Introduction - Biomass Gasification, Pyrolysis and Torrefaction - page 9

Water

Sugar, corn
feedstock

Ethanol

Sugar
fermented to
alcoholic
“beer”

Yeast

Liquid beer

Residues Animal feed

(A)

Enzymes
and Water

Acid and Water

Cellulosic Feedstock

Hemicellulose
syrup for
pentose
fermentation

Acids break
biomass into
base sugars
and fibers

Cellulosic
ethanol

Cellulose and lignin fibers

Cellulose
solids for
hydrolysis and
ethanol
fermentation

Liquid beer

Enzymes
and water

Boiler to
generate
steam for
process

Lignin

(B)

FIGURE 1.5 Two biochemical routes for production of ethanol from sugar (noncellulosic) and
cellulosic biomass: (A) Conversion of food-feedstock into ethanol and (B) conversion of cellu-
losic feedstock into ethanol.

the case with cellulosic biomass feedstock because of the expense and diffi-
culty in breaking down (hydrolyzing) the materials into fermentable sugars.
Lignocellulosic feedstock, like bagasse, requires hydrolysis pretreatment
(acid, enzymatic, or hydrothermal) to break down the cellulose and hemicel-
lulose into simple sugars needed by the yeast and bacteria for the fermenta-
tion process ( Figure 1.5B ). Acid hydrolysis technology is more mature than