| The dehydration and recovery of organic solvents is very important in the fine chemicals, pharmaceutical chemicals, household chemicals,new energy and other fields. Traditionally, distillation, extraction or molecular sieves have been used to achieve the purpose of separating organics and water. Pervaporation, a new type of membrane separation technology, has rapidly developed and become efficient industrial separation technology. Studying the effect of different groups and polymers on the membrane separation performance at the molecular level is critical to the design of pervaporation membranes for specific functions and properties. By studying the adsorption and diffusion of small molecules on the membrane at the molecular level, it is possible to understand the mechanism of dissolution and adsorption of the permeable gas membrane better at the microscopic angle.In this paper, the molecular dynamics and the Monte Carlo method were used to study the modification and addition of new materials (ZIF,COF) of Polydimethylsiloxane (PDMS) on the separation performance of organic solvents. The main work is as follows:1. Study on the dissolution and diffusion of furfural/water molecules in PDMS membrane and PDMS / VTES membrane. It was found that when the introduction of vinyl content was half the molar amount of Si, the free volume of the membrane was twice as much as that of the original PDMS membrane, and the chain distance of the polymer chain changed from 7.05 to 7.59 Angstrom. These are favorable factors for the diffusion of small molecules. It can be seen that the diffusion of furfural in the membrane of vinyl: Si = 1/2 is the fastest. The more the amount of vinyl is introduced into the membrane, the higher the adsorption capacity of furfural is, while the amount of water adsorption almost unchanged. Finally, it was found that the selectivity of vinyl: Si ?1/2 membrane was 49.85, which was much higher than that of pure PDMS membrane (30.67), confirming the previous simulation conclusion.2. ZIF materials have been used by many researchers to construct PDMS-based mixed matrix membranes due to their excellent thermodynamic stability, flexible network structure and superhydrophobicity. In this paper, we mainly use the kinetic model to study the difference of the adsorption performance of various ZIF structures to butanol and the application of ZIF materials in gasoline desulfurization. The results showed that ZIF-3, ZIF-6 and ZIF-8 had better adsorption properties to butanol, and the adsorption capacity was much larger than that of PDMS. In the thiophene / benzene / isooctane simulation, it was found that the adsorption amounts of thiophene and benzene in ZIFs were higher than those of isooctane, but under medium and high pressure, Isooctane are hardly adsorbed in ZIF-8, which is superior to ZIF-3 and ZIF-6.3. COF-300 has large pore, hydrophobic characteristics,. Adding COF-300 to PDMS membrane will be a good way to improve the membrane separation of organic matter. The adsorption and diffusion properties of COF-300 material for butanol / water and the application of gasoline desulfurization were studied by molecular simulation. The results showed that the adsorption performance of COF-300 to butanol was not only much higher than that of PDMS, but also better than that of ZIFs. Although the diffusion rate of water was higher than that of butanol,in general, COF-300 is better in separating butanol / water mixtures relative to PDMS. In the adsorption of thiophene / benzene / isooctane, it was found that the adsorption capacity was very high when the three components were adsorbed separately. However, when the three components were adsorbed simultaneously, the amount of isooctane adsorbed decreases sharply with the increase of the total pressure. The amount of adsorption in the middle and high pressure zone is almost zero, which proves that it is effective to separate thiophene and benzene from isooctane. |
PDF Full Text Request