Preparation method of CO2 separation composite membrane with both fixed / movable amino carriers

Abstract

The present invention is applicable to the field of gas membrane separation technology, and relates to a preparation method of a CO2 separation composite membrane with both fixed / mobile amino carriers. The polyacrylonitrile nanofiber membrane is prepared by electrospinning technology, and the PAN fiber membrane is hydrolytically modified with sodium hydroxide alkaline solution to introduce the fixed carrier amino group for transporting CO2. However, only the fixed carrier is prone to the "carrier saturation" phenomenon under the condition of relatively high CO2 partial pressure, and it is necessary to introduce the mobile carrier aniline to overcome the "carrier saturation" phenomenon. Aniline is mixed with a small molecule PEO series, and a dense gas separation membrane is in-situ photopolymerized in the pores of the PAN nanofiber membrane. After polymerization, the mobile carrier aniline is not easily lost. The fixed / mobile amino carriers can effectively promote the selective transport of CO2, realizing the high permeability and selectivity of the fiber composite membrane. At the same time, the interpenetrating network structure of the fibers can ensure that the membrane still has good dimensional stability under high amino carriers and moisture.

Description

Technical Field

[0001] The present invention is applicable to the technical field of gas membrane separation. The main content is to design a fiber composite membrane with both fixed / movable amino carriers, and utilize the facilitated transport effect of amino groups to improve the CO2 separation performance of the fiber composite membrane. Background Art

[0002] At present, carbon peak and carbon neutrality have attracted wide attention. The emission of carbon dioxide has led to many problems, such as the greenhouse effect, glacier melting, pipeline corrosion, and deterioration of the animal living environment. Therefore, CO2 capture is an important issue that needs to be solved urgently in human society in the 21st century. Traditionally, the separation of CO2 mainly uses cryogenic separation, adsorption, solvent absorption, etc. Gas membrane separation technology is a new separation technology for CO2 capture. Compared with traditional separation methods, it has the advantages of low energy consumption, small footprint, low investment, and convenient operation. It is a low-energy sustainable development technology with great application potential. The key to membrane separation technology is to prepare membrane materials with excellent performance.

[0003] Among numerous CO2 separation membranes, polymer membranes based on solution-diffusion are the most widely studied gas separation membranes. However, due to the mutual restriction between permeability and selectivity, it is difficult for polymer membranes based on solution-diffusion to break through the Robeson upper bound in terms of CO2 separation performance. Polymer membranes based on facilitated transport principle introduce CO2 facilitated transport carriers into the membrane, and the transport of CO2 is achieved through the movement of the carriers or the jump of CO2 from one carrier to another. The CO2 separation performance of this type of membrane is extremely excellent and can break through the Robeson upper bound. According to whether the carrier can migrate, facilitated transport membranes can be divided into three types: (1) mobile carrier membranes, where the carriers can migrate freely in the membrane; (2) semi-mobile carrier membranes, where the carriers are attracted in the membrane and can migrate from one place to other places; (3) fixed carrier membranes, where the carriers can only vibrate within a limited nanospace and cannot migrate to other places. Carriers are groups such as amino and carboxyl groups. CO2 carriers can transport CO2, thereby separating CO2 from other gases such as N2 and CH4. From a thermodynamic perspective, compared with the solution-diffusion mechanism, introducing reversible reactions is beneficial to obtaining higher energy efficiency. By introducing facilitated transport carriers, the reactive selectivity of the carriers is borrowed to overcome the mutual restriction between permeability and selectivity. Currently used types of fixed carrier membranes include polyvinylamine (PVAm) series, polyetherimide (PEI) series, etc. Due to their high crystallinity (DOI: 10.1016 / j.cjche.2018.07.010), the permeability of these membranes is relatively poor; the main type of mobile carrier membranes is liquid membranes, such as supported liquid membranes (SLM) loaded with ionic liquids or small molecule amine carriers. Due to insufficient stability and easy loss of carriers or solvents (DOI: 10.1021 / acs.chemrev.7b00072), such membranes are rarely applied on a large scale. Therefore, the present invention proposes to introduce amino fixed carriers by electrospun fibers and then introduce amino mobile carriers by in-situ polymerization in the fiber gaps. The fixed / mobile amino carriers can effectively promote the selective transport of CO2, achieving high permeability and selectivity of the fiber composite membrane. At the same time, the interpenetrating network structure of the fibers can ensure that the membrane still has good dimensional stability under high amino carrier and humid conditions. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to design a fiber composite membrane rich in fixed / mobile amino carriers, which promotes the selective transport of CO2 by introducing amino carriers to achieve high gas selectivity and permeability. At the same time, the interpenetrating network structure of the fibers can ensure that the membrane still has good dimensional stability under high amino carrier and humid conditions.

