A CPOS-based mixed matrix membrane, its preparation method and application

Abstract

The present invention belongs to the technical field of membrane separation, and specifically relates to a CPOS-based mixed matrix membrane and its preparation method and application. In the present invention, polyethylene glycol is used as the polymer matrix, and crystalline porous organic salt is used as the filler. The crystalline porous organic salt is introduced into the polymer matrix to construct a CPOS-based mixed matrix membrane; the mass of the crystalline porous organic salt is 14% - 34% of the total mass of the CPOS-based mixed matrix membrane. For the CPOS-based mixed matrix membrane of the present invention, at a pressure of 1 bar, when the mass of the crystalline porous organic salt is 33.33% of the total mass of the CPOS-based mixed matrix membrane, the separation factor for 1,3-butadiene and n-butane can reach 4.21, and the separation factor for 1,3-butadiene and isobutene can reach 4.78, showing good separation performance.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane separation, and in particular relates to a CPOS-based mixed matrix membrane and a preparation method and application thereof. Background Art

[0002] 1,3-Butadiene is an important light olefin and a key raw material for the production of synthetic rubber, synthetic resin and other chemicals. In the petrochemical industry, 1,3-Butadiene is mainly derived from petroleum cracking and coexists with other C4 hydrocarbon compounds such as n-butane, n-butene, isobutane and isobutylene. Separating 1,3-Butadiene from the C4 mixture is of great significance for improving the quality and production efficiency of downstream products.

[0003] The difficulty in separating 1,3-butadiene lies in the similarity of physical and chemical properties between C4 hydrocarbon compounds, especially their similar boiling points and molecular polarity, which makes traditional distillation methods inefficient and energy-intensive. In addition, 1,3-butadiene is extremely active at high temperatures and is prone to polymerization, which requires special attention during the distillation process to avoid losses and ensure product purity. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a CPOS-based mixed matrix membrane and a preparation method and application thereof.

[0005] In the previous exploration of using mixed matrix membranes for C4 gas separation of 1,3-butadiene in the present invention, the physical and chemical properties and structures of crystalline porous organic salts were studied. Crystalline porous organic salts, with the full English name of Crystalline Porous Organic Salts and the English abbreviation of CPOSs, are a class of porous materials formed by the self-assembly of organic acids and organic bases through ionic bonds, having a fixed structure and permanent porosity. The first crystalline porous organic salt, abbreviated as CPOS-1, as a member of the CPOS family, exhibits a series of unique physical and chemical properties and potential applications. At the same time, the structural characteristics of CPOS-1 include frameworks composed of organic salts, which are usually formed by the close packing of ion clusters through ionic bonds. Due to the abundant sulfonic acid groups and amino groups in its internal pores, CPOS-1 shows a high selective adsorption ability for specific molecules. The kinetic diameter of 1,3-butadiene molecules is 0.431 nm, and 1,3-butadiene has a planar configuration structure, containing hydrogen atoms and delocalized π electron clouds, which enhance the electrostatic interaction ability between it and the sulfonic acid groups and amino groups in the CPOS-1 pores, thus enhancing the adsorption force between the two; the kinetic diameter of 1-butene molecules is 0.446 nm, and it only contains one double bond and has an asymmetric structure, resulting in a weaker interaction force with the functional groups in the CPOS-1 pores than that of 1,3-butadiene; the kinetic diameter of n-butane molecules is 0.469 nm, and it is a saturated alkane without double bonds and has a three-dimensional structure, which also leads to the interaction with the functional groups in the CPOS-1 pores being mainly weak van der Waals forces, lacking electron cloud overlap; the kinetic diameters of isobutene and isobutane molecules are 0.484 nm and 0.528 nm, and the relatively large molecular size hinders their diffusion, so the adsorption force is weak.

[0006] The present invention introduces CPOS-1 as a filler into the polyethylene glycol matrix to construct a CPOS-based mixed matrix membrane, and utilizes the electrostatic interaction between the sulfonic acid groups and amino groups in the CPOS-1 pores and the planar configuration structure containing hydrogen atoms and delocalized π electron clouds in 1,3-butadiene to improve the adsorption selectivity of the CPOS-based mixed matrix membrane for 1,3-butadiene, and further improve its separation efficiency for 1,3-butadiene; then utilizes the film-forming ability and flexibility of polyethylene glycol to enhance the film-forming property of the CPOS-based mixed matrix membrane, thereby enhancing the mechanical stability of the CPOS-based mixed matrix membrane.

[0007] The first object of the present invention is to provide a CPOS-based mixed matrix membrane; the present invention uses polyethylene glycol as the polymer matrix and CPOS-1 as the filler, and introduces CPOS-1 into the polyethylene glycol matrix to construct a CPOS-based mixed matrix membrane.

