A post-synthesis treatment method for a tubular polycrystalline membrane, the obtained membrane and its application

Abstract

The present invention relates to a method for treating a tubular polycrystalline membrane, the obtained membrane and its application. The tubular polycrystalline membrane is supported by a carrier. The treatment method includes the step of coating a solution on the inner surface of the tubular polycrystalline membrane by a perfusion method. The solution includes a prepolymer and a crosslinking agent, and the step of performing roll coating on the coated tubular polycrystalline membrane. In the roll coating, an in-situ crosslinking reaction occurs between the prepolymer and the crosslinking agent, and the in-situ crosslinking temperature is 25 to 60 °C. This treatment method can obtain a polymer coating with uniform coverage on the surface of the tubular polycrystalline membrane, thereby achieving the purpose of significantly repairing the defects of the tubular polycrystalline membrane and improving its gas separation selectivity.

Description

Technical Field

[0001] The present invention specifically relates to a post-treatment method for synthesizing a tubular polycrystalline membrane, the obtained membrane and its applications. Background Art

[0002] Membrane separation technology has the characteristics of small carbon footprint, environmental friendliness and low investment cost, and is expected to replace / couple with cryogenic distillation technology to achieve efficient separation of low-carbon hydrocarbons in the petrochemical industry. At present, a variety of crystal membranes have been reported to be able to effectively carry out the separation process of mixed gases. For example, metal-organic frameworks (MOFs) have a finely designed and functionalized pore structure, high porosity and surface area; zeolite molecular sieves have uniform pore sizes and good chemical and thermal stability, providing solutions for the separation of many challenging gases (hydrocarbons with the same carbon number, hydrocarbon isomers, etc.).

[0003] From the perspective of industrial applications, while ensuring high separation performance, the separation membrane should meet the requirements of high preparation repeatability, high stability, durability and anti-pollution ability. Carrier-supported polycrystalline membranes, such as ceramic-supported polycrystalline membranes, have the characteristics of high packing density and mechanical strength, and can meet the harsh conditions of industrial applications. However, due to the brittleness, symbiosis and preparation repeatability of polycrystalline membranes, non-selective defects of the membrane will inevitably occur. Especially when the inner surface curvature of the carrier increases, especially for tubular carriers, it will exacerbate the further formation of non-selective defects on the membrane surface.

[0004] Therefore, developing new technologies for defect repair of polycrystalline membranes supported by tubular carriers is crucial for promoting the industrial application of membrane separation in the petrochemical industry. Existing technologies usually focus on coating modification on flat-supported polycrystalline membranes to repair the defects of polycrystalline membranes. For example, Chinese Patent CN108939958A discloses coating a polymer solution on a flat-supported MOF membrane for modification and defect repair, where the polymer is silicone rubber, polyether-polyamide copolymer, PTMSP, polyimide or PIM polymer. The above polymers are fully cross-linked polymers, and directly coating them is likely to cause bubbling and peeling of the polymer coating, resulting in a decrease in the separation selectivity of the composite membrane. In addition, the polymer solution has a certain viscosity, and it is usually difficult to form a continuous coating with a uniform thickness on the inner surface of the tubular membrane with limited space, making it difficult to effectively repair the defects of the tubular polycrystalline membrane. Summary of the Invention

[0005] The object of the present invention is to provide a treatment method for a tubular polycrystalline membrane, which can obtain a uniformly covered polymer coating on the surface of the tubular polycrystalline membrane, so as to significantly repair the defects of the tubular polycrystalline membrane and improve its gas separation selectivity.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for treating a tubular polycrystalline membrane, the tubular polycrystalline membrane being supported by a carrier, the treatment method comprising the step of coating a solution on the inner surface of the tubular polycrystalline membrane by perfusion, the solution comprising a prepolymer and a crosslinking agent, and the step of performing roll coating on the tubular polycrystalline membrane after perfusion coating is completed. In the roll coating, an in-situ crosslinking reaction occurs between the prepolymer and the crosslinking agent, and the temperature of the roll coating is 25 to 60 °C.

[0008] In the present invention, the perfusion method refers to perfusion of a prepolymer solution inside a tubular polycrystalline membrane supported by a carrier, allowing the prepolymer solution to spontaneously infiltrate and gradually penetrate the inner surface of the tubular polycrystalline membrane. After coating is completed, the excess solution in the tubular polycrystalline membrane is discarded.

