Deep desulfurization of oil refinery streams by extraction with ionic liquids

TLDR

Ionic‑liquid extraction can remove sulfur and nitrogen compounds from gasoline and diesel to levels below 10 ppm, targeting hard‑to‑remove species such as dibenzothiophene derivatives in diesel. The study demonstrates that halogen‑free ionic liquids, notably [BMIM][OcSO4] and [EMIM][EtSO4], selectively extract these sulfur species under mild, hydrogen‑free conditions, offering a promising alternative to hydrodesulfurization that preserves octane number and is applicable to both diesel and FCC‑gasoline.

Abstract

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][OcSO4] 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.