Fischer-Tropsch Waxes UpgradingviaHydrocracking and Selective Hydroisomerization

In recent years, the production of hydrocarbon cuts from various sources via the Fischer-Tropsch process has lived a renewed interest. Paraffinic cuts produced via the Fischer-Tropsch reaction can be upgraded either to liquid fuels (middle distillates) or to lubricant base oil of high quality. The first kind of upgrading involves the use of a hydrocracking catalyst whereas for the second kind of upgrading selective hydroisomerization catalysts can be selected. Both catalysts are bifunctional and contain an hydrogenation/dehydrogenation function and an acidic function; however, it is shown that depending of the kind of upgrading needed, the acidic function has to fulfill various requirements. The first part of this article is a short review dealing with long chain n-paraffin hydrocracking mechanisms and catalysts. Specificities of Fischer-Tropsch feedstocks compared to conventional ones as well as the potential impact of oxygenate compounds on the hydrocracking catalysts are underlined. The second part of this article is devoted to the selective hydroisomerization mechanisms and catalysts. It is shown that the topology of the solid acid porosity is a key factor for governing the selectivity of the catalyst towards hydroisomerization.