JPH0322408B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for drying an acrylamide-based polymer aqueous solution, and its purpose is to dry a highly concentrated high molecular weight polymer aqueous solution into pieces in order to prevent the formation of insoluble matter. It allows for efficient drying in a short period of time. Furthermore, the water-soluble acrylamide polymer obtained by the present invention is extremely porous and therefore bulky, and can be easily pulverized into powder. Polymers containing acrylamide as a main component have traditionally been used as paper strength agents, aqueous properties improvers, tenner retention improvers, surface sizing agents, viscosity agents for paper and nonwoven fabric manufacturing, thickeners, flocculants for wastewater treatment, Widely used as a super-dehydration aid. BACKGROUND ART A polymer having a high molecular weight and good water solubility is required for a flocculant, especially a flocculant for treating paper manufacturing wastewater. In addition, in recent years, the finiteness of oil resources has been well recognized, and as a result, secondary oil,
Tertiary recovery is being carried out in earnest, and the acrylamide-based polymers used there are now in the spotlight. This oil mining polymer is also required to have a high molecular weight and extremely good water solubility. Polymerization of acrylamide monomers can be carried out by reverse-phase suspension polymerization, reverse-phase emulsion polymerization, precipitation polymerization, bulk polymerization, and solution polymerization using ordinary radical initiators as well as light, photosensitization, radiation, heat, etc. etc., but since both the monomer and the resulting polymer are soluble in water,
Aqueous solution polymerization has also been widely adopted. In recent years, the use of powder products has been expanding in coagulants and other fields due to ease of handling and rationalization of transportation.
Most are supplied as powders. Furthermore, when the obtained polymer has a high molecular weight or a high concentration, the acrylamide polymer aqueous solution has extremely low fluidity or becomes a hydrogel-like material having adhesiveness and viscoelasticity. Even if an attempt is made to dissolve this gel-like substance in water, the dissolution rate is extremely low and is not practical. For this reason, after polymerization, such hydrogels are dried and shipped as powder or granular products for use. Aqueous solution polymerization of acrylamide monopolymers at low concentrations, which has been widely employed in the past, requires more energy for drying, which is not preferable. Therefore, if a higher concentration acrylamide monomer aqueous solution is polymerized to produce a hydrous agar-like gel of the polymer,
This is used as a product, reducing the energy required for drying. However, when polymerizing at a high concentration for efficient polymerization, the hydrous gel becomes hard and exhibits viscoelasticity as described above, and it is difficult to cut or shred it as it is. If you try to heat dry it without cutting or shredding it, it will take a lot of time to dry it. For this reason, it is manufactured industrially at a concentration below about 30%, which allows it to be cut and shredded. Furthermore, it is a well-known phenomenon that when an acrylamide polymer aqueous solution is heated and dried, a crosslinking reaction occurs and the polymer becomes insolubilized. This tendency is greater as the molecular weight becomes larger. If air drying at low temperature, drying under reduced pressure, etc. are attempted to avoid the formation of insoluble polymers, it takes a very long time and is not industrially advantageous. Furthermore, if dehydration and drying using methanol, acetone, etc. is attempted, the amount of these materials used will be enormous, and additional equipment for recovering the solvent will be required, which is still inconvenient. Under these circumstances, the present inventors have conducted intensive studies on an economically advantageous and industrially possible method for drying a high-concentration, high-molecular-weight polymer aqueous solution in a short time without producing water-insoluble polymers. As a result, the present invention was completed. That is, the present invention involves microwaving an aqueous solution of an acrylamide polymer containing 0.5 to 30% by weight of a carbonate and/or bicarbonate compound with a concentration of 30% by weight or more based on the water-soluble acrylamide polymer. The present invention relates to a method for drying an acrylamide polymer aqueous solution, which comprises irradiating the acrylamide polymer aqueous solution to decompose the compound at a temperature of 120° C. or less, foaming the aqueous solution with carbon dioxide generated and evaporating water. The present invention will be explained in detail below. The water-soluble acrylamide-based polymer in the present invention refers to an acrylamide homopolymer, a modified product thereof, and a copolymer of acrylamide and one or more other copolymerizable monomers. In the case of copolymers, examples of comonomers include methacrylamide, N-substituted (meth)acrylamide, N,N
