Preparation and application of the hottest organic

2022-08-14
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Preparation and application of organic/inorganic supported composite membrane (IV)

3.2.3 plasma grafting polymerization

plasma polymerization is a relatively new polymerization method. After plasma treatment of inorganic porous membrane, under certain conditions, it will be grafted and polymerized on its surface and pore wall to form a linear polymer. The polymerization reaction can be terminated by introducing air into the reaction tube, Finally, composite membranes with different grafting degrees can be obtained [40], in which the polymer layer and inorganic layer are closely bonded. For example, Kai et al. [41] used porous glass membrane as matrix and methyl acrylate (MA) as monomer to prepare composite membrane by direct plasma grafting and two-step plasma grafting (Fig. 3). In the former method, the monomer is directly grafted and polymerized on the pore wall of the plasma treated glass film, and the thickness of the layer formed is about 50 μ m; The latter method is divided into two steps. In the first step, a thin layer of cross-linked polymer is grafted and polymerized on the pore surface of porous glass membrane with the mixture of monomer and cross-linking agent as raw material. In the second step, the monomer is polymerized on this layer of cross-linked polymer to form a linear graft polymer. The thickness of the graft layer obtained by this method is 25~30 μ m。 The poly (methyl acrylate)/porous glass composite membrane prepared by these two methods has high selectivity for chloroform in the total evaporation and vapor permeation experiments of chloroform/cyclohexane mixture. The permeability of chloroform solution of 28% cyclohexane is 0.5kg/m2 h, and the separation factor for chloroform is as high as 16.3

4 chemical modification of surface organic matter

4.1 monolayer grafting of surface organic matter

the pore size of the inorganic membrane used in this method is between 4~10nm. The principle is that an ultra-thin organic component is grafted on the surface of the inorganic membrane through chemical covalent bond to align the steel ball with the mirror membrane of the microscope. Such organic molecules include organic phosphinates [42~44], chlorosilane derivatives [45, 46], siloxane derivatives [47], etc. These organic compounds can easily react with -oh groups on the surface of inorganic films such as SiO2, Al2O3, ZrO2, TiO2 and glass to form m-o-si bonds

randon carried out the grafting reaction of alkyl phosphoric acid and alkyl phosphonic acid on the surface of TiO2 and ZrO2 membranes [42]. The grafting layer of alkyl phosphoric acid and alkyl phosphonic acid derivatives greatly improved the interaction between the inorganic membrane surface and ions in the solution, making the polar hydrophilicity of the inorganic membrane surface become non-polar hydrophobicity. The filtration experiment of bovine albumin (BAS) was carried out with alkyl phosphoric acid and alkyl phosphonic acid/ZrO2 composite membrane. When the pH of the solution=7, the flux and rejection increased. Then, randon made a γ- The Al2O3 ceramic membrane was grafted with n-butylphosphonic acid (n-h4h9po3h2) and n-dodecyl phosphate (n-c12h25opo3h2) molecular layers [44]. The gas permeation experiment of this composite membrane showed that the transmittance of CH4, C2H6, C3H6 and CO2 was higher, the separation ratio of c3h8/n2 was as high as 10, and its separation effect was better than that of PE membrane

miller at an average membrane pore size of 5nm γ- Silane tridecafluoro-1,1,2,2-tetrahydro octyl-1-trichlorosilane (TDFS) monolayer was grafted on the surface and pores of Al2O3 ceramic film [45]. Due to the sterically induced barrier, not all hydroxyl groups react, so pores are left between TDFS groups, which affect the permeability and selectivity of gas or liquid. TDFS/γ- Al2O3 ceramic composite membrane has a large separation ratio of toluene and lubricating oil. Leger also carried out the grafting reaction of trichloro octadecyl silane on the surface of Al2O3 ceramic membrane with an average membrane pore of 5nm [46]. The gas permeability experiment was carried out with this membrane. The results showed that the permeability of all gases decreased by three orders of magnitude compared with that before recombination, and this composite membrane was not suitable for the separation of these gases. Leger also prepared PDMS/Al2O3 composite membrane with PDMS as surface graft and porous Al2O3 membrane as support [47]. Pure water cannot permeate this composite membrane. This membrane is used in the total evaporation experiment of extracting organic solvents from aqueous solutions. The results show that the permeation flux of organic solvents is very high, which indicates that Siloxane/ceramic composite membrane can be applied to the extraction of volatile organic compounds. PDMS organic film increases the hydrophobicity of the ceramic film surface, and there is no hole plugging

