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.
