Process analysis overview of ionic liquids on CO2 chemical capture

Abstract

A process analysis overview of the ionic liquids (ILs) performance as chemical absorbents in post-combustion, biogas and pre-combustion CO2 capture systems was carried out. Six representative ILs, among them carboxylate, aminoacid and aprotic heterocyclic anion-based ILs -with remarkably different CO2 absorption thermodynamics and kinetics- were selected. COSMO-based/Aspen Plus methodology, supported with available experimental data, was successfully applied to design the absorption and regeneration stages in commercial packed columns to reach a 90% CO2 recovery at different CO2 partial pressures and given operating conditions, for comparison purposes. The IL performance in CO2 capture process was evaluated by means of solvent need, energy consume and column size. The CO2-IL reaction enthalpy and IL viscosity were identified as key properties to guide solvent selection. For the considered ILs, increasing the reaction exothermicity means lower solvent, energy and equipment requirements as liquid viscosity descends, overcoming mass transfer limitations at adiabatic conditions. The CO2 capture process efficiency was successfully related to the thermodynamic gap capacity given by CO2-IL isotherms at the absorption/regeneration operating conditions. AHA-IL family is aimed as a promising alternative to industrial CO2 chemical absorbent benchmark (aqueous amine solution) due to their advantageous key properties: moderate viscosity and adequate compromise between high CO2 solubility and reaction enthalpy. Current results indicated the technical viability of ILs-based CO2 capture processes compared to available technologies, but further analysis (i.e cost estimations, environmental impacts and life cycle assessment) are required to ensure the sustainability of a new process.