Sustainable separation of oil from oily wastes using ionic liquids regulated by CO2

Abstract

Oily wastes are easily generated in many processes of exploitation, solvent extraction is the common method for treating the oily waste. However, traditional solvent extractions are difficult to recycle the solvent, and oil is difficult to separated. As a low-volatility solvent, ionic liquid is simple in synthesis, low in cost, so it has good application prospect. In this work, the sustainable separation of oil from oily waste was implemented by using CO2-switchable ionic liquids. On the basis of solvent extraction, ionic liquids can reduced losses and costs. The CO2-switchable ionic liquids were prepared by poly (propylene glycol) bis(2-aminopropyl ether) D-230 and fatty acids with low volatility at the mole ratio of 1:2. Upon the alternate bubbling CO2 and N2, ionic liquids could be transformed alternately from water-miscible state to water-immiscible state. The water-immiscible state was bi-phasic system containing hydrophobic fatty acids and ammonium bicarbonate solution by bubbling CO2. Based on the bi-phasic system, the oil (kerosene, paraffin oil and crude oil) could be mixed with fatty acids, and were separated from fatty acids in the hydrophilic state upon N2, where the recovery rate of oil was more than 97% and fatty acids was not residual in recovered oil. Treating oily waste, the oil could be extracted from oily waste by the bi-phasic system. The ionic liquids were reused and the oil was separated by bubbling N2 without extra additives, where the recovery rate of oil from oily waste was more than 85.57%. Due to the simplified process and negligible solvent loss, the economic benefit of recovering per barrel crude oil reached 76.7% of the price of crude oil. Compared with the existing technology, this sustainable separation is simpler, more economical and more environmentally friendly. Hence, it is expected that this sustainable separation based on CO2-switchable ionic liquids will meet the development of green separation with low-energy consumption.