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Investigation of Influential Parameters in Deep Oxidative Desulfurization of Dibenzothiophene with Hydrogen Peroxide and Formic Acid

DOI: 10.1155/2013/951045

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Abstract:

An effective oxidative system consisting of hydrogen peroxide, formic acid, and sulfuric acid followed by an extractive stage were implemented to remove dibenzothiophene in the simulated fuel oil. The results revealed such a great performance in the case of H2O2 in the presence of formic and sulfuric acids that led to the removal of sulfur compounds. Sulfuric acid was employed to increase the acidity of media as well as catalytic activity together with formic acid. The oxidation reaction was followed by a liquid-liquid extraction stage using acetonitrile as a polar solvent to remove produced sulfones from the model fuel. The impact of operating parameters including the molar ratio of formic acid to sulfur ( ), hydrogen peroxide to sulfur ( ), and the time of reaction was investigated using Box-Behnken experimental design for oxidation of the model fuel. A significant quadratic model was introduced for the sulfur removal as a function of effective parameters by the statistic analysis. 1. Introduction Deep desulfurization of diesel fuel has become an important issue due to the legislative regulations to reduce sulfur content in most countries (e.g., 15?ppmw since 2006 in the US and 10?wppm since 2008 in the EU) [1, 2]. Hydrodesulfurization (HDS) is the process most widely used in refineries to remove sulfur compounds from liquid hydrocarbons by transforming them to hydrogen sulfide. This process is catalytically carried out in the presence of hydrogen under severe reaction conditions such as high temperature and high pressure [3]. However, it has been recognized that the achievement of almost zero values of sulfur in fuels has to be done through the combination of HDS process with complementary reactions. Studies reveal that sulfur compounds remaining in diesel fuel after HDS process, at sulfur level lower than 0.1% wt., are generally thiophene, benzothiophene, dibenzothiophene, and their derivatives. These compounds exhibit low HDS reactivity because of the strict hindrance for the interaction between sulfur and active sites on the catalyst [3]. As a result, to remove refractory sulfur compounds with HDS, more severe operating conditions are needed, including higher temperature and pressure, more active catalysts, and longer residence time, which lead to large hydrogen consumption and reduction of catalyst life. To solve the shortcomings of the HDS process to remove refractory sulfur compounds, several new processes including oxidative desulfurization (ODS), selective adsorption, and biodesulfurization have been developed as alternative or complementary

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