Preparation and application of the hottest organic

2022-07-23
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Preparation and application of organic/inorganic supported composite membrane (II)

3 surface polymerization method

the polymer is compounded on the surface or pore of inorganic supported membrane by chemical method. One is to copolymerize or homopolymerize monomers directly on the surface of the inorganic membrane, which will cause the sample to break at the fixture and lead to the failure of the experiment. There is a physical interaction between the inorganic membrane and the polymer membrane; The second is to modify the surface of the inorganic membrane so that the surface of the inorganic membrane has an active site, and then carry out monomer graft polymerization through the active site. Here, the inorganic membrane and the polymer membrane are connected by chemical bonds

3.1 surface in situ polymerization

3.1.1 gas phase polymerization

li siloxane (SP)/inorganic composite membranes were prepared by gas phase polymerization on porous glass. The monomers used are dichlorodimethyl silane and dichloromethyl vinyl silane, and the catalyst is NH3 or (NH2) co3 H2O。 The gas permeation experiment of SP/glass composite membrane is carried out. The experimental results are as follows: for gases with low solubility, such as he, H2, N2, Co, O2, AR, their permeation rate increases with the increase of temperature; On the other hand, for highly soluble gases, such as C2H4 and CO2, their penetration rate decreases with the increase of temperature [27]

3.1.2 solution polymerization

one of the significant organic materials for preparing composite membranes is gel. A remarkable property of gel is that when oil leakage, pH, ionic composition, solvent composition or electric field are found in the internal environment of gel, reversible volume changes will occur in the gel. It is this reversible change in the internal volume of gel that makes the gel membrane effectively separate the organic solvent/water mixture [28~30]. The mechanical strength of the gel is too strong to form its own separation membrane, so it must be compounded on the support membrane. Sakohara prepared polyacrylamide gel (PAM)/ceramic composite membrane [28], immersed the cleaned ceramic membrane in ammonium persulfate initiator solution, took it out and washed the ammonium persulfate on the outer wall of the ceramic membrane with distilled water; Then the membrane was quickly immersed in the mixed solution of acrylamide, N, n '- methylene bisacrylamide and N, N, n', n '- tetramethyl vinyl diamine crosslinker at 70 ℃, and reacted for 2h under the protection of N2. The membrane was taken out of the solution and soaked in boiling water for 2h to prepare paa/ceramic composite membrane. Applying this membrane to the total evaporation of acetone/water is bound to constitute a demonstration driving effect experiment, and a considerable water flux is obtained. When the content of acetone in the raw material reaches 95 mol%, the separation coefficient of this membrane is as high as 2000. This high separation coefficient is mainly due to the shrinkage of the complex structure of PAA with the increase of the content of acetone in the raw material, which blocks the penetration of acetone molecules

3.1.3 electrochemistry and photochemical synthesis

these two methods are to compound a layer of ultra-thin polymer film on the microporous inorganic film. Liu studied the polymerization of divinyl (DVB) and ethyl vinyl benzene (EVB) on the surface of ceramic membrane by electrochemical method [31]. These two monomers were electrochemically reduced to anions in electrolyte solution, and then polymerized on the surface of modified ceramic membrane through anionic polymerization mechanism to form DVB EVB copolymer. The results of gas transport experiment, chronoamperometry and chronoamperometry show that the composite film is selective and defect free. In photochemical synthesis, free radical polymerization is carried out for monomers, so there are many organic monomers used to prepare composite membranes. Table 2 lists the composition of some membranes prepared on inorganic support membranes by photochemical synthesis and their monomers. The gas permeation experiment was carried out with No. V vinyl ferrocene divinylbenzene copolymer/al2o3 ceramic membrane in Table 2. The separation coefficient of o2/n2 was 8.0 and the membrane thickness was 40~3200 nm[32]

3.2 surface grafting polymerization

3.2.1 nanotechnology grafting method

can also introduce the third and fourth monomers x3-r3-x3 and x4-r4-x4 into the membrane for contact reaction when the copolymerization reaches a certain degree. Theoretically, by controlling the number of repeated reactions, the length of polymer chains bonded on the surface of ceramic membrane and the pore wall of membrane can be controlled, so as to control the pore diameter of composite membrane. Therefore, this method is of great significance in both theoretical research and practical application

okazaki and sawamoto et al. Modified the surface of porous ceramic membrane with (C2H5O) 3si- ch2ch2ch2nh2 (3-aminopropyltriethoxysilane) to make the inorganic membrane surface with -nh[33, 34]2. Okazak adopts a liquid-phase nanotechnology grafting process. The solution of anhydride and diamine contacts with the modified ceramic film respectively to form a polyimide (PI) composite film on the surface. The repeated reaction process of anhydride and diamine on -nh2 modified ceramic membrane is shown in Figure 2. The separation coefficient of co2/ch4 by pi/ceramic composite membrane varied from 1.0 to 6.4, and the molecular retention ranged from 400 to 4000. In the grafting process of liquid phase nanotechnology, the residual monomers after each reaction were not cleaned, and these monomers participated in the reaction in the subsequent reaction, resulting in the blockage of membrane pores. In view of the difficulty in cleaning the residual monomers, sawamoto switched to the gas phase nano grafting process. The reaction raw materials and steps were similar, but each reactant was in contact with the ceramic membrane in the gaseous form. The separation coefficient of the obtained pi/ceramic composite membrane for co2/ch4 ranged from 0.87 to 16[34]

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