In a similar manner to water scrubbing, it is possible to use other chemicals to absorb CO2. The technology is also composed by AN absorption tower where the chemical solvent is flushed to selectively absorb CO2. The saturated absorbent is then heated in a regeneration tower, releasing CO2. This technology is widely employed to clean large facilities in the natural gas industry. The selection of the solvent for this process is quite important since the "energy" of CO2 absorption dictates the final consumption of energy of the system. Chemicals which strongly absorb CO2 (like amines) are more suitable to upgrade methane with relatively low content of CO2 to a very high purity. This process may have higher energetic penalties since the CO2 removal in biogas is a bulk removal process. On the other side, for bulk CO2 removal to obtain a CH4 purity in the range 97-98%, physical solvents consume less energy being more energy efficient. Different examples of physical absorbents are: methanol, Selexol, Rectisol, Genosorb, Morphysorb, etc. Plants able to process biogas flowrates of 55 to 13000 m3/hour are in operation. Several companies provide this technology(Pettersson and Wellinger, 2009).