[0008] It should be noted that as a filler, the sulfonic acid groups and amino groups inside the pores of CPOS-1 are combined with the ether oxygen bonds of polyethylene glycol through hydrogen bonds or other non-covalent interactions. The sulfonic acid groups in CPOS-1 contain hydrogen atoms and can act as proton donors, that is, donors of hydrogen bonds; the oxygen atoms in the ether oxygen bonds of polyethylene glycol have strong electronegativity and can act as acceptors of hydrogen bonds; hydrogen bonds are formed between the hydrogen atoms of the sulfonic acid groups of CPOS-1 and the oxygen atoms in the ether oxygen bonds of polyethylene glycol. The amino groups in CPOS-1 can also act as donors of hydrogen bonds and form hydrogen bonds with the oxygen atoms in polyethylene glycol, enabling good interaction and compatibility between CPOS-1 and polyethylene glycol; preferably, the mass of the crystalline porous organic salt is 14% - 34% of the total mass of the CPOS-based mixed matrix membrane.

[0009] As a polymer matrix, the molecular weight of polyethylene glycol is one of the key factors affecting membrane formation. Polymers with higher molecular weights can provide better mechanical strength and a more compact pore structure, which helps to improve the separation performance and stability of the mixed matrix membrane. However, excessively high molecular weights may lead to increased processing difficulty of the membrane and reduced dispersibility and compatibility of the filler in the mixed matrix membrane. Preferably in the present invention, the molecular weight of the polymer matrix is 10,000.

[0010] The mass ratio of CPOS-1 to polyethylene glycol is one of the key factors affecting the formation of the CPOS-based mixed matrix membrane. An appropriate mass ratio can promote good interfacial bonding between the CPOS-1 filler and the polyethylene glycol matrix, which is crucial for the gas separation performance. Excessive CPOS-1 may lead to filler agglomeration, while too little CPOS-1 cannot fully exert the separation performance of the CPOS-based mixed matrix membrane. Therefore, by exploring the influence of the mass ratio of the two on the performance of the CPOS-based mixed matrix membrane, preferably, the mass ratio of CPOS-1 to polyethylene glycol is 1:2 - 6. The preferred mass ratio helps to ensure that the CPOS-1 filler is evenly dispersed in the polyethylene glycol matrix, while avoiding the aggregation of the CPOS-1 filler, reducing interfacial defects, and improving the overall separation efficiency and mechanical stability of the CPOS-based mixed matrix membrane.

[0011] The second object of the present invention is to provide a method for preparing the above-mentioned CPOS-based mixed matrix membrane, comprising the following steps:

[0012] Step 1: Dissolve CPOS-1 in a solvent so that CPOS-1 is evenly dispersed in the solvent as a filler to obtain a CPOS-1 solution.

[0013] Step 2: Dissolve polyethylene glycol in water so that polyethylene glycol is evenly dispersed in water as a matrix to obtain a polyethylene glycol solution.

[0014] Step 3: Mix the CPOS-1 solution and the polyethylene glycol solution to obtain a film-forming solution; then coat the film-forming solution onto a substrate so that the sulfonic acid groups and amino groups in the first crystalline porous organic salt solution combine with the ether oxygen bonds in the polyethylene glycol solution to form a dense layer, thereby obtaining a CPOS-based mixed matrix membrane.

[0015] It should be noted that, in order to uniformly disperse and fix the CPOS-1 filler in the polyethylene glycol matrix and enable better combination of the CPOS-1 filler and the polyethylene glycol matrix, in the present invention, CPOS-1 is dissolved in a solvent to form a CPOS-1 solution, and polyethylene glycol is dissolved in water to form a polyethylene glycol solution; then the CPOS-1 solution and the polyethylene glycol solution are mixed to obtain a film-forming solution; coating the film-forming solution onto a substrate is beneficial to improving the separation performance of the subsequently prepared CPOS-1 mixed matrix membrane. This is because directly mixing CPOS-1 and polyethylene glycol may result in uneven dispersion of the filler, thereby causing an interfacial incompatibility phenomenon at the interface between CPOS-1 and polyethylene glycol.

[0016] Preferably, the solvent is one of an aqueous solution of ammonia, an aqueous solution of sodium hydroxide, and an aqueous solution of hydrochloric acid; more preferably, the solvent is an aqueous solution of ammonia. Ammonia can break the ionic bonds of CPOS-1 and is easily volatilized and removed during the film-forming and drying processes. In order to better dissolve CPOS-1 in the solvent, in the present invention, CPOS-1 is completely dissolved in the solvent under ultrasonic action to obtain a CPOS-1 solution. Preferably, the ultrasonic time for preparing the CPOS-1 solution is 5 min to 10 min, and the ultrasonic temperature is room temperature.

