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 (C1-C4), naphtha (C5-C11), diesel (C12-C20) and heavier hydrocarbons (>C20). Even though the Fisch- er-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.