Biomethane purification with quaternary ammonium salts-based deep eutectic solvents: Experiment and computational thermodynamics

•The quaternary ammonium-based DESs were first used as biogas purification absorbent.•DESs still had good absorption effect after 5 absorption - desorption cycles.•The structure–activity relationship between DESs and biogas molecules was revealed.•The absorption mechanism was explored based on QC calculations and MD simulations.•This provides theoretical insights for the development of novel DES for biomethane purification.