[0017] The specific preparation process of CPOS-1 in the present invention is as follows: Dissolve strong acid tetrakis(4-sulfophenyl)methane in methanol to obtain a first mixed solution; dissolve strong base trans-1,4-cyclohexanediamine in methanol to obtain a second mixed solution; filter the first mixed solution and the second mixed solution respectively with a nylon filter head to obtain a first clarified solution and a second clarified solution; then slowly add the first clarified solution to the second clarified solution, and let it stand at room temperature for 12 h, and filter to obtain light yellow crystals of CPOS-1. Preferably, the molar ratio of the first mixed solution to the second mixed solution is 1:2.

[0018] It should also be noted that polyethylene glycol 10000 is a polymer with a medium molecular weight and has good solubility in water. The solubility of polyethylene glycol 10000 in water is greater than 50%, and as the temperature increases, its solubility will increase sharply. At 60 °C, all fractions of solid polyethylene glycol can be miscible with water in any proportion. In addition, water is easily volatilized and removed during the film-forming drying process. In the present invention, polyethylene glycol is dissolved in water. In order to better dissolve polyethylene glycol in water, the present invention accelerates dissolution by stirring and ultrasonic waves at room temperature. The stirring time is 30 min to 40 min, and the ultrasonic time is 30 min to 40 min.

[0019] Preferably, the total amount of the solvent and water: the dosage of CPOS-1 is 1 mL: 5 mg to 15 mg.

[0020] Preferably, the substrate is one of polyacrylonitrile, alumina sheet and polysulfone membrane. Polyacrylonitrile, also known as PAN, has a breathable pore structure with a pore size of about 20 nm, and has excellent mechanical properties, chemical stability and thermal stability. More preferably, the substrate of the present invention is PAN. In the present invention, by pretreating PAN, while removing the surface contaminants of PAN, a water barrier is formed by water infiltrating into the pores, thereby effectively preventing the casting solution from penetrating into the pores of the PAN substrate. The specific operation of the pretreatment of the present invention is to immerse the cut PAN substrate in deionized water, fix the wetted PAN on a glass plate during film formation, and gently wipe off the residual water droplets on the surface of the PAN substrate with a dust-free paper to ensure that the casting solution remains undiluted.

[0021] The number of cyclic spin-coating times affects the film thickness, film uniformity and mechanical strength of the film, and thus affects the separation efficiency and selectivity of the film. In the present invention, by increasing the number of cyclic spin-coating times, on the one hand, by increasing the film thickness to ensure that the prepared CPOS-based mixed matrix membrane can cover the substrate PAN, and then form a dense and continuous film; on the other hand, by improving the uniformity of the CPOS-based mixed matrix membrane, the film layer becomes more compact and flat. In addition, the mechanical strength of the film is enhanced by a multi-layer structure, and better support and stability are provided, thereby improving the separation efficiency and selectivity of the CPOS-based mixed matrix membrane.

[0022] For the CPOS-based mixed matrix membrane of the present invention, before spin-coating, ensure that the casting solution remains undiluted. The present invention adopts 10 cyclic spin-coatings. The specific cyclic process is: the process from adding the casting solution to completing spin-coating is regarded as one cycle, and the volume of the solution in each cycle is 2 mL. Preferably, during spin-coating, the rotation speed of the casting solution is 1500 rpm to 2000 rpm, and the duration of the spin-coating step is fixed at 30 s to 35 s. The spin-coated film is dried at 40 °C to 50 °C for 48 h and at 60 °C to 80 °C for 24 h to obtain the CPOS-based mixed matrix membrane.

[0023] The third object of the present invention is to provide the application of the above CPOS-based mixed matrix membrane in separating 1,3-butadiene from C4 gas.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In the present invention, a crystalline porous organic salt is introduced into the polymer matrix polyethylene glycol as a filler to construct a CPOS-based mixed matrix membrane. The sulfonic acid group in CPOS-1 contains hydrogen atoms and can act as a proton donor, that is, a donor of hydrogen bonds; the oxygen atom in the ether oxygen bond of polyethylene glycol has a strong electronegativity and can act as a hydrogen bond acceptor; a hydrogen bond is formed between the hydrogen atom of the sulfonic acid group of CPOS-1 and the oxygen atom in the ether oxygen bond of polyethylene glycol. At the same time, the amino group in CPOS-1 can also act as a hydrogen bond donor and form a hydrogen bond with the oxygen atom in polyethylene glycol; thus, CPOS-1 and polyethylene glycol have good interaction and compatibility, forming a CPOS-based mixed matrix membrane. Due to the abundant sulfonic acid groups and amino groups in the internal pores of CPOS-1, and 1,3-butadiene has a planar configuration structure, containing hydrogen atoms and delocalized π electron clouds; these characteristics enhance the electrostatic interaction ability between 1,3-butadiene and the sulfonic acid groups and amino groups in the pores of CPOS-1, thereby enhancing the adsorption force between the two, improving the adsorption selectivity of the CPOS-based mixed matrix membrane for 1,3-butadiene, and further improving the separation efficiency of the CPOS-based mixed matrix membrane for 1,3-butadiene.

