JPH0212945B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aqueous acrylamide solution for producing polyacrylamide adhesives and the like. More specifically, the present invention relates to a method for producing an aqueous acrylamide solution using a contact hydration method for synthesizing high molecular weight polyacrylamide in which the content of 2-cyanoethyl acrylate is 5 ppm or less when producing polyacrylamide adhesives and the like. Polyacrylamide can be obtained by homopolymers, copolymers, or appropriate modification treatments such as methylolization and cationization, and can be used as paper strength agents, fiber treatment agents, polymer flocculants, and oil recovery aids. It has many uses such as Paper-making sticky agents, one of the uses related to paper pulp, have long been known to be made from natural products such as mucilage extracted from the root mallow root, or synthetic products such as polyethylene oxide. Since the latter has drawbacks such as a decrease in paper-making ability due to foaming and the occurrence of color unevenness, recently polyacrylamide-based adhesives, which do not have these drawbacks, have been increasingly used. When manufacturing paper, what is necessary in the papermaking process is to uniformly disperse the fibers in the dispersion liquid at this stage and to prevent the dispersed fibers from re-entangling or settling. Sometimes, the purpose is to provide an appropriate aqueous property to stably form a uniform wet paper, and for this purpose, a dispersing adhesive is added. Polyacrylamide-based adhesives are widely used because they sufficiently provide these functions and have good performance. The function of a polyacrylamide adhesive as a sticky agent is thought to depend on its molecular weight and the amount of ionic groups present in the molecule. In particular, the higher the molecular weight, the higher the performance (Paper Technology Association Journal Vol. 25,
522 pages, 1971). When paper layer forming ability is evaluated by the usage rate of polyacrylamide sticky agent in paper formation, it varies greatly depending on the molecular weight. In the case of polyacrylamide sticky agent with a hydrolysis rate of 20%, it is 1.88% with a molecular weight of 3 million, and 1.88% with a molecular weight of 5 million.
It is known that as the molecular weight increases, the paper layer forming ability also increases as the molecular weight increases. Recent polyacrylamide adhesives have molecular weight
Currently, aqueous acrylamide solutions, which are the main raw material for acrylamide-based adhesives, are mostly produced by catalytic hydration of acrylonitrile in the presence of a catalyst whose main component is metallic copper. It is manufactured industrially by When the acrylamide aqueous solution obtained by this contact hydration method is used as a raw material for the synthesis of polyacrylamide-based adhesives, it is possible to synthesize relatively low-molecular-weight polymers or copolymers with a small proportion of acrylamide, as well as to synthesize high-molecular-weight polymers. When synthesizing a polymer with a large proportion of acrylamide, the resulting acrylamide-based adhesive has very poor water solubility, and in extreme cases, it simply swells and is hardly soluble in water. This has been a major constraint in producing acrylamide adhesives. Due to incomplete dissolution of the polyacrylamide sticky agent, the presence of water-insoluble substances will cause pinholes in the paper during papermaking, and will also tend to stick strongly on the dryer surface, causing paper breakage. A sticky agent with a high molecular weight and good water solubility without these drawbacks has been desired. The present inventors conducted intensive studies on acrylamide aqueous solutions, which are raw materials for the synthesis of sticky agents, and surprisingly found that acrylamide-based sticky agents synthesized from acrylamide aqueous solutions that do not substantially contain 2-cyanoethyl acrylate are It has been found that substantially no or very little insoluble matter is produced. The present inventors conducted a detailed study on contact hydration acrylamide aqueous solutions, and found that in order to obtain a good acrylamide-based adhesive, 2-cyanoethyl acrylate should be added at 5 ppm by weight based on the acrylamide.
or less, preferably 3 ppm or less, more preferably
The present invention was achieved by discovering that it is necessary to use an acrylamide aqueous solution prepared to a concentration of 1 ppm or less as a raw material. Accordingly, the present invention relates to a method for producing an aqueous acrylamide solution using a catalytic hydration method for synthesizing high molecular weight polyacrylamide containing 2-cyanoethyl acrylate of 5 ppm or less. Using the acrylamide aqueous solution of the present invention as a raw material,
When a polyacrylamide-based sticky agent is synthesized, it is possible to synthesize a sticky agent with excellent performance in which substantially no or almost no water-insoluble substances are generated even in the extremely high molecular weight range of the polymer. In the case of the present invention, the details of why the formation of water-insoluble substances can be suppressed are not clear, but a commercially available acrylamide aqueous solution containing about 10 to 30 ppm of 2-cyanoethyl acrylate on a weight basis to acrylamide is purified. By doing so, the quality of the polyacrylamide adhesive can be easily improved. Next, the present invention will be explained in detail. The crude acrylamide aqueous solution applied to the present invention is obtained by catalytically hydrating acrylonitrile in the presence of a copper-containing catalyst. Various types of copper-containing catalysts have been proposed for use in the production of acrylamide, any of which can be used in the present invention. For example, (1) a method using copper in the form of copper wire, copper powder, etc. and copper ions as a catalyst, (2) a method using copper compounds such as copper oxide, copper hydroxide, copper salt, etc. with hydrogen or carbon monoxide, etc.
