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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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