Energy, exergy and economic (3E) evaluation of CO2 capture from natural gas using pyridinium functionalized ionic liquids: A simulation study

Abstract

Sweetening of natural gas is a necessary process step to meet transportation and commercial standards. Amine-based solvents have been conventionally used for absorption-based removal of contaminants, like acid gas from natural gas. The process has inherent high energy penalty issues during solvent recovery and large fugitive emissions due to the solvent's low vapor pressure. Contrarily, ionic liquids (ILs) have lower solution enthalpies and vapor pressure compared to conventional alkanolamine solvents. Hence, ILs can offer an energy-saving pathway for the carbon dioxide removal. However, understanding their application at plant-wide scale is limited. This study presents an energy, exergy and economic (3 E) analysis of an ionic liquid-based process for removing carbon dioxide from natural gas in a simulated environment. Pyridinium cation-based IL is analysed as a CO2 capturing solvent and compared to the monoethanolamine (MEA) and 1,2-dimethoxyethane (DME). Optimal operating conditions for the IL-based carbon capture are evaluated with 99% CH4 recovery and 99% CH4 purity as benchmark conditions. The energy analysis shows that 3-methyl-1-ethylpyridinium bis(trifluoromethylsulfonyl)imide (3MEPYNTF2) ionic liquid provides 90.08% and 80.28% overall energy savings relative to MEA and DME. The exergy analysis further complements the energy analysis as 3MEPYNTF2 is energy proficient with overall anergy of 13.3 MW, while MEA and DME gives a higher value of 57.45 and 30.98 MW, respectively. Furthermore, economic analysis indicates that at average, 3MEPYNTF2 offers savings in overall capital (65.86%), operating costs (81.09%), and total annualized costs (78.33%) compared to MEA and DME. The 3 E analysis suggests that pyridinium cation based ILs are a potential replacement for amine-based high pressure natural gas sweetening processes.