JPH11246498A - Purification method of acrylamide aqueous solution and method of producing acrylamide polymer - Google Patents

Abstract

(57) [Problem] To provide a method for purifying an aqueous acrylamide solution more easily and with higher quality than a conventionally known method. The acrylamide aqueous solution produced by such a method has a molecular weight of particularly 15,000,000 to
An acrylamide polymer having a high molecular weight of about 20 million can be obtained, and a polymer having high performance such as water solubility can be obtained. SOLUTION: An aqueous acrylamide solution obtained by hydrating acrylonitrile in the presence of a copper catalyst is decopperized and then kept at 5 to 40 ° C. and pH = 10 to 12. A purification method, and a method of obtaining an acrylamide polymer by homopolymerization or copolymerization using an aqueous acrylamide solution obtained by the purification method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying an aqueous acrylamide solution obtained by a contact hydration method of acrylonitrile and a method for producing an acrylamide polymer using the purified aqueous acrylamide solution.

[0002]

2. Description of the Related Art Acrylamide is used in the production of acrylamide-based polymers used as flocculants, petroleum recovery chemicals, fiber treatment agents, papermaking adhesives, paper strength agents, etc., and is used in large quantities in various fields. It is an industrially useful monomer. Such polymers, particularly for flocculants and petroleum recovery chemicals, have recently been required to have a high molecular weight. A method of obtaining an aqueous acrylamide solution by subjecting acrylonitrile to a catalytic hydration reaction in the presence of a copper catalyst is already well known. However, acrylamide produced using this catalytic catalyst method contains impurities such as impurities derived from raw material acrylonitrile, hydration by-products, and eluates from the catalyst.

[0003] There is usually no problem in producing an acrylamide polymer having a relatively low molecular weight such as a paper strength agent using an aqueous acrylamide solution obtained by such a catalytic catalyst method. However, such an aqueous solution is used, for example, as a flocculant or a petroleum recovery agent,
It is very difficult to obtain a high molecular weight acrylamide polymer having a molecular weight of about 15 to 20 million. Moreover, the obtained acrylamide-based polymer has poor water solubility, which has been a major problem in producing a high-performance acrylamide-based polymer.

From such a viewpoint, many methods for purifying an aqueous acrylamide solution obtained by a contact hydration method have been proposed, for example, a method of adsorbing copper ions and then treating them with activated carbon (Japanese Patent Application Laid-Open No. 48-62714). A method of treating with a weakly basic anion exchange resin after treating with a strongly acidic cation exchange resin (Japanese Patent Laid-Open No. 52-91819), and using a weakly basic anion exchange resin after treating with oxygen and a strongly acidic cation exchange resin. Processing method (Japanese Patent Application Laid-Open No.
No. 8), a method of membrane permeation treatment (JP-A-55-62054).
No.) and the like.

[0005] However, all of the above methods involve complicated auxiliary equipment and complicated control of the operation conditions. Further, acrylamide is very reactive and it is well known that polymerization of acrylamide often occurs during the above operation, which may induce a side reaction. JP-A-49-49506 discloses that at a temperature of up to 60 ° C., 0.1 to 1.5% by weight of an inorganic salt excluding ammonia is added to acrylamide, and the pH is 12 to 13.7. Although a method of blowing an active gas is disclosed, when an aqueous acrylamide solution is treated under the preferable conditions, impurities such as acrylic acid increase remarkably, and the polymerization results are unfavorable.

[0006]

DISCLOSURE OF THE INVENTION In view of the above situation, the present invention makes it possible to convert an aqueous acrylamide solution more easily than conventionally known methods without causing side reactions such as polymerization of the aqueous acrylamide solution obtained by the contact hydration method. An object of the present invention is to provide a purification method for achieving high quality.

[0007]