[0009] Although the prior art discloses coating a polymer coating on a polycrystalline membrane supported by a flat plate to repair polycrystalline membrane defects, ordinary coating methods are difficult to coat a uniform polymer film layer on the inner surface of a tubular polycrystalline membrane, easily resulting in uneven thickness of the polymer film layer in different regions of the upper and lower parts of the tubular polycrystalline membrane. Moreover, in the prior art, a crosslinked polymer is directly coated on the surface of the polycrystalline membrane, and coating bubbling and peeling are likely to occur during the membrane testing process, making it difficult to effectively repair polycrystalline membrane defects, and the separation selectivity of the composite membrane is greatly reduced under high-pressure conditions.

[0010] In the present invention, a solution comprising a prepolymer and a crosslinking agent is first pre-coated on the surface of a tubular polycrystalline membrane by perfusion, and then roll coating is performed on it. During the roll coating process, the prepolymer and the crosslinking agent are in-situ crosslinked and cured on the inner surface of the tubular polycrystalline membrane, generating a polymer film layer with a crosslinked network structure on the inner surface of the tubular polycrystalline membrane, thereby obtaining a uniform and continuous polymer coating on the inner surface of the tubular polycrystalline membrane. At the same time, by controlling the temperature of the roll coating, on the one hand, at this temperature, the prepolymer and the crosslinking agent can undergo sufficient crosslinking reactions during the roll coating process. On the other hand, controlling this temperature enables partial solvents in the coating solution to slowly volatilize at this relatively low temperature (relative to the boiling point of the solvent), avoiding the rapid volatilization of solvents in the coating during the subsequent drying process, which may lead to pore-like defects in the polycrystalline membrane coating and is not conducive to improving the selectivity when the membrane is used for gas separation. Using the treatment method of the present invention can effectively repair defects of a large-area tubular polycrystalline membrane and improve its durability, anti-pollution property and separation stability under high pressure in practical applications.

[0011] In some embodiments, the prepolymer is selected from one or both of divinyl-terminated polydimethylsiloxane and divinyl-terminated polydimethylsiloxane with a C1-C6 fluoroalkyl group in the side chain, and the crosslinking agent is a siloxane compound containing two or more silicon-hydrogen bonds. The two vinyl end groups on the above prepolymer react with two or more silicon-hydrogen bonds on the crosslinking agent to form a crosslinked polymer network structure.

[0012] In some embodiments, the C1-C6 fluoroalkyl group is selected from fluoropropyl.

[0013] In some embodiments, the prepolymer is selected from one or both of dihydroxy-terminated polydimethylsiloxane and dihydroxy-terminated polydimethylsiloxane having a C1-C6 fluoroalkyl group in the side chain, and the crosslinking agent is selected from a combination of one or more of tetraethyl orthosilicate, tetramethyl orthosilicate, and tetrapropyl orthosilicate. The two hydroxyl end groups on the prepolymer undergo a condensation reaction with the silicate groups on the crosslinking agent, thereby forming a crosslinked polymer network structure.

[0014] In some embodiments, the C1-C6 fluoroalkyl group is selected from fluoropropyl.

[0015] In some embodiments, the solution further includes a catalyst for catalyzing the crosslinking reaction between the prepolymer and the crosslinking agent. Under the action of the catalyst, the prepolymer and the crosslinking agent are more likely to undergo a crosslinking reaction, and the crosslinking and curing rate is faster.

[0016] In some embodiments, the catalyst is selected from a platinum catalyst or an organotin catalyst. The platinum catalyst is used to catalyze the addition reaction between vinyl and silicon-hydrogen bonds, and the organotin catalyst is used to catalyze the condensation reaction between hydroxyl groups and silicate groups. When the prepolymer is selected from one or both of divinyl-terminated polydimethylsiloxane and divinyl-terminated polydimethylsiloxane having a C1-C6 fluoroalkyl group in the side chain, and the crosslinking agent is a siloxane compound containing two or more silicon-hydrogen bonds, the catalyst is a platinum catalyst. When the prepolymer is selected from one or both of dihydroxy-terminated polydimethylsiloxane and dihydroxy-terminated polydimethylsiloxane having a C1-C6 fluoroalkyl group in the side chain, and the crosslinking agent is selected from a combination of one or more of tetraethyl orthosilicate, tetramethyl orthosilicate, and tetrapropyl orthosilicate, the catalyst is an organotin catalyst, for example, it can be dibutyltin dilaurate.

[0017] In some embodiments, the roll coating is carried out at a rotation speed of 30-180 r / min.

[0018] In some embodiments, the time of roll coating is 1-9 h.

[0019] In some embodiments, the time of perfusion coating is 5-20 min.

