Investigation of Dibenzothiophene Removal from I Organic Phase: Enzymatic Approach vs. Ionic Liquids

Sulfur in fuel fractions like gasoline and diesel is responsible for acid-rain. The low levels of sulfur in fuels imposed by the environmental regulations of 15 ppm by 2006, have led to the search of alternative methods to comply with these new demands. The conventional process of hydrodesulfurization is unable to achieve the desired sulfur level even with the use of high temperatures and pressures to achieve a maximum reduction of the heavy sulfur compounds. Recently, ionic liquids have emerged as attractive “green” solvents. Enzymes have also been reported previously for oxidation of organic sulfur compounds. In this study, two approaches were adopted for sulfur removal; first an enzymatic approach was attempted for sulfur oxidation. This approach was found to be unsuccessful. Next, extractive desulfurization using an ionic liquid was investigated and successfully demonstrated using a biphasic system involving dibenzothiophene (DBT) hexane solution and 1-Butyl- 3-methyimidazolium tetraflouroborate, which forms the heavier layer in the system. The effects of different factors that may influence the extraction process with the ionic liquid were studied. The recycling of the ionic liquid used in the extraction was demonstrated by precipitating the sulfur compounds through the addition of water by 50%. After the diluted ionic liquid was concentrated by removing the water, it was used again in the extraction process. The sulfur level is reduced by 50% after each stage. The DBT Distribution coefficient in hexane/ionic liquid was determined to be around 0.73.