Zigzag pore based molecular simulation on the separation of CO2/CH4 mixture by carbon membrane

A zigzag-type pore structure was proposed for the separation of a CO2/CH4 binary mixture by carbon molecular sieve membrane (CMSM). A defect-free pore and three kinds of defect pores, i.e., random, uniform, and partial defect, were considered to improve the separation performance. Adsorption and diffusion behaviours of pure gases and a gas mixture were simulated by the grand canonical Monte Carlo (GCMC) method and non-equilibrium molecular dynamics (NEMD) method, respectively. The pressure ranged from 10-100 kPa and the temperature was between 273-348 K during simulation. The calculated isotherms of CO2 and CH4 showed an acceptable agreement with the experimental data for the defect-free pores of 0.67 nm in size at 298 K. Examination on the effect of pore sizes showed that 0.67 nm was the appropriate option for separation. The total selectivity was 20.1 at 298 K and 100 kPa with the pore size of 0.67 nm, which is consistent with the experimental value. The adsorption was determined as the dominant separation mechanism between adsorption and diffusion. Compared with the defect-free pores, the introduction to the random and uniform defect pores can improve the total selectivities and the random defect provided superior separation performance. An appropriately low temperature and small pore size were beneficial to the separation.