DE2557325C3 - Process for drying acrylamide polymers - Google Patents

Description

15th

Water-soluble acrylamide polymers are used for many applications, for example as Sedimentation aids, flocculation aids, filtration aids and thickeners. The effectiveness of the polymers is particularly high in these applications the higher the molecular weight, the greater the acrylamide polymers are, for example, by solution polymerization, reverse suspension polymerization or reverse emulsion polymerization prepared. In all cases, the result is aqueous polymer solutions, which are essentially only characterized by their state of distribution and the presence or absence of a Differentiate auxiliary phase. However, aqueous solutions of acrylamide polymers are only flowable when the polymer concentration is below 10% by weight. Highly concentrated acrylamide polymer solutions have a gel-like or rubber-like character and are sticky. With increasing solids content)> the tack decreases, so that the polymer with a solids content of more than 85% by weight generally increases without can be stored baked.

It is therefore necessary to dry the polymer solutions. A well-known method is the extractive 4 <i Drying in which a solvent is used that does not dissolve the polymers, but dissolves with water mixes, for example methanol or acetone. The polymer to be dried is finely divided over longer time with a solvent in intimate 4ί Brought in contact. This process must be repeated several times with fresh solvent so that the Although the process is a gentle drying method, it is very expensive. By the others During the drying process, water is evaporated with the addition of 5 »heat. For example, you can use diluted Flowable polymer solutions are dried on heated rollers. It is also known to have gelatinous products Finely divided to dry in a hot air fluidized bed. From DE-PS 14 94 967 it is known to use water with a remove the boiling auxiliary phase by azeotropic distillation.

These processes have the common disadvantage that, as a result of the elevated temperatures, the polymers are damaged, namely the more and the easier the higher the average molecular weight of the Is polymerizate. Insoluble products are formed which only contain gel components that can be swelled in water. the Insoluble products interfere with the application and at the same time reduce the effectiveness of the acrylic b> amide polymers. It is therefore of the utmost importance to avoid any damage to the polymer during drying to avoid. For example, the drying temperature can be increased under reduced pressure However, this makes the known drying processes even more complicated and expensive.

From US 32 34 163 is known aqueous polyacrylamide solutions stabilize with thioureas. However, the effect of these additives is insufficient.

The invention relates to a process for drying water-containing acrylamide polymers or their aqueous solutions by evaporation of the water with the addition of heat, which thereby is characterized in that the water in the presence of 0.1 to 1 wt .-%, based on the acrylamide polymer, a water-soluble hydroxylamine or hydroxylammonium salt is distilled off.

The process can be used on acrylamide polymers that have already been partially dehydrated or have already accumulated in a high concentration in a polymerization process. Besides, it is possible to dry aqueous acrylamide polymer solutions according to the invention. The procedure by which the acrylamide polymers made is not critical. The acrylamide polymers can, for example by solution polymerization, reverse suspension polymerization and reverse emulsion polymerization getting produced. The composition of the acrylamide polymers is also not critical. Both homopolymers and copolymers can be used in the process according to the invention dry the acrylamide with cationic and / or anionic monomers. Be considered for example copolymers of acrylamide and acrylic acid, acrylamide and methacrylic acid, copolymers from acrylamide and dialkylaminoalkyl acrylates, such as dimethylaminoethyl acrylate or methacrylate, as well as copolymers of acrylamide, dialkylaminoalkyl acrylates and a, j3-ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid or itaconic acid. The acrylamide content of the polymers can be in the Range from 40 to 100% by weight. The molecular weight of the polymers is from 1,000,000 to 25,000,000.

The acrylamide polymers to be dried, which contain, for example, 1 to 99% by weight of water, are, before drying, 0.01 to 1, preferably 0.01 to 0.5% by weight, based on the acrylamide polymer, of a water-soluble polymer Hydroxylamine or hydroxylammonium salt mixed. Preference is given to using hydroxylamine, C ₁ - to C ₈ -monoalkyl-substituted hydroxylamines, and monosubstituted acrylic hydroxylamines. Cyclic alkyl radicals whose ring system contains 3 to 7 carbon atoms are also suitable as alkyl groups.

