JPS6343381B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for purifying an aqueous acrylamide solution obtained by reacting acrylonitrile and water in a liquid phase in the presence of a copper-based catalyst. Acrylamide has traditionally been used as an acrylamide-based polymer in paper-making agents, flocculants, oil recovery agents, soil solidification agents, etc., and also has a wide range of uses as a comonomer for other polymers.
In the past, acrylamide used for these purposes was produced by the so-called sulfuric acid method, but in recent years a contact method in which the reaction is carried out in the presence of a copper catalyst has been developed, and the sulfuric acid method has now been replaced by a contact method. It is practiced industrially. Among the above-mentioned uses of acrylamide, its use as a flocculant has recently been expanded to include wastewater treatment, and in conjunction with this, significant efforts have been made to improve quality and performance. In particular, there is a remarkable tendency towards higher molecular weights, which are said to directly contribute to the performance of acrylamide polymers used as flocculants, and polymers with high molecular weights of 10 million or more, especially around 14 million, are in demand. This is much higher than the molecular weight required for acrylamide-based polymers or other polymers used for other purposes, which is usually less than 1 million. In addition, the obtained acrylamide-based polymer is usually used as a flocculant by being dissolved in water, so it dissolves quickly in water without leaving any insoluble matter, and because the acrylamide monomer is toxic. It is also required that the amount of unreacted monomer in the polymer is small, for example, 0.2% or less.
The above two requirements are generally incompatible with increasing the molecular weight, and this is why significant efforts are being made to achieve them. In addition, the molecular weight referred to in the present invention is determined by the test method shown in Example 1, which will be described later.Water solubility is usually a problem when the polymer obtained in an aqueous medium is dried to remove water.
This is the case when the dry powder is 20% or less, particularly about 10%, and water-soluble in the present invention is mainly used in this sense. Many proposals have been made regarding the production of high molecular weight acrylamide polymers with good water solubility. For example, a method in which urea-based substances, various amines, nitrilotriscarboxylic acid, etc. are added as an insolubilization inhibitor before, during, or after the polymerization reaction of acrylamide; A method using a polymerization initiator system, or a method in which extractive dehydration with a solvent is used in combination with the drying of a hydrogel obtained by a polymerization reaction, or a method in which drying is performed in two stages under different conditions is known. Therefore, it is said that the solution to the above problem depends not only on the production method of the acrylamide-based polymer but also on the quality of the acrylamide. For example, in JP-A-52-68118, the acrolein content in the raw material acrylonitrile must be 1.5 ppm or less, and in JP-A-52-138,585, the amount of 3,3',3''-nitrilotrispropionic acid in acrylamide must be 0.1 ppm or less. It is stated that organic impurities in acrylamide, or even in the raw material acrylonitrile, at a level of 1 ppm or less, are considered harmful and require extremely high levels of purification. When carrying out such purification, care must be taken, as it is well known that acrylamide is an extremely reactive compound and should not be subjected to vinyl polymerization type polymerization reactions, carbamoylethylation reactions, or the transfer of hydrogen from the amide group. Because it has reactivity such as reactions involving Even though the amount is small, it cannot be ignored.From this perspective, the conventional crystallization method among the purification methods for acrylamide is reliable and excellent, but it requires a large increase in cost. The reason for this is that when acrylamide is produced by the contact method, it is necessarily produced in the form of an aqueous solution and marketed as is, whereas acrylamide-based polymers require aqueous solution polymerization using acrylamide in the form of an aqueous solution or water-in-oil emulsion. This is because it is most commonly produced by polymerization.
Considering this, it must be said that it is extremely uneconomical to include a crystallization step in the production process of acrylamide monomer. Therefore, many methods have been proposed for purifying acrylamide obtained by the contact method in its aqueous solution state, such as methods involving specific cation exchange treatment or chelate resin treatment (Japanese Patent Application Laid-open Nos. 48-62715, 1983-80016, etc.). ,
Method of performing specific anion exchange treatment
-82011), a method of performing air or oxygen gas treatment (JP-A-51-22790), a method of combining two or more of these three (JP-A-50-83323, 52-
91818, etc.) and a method of performing a specific activated carbon treatment (Japanese Patent Application Laid-open No. 48-62714). The present inventors have studied these methods and their combined methods in detail, but have not found a method for purifying acrylamide suitable for producing the above-mentioned high molecular weight acrylamide polymer. That is, when acrylamide purified by the above method is used to produce a dry powder product of a high molecular weight acrylamide polymer, there is a disadvantage that the quality, especially the water solubility, is often unsatisfactory and inconsistent. This phenomenon is due in part to the formation of new impurities when acrylamide comes into contact with active materials such as cation or chelate resins, anion exchange resins, air or oxygen gas, and activated carbon used in the purification process described above. It is assumed that this is due to the leaching of other impurities from these materials. Therefore, even if the purification treatment described above is effective to some extent, it is desirable to further remove impurities as a final step. The final purification process itself should be carried out in a mild atmosphere that does not cause the formation of new impurities, and should not become a source of contamination with other impurities. The purpose of the present invention is to solve the above-mentioned technical problems, and the first purpose is to
