Simultaneous Extraction of Sulfur and Nitrogen Compounds from Model Diesel Fuel Using Neoteric Green Solvents

Removal of nitrogen and sulfur compounds from diesel fuel is essential to comply with the increasing stringent regulations. The extraction capability of two deep eutectic solvents, namely, tetrabutylphosphoniumbromide/ethylene glycol, TBPBr/EG, with molar ratio 1:2, and tetrabutylammoniumbromide/ethylene glycol, TBABr/EG, with molar ratio 1:2, in simultaneously extracting basic nitrogen, nonbasic nitrogen, and sulfur compounds represented by pyridine, indoline, and dibenzothiophene (DBT) from n-hexadecane, was investigated. Two pseudo-ternary phase diagrams of (TBPBr/EG + (pyridine + indoline + DBT) + n-hexadecane) and (TBABr/EG + (pyridine + indoline + DBT) + n-hexadecane) were predicted via a conductor-like screening model for real solvents (COSMO-RS) and experimentally validated at 298.15 K and 1 atm. Both solvents showed zero cross-contamination, indicating the suitability of all solvents as extraction solvents. The tie lines obtained for both COSMO-RS and experiments were in agreement and had root-mean-square deviation (RMSD) values of less than 5% for both systems. Selectivity and distribution ratio calculated indicates the suitability of both solvents in extracting sulfur and nitrogen compounds from hexadecane. Two new parameters, namely, extraction efficiency, α, and extraction affinity, β, were introduced to ease the performance comparison of both solvents. TBPBr/EG shows a slightly better performance than TBABr/EG. Other than that, the presence of multiple solutes shows low effects on the performance of these solvents.