Deep Desulfurization of Diesel Oil with Extraction Using Pyridinium-Based Ionic Liquids

The pyridinium-based ionic liquids (ILs) 1-butyl-3,5-dimethylpyridinium tetrafluoroborate [((C4DMPy)-D-3,5][BF4]), 1-hexyl-3,5-dimethylpyridinium tetrafluoroborate [((C6DMPy)-D-3,5][BF4]) and, 1-octyl-3,5-dimethylpyridinium tetrafluoroborate [((C8DMPy)-D-3,5] [BF4]) were found to be effective for the selective removal of aromatic heterocyclic sulfur compounds from diesel. The results suggested that the structure and size of the cation greatly affect the extractive performance of ILs. For each sulfur compound studied here (4,6-Dimethyldibenzothiophene (4,6-DMDBT), dibenzothiophene (DBT), benzothiophene (BT), and thiophene (TS)), the extractive performance using pyridinium-based ILs followed the order of [C4Py][BF4] < [C6Py][BF4] < [C8Py][BF4] < [(C4MPy)-M-3] [BF4] < [(C4DMPy)-D-3,5][BF4] < [(C6MPy)-M-3][BF4] < [(C8MPy)-M-3][BF4] < [(C6DMPy)-D-3, 5][BF4] < [(C8DMPy)-D-3,5][BF4]. In addition, the pyridinium-based ILs would not contaminate the diesel due to their insolubility. On the other hand, diesel has a certain solubility in pyridinium-based ILs, varying from 0.49 wt% for [C4Py][BF4] to 19.6 wt% for [(C8DMPy)-D-3,5][BF4]. Considering these results, ILs studied in this work are more competitive and feasible for extractive desulfurization applications. Moreover, the extractive desulfurization using pyridinium-based ILs could be used at least as a complementary process to hydrodesulfurization (HDS).