The performance of carbon molecular sieves and zeolite 5A was compared in a four-bed vacuum pressure swing adsorption process. The purpose of the process is to sequester CO2 from a CH4/CO2 mixture gas, such as coal bed methane or landfill gas. This study investigated the effects of the design variables and operating variables on methane purity, recovery, and specific power through simulations of the process using the two adsorbents. The adopted design variables for the investigation are the packing bed length and the diameter of the adsorption bed, and the selected operating variables are the adsorption pressure and vacuum pressure. The simulation results show that zeolite 5A is better than carbon molecular sieve in terms of power, especially under low-pressure operating conditions with a vacuum pressure of 1,000 Pa. However, carbon molecular sieves are better in terms of purity enhancement when the vacuum pressure is higher than approximately 2,000 Pa.