-Substituted (meth)acrylamide, (meth)acrylonitrile, (meth)acrylic acid, (meth)acrylate, 2-(meth)acrylamide-2methylpropanesulfonic acid and its salts, methyl (meth)acrylate, ( meth)ethyl acrylate, (meth)
Butyl acrylate, dimethylaminoethyl (meth)acrylate and its salts and quaternary ammonium salts, diethylaminoethyl (meth)acrylate and its various salts and quaternary ammonium salts, N-
Dimethylaminomethyl (meth)acrylamide and its salts and quaternary ammonium salts, N-dimethylaminopropyl (meth)acrylamide and its salts and quaternary ammonium salts, styrene, vinylpyridine and its various salts and quaternized products, vinylpyrrolidone , vinyl hydroxyethyl acetate (meth)
Examples include acrylate. The proportion of comonomer in the copolymer is suitably 3 to 50%. A known method may be used to obtain an acrylamide polymer aqueous solution having a concentration of 30% by weight or more. Generally known polymerization initiators can be used, but persulfates,
Redox initiators using peroxides such as hydrogen peroxide and peracetic acid alone or in combination with reducing agents such as sulfites, amides, and amidonoalcohols; 2.
2'-azobis(2-amidinopropane) hydrochloride,
It is preferable to use azo compounds such as azobisN,N'-dimethyleneisobutyramidine sulfate, azobisisobutyronitrile, or combinations thereof, as well as combinations of reducing agents and azo compounds. In addition, initiation by radiation or light in a photosensitizer-added system is also possible. Of course, it is also possible to use a chain transfer agent or a gelling inhibitor in combination. In the present invention, the purpose of using a carbonate or bicarbonate compound is to irradiate an aqueous polymer solution with microwaves and heat it, and the heat generated at that time decomposes the compound, and the carbon dioxide generated is used to dissolve the aqueous polymer solution. It is desirable to decompose and foam uniformly within the aqueous polymer solution. Therefore, it is desirable that they be uniformly mixed in the aqueous polymer solution. Therefore, substances with high solubility in water are preferable. Furthermore, substances whose decomposition temperature in water is too high are undesirable. Carbonates and bicarbonates with high solubility in water include ammonia and alkali metal salts, but among these, ammonium carbonate, ammonium bicarbonate, sodium carbonate, bicarbonate, Particularly useful are sodium carbonate, potassium carbonate, and potassium bicarbonate. These carbonate or bicarbonate compounds are preferably present in an amount of 0.5 to 30% by weight, preferably 1 to 20% by weight, based on the water-soluble acrylamide polymer, depending on the type and polymer concentration.
If it is less than 0.5% by weight, it will not show sufficient effect, and 30
Even if it exceeds the weight percentage, the effect beyond the objective of the present invention cannot be obtained and it is economically disadvantageous. Methods for making these carbonate or bicarbonate compounds present in the polymer aqueous solution during microwave drying include adding the necessary amount to the polymer aqueous solution after polymerization, mixing, and irradiating with microwaves, or added before and decomposed during polymerization,
There is a method in which the polymerization temperature is adjusted so as not to cause foaming, and after the polymerization is completed, irradiation with microwaves is performed. In either method, the pH of the polymer aqueous solution should be 7.5 or higher because carbonate and bicarbonate compounds may generate carbon dioxide gas on the acidic side and decompose before microwave irradiation. It is best to carry out the process under alkaline conditions, preferably pH=8 or higher. Further, if a carbonate or bicarbonate compound and a low boiling point organic solvent are used in combination, the drying effect will be further improved.
