Influence of ionic liquids in the reverse water-gas shift reaction: a thermodynamic study

Abstract

Carbon dioxide (CO2) conversion processes can be a promising alternative to replace conventional processes toward a more sustainable industry. The addition of ionic liquids (IL) was reported to increase the performance of related reactions; however, their thermodynamic influence in the reactive chemical equilibrium has been poorly investigated. This study evaluated the effect of the ionic liquids (ILs) [BMIm]BF4], [BMIm][PF6], or [BMIm][NTf2] on the CO2 hydrogenation to carbon monoxide (CO) chemical equilibrium. Predictive and nonpredictive approaches based on the Predictive Soave-Redlich-Kwong equation of state were applied to represent pure ILs densities and vapor pressure. The nonpredictive approach presented the most suitable representation and was applied to represent binary vapor-liquid and liquid-liquid phase equilibria of ILs + CO2, hydrogen (H2), CO, or water (H2O). The influence of temperature pressure, and IL content on CO2 hydrogenation to CO reaction were evaluated. Higher ILs’ molar ratio increased the equilibrium conversion. IL-containing systems are significantly influenced by pressure, and high pressures enhance CO2 conversion. High temperatures increased the reaction’s conversion of systems containing the hydrophobic ILs [BMIm][PF6] or [BMIm][NTf2], while low temperatures increased the CO production of systems containing the hydrophilic IL [BMIm][BF4]. This effect was attributed to the high influence of temperature on the water sorption in the IL. The hydrophilic IL, [BMIm][BF4], promoted the highest increase in CO2 conversion. At 348 K and 2.0 MPa, the CO2 conversion was increased from 1.1–54.1%; roughly an increase of ~ 50 times the original conversion without IL addition.