The hydroxylamines or the corresponding hydroxylammonium salts acting as stabilizers, for example Salts obtained by neutralizing hydroxylamines with sulfuric acid, hydrochloric acid, phosphoric acid or organic acids, such as formic acid, acetic acid and propionic acid, are used aqueous polymer solutions before drying. If polymers are to be dried, the have been prepared by reverse suspension or emulsion polymerization, one can proceed as follows: that an aqueous solution of the hydroxylamine is added and the components are stirred together mixes. Hydroxylamines can then also be used in the form of an aqueous solution with the acrylamide polymer be mixed when a gel-like, no longer flowable polymer solution is present.

The water is distilled off from the polymer solutions or the water-containing polymers by known methods, e.g. B. on heated rollers, in a hot air fluidized bed or by azeotropic distillation. The acrylamide polymers are preferably dried by the azeotropic distillation process. Suitable organic liquids for azeotropic distillation are, for example, n-heptane, carbon tetrachloride, tetrachlorethylene, amyl acetate or dibutyl ether. Gasoline in the boiling range from 65 to 80 ^° C. is preferably used, as are aromatic hydrocarbons such as benzene, toluene and xylene and aliphatics such as cyclohexane, hexane and heptane. These solvents can also be used in a mixture with one another. They can also form the continuous phase of the water-in-oil dispersion of the aqueous polymer solution which is currently to be dewatered.

The distillation temperature during dehydration can be determined by known methods, for example by regulation the pressure and, in the case of azeotropic distillation, also through the choice of solvents to a large extent

Areas can be varied. The following examples explain the invention in more detail.

example 1

A suspension of 510 g of a gel-like 35% gene aqueous solution of a copolymer of 64 parts of acrylamide and 36 parts of sodium acrylate in 1 l Cyclohexane, which contains 2 g of sorbitan monostearate,

ίο has been using hydroxylammonium sulfate as well in several Comparative experiments with the substances indicated in Table 1 added or even in their absence an additive dried by azeotropic distilling off of water. After azeotropic removal The residue was filtered off from the water and removed from adhering solvent at 50 ° C. in vacuo freed The result was free-flowing solid products that did not bake even during storage.

A 0.1 percent strength by weight aqueous polymer solution was prepared from each of them, which was visually identified the content of insoluble gel particles was assessed. The results are summarized in Table 1.

Table 1 additive Comparison 40
No. 4th Amount added,% by weight, Insoluble parts Encore 0.067 Unsolvable examples 5 based on polymer amount, be 0.133 liche Hydroxylammonium sulfate 1 0.011 no pulled up 0.267 Shares 2 guanidinium chloride 6th Polymer 0.533 3 urea T. 45 Wt% 0.022 4 Thiourine stolT 7th 0 many many Example 2 8th 0.011 many 0.044 The procedure described in Example 1 is followed 55 ₉ 0.011 many 0.089 0.089 no however, the compounds given in Table 2 in 10 0.011 some 0.178 0.178 no the amount also described in the table. Il 0.356 As can be seen from the table, contains 0.1% Hydroxylamine Cyclohexyl hydroxyl-0.033 no aqueous solution obtained by dissolving the dried W) 12 ammonium chloride Acrylamide polymer was produced, no insoluble 13th the same no union proportions, while a solution of the Copolymerisa 14th the same no tes obtained by drying the same copolymer in 15th the same no Absence of a stabilizing agent produced the same no contains a large amount of insoluble matter. Isopropyl hydroxyl no the same ii ni ni on i 11 m ζ 111 Γίΐ I Table 2 the same Cl 11 11 II KJ IllUllloUlltll
the same no the same no the same no No. Hydroxylamine addition insoluble the same no amount, borrowed
drew on shares Polymer Weight% I hydroxylammonium-0.011 none sulfate 2 same 0.022 none 3 also 0.044 none

Claims (1)

Claim: Process for drying water-containing acrylamide polymers or their aqueous solutions by evaporating the water with the supply of heat, characterized in that the water in the presence of 0.1 to 1 wt .-%, based on the AcryJamidpolymerisat, of a water-soluble Hydroxylamine or hydroxylammonium salt is distilled off.