[0020] In some embodiments, the mass concentration of the solution is 5%-30%.

[0021] In some embodiments, the mass ratio of the prepolymer to the crosslinking agent is 5-20:1.

[0022] In some embodiments, the tubular polycrystalline film is selected from one or both of a MOF film and a zeolite film.

[0023] The tubular polycrystalline film in the present invention can be prepared by a secondary growth method or an in-situ synthesis method. Among them, the secondary growth method refers to a process of pre-introducing a layer of nanocrystalline seeds on the surface of a carrier by chemical methods such as impregnation, spraying, or in-situ crystallization, and then immersing the carrier in a reaction solution to obtain a dense polycrystalline film by secondary growth. The in-situ synthesis method refers to a method of immersing the carrier vertically or horizontally in a reaction solution, and allowing polycrystalline materials to nucleate, crystallize, and finally grow together on the surface of the carrier to form a dense film at a certain temperature.

[0024] In some embodiments, the carrier is selected from one or a combination of more of a porous alumina ceramic tube, a hollow fiber alumina ceramic tube, and a porous stainless steel sintered tube.

[0025] In some embodiments, the carrier is selected from one or a combination of more of a single-channel tube, a 4-channel tube, a 7-channel tube, a 19-channel tube, and a 61-channel tube.

[0026] In some embodiments, the roll coating is carried out on a temperature-controlled roll coater.

[0027] In some embodiments, the temperature-controlled roll coater includes a main body with a chamber inside, a plurality of rollers located inside the main body, a motor, a temperature controller, and a conveyor belt located inside the main body. The rollers are used to drive the tubular polycrystalline film to roll, the motor drives the rollers to rotate through the conveyor belt, and the temperature controller is used to control the temperature inside the main body.

[0028] In some embodiments, the motor is located outside the main body.

[0029] In some embodiments, the tubular polycrystalline film is placed between two of the rollers.

[0030] In some embodiments, the number of the rollers is 4 - 8.

[0031] In some embodiments, the temperature controller is located on the outer wall of the main body.

[0032] In some embodiments, the treatment method further includes a step of drying after roll coating.

[0033] In some embodiments, the drying temperature is 60 - 100 °C.

[0034] In some embodiments, the drying time is 6 - 24 h.

[0035] The present invention also provides a tubular polycrystalline membrane obtained by the treatment method of the above tubular polycrystalline membrane. After the above treatment, the defects of the tubular polycrystalline membrane are significantly repaired, the polymer coating on its inner surface is uniform, and the gas separation selectivity of the tubular polycrystalline membrane is significantly improved.

[0036] The present invention also provides the use of the above tubular polycrystalline membrane for gas separation, and the gas is selected from one or a combination of more than one of hydrogen, nitrogen, carbon dioxide, methane, ethane, ethylene, propane, and propylene.

[0037] Due to the application of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0038] (1) The inner tube space of the tubular polycrystalline membrane is limited, and the polymer solution usually has a certain viscosity. It is difficult to obtain a uniform polymer coating on the inner surface of the tubular polycrystalline membrane by traditional dip coating, spin coating and other methods; in the present invention, a solution including a prepolymer and a crosslinking agent is pre-coated on the surface of the carrier-supported tubular polycrystalline membrane in a perfusion coating manner, and then roll coating is carried out on it. During the roll coating process, the prepolymer and the crosslinking agent are in-situ crosslinked and cured on the inner surface of the tubular polycrystalline membrane, and a polymer film layer with a crosslinked network structure is generated on the inner surface of the tubular polycrystalline membrane, so as to obtain a uniform and continuous polymer coating on the inner surface of the tubular polycrystalline membrane, avoiding the uneven thickness distribution caused by the self-gravity of the polymer solution, thereby achieving the purpose of effectively repairing the defects of the polycrystalline membrane.

[0039] (2) The present invention uses a prepolymer and a crosslinking agent for in-situ curing crosslinking, combined with a roll coating process, which can uniformly cover the inner surface of the tubular polycrystalline membrane with limited space with the polymer and in-situ crosslink and cure on the surface of the polycrystalline membrane, so that the low-molecular-weight prepolymer penetrates into the intercrystalline defects, and then effectively repairs the intercrystalline defects through in-situ crosslinking, and strengthens the interfacial bonding force between the coating and the membrane layer. At the same time, it avoids the phenomenon that the coating formed due to the increase in viscosity after the polymer is completely crosslinked is too thick, and the bonding force with the crystal membrane is weak, resulting in bubbling and peeling of the polymer coating.

