Deep desulfurization of oil refinery streams by extraction with ionic liquids

Extraction of S- and N-compounds from gasoline and diesel oil by ionic liquids (ILs) indicates that such a process could be an alternative to common hydrodesulfurization (HDS) for deep desulfurization down to values of 10 ppm S or even lower. The results show the selective extraction properties of ILs, especially with regard to those S- compounds which are hard to remove by HDS, e. g. dibenzothiophene derivatives present in middle distillates like diesel oil. The application of mild process conditions ( ambient pressure and temperature) and the fact that no hydrogen is needed, are additional advantages compared to HDS. Very promising ILs are [BMIM][OcSO(4)] and [EMIM][EtSO4], as they are halogen-free and available from relatively cheap starting materials. Extraction with ILs is not limited to diesel oil, but probably even more attractive for FCC-gasoline. Although HDS of S- species present in this gasoline constituent mainly thiophenes-is relatively straightforward, a major drawback is the loss in octane number by olefin saturation, which favours extraction with ILs.