DE1298989B - Process for the production of acrylic or methacrylic acid amide sulfate - Google Patents

Description

The invention relates to an improved process for the preparation of amide sulfates of acrylic acid and methacrylic acid, which are free from crosslinking impurities.

The monomeric acrylamide is of considerable interest, as it has been increasing in recent years Number of uses for water-soluble acrylamide polymers, such as soil conditioning agents, flocculants for mineral suspensions and thickeners for aqueous systems have been proposed, using high molecular weight polymers are generally preferred.

The starting material for such polymers, the monomeric acrylamide, is generally by acid hydrolysis of acrylonitrile produced. Normally, however, contain those produced in this way Monomers crosslinking impurities that the polymers made from them in water make insoluble. This water insolubility or crosslinking in the resulting polymers occurs in the increases when the polymerization is carried out at higher monomer concentrations.

It is believed that these crosslinking impurities are at least partially made up of larger and lesser amounts of the following compounds exist:

1. CH ₂ = CH-C-NH-C-CH = CH ₂ (diacrylimide)

O O

Il H H Il

2. CH ₂ = CH-CNRNC-CH = CH ₂

(Alkylenebisacrylamide)

R = radical with 1 to 4 carbon atoms.

Direct experimental evidence for the foregoing inferences is due to the difficulty the analysis for the small amounts of the contaminants in question can hardly be obtained. It is known, however, that acids and heat promote the formation of diacrylimide will. Such conditions exist during the hydrolysis of acrylonitrile. The emergence of Alkylenbisacrylamiden is believed to be the result of a reaction between two amide molecules and one Be aldehyde molecule. Aldehydes are usually found in trace amounts in commercially available acrylonitrile; they can also be caused by oxidation of the nitrile during hydrolysis at elevated temperatures are formed.

The impurity present as an imide can be easily extracted from the bulk of an α, / J-unsaturated amide monomer remove by subjecting them to tired hydrolysis conditions. Preferably this operation is carried out immediately prior to the polymerization of the monomer. Though a a considerable proportion of the crosslinking impurities is effectively removed in this way, remains nevertheless a sufficient amount of crosslinking impurities in the monomer mass, to hinder the production of high molecular weight linear polymers. In case of High molecular weight polymers from acrylamide used in polymerization systems made from monomer concentrations above about 10 weight percent of the system such crosslinking impurities are formed by the formation of water-insoluble ones More polymer to recognize.

Based on the assumption of the presence of alkylenebisacrylamides as crosslinking impurities, A number of attempts have been made to determine the meaning of its presence

ίο to occupy such monomers in acrylamide.

Essentially, these attempts consisted in the polymerization of a purified acrylamide monomer in aqueous solution at special monomer concentrations. At any monomer concentration a number of aliquot runs were carried out in which different proportions of Methylenebisacrylamide (MBA) was added into the polymerization system. In this way, since the other conditions of the polymerization were kept identical in all batches that Amount of these cross-linking impurities determined at which the formation of a cross-linking Polymer begins. The term "crosslinked" as used here means that the polymer mass What is insoluble in water is that the polymer does not disperse in water and is not homogeneous Phase forms that can be infinitely diluted with additional water. The results of this series of tests are listed in Table I below.

Table I.

From the above it can be seen that even low concentrations of these crosslinking agents Impurities exert a decisive influence on the course of the polymerization reaction can. It is observed that the amount of gelation or crosslinking of the obtained Polymers require a crosslinking agent to be an inverse quadratic function of the monomer concentration is, d. H.

Acrylamide concentration in
the polymerization system Concentration on MBA where
gel formation (cross-linking
Polymeres) begins (Weight percent) (Parts per million, based on acrylamide) 5 250 10 50 20th 10 30th 5 50 2

[MBA] =

where [MBA] is the concentration of the difunctional MBA monomer, [M] is the concentration of the Amide monomers and k is a constant for the system. By the method of the invention it is possible to remove these impurities and thus the disadvantages of the previously known methods to eliminate.