The present inventors have made various studies to solve the above-mentioned problems, and as a result, by maintaining an aqueous acrylamide solution under certain conditions, the above-mentioned problems have been solved. I found that the point could be solved.
That is, the gist of the present invention is that an acrylamide aqueous solution obtained by subjecting acrylonitrile to a hydration reaction in the presence of a copper catalyst is subjected to copper removal treatment, and then subjected to 5 to 40 ° C. and pH = 10 to 12
(Hereinafter, the treatment after the copper removal treatment may be referred to as “alkali treatment”).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the contents of the present invention will be described in detail. The reaction conditions in the method for producing an aqueous acrylamide solution which is the subject of the present invention is a method in which acrylonitrile is reacted with water in the presence of a copper catalyst to obtain an aqueous solution of acrylamide, and is described, for example, in JP-B-55-35376. Have been. Copper catalysts include metallic copper; Ullman copper; Raney copper; reduced copper; copper oxide; copper sulfate; copper nitrate; copper phosphate; copper thiocyanate; copper salts of inorganic acids such as copper chloride; And copper salts of organic acids. In the copper catalyst, Cr, Ni, Co, Mo, Zn, Fe, W, Pd, T
Metals such as i, Pt, Si, Rh, Rb, V
Alternatively, they may be added as oxides or sulfides thereof,
Alternatively, copper and copper may be combined to form a composite compound. Further, these catalysts may be those supported on a carrier such as asbestos, silica gel, graphite, carbon black, and ion exchange resin.

The hydration of acrylonitrile is carried out continuously or batchwise in a fixed bed or a suspension bed in the presence of the above-mentioned catalyst. The reaction temperature is usually 50 to 200C, preferably 70 to 150C. The reaction pressure is usually from normal pressure to 2 MPa, preferably from normal pressure to 0.6 MPa. The amount of water used may be at least the stoichiometric amount of acrylonitrile, but the solubility of acrylonitrile in water is not so large and it is difficult to carry out a homogeneous reaction, so that the stoichiometric amount of acrylonitrile is usually several times to several tens of times. Double is used. In some cases, alcohols such as methanol and ethanol can be used in combination. Since the acrylamide produced is rich in polymerizability, it is desirable to use a polymerization inhibitor such as hydroquinone or t-butylcatechol when conducting the reaction, and the reaction system should be kept in the absence of oxygen to maintain the catalyst life. You may. In the case of a continuous reaction, acrylonitrile as a raw material is continuously supplied to a reactor, stays in the reactor for a predetermined time, and is continuously extracted as a reaction liquid containing unreacted raw materials. 1 reactor
In addition to stages, a multistage reaction using a plurality of reactors of about 2 to 5 stages may be employed.

The reaction product thus obtained is separated from the catalyst,
An acrylamide aqueous solution is obtained. When the obtained acrylamide aqueous solution is purified by the method of the present patent, if unreacted acrylonitrile remains in the aqueous solution, the quality will be adversely degraded, so that the unreacted acrylonitrile is separated. Is preferred. Examples of a method for separating acrylonitrile from the aqueous acrylamide solution containing acrylonitrile include methods such as separation by distillation and separation by stripping using an inert gas or air.

The aqueous solution of acrylamide thus obtained contains trace amounts of copper ions and by-product impurities which cause inhibition of the polymerization reaction, and is usually brought into contact with a cation exchange resin or an anion exchange resin. Or treated by a method such as activated carbon treatment. Acrylamide before the treatment with an ion exchange resin usually contains copper ions eluted from the catalyst at several ppm to several tens ppm.

When the above-described copper removal treatment is performed after the alkali treatment described below, these dissolved coppers change into copper hydroxides during the alkali treatment, and the copper removal efficiency (in the case of using an ion exchange resin, To reduce the exchange resin efficiency), copper ions must be removed prior to the alkali treatment. The contact between the acrylamide aqueous solution and the resin is performed by a suspension method,
Either a fixed bed method or a moving bed method may be used, but the fixed bed method is usually employed. The passing temperature is below the service temperature of the resin,
A temperature at which acrylamide does not deteriorate, that is, usually 60 ° C. or less is good. However, in these processes,
It is expected that a very small amount of unspecified impurities affecting the polymerization quality remain.

When a contact treatment with an ion exchange resin is employed as a method of copper removal treatment, the ion exchange resin that can be used is a porous or gel type strongly acidic or weakly acidic cation exchange resin such as diamond. Ion (registered trademark, hereinafter the same) SK1B, Diaion PK-208 and Diaion WK-10 (all trade names, products of Mitsubishi Chemical Corporation), Amberlite (registered trademark, the same applies hereinafter)
IR-120B and Amberlite IRC-718 (both trade names, products of Rohm and Haas Company), Dowex (registered trademark, the same applies hereinafter) HCR-W2 and Dowex MWA-1 (both trade names, products of Dow Chemical Company) ),
Levatit (registered trademark, hereinafter the same) SP-112 and Levatit CNP-80 (both are trade names, products of Bayer AG) and the like. The concentration of the aqueous acrylamide solution to be decoppered using an ion exchange resin is usually 10
% By weight or more, preferably 15 to 50% by weight. However, a high-concentration aqueous solution that can be obtained by concentrating the reaction solution can be applied as long as it exhibits a uniform aqueous solution state.

