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212 Advances in Eco-Fuels for a Sustainable Environment
contains lower energy content compared to gasoline (66%–68% of pure gasoline), the
high octane number (106–110) of ethanol increases the performance of the
gasoline-ethanol blend [8, 9]. Moreover, bioethanol contains higher oxygen content
(roughly 34.7%) compared to no oxygen in gasoline [10]. The high oxygen content
in bioethanol leads to clean combustion [11]. Consequently, the combustion of bio-
ethanol reduces the emission of toxic substances when compared with gasoline com-
bustion. It is estimated that bioethanol can reduce up to 90% of CO 2 and 60%–80% of
SO 2 emissions when blended with 95% gasoline fuel [12]. Table 8.1 shows the com-
parison of the GHG emission and energy intensity among gasoline and various bio-
ethanols. Therefore, bioethanol is considered the cutting-edge technology for the
production of low-emission renewable energy. In addition to these, the higher heat
of vaporization of ethanol enhances the volumetric efficiency of gasoline when
blended with ethanol [16]. However, the selection of a suitable microorganism, the
harnessing of promising feedstocks, and the development of proficient bioethanol
technology are the key challenges. In recent years, research and development have
been carried out for developing bioethanol technology that is feasible for commercial
implementation.
In this study, an overview of bioethanol as an ecofuel, including the history, poten-
tial resources, current technological status, challenges, and future scopes, is presented.
The chapter is structured as follows: Section 8.2 highlights the historical background
of ethanol production. Section 8.3 presents a brief description of current bioethanol
production technology. Section 8.4 discusses the major bioethanol feedstock potential
and current global cellulosic ethanol production plant status in detail. Moreover, the
challenges of the existing technologies and future prospects for cellulosic ethanol pro-
duction are presented in Section 8.5.
Table 8.1 GHG emission and energy of ethanol from various feedstock compared to gasoline
[13–15]
a
Energy intensity Energy balance
GHG emission (CO 2
Fuel e/MJ) (MJ/L) (MJ/L)
Gasoline 94 35.4 28.3
Corn ethanol 76 21.3 10.1
Sugarcane 45 21.3 16.4
ethanol
Switchgrass 43 21.3 21.0
ethanol
Corn stover 43 21.3 20.4
ethanol
Miscanthus 43 21.3 21.4
ethanol
a
Net energy in the fuel after compensating the energy required for the production.