Molecular Thermodynamic Modeling of Hybrid Ionic Liquids for Biogas Upgrading

This work focuses on the use of hybrid ionic liquids (ILs) solvents from mixtures of ILs with physical diluents as potential low viscosity solvents for biogas upgrading. The thermodynamic and thermal properties of hybrid solvents composed of [C(4)mim][BF4] mixed with several diluents such as water, methanol, acetone, or N-Methyl-2-pyrrolidone (NMP) were quantified using polar soft-SAFT. Results revealed that all diluents contributed equally to reducing the solvents viscosity of the pure IL, however, at the expense of increased isobaric heat capacity, vaporization enthalpy, and sometimes, reduced solubility in the case of water addition. We find that acetone is good a diluent, yielding an acceptable increase in CH4 and CO2 solubility and with favorable decreases in viscosity and the heat of absorption among selected solvents. The collection of acquired results confirmed the reliability of polar soft-SAFT as an attractive and valuable platform toward the rational design of hybrid solvents for biogas upgrading.