The use of membranes for gas cleaning is a well established technology in chemical industries. The membrane is a porous material that let some gases permeate through its structure. Employing an adequate material, it is possible to have selectivity between the gases of the mixture to be separated. For this particular application, two different streams are obtained: a permeate gas (mainly CO2, water and ammonia) and the retentate (concentrated CH4). The most commonly employed materials are hollow fibres made of different polymers. Several companies provide this technology, being Air Liquide the largest company in this area (Air Liquide, 2011). In their process, the biogas is compressed to 16 bars and then routed to a two-stage membrane process where methane with purity higher than 90% can be obtained. To upgrade CH4 to a higher purity, a PSA process can be used in series.