| Through an extractive desulfurization process, ionic liquids have been identified as effective solvents in the removal of aromatic sulfur compound such as thiophene (TS) and dibenzothiophene from both model and real fuel oils. The justification for the use of ionic liquids as an extractant is because of the incapacity of the conventional hydrodesulfurization (HDS). Evidence indicates that many ILs and few low viscosity ILs have been studied in various published works. However, only few research works have been done on desulfurization using real fuel oils. In this work, we prepared four new ILs with low viscosity based on dicyano(nitroso)methanide (dcnm) anion ie., l-butyl-3-methylimidazolium [C4mim][dcnm], l-ethyl-3-methyl-imidazolium dicyano(nitroso)methanide [C2min][dcnm], N-ethyl-N-methylpyrrol-idinium dicyano(nitroso)methanide [C2mpyr][dcnm], N-butyl-N-methylpyrrolidinium dicyano(nitroso)methanide [C4mpyr][dcnm] and evaluated their performance in the extractive desulfurization of model diesel, model gasoline and real gasoline. The dcnm-based ILs proved to be adequate extractants for reducing DBT and TS content from model diesel and model gasoline respectively. For both DBT and TS analysis, the desulfurization ability followed the order [C4min][dcnm]>[C4mpyr][dcnm]>[C2min][dcnm]>[C2mpyr][dcnm] with the desulfurization efficiency for DBT removal from model diesel being66.0,57.1,52.3,48.3%and TS from model gasoline being53.0,52.2,44.7,43.5%respectively.[C4min][dcnm] exhibited the highest efficiency of66%DBT and53%TS extraction after one cycle from their respective model oils with initial S-content of500ppm,25℃,15min, and IL:oil(w/w)1:1. Evidently, the butyl chain on the imidazolium and pyrrolidinium cation had the highest efficiency compared to the ethyl chain of the respective cation. Also, DBT was extracted more from model diesel than TS from model gasoline. As [C4min][dcnm], exhibited the lighest performance, it was chosen to undergo further evaluation to analyze me optimal operational conditions for the dcnm-based ILs.[C4min][dcnm] was found to lave negligible solubility in the model oil however, model oil showed some solubility n the IL.[C4min][dcnm] was also found to have slight insensitivity to temperature ilthough the desulfurization efficiency for TS extraction from model gasoline was found to decrease as the temperature increased, nonetheless the difference in the efficiency was not very significant. Next, it was observed that [C4min][dcnm] extraction of model diesel and model gasoline was influenced by the IL:oil ratio. A high IL:oil ratio exhibited higher desulfurization efficiency and subsequently a lower [L:oil ratio had lower efficiency. Furthermore, the initial S-content also influenced the desulfurization efficiency, a high S-content was more difficult to extract and it was noted that different ILs exhibited different S-removal rate in the fuel. For multiple extractions, almost negligible S-content was obtained for model diesel extraction after4cycles, while for model gasoline less than10ppm was achieved after5cycles. Also,[C4min][dcnm] was used to investigate its extraction ability in real FCC gasoline with an initial S-content of252ppm. After an equilibrium time of15min,34%extraction efficiency was achieved, the result was observed to be quite better than some previous results using other ILs. Mutual solubility, IL:oil ratio, multiple extractions and temperature were also studied which showed the same trend as that observed in model oil analysis. IL:oil ratio, temperature and initial S-content influenced the extraction in real gasoline. For multiple extraction,[C4min][dcnm] obtained nearly30ppm of S-compounds in the real fuel after6extraction cycles. Regeneration of [C4min][dcnm] was also studied for model diesel and model gasoline and real gasoline which was found to be successful. These dcnm-based ILs are competitive extractive reagents compared with other ILs, to remove those aromatic S-containing components from fuel oils. |
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