FIGURE 3.1 Comparison of biochemical and thermochemical routes for converting biomass to fuels.

Source: Dayton, 2007.

blocks, such as carbon monoxide (CO) and hydrogen (H₂), which can be used for the synthesis of fuels (Figure 3.1). Other thermochemical conversion processes include pyrolysis and liquefaction.

Biochemical conversion uses enzymes to break down structural carbohydrates (for example, the cellulose¹ and hemicellulose² found in plant cell walls) into sugars, which are transformed into alcohols, organic acids, or hydrocarbons by microorganisms in fermentation. The conversions typically take place at atmospheric pressure and temperatures ranging from ambient to 70°C.

Early ethanol production technology based on biochemical conversion of sugar and starch has been deployed commercially. In that technology, ethanol is