[0040] (3) By controlling the temperature of the roll coating, on the one hand, at this temperature, the prepolymer and the crosslinking agent can undergo sufficient crosslinking reactions during the roll coating process. On the other hand, controlling this temperature enables some solvents in the coating solution to slowly volatilize at this relatively low temperature (relative to the boiling point of the solvent), avoiding that during the subsequent drying process, too fast volatilization of the solvent in the coating due to the high drying temperature will lead to the appearance of pore-like defects in the polycrystalline membrane coating, which is not conducive to the improvement of the selectivity of the composite membrane for gas separation. Using the treatment method of the present invention, the defects of the large-area tubular polycrystalline membrane can be effectively repaired, and its durability, anti-pollution property and separation stability under high pressure in practical applications can be improved.

[0041] (4) For low-selectivity tubular polycrystalline membranes where defect problems are the dominant factor, the treatment method of the present invention can effectively fill the non-selective defects generated during the preparation of tubular polycrystalline membranes, thereby improving their gas separation performance under normal pressure; for some tubular polycrystalline membranes where flexible framework problems are the dominant factor, this method can further restrict their flexible framework structure on the basis of defect repair, thereby improving their gas separation performance under high-pressure environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 : Schematic structural diagram of the temperature-controlled rolling coating instrument for implementing the rolling coating process of the present invention, where: 1 - roller, 2 - motor, 3 - conveyor belt, 4 - temperature controller, 5 - main body.

[0043] Figure 2 : Cross-sectional electron micrograph of the tubular polycrystalline membrane after being treated in Example 1.

[0044] Figure 3 : Cross-sectional electron micrograph of the tubular polycrystalline membrane after being treated in Comparative Example 1.

[0045] Figure 4 : Graph showing the change relationship of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Example 1 with the increase in pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0046] Figure 5 : Graph showing the change relationship of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Example 2 with the increase in pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0047] Figure 6 : Graph showing the change relationship of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Example 3 with the increase in pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0048] Figure 7 : Graph showing the change relationship of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Example 4 with the increase in pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0049] Figure 8 : Graph showing the change relationship of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Example 5 with the increase in pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0050] Figure 9 : Graph showing the change relationship of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Example 6 with the increase in pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0051] Figure 10:Relationship diagram of the separation selectivity of the tubular polycrystalline membrane before and after being treated in Comparative Example 2 with the increase of pressure. Among them, the left figure is before treatment, and the right figure is after treatment.

[0052] Figure 11 :Cross-sectional electron micrograph of the tubular polycrystalline membrane after being treated in Comparative Example 3. Detailed implementation manners

[0053] The technical solutions of the present invention will be 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, but the present invention is not limited to the scope of the described examples.

[0054] The rolling coating of the present invention is carried out in a temperature-controlled rolling film coater as Figure 1 shown. Among them, the temperature-controlled rolling film coater includes a main body 5 with a chamber inside, several rollers 1 located inside the main body 5, a motor 2 located outside the main body 5, a temperature controller 4, and a conveyor belt 3 located inside the main body 5. The rollers 1 are used to drive the tubular polycrystalline membrane to roll, the motor 2 drives the rollers 1 to rotate through the conveyor belt 3, and the temperature controller 4 is used to control the temperature inside the main body 5. The number of rollers 1 can be 4-8, Figure 1 in which the number of rollers 1 shown is 4, as Figure 1 shown, the temperature controller 4 can be located on the outer wall of the main body 5 for convenient operation. The main body 5 is provided with a hole for the conveyor belt 3 to pass through. The conveyor belt 3 is sleeved on the motor 2 and the rollers 1, and adjacent two rollers 1 are also connected by the conveyor belt 3.

[0055] The rolling coating in the following examples is operated using the aforementioned temperature-controlled rolling film coater, and the tubular polycrystalline membrane is placed between two rollers 1.

[0056] Example 1

[0057] This example provides a single-channel tubular ZIF-8 polycrystalline membrane and processes it as follows:

[0058] 1) Preparation of a single-channel tubular ZIF-8 membrane supported by porous alumina ceramics: Immerse a 13 cm porous alumina ceramic tube after cleaning in a seed solution (prepared by mixing Zn(NO3)·6H2O:2-methylimidazole (2-MIM):H2O in a molar ratio of 1:60:1200, stirring at room temperature for 12 h, washing and centrifuging three times with methanol, and then dispersing the particles in fresh methanol to obtain the seed solution) for 2 min. After completing the seed inoculation procedure, dry at room temperature, and then place the tubular membrane in a reaction kettle filled with a secondary synthesis solution (Zn(NO3)·6H2O:2-MIM:H2O in a molar ratio of 1:60:6000, stirring evenly to obtain the secondary synthesis solution) and react for 12 h. Finally, take it out and wash it 2-3 times with a methanol solution to obtain a single-channel ZIF-8 tubular membrane.

