CHEMISTRY OF BIOFUELS AND BIOFUEL ADDITIVES FROM BIOMASS - Biomass as a Sustainable Energy Source for the Future - page 548

18.1 INTRODUCTION

First-generation biodiesel (fatty acidmethyl esters (FAME)) and bioethanol have paved
the way for the use and public awareness of biofuels in a socio- and technoeconomic
context. FAMEandbioethanol have achievedcommercial status andmarket acceptance.
At present, new generations of biofuels are progressing as alternatives, and enormous
efforts are made by knowledge institutes and companies and stimulated by governmen-
tal or broader policies and legislations in finding the best biofuel, both in terms of
biomass source and the final desired structure of the fuel. The present chapter is meant
to provide understanding of the molecular structure of biofuels and of the organic
chemistry behind the conversion of biomass to biofuel. With this knowledge in hand,
chemical engineers can rank the potential of novel biofuels continuously appearing
in the literature by comparing molecules of similar structures and origins. In addition,
the potential and greenness of alternative biofuels and their production methods are
discussed in viewof their atomeconomy and compliance with the 12 principles of green
chemistry. These principles are a possible instrument of predicting how good new
biofuels will score from a socioeconomic and technical perspective (Sheldon, 2011).
The emphasis in this chapter is on liquid biofuelswith awell-defined organic structure
that can replace the current fossil-derived gasoline and diesel components. The concept is
to directly transform biomass feedstocks based on, e.g., cellulose and plant oils into
organics with a high energy density. The alternative route, gasification of biomass to
CO/H 2 and further conversion to liquid fuels, falls outside the scope of this chapter.
For an overview of this technology, the reader is referred to Chapters 10 and 15 as well
as excellent reviews available in the literature (Demirbas, 2007; Ragauskas et al., 2006).
Similarly, the description of thermochemically (i.e., catalytic pyrolysis) produced bio-
oils,whichhavea largepotential as, e.g., heavyoil substitutes, canbe found inChapter 11.
In terms of gaseous feedstocks, hydrogen (produced by, e.g., gasification of
biomass) and methane (from biogas) have a high energy density (with a HHV of
142 MJ kg −1 , respectively) and can in principle be considered as

biofuels. However, their gaseous nature still necessitates special requirements.
In the global energy market, the main nonfossil options are solar, wind, hydro,
biomass, and geothermal energy. These primary energy sources need to be converted
into energy carriers such as electricity, hydrogen, and biofuels. Electrical cars are
emerging, but efficient storage of large amounts of electrical energy is still a
challenge. Similarly, the storage and distribution of hydrogen faces many obstacles.
Biofuels offer a nonfossil alternative to the current high energy density liquids used in
cars, trucks, and airplanes.

kg −1 and 56 MJ

18.2 BIOETHANOL AND BIODIESEL

The massive use of fossil gasoline and diesel is linked to their higher heating value
(HHV) of 44 kg −1 (tinyurl.com/oms56vw). This heating value can be easily

calculated using Dulong

− 48 MJ

s formula (derived originally for coal, and here, it is assumed
that no sulfur is present in the fuel):

'