Dual-reflux pressure swing adsorption in biogas upgrading-a parametric optimization

The efficient upgrading of biogas is critical for advancing renewable energy technologies, reducing greenhouse gas emissions, and enhancing the circular carbon economy. This study systematically investigates the application of dual-reflux pressure swing adsorption (DR-PSA) for biogas upgrading, enabling simultaneous enrichment of CH4 and CO2 to high purities. A two-bed, six-step PHA (feed to high-pressure, PH, and pressure reversal using heavy component, A) was analyzed using rigorous non-isothermal numerical simulations framework within the Aspen Adsorption software. To systematically enhance the process performance, a two-level fractional factorial design was employed to identify the most influential parameters, followed by the Box-Behnken design optimization to determine optimal operating conditions. The screening analysis identified the feed/light reflux (FE/LR) time, light reflux ratio, and bed column height as the most influential parameters governing separation efficiency. Under optimized conditions of FE/LR time of 49 s, light reflux ratio of 0.259, and bed column height of 1.97 m, the DR-PSA achieved a CH4 purity of 91.69% in the light product and CO2 purity of 89.36% in the heavy product, marking improvements of 15% and 19%, respectively, over the base case. Additionally, the optimized conditions demonstrated a bed productivity of 1.09 mol CH4/h/kg silica gel and an energy-efficient cycle work of 56.25 kJ/mol CH4 captured, highlighting its potential for scalable deployment. Compared to other PSA systems of similar purpose, the DR-PSA process exhibited comparable separation performance, operating as a single train process, with a moderate pressure ratio, and without vacuum operation, making it a promising alternative for sustainable and cost-effective biogas upgrading. This study represents the first systematic optimization of DR-PSA for biogas upgrading using a statistical design of experiments approach, offering a novel and practical pathway for enhancing renewable energy technologies.