JPS63218702A - Production of highly water-absorbing polymer - Google Patents

Abstract

PURPOSE:To produce a highly water-absorbing polymer in high production efficiency, preventing the deposition of polymer particles in a reactor, by continuously carrying out polymerization reaction, control of water-content and crosslinking steps in individual reactors. CONSTITUTION:The objective highly water-absorbing polymer can be produced by continuously carrying out the following stage using one or more reactors for each stop. (1) A step to produce a slurry containing polymer phase by dissolving a water-soluble vinyl monomer (e.g. acrylic acid and itaconic acid) and a water-soluble polymerization initiator (e.g. potassium persulfate and sodium persulfate) in water, suspending the obtained aqueous solution in a hydrocarbon (e.g. n-pentane and cyclohexane) and subjecting the dispersion to suspension polymerization. (2) A step to remove water in the polymer phase of the slurry together with the hydrocarbon from the system. (3) A step to add a water-soluble crosslinking agent to the slurry containing the polymer phase and carry out crosslinking reaction in the polymer phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a super absorbent polymer with excellent water absorption performance.

[Conventional technology]

When producing polymers by suspension polymerization, it is necessary to control the particle size of suspended particles and to prevent them from adhering to the reactor, as is known in the polymerization of vinyl chloride. Particle size control is extremely important, and particle size control is described in JP-A-51-56888 and JP-A-57-205.
Adhesion prevention is carried out by a method such as that disclosed in Japanese Patent Application Laid-Open No. 163103/1983. However, from the perspective of improving productivity, the particle size control by classification disclosed in the above publication is not effective, and as a measure to prevent the adhesion of suspended particles, etc., the target polymer is When used in sanitary materials such as the above, the method described in the above-mentioned publication using a conventionally proposed anti-adhesion agent has a problem from the viewpoint of safety for the human body.

Superabsorbent polymers have conventionally been produced under batch operations, and in this case, as the polymerization reactor is used repeatedly, the walls of the reactor, the vicinity of the gas-liquid interface of the stirring shaft, and the suspension in the panfur are damaged. The adhesion of turbid particles, etc. increases, and as a result, the flow state inside the polymerization reactor changes, the particle size distribution of suspended particles changes, and this causes problems such as secondary agglomeration of particles. . In other words, super absorbent polymers are in the form of particles! ! ! Changes in (average particle size, particle size distribution, amount of secondary agglomeration) greatly affect absorption performance such as absorption amount, absorption rate, and solubility, resulting in a significant decrease in performance.

Therefore, in order to obtain highly water-absorbent polymers of consistent quality, the polymerization tank has been forced to be frequently cleaned to remove deposits, which has led to problems in production efficiency and labor. This causes great sanitary disadvantages.

Therefore, an object of the present invention is to solve the above-mentioned problems and provide a method for producing a superabsorbent polymer having excellent absorption performance with high production efficiency.

[Problem that the invention seeks to solve]

As a result of various studies by the present inventors, according to the following method,
We have discovered that it is possible to efficiently produce superabsorbent polymers with excellent absorption performance by eliminating problems such as the risk of polymer particles (!Qfi particles) adhering to the inside of the reaction tank, leading to the present invention. did.

A first step of obtaining a slurry containing a polymer phase by dispersing an aqueous solution of a water-soluble vinyl monomer and a water-soluble polymerization initiator in a hydrocarbon and carrying out suspension polymerization, and polymerization of the slurry obtained in the first step. A second step in which water in the combined phase is removed from the system along with hydrocarbons to control the water content; and a water-soluble crosslinking agent is added to the slurry containing the polymer phase obtained in the second step, and the water in the polymer phase is removed. A method for producing a superabsorbent polymer, comprising: a third step in which a crosslinking reaction is carried out, and each of the above steps is carried out continuously using one or more reaction vessels.

According to the method for producing a superabsorbent polymer of the present invention, the following effects are mainly achieved, and as a result, the above object is achieved.

By performing the first, second, and third steps continuously using one or more reaction vessels, the movement of the liquid level in each reaction vessel is substantially eliminated, and the liquid level drops. Sometimes, suspended particles (polymer particles) in the system adhere to the inner surface of the reaction tank, etc., and then heating from the jacket causes the dispersant in the adhered polymer particles to become sticky, causing the adhesion to become stronger. can be avoided. When manufacturing superabsorbent polymers, in order to improve water absorption performance, it is necessary to control the water content and crosslink it with a crosslinking agent. Therefore, according to the conventional method, when controlling the water content, a large amount of water is removed from the polymerization system. Therefore, the liquid level in the reaction tank will fall.

