Air pollution: new bio-based ionic liquids absorb both hydrophobic and hydrophilic volatile organic compounds with high efficiency

Abstract

Emission of volatile organic compounds (VOCs) in the atmosphere is a major health concern for the World Health Organization (WHO). For instance, more than 4 million premature deaths are attributed yearly to outdoor air pollution, thus calling for advanced remediation techniques. Absorption systems using solvents are commonly used to remove air pollutants, yet efficiency is limited by a solvent property, which is either hydrophilic or hydrophobic. As a consequence, classical solvents are not able to capture both hydrophilic and hydrophobic contaminants. Therefore, we synthesized the following ionic liquids from choline chloride and fatty acids: hexylcholinium levulinate, octylcholinium levulinate, hexylcholinium lactate and octylcholinium lactate. Ionic liquids were then tested for absorption of toluene, dichloromethane (CH2Cl2) and methyl ethyl ketone. Ionic liquids were characterized by 1H and 13C NMR, infrared spectroscopy, differential scanning calorimetry and thermal gravimetric analysis, density, viscosity and polarity. Vapor–liquid partition coefficients of VOC were determined for ionic liquids. We found that solvents were able to solubilize both hydrophobic and hydrophilic VOC. Moreover, no saturation was detected up to an initial VOC concentration of 3000 g/m3, whereas classical absorption processes usually involve gas streams containing VOC concentrations up to 1000 g/m3. Moreover, the solvent can be successfully recycled with unchanged capacity during five absorption–desorption cycles. Overall, our solvents appear promising for the treatment of industrial gaseous effluents.