CN111978436A - High-efficiency and low-consumption reverse suspension polymerization preparation process of water-absorbing compound - Google Patents

Abstract

The present invention provides a high-efficiency and low-consumption reverse-phase suspension preparation process of a water-absorbing compound, comprising: a. a first-stage reverse-phase suspension polymerization is carried out after mixing a first-stage water-phase mixed solution (in-situ neutralization) and an oil-phase solution Reaction to obtain the first suspension; b. the oil phase dissolved with most dispersants is filtered and replaced by a new oil phase without dispersants, and the second-stage water phase is continued to be added to the first suspension The mixed solution is subjected to the second-stage reversed-phase suspension polymerization to obtain a second suspension. Before the second-stage polymerization, a corresponding amount of dispersant should be added again; c. the second suspension is azeotropically dehydrated and surface-crossed. The water-absorbent resin can be obtained by filtration and drying.

Description

A kind of high-efficiency, low-consumption preparation process of reversed-phase suspension polymerization of water-absorbing compounds

technical field

The invention relates to a reverse-phase suspension preparation process of a water-absorbent resin.

Background technique

Superabsorbent polymer (SAP, Superabsorbent Polymers) is a kind of lightly cross-linked polymer compound. Due to its strong water absorption and water retention capacity, it is widely used in the field of sanitary materials such as diapers and sanitary napkins. Water materials and water-retaining agents for agriculture, forestry, and gardening, etc. As water-absorbent resins for sanitary materials, partially neutralized products of polyacrylic acid, neutralized products of starch-acrylic acid graft polymers, hydrolyzed products of starch-acrylonitrile grafted polymers, and vinyl acetate-acrylate copolymers are known. Saponifications of substances, etc.

As a method for producing such a water-absorbent resin, an aqueous solution polymerization method, a reversed-phase suspension polymerization method, and the like are known. Among them, the water-absorbent resin prepared by reversed-phase suspension polymerization has formed a unique competitive advantage in the domestic composite core market due to its unique product morphology and extremely fast liquid absorption rate. gained a large share of the market. Although reversed-phase suspension polymerization does not need to go through the pulverization and granulation process and its heat of polymerization is easy to remove, its polymerization process is complex and has many procedures, and it has high requirements on technology and equipment. Currently, only Japan's Sumitomo Seika Co., Ltd. has industrialized production. ability.

The reversed-phase suspension polymerization itself is a thermodynamically unstable system, which requires a large amount of dispersant and vigorous stirring to maintain the metastable state. However, the particle size of water-absorbent resin products prepared by traditional reverse-phase suspension polymerization is usually relatively small (less than 150 microns), which cannot meet the particle size requirements of water-absorbent resins in the field of sanitation and hygiene (150-850 microns, preferably 150-710 microns). micrometer), thus Sumitomo Refinery (CN 1053796A) introduced secondary feeding into it, and a product meeting the particle size requirements could be obtained, but it was necessary to reduce the temperature after one stage of polymerization to below room temperature, so that conventional surfactants were precipitated (solubility decline), thereby losing most of its dispersal and protection capabilities. In this way, the newly added monomer droplets will swell and stick to the water-absorbent resin particles obtained by a stage of polymerization due to the lack of the protective effect of the dispersant, so that the particle size becomes larger, and the product changes from a single spherical particle to an agglomerated state. grape bunches. However, this method (see patent CN104507565B, CN 101466740B) needs to lower the temperature of the system from the polymerization temperature to room temperature, otherwise the product with the desired particle size cannot be obtained (see patent CN 100439425C), so in addition to wasting a lot of energy, for Production efficiency and production stability have huge losses; Mitsubishi Chemical (Application Publication No. CN 1146997A) adopts a two-step polymerization process, and adds a surfactant with HLB greater than 7 in the second-stage acrylic acid neutralization solution, so that after the first-stage polymerization is completed The addition of two-stage monomer droplets does not have to lower the temperature to obtain large SAP particles. The patent (JP 62310108) uses the W/O type reversed-phase suspension polymerization process to add SAP fine powder less than 100 meshes to the second polymerization kettle for surface treatment. The obtained resin has good strength, fast water absorption and narrow particle size distribution. 100 mesh particles can reach 99%; Asahi Kasei Chemical (Application Publication No. CN 101410419A) adds hydrophilic solvents such as alcohols to the slurry obtained by the end of the phase one-step reversed-phase suspension polymerization polymerization to obtain SAP with a particle size of 200-2000um particle.

However, how to effectively remove the heat of reaction during the polymerization process and reduce the energy loss and efficiency reduction during the multi-stage polymerization process (frequent heating and cooling) is a difficulty that limits the large-scale industrialization of reversed-phase suspension polymerization. Therefore, it is still necessary to develop a more efficient, low-consumption and simple particle size control process for preparing water-absorbent resin by reversed-phase suspension polymerization.

