DE2243155C3 - Process for the production of acrylamide polymers and their use as flocculants - Google Patents

Description

Acrylamide polymers are used as sizing agents, fillers, binders, paints and dispersants used. Acrylamide polymers with high intrinsic viscosity and high molecular weight are particularly suitable as flocculants.

Numerous processes are known for the production of such polymers, including radical polymerization with free radical initiators or redox catalysts in aqueous or organic phase in technology is most widespread. Suitable organic phases are solvents in which the monomers are soluble, but the polymers obtained are insoluble. In this so-called "precipitation polymerization" It is difficult to achieve reactions because of the ket: en transfer that takes place higher degrees of polymerization. This process is therefore for the production of acrylamide polymers unsuitable with high intrinsic viscosity and high molecular weight.

In contrast, the so-called "solution polymerization" in the aqueous phase leads to acrylamide polymerization with a high degree of polymerization. However, this process has the disadvantage that a considerable heat of reaction is released and the reaction can only be controlled more closely if the concentration of the starting monomers is high. In addition, the high degree of polarization causes. that the Rcaktionssvstcm is viscous außermder.tlich and so stirring <\ rJ work-up more difficult. If one does not conduct the polarization heat as required, May '··> H. c · .Ia ^ · '(■■>. ■. · ■. ■ -

Risat on the amide group to water-insoluble products, which are useless as flocculants.

To avoid these disadvantages of solution polymerization, the reaction is carried out at low levels Monomer concentrations, e.g. B. 10 "/ i> or less, through. Since here the concentration of the polymer in the solution obtained is also relative is low, the polymer is precipitated with an organic, water-miscible solvent,

ίο vvie methanol, and separates it from the slurry away. However, this involves large amounts of the organic, water-miscible solvent required so that the process is not practical from an industrial point of view.

In addition, polymerization processes in suspension and emulsion are known in which the implementation in »Ö [-in-Wasser << - or» Water-in-CU-Dispersion using a suitable organic solvent such as n-heptane, carbon tetrachloride

«Fuel. Toluene or xylene, as well as a surface-active one Connection is carried out. However, the dispersions are not sufficiently stable; aside from that the flammability of the solvent is disadvantageous. Furthermore, because of the precipitation of the polymer

»5 large quantities of an organic solvent required are, these polymerization processes are in suspension and in emulsion for technical Application not very suitable.

From British patent 893 005, the copolymerization of a 5 to 30% solution of acrylamide and N-tert. Butyl acrylamide in a water-solvent mixture known. Mixtures of water and acetone with about 9 to 23 ⁰ O acetone are also used as a solvent mixture. However, this initially results in viscous solutions that must first be dried and not slurries.

From the Belgian patent 717 128 a method for precipitation polymerization is known at

* ° where acetone is used. Acrylamide or mainly Acrylamide-containing monovinyl monomers are polymerized in an acetone / water mixture, which contains 30 to 70 percent by weight, based on the total weight of the mixture, of acetone, the polymer being obtained as a slurry. However, the process has the disadvantage that the polymer particles Bake together to form aggregates the size of a grain of rice. In addition, are stored in the course polymerisation because of the stickiness of the resultant Polymerisats Waiidansätze on the inner walls of the reaction vessels. On the one hand, this is humiliating the product yield, on the other hand the sticky polymer makes filtration more difficult and sinters during drying, so that the preparation of the slurry to make a commercial product is cumbersome. Although it is known from the Belgian patent, due to the stickiness of the polymer particles Problems caused to solve by the fact that the reaction system inorganic

^ ⁰ salts, such as potassium chloride. Sodium chloride or ammonium sulfate, and / or buffers such as ammonium chloride / ammonia. clogs, however, no satisfactory red cheeses can be obtained. Even if such additives are used, a few IO ° 'n remain

^e 5; _r -. (Tchildeten polymer> n <inner wall of R'MkMnnsgefälics zuriete On page i4 this Palciif- ■ •• he is hnft iv, Example 1, an Ace '-. tn · ^F asscr-Mic.Y.inü with. '.' Οiwι ·. H '~ pn.'z <: nt \ t :: - ^f tin used

and shown that this comparative example is unsuitable and the reaction mixture is so becomes highly viscous. Products are obtained that are not fully polymerized.

The object of the invention is to provide a process for the production of water-soluble, pulverulent acrylamide polymers to create with a high intrinsic viscosity and high molecular weight, which avoids the disadvantages described.

