Techno-Economic Feasibility of Selective CO2 Capture Processes from Biogas Streams Using Ionic Liquids as Physical Absorbents

Abstract

Biogas from anaerobic digestion of sewage sludge is a renewable resource with high energy content, which is composed mainly of CH4 (40–75 vol %) and CO2 (15–60 vol %). Other components, such as water (H2O, 5–10 vol %) and trace amounts of hydrogen sulfide and siloxanes, can also be present. A CH4-rich stream can be produced by removing the CO2 and other impurities so that the upgraded biomethane can be injected into the natural gas grid or used as a vehicle fuel. The main objective of this paper is to assess the technical and economic performance of biogas upgrading processes using ionic liquids that physically absorb CO2. The simulation methodology is based on the COSMO-SAC model as implemented in Aspen Plus. Three different ionic liquids, namely, 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, 1-hexyl-3-methylimidazoliumbis[(trifluoromethyl)sulfonyl]imide, and trihexyl(tetradecyl)phosphonium bis[(trifluoromethyl)sulfonyl]imide, are considered for CO2 capture in a pressure-swing regenera...