Published: November 23, 2011 r2011 American Chemical Society 147 dx.doi.org/10.1021/ie2024068 | Ind. Eng. Chem. Res. 2012, 51, 147–157 ARTICLE pubs.acs.org/IECR Kinetic Study and Optimization of Oxidative Desulfurization of Benzothiophene Using Mesoporous Titanium Silicate-1 Catalyst Aryav Sengupta, Prashant D. Kamble, Jayanta Kumar Basu, and Sonali Sengupta* Department of Chemical Engineering, Indian Institute of Technology, Kharagpur India 721302 ABSTRACT: The oxidative desulfurization (ODS) of benzothiophene (BT) in isooctane as a model fuel with 30% aqueous H 2 O 2 was studied using three different titanium silicate (TS) zeolites, synthesized mesoporous TS-1, synthesized mesoporous titanium beta, and commercial TS-1 catalyst, which were found to give 85.6, 45.74, and 25.31% conversions, respectively. Therefore, mesoporous TS-1 was selected as the catalyst for ODS of BT. Reaction time, temperature, catalyst loading, and molar ratio of H 2 O 2 :S were selected as the pertinent parameters for the optimization of conversion based on the BoxBehnken design. The predicted maximum conversion was observed to be 89.9% at a temperature of 60 °C, catalyst loading of 0.064 g, and mole ratio of BT and H 2 O 2 of 0.209. An empirical kinetic model was used to fit the rate data. The activation energy was found to be 25.20 kJ/mol. 1. INTRODUCTION The presence of organosulfur compounds such as thiophene (Th), benzothiophene (BT), dibenzothiophene (DBT), and their alkyl derivatives are the major unwanted species present in crude oil fractions. These lead to corrosion in refinery equipment and engines of automobiles, to poisoning of catalysts used in sec- ondary treatment in refineries, and to formation of sulfur oxides after combustion of fuel that cause severe environmental pollu- tion such as acid rain, depletion of the ozone layer, and smog generation. 1 Hence it is very essential to reduce the sulfur content in sulfur-bearing petroleum fractions by suitable tech- niques which are both technologically and economically feasible. Legislation in Japan and Europe have limited the sulfur content in light oil to a maximum of 50 ppm. The U.S. Environmental Protection Agency (EPA) issued new sulfur standards of 30 ppm by 2004 and of 15 ppm by 2006 in diesel fuels and gasoline. 2 The Indian government also issued a notification to introduce the EURO IV standards and a sulfur level of 50 ppm in fuel. 3 At present, there are several methods which are available for the removal of sulfur compounds from hydrocarbon fuels such as selective adsorption, extractive separation, biodegradation, hy- drodesulfurization (HDS), and oxidative desulfurization (ODS). Currently, catalytic HDS is the most popular method for reducing sulfur content in petroleum fractions. HDS is a high severity process which accompanies large operating and capital costs. Moreover, it is difficult to remove polyaromatic sulfur compounds such as BT, DBT, and their derivatives because of very low reactivity. 4 By contrast, oxidative desulfurization (ODS) was considered as one of the most effective and alternative methods to produce fuels with very low sulfur content. 2,57 ODS is advantageous over HDS because the former process can be carried out at near-ambient conditions such as 50 °C and atmospheric pressure in the liquid phase. The mechanism of the ODS reaction is the electrophilic addition of oxygen atom to divalent sulfur with the formation of unstable sulfoxides (1-oxides) and then sulfones (1,1-dioxides) in the heterocyclic thiophene ring. 8 The di fference between the physico- chemical properties of the sulfones and those of the hydrocarbons present in fuel oil makes easy separation of sulfones from the fuel oil by solvent extraction, distillation, adsorption, etc. The selective oxidation of thiophene and its alkyl derivatives in n-octane solvent using titanium silicate-1 (TS-1) as catalyst, H 2 O 2 as oxidant, and tert-butyl alcohol or water as solvent was reported. 9 Also, ODS of Th, BT, DBT, and their derivatives with tert-butyl hydroperoxide (t-BuOOH) as oxidant were studied using catalysts such as titanium zeolites, MoAl 2 O 3 , and cobalt aluminum phosphate. 10,11 Improved reactivities of aromatic sulfur compounds were observed at mild conditions using V 2 O 5  Al 2 O 3 and V 2 O 5 TiO 2 catalysts, when the oxidant H 2 O 2 was added slowly. 12 The use of peroxy acids such as performic acid, pertrifluoroacetic acid, and a mixture of formic acid and H 2 O 2 as efficient oxidants was reported for selectively oxidizing sulfur compounds in fuel oil. 10 The oxidation of tetrahydrothiophene, diphenyl sulfide, 2-acetylthiophene, and 2,5-dimethylthiophene with H 2 O 2 as oxidant and molecular sieve catalysts such as TS-1, titanium-beta, and TiHMS has been studied. 1 The use of H 2 O 2 as oxidant over catalysts such as formic acid, polyoxometalate, and molecular sieve zeolites for selective oxidation of thiophene- based compounds has also been reported. 13 Among these catalysts, titanium silicates were found to give the maximum conversions under mild conditions. The use of complexes as catalysts, containing transition metals such as Ti, Mo, Fe, Ru, and Re, with H 2 O 2 ,O 2 , and O 3 as oxidants was investigated for oxidizing sulfur compounds in fuel oil. 11 The use of an ultrasound-assisted ODS process was found to enhance the reaction rate of sulfur compounds greatly compared to that of ODS without ultrasound. 14 The two-phase ODS reactions faced decreased reaction rate and low conversions because the reaction occurs only at the interface. The use of specific phase-transfer catalysts (PTC) in ODS reactions was proved to be of great advantage compared to ordinary catalysts as PTC transport reactants from one phase to another and hence improve the reaction rate. Hence the application of PTC is of great importance to the industrial use of ODS processes. The use of quaternary ammonium salts such as tetramethylammonium Received: June 24, 2011 Accepted: November 23, 2011