Pebax carbon membranes, methods of making the same, and use in h2 / co2 separations

Abstract

The application discloses a Pebax carbon film, a preparation method thereof and application of the Pebax carbon film in H2 / CO2 separation. As a kind of polyamide with the thermoplastic elastomer and rubber body, the polymer film of Pebax itself shows excellent gas selectivity. Pebax has high thermal stability and carbon yield, and is a suitable choice as a precursor of carbon film. Polyphenolic substances can enhance the interaction between Pebax and the substrate, and still maintain an integrated structure after calcination, and provide a local defect vacancy structure, which is beneficial to the transmission of hydrogen, and endows it with great potential in hydrogen carbon dioxide separation. The performance of the application is improved, and the anti-aging performance of the prepared carbon film is effectively improved, the operation steps are simple, and a new idea is provided for the preparation of hydrogen membrane separation material.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a Pebax carbon membrane for H2 / CO2 separation, belonging to the field of gas separation membranes. BACKGROUND

[0002] With the increasing demand for global energy and environmental protection, hydrogen (H2) energy is considered to be the most promising alternative to traditional fossil fuels and has the potential to effectively alleviate the serious energy crisis and greenhouse effect due to its unique advantages such as abundant sources, high energy density and clean combustion without carbon emissions. Currently, industrial hydrogen products mainly use fossil fuels, water electrolysis, industrial by-products and methanol reforming. H2 products are inevitably mixed with carbon dioxide, methane and other gases, and cannot be directly used, and need to be further purified to meet the purity requirements of various applications. Compared with traditional pressure swing adsorption, cryogenic distillation and other separation technologies, membrane separation has the advantages of low energy consumption, no secondary pollution, simple process, etc., and is increasingly attracting people's attention.

[0003] He (He, K. Q.; Hu, Y. X.; Low, Z. X.; Wang, R. X.; Wang, F. M.; Ma, H. Y.; Chen, X. F.; MacFarlane, D. R.; Wang, H. T., Metal oxyhydroxide nanosheet-assisted fabrication of ultrathin carbon molecular sieve membrane for hydrogen separation. Journal of Materials Chemistry A 2022, 10 (35), 18095-18102.) demonstrates an effective strategy for the fabrication of ultrathin carbon molecular sieve membranes from polyfurfuryl alcohol (PFA) using FeCoNi oxyhydroxide nanosheets as scaffolds. The introduction of nanosheets effectively prevents the monomer / polymer solution from penetrating into the porous substrate, promoting the formation of defect-free selective carbon layers with greatly reduced thickness. During pyrolysis, the nanosheets embedded in PEA are converted into nanoporous nanosheets to enhance the gas transport performance of the carbon membrane. For H2 / N2, H2 / CH4 and H2 / CO2 gases, the separation coefficients of CMSMs are 46, 38 and 11.4, respectively.

[0004] Recently, Katerina Setnickova studied CMSMs on porous alumina supports coated with an intermediate titania layer for gas separation (Setnickova, K.; Huang, T.C.; Wang, C.T.; Lin, Y.C.; Lee, S.L.; Zhuang, G.L.; Tung, K.L.; Tseng, H.H.; Uchytil, P., Realizing the impact of the intermediate layer structure on the CO2 / CH4 separation performance of carbon molecular sieving membranes: Insights from experimental synthesis and molecular simulation. Separation and Purification Technology 2021, 269.). In this paper, it is mentioned that a thicker titania intermediate layer can avoid defects and rough surfaces, thus improving the performance of the membrane, since polymers tend to interact with the alumina layer. In this study, the authors also mention that by controlling the pH of the sol-gel used for the interlayer preparation of the titania layer, the thickness of the titania layer and the thickness of the selective carbon layer, high performance CMS can be achieved. Simply put, by optimizing the sol-gel pH to 5, the number of titania coating cycles to 5, and the number of polymer solution coating cycles to 5, the separation factor of CO2 / CH4 gas is 64.9.

[0005] However, high-performance membrane materials are the key to further development of membrane separation technology, mainly because traditional polymer membrane materials are difficult to obtain high gas permeability and high selectivity due to their inherent properties; and inorganic membranes are difficult to industrialize due to high cost and complex preparation process. Therefore, it is urgent to develop new high-efficiency gas separation membrane materials. Carbon molecular sieve (CMS) membranes prepared based on polymer membrane precursors have outstanding advantages such as high permeability and high selectivity, and are gradually becoming a new type of membrane material to replace traditional industrial separation membranes. SUMMARY

[0006] In order to purify hydrogen in mixed gas, alleviate the serious energy crisis and greenhouse effect and other problems, the present application provides a Pebax carbon membrane with high gas permeability and high selectivity, its preparation method and application in H2 / CO2 separation.

