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 (TrpBF4/U) was synthesized using l-tryptophan, fluoroboric acid and urea. The melting point of TrpBF4/U was over 100 K lower than that of TrpBF4. It is found that the TrpBF4/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 TrpBF4/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 TrpBF4/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 TrpBF4/U, including lowering the interfacial tension and increasing solid wettability. Assisted by the TrpBF4/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 TrpBF4/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.