Simultaneous production during biogas upgrading: Foundational insights from numerical simulation of dual-reflux pressure swing adsorption

Abstract

Biogas upgrading is a key step in improving the properties of biogas, particularly its methane concentration and, consequently, its energy content, by separating carbon dioxide. This process holds significant environmental and economic relevance, especially when high-purity methane and carbon dioxide can be simultaneously produced. In this regard, dual-reflux pressure swing adsorption (DR-PSA) emerges as a promising technology that achieves the separation objective. In this study, a numerical simulation model of a non-isothermal DR-PSA was established using the Aspen Adsorption simulation tool to evaluate the dynamics of the system for binary separation of biogas feed mixture containing 45 mol% CO₂ + 55 mol% CH₄, using a CO₂-selective silica gel as the solid adsorbent. The goal was to provide preliminary insights into the capability of the DR-PSA process (with silica gel) to produce two useful products, CH₄ and CO₂, under typical biogas feed conditions. The behavior of the DR-PSA is described through pressure and temperature profiles within the bed column at cyclic steady-state conditions. The results indicate that, under preliminary unoptimized conditions, 86.0% of CH₄ could be recovered with a purity of 85.8% as a light product, whereas CO₂ enriched to 82.9% was achievable as a heavy product, with a recovery of 82.9%, using a pressure ratio, P_H/P_L of 5. Further work is recommended to investigate several operating parameters to achieve optimal binary separation with the highest possible recoveries.