[0007] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0008] In a first aspect, the present application provides a Pebax carbon membrane, which is prepared by the following method:

[0009] (1) immersing the pretreated hollow fiber membrane into an aqueous amine solution with a volume concentration of 1-10% (preferably 4-6%, most preferably 5%), and heat treating at 50-100°C for 12-36 hours (preferably heat treating at 70-80°C for 20-21 hours, and particularly preferably heat treating at 80°C for 20 hours), and then washing the obtained membrane with deionized water and ethanol in sequence, and drying, to obtain an amine-modified hollow fiber membrane; the hollow fiber membrane is made of PVDF or PVC (preferably PVDF); the aqueous amine solution contains one or both of ethylenediamine and diethylenetriamine (preferably ethylenediamine);

[0010] (2) immersing the amine-modified hollow fiber membrane of step (1) into a polyphenol-containing buffer solution with a concentration of 1-5 mg / ml (preferably 1-2 mg / ml, most preferably 1.5 mg / ml) and a pH of 7-9 (preferably 8.5), and reacting on a constant-temperature shaker at 20-50°C for 16-32 hours (preferably reacting on a constant-temperature shaker at 30-35°C for 23-24 hours, and reacting on a constant-temperature shaker at 30°C for 24 hours), and then washing the obtained membrane with deionized water and drying, to obtain a polyphenol-loaded hollow fiber membrane;

[0011] (3) sealing one end of the polyphenol-loaded hollow fiber membrane of step (2), and then repeating the following operation 1-5 times (preferably twice): immersing in an alcohol aqueous solution of polyether block polyamide with a concentration of 3-12 wt% (preferably 6%) for 40-80 s (preferably 60 s), and drying, to obtain a Pebax-PDA-NPVDF membrane;

[0012] (4) calcining the Pebax-PDA-NPVDF membrane of step (3) under a protective atmosphere at a rate of 0.5-5°C / min (preferably 1°C / min) to a temperature of 300-700°C for 45 min-90 min (preferably calcining at 400°C for 1 h), to obtain the Pebax carbon membrane.

[0013] As a preferred scheme of the present application, the hollow fiber membrane of step (1) is a polyvinylidene fluoride (PVDF) microfiltration membrane with an outer diameter of 2 mm and a pore size of 30 nm.

[0014] Further, the pretreatment in step (1) is soaking and cleaning the hollow fiber membrane in a mixed solvent of ethanol and water at a volume ratio of 1:1 (each for 30 min, repeated three times), to obtain the pretreated hollow fiber membrane.

[0015] Further, the polyphenol in the polyphenol aqueous solution of step (2) is one or more of dopamine, gallic acid, tannic acid, and catechin, and is preferably dopamine.

[0016] In one embodiment of the present application, the buffer salt contained in the polyphenol-containing buffer is Tris-HCl.

[0017] In one embodiment of the present application, the sealing in step (3) uses epoxy resin. The purpose is to avoid the polyether block polyamide from entering the hollow pipe, resulting in smaller flux.

[0018] Preferably, the solvent of the alcohol aqueous solution of the polyether block polyamide in step (3) is a mixed solvent of ethanol and water, wherein the mass of ethanol is 25%-75% of the mixed solvent of ethanol and water, preferably 70%.

[0019] As a preferred scheme of the present application, in step (4), the protective atmosphere is a nitrogen atmosphere. The composite film is placed in a quartz tube and put into a tube furnace with a stable nitrogen gas flow, the nitrogen flow rate is adjusted to 100ml / min; the heating rate is 1℃ / min, and the constant temperature is maintained for one hour.

[0020] In a second aspect, the present application also provides the application of the above-mentioned Pebax carbon film in H2 / CO2 gas separation.

[0021] The Pebax carbon film separates H2 / CO2 gas through the hollow pipe, and the mixed gas is separated through the pipe wall, and more hydrogen enters the hollow pipe.

[0022] The present application uses Pebax and PVDF hollow fiber membrane as raw materials to prepare a Pebax carbon molecular sieve membrane for H2 / CO2 gas separation. Scanning electron microscopy (SEM) and infrared spectroscopy prove that the preparation is successful, and the material has good thermal stability through thermogravimetric analysis (TGA).

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) PVDF hollow fiber membrane is not suitable as a substrate due to its characteristic of pore collapse under high temperature conditions, but after amination operation, its thermal stability is enhanced. The present application uses PVDF hollow fiber membrane as a substrate material, and after amination, a membrane material containing N active sites and excellent thermal stability can be formed, which is beneficial to improve the anti-aging performance of the carbon molecular sieve membrane.