The process of the invention for the preparation of acrylic or methacrylic acid amide sulfate by hydrolysis the corresponding nitriles with aqueous sulfuric acid solution with a content of 1.0 to 1.4 mol Water per mole of sulfuric acid in an amount of

the phenols were added in amounts between 0.05 and 2 percent by weight of the nitrile used. The amount used is preferably in the range between 0.1 and 1 percent by weight.

The heavy metal ion used is an inorganic cation, which is usually added as a salt will. Preferred heavy metal ions are iron, cerium, manganese and titanium ions, where Iron, especially iron (II) ions are preferred.

1.0 to 1.1 moles of sulfuric acid per mole of the nitrile,
at a temperature of 50 to 110 ⁰ C and in
The presence of heavy metal ions, especially iron (II) ions, as a polymerization retarder exists
in that you can do the hydrolysis in oxygen-free
Atmosphere and in the additional presence of
0.05 to 2 percent by weight, based on the nitrile,
a mono-, di- or trihydroxybenzene soluble in the nitrile or an alkyl or halogen derivative thereof, preferably resorcinol or phloro, above a certain minimum amount, in the case of glucine. 'which has sufficient polymerization retardation

When the hydrolysis is complete, what is achieved is the concentration of metallic

Acrylic or methacrylic acid sulfate, in a suitable manner, ions in the reaction mixture are not critical. In the event of

of the sulfuric acid, for example by adding iron ions, at least 0.05 weight

of lime or by using ionic 15 percent, based on the weight of the reaction

exchange, liberated. mixed, to use.

The aqueous amide sulfate solution obtained can be concentrated in such a way that it can be used directly for the polymerization of a sufficient amount of the phenolic vertion, or it is further dissolved in the nitrile in question and evaporated until a solid, Obtains impurities free monomer from crosslinking solution by flushing with nitrogen from the air. Also exempt. This solution is then slowly added to the atmosphere using other methods in which the acrylamide sulfate is thoroughly mixed to form sulfuric acid monohydrate and the amide monomer obtained is separated off from the neutralized mass which has been substantially de-oxygenated; the acid contains an applied e.g. B. Neutralization with NH3, a sufficient amount of an iron compound. The addition-Na2CÜ3, NH3 + (NH,) 2SQi with feedback of the speed of the nitrile to the acid is controlled so mother liquor, separation of the amide and amide sulphate, that temperatures in the reaction mixture by ion exchange, acid removal are avoided by ion of more than 100 ⁰ C. . After exchange. Some of the end features of the process of ending addition to the reaction mixture for as long as the invention were known. So it was heated to a temperature between 50 and HO ⁰ C, known, the saponification of the acrylonitrile with until the nitrile is completely converted into the amide.
concentrated sulfuric acid in the presence of water and up to 1.4 moles of water per mole of sulfur. It was also known that phenols contained in acid. At least 1 mole of sulfur in the 0- and p-positions to the hydroxyl group non-subacid is added per mole of acrylonitrile. If substituted, a slight excess such as 1.1 mol can be reacted very easily with aldehydes. However, it was not known that sulfuric acid and 1.1 moles of water per mole of acrylics give good results in the hydrolysis of acrylonitrile and methacrylonitrile,
Nitrile is crucial, as an impurity before the reaction has ended, the aldehydes in the reaction are removed. Also was not 40 mixture to temperatures below 50 ⁰ C, preferably to predict whether the known reaction of Phe, up 3O ⁰ C, cooled to 20, and may now nole with aldehydes in the present here loading an atmosphere containing oxygen werdingungen exposed and concentrations at all expire. Then an appropriate procedure is used to dignify. Neutralization of the sulfuric acid and

According to the method of German patent 45 separation of the amide monomer applied.

