Amine-based adsorbent for biogas upgrading to RNG: Experimental, techno-economic analysis, and life cycle assessment.

Upgrading biogas to renewable natural gas (RNG) lowers greenhouse gas emissions and enables a sustainable energy transition. In this study, we evaluate polyethyleneimine (PEI)-functionalized resin supports as amine-based adsorbents for direct biogas upgrading using a temperature swing adsorption (TSA) process. Static CO2 isotherms indicate combined low-pressure chemisorption and physisorption at high pressures. Dynamic breakthrough experiments with real landfill gas confirm high CO2 selectivity over CH4 and no measurable breakthrough of trace impurities, while cyclic testing over 50 adsorption-desorption cycles indicate a gradual ∼20% capacity loss attributed to amine leaching. Technoeconomic analysis shows that regeneration, compression, and adsorbent replacement dominate operating costs, yielding a levelized cost of $6.32 per MMBtu. Profitability requires revenue from U.S. 45Q carbon capture credits and voluntary carbon offsets in addition to RNG sales. Life cycle assessment (LCA) demonstrates that RNG produced via the PEI-TSA pathway achieves significantly lower emissions than fossil natural gas and PSA-based upgrading, with net emissions of -49.7 gCO2e/MJ when flaring avoidance credits are included. Collectively, these results indicate that amine-functionalized TSA processes represent a promising pathway for economically and environmentally viable biogas upgrading to RNG, guiding future technology development and deployment.