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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
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