Environmental Engineering Reference
In-Depth Information
for ethanol vehicles in Brazil (Wyman and Hinman 1990). Also, low proportions of gasoline can be
blended with pure ethanol for use as fuel. Such fuels are environmentally advantageous because of
their clean-burning characteristics and reduced emissions of ethanol into the atmosphere. Engines
designed for dedicated ethanol use can be tuned to achieve higher efficiencies than conventional
gasoline engines (Lynd et al. 1991).
Ethanol can be produced from renewable resources such as raw materials containing sugar
(sugarbeet, sugarcane, etc.), starch (potato, com, grain, etc.), and cellulose (lignocellulosic materials).
Currently molasses and starch are being used worldwide for ethanol production. These substances
are expensive because of their other industrial uses; therefore, they cannot be used for economical
alcohol production as an alternative fuel. Molasses is used in refining tobacco, in preparing poultry
feed, etc., and starchy materials are hardly sufficient to meet the food requirements of teeming
millions. Therefore, research emphasis needs to be directed toward finding a cheap and abundantly
available substrate for ethanol production.
World ethanol production is estimated to be 21.6 billion gallons, with approximately 14 billion
gallons coming from the United States and Brazil and an Indian share of 0.6 billion gal (Market
Research Analyst 2008). Although use of bioethanol as a source of energy would be more for than
just complementing solar, wind, and other intermittent renewable energy sources in the long run
(Lin and Tanaka 2006), the growing demand of bioethanol can only be met from lignocellulosics
(Nguyen and Saddler 1991).
30.2 lIGnocellulosIc BIomass
Various lignocellulosic biomass sources, such as agricultural residues (straws, hulls, stems, stalks,
bagasse, etc.), fruit and vegetable wastes, deciduous and coniferous woods, municipal solid wastes
(paper, cardboard, yard trash, wood products, etc.), waste from the pulp and paper industry, and
herbaceous energy crops have the potential to serve as low-cost and abundant feedstocks for
production of fuel ethanol. The major component of these materials is cellulose (35-50%), followed
by hemicellulose (20-35%) and lignin (10-25%). Proteins, oils, and ash in widely varying ratios
make up the remaining fraction of lignocellulosic biomass (Wyman 1994). In lignocellulosic
materials, cellulose, a linear polymer of glucose, is associated with hemicellulose and surrounded
by a lignin seal. Lignin, a complex three-dimensional polyaromatic matrix, prevents enzymes and
acids from accessing some regions of the cellulose polymers.
Crystallinity of the cellulose further impedes acid or enzymatic hydrolysis (Weil et al.
1994;
Bothast and Saha 1997). Production of ethanol from lignocellulosic materials involves: (1)
detachment of cellulose fibers from the lignocellulosic structure, which is accomplished by physical
or chemical means; (2) acid or enzymatic hydrolysis of the cellulose fibers; and (3) fermentation of
sugars to ethanol, which is then distilled to yield the final product (von Sivers et al. 1994;
Bothast
and Saha 1997). During the last 2 decades, advances in technology for ethanol production from
biomass have been developed to the point that large-scale production will be a reality in next few
years (Yu and Zhang 2004; Moiser et al. 2005).
Although various lignocellulosic crop residues (e.g., wheat straw, rice straw, cotton stalks, corn
stalks and cobs, groundnut shells, etc.) have been used for ethanol production, little effort has been
made to use sunflower wastes as a substrate for ethanol production. Biomass resources are essential
for bioenergy production. There are two major criteria for determining whether a crop is suitable
for energy use. The first is the high dry matter yield per land unit and the second is the net gain
in energy (the amount of energy produced from the biomass should be higher than the amount of
energy required to grow the crop). Being one of the major oil crops cultivated worldwide, sunflower
(
Helianthus annuus
L.) has the potential to become a biomass crop. As a member of the Compositae
family, sunflower is relatively easy to grow in a wide range of environments, from the equator to a
latitude of 55° north. Young sunflower plants withstand mild freezing. Sunflower has a strong root
system and shows a considerable level of drought tolerance (Hu 2008). This crop was cultivated in