[0005] The present invention designs a CO2 separation composite membrane with both fixed / mobile amino carriers. First, polyacrylonitrile (PAN, average molecular weight: 149,000 - 151,000) is selected as the spinning material, and polyacrylonitrile can be easily spun into a fiber membrane. The spun fiber membrane has a high specific surface area to volume ratio and good mechanical properties, making it very suitable for application in the field of membrane separation. Since there is no CO2 carrier on the fiber membrane spun from polyacrylonitrile, a sodium hydroxide alkaline solution is used to hydrolyze and modify the electrospun PAN fiber membrane (PAN NFM). This is because the nitrile group (-CN) on polyacrylonitrile can be easily modified and modified by primary amines, ethanolamine, sodium hydroxide, and oxygen plasma. The hydrolyzed fiber membrane (HPAN NFM) contains a fixed carrier amino group. Due to the high porosity, large specific surface area to volume ratio of the electrospun fiber membrane, it can provide a large number of sites for the facilitated transport of CO2. However, only the fixed carrier is prone to the phenomenon of "carrier saturation" under relatively high CO2 partial pressure conditions. Therefore, introducing a mobile carrier can overcome "carrier saturation". Here, polyethylene glycol diacrylate (PEGDA, average molecular weight: 600) in the small molecule PEO series polymer and small molecule aniline are used to infiltrate into the internal voids of the HPAN fiber membrane through ultrafiltration assistance, and in-situ polymerization in the voids under UV ultraviolet light irradiation is used to fill the voids of the electrospun fiber, preparing a dense aniline / PEO@HPAN fiber composite membrane (NFCM). The HPAN fibers interspersed, interconnected, and misaligned and stacked in the membrane contain abundant amino groups, forming a fixed carrier. In addition, the small molecule aniline also contains an amino group, forming a mobile carrier that can transport CO2. The ether oxygen bond (-O-) of PEO has a strong affinity for CO2, making the mobile carrier aniline not easily lost after photopolymerization. On the other hand, the HPAN fibers form a gas transport path that zigzags along one-dimensional fibers in the membrane, increasing the gas transport path, thereby increasing the CO2 / N2 selectivity of the membrane. At the same time, the HPAN fibers and the aniline / PEO polymer form a "steel bar - concrete" structure, which can ensure that the membrane still has good dimensional stability under high amino carrier and humid conditions.

[0006] The technical solution of the present invention:

[0007] A preparation method of a CO2 separation composite membrane with both fixed / mobile amino carriers, the steps are as follows:

[0008] (1) Prepare a polyacrylonitrile fiber membrane by electrospinning technology

[0009] Configure an N,N-dimethylformamide solution of polyacrylonitrile with a concentration of 10wt%, prepare a polyacrylonitrile fiber membrane by electrospinning, and dry the polyacrylonitrile fiber membrane under vacuum conditions to completely remove the residual N,N-dimethylformamide.

[0010] (2) Introduction of a fixed amino group carrier by hydrolysis of the polyacrylonitrile fiber membrane

[0011] Prepare a 2 mol / L sodium hydroxide solution. Immerse the polyacrylonitrile fiber membrane in the 2 mol / L sodium hydroxide solution at 50 °C for 3 hours. After taking it out, wash the polyacrylonitrile fiber membrane with deionized water multiple times until it is neutral, and then dry it to obtain a functionalized hydrolyzed polyacrylonitrile fiber membrane.

[0012] (3) Introduction of a mobile amino group carrier into the polyacrylonitrile fiber membrane

[0013] Prepare a polyethylene glycol diacrylate solution of the mobile carrier aniline with a concentration of 5 - 15 wt%. Then add 1 wt‰ photoinitiator 1-hydroxycyclohexyl phenyl ketone to obtain a polymer filling solution. Place the filling solution in a light-proof environment, stir it evenly, and perform ultrasonic degassing for standby. Then use the ultrafiltration method to fully wet the functionalized hydrolyzed polyacrylonitrile fiber membrane. During the ultrafiltration process, the polymer filling solution should completely penetrate into the voids of the functionalized hydrolyzed fiber membrane. Wipe the excess filling solution on the surface with filter paper. Irradiate the fiber composite membrane with a UV lamp of 308 - 312 nm in an argon environment for more than 10 minutes to cure and crosslink the filling solution to obtain an aniline / PEO@HPAN fiber composite membrane.