A feature of the present invention is that the acrylamide aqueous solution obtained by the above-described copper removal treatment is made basic and kept under a certain condition. The treatment of the present invention is carried out under mild conditions such that acrylamide itself does not change due to hydrolysis or the like. The basic compound used in the alkali treatment is not particularly limited as long as it dissolves in an aqueous acrylamide solution, and may be ammonia, an organic amine, or a hydroxide, oxide or carbonate of an alkali metal or alkaline earth metal. There is. Of these, sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate are preferred, and sodium hydroxide is particularly preferred.

The basic compound is added when the pH of the acrylamide aqueous solution is 10 to 12, more preferably 11.
It is preferable to add so as to give 0 to 11.5. If the pH is lower than 10, the expected purification effect cannot be sufficiently obtained, and if the pH is higher than 12, the decomposition of acrylamide itself is undesirably induced. The basic compound may be added as a solid or in an aqueous solution, but is usually added in the form of an aqueous solution to avoid a local reaction. As a mixing method with the acrylamide aqueous solution, any of a flow type and a batch type may be used. The temperature condition of this treatment is equal to or higher than the temperature at which acrylamide is precipitated, and 40 ° C.
If the temperature exceeds the above range, acrylic acid is produced as a by-product due to hydrolysis of acrylamide, etc., so that the temperature is 5 to 40C, preferably 10 to 30C, more preferably 15 to 25C.

The time of the alkali treatment is not particularly limited. However, since the acrylamide is deteriorated by the long-term treatment, it is usually 1 to 72 hours, preferably 1 to 24 hours, more preferably 2 to 6 hours. It is. During these times, no special operation is required for the aqueous solution, and it is usually sufficient to simply leave it. After the alkali treatment, it can be used as it is or neutralized if necessary, and can be used as a raw material of the acrylamide polymer. When used as a raw material for the cationic polymer, the aqueous solution of acrylamide after the alkali treatment is usually neutralized and the pH is adjusted to about 3-8. Examples of the acidic compound used for neutralization include inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid, and organic acids such as acetic acid, formic acid, citric acid, and succinic acid. These acids may be used directly or diluted.

The purified, preferably neutralized acrylamide aqueous solution may be polymerized alone or after being mixed with a monomer copolymerizable with acrylamide. As the polymerization method, general methods such as aqueous solution polymerization, emulsion polymerization, suspension polymerization, and precipitation polymerization are used.

Examples of the monomer copolymerizable with acrylamide include methacrylamide; acrylic acid, methacrylic acid or an ester thereof; aminoalkyl acrylate or aminoalkyl methacrylate (or a salt thereof or a quaternary ammonium salt thereof). ); Acrylonitrile; 2-acrylamido-2-methylpropanesulfonate; vinyl acetate and the like. Specific examples of preferred monomers include acryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyldiethylmethylammonium chloride, acryloyloxy-2-
Cationic monomers such as hydroxypropyltrimethylammonium chloride and dimethylaminoethyl methacrylate benzyl chloride can be mentioned. In order to sufficiently obtain the effects of the present invention, the ratio of the monomers to be mixed is preferably in the range of 0 to 70 mol%, more preferably in the range of 0 to 40 mol%.

Examples of the polymerization initiator used for producing the acrylamide polymer include 2,2-azobis (2-amidinopropane) hydrochloride, azobisisobutyronitrile,
Azo compounds such as 2,2-azobis (4-methoxy-2,4-dimethylvaleronitrile) and 1,1-azobis (cyclohexanecarbonitrile), ammonium persulfate,
Inorganic peroxides such as potassium persulfate and hydrogen peroxide, organic peroxy compounds such as benzoyl peroxide and tertiary butyl peroxide, ferrous sulfate, ferrous chloride, sodium bisulfite, sodium metasulfite, and sodium thiosulfate And organic compounds containing groups such as a sulfine group, a tertiary amino group and a hydrazine group (for example, toluenesulfinic acid, dimethylaniline, phenylhydrazine, etc.).

When an aqueous solution of acrylamide purified according to the present invention is used, homopolymerization of the acrylamide or copolymerization with the above-mentioned appropriate monomer causes a molecular weight of 15,000,000 or more.
In particular, the production of 20 million or more polymers becomes easy. The polymer obtained by the present invention is of high quality, especially for flocculants and petroleum recovery chemicals, etc., as well as fiber treatment agents,
It is also useful for adhesives for papermaking and paper strength enhancers.

