The thermochemical conversion route is largely based on existing technologies that are in operation for several decades (IEA 2008). In the past, the focus was on conversion of coal to liquid fuels and chemicals; however, in the recent years, the focus has also been on the conversion of natural gas resources into fuels. The thermochemical route basically involves the production of syngas (synthesis gas), which should be purified before it can go into the Fischer-Tropsch (FT) process to synthesize liquid fuels for application in aviation and marine industries, and chem­icals chiefly synthetic diesel. Syngas (mix of CO and H2 with some CO2, meth­ane, and higher carbon compounds) is produced by a severe heat treatment process of dry lignocellulosic feedstock in a controlled atmosphere, so that gasification is
initiated. The main stages of thermochemical route involve: (1) biomass fuel con­ditioning, (2) gasification process, (3) gas purification, and (4) FT conversion.

The thermochemical route can provide a number of additional co-products in addition to biofuels. These co-products can be exploited as a feedstock for produc­tion of value-added chemicals. The products profile from FT conversion can vary significantly depending on the synthesis temperature. High temperature leads to production of synthetic gasoline and chemicals, whereas low temperature produces waxy products that can be further cracked to make naphtha, kerosene, or diesel fuel (Griffin and Schultz 2012). The advantage of thermochemical route over biochemi­cal route is that the former can essentially convert all organic component of the bio­mass into products. However, the major limitation of thermochemical route is the need of high-temperature gasifier that imparts high cost to the process.