Acrylamide based flocculants, water

The preparation of high molecular weight, water soluble acrylamide-based flocculants as water continuous dispersions is described. This innovative method of manufacture eliminates many of the undesirable characteristics associated with the production and application of these flocculants as conventional water-in-oil emulsions or as dry powders. The monomers and their polymers, the role of the stabilizer polymer, particle characteristics, viscosity considerations, and the thermodynamic and physical stability of these polymer diversions is discussed. 

Based on animal studies and mutagenicity studies, trace amounts of organic polymers do not appear to present a toxicity problem in drinking water. The reaction products with both chlorine and ozone also appear to have low toxicity. The principal concern is the presence of unreuctcd monomer and other toxic and potentially carcinogenic nonpolymeric organic compounds in commercial polymeric flocculants. The principal contpuimds are acrylamide in acrylamide based polymers, dimethyldiallyammonium chloride in allylie polymers, and epichlorohydrin and chlorinated propanols in polyamines, as well as the rcaclion products of these compounds with ozone and chlorine. 

The inverse emulsion polymerization mechanisms and kinetics can be found in the literature [10,66-68]. The area of inverse emulsion polymerization has not been studied extensively, except perhaps for the inverse microemulsion polymerization of acrylamide. The most important applications for these acrylamide-based products are as polymeric flocculants in water treatment. The two major advantages of this polymerization process are the very high polymer molecular weight and a colloidal system that results in rapid dissolution of the polymer in water. 

Acrylamide is the first bulk chemical manufactured using an industrial biotransformation. Acrylamide which is produced 200000 t/a is an important industrial chemical that is mainly processed into water-soluble polymers and copolymers, which find applications as flocculants, paper-making aids, thickening agents, surface coatings, and additives for enhanced oil recovery. The chemical manufacture of acrylamide has been established for a long time, it is based on Cu-catalysis. The production of acrylamide using immobilized whole cells of Rhodococcus rhodochrous is a remarkable example of a lyase-catalyzed commercial process. The enzyme responsible for water addition to the double bond of acrylonitrile is nitrile hydratase (Eq. 4-17) ... 

Typical synthetic water soluble flocculants are polyelectrolytes that are most often based upon copolymers of acrylamide or substituted derivatives. Acrylamide monomer is obtained industrially by the catalytic hydration of acrylonitrile and occurs in both crystaUine form and in aqueous solution. The 50% aqueous form is the preferred form for polymerisation systems in which water can be tolerated. Acrylamide has a very fast propagation rate and a high exothermic heat of polymerisation. 

Under certain circumstances, acrylamide may infiltrate into drinking water treated using polymers based on acrylamide, which are used as flocculants. With regard to the toxicity of acrylamide and health risks associated with its intake, the hygienic limit for water intended for human consumption is 0.1 pg/1 (European Council Directive 98/83/EC). 

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