Hydrogen Production by Reforming of Logistic Diesel Fuel in Supercritical Water

Compared with other fuels, diesel fuels still have significant advantages in terms of logistic properties such as energy density, availability and ease of handling. However, diesel fuels also have their draw backs. For an example, the only established technology to convert the chemical energy of diesel fuels into electrical energy is engine-based internal combustion generators. These emit large quantities of pollutants and noise as well as a strong IR-signature. Furthermore diesel combustion engines become rather inefficient if scaled down to power ranges of a few kilowatts, e.g. for APU uses. Fuel cells, on the other hand, are highly efficient even under partial load conditions or as smaller systems. They are also silent with low emission of pollutants and have only a weak IR-signature, at least for the low temperature types. However, low temperature fuel cells can only use hydrogen or methanol as fuels and even high temperature fuel cells can currently not be fed with diesel fuels directly. A combination of both technologies, i.e. fuel cells directly or indirectly using diesel fuels, would be a promising solution for many applications. A major obstacle in using diesel fuels in high-temperature fuel cells, or producing hydrogen by reforming diesel, is soot formation during the evaporation. In this contribution a different approach to diesel reforming will be presented. This approach relies on the different salvation properties of water in its supercritical phase. Once water has achieved supercritical state its properties change so that it becomes sort of a non-polar solvent with the ability to dissolve most organic substances In that way diesel fuels can be dissolved in the supercritical water upstream of the reformer reactor. In the reactor, the diesel fuel is than reformed in a reaction analogue to the steam reforming reaction. However, this reaction can proceed at much lower temperatures than in a regular steam reforming reactor down to 550 °C, decreasing the CO yield. Furthermore, it was found that the conditions can enhance the stability of the catalysts against sulphurous impurities. In our contribution we will show the results of laboratory-scale tests in a micro-reactor for low sulphur and high sulphur content fuels as well as initial results obtained with a demonstration unit created on behalf of the German armed forces.