Production methods used by polyacrylamide manufacturers:
1. Aqueous polymerization method
Acrylamide aqueous solution polymerization method is the main method used in industrial production. The monomer solution in the formula must be purified by ion exchange. The reaction medium water should be deionized water, and the initiator is mostly an oxidation-reduction initiator composed of persulfate and sulfite
System to lower the reaction initiation temperature. In addition, a chain transfer agent is required, and isopropanol is commonly used. In order to eliminate the influence of possible metal ions, if necessary, add a chelating agent ethylenediaminetetraacetic acid (EDTA). In order to easily control the reaction temperature, the monomer
The concentration is usually less than 25%. Production method used by polyacrylamide manufacturers.
Since the heat of polymerization of acrylamide is as high as 82.8kJ/mol, the heat of polymerization must be derived in time. If the monomer concentration is 25%~30%, even if the polymerization is initiated at 10℃, if the heat of polymerization is not derived, the solution temperature will automatically rise to 100℃ , Will generate a large number of non-subjects. Therefore, the problem of heat conduction has become one of the key issues in production.
When producing low molecular weight products, it can be operated intermittently in a tank reactor or continuous production in series with multiple tanks. The jacket cooling keeps the reaction temperature at 20-25℃, and the conversion rate reaches 95%-99%. When producing high molecular weight products, because the products
It is jelly-like and cannot be stirred. In order to derive the reaction heat in time, the industry uses the reaction kettle to mix the materials in the formula evenly, and immediately send them to the polyethylene pouch, and put the reaction material in the polyethylene device water tank Perform a cooling reaction. It should be noted that because the oxygen in the air has an obvious inhibitory effect, the preparation and feeding must be carried out in N,. When persulfate-sulfite initiator system is used, the initiation temperature is usually 40℃. If the production of ultra-high molecular weight products is required, the initiation temperature should be lower than 20℃.
Since the monomer is not volatile and cannot be removed after the reaction, the unreacted monomer will remain in the polyacrylamide. Prolong the reaction time and increase the reaction temperature. Although the amount of residual monomer can be reduced, the production capacity will decrease and the insoluble content will increase. In order to drop
Some factories with low residual monomers use a composite initiation system, which consists of an oxidation-reduction initiator and a water-soluble azo initiator. Under low temperature conditions, the oxidation-reduction initiator plays a role. When the temperature of the reaction material rises in the later stage, the azo initiator is decomposed to further play a role. The residual monomer content of polyacrylamide produced by this method can be as low as 0.02% (gas color Harmonic method determination). The water-soluble azo initiators are 4,4'-azobis-4-cyanovaleric acid, 2,2'-azobis-4-methylbutyronitrile sodium sulfate and 2,2'-azobis- 2-Methylpentane dihydrochloride, etc.
The method for the determination of residual acrylamide is mainly the bromination method in industry, but its sensitivity is poor. For very small amounts of monomers, flame ionization or high performance liquid chromatography can be used for determination. In order to produce polyacrylamide with a small amount of carboxyl groups, an appropriate amount of sodium carbonate can be added to the polymerization formula to hydrolyze a small amount of amide groups into carboxyl groups and reduce the formation of insolubles.
The polyacrylamide synthesized by the above method is a high-viscosity fluid or a gel-like non-flowing animal. It can be directly used as a commodity, supplying monomers that are closer to the production plant. During long-distance transportation, it should be dried to produce powdery solids. The method of drying the colloid can be the kneading drying method, but this method consumes a lot of energy and the product degrades seriously. When the production scale is small, the extruder granulation can be used for drying in the drying room, and then crushed to obtain a powdery product. The more advanced method with large output is to granulate by extruder, send it to a drum dryer, and pulverize it to obtain powdered commodities after drying.
2. Inverse emulsion polymerization
Acrylamide monomer is formulated into an aqueous solution with a concentration of 30% to 60% as the dispersed phase, with a small amount of diethyleneamine tetraacetic acid and NazSO added. As well as oxidation-reduction initiators and appropriate water-soluble surfactants, the HLB value should be lower. Use aromatic warp or saturated fat warp as the continuous phase, in which oil-soluble surfactants are added, and the HLB value should be higher, such as sorbitan oleate. NagSO has the effect of preventing the adhesion of milk particles. The ratio of the dispersed phase to the continuous phase is usually 3:7. The particle diameter of the dispersed phase latex obtained by polymerization is 0.1~10um, which is related to the amount of surfactant. The reaction temperature is generally 40°C, and the conversion rate can reach 98% within 6 hours. The advantage of this method is that the heat of reaction is easy to derive, the viscosity of the material system is low, it is easy to operate, and the product can be used directly without drying. The disadvantage is that organic solvents are used, which is flammable, and the effective production capacity is lower than the solution polymerization method.
3. Suspension polymerization
The polymerization reaction of monomer aqueous solution in which small liquid beads are suspended in an organic solvent is called suspension polymerization, also called bead polymerization. Suspension polymer is mainly composed of monomer, initiator, organic solvent and suspending agent. The initiator is dissolved in the monomer aqueous solution
in. Dispersant is also called suspending agent. Its function is to disperse the monomer aqueous solution into small liquid beads suspended in an organic solvent under stirring to prevent polymerized particles from sticking to each other during the polymerization process. The particle size of the product is generally 100 ~ 2000 pumo.
Different from emulsion polymerization, the dispersion of the monomer solution is low, and it is generally suspended in the organic phase as bead particles. Therefore, the organic vehicle used is a solvent with a large specific gravity such as xylene, methyl chloride and the like. Dispersants generally do not need to be emulsified with high activity
The stirring strength is also lower than that of emulsion polymerization; the product obtained by suspension polymerization is in granular form, which is convenient to use.
In the suspension polymerization solution, AM aqueous solution forms a stable suspension in gasoline, xylene, and methyl chloride in the presence of suspending agents (dispersion stabilizers) such as Span60, inorganic amides, C~Cg fatty acid sodium or cellulose acetate butyrate. Liquid, initiate polymerization. After the suspension polymerization is completed, it is subjected to azeotropic dehydration, separation, and drying to obtain a bead or powder product. Add inorganic salt NaCI, NaNO, or NagCO during polymerization. The surface tension of the system can be adjusted to increase the suspension stability, but has little effect on the polymerization process. However, adding a small amount of monobasic, dibasic or polycarboxylate can generally increase the relative molecular weight of the product and decrease the polymerization rate.