Hydrodesulfurization of jet fuel by pre-saturated one-liquid-flow technology for mobile fuel cell applications

To prevent the catalysts in fuel cell systems from poisoning by sulfur containing substances the fuel to be used must be desulfurized to a maximum of 10 ppm of sulfur. Thereby, damage to the catalysts in the fuel cell and the reformer can be avoided. Diesel fuel for road vehicles within the EU is already desulfurized at the refinery. However, jet fuel is permitted to have up to 3000 ppm of sulfur. Since the hydrodesulfurization process used in refineries is not suitable for mobile applications, the aim of the present work was to develop an alternative desulfurization process for jet fuel and to determine its technical feasibility.To this end, many processes were assessed with respect to their application in fuel cell based auxiliary power units (APUs). Among them, hydrodesulfurization with pre-saturation was selected for detailed investigations. Laboratory tests revealed that also syngas operation is possible without any performance loss in comparison to operation with hydrogen. Pure hydrogen is not available in a fuel cell system based on reforming of jet fuel. The effects of reaction temperature, operating pressure and liquid hourly space velocity (LHSV) were investigated. Different jet fuel qualities with up to 3000 ppm of sulfur were desulfurized to a level of 15–22 ppm.Finally, the technical applicability of hydrodesulfurization with pre-saturation was demonstrated in a pilot plant with an electrical power of 5 kW, going beyond the laboratory scale. In a 200-h experiment, a commercial jet fuel with 712 ppm of sulfur was desulfurized to a maximum sulfur content of 10 ppm. Besides this, H2S separation by stripping with air turned out to be a suitable method for APU applications. The aim of developing a suitable process for the desulfurization of jet fuel in fuel cell APUs has thus been achieved.