[0014] Advantages of the present invention: Aiming at the problems of poor gas permeability, low selectivity, low mechanical properties, high crystallinity of the facilitated transport membrane, and easy loss of the carrier in traditional polymer membranes, the present invention proposes to prepare a polyacrylonitrile fiber membrane by electrospinning. Functionalized hydrolysis makes the fiber filaments contain fixed carrier amino groups. The functionalized hydrolyzed polyacrylonitrile fiber membrane has a large specific surface area and good mechanical properties, providing a tortuous transport channel for gas transmission. At the same time, the amino group is beneficial to enhancing the affinity between the membrane and CO2, improving the CO2 / N2 selectivity. Using aniline / PEGDA as the filling solution fills the voids between the fibers. The polymerization of PEGDA makes the mobile carrier aniline not easy to lose. Aniline as a mobile carrier can transport CO2, making the membrane have high permeability and selectivity. At the same time, the interpenetrating network structure of the fibers can ensure that the membrane still has good dimensional stability under high amino group carriers and moisture, and has more practical value in industry. Description of the Drawings

[0015] Figure 1 It is the SEM image of the surface of the PAN fiber membrane in the example.

[0016] Figure 2 It is the SEM image of the surface of the HPAN fiber membrane in the example.

[0017] Figure 3 It is the SEM image of the surface of the aniline / PEO@HPAN fiber composite membrane in the example.

[0018] Figure 4SEM cross-sectional view of aniline / PEO@HPAN fiber composite membrane in the embodiment. Specific Embodiments

[0019] The following further illustrates the specific embodiments of the present invention in conjunction with the accompanying drawings and technical solutions.

[0020] Example 1

[0021] Prepare a polyacrylonitrile electrospun fiber membrane: Prepare 10 g of an N,N-dimethylformamide solution with a concentration of 10 wt% polyacrylonitrile. After dissolution, use an electrospinning machine to prepare a PAN electrospun fiber membrane. Dry the fiber membrane under vacuum at 50 °C for 12 hours to completely remove the residual N,N-dimethylformamide. Cut it into strips of 7×12 cm for later use.

[0022] Prepare a functionalized hydrolyzed polyacrylonitrile fiber membrane: Prepare a 2 mol / L sodium hydroxide solution and place it in an oven at 50 °C for later use. Put the prepared polyacrylonitrile fiber membrane into a crystallization dish, use a glass rod to drain the sodium hydroxide solution, drive away the bubbles, then place it in an oven at 50 °C for 3 hours. Then wash the polyacrylonitrile fiber membrane with deionized water until neutral, dry it at room temperature for 1 hour, and dry it in a vacuum oven at 50 °C for 12 hours to obtain a functionalized hydrolyzed polyacrylonitrile fiber membrane.

[0023] Prepare a gas separation membrane: Prepare 20 g of a poly(ethylene glycol) diacrylate (PEGDA) solution with a mobile carrier aniline at concentrations of 5, 10, and 15 wt%. Then add 1 wt‰ photoinitiator 1-hydroxycyclohexyl phenyl ketone to prepare a polymer filling solution. After preparation, place it in a dark environment and stir evenly at room temperature. Before use, perform ultrasonic treatment to remove the bubbles in the solution. Put the prepared functionalized hydrolyzed polyacrylonitrile fiber membrane into an ultrafiltration cup, add an appropriate amount of filling solution, perform ultrafiltration with 0.1 Mpa of N2. After ultrafiltration, wipe the excess filling solution on the membrane surface with filter paper, put it into a glass tube, introduce argon to drive out the air, and irradiate it with an ultraviolet lamp for more than 10 minutes to obtain an aniline / PEO@HPAN fiber composite membrane.

[0024] Comparative Example 1

[0025] Prepare a PEO@PAN fiber composite membrane without amino groups: First, the steps for preparing a polyacrylonitrile electrospun fiber membrane are the same as in Example 1. Then prepare a gas separation membrane. Prepare 20 g of a poly(ethylene glycol) diacrylate solution, and then add 1 wt‰ photoinitiator 1-hydroxycyclohexyl phenyl ketone to prepare a polymer filling solution. The ultrafiltration process is the same as in Example 1.