A method using reduced copper obtained by reduction at a high temperature such as 100 to 400°C as a catalyst, (3) copper oxide, copper hydroxide,
A method in which reduced copper obtained by reducing a copper compound such as a copper salt in a liquid phase using hydrazine, a borohydride compound of an alkali metal or alkaline earth metal, and a reducing agent such as formaldehyde is used as a catalyst, (4) Oxidation (5) A method in which reduced copper obtained by treating copper compounds such as copper, copper hydroxide, and copper salts in a liquid phase with metals that have a greater ionization tendency than copper, such as zinc, aluminum, iron, and tin, as a catalyst; (5) Aluminum , a method using Raney copper obtained by developing a Raney alloy consisting of zinc or magnesium, etc. and copper as a catalyst;
(6) Organic lead compounds such as copper formate and copper oxalate,
For example, metals found in methods such as using metallic copper obtained by thermal decomposition as a catalyst in a temperature range of 100 to 400°C, (7) or methods using thermal decomposition products of copper hydride as a catalyst. Examples include catalysts containing copper or metallic copper. These copper-containing catalysts may contain, in addition to commonly used carriers, other commonly used metals such as chromium or molybdenum. The reaction of acrylonitrile with water in the presence of the copper-containing catalyst described above usually uses almost any amount of water relative to the acrylonitrile, preferably 50 to
Using a catalyst bed consisting of a suspended bed or a fixed bed and a continuous or batch reaction type, the reaction materials and copper-containing catalyst are mixed with oxygen or This is done while preventing contact with oxygen-containing gases. Next, the reaction solution is subjected to distillation removal of unreacted acrylonitrile contained in the solution and, for example, 30%
It is usually subjected to a distillation operation for the purpose of concentration to obtain an aqueous acrylamide solution having a concentration of about 50% by weight. The aqueous acrylamide solution thus obtained is treated according to the invention. Methods for removing 2-cyanoethyl acrylate from acrylamide include a recrystallization method by cooling an aqueous acrylamide solution, a physical adsorption method in which the aqueous solution is treated with activated carbon or activated clay, and a method for removing 2-cyanoethyl acrylate by bringing the aqueous solution into contact with an ion exchange resin. These include the hydrolysis method in which the aqueous solution is hydrolyzed, the extraction method in which the aqueous solution is treated with chloroform or carbon tetrachloride, and the reaction adsorption method in which the aqueous solution is treated with a compound having a primary and/or secondary amino group. The methods may be used alone or in combination. As the polymerization initiator used in producing polyacrylamide using the acrylamide aqueous solution of the present invention as a raw material, there can be mentioned various conventionally known initiators, such as azobisdimethylvaleronitrile, azobiscyanovaleric acid sodium salt, Azo compounds such as azobisisobutyronitrile, azobisaminopropane hydrochloride, benzoyl peroxide, lauroyl peroxide,
Examples include organic peroxides such as tertiary butyl hydroperoxide, and inorganic peroxides such as potassium persulfate, sodium perbromate, ammonium persulfate, and hydrogen peroxide. Reducing agents include inorganic compounds such as ferrous sulfate, ferrous chloride, sodium bisulfite, sodium metasulfite, sodium thiosulfate, and nitrite; organic compounds include dimethylaniline and 3-dimethylaminopropionitrile. , phenylhydrazine, and the like. In the method of the invention, the monomer used to obtain the high molecular weight polyacrylamide is acrylamide alone or a mixture of acrylamide and a monomer copolymerizable with it. Examples of monomers copolymerizable with acrylamide include methacrylamide, acrylic acid or salts thereof, N-methylacrylamide, N,N'-dimethylacrylamide, N-methylolacrylamide, and 2-acrylamide. 2-Methylpropanesulfonic acid or salts thereof, methacrylic acid or amino alcohol esters of acrylic acid (e.g. dimethylaminoethyl methacrylate, diethylaminoethyl acrylate) and salts or quaternary ammonium salts thereof, methacrylic acid or Examples include ester compounds of acrylic acid (eg, methyl methacrylate, hydroxyethyl acrylate), acrylonitrile, and the like. Next, the present invention will be specifically explained using examples. Examples 1 and 2 When two types of 40% acrylamide aqueous solutions (A and B) prepared by a commercially available contact hydration method were analyzed by gas chromatography, the content of 2-cyanoethyl acrylate in acrylamide aqueous solution A was 14.1%. ppm, and 16.0 ppm in aqueous solution B. This acrylamide aqueous solution was passed through an ion exchange resin as described below, and then a polymer was produced and evaluated. Purification of acrylamide aqueous solution: Prepare two glass ion exchange columns (columns, ) with an inner diameter of 20 mm and a length of 50 cm.