The second objective is to provide a method for producing a high molecular weight acrylamide polymer having a molecular weight of more than 14,000,000 and is easily soluble in water and has a trace amount of unreacted monomer, for example, 0.2% or less. It is an object of the present invention to provide a method for highly and economically purifying an acrylamide aqueous solution obtained by a contact method prior to its use in the production of such an acrylamide polymer. To provide a new method for purifying an aqueous acrylamide solution suitable for removing impurities that could not be removed and finally removing impurities that are thought to be generated or mixed during purification in a mild atmosphere. It is in. Examples of copper-based catalysts used in the method of the present invention include (A) a combination of copper in the form of copper wire, copper powder, etc. and copper ions, and (B) a catalyst obtained by reducing a copper compound with a reducing agent. (C) those obtained by decomposing copper compounds with heat, etc. (decomposed copper), and (D) those obtained by developing Raney alloys of copper with alkalis, etc. (Raney copper). . Examples of the above methods for producing reduced copper include (1) reducing copper oxide with hydrogen, carbon monoxide, or ammonia in the gas phase; (2) reducing copper salts or hydroxides with formalin or hydrazine in an aqueous solution; or (3) reducing a copper salt or hydroxide with elemental aluminum, copper or iron in an aqueous solution, and the main catalyst component of the resulting product is It is considered to be elemental copper. Examples of the above methods for producing decomposed copper include (1) a method of thermally decomposing copper hydride obtained by treating a copper compound with sodium hypophosphite in alkaline water, (2) a method of thermally decomposing copper formate or copper oxalate. Method of disassembling, (3) Japanese Patent Application Laid-open No. 1973-
108015, and (4) adding copper acetylide or copper nitride directly to the acrylonitrile hydration reaction system, the main catalyst component of the resulting product is the one in item (4). It is considered to be elemental copper. Examples of the Raney copper manufacturing methods mentioned above include (1) a method in which a copper-aluminum alloy is almost completely expanded with caustic soda, sulfuric acid, water, an organic amine, etc.; There are methods such as partial development with organic amines and the like to leave some of the aluminum together with the copper, and the main catalyst component of the resulting product is thought to be elemental copper. These copper-based catalysts may be supported on commonly used carriers, or may contain metals other than copper, such as chromium or molybdenum. It is desirable to avoid contact of the catalyst with oxygen and oxygen-containing gases before and during use. The reason for this is that the catalytic activity is impaired and by-products such as ethylene cyanide and hydrin increase. The hydration reaction of acrylonitrile of the present invention is carried out in the presence of the above-mentioned copper catalyst as follows. The reaction type is a suspended or fixed catalyst bed in a liquid phase, and a flow type or batch type is carried out. The weight ratio of acrylonitrile and water to be subjected to the hydration reaction is substantially arbitrary, but is preferably from 60:40 to
The ratio is 5:95, more preferably 50:50 to 10:90. The preferred reaction temperature for hydration reaction is 50-200℃
The temperature is more preferably 70 to 150°C. The reaction rate of acrylonitrile is preferably 10 to 98%, more preferably 30 to 95%. In the above-mentioned weight ratio of acrylonitrile and water, reaction temperature and reaction rate of acrylonitrile,
Unreacted acrylonitrile, unreacted water, and acrylamide produced may prevent a homogeneous solution system from being formed, but to avoid this, acrylamide or other co-solvent may be added. The inside of the reactor is maintained at the vapor pressure at the above-mentioned temperature and composition or at a pressure obtained by adding an inert gas such as nitrogen to the vapor pressure, and the pressure is usually from normal pressure to 10 atmospheres. Dissolved oxygen contained in the catalyst, acrylonitrile, water, co-solvent, etc. fed to the reactor will impair the activity of the catalyst and increase by-products such as ethylene cyanohydrin, so be sure to For the same reason, it is desirable to maintain an oxygen-free atmosphere in the reactor. The reaction solution taken out from the reactor after the hydration reaction mainly consists of unreacted acrylonitrile, unreacted water, acrylamide, and if a co-solvent other than acrylamide is used, the co-solvent, and also by-products such as ethylene cyanohydrin. Contains copper. The reaction solution obtained in the above reaction is subjected to a conventional evaporation or distillation operation if necessary to obtain a concentrated aqueous acrylamide solution, as well as unreacted acrylonitrile and water (and if a light co-solvent other than acrylamide is used) The co-solvent) is distilled and recovered. The above-mentioned reaction solution or concentrated aqueous acrylamide solution (hereinafter referred to as monomer aqueous solution) is then subjected to cation exchange treatment, chelate resin treatment, anion exchange treatment, air or oxygen gas treatment, activated carbon treatment, etc. It is purified by various known purification methods. Also, so-called synthetic adsorption resins (for example, manufactured by Hokuetsu Tanso Kogyo Co., Ltd., trade name: Adsorption Resin), which are used in a similar manner to activated carbon and ion exchange resins, can also be used. The aqueous monomer solution may be subjected to the above concentration treatment during or after these purification steps, or may be concentrated again. Note that, although purifying acrylamide by a crystallization method in addition to the above-mentioned purification step is not in accordance with the spirit of the present invention due to the uneconomical nature of the crystallization method described above, this does not preclude its implementation. The main purpose of using the acrylamide obtained by the method of the present invention is the production of high molecular weight acrylamide polymers used as flocculants, etc., and the production method is generally as follows. Acrylamide may be used alone or with other vinyl polymerizable comonomers. Comonomers include acrylic acid and methacrylic acid or water-soluble salts thereof; alkylaminoalkyl esters of acrylic acid and methacrylic acid or quaternary ammonium derivatives thereof; 2-vinylimidazoline and 2-vinylimidazoline;
- Vinylpyrimidine or its quaternary ammonium derivatives: vinyl acetate: acrylonitrile, etc. The mixing ratio of these comonomers and acrylamide is usually acrylamide.