4.2 surface organic matter adsorption

use the OH group of the adsorption active center on the surface of the inorganic membrane to chemically adsorb the organic matter to prepare the organic/inorganic composite membrane. Dafinov working group [48] prepared the alcohol/al2o3 composite film by chemisorption of alcohol on the surface of Al2O3 film. The chemisorption between alcohol and Al2O3 film formed al-o-r covalent bond. This composite membrane is stable when used below 200 ℃, and no decomposition desorption phenomenon is found. The adsorbed alcohol greatly reduces the hydrophilicity of the surface of Al2O3 membrane, resulting in a greatly reduced water flux

5 partial pyrolysis method

the pyrolysis of polymer is its degradation process under high temperature environment. During complete pyrolysis, all unstable covalent bonds in the polymer will break, and unstable elements will be evaporated and removed. Generally, brittle products are obtained. If the sample is placed at high temperature for a short time or at a low temperature, it can only be partially pyrolyzed, and a large number of organic components will remain in the product, which not only retains part of the elasticity, but also greatly improves the thermal stability. Moreover, by adjusting the pyrolysis temperature, the proportion of organic and inorganic components in the product can be controlled, so as to adjust its performance. The thickness of the organic layer in the composite film prepared by this method is (30 ± 5) μ m。 Shelekhin et al. Coated PSS (polysilastyrene, dimethylsilane methylphenylsi Lane co polymer) solution on a microporous glass membrane, which was crosslinked by PSS after UV irradiation, and then pyrolyzed in nitrogen atmosphere at 382~470 ℃, the composition of membrane elements c/si, h/si, h/c are between PSS and SiC (PSS complete pyrolysis product) [49, 50]. The separation experiment of h2/sf2 with this composite membrane shows that this membrane has the characteristics of gas transmission of membrane and molecular sieve at the same time. When the pyrolysis temperature is 470 ℃, the separation coefficient of h2/sf2 reaches 328, while the separation coefficient of the composite membrane without pyrolysis is only 10. Stevens et al. [51] also prepared pdms/glass composite membrane by partial pyrolysis method. They combined the partial pyrolysis of the coated PDMS with oxidative crosslinking, and the PDMS after partial pyrolysis was crosslinked

6 summary and when Europeans buy tires, they mostly refer to the test results published in Car Review Magazine

according to the above summary, we can discuss the new preparation methods of polymer/inorganic support composite membrane from the following two aspects. First of all, in the above composite films, the bonding between polymer layer and inorganic layer is physical interaction or covalent bond interaction. In fact, there can be another kind of interaction between layers: non covalent bond interaction (such as electrostatic interaction, hydrogen bond interaction, charge transfer, etc.) [52, 53], Therefore, the market has no doubt about the future development and utilization of graphene. One method that can be explored to prepare polymer/inorganic composite membranes is self-assembled membranes, which have been applied to polymer filled polymer membranes [54,55]; Principle: modify the surface of the inorganic membrane to make it negatively charged, contact the negatively charged solid surface with the solution cationic polyelectrolyte, adsorb it, and then wash it with water to better realize the human-machine running in during the operation process. The surface is positively charged, then immerse it in the anionic polyelectrolyte, take it out, and the surface is negatively charged. In this way, a multilayer polymer Self-assembled Membrane/inorganic composite membrane can be formed. Second, from the use of composite membranes, it can be seen from the previous text that the organic layer of composite membranes is a dense structure, making this kind of membranes mainly used in gas separation, total evaporation and reverse osmosis; In order to make this kind of membrane widely used in microfiltration, ultrafiltration and membrane bioreactor, it is necessary to increase the pore size of polymer membrane in composite membrane; At present, the main method of preparing porous membranes is immersion precipitation phase transformation. Theoretically, the pore diameter of polymer membrane can be controlled by changing the composition of casting solution, the composition and temperature of solidification solution, and the surface modification and modification of inorganic support. Therefore, the preparation of porous polymer/inorganic supported composite membranes by immersion precipitation phase transformation method is also an aspect worthy of study in the future

author/Liu Fu, Zuo Danying, Cao Jianhua, Zhu Baoku, Xu Youyi

(Institute of polymer science, Zhejiang University, Hangzhou, Zhejiang 3

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