DE2717630A1 - Dry, solid polyacrylamide prodn. - by mixing catalyst and monomer solns. on heated moving surface - Google Patents

Abstract

Dry solid polyacrylamide is produced by depositing an aq. soln. of acrylamide (I) and an aq. soln. of polymerisation catalyst (II) onto a heated moving surface so that the acrylamide exothermically polymerises and all of the water evaporates. The acrylamide soln. comprises 60-80wt. % (I) and 20-40wt. % water and is first heated to 50-100 degrees C. The moving surface is heated to between 50 degrees C and the charring pt. of (I). The catalyst (II) is pref. an alkali metal or ammonium sulphite, bisulphite or persulphate, used as pref. 0.1-5 wt. % (on wt. of (I)). Pref. (II) is sodium bisulphite or ammonium persulphate. Dry solid polyacrylamide is used e.g., in conjunction with bentonite to prevent seepage of water in earth filled dams and together with expanding lattice clays (e.g., bentonite) in drilling muds. Process is efficient and no monomer is lost or wasted. The prod. is ready for use without further processing except for grinding to the desired particle size.

Description

CONTINUOUS PROCESS OF MANUFACTURING

OF DRY, SOLID POLYACRYLAMIDE The invention relates to a process for the production of dry, solid polyacrylamide.

Polyacrylamide is essentially a white, solid polymer with relatively large molecular weight and of the formula CH2CHCONH2; it takes place diverse Use. For example, it is used in the dry state when building earth dams in Used in conjunction with bentonite to prevent water seepage. It is also used in drilling mud - again in connection with swelling Clays, like bentonite.

Since polyacrylamide is considered drier in these and other applications If solid is used, it is usually desirable that the polymer with the production in the form of a dry, solid polymer, which in itself none further processing is required, at most a comminution of the solid in smaller grain sizes.

As mentioned, a polymer to be used in the dry state should in this form of use.

It is therefore not surprising that attempts have already been made were able to make dry polymers of acrylic acid. In this context, let See U.S. Patents 2,833,745, 2,956,046 and 3,058,958. These publications primarily describe the manufacture of dry sake from acrylic resins. Her Typically, teachings are not applicable to polyacrylamide polymers; in particular the methods described are relatively complicated and uneconomical.

For example, U.S. Patent 3,058,958 discloses a process for ittymerization of acrylic salts in the form of thin films.

It gets the polymerization solution up in a very complicated way dripped on rollers driven in the opposite direction.

The polymerization solution is an aqueous solution of calcium acrylate, Sodium acrylate and an initiator. The calcium acrylate is said to have the effective rate of polymerization accelerate.

The initiator is in the same solution as the sodium and calcium acrylate, and the solution is not preheated, which according to the publication is essential.

In US Pat. No. 2,956,046 there is a very complicated method of manufacture of dry acrylic acid polymers using spray polymerization. The watery one Dispersion of sodium acrylate in a catalyst is dispersed in heated air, which has a temperature of 1770C to 2040C, which - as mentioned above - very is uneconomical and, moreover, not in the process according to the invention can be carried out.

Finally, U.S. Patent No. 2,833,745 is devoted to a method of manufacture of sodium polyacrylate, the prior inventor apparently the essential Feature in it sees that the initiator during the evolution of carbon dioxide is admitted. It is obvious that this is also a complicated one Process for the production of a dry salt, which process in turn is not applicable to the production of polyacrylamide.

The object of the invention is to provide a method for production of polyacrylamide in dry, solid form, which is directly in the Follow-up to the production without any further treatment steps with the exception of one Milling can be used to achieve the desired grain size.

This object is achieved according to the invention in that initially a single phase, liquid, aqueous composition formed from water and acrylamide will. This single phase composition is made by mixing acrylamide and water and heating the mixture to a temperature between about 500C and 1000C. According to the invention it is necessary that this mixture is preheated.

The amount of acrylamide in the aqueous composition is not as crucial as the temperature, and usually one becomes the aqueous composition from about 60 to 80% by weight Acrylic amide and 20 to 40 wt% water the percentages based on the total weight of acrylamide and water are.

The invention includes an economical method of manufacture of polyacrylamide in dry and solid form and avoids the various disadvantages of the prior art, after which it was attempted to use various polymers in dry, to produce a solid form. The method according to the invention is essentially distinguished by carefully mixing a certain amount of acrylamide with water and that this mixture is preheated so that a solution prior to mixing with the catalyst of the polymerization reaction is formed. Because the polymerization reaction exooerm and because the surface on which the polymerization takes place is preheated or is preheated, the water is discharged as steam. Furthermore, neither will of the acrylic amide monomers involved are discarded or lost, and the polyacrylamide polymer obtained is obtained in dry, solid form and does not contain water.