[0025] (2) Polyphenolic substances can enhance the interaction between Pebax and the substrate due to their multiple phenolic groups, and they still maintain an intact structure after calcination and provide local defect vacancy structures, which is conducive to the transmission of hydrogen, giving it great potential in hydrogen-carbon dioxide separation. The present application modifies the amine PVDF hollow fiber membrane with an organic interlayer. Compared with inorganic interlayers applied to organic polymer substrates, first of all, due to material compatibility, the adhesion between the organic interlayer and the CMS layer is good, which may be conducive to the stability of the membrane during the long process; secondly, the organic interlayer is often manufactured under relatively simple conditions, such as room temperature, which is less destructive to the polymer substrate; finally, inorganic interlayers are more expensive than organic interlayers, and the cost performance is low. The organic interlayer can effectively avoid pore penetration and achieve the improvement of gas flux and selectivity, breaking the "trade-off" effect that hinders gas separation performance.

[0026] (3) The carbon molecular sieve membrane prepared by carbonizing the Pebax composite membrane as a precursor has a multi-level pore structure, adjusts the pore distribution, can enhance the gas separation selectivity, has strong anti-aging ability, high temperature resistance and other advantages. The application range of Pebax material is expanded.

[0027] (4) The raw materials used in the present application are cheap and easy to obtain, and at the same time have good separation performance. The above shows that the Pebax carbon membrane has good prospects for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Flow chart of the carbonization process of the Pebax carbon membrane prepared in Example 1;

[0029] Figure 2 SEM images of the Pebax composite membrane prepared in Example 1: a-c are the surface (a) NPVDF (b)

[0030] PDA-NPVDF (c) Pebax-PDA-NPVDF

[0031] d-f are cross-sections (d) NPVDF (e) PDA-NPVDF (f) Pebax-PDA-NPVDF;

[0032] Figure 3 Thermogravimetric analysis TGA image of the Pebax composite membrane prepared in Example 1 (a) Thermogravimetric analysis TG; (b) Differential thermal analysis DTG;

[0033] Figure 4 SEM images of the Pebax carbon membrane prepared in Example 1: 1 is the cross-section, 2 is the surface; (a) 300℃; (b) 400℃; (c) 500℃; (d) 600℃; (e) 700℃.

[0034] Figure 5 Gas separation performance of Pebax carbon membranes prepared in Example 1.

[0035] Figure 6 Different performance comparison chart in the present application (prepared by calcination at 400℃)

[0036] Figure 7 Schematic diagram of gas separation membrane permeation test device DETAILED DESCRIPTION

[0037] The present application will be described in detail below with reference to examples and drawings.

[0038] PVDF microfiltration hollow fiber membrane (Janus Beijing Technology Co., Ltd., outer diameter 2 mm, pore size 0.03 μm), polyether block polyamide (Arkema Company, Pebax 2533)

[0039] Example 1:

[0040] Pebax / PDA / PVDF carbon membrane

[0041] 1) Ammoniation of PVDF hollow fiber membrane

[0042] First step, using PVDF microfiltration hollow fiber membrane, PVDF microfiltration membrane was immersed in ethanol and water with a volume ratio of 1:1 for 30 min, repeated three times, and dried for standby;

[0043] Second step, immerse the hollow fiber membrane in ethylenediamine aqueous solution (5%, v / v), then transfer to the reaction kettle, heat treatment at 80℃ for 20 hours. After the reaction, the ammoniated hollow fiber membrane was washed with deionized water and ethanol several times, and finally, the hollow fiber was dried at room temperature for use, recorded as NPVDF;

[0044] 2) Dopamine coating

[0045] First step, dissolve dopamine (1.5 mg / mL) in 10 mM Tris-HCl (pH = 8.5) solution.

[0046] Second step, after dissolution, immerse NPVDF in the solution, transfer to a constant temperature shaker at 30℃, react for 24 hours, after the reaction, wash several times with deionized water, and finally, dry the hollow fiber at room temperature for use, recorded as PDA-NPVDF.

[0047] 3) Preparation of Pebax composite membrane

[0048] First step, polyether block polyamide (Pebax) powder (6wt%) was dispersed in ethanol / water (mass ratio 7:3) mixed solution, heated and stirred at 75℃ for 20 hours until completely dissolved, and then cooled and stored for later use.

[0049] Second step, one end of the PDA-NPVDF membrane was sealed with epoxy resin and then immersed in the Pebax solution for 60s. After the surface was dried, it was dried in a vacuum drying oven at 70℃ for 8h. The above operation was repeated twice, dried and stored, and recorded as Pebax-PDA-NPVDF.

[0050] 4) Preparation of Pebax carbon membrane

[0051] The Pebax composite membrane was placed in a tube furnace, and the nitrogen flow was 100ml / min. The temperature was increased from room temperature to 300-700℃ at a rate of 1℃ / min (5 samples, gradient 100℃), and the temperature was kept for one hour to obtain carbon molecular sieve membranes calcined at different temperatures. Recorded as CMS-A, A is the target temperature.

