SU897776A1 - Method of preparing polyacrylamide - Google Patents

Description

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The invention relates to the production of high molecular weight substances used as flocculating reagents, and can be used in the chemical, coal, hydrometallurgical and petroleum industries.

A known method for producing polyacrylamide is that acrylonitrile is hydrolyzed in an aqueous medium in the presence of sulfuric acid. The resulting sulfoacrylamide is neutralized with a suspension of Ca (OH), in water. At the same time in the sediment get gypsum - CaSOj., Which is pressed from the aqueous solution of acrylamide. The acrylamide solution (10–15%) is subjected to fine filtration and sent to vacuum distillation (film evaporator) at 20–40 mm Hg. and 44-54 C. A solution flowing out of the evaporator with a concentration of acrylamide of 75-80% is fed to a suspension polymerization in a known manner.

A disadvantage of the known method is the difficulty of separating solid granules of poly acrylic amide.

The closest to the proposed technical essence is a method of producing polyacrylamide by hydrolysis of acrylonitrile in an aqueous solution of sulfuric acid, neutralizing gaseous resulting from the hydrolysis of sulfoacrylamide

ammonia, introducing a radical initiator into the reaction medium and polymerizing acrylamide without isolating ammonium sulfate 2 from the reaction medium.

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The disadvantage of the method is the difficulty of separating the target product from the reaction solution in the form of granules.

To obtain from the resulting

20 polyacrylamide gel in the form of granules using a known method 3, in which the gel is crushed, salted out in a saturated solution of ammonium sulfate with the addition of dry salt or a suspension of ammonium sulfate, squeeze the wet granules and dry them. The ammonium sulphate solution is removed, evaporated or utilized in other processes.

The purpose of the invention is to simplify the release of polyacrylamide in the form of granules.

This goal is achieved in that according to the method of producing polyacrylamide by hydrolyzing acrychunitrile in an aqueous solution of sulfuric acid, neutralizing the sulfo-acrylamide obtained by hydrolyzing sulfo-acrylamide, introducing a radical initiator into the reaction medium and polymerizing the obtained acrylamide, polymerizing acrylamide was carried out. % and addition of sodium dimethyldithiocarbamate to the reaction medium in an amount of 0.05-0.2% by weight of acrylamide.

According to method 21, the polymerization of acrylamide is carried out at a concentration of 6-8%. An increase in the initial concentration of acrylamide before polymerization above 8% is impossible, since this results in crosslinked, insoluble in water products that do not possess flocculating properties.

Additional introduction of acrylamide into technological solutions immediately before polymerization of an effective polymerization regulator — sodium dimethyldithiocarbamate (carbamate III), preventing crosslinking, and increasing the acrylamide concentration in the same solutions from 6–8% to 5–23%, allows to obtain a gel after polymerization the initial concentration of ammonium sulfate is 23% in its moisture, which leads to self-gelsing of the gel-like polyacrylamide during the polymerization process and the formation of a non-sticky, well-crushing (cutting) gel.

The polymer is self-draining only due to ammonium sulfate, which is present in the gel and is formed upon the neutralization of sulfoacrylamide, and its additional administration is not required. Next, the crushed granules are directed to squeezing moisture and drying in the usual way.

When increasing the concentration of acrylamide in water (mixed with ammonium sulfate) over the optimum (more than

23%) instead of a solution, only a slightly moistened acrylamide powder is formed, which is almost impossible to displace with the initiator due to the possibility of spontaneous polymerization. In addition, in order to obtain water-soluble polymers under these (non-optimal) conditions, it is necessary to substantially increase the content of the regulator (0.3-0.5%), which inevitably results in a low molecular weight polymer with low flocculating properties, and in the absence of carbamate MP Get only gel gels. When the concentration of acrylamide is lower than} 5%, pouring the polymer without additional addition of ammonium sulfate to the gel does not occur. The use of an added amount of carbamate MN in the indicated range (0.05-0.20% of the monomer) provides an effective high molecular weight flocculant that is completely soluble in water.

Example 1 15 g of water, 222 g of 93. 33% sulfuric acid (207 g of 100% substance) J are charged to the reactor (1.0 l) with a stirrer and reflux condenser. 2.1 g mol), 0.22 g of hydroquinone and the mixture is heated to 80 ° C, after which 113.3 g of technical 98.7% acrylonitrile AN (2.11 g mol, 112 g 100 % substance) for 50 min (molar ratio AHiHjO:

1: 1: 1), after chepo mixture

The filter is diluted at 90-100 ° C with stirring for another 1 hour. The resulting reaction mixture is diluted with water to 0.7 l and neutralized with gaseous 1m ammonia to pH 4.5 at 38-42 ° C, then diluted again with water to a density of 1151 kg / m and analyze the content of acrylamide.

The synthesis process takes 4 hours, and 1 kg of 15% technological acrylamide is obtained (its composition is 150 g of acrylamide, 279 g of ammonium sulfate, 571 g of water). Then, the pH was adjusted to 9.0 with aqueous ammonia and 0.15 g of dimethyldithiocarbamam sodium (0.1% by weight of acrylamide) was added at 20 ° C and moved for 5 s, after which the oxidative initiator (NHq) jSj was added, Oa in the amount of 0.75 g (0.5% by weight of acrylamide), stirred for another 15 s and then polymerized without stirring for 6 hours.

Claims (1)

Claim The method of producing polyacrylamide 30 by hydrolysis of acrylonitrile in an aqueous solution of sulfuric acid, neutralizing the resulting hydrolysis of sulfoacrylamide with gaseous ammonia, introducing into the reaction medium _{35 a} radical initiator and polymerizing the obtained acrylamide, characterized in that, in order to simplify the isolation of polyacrylamide in the form of granules, the polymerisation is carried out with acrylamide its concentration of 15-25 wt.% and the additional introduction into the reaction medium of sodium dimethyldithiocarbamate in an amount of 0.05-0.2% by weight of acrylamide.