Desulfurization of diesel oil by selective oxidation and extraction of sulfur compounds by ionic liquids-a contribution to a competitive process design

Extraction of S-compounds like dibenzothiophenes from diesel oil by ionic liquids (ILs) indicate that such a process could be an attractive alternative to common (deep) desulfurization by hydrotreating. The efficiency of the extraction increases if the S-species are previously oxidized to the corresponding sulfoxides and sulfones as these species have a much higher distribution coefficient compared to the non-oxidized derivatives. The present work combines the extraction of oxidized S-compounds from diesel oil by ILs and the subsequent IL regeneration, i.e. the removal of the oxidized S-species from the S-loaded IL by means of water addition which leads to a displacement of the S-compounds from the IL. Thus, water separation by evaporation is needed before the IL can be re-used for extraction. Model oils containing single sulfones as well as real pre-oxidized diesel oils were investigated. Based on the experimental results the energy consumption of the extractive desulfurization process was estimated. The evaporation of water from the IL is the crucial step with regards to the energy consumption of the process. The energy demand is comparable to classical hydrotreating, if a multi-stage evaporation is used.