Modification method for improving gas separation performance of carbon molecular sieve membrane

Abstract

The invention belongs to the technical field of membrane preparation and application, and discloses a modification method for improving the gas separation performance of a carbon molecular sieve membrane. The hydrogen / methane, hydrogen / nitrogen and hydrogen / carbon dioxide separation performance of the carbon molecular sieve membrane is improved in a manner of dipping the oxidation reagent. The hydrogen / methane, hydrogen / nitrogen and hydrogen / carbon dioxide selectivity of the carbon molecular sieve membrane is changed by introducing an oxygen-containing functional group into the carbon molecular sieve membrane, and the carbon molecular sieve membrane has a wide application prospect in the field of gas separation membranes.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane preparation and application, and discloses a modification method for improving the gas separation performance of a carbon molecular sieve membrane. Background Art

[0002] As one of the important components of future energy, hydrogen has diverse sources. The mainstream hydrogen production process is usually accompanied by the production of a variety of impurities, such as H2O, CO2, CO, N2 and hydrocarbons, which will have a great impact on the subsequent use of hydrogen. Therefore, the efficient separation of H2 from other impurity gases becomes the key to the production of high-purity H2.

[0003] Membrane separation technology has a series of advantages such as high energy efficiency, low cost, small space occupation and simple maintenance, and has great potential for H2 purification. Carbon molecular sieve membranes can be produced by pyrolysis of polymer membranes at a specific temperature program. Carbon molecular sieve membranes have an adsorption / diffusion mechanism, thereby showing selective separation of specific gas pairs. The adsorption and diffusion properties of carbon molecular sieve membranes depend largely on their surface properties. Steam activation, ammonia activation and fluorine treatment have been applied to carbon molecular sieve membranes and have been shown to improve the specific gas separation performance of carbon molecular sieve membranes. For example, the post-surface treatment of existing carbon molecular sieve membranes by fluorine / nitrogen purging can significantly improve their He / H2 separation performance (Qi Wu, Lu Liu, Yang Jiao, Zhenyuan Li, Ju Bai, Prof. Xiaohua Ma, Prof. Shuangjiang Luo, Prof. Suojiang Zhang, Precise Helium Sieving from Hydrogen Using Fluorine-Decorated Carbon Hollow Fiber Membranes, Angew. Chem. Int. Ed, 2024, 63(33), e202400688). Steam activation post-treatment can also change the gas permeability of carbon molecular sieve membranes (Hui-Chun Lee, Majid Monji Doug Parsley, Muhammad Sahimi, Paul Liu, Fokion Egolfopoulos, Theodore Tsotsis, Use of Steam Activation as a Post-treatment Technique in the Preparation of Carbon Molecular Sieve Membranes, Ind. Eng. Chem. Res., 2013, 52 (3), 1122-1132). However, the existing carbon molecular sieve membrane post-treatment methods are complicated to operate and have high energy consumption. The present invention intends to develop a low-energy consumption, simple-to-operate carbon molecular sieve membrane modification method for improving its hydrogen / methane, hydrogen / nitrogen and hydrogen / carbon dioxide separation performance. Summary of the invention

[0004] In view of the insufficient hydrogen separation performance of existing carbon molecular sieve membranes, the present invention provides a modification method for improving the gas separation performance of carbon molecular sieve membranes.

[0005] The technical solution of the present invention:

[0006] A modification method for improving the gas separation performance of a carbon molecular sieve membrane, wherein oxygen-containing functional groups are introduced into a prepared carbon molecular sieve membrane by an impregnation method, thereby obtaining a carbon molecular sieve membrane with high hydrogen / methane, hydrogen / nitrogen and hydrogen / carbon dioxide separation performance, thereby further improving the screening ability of the carbon molecular sieve membrane for small molecule gases such as hydrogen;

[0007] The specific steps include:

[0008] (1) Preparation of polymer precursor film: polymer A is dissolved in solvent B to form a casting solution, the casting solution is fully stirred, poured into a watch glass, and after the solvent is completely evaporated at a certain temperature, the solvent is further dried under vacuum conditions to obtain a polymer precursor film;

[0009] (2) Preparation of carbon molecular sieve membrane: The polymer precursor membrane was heated to 550°C in a tube furnace under an inert gas N2 atmosphere and maintained for 2 hours, and then naturally cooled to room temperature to obtain a carbon molecular sieve membrane;

[0010] (3) Post-treatment of carbon molecular sieve membrane: Place the carbon molecular sieve membrane in solution D, stir it constantly, soak it for a certain period of time, take out the carbon molecular sieve membrane and dry it under vacuum conditions.