According to the invention is also a polymerization catalyst for Acrylamide required. Such catalysts belong to the state of the art, and the invention is not based on the use of such catalysts. Only for reasons of explanation, reference is made to various sulfites, bisulfites, persulfates, Peroxides etc referenced; the only The criterion is that the polymerization catalyst must be soluble in water. For example, it was found that alkali metal sulfites, bisulfites and persulfates produce excellent results, as well as ammonium sulfite, bisulfite and persulfate.

The amount of catalyst is also not of critical importance and can range from 0.1 to 5 weight percent based on the weight of the acrylic amide. Since the aqueous solution of the acrylamide must be mixed with the catalyst, will the latter is preferably added to the acrylamide in aqueous solution. The amount of Catalyst in the aqueous solution is not important. For example, can the catalyst concentration from 10 wt .-% to the saturation point of the respective Catalyst run, which, in the case of ammonium persulfate, at 40 wt .-% at OOC lies.

To bring about a continuous process, the area on which the acrylamide and the catalyst are applied, preferably agitated. It has been mentioned that this moving surface is preferably flat and coincides with a such a speed that the polyacrylamide formed by the reaction not with the acrylamide monomer or the aqueous solution of the polymerization catalyst comes into contact. In the preferred embodiment, the moving surface is a circumferential metal disc (e.g. steel, aluminum, or the like) with a diameter from 1.8 m.

The rotating metal disc is turned on by means of natural gas burners Temperature between 500C and the coking point of the polyacrylamide heated. she is moved at such a speed that the polymer formed is in front of the area can be removed, in which the disc with the aqueous solution of the acrylamide and the aqueous solution of the polymerization catalyst is applied.

Example: Solid acrylic amide was mixed with water at room temperature.

The amount of the acrylamide was 60% by weight and that of the water was 40% by weight. The mixture so formed was then heated to about 550C. At this temperature a single phase aqueous liquid composition was obtained. About the same In time two saturated solutions of ammonium persulfate and sodium bisulfite were made. The three solutions were poured onto a rotating metal disc, which one Temperature of about 90 ° C and a diameter of 1.8 m.

The metal disc was heated with natural gas burners on the side were arranged that was opposite the side of the pane on which the aqueous, liquid Compositions were poured onto the disc. The amount of used Bisulfite was 0.3 wt% based on the weight of the acrylic amide, and the amount of the ammonium persulfate 1% by weight, also based on the weight of the acrylamide. The three solutions were applied to the surface in such a way that they were mixed together became and that practically immediately thereafter a polymerization reaction occurred at which the polyacrylamide was formed.

At the same time, the water was partly due to the steam as a result exothermic polymerization removed. The dry, solid polyacrylamide was made then removed from the rotating disk, for example by means of a scraper and, if so desired, milled to a specific grain size.

From the above it follows that the invention, although them with reference to specific polymerization catalysts, concentrations and temperatures has been described, also deviating from these parameters can be carried out without thereby departing from the basic concept of the invention will.

Claims (4)

PATENT CLAIMS 1. Process for the production of dry, solid Polyacrylamide, characterized in that an aqueous mixture of essentially 60-80% by weight of acrylamide and 20-40% by weight of water are formed by making them aqueous Mixture to form a single phase, liquid, aqueous composition a temperature between about 500C and 1000C heated that once this aqueous, single-phase liquid and, on the other hand, a catalytically effective amount of an aqueous one Solution of a water-soluble polymerization catalyst for acrylamide such an area gives up a mixture of the single-phase, aqueous liquid and the aqueous solution is formed, the surface being at a temperature between about 50 0C and the coking point of acrylamide is heated, so that the acrylamide Polymerizes exothermically to form polyacrylamide and thereby all of the water evaporated with the formation of dry, solid polyacrylamide and that the polyacrylamide away from the surface. 2. The method according to claim 1, characterized in that the polymerization catalyst consisting of an alkali metal and ammonium sulfite, bisulfite and persulfate Group is selected. 3. The method according to claim 1, characterized in that the polymerization catalyst is selected from the group consisting of sodium bisulfite and ammonium persulfate will. 4. The method according to claim 1, characterized in that the polymerization catalyst added in an amount of 0.1 to 5 wt .-% based on the weight of the acrylamide will.