[0052] 5) Performance test

[0053] The prepared carbon molecular sieve membrane was tested for performance under dry conditions at 25℃ and a pressure difference of 0.1MPa. The results are shown in Figure 5 . Among them, the selectivity is the highest at 400℃, and the measured H2 permeability coefficient is 2.67*10 -6 mol m -2 s -1 Pa -1 , and the H2 / CO2 selectivity is 22.56.

[0054] Example 2:

[0055] Pebax / TA / PVDF carbon membrane

[0056] 1) Amination of PVDF hollow fiber membrane

[0057] First step, PVDF microfiltration hollow fiber membrane was used. The PVDF microfiltration membrane was soaked in ethanol and water with a volume ratio of 1:1 for 30min, repeated three times, and dried for standby;

[0058] Second step, the hollow fiber membrane was immersed in an aqueous solution containing ethylenediamine (5%, v / v), and then transferred to a reaction kettle for heat treatment at 80℃ for 20 hours. After the reaction was completed, the aminated hollow fiber membrane was washed with deionized water and ethanol several times in turn, and finally dried at room temperature for use, recorded as NPVDF;

[0059] 2) Tannin coating

[0060] First step, dissolve tannic acid (1.5mg / mL) in 10mM Tris-HCl (pH=8.5) solution.

[0061] Second step, after dissolving, immerse NPVDF into the solution, transfer to constant temperature shaker at 30℃, react for 24 hours, after reaction, wash with deionized water for several times, finally, dry the hollow fiber at room temperature for use, mark as TA-NPVDF.

[0062] 3) Pebax composite membrane preparation

[0063] First step, disperse polyether block polyamide (Pebax) powder (6wt%) in ethanol / water (mass ratio 7:3) mixed solution, heat and stir at 75℃ for 20 hours until completely dissolved, after cooling, reserve for use.

[0064] Second step, immerse one end of PTA-NPVDF membrane into Pebax solution for 60s after sealing with epoxy resin, then take out and dry the surface, dry in vacuum drying oven at 70℃ for 8h, repeat the above operation 2 times, dry and save, mark as Pebax-TA-NPVDF.

[0065] 4) Pebax carbon membrane preparation

[0066] Put the Pebax composite membrane into the tube furnace, increase the temperature from room temperature to 400℃ at a rate of 1℃ / min with nitrogen flow of 100ml / min, and keep for one hour to obtain carbon molecular sieve membrane.

[0067] 5) Performance test

[0068] The prepared carbon molecular sieve membrane is measured under dry conditions at 25℃, pressure difference of 0.1MPa, and the permeation coefficient of H2 is 2.95*10-7mol m s Pa, and the selectivity of H2 / CO2 is 13.72. -6 mol m -2 s -1 Pa -1

[0069] Example 3:

[0070] Pebax / GA / PVDF carbon membrane

[0071] 1) Ammoniation of PVDF hollow fiber membrane

[0072] First step, use PVDF microfiltration hollow fiber membrane, immerse the PVDF microfiltration membrane in ethanol and water with a volume ratio of 1:1 for 30min, repeat three times, and dry for use;

[0073] ​Second step, the hollow fiber membrane was immersed in an aqueous solution containing ethylenediamine (5%, v / v) and then transferred to a reaction kettle for heat treatment at 80°C for 20 hours. After the reaction was completed, the aminated hollow fiber membrane was washed several times with deionized water and ethanol in turn, and finally, the hollow fiber membrane was dried at room temperature for use, denoted as NPVDF;

[0074] 2) Gallic acid coating

[0075] First step, dissolve gallic acid (1.5 mg / mL) in a 10 mM Tris-HCl (pH = 8.5) solution.

[0076] Second step, after dissolution, immerse the NPVDF in the solution and transfer it to a constant temperature shaker at 30°C for 24 hours. After the reaction is completed, wash several times with deionized water, and finally, dry the hollow fiber at room temperature for use, denoted as GA-NPVDF.

[0077] 3) Pebax composite membrane preparation

[0078] First step, disperse polyether block polyamide (Pebax) powder (6wt%) in a mixed solution of ethanol / water (mass ratio 7:3), heat and stir at 75°C for 20 hours until completely dissolved, and then cool and reserve for use.

[0079] Second step, immerse one end of the PTA-NPVDF membrane in the Pebax solution for 60 seconds after sealing with epoxy resin, then dry the surface after taking it out, and then dry it in a vacuum drying oven at 70°C for 8 hours. Repeat the above operation 2 times, dry and store, denoted as Pebax-TA-NPVDF.

