State-of-the-art process simulations and techno-economic assessments of ionic liquid-based biogas upgrading techniques: Challenges and prospects

Biogas has emerged as an alternative renewable fuel to natural gas. However, the presence of trace contaminants and large quantities of CO2 in biogas necessitates its purification and upgrading to increase its calorific value. Different technologies have been developed to upgrade biogas to biomethane. Among these, chemical absorption is commonly employed due to its high process efficiency and less solvent requirement due to high selectivity compared to physical absorption. However, the chemical decomposition of amine-based solvents, toxicological impact, high plant maintenance costs, high enthalpy of reaction, and corrosivity associated with chemical absorption limit its large-scale application. Recently, ionic liquids (ILs) have garnered attention as alternative absorption media to conventional solvents. ILs have a high CO2 uptake, thermal stability, and negligible vapor pressure. Recent process simulation studies featuring ILs as solvents for biogas upgrading reveal the suitability of these approaches as alternatives to laborious experimental work to assess the practical, technical, and economic viability of ILs. As per the authors' knowledge, this is the first review comparing biogas upgrading technologies from a technical, environmental, and economic perspective. Primarily, studies relating to IL-based biogas upgrading are considered, and challenges associated with the large-scale adoption of ILs as absorption media are discussed. Process simulations and techno-economic assessments of IL-based biogas upgrading techniques are presented. A conceptual design approach is proposed for the successful scale-up of IL-based biogas upgrading. Based on results, deep eutectic solvents are recommended as next-generation solvents for absorption as technical and economic aspects are found superior to conventional amines and ionic liquids