Biodiesel, ethanol, and biogas are transport fuels produced from biomass that are used in the transportation industry. The composition of biodiesel and biogas may not be exactly the same as their equivalence from petroleum, but they perform the same task. Ethanol derived from biomass is either used as the sole fuel or mixed with gasoline in spark-ignition engines.

There are two thermochemical routes available for the production of diesel and gasoline from syngas: (1) gasoline, through the methanol-to-gasoline (MTG) process; and (2) diesel, through the FT process. The two biochemical means for production of ethanol and diesel are

• Diesel, through the transesterification of fatty acids

• Ethanol, through the fermentation of sugar

It may be noted that in both schemes part of the syngas’s energy content (30-50%) is lost during conversion into liquid transport fuel. It is apparent from Table 9.4 that this loss in conversion from biomass to methanol or ethanol can be as high as 50%, and further loss can occur when the methanol is converted into a transport fuel like gasoline. For this reason, when we con­sider the overall energy conversion efficiency of a car run on biogas and compare that with an electric car, the former shows a rather low fuel-to-wheel energy ratio.