[0026] The present invention selectively adsorbs 1,3-butadiene in C4 gas by using a CPOS-based mixed matrix membrane, thereby realizing the separation of 1,3-butadiene in C4 gas, avoiding the separation of C4 gas at high temperature in the prior art, resulting in the polymerization reaction of 1,3-butadiene at high temperature and low separation efficiency.

[0027] For the CPOS-based mixed matrix membrane of the present invention, at a pressure of 1 bar, when the mass of the crystalline porous organic salt is 33.33% of the total mass of the CPOS-based mixed matrix membrane, the separation factor for 1,3-butadiene and n-butane can reach 4.21, and the separation factor for 1,3-butadiene and isobutene can reach 4.78, showing good separation performance. Description of the Drawings

[0028] Figure 1 XRD pattern of CPOS-1 prepared in Comparative Example 1.

[0029] Figure 2 XRD patterns of CPOS-based mixed matrix membranes prepared in Examples 1 to 3 and CPOS-1 prepared in Comparative Example 1.

[0030] Figure 3 Scanning electron micrograph of the CPOS-based mixed matrix membrane prepared in Example 1; among them, (a) is the surface topography map, and (b) is the cross-sectional view.

[0031] Figure 4 Scanning electron micrograph of the CPOS-based mixed matrix membrane prepared in Example 2; among them, (a) is the surface topography map, and (b) is the cross-sectional view.

[0032] Figure 5 Scanning electron micrograph of the CPOS-based mixed matrix membrane prepared in Example 3; among them, (a) is the surface topography map, and (b) is the cross-sectional view.

[0033] Figure 6 Isothermal physical adsorption curve of the C4 gas adsorption performance of CPOS-1 prepared in Comparative Example 1 at 298K.

[0034] Figure 7 Ideal adsorbed solution theory diagram of C4 gas of CPOS-1 prepared in Comparative Example 1 at 298K; among them, (a) the C4 gas is 1,3-butadiene and n-butane, and (b) the C4 gas is 1,3-butadiene and isobutene. Detailed implementation manners

[0035] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0036] In the description of the present invention, unless otherwise specified, the reagents used are all commercially available, and the methods used are all conventional techniques in the art.

[0037] The following is further illustrated through specific examples.

[0038] Example 1

[0039] This example provides a CPOS-based mixed matrix membrane.

[0040] In this example, polyethylene glycol is used as the polymer matrix, and crystalline porous organic salt is used as the filler. The crystalline porous organic salt is introduced into the polymer matrix to construct a CPOS-based mixed matrix membrane; the mass of the crystalline porous organic salt is 14.29% of the total mass of the CPOS-based mixed matrix membrane.

[0041] The CPOS-based mixed matrix membrane of this example is prepared through the following steps:

[0042] Step 1. Preparation of CPOS-1 solution:

[0043] (1.1) Dissolve 42.8 mg of tetrakis(4-sulfophenyl)methane in 6.0 mL of methanol to obtain a first mixed solution; dissolve 11.4 mg of trans-1,4-cyclohexanediamine in 6.0 mL of methanol to obtain a second mixed solution; filter the first mixed solution and the second mixed solution respectively with a nylon filter head to obtain a first clear solution and a second clear solution; then, slowly add the first clear solution to the second clear solution, let it stand at room temperature for 12 h, and filter to obtain light yellow crystals of CPOS-1.

[0044] (1.2) Add 10 mg of CPOS-1 to 40 μL of ammonia water and 1 mL of distilled water, and ultrasonicate for 5 min at 25 °C to obtain a CPOS-1 solution.

[0045] Step 2. Preparation of polyethylene glycol solution:

[0046] Add 60 mg of polyethylene glycol with a molecular weight of 10,000 to 0.96 mL of distilled water, stir at room temperature for 30 min, and ultrasonicate for 30 min at 25 °C to obtain a polyethylene glycol solution.

[0047] Step 3. Preparation of CPOS-based mixed matrix membrane:

[0048] (3.1) Mix the CPOS-1 solution and the polyethylene glycol solution, stir at room temperature for 10 min, and ultrasonicate for 5 min to obtain a membrane-forming solution.

[0049] (3.2) Immerse the PAN substrate in distilled water, fix the wetted PAN substrate on a glass plate, gently wipe off the residual water droplets on the surface of the PAN substrate with a dust-free paper, fix the glass plate with the PAN substrate on the pressing plate of a spin coater, dropwise spin-coat the membrane-forming solution onto the PAN substrate at a rotation speed of 1500 rpm, and fix the duration of the spin-coating step at 30 s. Spin-coat 10 times in a cycle, and the volume of the membrane-forming solution for each cycle is 2 mL. Dry the spin-coated membrane at 40 °C for 48 h and at 60 °C for 24 h to obtain a CPOS-based mixed matrix membrane.

