Page 191 - Advances in bioenergy (2016)

During thermochemical conversions, the polymeric components of biomass such as cellulose,
hemicellulose, and lignin undergo a series of complex thermal degradation reactions. In most
cases, cellulose and hemicellulose undergo cycloreversion and dehydration followed by
transglycosylation reactions. This series of reactions results in the yield of both low- and high-
molecular weight compounds in the bio-oil fractions. The typical degradation products of
cellulose and hemicellulose in bio-oils include acids, esters, alcohols, ketones, aldehydes,
sugars, furans, and oxygenates, while lignin derivatives include phenols, guaiacols, and

syringols. 12-17 The primary products of cellulose and hemicellulose decomposition are
condensable vapors (yields to liquid products) and gases. Extractives contribute to liquid and
gas products either through simple volatilization or decomposition. This distribution of
components into products is shown schematically in Figures 8.1 and 8.2. Vapors formed by
primary decomposition of biomass components can be involved in secondary reactions in the
gas phase, forming soot and/or hot char surfaces, where secondary char is formed. 5,10

LIGNO(HEMI)CELLULOSIC BIOMASS CONVERSION

Current status defines that 90% of the H is produced through the reforming of CH or the light
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oil fraction with steam at high temperatures thereby producing CO , which has forced the
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research community to explore new horizons through renewable sources such as biomass or its
derived solvents to produce hydrogen. Hydrogen as a fuel possesses the highest energy content
per unit of mass (i.e., 120.7 kJ/g), compared with any of the known fuels. The advantage
involved with hydrogen production from biomass is that the CO emissions reduced manifold
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when using biomass as the starting material. Steam reforming of methane produces
approximately 13.6 kg of CO per kilogram of hydrogen production. It can easily replace older,
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unclean fuels, and reduce greenhouse gas emissions by improving ambience air quality. H is
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an ideal fuel source for fuel cells and many applications, as its by-products are H O, heat,
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electricity, and it contributes to country's economic growth through job development,
investment opportunities, and the creation of a sustainable, secure energy supply. 14-19