Non-equilibrium Molecular Dynamic Simulation On Separation Of CO₂/CH₄ In Carbon Membranes

Natural gas as a clean energy and chemical raw materials are playing an increasingly important role to the development of national economy and environmental protection. Natural gas often contains carbon dioxide which was not only affect the gas calorific value but pipeline corrosion. So before application the separation and purification was needed. In this aspect, membrane especially carbon membrane separation technology is preferred in the existing technology for natural gas separation. Although many researches have been carried out in laboratory, there's still a long distance for industrial application. In the present time, the faultiness of the mechanism of gas separation in carbon membranes is one of the main reasons, which embarrasses the industrial application of the technology of gas separation in carbon membranes what is investigated using molecular dynamics simulation. In this paper, the slit-like pore model is revised for research.The permeation and separation of CO2 and CH4 binary mixtures in nanoporous carbon membranes and the gas separation mechanism are investigated using a dual control volume grand canonical molecular dynamics (DCV-GCMD) method in this paper.First, we focused on the carbon membrane pores are modeled as slit-like pore with buffer regions. The effects of the temperature, feed gas pressure and molar fraction of methane on flux and dynamic separation factor are discussed. The simulation results indicate that the flux of CH4 increases with the increase of temperature, while the separation factor declines, as pressure increases the effect of temperature on separation factor declines; With the increase of the pressure, the flux both of CO2 and CH4 increase but the separation factor declines; The effect of gas composition was studied, while the CH4 mole fraction increases, the flux declines, the separation factor declines, and there was no separating effect when the CH4 mole fraction is 0.7-0.9.Secondly, the effect of pore size distribution on gas separation through carbon membrane is preliminary studied by slit-like pore model. The simulation results indicate that the flux both of CO2 and CH4 increase with the increase of pore density parameter s, while the separation factor declines. When the s increase, the probability of macroporous increased, then gas flux increased; Compared with experimental data, conclusion that 0.3 is the optimum value of system. The model consider of pore size distribution is more similar with the actual membrane separation process.