[0080] 4) Pebax carbon membrane preparation

[0081] Place the Pebax composite membrane in a tube furnace, increase the temperature from room temperature to 400°C at a rate of 1°C / min with a nitrogen flow of 100 ml / min, and keep the temperature for one hour to obtain a carbon molecular sieve membrane.

[0082] 5) Performance test

[0083] The carbon molecular sieve membrane prepared was measured under dry conditions at 25°C with a pressure difference of 0.1 MPa, and the permeation coefficient of H2 was 3.3*10 -7 mol m -2 s -1 Pa -1 , and the selectivity of H2 / CO2 was 12.79.

[0084] Example 4:

[0085] Pebax / PDA / DPVDF carbon membrane

[0086] 1) PVDF hollow fiber membrane amination

[0087] First step, PVDF microfiltration hollow fiber membrane was used. PVDF microfiltration membrane was soaked and cleaned in ethanol and water with a volume ratio of 1:1 for 30 min, repeated three times, and dried for standby;

[0088] Second step, the hollow fiber membrane was immersed in ethylenediamine aqueous solution (5%, v / v), and then transferred to a reaction kettle for heat treatment at 80°C for 20 hours. After the reaction was completed, the aminated hollow fiber membrane was washed several times with deionized water and ethanol, and finally dried at room temperature for use, denoted as DPVDF;

[0089] 2) Dopamine coating

[0090] First step, dopamine (2 mg / mL) was dissolved in 10 mM Tris-HCl (pH = 8.5) solution.

[0091] Second step, after dissolution, NPVDF was immersed in the solution and transferred to a constant temperature shaker at 30°C for 24 hours. After the reaction was completed, the hollow fiber was washed several times with deionized water, and finally dried at room temperature for use, denoted as PDA-NPVDF.

[0092] 3) Pebax composite membrane preparation

[0093] First step, polyether block polyamide (Pebax) powder (9 wt%) was dispersed in a mixture of ethanol / water (mass ratio 7:3) solution, heated and stirred at 75°C for 20 hours until completely dissolved, and cooled for standby.

[0094] Second step, after one end of the PDA-NPVDF membrane was sealed with epoxy resin, it was immersed in the Pebax solution for 60 s, then the surface was dried after taking out, and dried in a vacuum drying oven at 70°C for 8 h. The above operation was repeated 2 times, dried and stored, denoted as Pebax-PDA-NPVDF.

[0095] 4) Pebax carbon membrane preparation

[0096] The Pebax composite membrane was placed in a tube furnace, the nitrogen flow was 100 ml / min, the temperature was increased to 400°C at a rate of 1°C / min from room temperature, and the temperature was kept for one hour to obtain a carbon molecular sieve membrane.

[0097] 5) Performance test

[0098] The carbon molecular sieve membrane prepared was measured under dry conditions at 25°C and a pressure difference of 0.1 MPa, and the permeation coefficient of H2 was 8.37*10 -7 mol m -2 s-1 Pa -1 , the selectivity of H2 / CO2 was 14.61.

[0099] Example 5:

[0100] Pebax / PDA / PVDF carbon membrane

[0101] 1) PVDF hollow fiber membrane amination

[0102] First step, PVDF microfiltration hollow fiber membrane was used, and the PVDF microfiltration membrane was soaked and cleaned in ethanol and water with a volume ratio of 1:1 for 30 min, repeated three times, and dried for standby;

[0103] Second step, the hollow fiber membrane was immersed in ethylenediamine aqueous solution (5%, v / v), and then transferred to a reaction kettle for heat treatment at 80°C for 20 hours. After the reaction was completed, the aminated hollow fiber membrane was washed with deionized water and ethanol several times in turn, and finally the hollow fiber was dried at room temperature for use, denoted as NPVDF;

[0104] 2) Dopamine coating

[0105] First step, dopamine (2 mg / mL) was dissolved in 10 mM Tris-HCl (pH = 8.5) solution.

[0106] Second step, after dissolution, NPVDF was immersed in the solution and transferred to a constant temperature shaker at 30°C for 24 hours. After the reaction was completed, it was washed with deionized water several times, and finally the hollow fiber was dried at room temperature for use, denoted as PDA-NPVDF.

[0107] 3) Preparation of Pebax composite membrane

[0108] First step, polyether block polyamide (Pebax) powder (3wt%) was dispersed in a mixed solution of ethanol / water (mass ratio 7:3), heated and stirred at 75°C for 20 hours until completely dissolved, and cooled for standby.

[0109] Second step, after one end of the PDA-NPVDF membrane was sealed with epoxy resin, it was immersed in the Pebax solution for 60s, then the surface was dried after taking out, and dried in a vacuum drying oven at 70°C for 8h. The above operation was repeated 2 times, dried and stored, denoted as Pebax-PDA-NPVDF.