[0050] Example 2

[0051] This example provides a CPOS-based mixed matrix membrane.

[0052] In this example, polyethylene glycol is used as the polymer matrix, and crystalline porous organic salt is used as the filler. The crystalline porous organic salt is introduced into the polymer matrix to construct a CPOS-based mixed matrix membrane; the mass of the crystalline porous organic salt is 25.00% of the total mass of the CPOS-based mixed matrix membrane.

[0053] The CPOS-based mixed matrix membrane of this example is prepared through the following steps:

[0054] Step 1: Prepare the CPOS-1 solution:

[0055] (1.1) Dissolve 42.8 mg of tetrakis(4-sulfophenyl)methane in 6.0 mL of methanol to obtain a first mixed solution; dissolve 11.4 mg of trans-1,4-cyclohexanediamine in 6.0 mL of methanol to obtain a second mixed solution; filter the first mixed solution and the second mixed solution respectively with a nylon filter head to obtain a first clear solution and a second clear solution; subsequently, slowly add the first clear solution to the second clear solution, let it stand at room temperature for 12 h, and filter to obtain light yellow crystals of CPOS-1.

[0056] (1.2) Add 20 mg of CPOS-1 to 80 μL of ammonia water and 0.96 mL of distilled water, and ultrasonicate for 5 min at 25 °C to obtain the CPOS-1 solution.

[0057] Step 2: Prepare the polyethylene glycol solution:

[0058] Add 60 mg of polyethylene glycol with a molecular weight of 10,000 to 0.96 mL of distilled water, stir at room temperature for 30 min, and ultrasonicate for 30 min at 25 °C to obtain the polyethylene glycol solution.

[0059] Step 3: Prepare the CPOS-based mixed matrix membrane:

[0060] (3.1) Mix the CPOS-1 solution and the polyethylene glycol solution, stir at room temperature for 10 min, and ultrasonicate for 5 min to obtain the film-forming solution.

[0061] (3.2) Immerse the PAN substrate in distilled water, fix the wetted PAN substrate on a glass plate, gently wipe off the residual water droplets on the surface of the PAN substrate with a dust-free paper, fix the glass plate with the PAN substrate on the pressing plate of a spin coater, dropwise spin coat the film-forming solution onto the PAN substrate at a rotation speed of 1500 rpm, and fix the duration of the spin coating step at 30 s. Spin coat 10 times in a cycle, and the volume of the film-forming solution for each cycle is 2 mL. Dry the spin-coated film at 40 °C for 48 h and at 60 °C for 24 h to obtain the CPOS-based mixed matrix membrane.

[0062] The difference between this example and Example 1 is:

[0063] In this example, the mass of CPOS-1 is 25.00% of the total mass of the CPOS-based mixed matrix membrane.

[0064] Example 3

[0065] This example provides a CPOS-based mixed matrix membrane.

[0066] In this embodiment, polyethylene glycol is used as the polymer matrix, and crystalline porous organic salt is used as the filler. The crystalline porous organic salt is introduced into the polymer matrix to construct a CPOS-based mixed matrix membrane; the mass of the crystalline porous organic salt is 33.33% of the total mass of the CPOS-based mixed matrix membrane.

[0067] The CPOS-based mixed matrix membrane of this embodiment is prepared by the following steps:

[0068] Step 1: Prepare the CPOS-1 solution:

[0069] (1.1) Dissolve 42.8 mg of tetrakis(4-sulfophenyl)methane in 6.0 mL of methanol to obtain a first mixed solution; dissolve 11.4 mg of trans-1,4-cyclohexanediamine in 6.0 mL of methanol to obtain a second mixed solution; filter the first mixed solution and the second mixed solution through a nylon filter head to obtain a first clear solution and a second clear solution; then, slowly add the first clear solution to the second clear solution, let it stand at room temperature for 12 h, and filter to obtain light yellow crystals of CPOS-1.

[0070] (1.2) Add 30 mg of CPOS-1 to 120 μL of ammonia water and 0.92 mL of distilled water, and ultrasonicate for 5 min at 25 °C to obtain a CPOS-1 solution.

[0071] Step 2: Prepare the polyethylene glycol solution:

[0072] Add 60 mg of polyethylene glycol with a molecular weight of 10,000 to 0.96 mL of distilled water, stir at room temperature for 30 min, and ultrasonicate for 30 min at 25 °C to obtain a polyethylene glycol solution.

[0073] Step 3: Prepare the CPOS-based mixed matrix membrane:

[0074] (3.1) Mix the CPOS-1 solution and the polyethylene glycol solution, stir at room temperature for 10 min, and ultrasonicate for 5 min to obtain a film-forming solution.