The amount is 100 mol or less, particularly 50 mol or less, per 100 mol. Polymerization of acrylamide and a comonomer can be carried out by well-known methods such as aqueous solution polymerization and emulsion polymerization, among which the most widely used general method of aqueous solution polymerization will be described. The total concentration of acrylamide and comonomer is usually between 5 and 50%, especially between 15 and 40%. Polymerization initiators include potassium persulfate, ammonium persulfate,
Peroxides such as hydrogen peroxide and benzoyl peroxide: azobisisobutyronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 4,4'-azobis(sodium 4-cyanovalerate) Azo free radical initiators such as: In some cases, reducing agents such as sodium bisulfite, triethanolamine, and ferrous ammonium sulfate, which form redox initiators with the above peroxides, are used. Regarding the temperature of the polymerization reaction, if the total concentration of acrylamide and comonomer is 15% or more and the resulting polymer has a high molecular weight of 10 million or more, it is difficult to control the temperature by cooling etc. An adiabatic polymerization mode is used, in which the temperature of the polymerization system increases as the polymerization progresses due to the heat of polymerization. In this case, the temperature at the start of polymerization is often selected from the range of -5 to 40°C, and the temperature at the end of the reaction reaches a high temperature of, for example, 55 to 100°C. In order to have a high molecular weight of 10 million or more, especially about 14 million, the total concentration of acrylamide and comonomer, the type and concentration of the polymerization initiator used, the reaction temperature, etc. are devised. Similar measures have been taken to reduce the amount of unreacted acrylamide to a trace amount of, for example, 0.2% or less, but in particular, many methods have been proposed and implemented in which two or more types of polymerization initiators are made to act in different temperature ranges. What is obtained by the above polymerization reaction is a hydrogel, that is, a rubber-like gel that contains almost all the water used to make the acrylamide and comonomer into an aqueous solution, but it is usually converted into a dry powder. In order to produce products, treatments such as water extraction or dehydration by heat drying, or crushing or pulverization of hydrous gels or dry gels are added. Note that, prior to or during these treatments, the acrylamide polymer may be chemically modified, such as by stirring caustic soda into a hydrogel and heating it to convert some of the amide groups into carboxyl groups. As a result of increasing the molecular weight as described above, reducing unreacted monomers, drying it into powder, and optionally chemically modifying it, the resulting acrylamide-based polymer is often difficult to dissolve in water and is used as a product such as a flocculant. tends to lose its value. To solve this problem, as mentioned above, methods include adding an insolubilization inhibitor before, during, or after the polymerization reaction, using a specific polymerization initiator system, or drying the hydrogel under specific conditions. will be carried out. Acrylamide to which the method of the present invention is applied is produced by a method consisting of the hydration reaction of acrylonitrile, evaporation or distillation operations, various purification treatments, and other incidental steps as described above, and has a high molecular weight as generally described above. Used for the production of acrylamide polymers. However, the water solubility and other properties of the acrylamide polymer thus obtained are by no means satisfactory, and the degree of such properties is variable depending on the production lot of acrylamide. Therefore, the present inventors investigated a new method for purifying acrylamide without particularly improving the method for producing an acrylamide-based polymer, and as a result, arrived at the following method of the present invention. That is, in the method of the present invention, when producing acrylamide by hydrating acrylonitrile in the presence of a copper-based catalyst, the acrylamide aqueous solution obtained by hydration is previously decoppered to reduce the copper content in the solution to 1 ppm or less. This is a method for purifying an acrylamide aqueous solution which is then subjected to membrane permeation treatment, and it is also possible to perform anion exchange treatment at the same time as copper removal treatment or after copper removal treatment, followed by membrane permeation treatment. The membrane permeation method referred to in the present invention includes so-called reverse osmosis method and ultrafiltration method. Here, the reverse osmosis method is based on the principle of osmotic pressure phenomenon, and by applying force above the osmotic pressure to the solution and allowing it to permeate through a semipermeable membrane that excludes solutes, the permeated liquid with a low solute concentration and the solute concentration are separated. It is understood as a method of obtaining a raised residual liquid (concentrated liquid). In addition, ultrafiltration is a process similar to reverse osmosis, using a membrane made to exclude high molecular weight solutes that contribute less to osmotic pressure than the solutes targeted by reverse osmosis. It will be held in When the aqueous solution of acrylamide obtained from the above manufacturing process (hereinafter also referred to as monomer aqueous solution) is treated with this membrane permeation method, the permeate and the acrylamide are almost the same in concentration. However, when acrylamide obtained as a permeate is used to produce a high molecular weight acrylamide polymer, its water solubility and other properties are significantly improved. This is the gist of the present invention, and in the present invention, obtaining the permeate in this manner is referred to as membrane permeation treatment. The concentrated solution obtained at the same time can be used for applications that do not have high quality requirements. The most widely used membranes for membrane permeation treatment (hereinafter referred to as membranes) are those made of cellulose acetate and aromatic polyamide. ”,
Various materials and manufacturing methods have been developed and used, such as those known in the publication (September 1, 1976), but in the present invention, any material that is chemically inert to acrylamide will suffice. . The ability of a membrane to exclude solutes is expressed by the salt rejection rate or fractional molecular weight when the solute has a low molecular weight (so-called reverse osmosis region), and when the solute has a high molecular weight (so-called ultrafiltration region).
