Page 34 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Solid waste biorefineries 13

400-500 C with a low heating rate allowing the biomass to undergo endothermic
degradation and release considerable amounts of biochar and pyrolysis gases. In
contrast, high heating rate (HHR) pyrolysis or fast pyrolysis typically occurs at tem-

peratures $ 400 C and has a heating rate . 300 C/min. These results show that
the physicochemical properties of biomass could play an important role in the liquid
yield, which means it will decide the liquid yield (Mohanty et al., 2011; Nanda
et al., 2014).

1.5.2 Chemical composition of biomass and its phases
Biomass composition and the thermal products, which include products through
pyrolysis (heating process), such as heating processes, are always interrelated with
each other, such as increasing the phenolic contents that are relative to carbohy-
drates, which results in reducing the oxygen concentration in bio-oil. Biomass con-
sists of several compounds such as cellulose, hemicellulose, lignin, structural
proteins, xylan, pectin, and mineral compounds in the cell wall. They are will
decide the liquid yields and their characteristics. The structures of the cellulose,
hemicellulosic polysaccharides, and some other sugar composition and linkages of
both cellulose and hemicellulose influence the liquid yield through pyrolysis. In
case of lignin, their major units vary based on the phases of pyrolysis process (Lin
et al., 2015).

1.6 Sludge derived bio-oil

Sludge is one of the most commonly used biomass alternatives in the biofuel pro-
duction due to its richness in volatile combustible matter than lignocellulosic feed-
stocks, especially sewage sludge; it consists of organic materials, including
proteins, carbohydrates, lipids and ash, heavy metals. Instead of dumping the sew-
age wastes in order to pollute the environment, they can be converted into valuable
products through several methods including thermochemical technologies, such as
direct combustion, gasification, and pyrolysis. Through these technologies the
wastes can be converted into valuable products and also the releases of toxic mate-
rials such as NO 2 ,SO 2 could be minimized. The products obtained from these
methods at different phases are solid materials (char), liquids (bio-oil), and gases
(methane). From these three methods the pyrolysis is the most commonly used
methods for the production of bio-oils, because we can modify the techniques eas-
ily. The major drawback of using sewage sludge is that it will produce the bio-oil
with high nitrogen and oxygen contents, which results in undesirable characteristics
in bio-oil such as

high instability,
viscosity,
corrosiveness,
low heating value, and