Modelling and experiment for simultaneous biogas upgrading and CO2 capture by an advanced VPSA-SMB process

Abstract

An advanced multicolumn vacuum pressure swing adsorption process (namely as the VPSA-SMB process) is developed to simultaneously recover high-purity methane and high-purity carbon dioxide from biogas feedstock, using commercial ZSM-5 zeolite as the adsorbent. In this novel process, the tandem multicolumn is adopted at the pressurization, adsorption and displacement steps to improve CH₄/CO₂ separation; one tower filled with high-purity CO₂ will go on the blowdown/purge steps for the regeneration of adsorbents; the cyclic operation is executed automatically with the simulated moving bed mode, shifting the inlet/outlet ports of gas streams one by one tower. In the laboratory, a six-tower VPSA-SMB unit packed with ZSM-5 zeolites was constructed, and the mathematical model appliable to predict the CH₄/CO₂ separation performance of the novel process was built. Through experiments and simulations, it is proved to be technically feasible and highly efficient for biomethane production with a purity >96 % and recovery >99 % while achieving CO₂-purity >99 % from the wide CH₄ content biogas using the novel adsorption process. Additionally, the selection of feed gas and replacement gas flow rates to improve CH₄/CO₂ separation, as well as the choice of switching time for the inlet and outlet ports of gases were discussed.