[0110] 4) Preparation of Pebax carbon membrane

[0111] The Pebax composite membrane was placed in a tube furnace, the nitrogen flow was 100 ml / min, the temperature was increased to 400°C at a rate of 1°C / min from room temperature, and the temperature was kept for one hour to obtain a carbon molecular sieve membrane.

[0112] 5) Performance test

[0113] The prepared carbon molecular sieve membrane was measured under dry conditions at 25°C and a pressure difference of 0.1 MPa, and the H2permeation coefficient was 7.69*10 -7 mol m -2 s -1 Pa -1 , and the H2 / CO2selectivity was 13.67.

[0114] Comparative Example 1:

[0115] Unlike Examples 1-5, here the carbon membrane was prepared by carbonizing an amine-treated PVDF original membrane.

[0116] 1) Amine treatment of PVDF hollow fiber membrane

[0117] In the first step, PVDF microfiltration membranes were used, and the PVDF microfiltration membranes were soaked and cleaned in ethanol and water at a volume ratio of 1:1 for 30 min, repeated three times, and dried for standby use;

[0118] In the second step, the hollow fibers were soaked in an ethylenediamine solution (5%, v / v), and then transferred to a reaction kettle for heat treatment at 80°C for 20 hours. After the reaction was completed, the amine-treated PDVF hollow fibers were washed several times with deionized water and ethanol, and finally, the hollow fibers were dried at room temperature for use, denoted as NPVDF;

[0119] 2) Preparation of NPVDF carbon membrane

[0120] The NPVDF membrane was placed in a tube furnace, the nitrogen flow was 100 ml / min, the temperature was increased from room temperature to 400°C, and the temperature was maintained for one hour to obtain a carbon molecular sieve membrane.

[0121] 3) Performance test

[0122] The prepared carbon molecular sieve membrane was measured under dry conditions at 25°C and a pressure difference of 0.1 MPa, and the H2permeation coefficient was 2.97*10 -5 mol m -2 s -1 Pa -1 , and the H2 / CO2selectivity was 5.69.

[0123] Comparative Example 2:

[0124] Unlike Examples 1-5, here the carbon membrane was not prepared using an intermediate layer assisted Pebax composite membrane.

[0125] 1) Amine treatment of PVDF hollow fiber membrane

[0126] The first step is to use a PVDF microfiltration membrane. Soak and wash the PVDF microfiltration membrane in ethanol and water at a volume ratio of 1:1 for 30 minutes, repeat three times, and then air dry for later use.

[0127] The second step involves immersing the hollow fibers in a solution containing ethylenediamine (5%, v / v), then transferring them to a reaction vessel and heat-treating them at 80°C for 20 hours. After the reaction is complete, the amination-treated PDVF hollow fibers are washed several times with deionized water and ethanol. Finally, the hollow fibers are dried at room temperature for use and designated as NPVDF.

[0128] 3) Preparation of Pebax composite membrane

[0129] The first step is to disperse 6 wt% of polyether block polyamide (Pebax) powder in a mixed solution of ethanol / water (mass ratio 7:3), heat and stir at 75°C for 20 hours until completely dissolved, and then cool before use.

[0130] The second step involves sealing one end of the NPVDF membrane with epoxy resin and then immersing it in the Pebax solution for 60 seconds. After removing it and air-drying the surface, it is dried in a vacuum drying oven at 70°C for 8 hours. This process is repeated twice. The membrane is then dried and stored, and it is designated as Pebax-NPVDF.

[0131] 4) Pebax carbon film preparation

[0132] The Pebax composite membrane was placed in a tube furnace, and nitrogen flow rate was 100 ml / min. The temperature was increased from room temperature to 400°C and held for one hour to obtain a carbon molecular sieve membrane.

[0133] 5) Performance Testing

[0134] The prepared carbon molecular sieve membrane was tested at 25°C under dry conditions with a pressure difference of 0.1 MPa, and the H2 permeability coefficient was measured to be 8.91 × 10⁻⁶. -7 mol m -2 s -1 Pa -1 The selectivity of H2 / CO2 is 9.97.

[0135] Comparative Example 3:

[0136] Unlike Examples 1-5, carbon films are prepared here by carbonizing the original PVDF film.

[0137] 1) Cleaning of PVDF hollow fiber membrane

[0138] PVDF hollow fiber microfiltration membrane was used. The PVDF microfiltration membrane was soaked and cleaned in ethanol and water at a volume ratio of 1:1 for 30 minutes, and the process was repeated three times. The membrane was then dried for later use.

[0139] 2) Dopamine coating

[0140] First step, dopamine (2 mg / mL) was dissolved in 10 mM Tris-HCl (pH = 8.5) solution.