is expressed by the molecular weight cutoff. The molecular weight cutoff here refers to the molecular weight at which 99% or more, that is, almost the entire amount of spherical molecules, which are said to be the most difficult to separate among molecules of the same molecular weight, can be separated. The membrane used in the present invention has a molecular weight cut-off of about 22,000 or less, which is effective in improving the quality of acrylamide, and particularly preferably 8,000 or less.
Membrane shapes include flat membranes, tubular membranes, and hollow membranes.
Although any of these can be used in the application of the present invention, flat membranes and tubular membranes are particularly easy to use. The concentration of the monomer aqueous solution subjected to the membrane permeation treatment is preferably 5 to 60%, more preferably 20 to 45%.
%. There is no essential restriction even if it is outside this range, but the lower the concentration, the larger the amount of liquid to be treated, which is uneconomical, and the lower the concentration of acrylamide than when producing general polyacrylamide polymers, It becomes necessary to concentrate. 60 again
% or more, the rate of permeation through the membrane is extremely slow and the rate decreases significantly over time, which is not preferred in practice. From the viewpoint of stability of the monomer aqueous solution, the pH of the monomer aqueous solution is preferably 3 to 9, especially 5 to 8.
However, at the same time, it must be within the tolerable pH range of the membrane. The temperature of the membrane permeation treatment is preferably 40℃ or less in order to keep the monomer aqueous solution stable, and the membrane's durability temperature is
If the temperature is lower than 40℃, it should be below the withstand temperature. Furthermore, since the aqueous monomer solution has a temperature at which acrylamide precipitates depending on its concentration, the temperature for membrane permeation treatment must be higher than that temperature. The pressure for membrane permeation treatment should be higher than the osmotic pressure, but in general
It is carried out at 20 to 80 Kg/cm ² G. It is thought that the smaller the weight ratio of the permeated liquid to the monomer aqueous solution subjected to membrane permeation treatment, the less impurities in the permeated liquid, which is preferable.
90% is preferred. As described above, the membrane permeation treatment of the present invention can be carried out under an extremely mild atmosphere as the purification treatment conditions for acrylamide. This is compatible with the purpose of the present invention to remove the The aqueous monomer solution obtained by the hydration reaction of acrylonitrile described above contains 10 to 1000 ppm (based on pure acrylamide content; the same applies hereinafter) of copper. The form of copper is not clear, and it is thought that nonionic copper such as colloidal particles of elemental copper is also included in addition to so-called copper ions or copper complex ions. Furthermore, since copper ions are effective as stabilizers for acrylamide, for example, 25 ppm of copper ions are added to the monomer aqueous solution from which copper has been removed before being shipped to the market. Since such a large amount of copper generally becomes a hindrance to the polymerization reaction of polymerizing acrylamide to produce an acrylamide-based polymer, the amount of copper is set to 1 ppm or less, preferably 0.1 ppm or less. As a method for removing copper from an aqueous monomer solution, that is, a method for decoppering treatment, a method using a cation exchange resin and a method using a chelate resin are widely known and excellent, but the present invention also uses these two methods.
Two methods are adopted. The above-mentioned nonionic copper cannot be removed or is difficult to remove as it is by these decoppering treatments, but it can be easily removed by making it ionic by contacting it with oxygen gas in advance. One of the features of the present invention is that such copper removal treatment is performed before membrane permeation treatment. On the other hand, when decoppering is performed later, the quality of the acrylamide obtained is unsatisfactory, and its degree is variable, which is probably due to the generation or contamination of impurities during the decoppering. . In addition, since the membrane permeation treatment itself has the property of removing copper ions, it is possible to omit the decopper treatment, but the present inventors have found that the membrane permeation treatment has the ability to remove copper ions from the monomer aqueous solution. is much lower than generally expected and is not practical. For example, when a monomer aqueous solution containing about 500 ppm of cupric ions was treated using a cellulose acetate membrane with an approximate molecular weight cutoff of 500, the concentration of cupric ions in the permeate was as high as about 100 ppm. It can also be understood from Therefore, if the copper removal treatment is performed in advance and then the membrane permeation treatment, which is the most important part of the present invention, is performed, the membrane permeation treatment can be carried out effectively and acrylamide of highly stable quality can be obtained. Various well-known cation exchange resins and chelate resins can be used. As the cation exchange resin, both strongly acidic cation exchange resins and weakly acidic cation exchange resins can be used, but strongly acidic cation exchange resins are easy to use, and may be of gel type or porous type. Further, it may be in a free acid form or a salt form such as a sodium salt type, but the free acid form is easy to use. Specific examples include Amberlite IR120B and IRC50 (all product names, manufactured by Rohm and Haas), Diaion SK1B, PK208, and WK10 (all product names, manufactured by Rohm and Haas).
