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This work discusses the processes for removing sulfur from fuels, and problems related thereto, including conventional and improved processes of hydrodesulfurization, and alternative tehnologies and processes for obtaining fuel with extremely low sulfur content, which are in the process of research and development. It is anticipated that alternative processes already developed or those being researched will be applied as an addition to the currently most commonly used process of hydrodesulfurization, which is based on selective heterogeneous catalysts. Reviewed are new achievements in the development of the hydrodesulfurization process regarding new catalysts and reactors, the research and development possibilities of the adsorption and extraction processes, as well as the biodesulfurization process.

Fixed bed adsorptive desulfurization was carried out with model fuel comprising dibenzothiophene dissolved in isomerizate and xylene and an activated carbon as the adsorbent. Sulfur and its various compounds, which could be found in petroleum fractions, are among the main sources of environmental pollution and also negatively affect the car exhaust gas treatment systems. In addition the reduction of sulfur content in petroleum fractions improves the efficiency of processing, and the improved quality of fuel reduces motor ware. Dibenzothiophene is a representative of the refractory sulfur compounds who cannot be easily removed in conventional hydrodesulfurization processes under normal conditions. That is why the alternative separation processes, such as adsorption, are being researched and developed for desulfurization. The application of adsorptive desulfurization in practice is envisioned as an upgrade to hydrodesulfurization process where the adsorption column system would be installed within the hydrodesulfurization plant, downstream to the reactor. In this work the effects of flow rate and bed depth were studied and the experimental data were used for modeling fixed bed adsorption. The batch experiments were also carried out in order to conduct the adsorption equilibrium investigation and to validate fixed bed model data.

In this work the processes for removing sulfur from fuels, and problems related thereto, including conventional and improved processes of hydrodesulfurization, and alternative technologies and processes for obtaining fuel with extremely low sulfur content, which are in the process of research and development, are discussed. It is anticipated that alternative processes, that are already developed or that are being researched, will be applied as an addition to the currently most used process of hydrodesulfurization, which is based on selective heterogeneous catalysts. New achievements in the development of hydrodesulfurization process regarding new catalysts and reactors, as well as research and development possibilities of adsorption and extraction processes and of biodesulfurization process are reviewed.

Adsorption was investigated as a perspective separation process for desulfurization of diesel fuel that can achieve sulfur concentrations of less then 10 mg/kg. Compared to the conventional hydrodesulfurization process, the adsorptive removal of sulfur compounds can be accomplished at relatively low temperature and pressure. In this work desulfurization of diesel fuel was carried out in a computer controlled and completely automated adsorption apparatus with fixed bed column and activated carbon SOLCARB C3 from Chemviron Carbon, Belgium, as the adsorbent. The process control software was specifically developed for the designed system using Microsoft Visual Studio package. The process of adsorptive desulfurization of diesel fuel in a fixed bed column was modeled in order to describe the kinetics and to estimate the breakthrough curves. The models ability to fit the experimental data was satisfactory.

The removal of sulfur compounds from petroleum fractions and as such from gasoline fractions, which are blended to form gasoline fuel, is carried out in order to lower the emissions of internal combustion engines. Dibenzothiophene (DBT), which could be found in gasoline, is one of the so called refractory sulfur compounds and is very difficult to remove by means of conventional and widely used hydrodesulfurization (HDS) process. One of the main difficulties is the fact that the hydrogen sulfide, which is formed during the HDS process, inhibits DBT hydrodesulfurization reactions. That is why alternative desulfurization processes are being intensely investigated and one of the most promising is the adsorption. In this work DBT was removed from model gasoline solution (MGS) by adsorption on three different commercial adsorbents. The adsorption experiments were conducted in a batch adsorption apparatus. The experimental data was used to compare the used adsorbents and to carry out kinetic analysis and equilibrium characterization of the adsorption process.

