Enzyme Technology
Preparation of acrylamide
Acrylamide is an important monomer needed for
the production of a range of economically useful polymeric materials. It may be
produced by the addition of water to acrylonitrile.
CH2=CHCN + H2O
CH2=CHCONH2
[5.11]
This process may be achieved by the use of a
reduced copper catalyst (Cu+); however, the yield is poor, unwanted
polymerisation or conversion to acrylic acid (CH2=CHCOOH) may occur at the
relatively high temperatures involved (80 -140°C) and the catalyst is
difficult to regenerate. These problems may be overcome by the use of
immobilised nitrile hydratase (often erroneously called a nitrilase). The enzyme
from Rhodococcus has been used by the Nitto Chemical Industry Co. Ltd, as it
contains only very low amidase activity which otherwise would produce unwanted
acrylic acid from the acrylamide.
Immobilised nitrile hydratase is simply
prepared by entrapping the intact cells in a cross-linked 10% (w/v)
polyacrylamide/dimethylaminoethylmethacrylate gel and granulating the product.
It is used at 10°C and pH 8.0-8.5 in a semibatchwise process, keeping the
substrate acrylonitrile concentration below 3% (w/v). Using 1% (w/v)
immobilised-enzyme concentration (about 50,000 U L−1) the process takes about a
day. Product concentrations of up to 20% (w/v) acrylamide have been achieved,
containing negligible substrate and less than 0.02% (w/w) acrylic acid.
Acrylamide production using this method is about 4000 tonnes per year.
The closely related enzymes cyanidase and
cyanide hydratase (see schemes [5.12] and [5.13], respectively) are used to
remove cyanide from industrial waste and in the detoxification of feeds and
foodstuffs containing amygdalin (see equation [6.12]).
HCN + 2H2O
HCOO− + NH4+
[5.12]
HCN + H2O
HCONH2
[5.13]
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