[0021]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the examples unless it exceeds the gist. All "%" are by weight.

Example 1 Production of Acrylamide Aqueous Solution: Reduced copper was charged into a reactor (90 parts by volume) equipped with a filter for separating a catalyst inside. Thereto, a 35% aqueous acrylonitrile solution was continuously supplied at 5 parts by volume / hr to suspend the reduced copper catalyst, and a catalytic hydration reaction was carried out under the conditions of a reaction temperature of 100 ° C. and a reaction pressure of 0.4 MPa to obtain acrylonitrile. , Acrylamide and water were continuously withdrawn at 5 parts by volume / hr. The extracted reaction solution was subjected to heat treatment to remove acrylonitrile and water and concentrated to obtain a 50% aqueous acrylamide solution, which was then treated with a cation exchange resin to obtain a 50% aqueous acrylamide solution.

Purification of acrylamide aqueous solution: 25% acrylamide aqueous solution produced by the above method was added to 25% acrylamide aqueous solution.
At 4 ° C., a 4% aqueous sodium hydroxide solution is added and p
H was set to 11.5. After maintaining this adjusted solution at 25 ° C. for 6 hours, a 6% acetic acid solution was added to adjust the pH of the acrylamide aqueous solution to 6.5. Acrylic acid and nitrilotrispropionamides in the acrylamide aqueous solution subjected to the above purification treatment were quantified by liquid chromatography. As a result, they were all 0.02% (vs. acrylamide), the same as untreated acrylamide aqueous solution. Content. In addition, confirmation of polymer formation in the above treatment was performed by adding methanol 4 to 5 mL of acrylamide aqueous solution.
5 mL of the mixture was mixed, and no acrylamide polymer was formed.

Production evaluation of acrylamide-based polymer: Using the aqueous solution of acrylamide obtained by the above treatment, a polymerization reaction was carried out by the method described below, and the performance of the obtained polymer was evaluated. First, 285 g of the acrylamide aqueous solution obtained in Example 1, 289 g of demineralized water, and 227 g of methacryloyloxyethyltrimethylammonium chloride were mixed, adjusted to pH = 4.0 using sulfuric acid, and then sealed in a 2 L polymerization tank. Was charged. Nitrogen gas 30
After L was blown into the aqueous solution and completely degassed, 3.2 g of a 10% 2,2-azobis (2-amidinopropane) hydrochloride aqueous solution was first added at a liquid temperature of 10 ° C., and then a 1% ammonium persulfate aqueous solution was added. 0.43 g and a 0.5% aqueous solution of 1% ferrous sulfate heptahydrate were sequentially added, and the mixture was left as it was to carry out polymerization. After the polymerization, the gel polymer was taken out, finely divided by a meat chopper, and dried with hot air at 100 ° C. for 1.5 hours. The obtained polymer was pulverized with a pulverizer to obtain a powdery acrylamide-based cationic polymer. This was sieved and a sample of 16 to 83 mesh was collected and used as a performance evaluation sample. The obtained acrylamide-based cationic polymer was converted into a 0.2% polymer aqueous solution, passed through a JIS standard sieve having an opening of 0.183 mm, and visually checked for remaining undissolved substances. The thing did not exist.

[Examples 2 to 4] In Example 1, the purification treatment was carried out under various conditions in which the pH, the holding time, and the holding temperature after the addition of the aqueous sodium hydroxide solution were changed, and acrylic acid and nitrilotrispropionic acid were converted. Quantitation and confirmation of polymer formation were performed. Further, the performance of the acrylamide polymer was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1] The aqueous solution of acrylamide used in Example 1 was not subjected to pH adjustment using an aqueous solution of sodium hydroxide and acetic acid.
An acrylamide-based cationic polymer was produced in the same manner as described above, and the performance of the obtained polymer was evaluated. The results are shown in Table 1.

[Comparative Examples 2 and 3] Purification treatment was performed in the same manner as in Example 1 except that the pH and the holding time after the addition of the aqueous sodium hydroxide solution were changed. As in Example 1, acrylic acid (ACA) and nitrilotrispropionic acid (NTPA)
Quantification, confirmation of polymer formation, and performance evaluation of the acrylamide polymer were performed. The results are shown in Table 1.

