Removal of Thiophene from Mixtures with n-Heptane by Selective Extraction Using Deep Eutectic Solvents

This work investigates the use of deep eutectic solvents (DESs) to extract sulfur-based compounds from n-heptane as model diesel compounds. Four DESs were prepared by combining tetrabutylammonium bromide or methyltriphenylphosphonium bromide with ethylene glycol, triethylene glycol, or sulfolane. All DESs showed good ability to extract thiophene with the best extraction efficiency (35%) being observed for the sulfolane-based DES. The extraction efficiency can be further enhanced to reach 98% when five extraction cycles are performed. Moreover, the DESs were easily regenerated using rotary evaporation. In addition, H-1 NMR analysis is used to elucidate the extraction mechanism. Finally, the COSMO-RS model was used to predict the ternary tie lines for the studied systems and the NRTL model allowed, correlating the experimental data with an average root-mean-square deviation of <2% for all DESs. These models can be utilized for further simulation analysis of the extraction process.