920 876 were water-insoluble polyacrylic acid although the added to the reaction mixture

amide by heating acrylonitrile with iron ions effective polymerization inhibitors in

obtained aqueous sulfuric acid; However, there have been absence of oxygen will be better

no precise information about properties and results are obtained if another polymer

Quality made of this polymer solution. After 5 ° sation inhibitor is added. Preferably will

This process does not lead to a further inhibitor after the monomers

usable products. Termination of the hydrolysis reaction during the

The cooling obtained by the process of the invention is added. Suitable for this purpose

Amido monomers can be used to produce linear, are copper (II) ions that are in the form of copper sulfate

d. H. Crosslink-free polymers with a high 55 or copper powder can be added.

Molecular Weight (8,000,000 and Above) Used The following examples serve to further elucidate.

The phenols that can be used in the process of the invention must be at least something in the employed

Soluble in nitrile. It is a mono-, di- 60 I _n a reaction vessel with a stirrer, heating system

or trihydroxybenzenes and their halogen, and and device for venting the contents of the kettle alkyl derivatives in which at least one position
of the benzene ring either in the o- or p-position
one of the hydroxyl groups occupied by hydrogen

* -> - χ

purification of the invention.

example 1

by purging with nitrogen and maintaining an inert atmosphere was 106 g of water, 2.58 g of commercial

is. The amount of 65 ferrous sulfate (FeSQj · 7HaO) added to the reaction mixture and 0.296 g of powdered phenolic compound must be sufficient to add iron. This mixture was then with all of the aldehydes present in the nitrile are added to 924 g of aqueous 95% strength sulfuric acid and tie. In general, the reaction system is purged with nitrogen for this purpose. At-

then 443 g of commercially available acrylonitrile, containing 0.222 g of dissolved resorcinol (500 parts per million parts) was added dropwise with stirring to the acidic solution added. The acrylonitrile had also been flushed with nitrogen beforehand.

The rate of addition of the acrylonitrile was adjusted so that the temperature of the reaction system was maintained at about 85 ° C. After completion of the addition of the acrylonitrile the reaction system was heated for 2 hours at 85 ⁰ C and then cooled to about 65 ° C. The reaction product was then mixed with 2.31 g of nitrogen-saturated water containing 2 g of cupric sulfate pentahydrate, and the solution was brought into contact with the air. When a portion of the acrylamide sulfate obtained in this way was diluted with ethanol, a clear solution resulted; this shows that no polymer was formed during hydrolysis.

The aqueous solution of the acrylamide sulfate was through an ion exchange column 1.83 m in length and 7.6 cm in diameter with a commercially available sulfonate-type cation exchange resin in acid form in order to free the acrylamide from most of the sulfuric acid. The replacement resin was then washed with water to elute the acrylamide; it was in the form of an approximately 10% aqueous solution obtained. The acrylamide solution thus obtained was used for removal of the resorcinol passed through activated carbon.

The sulfuric acid remaining in the acrylamide solution obtained in this way was brought to a pH of about 11 by adding sodium hydroxide. The basic monomer solution was then heated to 85 ⁰ C for about 30 minutes to hydrolyze crosslinking possibly present impurities. The solution was then acidified to a pH value of 5 by adding sulfuric acid and sodium acetate was added as a buffer in an amount of 1%, based on acrylamide. The dilute aqueous solutions of acrylamide prepared in this way were concentrated by vacuum distillation to the desired amount of monomer for the subsequent polymerization.

To an aqueous solution of 29.5 percent by weight of the above Acrylamide monomers produced were 1000 parts per 1 million parts of tetrasodium ethylenediamine tetraacetate and 0.5 percent by weight, based on monomer, tert-butyl hydroperoxide was added. The received Solution was brought to pH 5.0, purged of air with nitrogen and poured into enclosed in an ampoule and held at 70 ° C for 16 hours. The polymer gel obtained was in Dissolved water, and the viscosity of the dilute solution was found (0.5 percent by weight of the polymer) of 33.6 cP at a pH of 3.0.