[0075] (3.2) Immerse the PAN substrate in distilled water, fix the wetted PAN substrate on a glass plate, gently wipe off the remaining water droplets on the surface of the PAN substrate with a lint-free paper, fix the glass plate of the PAN substrate on the pressing plate of a spin coater, dropwise spin coat the film-forming solution onto the PAN substrate at a rotation speed of 1500 rpm, and fix the duration of the spin coating step at 30 s. Spin coat 10 times in a cycle, and the volume of the film-forming solution for each cycle is 2 mL. Dry the spin-coated film at 40 °C for 48 h and at 60 °C for 24 h to obtain a CPOS-based mixed matrix membrane.

[0076] The difference between this embodiment and Embodiment 1 is:

[0077] In this example, the mass of CPOS-1 is 33.33% of the total mass of the CPOS-based mixed matrix membrane.

[0078] Comparative Example 1

[0079] This comparative example provides a preparation method of CPOS-1.

[0080] Dissolve 42.8 mg of tetrakis(4-sulfophenyl)methane in 6.0 mL of methanol to obtain a first mixed solution; dissolve 11.4 mg of trans-1,4-cyclohexanediamine in 6.0 mL of methanol to obtain a second mixed solution; filter the first mixed solution and the second mixed solution respectively with a nylon filter head to obtain a first clear solution and a second clear solution; then, slowly add the first clear solution to the second clear solution, let it stand at room temperature for 12 h, and filter to obtain light yellow crystals of CPOS-1.

[0081] In Examples 1 to 3 of the present invention, mixed matrix membranes for C4 gas separation of 1,3-butadiene were all prepared. Taking Examples 1 to 3 and Comparative Example 1 as examples for research, the specific research methods and results are as follows:

[0082] I. Structural Characterization

[0083] From Figure 1 it can be seen that CPOS-1 has good crystallinity.

[0084] From Figure 2 it can be seen that there are characteristic peaks of CPOS-1 in the mixed matrix membrane, and CPOS-1 still maintains its crystallinity, indicating that the dissolution-regeneration strategy is feasible, and with the increase of the filler content, the peak intensity of CPOS-1 in the mixed matrix membrane gradually increases.

[0085] II. Surface Morphology Characterization

[0086] Perform SEM tests on the CPOS-based mixed matrix membranes prepared in Examples 1 to 3, and the results are as Figures 3 to 5 shown.

[0087] From Figures 3 to 5 in (a), it can be seen that the surfaces of the CPOS-based mixed matrix membranes prepared in Examples 1 to 3 are flat, without obvious filler aggregation phenomenon, and the interfacial compatibility is good; from Figures 3 to 5 in (b), it can be seen that the cross-sectional thickness of the CPOS-based mixed matrix membranes prepared in Examples 1 to 3 is 200 nm. This shows that the present invention can realize the preparation of ultra-thin mixed matrix membranes.

[0088] III. Adsorption Test

[0089] The CPOS-1 prepared in Comparative Example 1 was activated at 150 °C for 8 hours under a nitrogen atmosphere for adsorption testing, and all the tests were completed under standard atmospheric pressure. The results are shown in Table 1 and Figure 6 as follows.

[0090] Table 1 Adsorption performance data of CPOS-1 prepared in Comparative Example 1 for C4 gases at 298K

[0091]

[0092] It can be seen from Figure 6 that as the pressure increases, the adsorption amounts of CPOS-1 for 1,3-butadiene, n-butane, and isobutene gradually increase. At the same time, Table 1 shows the adsorption performance data of CPOS-1 prepared in Comparative Example 1 for C4 gases at 298K. It can be seen from Table 1 that at 298K, the adsorption amount of CPOS-1 for 1,3-butadiene is the largest.

[0093] It can be seen from Figure 7 part (a) of Figure 7 that for an equimolar gas mixture of 1,3-butadiene and n-butane, the ideal selectivity of 1,3-butadiene for n-butane is 7.07; it can be seen from

[0094] part (b) of

[0095] that for an equimolar gas mixture of 1,3-butadiene and isobutene, the ideal selectivity of 1,3-butadiene for isobutene is 43.74. This indicates that the CPOS-1 prepared in the present invention has an obvious affinity for 1,3-butadiene and determines its potential in the application of separating C4 gases.

[0096] IV. Gas separation test

[0095] The gas separation device was partially self-made in the laboratory and connected to a gas chromatograph. The gas chromatograph was mainly used to measure the concentration and content of each component in the mixed gas, and the carrier gas used was high-purity Ar with a purity of 99.999%.