[0028]

[Table 1] Polymer solubility ○: no insoluble content △: some insoluble content ×: large amount of insoluble content

Example 5 Using an aqueous solution of acrylamide subjected to the same purification treatment as in Example 1, a polymerization reaction was carried out by the method described below, and the performance of the obtained polymer was evaluated. Acrylamide aqueous solution 31 obtained in Example 1
7 g and demineralized water (92 g) were mixed, and sulfuric acid was used to adjust pH =.
After adjusting to 5.5, 1.0 mL of a 2% aqueous solution of tert-butyl peroxide was added to prepare an aqueous phase. In a 2 L glass container equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen blowing tube, 146 g of an isoparaffinic hydrocarbon (trade name: Isopar M, manufactured by Exxon Chemical Company), and Span80 (trade name: sorbitan monooleate) as an emulsifier 13 g was added to prepare an oily layer. The aqueous phase prepared above was added to this with stirring to form an emulsion solution. The temperature was adjusted to 21 to 22 ° C. while blowing nitrogen, and 0.0
0.04 mL / mi of 4% aqueous sodium bisulfite solution
Polymerization was initiated by addition at a rate of n. Solution temperature 39
The injection amount of the aqueous solution of sodium bisulfite was controlled so as to maintain the temperature at ４１41 ° C., and the reaction was continued until no increase in temperature due to the heat of polymerization was observed.

To 2.0 g of the obtained emulsion solution, 2.0 g of polyoxyethylene (9) nonylphenyl ether (trade name: Emulgen 910, a product of Kao Corporation) was added as a reversing agent, and the mixture was stirred with a magnetic stirrer. Stir for 10 minutes. The solution was filtered through a 20-mesh screen and diluted with ion-exchanged water to prepare a solution so that the concentration of acrylamide was 0.1 g / dL. 5 g of this solution and 2M-NaC
1 ml of the solution was mixed and homogenized with a vortex stirrer. Various concentrations of 1M-NaCl polymer solutions were prepared in the same manner, and the reduced viscosity at each concentration was measured using an Ubbelohde viscometer. From the obtained values, the intrinsic viscosity (I
When V) was calculated, a value of IV = 20.8 was obtained. The reduced viscosity and the intrinsic viscosity were determined as follows. Reduced viscosity = ((flowing time of polyacrylamide (PAAM) solution / flowing time of 1M-NaCl aqueous solution) -1) /
Polymer concentration Intrinsic viscosity: The polymer concentration (g / dL) is plotted on the horizontal axis, and the reduced viscosity is plotted on the vertical axis, and each polymer concentration (0.1, 0.05,
The values of the reduced viscosities of 0.035 and 0.025 g / dL) are approximated by a straight line, and the polymer concentration = 0 (the intersection between the straight line and the Y axis)
Is calculated as the intrinsic viscosity.

Comparative Example 4 An acrylamide-based polymer was prepared in the same manner as in Example 5 using an aqueous solution of acrylamide that had been subjected to the same purification treatment as in Example 1, without adjusting the pH with aqueous sodium hydroxide and acetic acid. When the performance of the produced polymer was evaluated, the intrinsic viscosity IV was 10.8, which was lower than that of Example 5.

[0032]

According to the present invention, when purifying an aqueous acrylamide solution obtained by hydration reaction using acrylonitrile and water as raw materials, by maintaining the aqueous acrylamide solution under certain conditions, it is possible to easily produce a high-quality aqueous acrylamide solution more easily than conventionally known methods. And a high quality polymer can be obtained using the same.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C07B 61/00 300 C07B 61/00 300 (72) Inventor Hidefumi Yamakawa 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City Mitsubishi Chemical Corporation (72) Inventor Yoshiaki Honda Inside Kurosaki Works, Mitsubishi Chemical Co., Ltd. 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu-shi

Claims (4)

[Claims] An aqueous acrylamide solution obtained by subjecting acrylonitrile to a hydration reaction in the presence of a copper catalyst is decopperized, and then maintained at 5 to 40 ° C. and pH = 10 to 12. A method for purifying an aqueous acrylamide solution. 2. The purification method according to claim 1, wherein the temperature during the holding is 15 to 25 ° C. 3. The purification method according to claim 1, wherein after the hydration reaction, the raw material acrylonitrile is removed and then decopperizing treatment is performed. 4. An aqueous acrylamide solution purified by the method according to claim 1, which is used for a polymerization reaction of acrylamide alone or a copolymerization reaction with a monomer copolymerizable therewith. For producing acrylamide-based polymers.