manufactured by Mitsubishi Kasei Corporation), Revachit SP100, PP112 and
Examples include CNP80 (all product names, manufactured by Bayer). As a chelate resin, styrene-
In addition to resins in which various chelate-forming groups are introduced into a divinylbenzene copolymer, various other resins are known, but among these, those in which a chelate-forming group is introduced into a styrene-divinylbenzene polymer are preferred. Specific examples include Diaion CR-10 (trade name, manufactured by Mitsubishi Kasei Corporation) and Revachit TP-207 (trade name, manufactured by Bayer AG). These chelate resins are usually used in the form of sodium salts. Next, the method of copper removal treatment will be described. Cation exchange resins or chelate resins can be used in any of fixed bed, moving bed and suspended bed formats, of which fixed bed is the best. The concentration of the monomer aqueous solution in the copper removal treatment is preferably 5 to 60%. There are no essential restrictions even if the concentration is outside this range, but if the concentration is lower than this, the amount of liquid to be treated is large and it is uneconomical. It becomes necessary to concentrate, and if the concentration is higher than this, the polymerization reaction of acrylamide is likely to be induced during the copper removal treatment. The processing temperature is set to keep the monomer aqueous solution stable.
The temperature is preferably 40° C. or lower, and since the aqueous monomer solution has a temperature at which acrylamide precipitates depending on its concentration, the temperature must be higher than that. The pH of the monomer aqueous solution before treatment is preferably 2 to 10, more preferably 3 to 9, in order to keep the monomer aqueous solution stable, but it can also be adjusted depending on the preferred range of use specific to the type of cation exchange resin or chelate resin used. be restricted. Copper removal treatment is performed under the above conditions and the amount of cation exchange resin or chelate resin used, and the copper content after treatment is determined.
The amount is 1 ppm or less, preferably 0.1 ppm. Generally, in the membrane permeation method, the permeation rate of the permeate decreases over time because the membrane becomes more compacted, chemically deteriorated, and gel-like substances adhere to the membrane as the membrane is used. The progress is as shown in Figure 2. If time and permeation rate are expressed in their respective logarithms, they are usually linear as shown in A and B, and the degree of decline over time is expressed as the absolute value of the slope m of the straight line. Expression is done.
Then, when the permeation rate decreases to a certain value, the membrane is renewed or regenerated by washing or the like. According to the findings of the present inventors, the characteristics of membrane permeation treatment of an aqueous monomer solution are that the permeation rate is lower than that of aqueous solutions of many other substances, and the degree of decrease over time, that is, the absolute value of m, is It is large and cannot be regenerated by washing. Therefore, the present inventors m
In order to find a method to reduce the absolute value of It has been found that the absolute value of m can be reduced by processing. A method for purifying acrylamide by anion exchange treatment is already known.
Although this effect is recognized, according to the findings of the present inventors, the effect is not only insufficient, but also that the treatment often causes a decrease in quality, and the degree of the effect is not constant. A considerable degree of variability is observed. This is thought to be because new impurities were generated in the resin or impurities were eluted and mixed in from the anion exchange resin used for treatment. However, it has been found that if membrane permeation treatment is performed after anion exchange treatment as in the present invention, such deterioration and fluctuation in quality can be avoided and the original purification effect of anion exchange treatment can be stably obtained. One of the features of the present invention is that the anion exchange treatment and the membrane permeation treatment complement each other in this way to bring out their original effects. The anion exchange treatment of the present invention is carried out using a so-called anion exchange resin. Various well-known anion exchange resins are used, and both so-called strongly basic anion exchange resins and so-called weakly basic anion exchange resins can be used, but from the viewpoint of stability of acrylamide, weakly basic anion exchange resins are used. Ion exchange resins are preferred. As a strongly basic anion exchange resin, a styrene-divinylbenzene copolymer into which a quaternary amino group is introduced as the main ion exchange group is widely used, and the type of amine used to introduce the quaternary amino group is widely used. It is also classified into types and types based on the criteria, and there are two types: gel type and porous type, but either of these types can be used. An example of this is Amber Light
IRA400 and IRA900 (both product names, manufactured by Rohm and Haas), Revachit M500 and MP500
(Product name, manufactured by Bayer), Diaion PA316
(trade name, manufactured by Mitsubishi Chemical Industries, Ltd.). Further, when used, it is preferable to use the counter ion in the form of a free base or a weak acid salt such as bicarbonate. On the other hand, as the weakly basic anion exchange resin, a styrene-divinylbenzene copolymer into which primary, secondary, or/and tertiary amino groups are introduced is used, such as Amberlite IRA93.
(Product name, manufactured by Rohm and Haas), Revachit
Examples include MP62 and MP64 (trade name, manufactured by Bayer) and Diaion WA10 (trade name, manufactured by Mitsubishi Kasei). Furthermore, when using it, it is preferable to use it in the free amine form rather than in the salt form. The impurities in the monomer aqueous solution that are removed by the anion exchange resin are not clear, but they include carboxylic acids such as acrylic acid, which are by-produced during the hydration reaction of acrylonitrile, and anionic acids, which are produced or eluted during copper removal treatment. Compounds are possible. The anion exchange treatment of the present invention may be performed after the copper removal treatment, or the cation exchange resin and anion exchange resin may be used as a so-called mixed bed to perform the copper removal treatment and the anion exchange treatment. Although it is possible to perform both at the same time, the former method is superior in terms of ease of implementation. Furthermore, if the anion exchange treatment is performed before the copper removal treatment, although the effects of the present invention may be obtained, other undesirable effects may occur, and this is not a good method. Next, a specific method of performing anion exchange treatment after copper removal treatment will be described. The anion exchange resin can be used in any of fixed bed, moving bed and suspended bed formats, but of these, fixed bed is the easiest to implement. The preferable concentration and temperature of the monomer aqueous solution to be treated are 5 to 5, respectively, from the same circumstances as in the case of copper removal treatment.
