The upgrading of biogas by pressure swing adsorption (PSA) was studied. Simulations of a process for binary separation of CH4-CO2 using zeolite 13X as selective adsorbent were carried out at 323 K. The results obtained with a two-column PSA process using a six-step cycle (pressurization, feed, depressurization, blowdown, purge, and pressure equalization) were compared with initial estimates by simulating the behavior of only one column. The recycle of highly contaminated streams was quantitatively evaluated in this paper. When recycled streams have purity lower than 99%, there is a significant decrease in the overall purity of biomethane. According to the simulations performed for a stream of biogas of 500 N m(3)/day, it is possible to obtain biomethane with a purity higher than 99% with a recovery of 85% and a power consumption of 0.12 kW/mol of produced methane.