Kinetic separation of methane—carbon dioxide mixture by adsorption on molecular sieve carbon

Abstract

Experimental and theoretical results are reported on pressure swing adsorption (PSA) for the separation of a methane/carbon dioxide mixture which has direct applications in landfill gas and tertiary oil recovery effluent separations. Molecular sieve carbon was used as the sorbent in which the diffusivity ratio for CO 2/CH 4 is 180 at 298 K. The difference in diffusivities was used as the basis for kinetic separation.The cycle time was chosen to allow substantial sorption of CO 2 but preclude penetration by CH 4 into the micropores. With a feed of 50/50 CO 2/CH 4, the typical results for a PSA cycle between 30 psig (3.04 atm) (feed pressure) and 5 psia (0.34 atm) at a cycle time of 120 s were: 90% CH 4 purity and over 90% CH 4 recovery at a feed throughput of 140 1STP/h/kg sorbent. Effects of the important kinetic separation parameters were shown. The separation results were simulated by a kinetic model in which a cycle-time-dependent linear-driving-force mass transfer coefficient was used. In addition, data are reported for equilibrium PSA separation using 5A zeolite. A comparison was made for: kinetic separation using molecular sieve carbon, equilibrium separation using 5A zeolite, and membrane separation. Based on separation performance, kinetic separation appeared to be superior.