Efficient oxidative desulfurization of diesel fuel using amide-based ionic liquids

A series of Brønsted acidic ionic liquids having a protonated amide- or lactam-based cation were synthesized and investigated as extractants and catalysts in the extraction combined with oxidative desulfurization (ECODS) of both model oil and diesel fuel, with hydrogen peroxide (H2O2, 30 wt%) as oxidant. Each of them showed obvious removal of benzothiophene (BT) and dibenzothiophene (DBT) in model oil. Among them, [HCPL][TFA] exhibited the best performance by completely removing BT and DBT in a short time. The detailed structure and conformation of [HCPL][TFA] were investigated by 1H NMR and FTIR as well as theoretical calculation. HCPL+ cation was verified to exist in an enol form, which was supposed to contribute to high desulfurization performance by improving the formation of peroxides. In the end, two kinds of diesel were used to evaluate its desulfurization performance. [HCPL][TFA] can reduce the S-content of real hydrogenated diesel from 659.7 ppm to 8.62 ppm with 98.69% S-removal efficiency after two ECODS processes. Furthermore, the total S-content of straight-run diesel fuel was reduced to 89.36 ppm from 11,034 ppm with a similar S-removal rate. The results of GC-PFPD before and after each ECODS process indicated that almost all the original S-compounds in diesel had been converted to their corresponding oxidation products. The desulfurization performance was actually restricted by extraction capability.