Biofuels production via the Fischer-Tropsch technology is a conversion process of solid bio­mass into liquid fuels (Biomass-To-Liquid or BTL) as it is depicted in Figure 2. More specifi­cally the solid biomass is gasified in the presence of air and the produced biogas rich in CO and H2 (synthesis gas), after being pretreated to remove coke residues and sulfur com­pounds, enters the Fischer-Tropsch reactor. The Fischer-Tropsch reactions allow the catalytic conversion of the synthesis gas into a mixture of paraffinic hydrocarbons consisting of light (Q-C4), naphtha (C5-Cu), diesel (C12-C20) and heavier hydrocarbons (>C20). Even though the Fischer-Tropsch reactions yields depend on the catalyst and operating parameters employed [43—45], the liquid product (naphtha, diesel and heavier hydrocarbons) yield is high (~95%). The produced synthetic naphtha and diesel fuels can be used similarly to their fossil coun­terparts. The heavier product however, which is called as Fischer-Tropsch wax, due to its waxy/paraffinic nature should get upgraded via catalytic hydrocracking to get converted to mid-distillate fuels (naphtha and diesel).

The conversion of Fischer-Tropsch wax into mainly diesel was studied in virtue of the Euro­pean Project RENEW [46]. During this project Fischer-Tropsch wax with high paraffinic con­tent of C20-C45 was converted into a total liquid product consisting of naphtha, kerosene and diesel fractions via catalytic hydrocracking. However the total liquid product content of die­sel molecules was the highest and the diesel fraction was further separated and character­ized having density of 0.78gr/ml and cetane index of 76 [47]. The schematic of the BTL process with actual images of the feedstock, Fischer-Tropsch wax and synthetic diesel are given in Figure 8.