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

Abstract

Abstract BACKGROUND Biogas upgrading is the process that increases the fraction of methane (CH 4 ) 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 CO 2 /CH 4 adsorptive separation should be well understood before application for biogas upgrading. In the first part of this study, characteristics of CO 2 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. RESULTS The simulations showed that the advantages of AC for CO 2 adsorption include relatively high dynamic adsorption capacity and high mass transfer coefficient of CO 2 ( K LDF,CO2 ) in AC and consequently relatively high CO 2 desorption rates. However, due to the relatively high mass transfer coefficient of CH 4 ( K LDF,CH4 ) in AC, the molecular sieving characteristics for CO 2 that were estimated from the ratio between K LDF,CO2 and K LDF,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). CONCLUSIONS The modeling results predicted that the VPSA process using zeolite, CMS and AC adsorbents gives a biomethane product of around 98%, 97% and 93% CH 4 , respectively. © 2023 Society of Chemical Industry (SCI).