Exergy-based sustainability analysis of biogas upgrading using a hybrid solvent (imidazolium-based ionic liquid and aqueous monodiethanolamine)

Document Type : Research Paper


1 Department of Applied chemistry and chemical technology, University of Karachi, Pakistan.

2 Department of Food Engineering, NED University of Engineering and Technology, Karachi, Pakistan.


Energy may be generated in large quantities from fossil fuels, but this comes with environmental concerns. Thus, renewable resources like biogas, comprising carbon dioxide and methane, should be used alone or in combination with fossil fuels to mitigate the environmental footprints of energy generation systems. In this study, a new concept of hybrid solvent was presented, which combines 1-octyl-3-methylimidazolium tetrafluoroborate with aqueous mono diethanolamine for biogas upgrading process to provide high purity (≥ 99 wt%) and recovery (≥ 99 wt%) of biomethane. The process was simulated in ASPEN Plus® V.11. The thermodynamic framework was validated against experimental data, and rigorous regression was conducted to obtain binary parameters. To establish the efficacy of the suggested hybrid solvent, three scenarios were studied by altering the concentration of ionic liquid (5–20 wt%) linked with amine and compared to aqueous mono diethanolamine as the base case (50 wt%). The results showed that a hybrid solvent with 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate could increase CH4 purity to 99% (mol%). The hybrid solvent led to an energy saving of 64.94% compared to the amine-based system. Thermodynamic irreversibilities showed that 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate improved exergy efficiency by 54% over the amine-based procedure. Environmentally, the hybrid solvent system also achieved a higher capture rate (99%) and lower emissions (0.017 kW/kmol). Comparing the economic prospects, 5 wt% 1-octyl-3-methylimidazolium tetrafluoroborate saved 56% on total capital cost, making it competitive from an investment perspective.

Graphical Abstract

Exergy-based sustainability analysis of biogas upgrading using a hybrid solvent (imidazolium-based ionic liquid and aqueous monodiethanolamine)


  • Biogas upgrading by ionic liquid (IL)-based hybrid solvent combined with aqueous monodiethanolamine investigated.
  • 5 wt% imidazolium-based IL with Aq.MDEA led to biomethane purity and recovery of ≥ 99 wt%.
  • Hybrid solvent-based biogas upgrading led to an energy saving of 64.94% vs. the base system.
  • Hybrid solvent-based biogas upgrading led to less exergy destruction of 54.25 MW with an overall exergy efficiency of 43.36%.
  • The proposed solvent was eco-friendly, with a high CO2 capturing rate (≥ 99 wt%) and less emission (0.015 kg CO2/kmol).


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