In a second approach carried out in an identical manner to the preceding, in which only 250 parts of resorcinol used as a scavenger became a high molecular weight polyacrylamide obtained what a viscosity of the dilute solution of 50.5 cP at a pH value of 3 had.

Example 2

An acrylamide sulfate monomer was made according to Example 1 produced except that no iron powder in addition to the ferrous sulfate as Inhibitor was used.

The hydrolysis stage of the acrylamide sulfate to the amide was carried out at a pH of 12 during Run at 85 ° C for 0.75 hours. This was then indicated in accordance with that in Example 1 Acrylamide monomers obtained by ion exchange processes through another ion exchange tube 30.5 cm long and 1.27 cm in diameter which contained an anion exchange resin with a chloride anion to remove the resorcinol.

That made from this acrylamide monomer

Polyacrylamide gave a viscosity of the dilute solution in water of 75 cP at a pH of 3.

B e i s ρ i e 1 3

In a series of experiments carried out in accordance with Example 2, monomeric acrylamide was prepared using various phenols. Resorcinol was used in an amount of 500 parts per 1 million parts based on acrylonitrile, and the other phenols were used in equivalent amounts based on the resorcinol.
The polymers prepared from the acrylic monomers obtained in each batch according to the procedures of the preceding examples were dissolved in a dilute salt solution containing 1 percent by weight of sodium chloride and the viscosity of the solutions obtained was determined.

Attempt 1 Viscosity ² ) Table Il Viscosity ¹ ) Attempt 3 Viscosity ² ) Attempt 4 Viscosity ² ) Monomeric Attempt 2 ' Monomeric Monomeric Phenolic compound focus XL Monomeric XL concentrate XL focus 46.9 tration ¹ ) XL focus XL tration ¹ ) 40.4 tration ¹ ) 28.6 29.8 XL tration ¹ ) XL 15.4 44.4 10.2 33.2 29.5 XL 20.2 XL 14.6 59.0 9.5 40.4 Hydroquinone 30.0 46.9 18.7 47.8 14.6 45.8 10.4 35.6 phenol 29.9 50.9 20.2 51.8 15.6 43.3 10.2 34.2 p-cresol 31.5 19.7 14.6 9.9 Phloroglucine 30.2 19.7 14.9 10.2 Resorcinol 20.1

¹ I monomer concentration means the weight percentage of acrylamide in the aqueous polymerization system.

²⁾ The viscosity values in centipoise were used for compositions with 0.5 weight percent of the polymer in an aqueous l _o sodium chloride solution, which was adjusted to pH 3 determines ° and were measured with an Ostwald viscometer at ^25; C received. The letters XL mean that the polymer obtained was crosslinked and insoluble in water.

From the results in Table II it can be seen that favorable results with each member of the specified class of phenols are obtained and that, however, extremely effective and surprising Results occur with phloroglucinol and resorcinol.

In a similar way as in Example 1, other 'phenols, such as 3,5-xylenol, m-cresol, 2,3,5-trimethylphenol, 3,4-xylenol, 2,5-xylenol, saligenin and o-cresol was used instead of resorcinol, resulting in acrylamide monomers which were practically free of cross-linking impurities.

Claims (1)

Claim: Process for the preparation of acrylic or methacrylic acid amide sulfate by hydrolysis of the corresponding nitriles with aqueous sulfuric acid solution containing 1.0 to 1.4 moles of water per mole of sulfuric acid in an amount of 1.0 to 1.1 moles of sulfuric acid per mole of the nitrile , at a temperature of 50 to 110 ⁰ C in the presence of heavy metal ions, especially iron (II) ions, as a polymerization retarder, characterized in that the hydrolysis in an oxygen-free atmosphere and in the additional presence of 0.05 to 2 percent by weight, based on the nitrile, a mono-, di- or trihydroxybenzene soluble in the nitrile or an alkyl or halogen derivative thereof, preferably resorcinol or phloroglucinol. 909 528/287