Investigation of catalytic hydrocracking of Fischer-Tropsch wax for the production of transportation fuels

The Fischer-Tropsch synthesis allows the production of high quality diesel fuel from biomass derived synthesis gas. Unfortunately the diesel yield of the synthesis step is restricted, since the synthesis is non-selective. To increase the overall diesel yield, the Fischer-Tropsch synthesis can be operated in a high-wax mode with subsequent hydrocracking of the long-chained n-paraffins to the desired fuel. In this article, hydrocracking of two high-boiling waxes was investigated in a small-scale pilot plant using a commercially available base metal catalyst on an amorphous support. The influence of the reaction temperature, the space velocity and the pressure on the hydrocracking process and the effect of the operating conditions on the achieved fuel qualitly have been studied. The reaction temperature and the space velocity showed a considerable impact on the conversion as well as on the isoparaffin to n-paraffin ratio and on the boiling range of the hydrocracking product. Further, it was found that varying the pressure at a relatively high level between 55 and 65 bar had no significant effect. At severe reactor conditions, an cant 0 increased hydrogenolysis activity of the base metal catalyst was observed, resulting in an increased methane formation. The quality of the obtained diesel fuel showed a strong dependence on the conversion achieved from hydrocracking. Cetane numbers of up to 80 (DCN) were achieved under low-conversion conditions due to lower isoparaffin to n-paraffin ratios of the hydrocracking products, whereas high-conversion conditions increased the iso-to-n ratio and led to improved cold flow properties with Cold Filter plugging Points down to below -27 degrees C.