The solvent used must be substantially dissolved in the aqueous solution, and must be a water-soluble organic solvent that has a high solubility in water, or a solvent that has a high solubility for the monomer even if the solubility in water is low, that is, a hydrophilic solvent. Solvents are also effective. This organic solvent is
Like carbonate and bicarbonate compounds, it foams during drying and has the effect of accelerating the drying speed. It is preferable to use an organic solvent that has at least one of its boiling point or azeotropic temperature with water of 100°C or less. If the temperature in both cases is 100°C or higher, the temperature inside the hydrous gel becomes too high during dehydration drying using a microwave, and undesirable reactions such as the formation of water-insolubilized substances and a decrease in molecular weight tend to occur. Organic solvents used include ketones with 3 to 6 carbon atoms, such as acetone, methyl ethyl ketone, and diethyl ketone, alcohols with 1 to 5 carbon atoms, such as methanol, ethanol, various propanols, various butanols, and various amyl alcohols. , acetic esters having 3 to 5 carbon atoms, such as methyl acetate and ethyl acetate, are preferred. In addition, propyl formate, acetonitrile, methyl propyl ether, various mercaptans, mercapto alcohols, etc. are also good. A combination of two or more of these organic solvents is also effective. Solvents with extremely low boiling points or azeotropic temperatures are undesirable because they boil during polymerization. As a method for making the solvent present in the polymer aqueous solution, it is possible to knead it into the polymer aqueous solution after polymerization, but it is preferable to add it before polymerization. The larger the amount of solvent added, the better the effect, but it varies depending on the solvent due to economic efficiency, affinity with the polymer, etc.
A suitable amount is 0.5 to 50% by weight, preferably 2 to 30% by weight. In the present invention, the polymer concentration is set to 30% by weight or more, but if it is less than this, the amount of water to be evaporated becomes too large, which is disadvantageous in terms of energy consumption and process simplification. In the present invention, the carbonate- or bicarbonate-containing acrylamide polymer aqueous solution obtained as described above is cut into appropriate sizes, if necessary, and then irradiated with microwaves to dehydrate and dry. When irradiating with microwaves, it is necessary to adjust the irradiation time, etc. in consideration of the microwave absorption efficiency of the aqueous polymer solution and the evaporation effect of water from the aqueous polymer solution. Although various microwave frequencies can be used, the purpose of the present invention can usually be fully achieved by using a microwave of 2450 MHz. Further, if necessary, a heat drying method can also be used in combination. According to the method of the present invention, these carbonate and bicarbonate compounds decompose and foam during microwave irradiation, creating many pores in the aqueous polymer solution, which makes water evaporation and transpiration extremely difficult. The process proceeds smoothly and the temperature of the aqueous polymer solution is kept low. Therefore, drying can be performed in a short time without causing imidization reactions that produce water-insoluble substances. Generally, when no salt is added, the temperature rises to over 140°C, but with the method of the present invention, it can be kept below 120°C. Furthermore, the time required for drying can be shortened because drying can be done efficiently. This method is particularly suitable for drying high molecular weight polymers that tend to produce water-insolubilized substances. Furthermore, since the drying method according to the present invention directly heats and evaporates the water inside the polymer aqueous solution, it is not necessary to cut the polymer aqueous solution into small pieces, and it is not necessary to cut the polymer aqueous solution into small pieces. It is tough and viscoelastic and can be used in cases where it is difficult to shred.
Industrially advantageous. When drying by heating, for example, if you try to dry a sheet-like material without cutting it into small pieces, a film of dry polymer will form on the surface, making it difficult for water to diffuse, and drying will take an extremely long time, resulting in polymer deterioration and insolubilization. happen. Furthermore, according to the drying method of the present invention, there is no need to consider the heat capacity of the drying container, and since the energy source is electricity, there is no risk of air pollution.