[0011] Further, polymer A is a Trog base polymer ( Base), 6FDA-DAM polymer, 6FDA-DAM-DABA, Matrimid, and P84 polymer; solvent B is one of chloroform, N-methylpyrrolidone, and N,N-dimethylformamide; solution D is one of sodium hypochlorite, potassium persulfate, sodium persulfate, hydrogen peroxide, and potassium permanganate, or a mixture of two or more thereof.

[0012] Furthermore, in step (1), the mass fraction of the casting solution is 2%-20%; the time for sufficient stirring is 12-24 hours; and the solvent volatilization temperature is 25-80°C.

[0013] Furthermore, in step (3), the concentration of solution D is 50-800 ppm; the stirring rate is 100-1000 r / min; and the soaking time is 12-48 h.

[0014] Compared with the prior art, the present invention has the advantages that: through a simple post-treatment solution impregnation step, an oxidizing functional group is introduced into the carbon molecular sieve membrane to adjust the membrane pore size, thereby greatly improving the hydrogen sieving performance of the carbon molecular sieve membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the XRD spectra of Control Example 1 and Example 1.

[0016] Figure 2 It is the infrared spectrum spectra of reference example 1 and embodiment 1. DETAILED DESCRIPTION

[0017] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0018] The preparation method of the carbon molecular sieve membrane used in the present invention is as follows: dissolving the polymer into a chloroform solution to form a casting solution with a mass fraction of 2%, and then drying the polymer membrane after fully volatilizing naturally; then, cutting the 2×2 cm 2 The polymer membrane was heated to 550°C in a tube furnace under an inert gas N2 atmosphere and maintained for 2 hours, and then naturally cooled to room temperature to obtain the final carbon molecular sieve membrane.

[0019] Gas permeability test: The permeability test of the carbon molecular sieve gas separation membrane in the present invention adopts the constant volume variable pressure method, and the test temperature is 35°C.

[0020] Comparative Example 1

[0021] 0.2 g of Trog base polymer was dissolved in 9.8 g of chloroform solvent. After the solvent was fully evaporated naturally, the formed polymer film was further dried. Then, the cut 2×2 cm 2The Trog base polymer membrane is heated to 550° C. in a tube furnace under an inert gas N 2 atmosphere and maintained for 2 hours, and then naturally cooled to room temperature to obtain a Trog base carbon molecular sieve membrane.

[0022] Comparative Example 2

[0023] 0.2 g of 6FDA-DAM-DABA polymer was dissolved in 9.8 g of chloroform solvent. After the solvent was fully evaporated naturally, the formed polymer film was further dried. After that, the cut 2×2 cm 2 The Trog base polymer membrane was heated to 550°C in a tube furnace under an inert gas N2 atmosphere and maintained for 2 hours, and then naturally cooled to room temperature to obtain a 6FDA-DAM-DABA carbon molecular sieve membrane.

[0024] Comparative Example 3

[0025] 0.2 g of 6FDA-DAM polymer was dissolved in 9.8 g of chloroform solvent. After the solvent was fully evaporated naturally, the formed polymer film was further dried. 2 The Trog base polymer membrane was heated to 550°C in a tube furnace under an inert gas N2 atmosphere and maintained for 2 hours, and then naturally cooled to room temperature to obtain a 6FDA-DAM carbon molecular sieve membrane.

[0026] Example 1

[0027] The Trog base carbon molecular sieve membrane was prepared according to the same preparation route. The prepared Trog base carbon molecular sieve membrane was placed in an 800 ppm sodium hypochlorite solution, and was immersed for 12 hours at a stirring rate of 800 r / min. The carbon molecular sieve membrane was taken out and placed in a vacuum drying oven at 80° C. for drying for 24 hours.