[0026] Comparative Example 2

[0027] Preparation of PEO@HPAN fiber composite membrane containing only fixed carriers: The steps of preparing polyacrylonitrile electrospun fiber membrane and functionalized hydrolyzed polyacrylonitrile fiber membrane are the same as those in Example 1. Then, a gas separation membrane is prepared. 20 g of polyethylene glycol diacrylate solution is configured, and 1 wt‰ photoinitiator 1-hydroxycyclohexyl phenyl ketone is added to configure a polymer filling solution. The ultrafiltration process is the same as that in Example 1.

[0028] Comparative Example 3

[0029] Preparation of aniline / PEO@PAN fiber composite membrane containing only mobile carriers: First, prepare a polyacrylonitrile electrospun fiber membrane, and then prepare a gas separation membrane. The two steps are the same as the first three steps in Example 1.

[0030] The gas separation performance of the aniline / PEO@HPAN fiber composite membrane prepared in Example 1, the PEO@PAN fiber composite membrane without amino groups prepared in Comparative Example 1, the PEO@HPAN fiber composite membrane containing only fixed carriers prepared in Comparative Example 2, and the aniline / PEO@PAN fiber composite membrane containing only mobile carriers prepared in Comparative Example 3 was tested. The gas separation performance is shown in Table 1. Among them, the best performance is the 10% wt aniline / PEO@HPAN fiber composite membrane. Its CO2 permeability reached 124.08 Barrer and the CO2 / N2 selectivity was 95.47 in the pure gas test at 0.3 Mpa and 25 °C. Compared with the PEO@PAN fiber composite membrane without amino groups, the PEO@HPAN fiber composite membrane containing only fixed carriers, and the 10% wt aniline / PEO@PAN fiber composite membrane with the best performance containing only mobile carriers, the CO2 permeation performance increased by 29.20%, 37.70%, and 5.06% respectively; the CO2 / N2 selectivity performance increased by 18.02%, 2.88%, and 7.51% respectively. This shows that adding fixed and mobile amino carriers to the fiber composite membrane can greatly improve the CO2 / N2 separation performance.

[0031] Table 1: Pure gas separation performance of the fiber composite membranes of the examples and comparative examples at 0.3 Mpa and 25 °C

[0032]

Claims

1. A method for preparing a CO2 separation composite membrane with both fixed / movable amino carriers, characterized in that, The steps are as follows: (1) Prepare a polyacrylonitrile fiber membrane by electrospinning Prepare a solution of N,N-dimethylformamide with 10 wt% polyacrylonitrile, and prepare a polyacrylonitrile fiber membrane by electrospinning. Dry the polyacrylonitrile fiber membrane under vacuum conditions to completely remove the residual N,N-dimethylformamide; (2) Hydrolyze the polyacrylonitrile fiber membrane to introduce a fixed amino carrier Prepare a 2 mol / L sodium hydroxide solution. Immerse the polyacrylonitrile fiber membrane in the 2 mol / L sodium hydroxide solution at 50 °C for 3 hours. After taking it out, wash the polyacrylonitrile fiber membrane with deionized water multiple times until it is neutral, and then dry it to obtain a functionalized hydrolyzed polyacrylonitrile fiber membrane; (3) Introduce a mobile amino carrier into the functionalized hydrolyzed polyacrylonitrile fiber membrane Prepare a polyethylene glycol diacrylate solution of a mobile amino carrier aniline with a concentration of 5-15 wt%, and then add 1 wt‰ photoinitiator 1-hydroxycyclohexyl phenyl ketone to obtain a polymer filling solution; Stir the polymer filling solution evenly in a light-shielded environment, and ultrasonically degas it for standby; Then use the ultrafiltration method to fully wet the functionalized hydrolyzed polyacrylonitrile fiber membrane. During the ultrafiltration process, the polymer filling solution should be completely infiltrated into the voids of the functionalized hydrolyzed fiber membrane. Wipe the excess filling solution on the surface with filter paper to obtain a fiber composite membrane; Then irradiate the fiber composite membrane with a UV lamp of 308-312 nm for more than 10 minutes in an argon environment to cure and crosslink the filling solution to obtain an aniline / PEO@HPAN fiber composite membrane, which is the CO2 separation composite membrane.

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