Simulation study of biomethane liquefaction followed by biogas upgrading using an imidazolium-based cationic ionic liquid

Abstract

To satisfy the ever-increasing global energy demand, biomethane is considered a promising sustainable and renewable energy source. Biomethane can be transported either in the gaseous phase (through pipelines, over a small distance) or in the liquid phase (through shipping, over a long distance). For transportation over long distances, liquefaction is one of the most economic and feasible approaches so far. However, biomethane is obtained as a result of biogas upgrading, i.e., CO2 removal from biogas. Conventionally, CO2 is removed through amine-based absorption, which consumes large amounts of energy to regenerate the amine-based solvent. Liquefaction of methane (obtained either from fossil-based or renewable resources) has also been recognized as an energy-intensive process. Hence, the major issue associated with biogas upgrading and subsequent biomethane liquefaction is their high energy consumption, which ultimately affords a cost-intensive process. In this context, we propose a simulation based an economical and energy efficient process for biomethane liquefaction following biogas upgrading using an ionic liquid (1-butyl–3–methylimidazolium hexafluoro phosphate [Bmim][PF6]). As such, biogas can be upgraded at an energy expense of 1.1048 kWh/kmol, while 11.26 kWh/kmol of energy is used for biomethane liquefaction. The specific total annualized cost for the proposed integrated process was calculated as $519.3/kg-biogas.