some preferred embodiments, the organic solvent includes a ketone solvent. More preferably, the organic solvent includes acetone.

[0038] In some embodiments, the mass concentration of the organic polymer in the treatment solution is 0.01% to 0.50%.

[0039] In some embodiments, the porous carrier is made of porous alumina, mullite, silica, or zirconia, preferably porous alumina.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 are not particularly limited in this application.

[0044] As another aspect of the technical solution of the present application, the present application provides a molecular sieve membrane obtained according to the preparation method in any of the above technical solutions.

[0045] 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.

[0046] As another aspect of the technical solution of the present application, the present application provides the use of the molecular sieve membrane in any of the above technical solutions in the preparation of isoprene from isopentane.

[0047] As another aspect of the technical solution of the present application, the present application provides a molecular sieve membrane reactor, comprising the molecular sieve membrane described in any one of the above technical solutions.

[0048] As another aspect of the technical solution of the present application, the present application provides a system for producing isoprene from isopentane in one step, comprising:

[0049] A feeding mechanism, used for providing a reaction raw material containing isopentane;

[0050] 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;

[0051] 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.

[0052] 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; 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; 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, and the hydrogen produced by the reaction passes through the molecular sieve membrane into the second cavity and flows out through the second discharge pipe.

[0053] 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.

[0054] 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.

[0055] Furthermore, the blocking member may be quartz wool, or other blocking members that have the function of blocking catalysts and are breathable.

[0056] As another aspect of the technical solution of the present application, the present application provides a method for producing isoprene from isopentane in one step, using the system described in any of the above technical solutions, comprising:

[0057] 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.

[0058] 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.

[0059] 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%.

[0060] 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.

[0061] In some embodiments, the inert carrier gas includes at least one of nitrogen, argon, helium, and neon.

[0062] 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 .

[0063] 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.

[0064] 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.

[0065] 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.

[0066] In some embodiments, the purge gas includes at least one of nitrogen, argon, helium, and neon.

[0067] The following is a more detailed explanation of the technical solution of this application in conjunction with several preferred embodiments and accompanying drawings. The specific embodiments described below are only intended to further illustrate and explain this application and are not intended to limit this application. All variations that can be associated with or derived from the content disclosed in this application are considered to be within the scope of protection of this application.

[0068] Example 1

[0069] This embodiment provides a method for preparing an MFI molecular sieve membrane:

[0070] 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;

[0071] The MFI molecular sieve membrane is grown on the above-mentioned porous support using a secondary growth method, specifically as follows:

[0072] 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.

[0073] This embodiment provides a molecular sieve membrane reactor containing the MFI molecular sieve membrane prepared as described above. As shown in FIG2 , the MFI molecular sieve membrane is grown on the inner wall of a hollow tubular α-Al2O3 carrier to form a tubular MFI molecular sieve membrane. The molecular sieve membrane reactor includes a shell having 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 both ends of the tubular molecular sieve membrane abut against the inner wall of the shell to separate the hollow cavity into a first cavity 16 and a second cavity 24. A graphite sealing ring 19 is further provided in the second cavity 24 near the abutment between the tubular molecular sieve membrane and the shell. Used 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 leaking from the feed pipe 15 and / or the first discharge pipe 22.

[0074] As shown in Figure 1, 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.

[0075] Specifically, as shown in Figure 2, 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 having 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, a graphite sealing ring 19 is further provided near the abutment between the tubular molecular sieve membrane and the shell 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).

[0076] 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.

[0077] The feeding mechanism 5 in this embodiment is a high-pressure feeding pump. Of course, other raw material supply mechanisms can also be used.

[0078] 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%.

[0079] Example 2

[0080] 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.

[0081] 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%.

[0082] Example 3

[0083] 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.

[0084] 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%.

[0085] Example 4

[0086] 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.

[0087] 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%.

[0088] Comparative Example 1

[0089] 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.

[0090] The isopentane conversion rate was 38.7%, the isoprene selectivity in the product was 42.0%, and the yield was 16.3%.

