A number of microorganisms are known to possess capability of converting nitrile compounds to the corresponding amides. A bacterial strain of Brevibacterium sp. CH1 has been isolated and used to produce an enzyme necessary for carrying out the reaction of acrylonitrile to acrylamide.
Chapter 1 summarizes the commercial use of acrylamide and its current production methods.
In chapter 2 screening and identification of Brevibacterium sp. CH1 are discussed. The culture and reaction conditions, and medium optimization were studied for the strain. The conversion yield was nearly 100% with a trace amount of acrylic acid produced. The strain showed strong activity of nitrile hydratase toward acrylonitrile and extremely low activity of the amidase toward acrylamide. The substrate specificity o the nitrile hydratase was investigated in a whole cell system.
Chapter 3 discusses the cell cultivation in batch and fed-batch system. pH control was very important to obtain high density cell culture and high specific enzyme activity. The maximum growth rate was obtained at a glucose concentration of 20 g/L because of substrate inhibition. For this purpose continuous feeding of complex media was more profitable than that of only glucose medium. The maximum cell density of fed-batch culrure was 68 g/L and the growth yield on cabon source was 0.5.
In chapter 4 the effect of different compounds on the enzyme activity of the nitrile-hydratase used for the bioconversion of nitrile was described. An excess of acrylonitrile as a substrate was shown to inhibit the enzyme activity. This inhibition occured only at relatively high substrate concentrations (0.2mol/L or more). The nitrile - bioconversion product (acrylamide, propionamide) and their structural analogues (acrylic acid) were also shown to inhibit the enzyme competitively. The most serious inhibitor found was that of cyanide (Ki=3.78 × 10 mol/L), a break down product of some nitriles.
In chapter 5 are discussed continuous production of acrylamide from acrylonitrile using Brevibacterium sp. CHl grown and immobilized in a dual hollow fiber bioreactor. The biomass reached as high as 200g/L based on the space available for the cell growth. The volumetric productivity of the reactor was 88g/L/h and the conversion of acrylonitrile varied with acrylonitrile concentration, pH, temperature and feed rate.
Chapter 6 discusses production of acrylamide by biotransformation of acrylonitrile to acrylamide using immobilized whole cell of Brevibacterium sp. CHl in a recycle fed-batch reactor. Acrylamide beads were found to be the best carriers tested in terms of stability and physicochemical strength. For a high final acrylamide concentration, the acrylonitrile concentration and the operational temperature were below 3%, 4℃ respectively, based on maximum acrylamide productivity per unit cell weight and restriction of polymerization.