[0059] 2) Membrane treatment: The liquid A (vinyl-terminated polydimethylsiloxane PDMS containing a platinum catalyst) and liquid B (crosslinking agent containing more than 2 silicon-hydrogen bonds) in the two-component silicone rubber compound RTV615 produced by General Electric Company were added to n-heptane solvent at a mass ratio of 10:1, and rapidly stirred for 15 min to dissolve, to prepare a solution with a mass concentration of 20 wt%. The solution was degassed by ultrasonic method for 5 min. One end of the tubular membrane was blocked with a rubber stopper, and the prepolymer solution was poured into the tube and coated for 10 min, then the excess solution was poured out. Then the tubular membrane was placed on a temperature-controlled rolling film coater and roll-coated for 6 h, while controlling the temperature of the temperature-controlled film coater at 40 °C, so that the prepolymer and crosslinking agent in the solution were in-situ crosslinked and cured on the inner surface of the tubular membrane, and part of the solvent was slowly volatilized. Finally, it was dried in an oven at a temperature of 100 °C for 24 h, and a uniform and continuous polymer coating that could effectively repair defects was obtained on the inner surface of the single-channel tubular ZIF-8 membrane, and finally the treated tubular polycrystalline membrane was obtained.

[0060] The cross-sectional electron micrograph of the above-mentioned treated tubular polycrystalline membrane is as Figure 2 shown. It can be seen that the polymer coatings in the upper and lower regions of the tubular polycrystalline membrane are very uniform, and the thicknesses of the polymer coatings in the two regions are basically the same, which can effectively repair the defects of the membrane.

[0061] The single-channel ZIF-8 tubular membranes obtained in multiple steps 1) and the treated tubular polycrystalline membranes obtained in multiple steps 2) were respectively subjected to the following gas separation performance tests:

[0062] The membranes were respectively placed in a self-made membrane module for propylene / propane separation experiment: propylene / propane (equimolar feed), the mixed gas flow rate was 80 ml / min, nitrogen was used as the purge gas, and the nitrogen gas flow rate was 240 ml / min, and the transmembrane pressure difference range was 1-6 bar. The results were as follows: The separation performance of the single-channel ZIF-8 tubular membrane obtained in step 1) was as Figure 4 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) was as Figure 4 shown in the right figure. It can be seen that after the treatment of the present invention, the gas separation ability of the membrane under both atmospheric pressure and high-pressure environments has been significantly improved, because the treatment method of the present invention repairs the defects of the membrane.

[0063] Example 2

[0064] This example provides a single-channel tubular SSZ-13 zeolite membrane and treats it as follows:

[0065] 1) Preparation of single-channel tubular SSZ-13 zeolite membrane supported on porous alumina ceramic: After cleaning the surface of a 13-cm porous alumina ceramic tube, a layer of seeds (prepared by mixing Na2O:Al2O3:SiO2:H2O:N,N,N-trimethyl-1-adamantylammonium hydroxide (TMAdaOH) in a molar ratio of 1:2.5:100:4400:20, putting it into a reaction kettle and reacting at 160 °C for 96 h, washing with water by centrifugation three times and drying, and calcining at 600 °C for 6 h to remove the structure-directing agent, then collecting the seeds) was coated. After completing the seed inoculation procedure, it was dried at room temperature. Then the tubular membrane was placed in a reaction kettle containing a secondary synthesis solution (Na2O:Al2O3:SiO2:H2O:TMAdaOH in a molar ratio of 1:1:20:1600:10, and obtaining the secondary synthesis solution after stirring evenly) and reacted for 48 h. Finally, it was taken out and washed with water 2 - 3 times, and calcined in an oxygen environment at 400 °C for 48 h to obtain a single-channel SSZ-13 tubular zeolite membrane.