The column was filled with 100 ml of a strongly basic anion exchange resin Revachit MP500 (manufactured by Bayer AG, trade name) in the OH form, and a strongly acidic cation exchange resin Amberlite IR-120B (manufactured by Rohm and Haas) in the H form. , trade name) and thoroughly washed with water. These two columns were connected in series, and the acrylamide aqueous solutions A and B were passed through each column individually at a rate of SV3 (300 ml/hr). At this time, 2 of the acrylamide aqueous solutions A and B
- Cyanoethyl acrylate content is 0.0, respectively.
It was 0.2 ppm. Production of polymer: The acrylamide aqueous solution obtained by the above method was adjusted to an acrylamide concentration of 20% by weight with distilled water,
After adjusting 100 parts of it to pH 10 with aqueous caustic soda solution,
Blow nitrogen gas to remove dissolved oxygen and clean the system for 30 minutes.
℃. To this, potassium persulfate as a catalyst and nitrotrispropionamide as a cocatalyst were added at 8.0 x 10 ^-5 mol and 20.0 x 10 ^-5 mol per mol of acrylamide, respectively, and the temperature was raised by the heat of polymerization and the resulting polymerization was allowed to proceed. The reaction was allowed to proceed for a while, and when no rise in temperature was observed, the polymerization reaction was terminated by being left for another 1 hour to obtain an agar-like substance. Next, the obtained agar-like material was crushed into pieces of 2 mm or less in size, and then poured into methanol to replace the water in the agar-like material with methanol, and then dried under reduced pressure at 50 ° C.
A polymer powder was obtained. Evaluation of the obtained polymer: The water solubility and viscosity of the polymer obtained by the above method were evaluated. (1) Water solubility is determined by dissolving the polymer powder to a concentration of 0.1% by weight and passing it through a 200 mesh wire mesh.
The water-insoluble matter was separated from the aqueous solution and the water-insoluble matter was determined. (2) Viscosity was measured in 1N sodium nitrate at a temperature of 30°C using the aqueous polymer solution obtained in the above water solubility test. The results are listed in Table 1 as Examples 1 and 2, respectively. Examples 3 to 5 The same acrylamide aqueous solution A used in Example 1 was diluted 3 times and 5 times, respectively, with the purified acrylamide aqueous solution treated with the ion exchange resin obtained in Example 1. , diluted 15 times and 2
- Three types of acrylamide aqueous solutions with different cyanoethyl acrylate contents (2-cyanoethyl acrylate content is 4.7 ppm, 2.8 ppm,
0.9ppm) was prepared. Polymers were produced using these three types of acrylamide aqueous solutions in the same manner as in Example 1, and the obtained polymers were further evaluated, and the results are listed in Table 1 as Examples 3, 4, and 5, respectively. Comparative Examples 1 and 2 Polymers were produced using the same commercially available acrylamide aqueous solutions A and B used in the examples in the same manner as in the examples without ion exchange resin treatment, and the resulting polymers were further evaluated. The results are listed in Table 1 as Comparative Examples 1 and 2, respectively. 【table】

Claims (1)

[Claims] 1 An acrylamide aqueous solution produced by a contact hydration method with a 2-cyanoethyl acrylate content of more than 5 ppm is purified, and the 2-cyanoethyl acrylate content is reduced.
A method for producing an aqueous acrylamide solution using a contact hydration method for synthesizing high molecular weight polyacrylamide, characterized in that the concentration is 5 ppm or less.