Environmental Engineering Reference
In-Depth Information
found within some types of biomass or readily formed from polysaccharides. As
discussed, simple saccharides can be viewed either as platform chemicals or
biomass, but for this chapter are viewed only as biomass [30, 31]. For the sake of
simplifying further discussions on platform molecules, the following are treated
as biomass feedstocks for the biorefinery and therefore feedstocks of platform
chemical production:
• polysaccharides (starch, cellulose, hemicellulose, chitin, inulin, etc.);
• lignin;
• protein;
• mono/disaccharides (glucose, fructose, sucrose, xylose, mixture of sugars);
• extractives (triglycerides, terpenes, pigments, waxes, etc.); and
• any combination of the above constituting raw, native biomass.
Biorefineries will normally process biomass in crude form containing mixtures of
these constituents, but the division in a theoretical sense is useful as each constitu-
ent typically leads to a different set of molecules (with the exception of gasification
routes). Platform molecules are therefore typically categorised based on the
constituents of the biomass they are derived from. For example, furans are derived
solely from the carbohydrates and not from lignin or protein, while vanillin will be
derived from lignin alone. These various biomass constituents are discussed in
greater detail in the following sections, with some examples given of the types of
platform molecules derivable from each. Considering both economics and avoidance
of competition with food production, biomass for platform chemical production
should ideally be waste from other industries (e.g. lignocellulosic agricultural or
forestry residues) and not specifically grown for chemical or energy production (i.e.
second-generation) [32]. Waste biomass will predominately be in mixed lignocel-
lulose form, although some examples exist where one constituent is the dominant
component of a waste stream, such as lignin from the pulp and paper industry. It is
also possible that the components may be separated prior to processing.
Along with the constituents described above, biomass additionally contains ash,
a variable mixture of inorganics. Although not specifically relevant to bio-based
platform molecules, the ash content of biomass is nevertheless important when
considering the production of chemicals from biomass as it could represent a
significant waste stream. On the other hand, ash minerals may also represent an
opportunity for biorefineries, for example offering routes to bio-based aluminosili-
cate catalysts that could be used for the production of chemicals from biomass [33].
4.4.1
Saccharides
Saccharides as a whole generally represent the most dominant component of
biomass. Edible carbohydrates such as starch, sucrose, glucose and fructose have
been used extensively for the formation of platform molecules (Figure 4.3). While
mono- and disaccharides can be used directly in fermentative, thermal and
