Physicochemical properties of some hydrophobic room-temperature ionic liquids applied to volatile organic compounds biodegradation processes

Abstract : BACKGROUNDIonic liquids (IL) are an interesting solvent choice for specific industrial applications since physicochemical properties can be fine-tuned by modifying the substituent groups or the cation/anion pair. Hydrophobic ILs are considered green solvents and known to be good absorbents for hydrophobic organic compounds. Given their physicochemical properties an industrial application of such compounds is conceivable. Classical physicochemical properties such as density, viscosity and surface tension have a strong influence on the fluid dynamics; they were therefore measured and determined. RESULTSThe density, viscosity and surface tension of 23 hydrophobic ILs were measured at room temperature. These compounds are potential candidates for the absorption and biodegradation of volatile organic compounds (VOCs) in a two-phase partitioning bioreactor. The thermal expansion coefficient, molecular volume, standard molar entropy and lattice energy were determined for each IL using empirical and semi-empirical equations based on the density values. Viscosity values were correlated by the Arrhenius equation. Then, the surface excess enthalpy and surface excess entropy were determined from the surface tension values. CONCLUSIONThe influence of the presence of different functional moieties (unsaturated bonding, oxygenated and cyanide) and the side chain length in the physicochemical properties of these hydrophobic ILs was discussed, since their presence affected directly the density, viscosity and surface tension.