[0028] Example 2

[0029] The 6FDA-DAM-DABA carbon molecular sieve membrane was prepared according to the same preparation route. The prepared 6FDA-DAM-DABA carbon molecular sieve membrane was placed in an 800 ppm sodium hypochlorite solution, and was immersed for 12 hours at a stirring rate of 800 r / min. After the carbon molecular sieve membrane was taken out, it was placed in a vacuum drying oven at 80°C for drying for 24 hours.

[0030] Example 3

[0031] The 6FDA-DAM carbon molecular sieve membrane was prepared according to the same preparation route. The prepared 6FDA-DAM carbon molecular sieve membrane was placed in an 800 ppm sodium hypochlorite solution and immersed for 12 hours at a stirring rate of 800 r / min. The carbon molecular sieve membrane was taken out and placed in a vacuum drying oven at 80°C for drying for 24 hours.

[0032] The gas separation performance of control examples 1, 2, 3 and examples 1, 2 / 3 at 35°C, 2Bar is shown in the following table. By comparing control example 1 with example 1, control example 2 with example 2, and control example 3 with example 3, we can find that the hydrogen / methane and hydrogen / nitrogen selectivities of the modified Trog base carbon molecular sieve are increased by 119.5% and 29.6% respectively; the hydrogen / methane and hydrogen / nitrogen selectivities of the modified 6FDA-DAM-DABA carbon molecular sieve are increased by 1167.6% and 458.5% respectively; the hydrogen / methane and hydrogen / nitrogen selectivities of the modified 6FDA-DAM carbon molecular sieve are increased by 470.2% and 106.2% respectively. At the same time, the originally low hydrogen / carbon dioxide separation capacity has also been significantly improved.

[0033] Table 1 shows the gas permeability and selectivity of the gas separation membranes prepared in Control Example 1, Control Example 2, Control Example 3, Example 1, Example 2 and Example 3.

[0034]

[0035]

Claims

1. A modification method for improving the gas separation performance of a carbon molecular sieve membrane, characterized in that: The following steps are involved: (1) Preparation of polymer precursor film: polymer A is dissolved in solvent B to form a casting solution, the casting solution is fully stirred, poured into a watch glass, and after the solvent is completely evaporated at a certain temperature, the solvent is further dried under vacuum conditions to obtain a polymer precursor film; (2) Preparation of carbon molecular sieve membrane: The polymer precursor membrane was heated to 550°C in a tube furnace under an inert gas N2 atmosphere and maintained for 2 hours, and then naturally cooled to room temperature to obtain a carbon molecular sieve membrane; (3) Post-treatment of carbon molecular sieve membrane: Place the carbon molecular sieve membrane in solution D, stir it constantly, soak it for a certain period of time, take out the carbon molecular sieve membrane and dry it under vacuum conditions.

2. The modification method according to claim 1, characterized in that: The polymer A is a Trog base polymer, One of 6FDA-DAM, 6FDA-DAM-DABA, Matrimid, and P84 polymers.

3. The modification method according to claim 1, characterized in that: The solvent B is one of chloroform, N-methylpyrrolidone and N,N-dimethylformamide.

4. The modification method according to claim 1, characterized in that: The solution D is one or a mixture of two or more of sodium hypochlorite, potassium persulfate, sodium persulfate, hydrogen peroxide and potassium permanganate.

5. The modification method according to claim 1, characterized in that: In step (1), the mass fraction of the casting solution is 2%-20%.

6. The modification method according to claim 1, characterized in that: In step (1), the time for sufficient stirring is 12-24 hours.

7. The modification method according to claim 1, characterized in that: In step (1), the solvent volatilization temperature is 25-80°C.

8. The modification method according to claim 1, characterized in that: In step (3), the concentration of solution D is 50-800 ppm.

9. The modification method according to claim 1, characterized in that: In step (3), the stirring rate is 100-1000 r / min.

10. The modification method according to claim 1, characterized in that: In step (3), the soaking time is 12-48 hours.

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