Sustainable Recovery of Petroleum Hydrocarbons by Deep Eutectic Solvents with CO2-Controllable Polarity

Cleaner recovery of petroleum hydrocarbons is a key process for waste oil and gas resources, especially oily waste solid. However, the direct recovery of petroleum hydrocarbons is difficult with deep eutectic solvents (DES) without other additives (such as water). In this work, ionic liquid-based DESs (ILs-DESs) with a controllable polarity were prepared for the sustainable recovery of petroleum hydrocarbons. Here, CO2-responsive ionic liquids were prepared by the neutralization reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene and iminazole (Im), pyrazol (Py), or triazole (Tri). Then, the ILs-DESs were separately prepared by using ionic liquids as proton acceptors and straight-chain alcohols (carbon number = 4, 6, 8, 10, and 12) as proton donors. The polarity transformation of the ILs-DESs was regulated only by the introduction and removal of CO2, which was caused by the reversible transformation from ILs-DESs with a lower polarity to alkyl carbonate and carbamate with higher polarity upon CO2. Because of the polarity changes, the simulated oil (such as n-dodecane or diesel oil) was mixed with ILs-DESs, and the samples were directly separated by introducing CO2. Finally, a sustainable process for treating oil sands and oily sludge by using ILs-DESs was developed, where the ILs-DESs were also reused more than twice. This implies that a sustainable approach for petroleum hydrocarbon recovery was realized by using DESs.