Page 267 - Synthetic Fuels Handbook

FUELS FROM BIOMASS 253

Agricultural biomass Forest biomass Urban biomass Legend
Harvesting
Dedicated Dedicated
crops trees
Processing/
Primary Recovered recovery
products Residues (2) biomass
Residues
(2)

Biomass

Sugar-based Starch-based Lignocellulosic-based

Pretreatment
e.g., sugarcane e.g., stalks, chaff,
beet pulp cobs, stover
Fractionation
Hemicellulose
Starch
Cellulose Lignin/
extractives
Extractives/ Hydrolysis
oils
Hexose Hexose Pentose
sugars sugars sugars
Fermentation

Product recovery

Bioproducts Bioenergy Biofuels Product decision
FIGURE 8.9 Bioconversion platform flowchart. (Source: Mabee, W. E., D. J. Gregg, C. Arato, A. Berlin, R.
Bura, N. Gilkes, et al.: “Update on Softwood-to-Ethanol Process Development,” Appl. Biochem. Biotechnol.,
2006a, 129–132:55–70. http://aic.uwex.edu/resources/documents/Comparingbiofueltechnology.pdf )
the type of pretreatment that is employed. Finally, a relatively small amount of extractives
may be retrieved from the process. These extractives are highly variable depending upon
the feedstock employed, but may include resins, terpenes, or fatty acids.
Once hydrolyzed, six-carbon sugars can be fermented to ethanol using yeast-based pro-
cesses. Five-carbon sugars, however, are more difficult to ferment and lack the efficiency
of six-carbon sugar conversion. Bacterial fermentation under aerobic and anaerobic condi-
tions is also an option to expand the variety of other products.