Chemistry Reference
In-Depth Information
Table 14.5
Current industrial-scale use of bioprocessing [10
8
]
Much of the work tries to focus attention on the
green nature of the polymers, but that aspect yet has
to be proven conclusively, and life-cycle analysis will
need to be carried out [115]. Other papers describe
some criteria for new polymers with regard to com-
posting and recycling [116]. The most publicised
class of biopolymers are the poly(hydroxyalkano-
ates) [117], but other materials that have been
reported include poly(g-glutamic acid) [118],
poly(aspartic acid) [119], polycarbonates and poly-
esters [120].
An important new example of industrial bio-
technology is the Mitsubishi Rayon process for
acrylamide, currently operating on a 3 ¥ 10
4
t year
-1
basis by the treatment of acrylonitrile with nitrile
hydratase from
Rhodococcus rhodochrous
[121]. This
methodology is unique because a non-sugar starting
material is treated with an enzyme to generate a
well-known and high-volume commodity chemical.
The same enzyme is being used for the production
of nicotinamide on a scale of 3 ¥ 10
3
t year
-1
[122]
and also has been reported as part of a new route to
acrylic acid [123].
New demonstrations of biotechnology are appear-
ing in the production of herbicides and agrochemi-
cals, materials that have a larger production volume
and market than many fine chemicals [124]. (In
1987, the synthetic herbicide market in the USA was
4.4 ¥ 10
5
t.) DuPont has reported a biochemical
route to glyphosate, the principal component of the
broad-spectrum herbicide Roundup (Scheme 14.20)
[125].
The investigation revealed that the ability to
oxidise glycolic acid to glyoxylic acid with oxygen
was improved by the presence of an amino-
methylphosphonic acid buffer. Hydrogenation and
acidification of the reaction mixture, which con-
tained an equilibrium concentration of several inter-
mediate species, eventually afforded glyphosate as
the final product. Proper adjustment of conditions
gave a 98% conversion of aminomethylphosphonic
acid to glyphosate.
A significant advantage for biocatalysis is seen
clearly in the manufacture of optically active ma-
terials. For example, BASF currently is investigat-
ing the use of a lipase from
Pseudomonas
for the pro-
duction of optically active amines. The technology
is being investigated on a scale of 100 t year
-1
and is
being directed at the production of a herbicide called
Frontier X2. Successful commercial production of
10
3
t year
-
1
US$ t
-
1
Glucose
15 000
600
Ethanol
13 000
400
Fructose
1 000
8
00
Citric acid
8
00
1 700
Monosodium glutamate
8
00
1 900
L
-Lysine
350
2 200
L
-Lactic acid
70
2 100
L
-Ascorbic acid
60
1 000
Gluconic acid
40
1 700
Xanthan
30
8
000
Penicillin G
25
20 000
Aspartame
15
40 000
ably large-scale biotechnology processes (Table 14.5)
[108]. In some of the cases, the operations have been
used for many years because there is no equivalent
non-biological route. Ethanol and lactic acid are of
particular interest because they represent chemicals
whose original non-biological production has been
replaced almost totally by biochemical manufacture.
In addition, the pulp and paper industry has started
to incorporate enzyme treatments into their pulping
and bleaching sequences [109] and low-lactose milk
is produced by treating milk with b-galactosidase. Up
to 250 000 l are converted daily [110].
Lactic acid is a good example of a platform
chemical available from bioprocessing [111]. Factors
affecting the fermentation of lactic acid have been
reviewed [112]. The primary interest in lactic acid
today is for the production of poly(lactic acid) as
a 'green' polymer that undergoes decomposition
upon disposal [113]. It is being positioned as a
biodegradable replacement for use in markets now
dominated by polyolefins. A 1.4 ¥ 10
5
t year
-1
pro-
duction facility currently is being built by Cargill-
Dow polymers. Lactic acid self-polymerises poorly, so
it is converted initially to the dilactide, a material
that readily forms a polyester with high molecular
weight (Fig. 14.8) upon ring opening. In addition,
lactic acid can serve as a starting material for several
other compounds of industrial interest, including
acetaldehyde, propylene glycol, acrylic acid and 2,3-
pentanedione [114].
Bioproduction of other polymers is also an emerg-
ing area of growth, although apart from the work on
polylactic acid there are few commercial examples.
