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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.
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