[0091] Comparative Example 2

[0092] The isopentane dehydrogenation reaction in this comparative example was carried out in a fixed-bed reactor: the difference from Example 1 was that the molecular sieve membrane tube in the membrane reactor assembly was replaced by a quartz tube, 0.5 g of Pt-Sn / γ-Al2O3 catalyst was filled into the quartz tube, both ends were blocked with quartz wool, and the temperature was raised to 400°C. The raw gas mixed uniformly during the preheating period was introduced, and 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 , the pressure inside the quartz tube was 100 kPa, the isopentane conversion under these reaction conditions was 23.2%, the isoprene selectivity in the product was 7.8%, and the isoprene yield was 1.8%.

[0093] Table 1 Relevant reaction conditions and effects of the examples and comparative examples of this application

[0094] As can be seen from Table 1, compared with traditional fixed-bed reactors, the method provided by this application effectively improves the conversion rate of the isopentane feedstock and significantly enhances the selectivity and yield of the isoprene product by selectively removing the hydrogen produced by the dehydrogenation reaction in the molecular sieve membrane reactor. Furthermore, pre-treating the porous support with a treatment solution containing an organic polymer effectively increases the conversion rate of isopentane and the yield of isoprene. This application achieves a one-step, efficient production of isoprene from isopentane, improving production efficiency and effectively reducing production costs.

[0095] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of this application. Their purpose is to enable those familiar with the art to understand the content of this application and implement it accordingly. They are not intended to limit the scope of protection of this application. Any equivalent changes or modifications made in accordance with the spirit and substance of this application shall be included within the scope of protection of this application.

[0096] 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.

[0097] Although the present application 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 without departing from the spirit and scope of the present application, and that substantial equivalents may be substituted for the elements of the described embodiments. In addition, many modifications may be made to adapt specific circumstances or materials to the teachings of the present application without departing from the scope of the present application. Therefore, it is not intended herein to limit the present application to the disclosed specific embodiments for carrying out the present application, but rather it is intended that the present application will 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 the terms first, second, etc. are used to distinguish one element from another.

Claims

1. A method for preparing a molecular sieve membrane, characterized in that, Comprising: Pre-treating a porous support by placing it in a treating solution containing an organic polymer; Then, using a secondary growth method, growing a molecular sieve membrane on the pre-treated porous support; Wherein, the organic polymer comprises one or more of acrylate polymers, vinyl ester polymers, vinyl alcohol polymers, and polyimide polymers.

2. The preparation method of the molecular sieve membrane according to claim 1, characterized in that: The organic polymer comprises methyl acrylate polymers; And / or, the organic polymer comprises one or more combinations of polymethyl methacrylate, polyvinyl alcohol, polyethyleneimine, and polyvinyl acetate; And / or, dissolving the organic polymer in an organic solvent to prepare the treating solution, and the organic solvent comprises one or more of alcohol solvents, ketone solvents, and carboxylic acid solvents; And / or, in the treating solution, the mass concentration of the organic polymer is 0.01% - 0.50%; And / or, the material of the porous support is porous alumina, mullite, silica, or zirconia; And / or, the pre-treatment specifically comprises: soaking the porous support in the treating solution for 0 - 0.5 h, taking it out after soaking, and then performing heat treatment at a temperature of 100°C - 200°C to complete the pre-treatment; And / or, the secondary growth method comprises: loading seeds on the surface of the pre-treated porous support, then performing high-temperature treatment at a temperature of 500°C - 1000°C for 0.5 - 2.0 h, and after the high-temperature treatment is completed, placing the porous support loaded with seeds in a film-forming mother liquor to grow the molecular sieve membrane.

3. The preparation method of the molecular sieve membrane according to claim 2, characterized in that: The organic solvent comprises ketone solvents; and / or, the material of the porous support is porous alumina.

4. The preparation method of the molecular sieve membrane according to claim 3, characterized in that: The organic solvent comprises acetone.

5. A molecular sieve membrane obtained by the preparation method according to any one of claims 1 - 4.

6. The molecular sieve membrane according to claim 5, wherein: The type of the molecular sieve membrane is LTA-type molecular sieve membrane, MFI-type molecular sieve membrane, FAU-type molecular sieve membrane, BEA-type molecular sieve membrane, CHA-type molecular sieve membrane, SOD-type molecular sieve membrane, MOR-type molecular sieve membrane, or DDR-type molecular sieve membrane.