This method is extremely superior to conventional methods. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited by the Examples unless the gist of the invention is exceeded. Examples 1 and 2 Comparative Examples 1 to 4 35 g of acrylamide and 22.36 g of demineralized water were taken into a 100 ml Erlenmeyer flask with a stopper and dissolved uniformly, followed by a 15% by weight aqueous ammonium carbonate solution or 50% ammonium carbonate aqueous solution.
11.67 g of potassium carbonate aqueous solution was added. Next, after adding 0.53 g of a 1% by weight ammonium persulfate aqueous solution and further adding 0.44 g of a 20% by weight diethanolamine aqueous solution, the contents were transferred to a stainless steel separable flat-bottomed flask with an inner diameter of 94 m/m, and heated under a nitrogen atmosphere for 30 min.
Polymerization was carried out for 1.5 hours in a constant temperature water bath at ℃. 10 g of the obtained rubbery hydrogel (aqueous solution) with a thickness of about 10 m/m was irradiated with microwaves at 2450 MHz and 600 W for 1.5 minutes using a household microwave oven model NE-6360 manufactured by Matsushita Electric Co., Ltd. Immediately after microwave irradiation, the polymer temperature and dry solid content of the polymer were measured. Also, 0.1 in normal saline solution
The reduced viscosity of the polymer solution (g/d) was measured using an Ostwald viscometer in a constant temperature water bath at 25°C. Comparative Example 1 is a case in which ammonium carbonate is not added, and Comparative Examples 2 to 4 are cases in which a hydrous gel is cut into approximately m/m cubes and hot air dried for 3 hours in a hot air dryer at 120°C. The results are shown in Table-1.

[Table] Examples 3 to 8 Comparative Examples 5 to 11 As in Example 1, the blending molar ratio of sodium acrylate and acrylamide was 30:70, and various carbonates or bicarbonates were added by weight of 5 weight to monomer. Using the hydrogel obtained by copolymerizing with the addition of %, microwave drying was performed. Comparative Example 5 is a case in which no carbonate is added, and in Comparative Examples 6 to 11, the gel is cut into approximately 2 m/m cubes and heated at 120°C.
Hot air drying was performed for 3 hours in a hot air dryer. The following description is based on Example 1. The apparent bulk density (g/ml) after drying was also measured. Display the results -
Shown in 2.

[Table] Example 9 24.28 g of acrylamide and 29.77 g of a 36% by weight aqueous sodium acrylate solution were placed in a 100 ml Erlenmeyer flask with a stopper, and further 9.56 g of demineralized water was added to dissolve them uniformly. Next, 1.75 g of ammonium carbonate and 3.5 g of acetone were added, and then 0.53 g of a 1 wt% ammonium persulfate aqueous solution and 0.61 g of a 20 wt% diethanolamine aqueous solution were added, and the contents were
The mixture was transferred to a 94 m/m stainless steel separable flat bottom flask, and polymerization was carried out for 1.5 hours in a constant temperature water bath at 30°C under a nitrogen atmosphere. 10 g of the obtained rubbery hydrogel with a thickness of about 10 m/m
Microwave drying was performed for 1.5 minutes in the same manner as in Example 1. The solid content of the hydrogel before drying was 59.3%, and after drying it was 95.8%. Furthermore, the drying rate was faster than in the case without acetone, and no deterioration of the copolymer due to drying was observed. The obtained dry polymer is a foam with a bulk density of 0.11 and is easily pulverized.

Claims (1)

[Claims] 1.0.5 for water-soluble acrylamide polymer
An aqueous acrylamide polymer solution containing ~30% by weight of carbonate and/or bicarbonate compounds with a concentration of 30% by weight or more is irradiated with microwaves to decompose the above compounds at a temperature of 120°C or less. A method for drying an acrylamide-based polymer aqueous solution, which comprises: bubbling the aqueous solution with generated carbon dioxide to evaporate water. 2. The acrylamide polymer aqueous solution contains 0.5 to 30% by weight of a carbonate and/or bicarbonate compound and an aqueous or hydrophilic organic solvent based on the water-soluble acrylamide polymer. A drying method according to claim 1.