60% and the precipitation temperature is above 40℃. The pH of the monomer aqueous solution before treatment is preferably 2-10, more preferably 3-9 in order to keep the monomer aqueous solution stable, but it is further restricted by the preferred range of use specific to the type of anion exchange resin used. . As is well known, after an anion exchange resin loses its exchange capacity due to use for a certain period of time, it is reused by treatment with a regenerating liquid such as caustic soda. This period of use is generally determined as the period until the concentration of a specific impurity exceeds a certain limit in the treated liquid.
In the present invention, it is preferable to carry out the following procedure. That is, when using a weakly basic anion exchange resin, the PH of the treated monomer aqueous solution decreases with the passage of time of use, so it can be determined until a certain PH value is reached, and in this case, the period of use is Preferably PH up to 4, more preferably PH
Up to 5. If the treatment continues beyond this limit, the effect of the anion exchange treatment, that is, the effect of suppressing the decrease in permeation rate over time in membrane permeation treatment, will be lost. When using a strongly basic anion exchange resin, it is difficult to determine the period of use based on the PH value, but it can be determined empirically by monitoring the effect of suppressing the decrease in permeation rate over time. As described above, the advantages obtained by carrying out the method of the present invention are (1) impurities that could not be removed by methods other than the method of the present invention can be removed, and Alternatively, impurities that are thought to be mixed in can be finally removed in a mild atmosphere, and no new impurities are created or mixed in. (3) If acrylamide obtained by the method of the present invention is used, the molecular weight can be reduced to 1000.
It is possible to easily produce an acrylamide-based polymer which has a molecular weight of 10,000 or more, particularly about 14,000,000, is easily soluble in water, and has a trace amount of unreacted monomer, for example, 0.2% or less. Next, the present invention will be further explained with reference to Examples. Example 1 Catalyst for hydration reaction: A Raney copper catalyst was prepared by expanding a Raney copper alloy of 80 mesh or less using caustic soda in a conventional manner. Contact with oxygen gas was avoided during manufacturing and subsequent handling. Hydration reaction: The above catalyst is charged into about 2 stainless steel reactors equipped with a stirrer and a catalyst separator, and acrylonitrile and water, which have been previously removed with nitrogen gas, are added at 600 and 900 mL, respectively.
The reaction was carried out by feeding at a rate of g/hr. The reaction liquid is stirred with the catalyst to form a suspension, and then passed through a catalyst separator and taken out from the reactor as a liquid containing almost no catalyst. This reaction continued for 24 hours. Concentration: The obtained reaction solution was subjected to batchwise vacuum concentration to remove the entire amount of unreacted acrylonitrile and a portion of unreacted water to obtain an aqueous monomer solution with a concentration of 40%. The aqueous monomer solution contained 350 ppm copper (based on acrylamide, the same hereinafter) and had a pH of about 6.5. Copper removal treatment: A glass tube column was filled with 150 c.c. of Amberlite IR-120B (product name: Rohm and Haas, strong acidic cation exchange resin) in the free acid form, and a monomer aqueous solution of 5900 ml/hr was added to the column. Passed at room temperature at speed. The copper content of the obtained liquid was 0.02ppm,
The pH was 3.7. This decopper treatment was continued for 24 hours. PH adjustment: During the copper removal process, the PH of the processing solution is adjusted every 4 hours.
was adjusted to approximately 6.5 using caustic soda. Membrane permeation treatment: Four types of membranes were used: flat membranes 999, 865, GR8P, and GR6P manufactured by DDS (Denmark).
The approximate molecular weight cutoff is 180, 500, 8000 and
It is called 22000. It was then treated according to the treatment steps shown in FIG. That is, the membrane permeation device 3 can be equipped with up to 20 flat membranes with a permeation area of 0.018 m ² (0.36 m ² in total), and 20 membranes 999 were first installed thereon. The monomer aqueous solution 4 obtained by the above PH adjustment is put into the monomer aqueous solution storage tank 1, and is supplied to the membrane permeation device 3 through the supply pipe 5 using the supply pump 2, and the permeate is passed through the permeate outlet 6 to the permeate receiver. 4 and the concentrated liquid was returned to the monomer aqueous solution storage tank via the pressure regulating valve 7 and the concentrated liquid outlet pipe 8. During this time, the temperature of the liquid is 28-30
℃, and the processing pressure is adjusted by adjusting the pressure regulating valve 7 to approx.
