Biogas upgrading technologies are crucial for the production of high-purity biomethane. Efficient CO2 removal methods that are currently commercialized rely on "catch-and-release" mechanisms, and the CO2 stream is usually discharged into the atmosphere without further utilization. From the standpoint of process sustainability, it would be advantageous to transform the CO2 in biogas streams into value-added products. Herein, we propose the cycloaddition of CO2 into epoxides as a biogas upgrader. Fed by propylene oxide (PO) and biogas with typical CO2 concentration, or CO2 separated from biogas following upgrading, reactions were conducted under optimal conditions using an ionic polymer as the catalyst. Based on the obtained PO conversions, process simulations were performed for the large-scale production of propylene carbonate (PC) using CO2 separated from biogas. The PC yield was improved to 99.9% by process optimizations and reactant recycling at a molar flow rate of 100 kmol/h, which was shown to be commercially viable.