[0141] Second step, after dissolving, PVDF was immersed in the solution and transferred to a constant temperature shaker at 30 °C for 24 hours. After the reaction was completed, it was washed several times with deionized water, and finally the hollow fiber was dried at room temperature for use, marked as PDA-PVDF.

[0142] 3) Preparation of Pebax composite membrane

[0143] First step, polyether block polyamide (Pebax) powder (6wt%) was dispersed in a mixed solution of ethanol / water (mass ratio 7:3) and heated and stirred at 75 °C for 20 hours until completely dissolved. After cooling, it was ready for use.

[0144] Second step, after sealing one end of the PDA-NPVDF membrane with epoxy resin, it was immersed in the Pebax solution for 60 s, then the surface was dried after taking it out, and then it was dried in a vacuum drying oven at 70 °C for 8 h. The above operation was repeated twice, dried and stored, marked as Pebax-PDA-PVDF.

[0145] 4) Preparation of Pebax carbon membrane

[0146] The Pebax composite membrane was placed in a tube furnace, the nitrogen flow was 100 ml / min, the temperature was raised from room temperature to 400 °C, and the temperature was kept for one hour to obtain a carbon molecular sieve membrane.

[0147] 5) Performance test

[0148] The prepared carbon molecular sieve membrane did not form a membrane.

[0149] Performance test method: the performance of the test membrane in this paper was tested by the constant pressure variable volume method, and the membrane module was self-made in the laboratory, as shown in Figure 7 The test temperature was 25 °C. Single gas test was used, and before testing, the raw material side exhaust valve was opened to purge the membrane module to prevent air from affecting the experimental results.

[0150] Using a self-made permeation testing device, single-component CO2 and H2 gases were tested, their fluxes were compared, and the H2 / CO2 selectivity was calculated. Before testing each gas, both sides of the membrane were purged, and the device was allowed sufficient time to stabilize. Each time the test gas was replaced, purging with the replacement gas was necessary to ensure the purity of the gas within the module; excess gas was discharged from the feed side. The specific testing method was as follows: the prepared carbon molecular sieve membrane was placed in the membrane module. Under a certain pressure Δp (0.1 MPa), gas entered from the selectivity layer side of the membrane, permeated through the membrane, and flowed into the permeate meter. A soap bubble flow meter was used to determine the volume V flowing through and the specific time t required for that volume. The permeation testing temperature was room temperature throughout the experiment.

[0151] The formula for calculating the gas permeation flux P is as follows:

[0152]

[0153] In the formula, P represents the gas permeation rate, expressed in mol / m³. -2 s -1 Pa -1 ,

[0154] V – Volume of gas flowing through (cm³) 3 ;

[0155] Δp — Transmembrane pressure, MPa;

[0156] A – Effective membrane area;

[0157] T – Temperature, K;

[0158] t — Test time, s.

[0159] The ideal selectivity of a gas is calculated using the following formula:

[0160]

[0161] Where, α A / B For the ideal gas separation ratio, P A and P B These are the gas permeation rates of single-component gases A and B, respectively.

[0162] Conclusion: From the appendix Figure 2 In this study, the morphology of the original and modified NPDVF films was observed using scanning electron microscopy (SEM). The SEM images are shown below. Figure 2 As shown, the skin layer can be clearly seen from the cross-sectional morphology of the NPVDF film after PDA deposition. Figure 2As shown, there are a large number of pores on the surface of the NPVDF film, and the gas separation performance is poor. After PDA deposition, it can be found from the figure that a large number of nanoparticles are aggregated on the surface, and then larger PDA spherical particles are adhered to the film surface, and the surface pores are obviously reduced.

[0163] From the attached Figure 3 , by thermal gravimetric image, we can find that the maximum pyrolysis temperature of PDA coated with coating is slightly higher than that of uncoated PDA, and the pyrolysis temperature tends to be flat. This also ensures that the matrix undergoes a small pore size shrinkage during pyrolysis without pore collapse.

[0164] From the attached Figure 4 , the scanning electron microscope images of the cross-sectional area around the outer surface of the CMS film at different temperatures. The scanning electron microscope images show that the CMS film has a similar asymmetric structure. The outer surface of these films has a carbonized skin layer. Except at 300℃, the skin thickness increases slightly, indicating that the degree of carbonization of the CMS film increases with the increase of the carbonization end temperature. For 300℃, the main reason for the film thickness is the insufficient carbonization.

