Research Article Modeling of the Adsorptive Desulfurization of Diesel Fuel in a Fixed-Bed Column Adsorptive desulfurization enables the attainment of ultra-low sulfur content in hydrocarbon fuels by removing the refractory sulfur compounds, which are diffi- cult to remove in hydrodesulferization (HDS) processing when sulfur concentra- tions below 10 mg kg –1 must be attained. In this work, diesel fuel was desulfurized by adsorption using activated carbon as an adsorbent and the adsorption was car- ried out in a fixed-bed column. The output sulfur content of less then 0.7 mg kg –1 was achieved for the lowest flow rate of 1.0 cm 3 min –1 and the highest bed depth of 28.4 cm at 50 °C. In all the experiments, at least one output sample contained less then 10.0 mg kg –1 of sulfur with a longest achieved breakthrough time of 11.8 h. A mathematical model of the fixed-bed adsorber was applied to describe the kinetics and to estimate the breakthrough curves. The model equations included a differential material balance for a liquid phase and a mass transfer rate expression. The ability of the model to fit the experimental data was shown to be satisfactory. Keywords: Adsorption, Columns, Desulfurization, Diesel fuel, Fixed-bed, Modeling Received: January 13, 2010; revised: April 06, 2010; accepted: April 23, 2010 DOI: 10.1002/ceat.201000013 1 Introduction The reduction of the sulfur concentration in fuels in order to lower overall emissions has become one of the most scruti- nized refinery activities from both legislative, i.e., environmen- tal, and technological standpoints. As a consequence, desulfur- ization of the hydrocarbon streams and/or final petroleum products is of the utmost importance to the refining industry and is being intensely researched [1–10]. The sulfur content is a key parameter for determining the quality of transportation fuels. It adversely affects several mo- tor systems, as well as the intensity and composition of emis- sions. Sulfur is a naturally occurring ingredient of crude oil and can be found in many different chemical compounds. The organic sulfur compounds formed from gasoline or diesel fuel during combustion in car engines are converted to SO x . This results in both the formation of acid rain and reduced efficien- cy of the catalytic converters in cars due to the high content of sulfuric oxides in the exhaust fumes. Sulfuric oxides are also known to poison catalysts in the catalytic converters used to reduce CO and NOx emissions causing the increase in the overall negative environmental impact of sulfur from fuel. The removal of sulfur from transportation fuels not only counters environmental issues but also increases the chemical stability and application properties of fuels in general. The feedstocks for catalytic processes, e.g., isomerization and reforming, are also desulfurized, since sulfur acts as a catalytic poison in these processes, as well [11–13]. One of the alternative processes for the removal of organic sulfur compounds from hydrocarbon motor fuels, including diesel fuels, is adsorptive desulfurization. This process reduces the total sulfur content by the removal of sulfur compounds, including benzothiophene, dibenzothiophene and their deriva- tives with a suitable adsorbent in relatively mild conditions involving low pressure and temperature. During the process, the fuel is brought in contact with a solid adsorbent that selec- tively adsorbs sulfur-containing compounds. This enables the achievement of an ultra-low sulfur concentration, while incur- ring minimal adverse effects on other fuel properties. The pro- cess does not consume H 2 and can be operated at ambient or lower temperature and pressure [14–18]. Several different aspects of the adsorption process are inves- tigated by many authors. The bulk of the research is directed towards determining high capacity adsorbents that selectively adsorb aromatic sulfur compounds, over other aromatic com- pounds, and olefinic compounds from the fuels. Novel or modified adsorbents are then, for the most part, tested in purely experimental conditions, involving batch adsorbers or very small adsorption columns, by using model hydrocarbon Chem. Eng. Technol. 2010, 33, No. 7, 1137–1145 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Marko Muzic 1 Zoran Gomzi 1 Katica Sertic-Bionda 1 1 Faculty of Chemical Engineering and Technology, University of Zagreb, Zagreb, Croatia. – Correspondence: Dr. M. Muzic (mmuzic@fkit.hr), Faculty of Chemical Engineering and Technology - Petroleum and Petrochemical Depart- ment, University of Zagreb, Marulicev trg 19, 10000 Zagreb, Croatia. Desulfurization 1137