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Water for Energy and Fuel Production
steam gasification with and without catalysts. Whitty [105] examined steam gasification of black liquor char under pressurized conditions.
4.5.1.6 lignin
The gasification of lignin has been investigated by a number of investigators
[106–108]. These and other studies have investigated various characteristics of
pyrolysis and gasification of lignin, the effect of alkali addition on gasification
and production of hydrogen and medium heating value gas during steam gasification of lignin. Most studies have examined lignin from paper and pulp industries
as well as Westvaco Kraft lignin. In the latter category, Kraft-1, Kraft-2, and
Alcell were gasified in the presence of steam at 600°C–800°C and they produced
gases with 30–50 vol% hydrogen. Most studies used a fixed-bed reactor.
4.5.2 STeAm reForming
4.5.2.1 ethanol
As discussed in a subsequent chapter 9, alcohols and in particular ethanol can be
easily obtained by the process of fermentation of sugar, glucose, fructose, and many
lignocellulosic biomass [109–116]. In Brazil, ethanol is extensively produced using
sugarcanes. Ethanol is easier and safer to store and transport because of its low toxicity and volatility and biodegradable characteristics. Ethanol can also be produced
from various energy plants, waste materials from agro industries, or forestry residue
materials as well as cellulosic and organic fractions of MSW. Easy availability of
ethanol makes it a good candidate for steam reforming to produce hydrogen.
Unlike methanol and gasoline derived from fossil fuel sources, ethanol derived
from biosources is carbon neutral to the environment. The carbon dioxide produced
from the steam reforming of ethanol can be used to regenerate additional biomass.
Bioethanol, generally containing about 12% ethanol in an aqueous solution, can be
directly subjected to steam reforming, thus eliminating the distillation step required
to produce pure ethanol. Since both water and ethanol can be converted to hydrogen,
the process of steam reforming avoids the separation stage. The thermal efficiency
of steam reforming of aqueous ethanol solution is very high (>85%) and this makes
the process economically very attractive. The steam reforming of ethanol is carried
out by the following reaction:
C H OH + 3H O  2 2 + 6 H
2 5
2
CO
2
(4.56)
This reaction follows a number of steps that involve the dehydrogenation of ethanol
to form acetaldehyde, which in turn decomposes to produce methane and carbon
monoxide. Further reforming of methane and water–gas shift reaction leads to the
formation of hydrogen. Since ethanol has high hydrogen content, the process produces a significant amount of hydrogen. There are, however, side reactions such as
dehydration and decomposition of ethanol which produce methane, diethyl ether,
and acetic acid that reduce the production of hydrogen. These side reactions can
be minimized by the use of selective catalysts. In addition, the formation of large