[0066] 2) Membrane treatment: Component A (containing vinyl-terminated polydimethylsiloxane PDMS and a platinum catalyst) and Component B (a crosslinking agent containing more than 2 silicon-hydrogen bonds) of the RTV615 two-component silicone rubber compound produced by General Electric Company were added to n-heptane solvent in a mass ratio of 10:1, and rapidly stirred for 15 min to dissolve, preparing a solution with a mass concentration of 20 wt%. The solution was degassed by ultrasonic method, and the ultrasonic time was 5 min. One end of the tubular membrane was blocked with a rubber stopper, and the prepolymer solution was poured into the tube and coated for 10 min, then the excess solution was poured out. Then the tubular membrane was placed on a temperature-controlled rolling film coater and roll-coated for 6 h, while controlling the temperature of the temperature-controlled film coater at 40 °C, so that the prepolymer and crosslinking agent in the solution were in-situ crosslinked and cured on the inner surface of the tubular membrane under the action of the catalyst, and part of the solvent was slowly volatilized. Finally, it was dried in an oven at a temperature of 100 °C for 24 h, and a uniform and continuous polymer coating that could effectively repair defects was obtained on the inner surface of the single-channel tubular Si-CHA zeolite membrane, and finally the treated tubular polycrystalline membrane was obtained.

[0067] The membranes obtained in multiple steps 1) and the treated tubular polycrystalline membranes obtained in multiple steps 2) were respectively subjected to the following gas separation performance tests:

[0068] The membranes were respectively placed into self-made membrane modules for carbon dioxide / methane separation experiments: carbon dioxide / methane (equimolar feed), the mixed gas flow rate was 80 ml / min, helium was used as the purge gas, and the helium gas flow rate was 240 ml / min, and the transmembrane pressure difference range was 1 - 6 bar. The results were as follows: The separation performance of the membrane obtained in step 1) was as Figure 5 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) was as Figure 5As shown in the right figure, it can be seen that after the treatment of the present invention, the gas separation ability of the membrane under both atmospheric pressure and high-pressure environments has been significantly improved. The reason is that the treatment method of the present invention repairs the defects of the membrane.

[0069] Example 3

[0070] This example provides a 19-channel tubular SSZ-13 zeolite membrane and treats it as follows:

[0071] 1) Preparation of a 19-channel tubular SSZ-13 zeolite membrane supported on porous alumina ceramics: Coat a layer of seeds (prepared with a molar ratio of SiO2:Al2O3:TMAdaOH:NaOH:H2O of 1:0.025:0.4:0.2:44, placed in a reaction kettle and reacted at 160 °C for 96 h, washed with water by centrifugation three times and dried, calcined at 600 °C for 6 h to remove the structure-directing agent, and then the seeds were collected) on the surface of a 6.5 cm clean porous alumina ceramic tube. After completing the seed inoculation procedure, dry at room temperature. Then place the tubular membrane in a reaction kettle containing a secondary synthesis solution (with a molar ratio of Na2O:Al2O3:SiO2:H2O:TMAdaOH of 1:0.025:0.2:0.2:25, stirred evenly to obtain the secondary synthesis solution) and react for 48 h. Finally, take it out and wash it with water 2-3 times, and calcine the single membrane in an oxygen environment at 200 °C for 48 h to obtain a 19-channel SSZ-13 tubular zeolite membrane.

[0072] 2) Membrane treatment: Add liquid A (containing vinyl-terminated polydimethylsiloxane PDMS and a platinum catalyst) and liquid B (a crosslinking agent containing more than 2 silicon-hydrogen bonds) of the RTV615 two-component silicone rubber compound produced by General Electric Company to n-heptane solvent at a mass ratio of 10:1, and quickly stir for 15 min to dissolve, and prepare a solution with a mass concentration of 20 wt%. Remove bubbles by ultrasonic method, and the ultrasonic time is 5 min. Seal one side of the 19-channel tubular membrane with plastic wrap, pour the prepolymer solution into the tube and coat for 20 min, then pour out the excess solution. Then place the tubular membrane on a temperature-controlled rolling film coater and roll-coat for 9 h, while controlling the temperature of the temperature-controlled film coater at 40 °C, so that the prepolymer and crosslinking agent in the solution crosslink and cure in situ on the inner surface of the tubular membrane under the action of the catalyst, and part of the solvent slowly volatilizes. Finally, dry in an oven at a temperature of 100 °C for 48 h, and a uniform and continuous polymer coating that can effectively repair defects is obtained on the inner surface of the 19-channel tubular ZIF-8 membrane, and finally the treated tubular polycrystalline membrane is obtained.

[0073] Perform the same carbon dioxide / methane separation experiment as in Example 2. The results are as follows: The separation performance of the membrane obtained in step 1) is as Figure 6 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) is as Figure 6As shown in the right figure, it can be seen that after the treatment of the present invention, the gas separation ability of the membrane under both normal pressure and high pressure environments has been significantly improved because the treatment method of the present invention repairs the defects of the membrane.

