Research Article Kinetic and Statistical Studies of Adsorptive Desulfurization of Diesel Fuel on Commercial Activated Carbons Diesel fuel desulfurization by different commercial activated carbons was studied in a batch adsorber. Experiments, carried out to determine the sulfur adsorption dependency on time, were used to perform kinetic characterization and to screen the best performing activated carbon. The equilibrium characterization of the adsorption process was also performed. The statistical study of the process was undertaken by way of a two-level one-half fractional factorial experimental design with five process parameters. Individual parameters and their interaction effects on sulfur adsorption were determined and a statistical model of the process was developed. Chemviron Carbon SOLCARB TM C3 was found to be the most effi- cient adsorbent. The kinetic pseudo-second order model and Freundlich iso- therm are shown to exhibit the best fits of experimental data. The lowest achieved sulfur concentration in treated diesel fuel was 9.1 mg kg –1 . Keywords: Activated Carbons, Adsorption, Desulfurization, Diesel Fuel, Kinetics Received: September 19, 2007; revised: December 19, 2007; accepted: December 19, 2007 DOI: 10.1002/ceat.200700341 1 Introduction The sulfur content in hydrocarbon fuels has become a very im- portant environmentally, scientifically and legally debated top- ic, such that significant removal of organosulfur compounds has been mandated by government legislation. Current EU leg- islation sets the upper limit of sulfur content in diesel fuel as well as gasoline fuels at 50 mg kg –1 , with the projected 2009 limit being reduced to 10 mg kg –1 . Since 2006, the US Envi- ronmental Protection Agency (EPA) has reduced the sulfur content of diesel fuel to 15 mg kg –1 and gasoline fuel to 30 mg kg –1 [1]. It is well known that sulfur has an adverse effect on the envi- ronment, while a high content of sulfuric oxides in exhaust fumes reduces the efficiency of catalytic converters in cars. This is so because the sulfur compounds in the fuel are converted to SO x during combustion, which not only results in acid rain, but also poisons catalysts in catalytic converters for reducing CO and NO x [2]. With the current hydrotreating technology, it is difficult to reduce the sulfur content for diesel fuel to less than 15 mg kg –1 , since the remaining refractory sulfur compounds, depending on the origin of the crude oil, contain a sulfur level of ca. 50 mg kg –1 . These refractory sulfur compounds are the alkyl dibenzothiophenes (DBTs) with one or two alkyl groups at the 4- and/or 6-positions, which strongly inhibit hydrode- sulfurization of the compounds [3]. The lower reactivity of these refractory sulfur compounds is largely attributed to steric hindrance. It has been reported that the removal of these sulfur compounds by the HDS process to the desired levels would require more than a three-fold increase in the catalyst volume/reactor size, resulting in an enormously high cost of operation for this high temperature and high pressure process [4, 5]. Adsorption is a viable option for motor fuel desulfurization and the idea behind this approach is to selectively separate less than 1 wt % of the fuel mass by using selective adsorption for sulfur removal and leave the 99 wt % of non-sulfur containing fuel mass untouched [3]. Compared to the hydrodesulfuriza- tion process, the adsorptive removal of sulfur compounds seems very promising with regard to energy consumption since adsorption can be accomplished at low temperature and pressure, and the sulfur in the fuels can be removed to a very low level [6]. Activated carbons have been widely used as adsorbents in separation and purification processes for gaseous or aque- ous solution systems. They have a high adsorption capacity towards some organic and inorganic compounds due to © 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Marko Muzic 1 Katica Sertic-Bionda 1 Zoran Gomzi 1 1 Faculty of Chemical Engineering and Technology, Zagreb, University of Zagreb, Croatia. – Correspondence: BSc. M. Muzic (mmuzic@fkit.hr), Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia. Chem. Eng. Technol. 2008, 31, No. 3, 355–364 355