The reversible shift in polarity or hydrophilicity/hydrophobicity of switchable solvents greatly simplifies the recovery capacity in extraction applications. However, the environmental and economical advantages of switchable solvents are not significant. In this work, we designed three pH-responsive natural deep eutectic solvents (NADESs) by combining the pH-switchable solvent fatty acids with the nonswitchable solvent ethyl lactate (EL), followed by the exploration of the solubilization and separation performance of these NADESs for petroleum hydrocarbons. EL can be miscible in fatty acids and water; however, when in contact with both at the same time, EL binds to fatty acids through stronger intermolecular hydrogen bonds, whereas when fatty acids are deprotonated to fatty acid salts, EL can bind to water. The deprotonation/protonation of fatty acids could reversibly change the NADES hydrophilicity, and the recovery of NADES HA/EL could exceed 95% after three cycles. Furthermore, after extractive separation of simulated oils of differing complexity, NADES HA/EL was selected as the best extractant. Compared with the extraction of oil sands with a single solvent, NADES provides better wetting of the sand surface, better stripping efficiency of the heavy components that adhere to the surface of oil sands, and better dispersion of the stripped petroleum hydrocarbons. Petroleum hydrocarbons can be separated by NaOH-induced hydrophilic changes in NADES, which can be regenerated upon the addition of HCl. The recovered NADES showed good reusability in the cleaning of oil sands. The oil removal rates were 96.9%, 94.4%, and 91.9% after three cycles of cleaning with NADES at 25 °C. This method is expected to expand the application of nonswitchable solvents in sustainable extraction.

中文翻译：

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pH 响应性天然深共熔溶剂：从油砂中可持续提取石油烃的环保替代方案


可切换溶剂的极性或亲水性/疏水性的可逆变化大大简化了萃取应用中的回收能力。然而，可切换溶剂的环境和经济优势并不显著。在这项工作中，我们通过将 pH 可切换的溶剂脂肪酸与不可切换的溶剂乳酸乙酯 （EL） 相结合，设计了三种 pH 响应的天然共熔溶剂 （NADES），然后探索了这些 NADES 对石油烃的溶解和分离性能。EL 可混溶于脂肪酸和水;然而，当同时与两者接触时，EL 通过更强的分子间氢键与脂肪酸结合，而当脂肪酸去质子化为脂肪酸盐时，EL 可以与水结合。脂肪酸的去质子化/质子化可逆地改变 NADES 的亲水性，3 次循环后 NADES HA/EL 的回收率可超过 95%。此外，在对不同复杂程度的模拟油进行萃取分离后，NADES HA/EL被选为最佳萃取剂。与使用单一溶剂提取油砂相比，NADES 提供了更好的砂表面润湿性，更好的粘附在油砂表面的重成分的剥离效率，以及更好的剥离石油烃分散。石油烃可以通过 NaOH 诱导的 NADES 亲水变化来分离，NADES 可以在添加 HCl 后再生。回收的 NADES 在油砂清洗中表现出良好的可再利用性。在 25 °C 下使用 NADES 清洗 3 个循环后，除油率分别为 96.9%、94.4% 和 91.9%。 该方法有望扩大不可切换溶剂在可持续萃取中的应用。