Characteristics of CO2 adsorption and desorption on activated carbon in comparison with zeolite 13X and carbon molecular sieve and applications in biogas upgrading using vacuum pressure swing adsorption

Abstract

AbstractBACKGROUNDBiogas upgrading is the process that increases the fraction of methane (CH4) in biogas, making the biogas suitable for use as vehicle fuel or as fuel with high and stable heating values for combustion engines. The advantages and disadvantages of activated carbon (AC) in CO2/CH4 adsorptive separation should be well understood before application for biogas upgrading. In the first part of this study, characteristics of CO2 adsorption and desorption on AC were investigated using Aspen Adsorption. In the second part, vacuum pressure swing adsorption (VPSA) was modeled, and the performances of the VPSA process using zeolite 13X, carbon molecular sieve (CMS) and AC were compared.RESULTSThe simulations showed that the advantages of AC for CO2 adsorption include relatively high dynamic adsorption capacity and high mass transfer coefficient of CO2 (KLDF,CO2) in AC and consequently relatively high CO2 desorption rates. However, due to the relatively high mass transfer coefficient of CH4 (KLDF,CH4) in AC, the molecular sieving characteristics for CO2 that were estimated from the ratio between KLDF,CO2 and KLDF,CH4 of AC were not significantly higher than that of zeolite 13X and significantly lower than that of CMS (9.85, 8.41 and 20.92 for AC, zeolite 13X and CMS, respectively).CONCLUSIONSThe modeling results predicted that the VPSA process using zeolite, CMS and AC adsorbents gives a biomethane product of around 98%, 97% and 93% CH4, respectively. © 2023 Society of Chemical Industry (SCI).