In the first step (polymerization step), second step (moisture control step), and third step (crosslinking step), reaction vessels of the same size can be used for each step, making it easy to control the particle size. be able to. That is, the dispersion of droplets in each reaction tank is caused by the rotational energy of the blades, and the larger the tank, the wider the energy distribution and the wider the particle distribution. Therefore, the smallest possible reactor is used in the polymerization process. The particle size distribution is narrower,
It was found that it became easier to control the particle size. Therefore, according to the present invention, the particle size can be controlled by reducing the size of the polymerization reaction tank.

Furthermore, according to a preferred embodiment of the present invention, by devising the transfer of the polymer suspension (slurry) from the polymerization tank to the moisture control tank (dehydration tank) and from the moisture control tank to the crosslinking tank, that is, each reaction By extracting the slurry in the tank from the side of the reaction tank at a depth of 40 to 90% of the depth of the reaction liquid and sending it to the next reaction tank, the slurry with a uniform or constant concentration is transferred to the next reaction tank. Therefore, the above objective can be more fully achieved.

Conventionally, it has been thought that continuous operation in an overflow type system is difficult in solid-liquid systems, especially in systems where the difference in specific gravity between solid and liquid is large. Therefore, the present inventors focused on the stirring state of the solid-liquid system in the present invention, and found that the above-mentioned liquid transfer method is more preferable in achieving the object of the present invention. In other words, in a solid-liquid system with a large difference in specific gravity, even if the stirring intensity is increased, the solid particle concentration will not become uniform throughout, resulting in a distribution of solid particle concentration in the vertical direction.In the case of the present invention, the overflow line creates a gas phase, so the overflow When trying to extract slurry, it is difficult to extract a constant slurry with a uniform concentration, and suspended particles tend to adhere to the transfer path (transfer pipe) due to overflow. By making the size small enough to allow the slurry to escape, or by providing an equivalent constriction part, the fluid resistance for extracting the slurry can be increased. By keeping the balance so that the extraction line is in the position of This makes it possible to transfer slurry with uniform and constant concentration to the next tank.

The water-soluble vinyl thread pick used in the present invention includes:
Examples include acrylic acid, methacrylic acid, itaconic acid, manic acid, and their alkali metal salts, and the method of the present invention is particularly suitable for using acrylic acid in its entirety or partially neutralized form,
For example, acrylic acid is subjected to suspension polymerization of sodium acrylate completely or partially neutralized with caustic soda. These monomers are used as an aqueous solution having a monomer concentration of 15% to saturation.

Examples of the water-soluble polymerization initiator used in the present invention include persulfates such as potassium persulfate and sodium persulfate, and other water-soluble initiators.

As the water-soluble cross-linking agent used in the present invention, a water-soluble cross-linking agent having two or more epoxy groups in the molecule is usually used, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, sorbitol polyglycidyl ether, etc. Polyglycidyl ether is passed through.

In the first step of the present invention, that is, suspension polymerization, in order to efficiently remove polymerization heat, it is preferable to adopt a method in which the above-mentioned monomer aqueous solution is dropped into a dispersion medium in which a dispersant is dissolved and polymerized.

As the above-mentioned dispersion medium, aliphatic and alicyclic hydrocarbons which are liquid at room temperature are used. Examples of the aliphatic group include n-pentane and n-hexane, and examples of the alicyclic group include cyclopenkune, cyclohexane, and sotylcyclohexane. It will be done. Further, as the dispersant, ethyl cellulose or the like is used.

Further, the first step (N combination step) is preferably carried out so that the ratio of the aqueous phase (monomer aqueous solution) to the oil phase (hydrocarbon> is 1:5 to 1:2, and the second The step (moisture control step) is preferably carried out so that the moisture content is 15% to 50% from 50% to 85%.

Next, preferred embodiments of the method for producing a superabsorbent polymer of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a flow sheet showing an overview of the suspension polymerization apparatus used in carrying out the present invention, in which 1 is an initiator melting tank, 2 is a monomer preparation tank, 3 is a continuous mixer such as a line mixer, and 4
5.6 and 7 are the first, second and third reaction tanks, respectively, 8 is a crosslinking reaction tank, and 9 is a polymer suspension transfer pipe (slurry transfer) installed on the side of each reaction tank. tube).

