µHDS system for desulfurization of logistic fuels for fuel cell applications

Abstract: Logistic fuels such as diesel and petrol, in which Jet A1 is included, are sulfur-containing fuels used for transports. The main problem with logistic fuels, when used in fuel cell (FC) applications, is their relatively high concentration of sulfur compounds. The sulfur compounds might poison the catalysts in all of the downstream processes, including the FC itself. Hydrodesulfurization (HDS) is an industrial approach for effective desulfurization of fuels by converting complicated organic sulfur compounds into hydrocarbons and hydrogen sulfide (H2S), which in turn can be trapped in an adsorption cartridge. This thesis focused on a miniaturization of said technology, i.e. a µHDS-system for logistic fuels, in small-scale fuel cell systems. The goal was to desulfurize Jet A1 for utilization in FC-applications. Through investigation and evaluation of different catalysts and process parameters, a catalytic reactor system was developed. Desirable was to achieve a sulfur level below 10 ppm which is low enough for injection into a FC. The approach was to set up a micro-scale plug flow reactor (PFR) in which the effects of temperature (260 °C – 450 °C), pressure (2 bar – 8 bar) and LHSV (1 h-1 – 4 h-1), on catalytic activity, was investigated. Incipient wetness impregnation was used for the preparation of six different catalysts, which were tested in said reactor. Detailed investigations were done on a Pt/alumina (PPt-47, manufactured by Stonemill AB) catalyst as well as on a CoMo/alumina catalyst impregnated with citric acid (CA). Their activity was determined based on the conversion of thiophene and dibenzothiophene (DBT). As a final test, Jet A1 was desulfurized using the same two catalysts. CoMo-CA was consistently the better performing catalyst compared with PPt-47, reaching a sulfur conversion of 98.2 %, compared to 93.2 % when tested with Jet A1 at the most severe reactor settings. A sulfur level of 13.3 ppm was achieved with the CoMo-CA, applicable in a high-temperature FC.