The polymerization technology of aqueous solution polymerization in PAM production is briefly introduced

Polyacrylamide，Polymerized Ferrous Sulfate aqueous solution polymerization is the main method used in industrial production Water Treatment Chemicals.

The monomer solution in the formulation must be purified by ion exchange. The reaction medium water should be deionized water, and the initiator mainly uses the oxidation-reduction initiator system composed of persulfate and sulfite to reduce the reaction initiation temperature. In addition, a chain transfer agent is needed, and isopropyl alcohol is commonly used. In order to eliminate the possible effects of metal ions, the human chelating agent ethylenediamine tetraacetic acid (EDTA) is added if necessary. In order to easily control the reaction temperature, the monomer concentration is usually less than 25%. Since the polymerization heat of acrylamide is as high as 82.8 kJ/mol, the polymerization heat must be exported in time. If the monomer concentration is 25% ~ 30%, even at 10c(= to trigger polymerization, if the polymerization heat is not exported, the solution temperature will automatically rise to 100'E, and a large amount of insoluble matter will be generated. Therefore, thermal conductivity becomes one of the key problems in production.

The production of low relative molecular mass products can be intermittent operation in the kettle reactor or continuous production of multiple reactors in series, the jacket cooling to maintain the reaction temperature of 20 ~ 25℃, the conversion rate of 95% ~ 99%. When producing high relative molecular weight products, because the product is gelled, it can not be stirred, in order to export the reaction heat in time, the industrial use of the reaction kettle will be mixed evenly in the formula of the material, immediately into the polyethylene bag, the polyethylene device equipped with the reaction material in the tank for cooling reaction.

It should be noted that due to the obvious inhibition effect of oxygen in the air, preparation and feeding must be carried out in N gas. When using the persulfate-sulfite initiator system, the initiation temperature is usually 40%, and the initiation temperature should be lower than 20% if the production of ultra-high relative molecular weight products is required.

Since the monomer is non-volatile and cannot be removed after the reaction, the unreacted monomer will remain in the polyacrylamide. Although the amount of residual monomer can be reduced by extending the reaction time and increasing the reaction temperature, the production capacity will be reduced and the content of insoluble matter will be increased.

In order to reduce the amount of residual monomers, some factories use a composite initiation system, which is composed of an oxidation-reduction initiator and a water-soluble azo initiator. Under the condition of low temperature, the oxidation-reduction initiator plays a role, and when the temperature of the reaction material rises in the later stage, the decomposition of the azo initiator further plays a role, and the residual monomer amount of polyacrylamide produced by this method can be as low as 0.02% (measured by gas chromatography). The water-soluble azo initiators are 4,4 '-azo bis -4 -cyanopentonic acid, 2,2' -azo bis -4 -methylbutyronitrile sodium sulfate and 2, 2 '-azo bis -2 amidinopentane dihydrochloride.