Desulfurisation goes green

Ionic liquids can remove sulfur from oil refinery streams.

German scientists have developed an environmentally-friendly method for removing sulfur from diesel oil and gasoline. Desulfurisation of oil refinery streams is an important step in the production of fuels, and has received increasing attention over the last 30 years since fuels high in sulfur produce exhaust gases containing SO _x, a major contributor to air pollution and acid rain.

Current state-of-the-art in desulfurisation technology is hydrodesulfurisation (HDS), in which organic sulfur compounds are converted to H ₂S and the corresponding hydrocarbons. The process requires high temperatures and pressures, typically 350°C and 30-100 bar hydrogen pressure, and large amounts of hydrogen, making HDS an expensive and relatively environmentally unfriendly process. Andreas Jess and Jochen Eßer, of Bayreuth University, together with Peter Wasserscheid at the University of Erlangen/Nuremberg, have developed an alternative procedure using halogen-free ionic liquids to extract the sulfur compounds.

The new process operates at close to room temperature and at ambient pressure, conserving significant amounts of energy, while the halogen-free ionic liquids are environmentally benign. In addition, the selective extraction properties of the ionic liquids used enable the removal of compounds such as dibenzothiophene derivatives, which are hard to remove from diesel oil by HDS.

Emphasising the practical aspects of their method, the authors have also investigated the regeneration of the sulfur-loaded ionic liquids and engineering aspects such as the design of the extraction process and integration into existing refinery networks. Future experiments will further investigate ionic liquid regeneration and selective extraction of nitrogen compounds.

Rowena Milan