Ethanol
Water
Enzyme
SSF
Water (if necessary)
Lime
Gypsum
Hydrolyzate
(water, acid, xylose)
Water–ethanol
Water–xylose
Xylose
fermentation
Cellulose–lignin
Pretreatment
(dilute acid)
Water
(if needed)
FiGUre 9.7 Integration of xylose fermentation and SSF. (Adapted from Lee, S. and
Shah, Y., Biofuels and Bioenergy—Processes and Technologies, CRC Press, Boca Raton,
FL, 2012; Wright, J.D., Chemical Engineering Progress, 84, 62–74, 1988.)
254
Water for Energy and Fuel Production
Slower fermentation was observed for pH <6 and addition of metal ions such as
calcium, magnesium, and ferrous ions stimulated ethanol production [51].
xylose fermentation does not require precise temperature control as long as the
temperature is between 25°C and 40°C. Higher concentration of xylose slows down
the fermentation. Ingram et al. [51–54] showed that E. coli of special type can efficiently convert both hexose and pentose sugars to ethanol. Ethanologenic E. coli
strains require simpler fermentation conditions, produce higher concentration of ethanol, and are more efficient than pentose-fermenting yeasts for ethanol production
from xylose and arabinose [55].
Sedlak et al. [56] successfully developed a genetically engineered Saccharomyces
yeast that can ferment both glucose and xylose simultaneously to ethanol, although
xylose was metabolized more slowly than glucose. Ideally, xylose should be consumed simultaneously with glucose at similar efficiency and speed [57]. This new
co-fermentation process has a very bright future. They also found that ethanol was
the most abundant product from glucose and xylose metabolism, but small amounts
of the metabolic byproducts glycerol and xylitol were also obtained [56].
9.4.4 eThAnol exTrACTion during FermenTATion
Significant research for concentration of dilute ethanol product to pure ethanol has
been carried out to reduce high energy consumption for purification of dilute end
products. Conventional distillation suffers from high energy cost and azeotropic
phenomenon that allows only about 95% pure ethanol. In the recent years, along
Water
Enzyme
SSF
Water (if necessary)
Lime
Gypsum
Hydrolyzate
(water, acid, xylose)
Water–ethanol
Water–xylose
Xylose
fermentation
Cellulose–lignin
Pretreatment
(dilute acid)
Water
(if needed)
FiGUre 9.7 Integration of xylose fermentation and SSF. (Adapted from Lee, S. and
Shah, Y., Biofuels and Bioenergy—Processes and Technologies, CRC Press, Boca Raton,
FL, 2012; Wright, J.D., Chemical Engineering Progress, 84, 62–74, 1988.)
254
Water for Energy and Fuel Production
Slower fermentation was observed for pH <6 and addition of metal ions such as
calcium, magnesium, and ferrous ions stimulated ethanol production [51].
xylose fermentation does not require precise temperature control as long as the
temperature is between 25°C and 40°C. Higher concentration of xylose slows down
the fermentation. Ingram et al. [51–54] showed that E. coli of special type can efficiently convert both hexose and pentose sugars to ethanol. Ethanologenic E. coli
strains require simpler fermentation conditions, produce higher concentration of ethanol, and are more efficient than pentose-fermenting yeasts for ethanol production
from xylose and arabinose [55].
Sedlak et al. [56] successfully developed a genetically engineered Saccharomyces
yeast that can ferment both glucose and xylose simultaneously to ethanol, although
xylose was metabolized more slowly than glucose. Ideally, xylose should be consumed simultaneously with glucose at similar efficiency and speed [57]. This new
co-fermentation process has a very bright future. They also found that ethanol was
the most abundant product from glucose and xylose metabolism, but small amounts
of the metabolic byproducts glycerol and xylitol were also obtained [56].
9.4.4 eThAnol exTrACTion during FermenTATion
Significant research for concentration of dilute ethanol product to pure ethanol has
been carried out to reduce high energy consumption for purification of dilute end
products. Conventional distillation suffers from high energy cost and azeotropic
phenomenon that allows only about 95% pure ethanol. In the recent years, along