7. Use of the molecular sieve membrane according to claim 5 or 6 in the production of isoprene from isopentane.

8. A molecular sieve membrane reactor, characterized in that, Comprising the molecular sieve membrane according to claim 5 or 6.

9. A system for directly preparing isoprene from isopentane, characterized in that, Comprising: A feeding mechanism (5) for providing a reaction raw material containing isopentane; A preheater (6), the preheater (6) is connected to the feeding mechanism (5) through a pipeline, and is at least used to vaporize the isopentane provided by the feeding mechanism (5); The molecular sieve membrane reactor (7) according to claim 8, the molecular sieve membrane reactor (7) 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 the product isoprene and hydrogen are separated.

10. The system according to claim 9, wherein: The molecular sieve membrane reactor (7) comprises a housing having a hollow cavity, and a feeding pipeline (15) and a first discharging pipeline (22) are arranged on the housing, and the feeding pipeline (15) is connected to the preheater (6); The molecular sieve membrane (20) as claimed in claim 5 or 6 is hermetically installed in the hollow cavity of the housing to divide 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) communicates with a second discharge pipeline (23). The vaporized isopentane enters the first cavity (16) through the feed pipeline (15) and contacts the catalyst (18) therein to carry out a reaction. The isoprene produced by the reaction flows out through the first discharge pipeline (22). The hydrogen produced by the reaction permeates through the molecular sieve membrane (20) into the second cavity and flows out through the second discharge pipeline (23).

11. The system according to claim 10, wherein: The system further includes a purge gas supply mechanism. A purge gas pipeline (21) connected to the purge gas supply mechanism is provided on the housing. The purge gas provided by the purge gas supply mechanism enters the second cavity (24) through the purge gas pipeline (21) to purge the hydrogen entering the second cavity (24) to flow out through the second discharge pipeline (23). And / or, a blocking member is installed in the first cavity (16) near the feed pipeline (15) and the first discharge pipeline (22) to prevent the catalyst (18) from flowing out.

12. A method for directly preparing isoprene from isopentane, characterized in that, Using the system as claimed in any one of claims 9 to 11, including: 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 carry out a dehydrogenation reaction to generate isoprene and hydrogen; wherein, the generated hydrogen permeates through the molecular sieve membrane to be separated from the isoprene.

13. The method for preparing isoprene from isopentane in one step according to claim 12, characterized in that: The active components of the catalyst include one or more of Pt, Sn, Zn, Re, Co, Cu, Fe, Ga, Mn, Na, K, Mg, and the carrier of the catalyst includes one or more of alumina, magnesium aluminate spinel, MFI-type molecular sieve, Beta-type molecular sieve, silica; And / or, in the catalyst, the mass ratio of the active component to the carrier is 0.01 to 10%; And / or, in the method, the feed mass space velocity of isopentane is 1 to 100 h -1 ; And / or, the reaction temperature of the dehydrogenation reaction is 300 to 600 °C; And / or, the pressure difference between the two sides of the molecular sieve membrane of the molecular sieve membrane reactor is controlled to be 0.1 to 10 MPa.

14. The method for directly preparing isoprene from isopentane according to claim 13, characterized in that: In the catalyst, the mass ratio of the active component to the carrier is 0.1% to 2%; and / or, the feed mass space velocity of the isopentane is 1 to 10 h -1 ; the reaction temperature of the dehydrogenation reaction is 400 - 500 °C; and / or, the pressure difference across the molecular sieve membrane is 0.1 to 2 MPa.

15. The method for preparing isoprene from isopentane in one step according to claim 14, characterized in that: In the catalyst, the mass ratio of the active component to the carrier is 0.1% to 1%; and / or, the reaction temperature of the dehydrogenation reaction is 400 - 450 °C; and / or, the pressure difference between the two sides of the molecular sieve membrane is 0.1 to 0.2 MPa.

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