The green CO2-controllable fatty acid-based deep eutectic solvents for sustainable oil separation

Abstract

Hydrocarbon pollutants are not only serious environmental hazards in the exploitation of petroleum resources, but also lead to incomplete utilization of resources. At present, a green solvent called deep eutectic solvents (DES) gradually replaces traditional organic solvents to recover petroleum hydrocarbons, but its recovery still needs to be optimized. For this reason, hydrophobic DES with hydrophilic and hydrophobic properties that can be controlled by CO2 was developed using fatty acid (FA) as raw material. In the process of using liquid FA to drop into solid FA to prepare DES with an adjustable melting point, DCS technology was used to accurately obtain the melting point and latent heat of the experimental reagent FAs, and the solid − liquid diagram of DES was predicted. Interestingly, the DES prepared by the addition of solid FA and liquid FA retains its strong hydrophobic properties, while the viscosity and melting point can be significantly reduced. FA can transform from oil-soluble physical property to water-soluble physical property by electrostatic binding to polyether amine (D230). This weak non-covalent bond force can be dissociated by CO2 stimulation, FA can be restored to oil-soluble state, and D230 in aqueous phase can be reduced by removing CO2 by heating or bubbling N2. The reversible pH transformation of the system and 1H NMR confirm this CO2-switchable behavior. In addition, sustainable oil separation (kerosene) was successfully achieved with a maximum oil recovery of 94.6%. Therefore, the novel FA-based DES is expected to be used as an effective extractant for the sustainable clean recovery of hydrocarbons from petroleum resources.