It was maintained at 40Kg/cm ² G. After the above operation, the permeate is about 2
He continued until he was captured. Membrane 865, same treatment
The procedure was repeated using GR8P and GR6P to obtain a total of four types of permeate. Method for producing acrylamide polymer: An acrylamide polymer was produced from an aqueous monomer solution using the following method. Add water to monomer aqueous solution to make concentration 20%
Put 500g of this into a polyethylene container,
Dissolved oxygen in the liquid was removed by passing nitrogen gas while maintaining the temperature at 18°C, and the liquid was immediately placed in a heat-insulating block made of styrofoam. This is then followed by 200×10 ^-6 mpm
(molar ratio to acrylamide) of 4,4'-azobis(sodium 4-cyanovalerate),
200×10 ⁻⁶ mpm of dimethylaminopropionitrile and 80×10 ⁻⁶ mpm of ammonium persulfate were each dissolved in a small amount of water and quickly injected in this order. Dissolved oxygen was removed from these reagents by passing nitrogen gas in advance, and a small amount of nitrogen gas was passed through the polyethylene container before and after the injection to prevent oxygen gas from being mixed in. After an induction period of several minutes after injecting the reagent, the temperature inside the polyethylene container was observed to rise, so the supply of nitrogen gas was stopped. After about 100 minutes, the temperature is about 70
After the temperature reached the peak, the polyethylene container was removed from the insulating block and immersed in water at 97°C for 2 hours.
It was then cooled by immersing it in cold water. The acrylamide polymer hydrogel thus obtained was divided into small pieces, ground in a meat grinder, dried with hot air at 100°C for 2 hours, and ground in a high-speed rotary blade grinder for 3 minutes to obtain dry powdered acrylamide polymer. Obtained. Further, this was sieved to separate 32 to 42 meshes, which were used as polymer samples for subsequent tests. The moisture content of the polymer samples was determined as the weight loss by hot air drying at 125°C overnight, and was found to be about 10% for all polymer samples. Test method for acrylamide polymer: The water solubility, molecular weight, standard viscosity, and unreacted acrylamide of a polymer sample were measured using the following method.
For water solubility, put 600ml of water in one beaker, add 0.66g of polymer sample (approx. 0.60g of pure content) while stirring with a stirring blade of a specified shape, stir at 500 rpm for 2 hours, and add the resulting solution. It was filtered through a 150-mesh wire mesh, and the residue (insoluble matter) was dried overnight with hot air at 125°C, then weighed, and expressed as a percentage of the pure content of the original polymer sample (0.60 g). In addition, in the case of polymer samples with poor water solubility, it may not be possible to separate the insoluble components using a wire mesh, and in this case, the sample was labeled as insoluble. To determine the molecular weight, prepare several acrylamide polymer aqueous solutions with different concentrations using the liquid obtained in the same manner as above, add sodium nitrate equivalent to 1M concentration, and measure the intrinsic viscosity using a capillary viscometer. It was calculated using the following formula. Intrinsic viscosity = 3.73 x 10 ^-4 [Weight average molecular weight ^0.66 ] There are some doubts about applying this formula to acrylamide polymers with a molecular weight of 10 million or more.
Reports on Progres in Polymer Physics in
Japan, 20 , 5 (1977), but it is also widely used. The liquid obtained by the above water solubility test is a polymer aqueous solution with a concentration of 0.1% if the water solubility is good, but sodium chloride equivalent to a concentration of 1M is added to this and the solution is measured using a BL type viscometer using a BL adapter.
Viscosity was measured at °C rotor rotation speed rpm (standard viscosity). Since the standard viscosity obtained by such a method is commonly used as a value correlated with molecular weight, it was also used in this example. The terminally reacted acrylamide was quantified by adding methanol containing 20% water to a polymer sample, shaking it overnight for extraction, and subjecting the extract to gas chromatography. Acrylamide polymer test results: The four types of monomer aqueous solutions obtained as the permeate in the above membrane permeation treatment and the monomer aqueous solution before the membrane permeation treatment were used as polymer samples by the above acrylamide polymer production method, and the acrylamide polymer It was tested according to the test method and the results shown in Table 1 were obtained.

[Table] That is, remarkable effects were observed in treatments with membranes 999, 865, and GR8P (approximate molecular weights of 180, 500, and 8000, respectively), and some effects were also observed with GR6P (also 2200). Example 2 From the PH adjustment solution obtained in the same manner as in Example 1, approximately 40% of the aqueous monomer solution was placed in a monomer aqueous solution storage tank, 20 membranes of 865 were attached to a membrane permeation device, and the monomer aqueous solution was
The treatment was carried out for 24 hours by supplying the permeate to the membrane permeation device at a temperature of about 40 kg/cm ² and returning the permeate to the monomer aqueous solution storage tank in the same way as the concentrate (the dotted line path in Figure 1). During this period, the permeation rate was measured at 1, 2, 5, 10, and 24 hours after the start of treatment by a method in which the permeate was collected into a measuring cylinder. Next, the liquid in the monomer aqueous solution storage tank was renewed with unused PH adjustment liquid, and the same treatment as the previous day was carried out for 24 hours.
It lasted for hours. Repeat the same thing twice for a total of 96
I processed time. During this period, the permeation rate of the permeate was measured at 48, 72 and 96 hours. The change in permeation rate over time obtained in this way is shown by straight line A (x mark) in Figure 2.