[0096] Testing the blank sample to fit the standard curve: The peak areas corresponding to 1,3-butadiene, n-butane, and isobutene gases in the gas chromatograph after mixing with the carrier gas were measured respectively when the concentrations of the three gases were 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, and 0.05 as the feed gas. Each concentration corresponded to a peak area. And keeping all the test conditions unchanged, 7 groups of data corresponding to the concentration of 1,3-butadiene, 7 groups of data corresponding to the concentration of n-butane, and 7 groups of data corresponding to the concentration of isobutene were obtained respectively, and the corresponding relationship between the concentration and the peak area was linearly fitted respectively, that is, the standard curves of 1,3-butadiene, n-butane, and isobutene gases. Among them, the test conditions were: Ar was used as the purge gas and the carrier gas, high-purity 1,3-butadiene, n-butane, and isobutene were used as the feed gases, and the pressure at both ends of the membrane was kept at 1 bar and the temperature was at room temperature.

[0097] The standard curve of the gas is the standard for calculating the gas concentration and content through the peak area in the gas separation test, and its accuracy directly affects the calculation of the gas permeation flux and separation coefficient. Therefore, it is required that the R 2 value is above 0.9999. Among them, the R 2 value, also known as the coefficient of determination, is a statistical index in regression analysis, which is used to measure the fitting degree of the model to the data. The value range of the R 2 value is between 0 and 1. An R 2 value of 1 means that the model perfectly fits the data and all data points fall on the regression line; 2 A value of 0 indicates that the model has no ability to explain the data. The closer the R 2 value is to 1, the higher the fitting degree of the model.

[0098] Gas separation test: When conducting the separation experiment of binary gases, high-purity Ar is used as the purge gas and carrier gas, and high-purity 1,3-butadiene, n-butane and isobutene are used as the feed gases. The CPOS-based mixed matrix membranes prepared in Example 1, Example 2 and Example 3 are respectively immobilized on the membrane module, and the gas flow is adjusted by a soap bubble flowmeter. The Ar flow rate as the purge gas is adjusted to 7.5 mL·min -1 , and the inlet end is a mixed gas of two feed gases with a volume ratio of 1:1, and the flow rate of each feed gas is 10 mL·min -1 . Before the separation experiment, the purge gas and each gas of the feed gas need to be subjected to gas distribution treatment and stabilized for at least 3 h. The mixed gas enters from the inlet end (the front side of the membrane) of the mold, and the gas permeating through the membrane is blown into the gas chromatograph by the purge gas at the permeation end of the membrane. By analyzing the gas composition permeating through the membrane, the peak areas of the two gases are obtained, and the concentration of each gas in the purge gas is obtained by using the standard curve, and then converted into the gas permeation flux. p represents the permeation flux, and the unit is mol·m -2 s -1 pa -1 . The results are shown in Tables 2 to 3.

[0099] Table 2 shows the separation test results of the CPOS-based mixed matrix membranes prepared in Example 1 to Example 3 of the present invention for the mixed gas of n-butane and 1,3-butadiene. It should be noted that the pure polymer membrane is airtight. As can be seen from Table 2, at a pressure of 1 bar, for the separation of 1,3-butadiene and n-butane, when the filler content is 14.29%, the permeation amount of 1,3-butadiene is 3.63E -08 , and the permeation amount of n-butane is 1.36E -08, the selectivity of 1,3-butadiene and n-butane is 2.67; when the filler content is 25.00%, the permeation rate of 1,3-butadiene is 4.60E -08 , the permeation rate of n-butane is 1.42E -08 , the selectivity of 1,3-butadiene and n-butane is 3.24; when the filler content is 33.33%, the permeation rate of 1,3-butadiene is 6.36E -08 , the permeation rate of n-butane is 1.51E -08 , the selectivity of 1,3-butadiene and n-butane is 4.21. As the filler content in the mixed matrix membrane increases, CPOS-1 plays a significant separation role, the permeation rate of 1,3-butadiene increases, the selectivity of the mixed gas increases, and the mixed matrix membrane has a separation effect.

[0100] Table 2 Separation test results of the CPOS-based mixed matrix membranes prepared in Examples 1 to 3 for the mixed gas of n-butane and 1,3-butadiene

[0101]

