The Simulation Of Removal Acidic Components From Natural Gas By Polymer Membrane

As an important energy, the demand of natural gas is growing rapidly, thus providing clean and efficient natural gas is becoming very significant. Membrane separation is a new and efficient method for the removal of acid gas of natural gas, so research for membrane materials have excellence performance is particularly important. Conventional gas separation membrane materials research and designing are time-consuming and non-economical. Molecular simulation can provide vehement supports for the research on the relationship between microstructure and macroscopic properties.Using Materials Studio molecular simulation software, the diffusion and dissolution behavior of CH4 and CO2 in polymer membrane materials was investigated. Through investigations, 10 typical polyimide materials were assured, simulation unit cell was built, Some basic parameters and properties of the models were confirmed, such as the fractional free volume, available free volume, dihedral angel distribution, the glass transition temperature, Wide Angle X-ray diffraction.The double adsorption model was adopted to simulate the solubility of models. The simulation results showed(1) Compared with polyimide based on PMDA, polyimide based on 6FDA and BTDA have better solubility and adsorption properties, and lower selectivity.(2) By investigating the relationship between the numbers of methyl replace and dissolve performance, it was found that the solubility coefficient of membrane is not simply increased as the increase number of methyl groups, the solubility coefficient of meta-substitution diamine was larger.(3) When the substituents in the polymer molecules were large or the three-dimensional structure of monomer is relatively complex, the free volume of polyimide is usual y higher.Using 3000 ps dynamics simulation time to simulate the diffusion process of gas in polymer. The simulation results showed(1) for the same main chain of polyimide materials, with the increase of replace methyl numbers, the spread of the overall performance was increased, too.(2) The selectivity of diffusion was not proportional to the complexity of the polyimide monomer molecules: the stronger diffusion ability of membrane materials had, the lower selectivity it had, among which 6FDA-TPPD had the best diffusivity and 6FDA-MPD had the best select diffusivity.(3)The change of molecular structure which was from meta-substitution diamine shift to para- substitution diamine can cause the coefficient of diffusion increased.Permeability coefficient and free volume of the membrane material has a dependency, increasing the free volume of the membrane material can enhance the permeability of the gas molecules.