Corrosion properties of steel in 1-butyl-3-methylimidazolium hydrogen sulfate ionic liquid systems for desulfurization application

Ionic liquids (IL) become more promising in industrial applications, especially in desulfurization processes. It is of great importance to investigate their corrosivity to steel and the effect of steel corrosion on desulfurization performance. In this work, the corrosion behavior of two typical metals, namely mild steel and stainless steel, in 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO4) IL systems for desulfurization application were investigated by weight loss and surface analyses. The model oil can inhibit the IL corrosivity, while the presence of water or H2O2 enhances the corrosion degree. The bonding information of [BMIM]HSO4 adsorbed on a steel surface was confirmed using ATR-FTIR. It was found that the IL film is mainly adsorbed on the metal surface by the interaction of the imidazolium group of the cation and HSO4− of the anion with the steel surface. From the ICP-MS and Raman analyses, the primary component of corrosion products is iron sulfate (ferric sulfate for mild steel and ferrous sulfate for stainless steel). Localized corrosion (pitting and/or intergranular corrosion) appears on steel surface from SEM observation, which could be a serious safety risk to the [BMIM]HSO4-based desulfurization systems for industrial application. The corrosion has a side effect on the desulfurization performance of [BMIM]HSO4.