Abstract
The solubility of CO2 in two biodegradable ionic liquids tris(2-hydroxyethyl)methylammonium methylsulfate [THMA][MeSO4] and 2-hydroxyethyl-trimethylammonium lactate [2HETMA][Lac] has been studied experimentally. A synthetic method was used to measure bubble-point pressures up to 8 MPa for a temperature range of 313 K to 363 K. The solubility of CO2 in [2HETMA][Lac] is much higher than in [THMA][MeSO4], but the solubility increment is lower at higher CO2 concentrations. The solubility of CO2 in [THMA][MeSO4] is much lower compared to ionic liquids containing the same anion, but lacking hydroxyl-groups in the cation. The hydroxyl-groups required for the biodegradability of the IL have a detrimental effect on the CO2 solubility. [THMA][MeSO4] and [2HETMA][Lac] are not suitable for CO2 capture and can be considered as an example of a contradictive design where the biodegradability is improved upon introducing hydroxyl-groups, while the CO2 solubility is reduced significantly. The experimental data has been modeled with good accuracy using the Peng-Robinson equation of state in combination with the Wong-Sandler mixing rules.