CO2/CH4 mixed-gas separation through carbon nitride membrane: A molecular dynamics simulation

We performed molecular dynamics simulations to study the performance of a pristine carbon nitride (C 2 N) membrane for separation of CO 2 /CH 4 gas mixture. The influences of system temperature (298, 323, and 348 K), applied pressure difference (up to 2000 kPa), and feed composition on the CO 2 /CH 4 separation were also explored. The permselectivity of the C 2 N membrane for separation of CO 2 /CH 4 mixture was theoretically determined. The highest CO 2 permeance of 1.32 × 10 6 GPU in the absence of applied external pressure was achieved. It is demonstrated that CO 2 molecules can easily diffuse through the membrane, while no CH 4 molecule was seen on the permeate side. Thus, an ultrahigh selectivity of CO 2 over CH 4 was achieved. The membrane indicated a superior performance, which easily exceeds the Robeson’s upper bound. The investigation of the gas permeation mechanism revealed that the preferential adsorption of CO 2 and suitable size of this molecule owing to proper orientation are two important factors for efficient separation of CO 2 from CH 4 by the C 2 N membrane. In fact, CO 2 molecules tend to reorient themselves close to the membrane nanopores to diffuse perpendicularly through. To this end, the density map and the potential of the mean force analysis were also conducted, which confirmed the simulation results. • Separation of CO 2 /CH 4 mixture was done through C 2 N membrane. • The C 2 N membrane showed the best CO 2 permeance of 1.32 × 10 6 GPU and ultrahigh CO 2 /CH 4 selectivity. • The C 2 N membrane performance surpassed the Robeson’s upper bound. • The permeation mechanism of CO 2 molecule was discussed. • The effect of feed composition on the separation performance was investigated.