[0074] Example 4

[0075] Basically the same as Example 1, the only difference is that: the RTV615 two-component silicone rubber compound in step 2) is replaced with an RTV107 two-component silicone rubber compound, where component A is hydroxyl-terminated polydimethylsiloxane PDMS, component B is crosslinking agent tetraethyl orthosilicate, and catalyst dibutyltin dilaurate, and the mass ratio of the three is 100:10:1.

[0076] The same propylene / propane gas separation experiment as in Example 1 was carried out, and the separation performance of the membrane obtained in step 1) was as Figure 7 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) was as Figure 7 shown in the right figure. It can be seen that after the treatment of the present invention, the gas separation ability of the membrane under both normal pressure and high pressure environments has been significantly improved because the treatment method of the present invention repairs the defects of the membrane.

[0077] Example 5

[0078] Basically the same as Example 1, the only difference is that: the temperature of the rolling coating in step 2) is replaced from 40 °C to 60 °C.

[0079] The same propylene / propane gas separation experiment as in Example 1 was carried out, and the separation performance of the membrane obtained in step 1) was as Figure 8 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) was as Figure 8 shown in the right figure. It can be seen that after the treatment of the present invention, the gas separation ability of the membrane under both normal pressure and high pressure environments has been significantly improved because the treatment method of the present invention repairs the defects of the membrane.

[0080] Example 6

[0081] Basically the same as Example 1, the only difference is that: the temperature of the rolling coating in step 2) is replaced from 40 °C to 25 °C.

[0082] The same propylene / propane gas separation experiment as in Example 1 was carried out, and the separation performance of the membrane obtained in step 1) was as Figure 9 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) was as Figure 9 shown in the right figure. It can be seen that after the treatment of the present invention, the gas separation ability of the membrane under both normal pressure and high pressure environments has been significantly improved because the treatment method of the present invention repairs the defects of the membrane.

[0083] Comparative Example 1

[0084] This comparative example provides a single-channel tubular ZIF-8 polycrystalline membrane and processes it as follows:

[0085] 1) The same as step 1) of Example 1;

[0086] 2) Membrane treatment: The liquid A (containing vinyl-terminated polydimethylsiloxane PDMS and a platinum catalyst) and liquid B (a crosslinking agent containing more than 2 silicon-hydrogen bonds) in the RTV615 two-component silicone rubber compound produced by General Electric Company are added to the n-heptane solvent at a mass ratio of 10:1, and rapidly stirred for 15 min to dissolve, to prepare a solution with a mass concentration of 20 wt%. Defoaming is carried out by ultrasonic method, and the ultrasonic time is 5 min. One end of the tubular membrane is blocked with a rubber stopper, and the prepolymer solution is poured into the tube and coated for 10 min, then the excess solution is poured out, and then the tubular membrane is vertically placed on the filter paper at 40 °C for 6 h, and finally dried in an oven at a temperature of 100 °C for 24 h to obtain the treated membrane. The cross-sectional electron micrograph of the above-treated tubular polycrystalline membrane is as Figure 3 shown. It can be seen that the polymer coatings in the upper and lower regions of the tubular polycrystalline membrane are uneven, the polymer coating in the upper region is thin, the polymer coating in the lower region is thick, and the coating is uneven.

[0087] Comparative Example 2

[0088] Basically the same as Example 1, the difference is only that: the temperature of the rolling coating in step 2) is replaced by 70 °C.

[0089] The propylene / propane gas separation experiment is carried out in the same way as in Example 1. The separation performance of the membrane obtained in step 1) is as Figure 10 shown in the left figure, and the separation performance of the treated tubular polycrystalline membrane obtained in step 2) is as Figure 10 shown in the right figure. It can be seen that when the temperature of the rolling coating is too high, the degree of polymer repairing defects is limited, and the improvement degree of the membrane separation performance is very low.

[0090] Comparative Example 3

[0091] Adopt the scheme of coating after complete crosslinking, which is as follows:

[0092] Basically the same as Example 1, the difference is only that: step 2) is different, and step 2) is specifically as follows:

[0093] The liquid A (containing vinyl-terminated polydimethylsiloxane PDMS and a platinum catalyst) and liquid B (a crosslinking agent containing more than 2 silicon-hydrogen bonds) in the two-component silicone rubber compound RTV615 produced by General Electric Company were added to n-heptane solvent at a mass ratio of 10:1, and stirred in a water bath at 30 °C for 24 h to completely crosslink the polymer. One end of the tubular membrane was blocked with a rubber stopper, and the crosslinked polymer was poured into the tube and coated for 10 min, then the excess solution was poured out. Then the tubular membrane was placed on a temperature-controlled rolling film coater and roll-coated for 6 h, while controlling the temperature of the temperature-controlled film coater at 40 °C, and slowly volatilizing part of the solvent. Finally, it was dried in an oven at a temperature of 100 °C for 24 h to finally obtain the treated tubular polycrystalline membrane.

