Simulation Of PI Mixed Matrix Membrane Modified Based On CO₂ Separation

Carbon dioxide is one of the main gases leading to global warming.How to effectively control and reduce carbon dioxide emissions is the focus of current research.Membrane separation has been widely used in the field of carbon dioxide separation because of its advantages of high separation efficiency,low energy consumption and simple operation.In the process of membrane separation,high gas permeability and selectivity has always been the research goal.And the preparation of new hybrid matrix membrane is an important approach to achieve this goal.At present,the study of membrane preparation and application of membranes to specific processes relies primarily on macroscopic experiments.However,there are few studies on the change of membrane microstructure and the effect of such change on gas separation performance by means of molecular simulation.Therefore,for polyimide（6FDA-DABA）system,molecular simulation technology was first used to simulate the structural properties and gas transmission characteristics of 6FDA-DABA membrane and aminosiloxane modified GO/6FDA-DABA membrane,and the transition states of two reaction processes of different aminosiloxane modified GO were simulated.The following conclusions are obtained:Molecular dynamics simulation was used to simulate the structure and properties of6FDA-DABA and the gas transport mechanism in the membrane.The dissolution coefficient（S）,S_CO2>S_N2,diffusion coefficient（D）and D_CO2is slightly less than D_N2.The calculated that the permeability of CO₂is 14.15 Barrer,and the selectivity of CO₂/N₂is 28.53.And in6FDA-DABA,the transport of CO₂and N₂in the membrane is dominated by the transport-dissolution selectivity of CO₂.Comparing the simulated data with the experimental data,the results of the two are consistent,which shows that the simulation results are reliable.Based on the above calculation,density functional theory（DFT）method is used to search the transition state of acyl amination reaction and esterification reaction of aminosiloxane modified GO,and the simulation results showed that the esterification reaction was easier to carry out.The adsorption isotherms of CO₂and N₂in NH/GO were simulated by Monte Carlo（GCMC）method and compared with the adsorption isotherms of CO₂and N₂of original GO materials.The simulation results show that 2NHGO has the best adsorption performance.Compared with the previous experimental results of the research group,the consistent result that 2NH/GO has the best adsorption capacity for CO₂,which supports the experimental results with simulations.Finally,the NH/GO modified 6FDA-DABA polyimide membrane was simulated.Firstly,the structural characteristics of modified PI membrane and the gas transport characteristics in the membrane were studied.The simulation results showed that the permeability of CO₂and N₂increased from 14.15 Barrer and 0.496 Barrer to 35.23 Barrer and 0.9 Barrer,respectively,and the selectivity increased from 28.53 to 39.15 for 2NH/GO/PI.The experimental values are basically consistent with the simulated values.The simulation results show that the larger the free volume is,the better the permeability of gas in the membrane material is.The increase of glass transition temperature increases the rigidity of polymer molecular chain and improves the diffusion performance of the membrane.The smaller the cohesion energy is,the smaller the intermolecular force is,and the better the diffusion performance of the polymer membrane is,which helps to explain the experimental phenomenon.