Biomethane production by adsorption technology: new cycle development, adsorbent selection and process optimization

Gas separation by adsorption processes such as pressure swing adsorption (PSA) presents an attractive alternative for upgrading biogas to biomethane. A new vacuum pressure swing adsorption (VPSA) cycle is proposed for a unit designed to purify pre-cleaned biogas (40% CO 2 and 60% CH 4 ) in industrial conditions (feed flow rate more than 500 Nm 3 /h and large-volume equipment). The process simulations performed to optimize the VPSA unit consider the kinetic separation of the feed components by using an appropriate carbon molecular sieve (CMS) adsorbent having a high kinetic separation selectivity for CO 2 with respect to CH 4 . The designed VPSA unit is composed of five columns that perform three equalization steps. Minimizing methane losses during the regeneration steps necessitates injecting part of the off-gas rich in CO 2 at the bottom of the column during the production step to push the CH 4 forward. The produced biomethane meets the specification (97% CH 4 ) of grid injection purity. The developed cycle allows a CH 4 recovery of 92% to be obtained with a specific energy consumption of 0.35 kWh/Nm 3 , thus meeting the initial requirements for industrial exploitation of VPSA technology for biomethane purification from biogas sources.