The invention thus relates to a process for the production of water-soluble acrylamide polymers high molecular weight as a fine particle slurry by polymerization of acrylamide or methacrylamide or of mixtures of monomers which are not less than 50 percent by weight these monomers contain, along with comonomers, which are soluble in acetone / water and their copolymers are insoluble therein, in a concentration of 10 to 30 percent by weight in an acevon / water mixture in the presence of acetone / water soluble radical or Redox catalysts at temperatures from 20 to 60 ° C, optionally in the presence of dispersion stabilizers, which is characterized in that an acetone / water mixture is used which Contains 23 to 30 percent by weight of acetone, and also 0.5 to 4 percent by weight of polyvinyl alcohol, based on the weight of the polymerizable monomers.

The presence of polyvinyl alcohol in an acetone / water mixture that is 23 to 30 percent by weight Contains acetone, allows the production of a barely tacky polymer, so that the the above-described difficult boar can be avoided. If the acetone concentration is below 23 Percentage by weight, the reaction mixture becomes highly viscous and gels immediately (“Weißenberg effect”). If the acetone concentration is above 30 percent by weight, the tackiness of the polymer particles decreases and rubber-like agglomerates are deposited on the inner wall of the reaction vessels, originating from the flocculated polymer particles. Only with acetone concentrations within of the specified range, the polymer is obtained as a slurry of fine particles which do not contain any of the cause mentioned difficulties.

In the process of the invention, acrylamide or methacrylamide or mainly is polymerized monovinyl monomers containing these compounds; H. Monomers that are not less than 50 percent by weight Contain acrylamide or methacrylamide. In the following, acrylamide and / or methacrylamide are used as the "main monomers" and the others The monomer units of the monovinyl monomers are referred to as "noble monomers".

Compounds which are soluble in acetone / water and whose copolymer with the main monomer is insoluble or hardly soluble in this mixture can be used as secondary monomers. Suitable examples are acrylonitrile, anionic monomers such as acrylic acid, methacrylic acid, or their metal or ammonium salts, sodium vinyl sulfonate or sulfonated styrene, or basic monomers which become cationic during quaternization, such as vinyl pyridine or dialkylaminoalkyl methacrylate. Such secondary monomers are particularly suitable thy obtained polymer anionic or ¹ .itionische FigenMh: ii "tci and / or to provide a better water solubility The Monovjnylmonornere may contain such secondary monomers, but this is not essential..

The monomer concentration in the reaction system S is 10 to 30 percent by weight, preferably 15 up to 25 percent by weight.

Compounds which form free radicals can be used as catalysts, which are present in acetone / Are soluble in water. Water-soluble ones are preferred

ίο peroxides, such as hydrogen peroxide, potassium persulfate or ammonium persulfate, and azobisisobutyronitrile. Also redox analyzer, such as potassium persulfate or Sodium hydrogen sulfite, amines or sodium formaldehyde sulfoxylate are suitable. Commonly used about 0.01 to 0.2 percent by weight of the catalyst, based on the weight of the monomers.

Polyvinyl alcohol is usually used in an amount of 0.5 to 4 percent by weight, preferably 1 to

ao 2 percent by weight, based on the weight of the Monomers.

Optionally, the reaction system contains a dispersion stabilizer, e.g. B. water-soluble high polymers such as carboxymethyl cellulose, inorganic salts such as potassium chloride, sodium chloride, ammonium chloride, sodium sulfate or sodium carbonate, or buffers such as sodium acetate / acetic acid or ammonium chloride / ammonia.
The polymerization is carried out in a manner known per se, the reaction temperature being from 20 to 60.degree.

In the process of the invention, an acrylamide or methacrylamide polymer is obtained, the particles of which are hardly sticky. Therefore, the undesired wall attachments in the reaction vessels are avoided. The slurry obtained is worked up by customary filtration, where appropriate it is washed with acetone in the reaction vessel. On drying, the polymer particles obtained give fine granules of uniform particle size which, when stirred, dissolve immediately and completely in cold water. The granules can optionally be ground to the desired particle size. The limiting viscosity number [η] at 30 ° C in sodium nitrate solution is usually 10 or more. A polymer the size of a grain of rice, obtained under similar polymerization conditions, but from an acetone / water mixture with more than 30 percent by weight of acetone, shows a lower intrinsic viscosity.

The slurry obtained in the process of the invention consists of fine particles and can can be used directly due to their excellent stability without detaching the Po-SS lymerisats from the reaction mixture would be required.

The advantage of the process according to the invention consists essentially in the fact that the starting monomers can be polymerized in high concentrations, a polymer with a molecular weight of more than 3 million being formed as a powder or granulate. A further advantage is that the acetone is used as the reaction medium / water mixture low Preparation ^1; conditionally costs. The acrylamide polymers obtained in the process of the invention are, in particular, ils Xusflockmittc! suitable.

The examples illustrate the invention.

Example I.

