Environmental Engineering Reference
In-Depth Information
O
O
O
O
H
N
OH
Hydrolysis
HO
HO
HO
OH
NH
2
O
NH
2
O
NH
O
Protein
e.g.
grain and
seed meal,
poultry feathers
HO
H
NH
2
HO
NH
2
NH
2
O
Thermal treatment
NH
2
Figure 4.9
Example platform molecules derived from protein.
(<8%) and fails to compete economically with current synthetic routes to vanillin
from petrochemicals; as such, it is only viable if consumers are happy to pay a
premium for bio-based over fossil-based [32].
4.4.3
Protein
Protein fractions of biomass are essential in human and animal nutrition and are
generally of greater economic value than edible carbohydrate fractions (sugars,
starch) [88]. Nevertheless, interest is increasing in the potential utilisation of
proteins for the production of platform chemicals [32]. The simplest route to
platform molecules from protein is via hydrolysis of the peptide bonds, which
yields a mixture of the various amino acids (Figure 4.9). Although complicated by
the difficult separation of the amino acids from one another, the hydrolysis route
results in a diverse set of potentially very useful molecules (Table 4.2). Options
for use of amino acids are extensive due to their diverse functionality and, with the
exception of glucosamine, amino acids represent the only nitrogen-containing
platform molecules under recent investigation. Some amino acids, such as proline,
aspartic acid and glutamic acid, have been researched extensively for conversion
to other chemicals or in catalysis for directing enantioselective reactions [89-91].
Others such as arginine, phenylalanine and lysine are of interest due to the
chemicals that can be produced from them, although their abundance is a matter
of concern. Arginine is present in the cyanobacterial polymer cyanophycin in an
equimolar ratio to aspartic acid in the peptide backbone, and it is proposed that the
arginine could be converted into 1,4-diaminobutane via sequential hydrolysis (to
ornithine) and decarboxylation [92-94]. Growth of cyanobacteria is slow and
therefore unlikely to prove economically feasible on a large scale, though modified
Escherichia coli
is being developed to increase rates of cyanophycin production
[95]. Phenylalanine can be converted to styrene via a deamination (to cinnamic
acid) and decarboxylation and, in a newer iteration, can simultaneously produce
acrylates with styrene via ethenolysis while lysine can be used to produce
caprolactam, a Nylon 6 precursor [94, 96, 97].
An important issue in the utilisation of amino acids as platform molecules is the
availability of the individual amino acids. Both glutamic and aspartic acid have
