Purification and upgrading biogas from anaerobic digestion using chemical asborption of CO2 with amines in order to produce biomethane as biofuel for vehicles: a pilot-scale study

Methane from biogas is a promising option for the transition to a circular economic system based on renewable and sustainable energy. Currently, there is a wide variety of technologies capable of efficiently extracting the impurities contained in biogas in order to produce biomethane. In the present study, work was carried out in a pilot plant for cleaning and upgrading real biogas from anaerobic digestion by means of the chemical absorption method. In contrast to other technologies, chemical absorption stands out for having the lowest CH4 losses, which was crucial for this study. The objective was to purify and upgrade the biogas from anaerobic digestion of a WWTP to achieve a high concentration of methane and use it as biofuel in vehicles. The two aqueous solutions used as absorbents were mono-ethanolamine (MEA) and N-methyldiethanolamine (MDEA), both at 20% and 40% concentrations. It was found that the most effective solution was the MEA at 20% concentration, since it has the highest CO2 removal efficiency (94%) and, therefore, CH4 richness (96%). Finally, for every 100 m3 of biomethane generated after the chemical absorption process, 62 Nm3 of biofuel were obtained.