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Biomass Pyr olysis and Bio-Oil Refineries 215

In the United States alone it is possible to sustainably produce
1.3 billion dry tons of biomass annually (Perlack et al. 2005). Processing
75 percent of this biomass via fast pyrolysis and bio-oil hydrotreat-
ment could result in the production of 273 million tons of green gas-
oline and green diesel annually with the potential to replace up to
66 percent of current U.S. gasoline consumption (410 million tons/
year). The impact of this new model of biomass economy in rural
areas could be significant. For example, 54,000 new mobile pyrolysis
units (at 50 tons/day each) will be needed in the United States to pro-
cess 975 million tons of biomass annually. Thousands of additional
jobs could be created to operate and maintain the bio-oil refineries.
The design, manufacture, and assembly of all components needed to
build these systems could have a multiplicative effect, generating
thousands of additional jobs in the broader economy.
The current status, opportunities, and challenges to convert bio-
mass into second-generation transportation fuels via pyrolysis and
bio-oil refineries have been discussed in this chapter. Excellent
reviews on state of the art of biomass pyrolysis technologies and on
the application of bio-oils as sources of fuels and chemicals have been
published (Bridgwater and Peacocke 1994; Diebold and Bridgwater
1999; Meier and Faix 1999; Oasmaa and Czernik 1999; Piskorz et al.
1999; Radlein 1999; Bridgwater et al. 2001; Czernik and Bridgwater 2004;
Mohan et al. 2006).

7.2 Biomass Composition
The composition of a biomass will influence the yield and properties
of the resulting crude bio-oils, charcoals, and gases. Trees can be clas-
sified as hardwoods (Angiospermae) or softwoods (Gymnospermae).
Biomasses are composed of cellulose, hemicelluloses, lignin, extractives,
and mineral materials (also known as ash) (Campbell 1983; Klass 1998).
The cellulose, hemicelluloses, and lignin are bio-polymers that form
the structure of biomass cell walls.
7.2.1 Cellulose
Cellulose is a linear polysaccharide with a flat, linear configuration
composed of between 10,000 and 15,000 glucose units linked by gly-
cosidic bonds (see Fig. 7.2) (Campbell 1983; Klass 1998). Cellulose
structure is reinforced by inter- and intrachain hydrogen bonds.
Cellulose can be found in amorphous and crystalline forms. Six
convertible polymorphs of cellulose (I, II, III , III , IV , and IV ) have
I II I II
been identified. The polymorph I, or native, cellulose is the only form
found in nature. Although it was initially thought that cellulose I was
single phase, it is now known that it is always a mixture of two allo-
morphs (Iα and Iβ). These allomorphs differ in their hydrogen bond-
ing patterns (O’Sullivan 1997). Cellulose Iβ is more abundant in
higher plants.