BIOCHEMICAL CONVERSION: BIOFUELS BY INDUSTRIAL FERMENTATION - Biomass as a Sustainable Energy Source for the Future - page 432

CO 2

C5 sugars C6 sugars Light

Pentose
phosphate
pathway

Glycolysis Calvin cycle

MEP path w ay

Pyruvate Cyanobacteria

MEV pathway

IPP

Acetyl-CoA Fatty acids

Isoprenoids Butanol Fatty aldehyde

Alkanes

FIGURE 13.12 Simplified pathways for the production of liquid biofuels other than ethanol.
The pathways of Cyanobacteria are at the right-hand side of the dashed line.

aldehyde — an intermediate of fatty acid metabolism — to an alkane or alkene (olefin).

So far, this approach has led to the secretion of C 13 - C 17 mixtures of hydrocarbons of

ca. 0.3 g L -1 . The process is currently under optimization, and pilot-plant fermenta-
tions (1 m 3 scale) have already been performed (Domínguez de María, 2011).

Figure 13.12 shows simplified pathways for the production of isoprenoids, butanol,
and long-chain alkanes.

13.6 STOICHIOMETRIC AND THERMODYNAMIC
COMPARISON OF FERMENTATIVE BIOFUELS

Worldwide, there are many studies for the development of novel biofuels by fermen-
tation as an alternative to the established ethanol. Examples include butanol, branched
alcohols, alkanes, alkenes, esters, and ketones. Evaluating the potential of certain