[0102] Table 3 shows the separation test results of the CPOS-based mixed matrix membranes prepared in Examples 1 to 3 of the present invention for the mixed gas of isobutene and 1,3-butadiene. It should be noted that the pure polymer membrane is airtight. As can be seen from Table 3, at a pressure of 1 bar, for the separation of 1,3-butadiene and isobutene, when the filler content is 14.29%, the permeation rate of 1,3-butadiene is 3.48E -08 , the permeation rate of isobutene is 1.27E -08 , the selectivity of 1,3-butadiene and isobutene is 2.74; when the filler content is 25.00%, the permeation rate of 1,3-butadiene is 4.32E -08 , the permeation rate of isobutene is 1.23E -08 , the selectivity of 1,3-butadiene and isobutene is 3.51; when the filler content is 33.33%, the permeation rate of 1,3-butadiene is 5.78E -08 , the permeation rate of isobutene is 1.21E -08 , the selectivity of 1,3-butadiene and isobutene is 4.78. As the filler content in the mixed matrix membrane increases, CPOS-1 plays a significant separation role, the permeation rate of 1,3-butadiene increases, the selectivity of the mixed gas increases, and the mixed matrix membrane has a separation effect. And because the molecular kinetic diameter of isobutene is larger than that of n-butane, for the mixed matrix membranes with the same filler content, when the diffusion effect dominates, isobutene is more hindered by diffusion, so the separation selectivity of 1,3-butadiene and isobutene is higher.

[0103] Table 3 Separation test results of the CPOS-based mixed matrix membranes prepared in Examples 1 to 3 for the mixed gas of isobutene and 1,3-butadiene

[0104]

[0105] Selectivity is one of the key performance indicators of gas membrane separation technology. An ideal gas separation membrane should have good separation performance, excellent thermal and chemical stability, and high mechanical strength at the same time. High selectivity means that the membrane can separate the target gas more effectively, thus improving the separation efficiency and product purity.

[0106] In the field of gas separation, the Knudsen coefficient is used to describe the flow mode of gas molecules passing through a porous membrane. When the Knudsen coefficient is large, gas molecules mainly diffuse through the membrane pores by Knudsen diffusion. In this case, the separation process is related to the size and shape of the molecules. The Knudsen diffusion coefficient is inversely proportional to the square root of the molecular mass, which means that gas molecules with smaller molecular mass are more likely to pass through the porous membrane.

[0107] It should be noted that when the present invention involves a numerical range, it should be understood that any value between the two endpoints of each numerical range and the two endpoints can be selected. Since the steps and methods adopted are the same as those in the examples, in order to prevent repetition, the present invention describes the preferred embodiments. Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept, and these changes and modifications all fall within the scope of the present invention.

[0108] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. If these modifications and variations of the present invention fall within the scope of the equivalent technology of the present invention, the present invention also intends to include these changes and modifications.

Claims

1. A CPOS-based mixed matrix membrane, characterized in that: Using polyethylene glycol as a polymer matrix and a first crystalline porous organic salt as a filler, introducing the first crystalline porous organic salt into the polymer matrix to construct a CPOS-based mixed matrix membrane; The mass of the first crystalline porous organic salt is 14% to 34% of the total mass of the CPOS-based mixed matrix membrane.

2. A method for preparing a CPOS-based mixed matrix membrane according to claim 1, characterized in that: The following steps are involved: dissolving the first crystalline porous organic salt in a solvent so that the first crystalline porous organic salt is uniformly dispersed in the solvent as a filler to obtain a first crystalline porous organic salt solution; Dissolving polyethylene glycol in water so that the polyethylene glycol as a matrix is ​​evenly dispersed in the water to obtain a polyethylene glycol solution; mixing the first crystalline porous organic salt solution and the polyethylene glycol solution to obtain a membrane-forming solution; The membrane-making solution is then coated on the substrate so that the sulfonic acid groups and amino groups in the first crystalline porous organic salt solution are combined with the ether oxygen bonds in the polyethylene glycol solution to form a dense layer, thereby obtaining a CPOS-based mixed matrix membrane.

3. The method for preparing a CPOS-based mixed matrix membrane according to claim 2, characterized in that: The mass ratio of the first crystalline porous organic salt to polyethylene glycol is 1:2-6.

4. The method for preparing a CPOS-based mixed matrix membrane according to claim 2, characterized in that: The solvent is one of an aqueous solution of ammonia water, an aqueous solution of sodium hydroxide and an aqueous solution of hydrochloric acid.

5. The method for preparing a CPOS-based mixed matrix membrane according to claim 2, characterized in that: The total amount of the solvent and water: the amount of CPOS-1 used is 1 mL: 5 mg to 15 mg.

6. An application of the CPOS-based mixed matrix membrane according to claim 1, characterized in that: The CPOS-based mixed matrix membrane is used for separation of 1,3-butadiene from C4 gas.

7. The use of the CPOS-based mixed matrix membrane according to claim 6, characterized in that: The CPOS-based mixed matrix membrane separates 1,3-butadiene from C4 gas by the following steps: The C4 gas is infiltrated from the CPOS-based mixed matrix membrane, and the CPOS-based mixed matrix membrane adsorbs 1,3-butadiene in the C4 gas, thereby achieving separation of 1,3-butadiene in the C4 gas.

8. The use of the CPOS-based mixed matrix membrane according to claim 7, characterized in that: The C4 gas is a mixed gas of normal butane, normal butene, isobutane, isobutene and 1,3-butadiene.

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