Page 80 - Biofuels Refining and Performance

Photosynthetic Plants as Renewable Energy Sources 63

High ethanol yield requires complete hydrolysis of both cellulosic and
hemicellulose with a minimum of sugar dehydration, followed by effi-
cient fermentation of all sugars in the biomass. Certain advantages of
using lignocellulose-based liquid biofuels are that they are evenly dis-
tributed across the globe and hence are readily available, less expensive
compared to agricultural feedstock, produced at a lower cost, and have
low net greenhouse gas emissions. Enzymatic processes (essentially
using bacteria, yeasts, or filamentous fungi) have been considered for
lignocellulosic processes. The enzymatic process when coupled with the
fermentation process is known as simultaneous saccharification and
fermentation. This has proved to be efficient in the fermentation of
hexose and pentose sugars [23]. Genencor International (www.genen-
cor.com/) and Novozymes, Inc., (www.novozymes.com) have been awarded
$17 million each by the U.S. Department of Energy with a goal to reduce
the enzyme cost tenfold (www.eere.energy.gov/). The Iogen Corp.
(www.iogen.ca/) demo-plant is the only one that produces bioethanol
from lignocellulose, using the enzymatic hydrolysis process. This plant is
known to handle about 40 ton/day of wheat, oat, barley, and straw and is
designed to produce up to 3 ML/yr of cellulose ethanol. Refer to Chap. 3
for bioethanol preparation, Chap. 6 for boidiesel processing, and Chap. 7
for ethanol and methanol used in engines.

2.6.3 Solid products
Refer to Sec. 1.14, Chap. 1, for more details on biomass. Solid products
fall under the following categories:

1. Direct outcome of photosynthesis: Products from forest, shrubs, agri-
cultures, and aquacultures.
2. Nonphotosynthesis: Mushrooms, animal biomass, indirect from
photofixation.
3. Wastes: Forests and agricultural products.
4. Municipal solid wastes: Not all solid biomass may be suitable for dif-
ferent end uses, i.e., energy production or energy recovery. For exam-
ple, mushrooms are notably useful as food, feed, or fodder, not
otherwise. Biomass properties are guidelines to further and more
fruitful end uses. The properties depend on the following:
a. Water or moisture content (aqueous/dry)
b. Calorific or combustion value
c. Dry residues/ash content/silicates, and so forth
d. Alkali metal/oxides in the ash
e. Ratio of cellulose/liquid/oils/fats/of other carbonaceous matters
f. Ratio of solid/liquid/volatiles