Therefore, when carrying out the present invention, first, the initiator and monomer are dissolved in water and adjusted to a predetermined concentration in the initiator dissolving tank 1 and the monomer adjusting tank 2, respectively, and then the initiator and the monomer are dissolved in the dispersing agent dissolving tank 4. contains a hydrocarbon (dispersion medium) in which a dispersant is dissolved at a predetermined concentration. Note that the above concentrations of 7-mer and initiator are obtained by continuous mixing using a line mixer, etc.
The concentrations in the aqueous monomer solution after mixing are adjusted to 15% to saturation and 0.1% to saturation, respectively. In addition, the first, second, and third reaction tanks 5, 6, and 7 are filled with the above-mentioned hydrocarbons in advance, and the first reaction tank 5.
In addition, a dispersant is also dissolved at the same concentration as in the dispersant dissolving tank 4.

Next, the seven-mer aqueous solution and the initiator aqueous solution are sent to a continuous mixer 3 such as a line mixer, where they are mixed, and then the monomer aqueous solution containing the initiator is sent to the first reaction tank 5 to perform the first reaction. It is added dropwise to the hydrocarbon in tank 5 to carry out the l'J polymerization reaction. The reaction in the first reaction tank 5 is controlled so that the monomer m content is in the range of 50% to 95%.

Next, the slurry containing the monomer phase obtained in the first reaction tank 5 is sent to the second reaction tank 6 and further to the third reaction tank via transfer pipes 9, respectively. The transfer pipe 9 is connected to the depth of the reaction liquid in order to transfer the polymer suspension from the first reaction tank 5 and the second reaction tank 6 to the second reaction tank 6 and the third reaction tank 7, respectively, at a uniform concentration. It is provided on the side of each reaction tank at a depth of 40 to 90% of the depth. In the second reaction tank 6 and the third reaction tank 7, the transferred polymer has a water content of 15 to 50%.
The slurry containing the polymer phase is then transferred to the next crosslinking reaction tank 8 from a transfer tube 9 provided similarly to the transfer tube 9 described above.

The water content in the second reaction tank 6 and the third reaction tank 7 is controlled by a hydrophilic mechanism 10 provided at the top of each reaction tank.
This is done by Such a dehydration mechanism 10 is also provided in the first reaction tank 5 and the crosslinking reaction tank 8, and dehydration can be performed in these reaction tanks as well, if necessary.

In the crosslinking reaction tank 8, an aqueous crosslinking agent solution (including the case of only a water-soluble crosslinking agent) having a crosslinking agent concentration of 0.1 to 100% is added and supplied from the tank 1 to the slurry from the third reaction tank 7, and crosslinking is carried out. Let the reaction take place.

As described above, the desired superabsorbent polymer can be obtained by continuing the polymerization reaction, moisture control, and crosslinking reaction and controlling the reaction conditions as appropriate.

Although FIG. 1 shows a system equipped with first, second, and third reaction vessels and a crosslinking reaction vessel, the number of reaction vessels may be at least one for each step of the present invention. , can be increased as needed. Moreover, in the reaction tank used in the second step, the polymerization reaction in the first step can be carried out in parallel. In addition, instead of a transfer pipe connecting each reaction tank,
It is also possible to provide a valve at the bottom of each reaction tank and provide the same function as the transfer pipe described above by adjusting the opening degree of this valve.

〔Example〕

Example 1 In the apparatus shown in FIG. 1, the first reaction tank 5 and the crosslinking reaction tank 8 have an inner diameter of 160 mm and a capacity of 21 mm, and the second reaction tank IW 6 and the third reaction tank 7 have an inner diameter of 126 mm.
Suspension polymerization reaction was carried out in the following manner using 0 mm and 121 volumes.

The initiator melting tank 1 contains a potassium persulfate aqueous solution with a concentration of 4.3%, and the monomer adjustment tank 2 contains acrylic acid and acrylic acid prepared by neutralizing an 80% acrylic acid aqueous solution with a 30% caustic soda aqueous solution in an amount of 75 molχ. A mixed monomer aqueous solution of soda was stored, and the dispersant dissolving tank 4 contained a cyclohexane solution having an ethyl cellulose concentration of 0.4%, which was prepared by melting ethyl cellulose at a temperature of 60° C. as a dispersant.