[0165] From the attached Figure 5 , the performance of the CMS film at different temperatures was measured, and from the figure we can see that the pyrolysis temperature has a huge impact on the gas separation performance of the carbon film, because it completely changes the morphological structure of the polymer film. High temperature on the polymer film drives it to form a graphite-like structure, and generates pores through structural changes. The selective increase from 300℃ to 400℃ indicates that a large number of micropores with size sieving effect are formed after pyrolysis. The increase in flux from 300℃ to 700℃ is mainly due to the further decomposition of organic segments and impurities in the CMS film's pores at high temperatures, and a large number of micropores are generated, and after 400℃, the proportion of micropores with sieving effect is lower than that of micropores without sieving effect, and at 400℃, the H2 / CO2 selectivity of the film is the best.

[0166] Compared with Comparative Example 1 and Comparative Example 2, the H2 / CO2 selectivity of the carbon molecular sieve membrane prepared in Example 1-5 is greatly improved. Obviously, the synergistic sieving effect of the intermediate layer assistance and the porous structure of the carbon matrix is more conducive to the transmission of H2. Through Examples 1-3, it can be found that different intermediate layer assistance methods for preparing carbon molecular sieve membranes will affect the H2 permeation flux and H2 / CO2 selectivity of the film. When the intermediate layer is dopamine, the permeation coefficient of H2 is 3.52*10 -6 mol m -2 s -1 Pa -1, H2 / CO2 selectivity is 21.94. Compared with 5.69 of Comparative Example 1 and 9.97 of Comparative Example 2, the H2 / CO2 selectivity is improved, which is mainly due to the intermediate layer assisting the preparation of the carbon molecular sieve membrane. The intermediate layer can more effectively prevent the penetration of Pebax into the substrate, and the intermediate layer can also provide effective pore size after carbonization to improve the H2 / CO2 selectivity. Through Example 4, it can be found that the preparation of carbon molecular sieve membranes with different concentrations of Pebax will affect the H2 permeation flux and H2 / CO2 selectivity of the membrane. This is mainly due to too little Pebax, which will cause defects on the surface, and too much Pebax, which will remain on the surface and block the pores, resulting in a decrease in selectivity.

Claims

1. A Pebax carbon film characterized in that The Pebax carbon membrane is prepared by the following method: (1) The pretreated hollow fiber membrane is immersed in an amine aqueous solution with a volume concentration of 1-10%, and is heat-treated at 50-100°C for 12-36 hours. The obtained membrane is washed with deionized water and ethanol in sequence, and is dried to obtain an amine-modified hollow fiber membrane; the material of the hollow fiber membrane is PVDF or PVC; the amine in the amine aqueous solution is one or both of ethylenediamine and diethylenetriamine, and the pretreatment method of the hollow fiber membrane is that the hollow fiber membrane is immersed in a mixed solvent of ethanol and water with a volume ratio of 1:1 for cleaning, thereby obtaining the pretreated hollow fiber membrane; (2) The amine-modified hollow fiber membrane in step (1) is immersed in a polyphenol-containing buffer solution with a concentration of 1-5 mg / ml and a pH of 7-9, and is reacted on a constant-temperature shaker at 20-50°C for 16-32 hours. The obtained membrane is washed with deionized water and dried to obtain a polyphenol-loaded hollow fiber membrane; (3) The polyphenol-loaded hollow fiber membrane in step (2) is sealed at one end and is repeatedly immersed in a 3-12 wt% polyether block polyamide alcohol aqueous solution for 40-80 seconds and dried for 1-5 times, thereby obtaining a Pebax-PDA-NPVDF membrane; (4) The Pebax-PDA-NPVDF membrane in step (3) is calcined at a rate of 0.5-5°C / min to 300-700°C for 45 min-90 min under a protective atmosphere, thereby obtaining the Pebax carbon membrane.

2. The Pebax carbon film of claim 1, wherein: The hollow fiber membrane in step (1) is a polyvinylidene fluoride microfiltration membrane with an outer diameter of 2 mm and a pore size of 30 nm.

3. The Pebax carbon film of claim 1, wherein: The polyphenol-containing buffer solution in step (2) contains one or more than two of dopamine, gallic acid, tannic acid, and catechin.

4. The Pebax carbon film of claim 1, wherein: The polyphenol-containing buffer solution in step (2) contains dopamine.

5. The Pebax carbon film of claim 1, wherein: The sealing in step (3) uses epoxy resin.

6. The Pebax carbon film of claim 1, wherein: The solvent of the polyether block polyamide alcohol aqueous solution in step (3) is a mixed solvent of ethanol and water, wherein the mass of ethanol is 25%-75% of the mixed solvent of ethanol and water.

7. The Pebax carbon film of claim 1, wherein: In step (4), the protective atmosphere is a nitrogen atmosphere.

8. The Pebax carbon film of claim 1, wherein: In step (4), the calcination temperature is 400°C.

9. The Pebax carbon membrane according to any one of claims 1-8 for use in H2 / CO2 gas separation.

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