The slope m was -0.23. In the figure, the horizontal axis is the usage time of the membrane, and the vertical axis is the permeation rate of the membrane per unit time, respectively, shown on a logarithmic scale. Next, we conducted an experiment on the effect of anion exchange treatment.
400 ml of Revachit MP-62 (trade name, manufactured by Bayer AG, weakly basic anion exchange resin) was packed into a glass tube column in the free amine form using caustic soda, and this was prepared for copper removal treatment in Example 1. The aqueous monomer solution was directly connected to a cation exchange resin column, and the pH of the monomer aqueous solution was adjusted after copper removal treatment and anion exchange treatment. Other than this, a PH adjustment solution was produced in the same manner as in Example 1, and the same procedure as in the previous 96-hour treatment using this solution was carried out.
The treatment was carried out for 96 hours. The time-dependent change in the permeation rate of the permeated liquid during this period is as shown in the straight line B (marked with ○) in Figure 2, and its slope m is -
It was 0.12. That is, the anion exchange treatment significantly improved the decrease in permeation rate over time. Example 3 In order to further compare and inspect the quality of the four types of membrane permeation treatment liquid and pre-treatment liquid obtained in Example 1, acrylamide polymer and acrylamide-sodium acrylate copolymer were prepared using these monomer aqueous solutions in the following manner. And so. Method for producing acrylamide polymer: Add water to an aqueous monomer solution to make a concentration of 27%, put 500 g of this in a polyethylene container, cool it with ice water, remove dissolved oxygen by passing nitrogen gas, and then store it in a styrofoam heat-insulating block. I put it in. This was then quickly injected with 200 mg of azobisisobutyronitrile dissolved in a small amount of methanol, 2.0 mg of ferrous ammonium sulfate dissolved in a small amount of water, and 4.0 mg of ammonium persulfate dissolved in a small amount of water. Dissolved oxygen was removed from these reagents by passing nitrogen gas in advance, and a small amount of nitrogen gas was also passed through the polyethylene container during and before and after the injection to prevent oxygen gas from entering.
After an induction period of several minutes after injecting the reagent, the temperature inside the polyethylene container was observed to rise, so the supply of nitrogen gas was stopped. The temperature eventually reached a peak, indicating that the reaction was almost complete, but after being left for about 2 hours, the polyethylene container was removed from the heat-insulating block and cooled. The acrylamide polymer hydrogel thus obtained was treated in the same manner as in Example 1 to obtain polymer samples of 32 to 42 meshes. Production of acrylamide-sodium acrylate copolymer: Produce a hydrous gel in the same manner as in the previous section except for adding 5% sodium acrylate in addition to 27% acrylamide to make the total concentration 32%. Then, it was treated in the same manner as in Example 1 to obtain a polymer sample of 32 to 42 meshes. Polymer test method: The water solubility, molecular weight, standard viscosity, and unreacted monomer of the polymer sample were measured in the same manner as the acrylamide polymer test method shown in Example 1. Polymer test results: Results shown in Tables 2 and 3 were obtained.

【table】

[Table] It was as follows.
That is, a remarkable effect was observed in the films 999, 865, and GR8P, and a slight effect was also observed in GR6P. Example 4 A hydration reaction similar to that in Example 1 was carried out, and an aqueous monomer solution with a concentration of approximately 40% was produced by concentration, and copper removal treatment was continued for 80 hours under the same conditions as in Example 1. 60-65, 65-70, 70-75 and 75-80
The treated solution obtained during the time period was fractionated. The copper content of each fraction was 0.02, 0.73, 5.2, and 38 ppm, respectively. In addition, the pH of each fraction was adjusted to approximately 6.5 using caustic soda. Each of these four aliquots was subjected to membrane permeation treatment using the membrane 865 in the same manner as in Example 1, and about two permeated liquids were collected. Polymer production and polymer tests similar to those in Example 1 were performed on these permeated liquids. Furthermore, for a portion of the permeate obtained from the 70-75 and 75-80 hour aliquots with high copper content,
Again, in the same manner as in Example 1, the copper removal treatment and pH adjustment were repeated until the copper content was both 0.01 ppm, and polymer production and polymer testing were performed. The results obtained above are shown in Table 4.

【table】 [Brief explanation of the drawing]

FIG. 1 shows the route through which the monomer aqueous solution was treated in the membrane permeation treatment of Example 1.
1: Monomer aqueous solution storage tank, 2: Supply pump, 3:
Membrane permeation device, 4: permeate receiver, 5: supply piping,
6: Permeated liquid outlet pipe, 7: Pressure regulating valve, 8: Concentrated liquid outlet pipe. FIG. 2 shows the change over time in the permeation rate in the membrane permeation treatment of Example 2.

Claims (1)

[Claims] 1. When producing an acrylamide aqueous solution by hydrating acrylonitrile in the presence of a copper-based catalyst, the acrylamide aqueous solution obtained by hydration is previously treated to remove copper to reduce the copper content in the solution to 1 ppm or less. After that,
1. A method for purifying an aqueous acrylamide solution, the method comprising membrane permeation treatment using a membrane having a molecular weight cut-off of 180 to 22,000. 2. The acrylamide aqueous solution obtained by hydration is subjected to an anion exchange treatment at the same time as or after copper removal treatment, and then membrane permeation treatment is performed using a membrane having a molecular weight cut-off of 180 to 22,000. The method described in Section 1.