Hydrophobic deep eutectic solvents as attractive media for low-concentration hydrophobic VOC capture

Abstract

Emissions of volatile organic compounds (VOCs) are known to be significant human health and ecological risks. Absorption is a classical process applied to eliminate air pollutants, yet the removal efficiency of gaseous contaminants is often curbed by the mass transfer resistance between absorption liquids and hydrophobic VOCs. This work aims to evaluate the feasibility of capturing VOCs from exhaust through the use of hydrophobic deep eutectic solvents (DESs). Among the examined DESs, hydrophobic DESs whose hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) are both fatty acids with long alkyl chains (i.e., decanoic acid [DecA] and lauric acid [LauA]) achieve the highest absorption capacity of toluene at 9.94 mg toluene per g DES at 30 °C and 800 ppm toluene with an HBA:HBD molar ratio of 1:3. Hydrophobic interactions between the fatty acids and toluene are critical for improving the VOC absorption ability of DESs, as the toluene solubility increases with an increase in the alkyl chain length of the fatty acid eutectics. The compiled results suggest that effective hydrophobic VOC removal can be realized by the proposed hydrophobic fatty acid eutectics, [LauA][DecA], and the physical absorption nature of toluene in fatty acid eutectics benefits facile recovery and recycling.