Alkylation catalytique des composés thiophéniques dans les essences – CatAlkThio

Sulfur compounds from gasoline have to be eliminated for well-known environmental reasons to avoid SOx, and also to preserve exaust gas converters catalysts which are very affected by the presence of sulfur. Beside hydrodesulfurization (HDS) which is an efficient process but needs hydrogen and high pressure and temperature, an alternative solution consists in a two steps process: the catalytic alkylation of sulfur compounds with olefins present in the gasoline follows by a distillation to eliminate heavier sulfur compounds. The OATS (olefinic alkylation of thiophenic sulfur) process has been patented and developed by BP. The catalysts used in this process are chosen among zeolites or supported inorganic acids. The selectivity of these catalysts has to be improved to avoid alkylation of aromatics or olefins oligomerization. Very few have been published on the mechanisms involved in this type of transformation when we start to work on. Depending of the catalytic system (zeolites, oxide-supported acid…), alkylation yield and selectivities towards monoalkylated or dialkylated products varied in a large extent showing that catalytic mechanisms could be quite different. After a first screening in the model alkylation of 3-methylthiophene with 2-methyl-2-butene, silica-supported heteropolyacids have appeared as the best catalysts for this type of reaction compared to supported phosphoric acids or zeolites. The preparation of silica-supported heteropolyacids has been optimized and some experiments have been made in real feed showing that those catalysts were less deactivated than the others. The objectives of this project are to evaluate deeply these solids in parallel with zeolites in model and real feed experiments using continuous fixed bed reactors. The real feed transformation will be followed by a very powerful technique, the two-dimensional GC in order to understand which compounds exactly in the feed are converted and to determine the selectivity associated with each catalyst.