Gasoline obtained by catalytic cracking process in fluidized bed (FCC gasoline) is one of the mayor components for the gasoline blending (cca 35 vol.%). Almost total amount of the sulfur present in the commercial gasoline derive from FCC gasoline, and this is way it is very important to enhance desulfurization process efficiency particularly for this fraction. Legislative restrictions regarding allowed sulfur content in motor fuels since 2009 are 10 mg kg-1. This is why increased number of scientific research involving in development of new desulfurization processes is emerging, i.e. processes that will be used as a supplement to the existing catalytic hydrodesulfurization process (HDS). Liquid extraction method is based on better solubility of sulfur compounds and aromatic hydrocarbons in relation to non aromatics in appropriate polar solvent. In petroleum refining industry sulfolane is a commercial extraction solvent mostly used for aromatics extraction from different petroleum fractions. Since part of the sulfur in petroleum is present in the form of aromatic compounds, sulfolane makes an interesting candidate as a solvent for extractive desulfurization of FCC gasoline. For the purpose of the investigation of continuous liquid extractive desulfurization of FCC with sulfolane, completely automated apparatus for continuous liquid extraction processes was build. Software allows acquisition of practically all of the measurable process variables and at the same time graphical display of their variations in real time. Increase of the extraction efficiency was achieved by introducing the pulsating plates into the extraction column (Karr column). With this design, simple finishing treatment of the obtained raffinate with water is enabled, as well as the possibility of the continuous solvent regeneration and reuse. Deployed demands for the apparatus are bind to the possibility of the following process variables regulation: feed and solvent flow, temperature, pressure and mixing speed at stabile phase interface level. Simulation of the liquid – liquid extractive desulfurization of FCC gasoline, as an upgrade of the HDS process, was achieved with ChamCad software package. The simulated and measured data were compared.

In this work adsorptive desulfurization of diesel fuel was investigated applying two Design of Experiments (DOE) methods. Experiments were carried out in a batch adsorption system using Chemviron Carbon SOLCARBTM C3 activated carbon as adsorbent. First DOE method employed was a full factorial with three factors on two levels and five center points, and second was Box-Behneken design with the same three factors but on three levels. Effects of individual factors and their interactions on sulfur concentration and sorption capacity were determined and statistical models of the process were developed. The first-order models predict the behavior of the system rather well but significant curvature was detected. Subsequently developed second-order models were able to give reasonably well descriptions of the system. The lowest achieved output sulfur concentration was 7.6 mg kg-1 with relatively low sorption capacity of 0.0861 mg g-1.

The removal of organic sulfur compounds from diesel fuel by activated carbon was investigated in a fixed bed column. The experiments were conducted to study the effects of process parameters such as flow rate, bed depth and temperature. Sulfur content of less then 0.7 mg/kg (the lowest level of detection of WD-XRF spectrometer used for analysis) was achieved for the lowest flow rate of 1 mL/min and highest bed depth of 28, 4 cm at 50 °C. In all the experiments at least one sample contained less then 10 mg/kg of sulfur with the largest achieved breakthrough volume of 660 mL. A mathematical model of the fixed bed adsorber was developed to describe the kinetics and to estimate the breakthrough curves. The model equations included the material balance for solute in liquid phase and the mass transfer rate expression. The ability of the model to fit the experimental data was satisfactory.

Removal of sulfur from diesel fuel by adsorption on a commercial activated carbon and 13X type zeolite was studied in a batch adsorber. Kinetic characterization of the adsorption process was performed applying Lagergren’ s pseudo-first order, pseudo-second order and intra-particle diffusion models using data collected during experiments carried out to determine the sulfur adsorption dependency on time. The experiments investigating adsorption efficiency regarding initial sulfur concentration were also performed and the results were fitted to Langmuir and Freundlich isotherms respectively. Activated carbon Norit SXRO PLUS was found to have much better adsorption characteristics. The process of sulfur adsorption on the fore mentioned activated carbon was further studied by statistically analyzing data collected during experiments which were carried out according to three factor two-level factorial design. Statistical analysis involved the calculation of effects of individual parameters and their interactions on sulfur adsorption and the development of statistical models of the process.

Alternative processes for desulfurization of transportation fuels are receiving increasing attention due to increasingly stringent regulations and fuel specifications in many countries for environmental protection purposes. Adsorption technology has been proposed for the removal of sulfur compounds in fuels. Compared to the hydrodesulfurization process, the adsorptive removal of sulfur compounds seems very promising since adsorption can be accomplished at low temperature and pressure, and the sulfur in fuels can be removed to a very low level. Design of Experiments, DOE, is a powerful statistical tool for exploring new processes or gaining detailed comprehension of existing ones, and then optimizing those processes. In this work organic sulfur compounds were removed from diesel fuel by selective adsorption with different types of commercial activated carbons. Adsorption was carried out in batch adsorbers. The model of the process was developed by way of two-level fractional factorial experimental design with four process parameters. Total sulfur content was measured with wave dispersive x-ray fluorescent spectrometer. Activated carbon Chemviron Carbon SOLCARB™ C3 has given the best desulfurization results. The process is well described within the experimental region by the developed model which was statistically validated.