Environmental Engineering Reference
In-Depth Information
Process economics will eventually determine which are formally platform
molecules and which are simply bio-based chemicals (i.e. derived from
platform molecules or produced in too small a quantity to be relevant as a
comparison to base chemicals).
There have also been difficulties in deciding if some chemicals are platform
molecules or biomass feedstocks. For example, mono/disaccharides can be viewed
as biomass feedstocks as they can be isolated from biomass in its crude form
(extracted from sugar beet, fruits and sugar cane), but can also be derived from
polysaccharides via biological and/or chemical processes; in this sense, they are
more like a platform molecule. For the purposes of this chapter, saccharides are
always viewed as biomass feedstocks.
The term 'sugar platform' is also used in some articles relating to biorefineries,
and this term is applied when a differentiation to other platforms (e.g. syngas) is
desirable. The sugar platform covers a very wide range of chemical products and
includes all the platform molecules derived via the biological (fermentation) or
chemical-catalytic processing of sugars.
It is important that platform molecules, and eventual bio-based products,
endeavour to avoid the use of fossil-derived elements and fuels in their production.
For example, for fatty acid methyl esters (FAMEs) to be wholly bio-derived
platform molecules they must use bio-based MeOH for the transesterification,
ensuring all carbons in the molecule are bio-based. It is also possible that some of
the bulk or commodity chemicals currently derived from petroleum could
potentially be sourced from biomass. These are known colloquially as 'drop-in
replacements', since they can be integrated into current petrochemical processes,
production chains and consumer markets without infrastructural changes. For
example, ethene is currently commercially available from bio-ethanol [28].
4.4 Where Platform Molecules Come From
Bio-based platform molecules must be derived from biomass and, as such,
biomass represents for the biorefinery what fossil resources (coal, gas and oil)
represent for the fossil-based refinery; biomass is the feedstock for the biorefinery.
With regard to platform molecules, biomass can therefore be defined as:
A biologically produced material (non-fossil) that occurs in sufficient abundance to
serve as a feedstock for the production of commodity products or platform
molecules.
Although simple in definition, plant biomass is complex and diverse in composition
[29]. Biorefinery feedstocks, and therefore platform chemical feedstocks, are
typically further differentiated into polysaccharides, lignin, protein and extractives
(e.g. triglycerides and terpenes), as all are found as constituent parts within typical
biomass in varying quantities. Mono- and disaccharides, such as glucose, fructose
and sucrose, should additionally be treated as biomass feedstock as they are also
