Study On The Relationship Between The Structure And The Property Of Polyimide Membranes For Gasoline Desulfurization By Molecular Simulation

Membrane is the core of a pervaporation process. Its separation performances depend onthe properties of the corresponding membrane. Thus how to design and synthesis polymermembranes with good properties became the focus of the membrane study. Currently, most ofthe studies about pervaporation performances of membranes are taken by experiments. Time,labors and money are wasted on the preparation and characterization of the polymericmaterials with bad separation properties. Therefore, structure-property study of polymermembranes by computer simulation techniques are gaining an increasing importance.According to dissolution-diffusion model, the separation performance of pervaporationprocess is based on the dissolution of solvents in polymers and its diffusion ability inpolymers. In this study, polyimide that has good mechanical properties as well as thermal andchemical stability were chosen as the membrane material. And the miscibility properties ofthese different-structure polyimides and five gasoline components was studied by MonteCarlo method, besides the diffusion properties of five gasoline properties in differentpolyimide membranes were studied by Coarse-Grained dynamics simulation method.The Monte Carlo simulation results show that, the thiophene selective properties werehigh while dianhydride monomer containing-SO2and-CF3. In the temperature range of300K-500K, the free energy value of thiophene dissolved in DSDA-3MPDAis less than thatof other gasoline components, which indicated that DSDA-3MPDA has excellent thiophenesolubility selective properties. The thiophene solubility selective properties of polyimidemembranes were decreased according to the increase temperature. Diffusion simulation resultshowed that DSDA-3MPDA, DSDA-ODA,6FDA-3MPDA,6FDA-ODA,6FDA-BZD and6FDA-PDA all have comparatively good diffusion selective properties for thiophene, but thegeneral diffusion properties of gasoline components were low. Therefore,6FDA-PDA andflexible chain segment copolymer was designed, and the diffusion behavior of five gasolinecomponents in the copolymer was studied. The results showed that inset a flexible chain segment can improve the diffusion property of gasoline components, as well as keeping goodthiophene selective property of6FDA-PDA.