A solution of 190g of acrylamide and 1 Og of acrylic acid in a mixture of 505 g water and 236 g of acetone is neutralized with about 22 ml of 30 ⁿ 'niger sodium hydroxide solution and then with 20 g of K) "Nigen aqueous solution of polyvinyl alcohol (saponification number 81.5 up to 89, limiting viscosity number 43 r 3 in 4 "V aqueous solution at 20 ° C). After replacing the air with nitrogen, the reaction mixture is mixed with 10 ml of a 1 ⁿ / o aqueous solution of potassium persulfate and 5 ml of an aqueous solution of sodium hydrogen sulfite added, whereby a clear solution is formed. After a few minutes, the reaction begins and the reaction mixture gradually becomes cloudy. During the four-hour polymerization in a stream of nitrogen with stirring at 40 ° C., no deposits were observed on the inner wall of the reaction vessel. The resulting suspension is then filtered off, the pulverulent polymer is washed with acetone and dried under reduced pressure. In this case, one obtains 198 g of a white polymer powder with an intrinsic viscosity of 12.1 (determined at 3O ⁰ C in In sodium nitrate solution). The acetone concentration in the reaction medium is 29.5%.

Example 2

29 g of acrylic acid are dissolved in 200 g of water with stirring and then with about 40 ml of 10N sodium hydroxide solution neutralized at a temperature below 35 ° C. The solution obtained is mixed with 162 g of acrylamide, 313 g water and 220 g acetone mixed and then with 20 g of a 10% aqueous solution of polyvinyl alcohol (saponification number 81.5 to 89, Limiting viscosity number 30 ± 3 in 4% aqueous solution at 20 ° C). After displacing the air the reaction mixture is diluted with 5 ml of a 1 "/ own aqueous solution of potassium persulfate by nitrogen and 2 ml of a 10% aqueous solution of sodium formaldehyde sulfoxylate added, whereby a clear solution is formed. After a few minutes, the reaction begins and the reaction mixture becomes cloudy gradually. The polymerization is carried out for 4 hours at 25 ° C, leaving a stable slurry is obtained without any deposition of the polymer being observed. The product is filtered off and dried according to Example 1, leaving white particles of excellent water solubility can be obtained. The yield amounts to about 90 "ι, the theory, the limiting viscosity number 17.2. The acetone concentration in the reaction medium is 27.5 "ii.

, o example 3

According to Example 2, acrylamide with a content of 35 mol percent Nalriumacrylut in one Acetone / water mixture with an acetone concentration of 23 percent by weight for 4 hours at 40

polymerized up to 45 ° C. This creates a homogeneous, stable slurry without any sticky deposits being observed. The reaction mixture is mixed with water and filtered. After six hours of drying of the product obtained under reduced pressure at r ') 0 ° C, a white powder in 99 ⁿ <üiger Au: yield. The high viscosity number is 10 (determined at 30 ° C in a sodium nitrate solution).

1.0 g of the polymer thus obtained are oei

^J 5 room temperature is added to 99 g of water with stirring, a clear solution being formed in 11 minutes without the formation of a residue. The viscosity of the 1% aqueous solution obtained is 176 ° C at 25 ° C.

Example 4

140 g of acrylamide and 60 g of acrylic acid become 111 Dissolve 450g of water and add 110g of 1On sodium hydroxide solution neutralized. Then the solution with 40 g of a 5% aqueous solution of Polyvinyl alcohol and 200 g of acetone are added so that the acetone concentration is 25.2%. After repression 0.1 g of potassium persulfate and 0.2 g of tetramethylethylenediamine are removed from the air with nitrogen admitted. After six hours of polymerization at 20 ° C., a stable slurry is formed. The received Product is filtered off and dried according to Example 1, with 210 g of a white polymer powder with an intrinsic viscosity of 16.5 can be obtained.

Claims (2)

Patent claims: 1. Process for the preparation of water-soluble acrylamide polymers with a high molecular weight as a slurry of fine particles by polymerizing acrylamide or methacrylamide or monomer mixtures, which contain not less than 50 percent by weight of these monomers, together with comonomers, which are soluble in acetone / water and their copolymers are insoluble therein, in one Concentration of 10 to 30 percent by weight in an acetone / water mixture in the presence of free-radical or redox catalysts soluble in acetone / water at temperatures of 20 up to 60 ° C, optionally in the presence of dispersion stabilizers, characterized, that an acetone-water mixture is used which is 23 to 30 percent by weight Contains acetone, and also 0.5 to 4 percent by weight of polyvinyl alcohol, based on the Weight of the polymerizable monomers, are used. 2. Use of the acrylamide polymers prepared according to claim 1 as flocculants.