Synthesis and application of amino acid ionic liquid-based deep eutectic solvents for oil-carbonate mineral separation

A novel amino acid ionic liquid-based deep eutectic solvent (TrpBF(4)/U) was synthesized using L-tryptophan, fluoroboric acid and urea. The melting point of TrpBF(4)/U was over 100 K lower than that of TrpBF(4). It is found that the TrpBF(4)/U could form non-aqueous surfactant-free micro-emulsion through mixing with ethanol and toluene. The size of the micro-emulsion droplets was less than 7 nm and was dependent on the concentration of toluene. This newly prepared TrpBF(4)/U-based micro-emulsion was applied to extract the extra-heavy oil from carbonate asphalt rocks. Results showed that the oil recovery was enhanced by at least 11% compared with that without the TrpBF(4)/U micro-emulsions. The enhancement in the oil-solid separation was mainly ascribed to the interfacial alteration at the oil and mineral surfaces by the TrpBF(4)/U, including lowering the interfacial tension and increasing solid wettability. Assisted by the TrpBF(4)/U micro-emulsion, the quality of oil product (less solids entrained) and residual solids (less solvents attached) were also improved compared with traditional ionic liquids (i.e., [Emim] BF4) at given conditions. It also demonstrated that the TrpBF(4)/U micro-emulsion could be recycled and reused at least 4 times without sacrificing its efficiency. The above findings suggested the potential applications of the amino acid ionic liquid-based deep eutectic solvent in oil-solid separations or other extractions. (C) 2018 Elsevier Ltd. All rights reserved.