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Potentials of postharvest rice crop residues as a source of biofuel 289
and leads to problems in pumping, combustion, and atomization in diesel engines.
The biodiesels are also not suitable for prolonged storage as it leads to degradation
of the fuel components. Biodiesel is found to deposit carbon on engine parts and
also leads to excessive wear of the engine, thus requiring the need to fabricate new
suitable engines (Hassan and Kalam, 2013).
13.7 Operating conditions for biofuel generation from
postharvest rice crop residues
The currently increasing energy demands and the depleting fossil fuel reserves have
brought about an increased interest in renewable fuels or the biofuels. Wastes gen-
erated from agricultural activities and municipal wastes are being used to produce
liquid and gaseous biofuels (Behera et al., 2015). Postharvest rice residues can act
as a potential source for the production of biofuel (Fig. 13.10). The residues are
rich in lignocellulosic biomasses that are converted to ethanol by various steps such
as physical and chemical treatment at first followed by enzyme catalyzed hydrolysis
of sugar polymers, fermentation of the sugars into ethanol, and finally distillation of
the crude ethanol (Cheng and Timilsina, 2011).
On-field production of rice grains in million metric tonnes per annum is corre-
lated with the production of huge amount of rice straw on the cultivable land
assigned for rice production. The rice straw is used as a cattle feed, but the high sil-
ica and lignin contents reduces its use as a cattle feed. The production of million
metric tonnes of postharvest rice crop residues such as rice straw per annum is
more than sufficient as has been required as cattle feed. The biomass of surplus
amount of rice straw could be used as a promising source of feedstock for biofuel
production. The postharvest lignocellulosic rice crop residues are rich in cellulose
or hemicellulose. The produced biomass of postharvest rice crop residues such as
straw is more than the biomass of the rice grains harvested (Kadam et al., 2000).
The high cellulose content of rice straw is a possible factor for its consideration as
a feedstock for the production of biofuel. It contains about 390 g of cellulose per
kilogram of rice straw biomass (Karimi et al., 2006).
13.7.1 The biofuel production process
13.7.1.1 Lignocellulosic biomass
Lignocellulosic biomass accounts for a major portion of the terrestrial biomass
present on the earth surface. Approximately 64% of this biomass is derived from
nontree plant species such as grasses (Umezawa, 2018; Takeda et al., 2019). The
lignocellulosic biomass constitutes the postharvest rice crop residues, such as the
straw, which is used as feedstock for biofuel production. The major ingredients of
lignocellulosic biomass are cellulose (33% 51%), hemicellulose (19% 34%), and
lignin (20% 30%) (van Maris et al., 2006). The rice straw biomass consists of