Biogas upgrading to fuel quality by dynamic adsorption of activated charcoal under non-isothermal conditions

Biogas is essential in our pursuit of sustainable energy solutions, in our journey towards a greener and sustainable future. To become commercially viable, biogas requires purification, particularly the removal of impurities like CO₂, so that it meets the fuel quality standards. This study evaluated activated charcoal’s potential as an adsorbent for biogas upgrading. The focus is on its ability to effectively remove impurities such as CO₂ in a four-step pressure swing adsorption (PSA) cycle. SEM, BET, FT-IR, and XRD analyses provide insights into its physical and chemical attributes. The study began by examining the dynamic fixed-bed adsorption behavior of CO₂ and CH₄ at 300 K and 2.5 bar. A numerical model was developed to elucidate the activated charcoal’s dynamic behavior during methane enrichment and CO₂ capture, considering both its characterization and the adsorption bed’s geometry. The model was further refined using the extended Langmuir model to enhance the representation of the multicomponent adsorption. A novel approach was introduced by incorporating non-isothermal/non-adiabatic assumptions into the dynamic simulations, thereby providing a more accurate reflection of a PSA system in real-world applications. Aspen Adsorption platform was utilized during dynamic simulations, and the model was validated using experimental breakthrough data. The model assessed how parameters like temperature, length-to-diameter (L/D) ratio, and CO₂ content in feed affect biomethane purity. Process optimization of the biogas upgrading was achieved through design of experiment (DoE) methodology, utilizing central composite design (CCD) and desirability analysis. The results demonstrated a biomethane purity level of 99.96% and a recovery rate of 96.22% at a temperature of 0 °C, an L/D ratio of 15, and a feed CO₂ content of 30%, underscoring the efficacy of activated charcoal and its capability to meet the stringent fuel standards, thereby positioning it as a reliable material for biogas upgrading. Graphical abstract: (Figure presented.)