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Acid hydrolysis reaction of polyacrylamide and its application
Acidic hydrolysis of polyacrylamide: partial acidic conditions under the hydrolysis of PAM, the hydrolysis rate with temperature increased and pH decreased and accelerate (Note: acid can strengthen the PAM hydrolysis, but under acidic conditions of hydrolysis of PAM rate is alkaline hydrolysis much slower, so often need to under high temperature. Under acidic conditions, the water and the protonated carbonyl groups are formed by the addition of the carbonyl group. After the elimination of ammonia (NH3), the structural unit of the acrylamide is hydrolyzed to the acrylic acid structure unit. The viscosity and pH value of the aqueous solution can be changed with the hydrolysis. In the reaction liquid PH < 8 without a buffer, ammonia becomes the solution pH increases, the viscosity increases. But the light scattering data shows that the PAM chain length of the hydrolysis process is basically unchanged. Therefore, the change of viscosity is caused by the change of the conformation of PAM chain caused by hydrolysis. The acidic hydrolysis of PAM showed significant catalytic effect, which was accelerated by the hydrolysis of the carboxyl group. This leads to an acceleration of the rate of acid hydrolysis with the increase of degree of hydrolysis. The hydrolysis rate of acrylamide acrylic acid copolymer or hydrolyzed polyacrylamide was significantly faster than that of acrylamide.
Because of the catalytic effect of the ortho group, the hydrolysis product tends to form the block structure when the degree of hydrolysis is lower. In the strong reaction conditions, the amide will be hydrolyzed to carboxylic acid.
Polyacrylamide PAM acidic hydrolysis, in addition to the AM structure produced by hydrolysis of carboxyl, but also prone to imidization. This reaction increases with the increase of the acidity of the ring, and even becomes the main reaction in the acid condition. In the case of PH 4, 3, 10% of the acyl groups were generated at 40, 6 h, 10% h, 24 h, h, and the higher temperature and stronger acid. Formation of imide structure in acidic medium with higher stability, under high temperature is not easy to hydrolysis; imide groups under neutral and alkaline conditions still has certain stability, but at higher temperatures or under the effect of alkali, rapid hydrolysis, carboxyl and amide formation. The dissolution of the polymer was caused by the dissolution of the polymer, and even the cross-linked gel was generated, and the hydrolysis of PAM was seldom used. However, the effect of acid medium on the structural change of PAM is not negligible in PAM application.
It was found that the hydrolysis of polyacrylamide PAM amino group was slow in neutral condition, and the hydrolysis degree was not changed in 10 days at 40. But the hydrolysis process can be promoted by acid, alkali and heat. Hydrolysis of PAM product structure, carboxyl and carbonyl amino sequence distribution, degree of hydrolysis and hydrolysis kinetics are significantly dependent on hydrolysis when the pH, solution temperature and small molecule electrolyte concentration. In general, the proportion of the anionic acrylic acid unit in PAM is called the degree of hydrolysis of PAM.
Cationic polyacrylamide widely used in sludge and sludge dewatering, municipal sewage and industrial wastewater, waste water treatment and industrial process of solid-liquid separation, greatly improve the sedimentation and clarification, flotation and thickening and dewatering speed, to improve the solid-liquid separation effect.
Specific applications such as municipal sludge thickening and dewatering and the type / drum / centrifugal thickener, thickener dewatering integrated machine, centrifugal thickening and dewatering machine, belt type filter press, centrifugal dewatering machine, screw press, plate and frame filter press, membrane type filter press.
Cationic polyacrylamide sewage treatment, municipal, paper, oil refining, wool spinning, dyeing, instrument, tanning, metallurgy and other, raw water treatment, sedimentation and clarification, filtration, sedimentation of sludge and filter backwash sludge dewatering; for urban sewage treatment plants, urban water plants and various industrial wastewater treatment station, sludge dewatering is the physicochemical and biochemical treatment produced a lot of, moisture content is very high, a flow state of sludge concentrating and dewatering, make its become Sinotrans and after treatment is convenient for solid material, thereby reducing Sinotrans and after treatment costs, eliminate the sludge secondary pollution to the environment. Therefore, for the sewage treatment plant and water plant, the sludge solidification and reduction is the main purpose of sludge mechanical dewatering.