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

Area of Science:

• Chemical Engineering
• Environmental Science
• Materials Science

Background:

• Biogas upgrading to renewable natural gas (RNG) is crucial for reducing greenhouse gas emissions and advancing sustainable energy.
• Amine-based adsorbents are effective for CO2 capture, but their application in direct biogas upgrading via temperature swing adsorption (TSA) needs further evaluation.

Purpose of the Study:

• To assess the efficacy of polyethyleneimine (PEI)-functionalized resin supports as amine-based adsorbents for direct biogas upgrading using TSA.
• To evaluate the technical and economic viability, as well as the environmental impact, of this PEI-TSA process for RNG production.

Main Methods:

• Utilized static CO2 isotherms to characterize adsorption properties (chemisorption and physisorption).
• Conducted dynamic breakthrough experiments with real landfill gas to assess CO2 selectivity and impurity removal.
• Performed cyclic testing over 50 cycles to evaluate adsorbent stability and capacity loss.
• Executed technoeconomic analysis and life cycle assessment (LCA) to determine costs and environmental benefits.

Main Results:

• PEI-functionalized resins demonstrated high CO2 selectivity over CH4 and effectively removed trace impurities during dynamic testing.
• Cyclic testing revealed a gradual capacity loss of approximately 20% over 50 cycles, attributed to amine leaching.
• Technoeconomic analysis indicated a levelized cost of $6.32 per MMBtu, with profitability dependent on carbon credits and RNG sales.
• LCA showed significantly lower net emissions (-49.7 gCO2e/MJ) for PEI-TSA derived RNG compared to fossil natural gas and PSA upgrading, especially with flaring avoidance credits.

Conclusions:

• Amine-functionalized TSA processes, specifically using PEI-resins, are a promising pathway for economically and environmentally viable biogas upgrading to RNG.
• The study provides valuable insights for future development and deployment of this technology, highlighting the importance of addressing adsorbent stability and integrating carbon credit revenues.
• The PEI-TSA method offers a sustainable alternative to conventional natural gas and presents a significant reduction in greenhouse gas emissions.