[0094] The propylene / propane gas separation experiment was carried out in the same way as in Example 1, and it was found that bubbling occurred on the membrane surface during the test.

[0095] The finally obtained coating of the tubular polycrystalline membrane was too thick and had weak binding force, resulting in the separation of the coating from the membrane layer and the occurrence of bubbling, as Figure 11 shown.

[0096] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it should not be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for treating a tubular polycrystalline membrane for gas separation, wherein the tubular polycrystalline membrane is supported by a carrier, and is characterized in that: The treatment method includes the step of coating a solution on the inner surface of the tubular polycrystalline membrane by perfusion, the solution includes a prepolymer and a crosslinking agent, and the step of roll coating the coated tubular polycrystalline membrane. In the roll coating, an in-situ crosslinking reaction occurs between the prepolymer and the crosslinking agent, and the in-situ crosslinking temperature is 25-60 °C; The prepolymer is selected from one or both of divinyl-terminated polydimethylsiloxane and divinyl-terminated polydimethylsiloxane with a C1-C6 fluoroalkyl group in the side chain, and the crosslinking agent is a siloxane compound containing more than two silicon-hydrogen bonds; or, the prepolymer is selected from one or both of dihydroxy-terminated polydimethylsiloxane and dihydroxy-terminated polydimethylsiloxane with a C1-C6 fluoroalkyl group in the side chain, and the crosslinking agent is selected from one or a combination of more than one of tetraethyl orthosilicate, tetramethyl orthosilicate, and tetrapropyl orthosilicate; The mass ratio of the prepolymer to the crosslinking agent is 5-20:1; The tubular polycrystalline membrane is selected from one or both of MOF membranes and zeolite membranes.

2. The processing method of the tubular polycrystalline membrane for gas separation according to claim 1, characterized in that: The roll coating is carried out at a rotation speed of 30-180 r / min.

3. The method for treating a tubular polycrystalline membrane for gas separation according to claim 1, wherein: The time of the roll coating is 1-9 h; and / or, the time of coating by perfusion is 5-20 min.

4. The method for treating a tubular polycrystalline membrane for gas separation according to claim 1, characterized in that: The mass concentration of the solution is 5%-30%.

5. The method for treating a tubular polycrystalline membrane for gas separation according to claim 1, characterized in that: The carrier is selected from one or a combination of more than one of porous alumina ceramic tubes and porous stainless steel sintered tubes.

6. The method for treating a tubular polycrystalline membrane for gas separation according to claim 5, characterized in that: The carrier is selected from one or a combination of more than one of single-channel tubes, 4-channel tubes, 7-channel tubes, 19-channel tubes, and 61-channel tubes.

7. The method for treating a tubular polycrystalline membrane for gas separation according to claim 1, wherein: The roll coating is carried out on a temperature-controlled roll coater; the temperature-controlled roll coater includes a main body with a chamber inside, several rollers located inside the main body, a motor, a temperature controller, and a conveyor belt located inside the main body. The rollers are used to drive the tubular polycrystalline membrane to roll, the motor drives the rollers to rotate through the conveyor belt, and the temperature controller is used to control the temperature inside the main body.

8. The method for treating a tubular polycrystalline membrane for gas separation according to claim 7, characterized in that: The number of the rollers is 4-8; the temperature controller is located on the outer wall of the main body.

9. The method for treating a tubular polycrystalline membrane for gas separation according to claim 1, characterized in that: The treatment method further includes the step of drying after the roll coating.

10. The method for treating a tubular polycrystalline membrane for gas separation according to claim 9, characterized in that: The drying temperature is 60-100 °C, and the drying time is 6-24 h.

11. A tubular polycrystalline membrane for gas separation obtained by the treatment method of the tubular polycrystalline membrane for gas separation according to any one of claims 1-10.

12. Use of the tubular polycrystalline membrane for gas separation according to claim 11, characterized in that: For the separation of gases, the gases are selected from a combination of two or more of hydrogen, nitrogen, carbon dioxide, methane, ethane, ethylene, propane, and propylene.

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