In addition, in advance, the first, second and third reaction tanks 5.6 and 7
1,250 g, 1 kg, and 1 kg of cyclohexane were respectively stored in the reactors, and 5.0 g of ethyl cellulose was dissolved in the cyclohexane in the first reaction tank 5 and maintained at 75°C.

Next, from the initiator melting tank 1 and the monomer adjustment tank 2, 1). 89 g/win and 0.348 g/mi
The neutralized acrylic acid and the aqueous initiator solution were flowed out at a rate of n, mixed with the mixer 3, and then supplied to the first reaction tank 5 to start the reaction. After 90 minutes from the start of the reaction, 28.3 g of the acrylic acid neutralized product and the initiator aqueous solution were added.
/+in and 0-8 g/sin, and at the same time, 42.3 g/l1in of cyclohexane in which ethyl cellulose was dissolved was supplied from the dispersant dissolving tank 4, and the continuous V
Switched to t operation.

In the second reaction tank 6 and the third reaction tank 7, the amount of dehydration is controlled at a suitable time using a seven-pressure feed, and the amount of dehydration is adjusted to an average amount at the outlet of the third reaction tank 7. In the crosslinking reaction tank 8, the crosslinking agent concentration is 4.85w. % aqueous solution was added dropwise at a rate of 0.1) cc/M, and the product obtained from the outlet of No. 8 was dried under reduced pressure at 80° C. to obtain a water-absorbing polymer (Product 1 of the present invention).

Comparative Example 1 A single reactor of the same type as the first reaction tank used in Example 1 was used, and 5 g of ethyl cellulose dissolved in 1200 g of cyclohexane was stored in the reactor, and this was maintained at 75 ° C. . On the other hand, add 510 g of 80% acrylic acid aqueous solution to 5
60g of 30% caustic soda water? The monomer neutralized with liquid g was mixed with an aqueous initiator solution prepared by dissolving 1.6 g of potassium persulfate in 30 g of water.

Next, the above aqueous sevenmer solution was added dropwise to the cyclohexane in the reactor to carry out a polymerization reaction.

After dropping for 60 minutes to complete polymerization, the water content in the polymer was controlled to 25%, a solution of 0.5 g of polyethylene glycol diglycidyl ether dissolved in 5 g of water was added, and after 1 hour a crosslinking reaction was carried out. The obtained product was dried in the same manner as in Example 1, and the water-absorbing polymer (
A comparative product 1) was obtained.

Regarding the present invention product 1 and comparative product 1 obtained as described above,
When the water absorption performance of each was investigated, the results shown in Table 1 below were obtained.

Table 1 [Effects of the Invention] According to the suspension polymerization method for superabsorbent polymers of the present invention, it is possible to eliminate problems such as the possibility that polymer particles (!! turbid particles) may adhere to the reaction tank. Super absorbent polymers with excellent performance can be manufactured with high production efficiency.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet schematically showing a suspension polymerization apparatus used in the suspension polymerization method for superabsorbent polymers of the present invention. l... Initiator dissolving tank 2... Monomer preparation tank 3... Continuous mixer (mixer) 4... Dispersant dissolving tank 5... First reaction tank 6... Second reaction tank 7... Third reaction Tank 8...Crosslinking reaction tank 9...Transfer pipe 10...Dehydration mechanism

Claims (2)

[Claims] (1) A first step in which an aqueous solution containing a water-soluble vinyl monomer and a water-soluble polymerization initiator is dispersed in a hydrocarbon and subjected to suspension polymerization to obtain a slurry containing a polymer phase; A second step in which water in the polymer phase of the slurry is removed from the system along with hydrocarbons, and a water-soluble crosslinking agent is added to the slurry containing the polymer phase obtained in the second step, and a crosslinking reaction is performed in the polymer phase. A method for producing a superabsorbent polymer, characterized in that each of the above steps is performed continuously using one or more reaction vessels. (2) Add the slurry in each reaction tank to a depth of 40 to 9
The method for producing a superabsorbent polymer according to claim 1, wherein the superabsorbent polymer is extracted from the side of the reaction tank at a depth of 0% and sent to the next reaction tank.