SUMMARY OF THE INVENTION

In view of this, the main purpose of the present invention is to provide a kind of method for preparing water-absorbent resin by reversed-phase suspension polymerization, adopt solvent replacement mode to replace the traditional violent cooling process, reduce the waste of heat exchange external cold source and the requirement of heat exchange equipment; In a preferred embodiment, on the one hand, a high/medium and low temperature type initiation system is used to reduce the initiation temperature and reduce the energy consumption required for heating and cooling; The thermal temperature rise assists in the dissolving process of the dispersant in the oil phase while realizing the preparation of the monomer phase and reduces the waste of external heat sources. In conclusion, the decrease in stability, energy loss and efficiency caused by severe cooling can be avoided in multiple polymerizations, and the controllable preparation of the particle size of the water-absorbent resin can be realized by the replacement of different proportions of solvents.

In order to realize the above-mentioned purpose of the invention, the present invention adopts the following technical solutions:

A method for preparing a water-absorbing compound with a controllable particle size by reversed-phase suspension polymerization, comprising the following steps:

(1) one-stage polymerization: carry out the reversed-phase suspension polymerization reaction of the first stage after mixing one-stage water-phase mixed solution and oil-phase solution to obtain the first suspension;

(2) Solvent replacement and particle agglomeration: filter the first suspension, remove part or all of the oil phase solvent, and then add fresh oil phase solvent to maintain the temperature of the system;

(3) Two-stage polymerization: continue adding two-stage water-phase mixed solution to the first suspension to carry out the second-stage reversed-phase suspension polymerization reaction to obtain a second suspension, which should be repeated before the two-stage polymerization Supplementary dispersant;

(4) Post-treatment: azeotropic dehydration and surface cross-linking of the second suspension, followed by filtration and drying to obtain a water-absorbent resin.

Wherein, the oil phase solution described in step (1) contains dispersant and petroleum hydrocarbon solvent (oil phase solvent);

The composition of the aqueous phase mixed solution described in the steps (1) and (3) includes water, a water-soluble ethylenically unsaturated monomer, an initiator and an internal crosslinking agent.

In the present invention, the petroleum hydrocarbon solvent in the oil phase solution described in step (1) is one or more of aliphatic hydrocarbons, alicyclic hydrocarbons or aromatic hydrocarbons; preferably, the aliphatic hydrocarbons are n-pentane One or more of alkane, n-hexane, n-heptane or petroleum ether, and the alicyclic hydrocarbon is one or more of cyclopentane, methylcyclopentane, cyclohexane or methylcyclohexane The aromatic hydrocarbon is one or more of benzene, toluene or xylene.

In the present invention, the dispersing agent described in step (1) is selected from sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, tripolyglycerol monostearic acid ester and octadecanoate One or more of alkyl monophosphates. Preferably, the dosage of the dispersant is 0.01-5% of the mass of the water-soluble ethylenically unsaturated monomer in step (1), preferably 0.5-3%, for example: 1.25%, 1.5%.

In the present invention, the water-soluble ethylenically unsaturated monomer is one or more of acrylic acid or its salt, acrylamide or N,N-dimethylacrylamide, and the water-soluble ethylenically unsaturated monomer in the aqueous phase mixed solution is water-soluble The mass concentration of the ethylenically unsaturated monomer is 20-50%, preferably 30-40%, such as: 34%, 36%;

The initiator is selected from high temperature initiation type initiator persulfate and medium and low temperature initiation type initiator water-soluble azo compound, wherein in step (1), the initiator is preferably high temperature initiation type initiator persulfate and medium and low temperature initiation type The mixed system of the initiator water-soluble azo compound, the persulfate is one or more of sodium persulfate, potassium persulfate or ammonium persulfate; the water-soluble azo compound is 2,2'-azobis One or more of isobutylamidine dihydrochloride (AIBA) or 2,2'-azabis(2-imidazoline) dihydrochloride (AIBI); The mass ratio of the low-temperature initiation type initiator is 1-5, for example: 1.0, 2.0. The use of the mixed initiator system, on the one hand, reasonably mixes initiators with different activities to carry out force accumulation to initiate polymerization, thereby reducing the initial initiation temperature; it is also beneficial to subsequent heat transfer and heat transfer, and energy consumption is saved. The amount of the initiator is 0.005-5% of the mass of the water-soluble ethylenically unsaturated monomer, preferably 0.01-0.5%, for example: 0.15%, 0.2%;

The internal crosslinking agent is one or more of a hydroxyl-containing compound, an epoxy group-containing compound or a double bond-containing compound, preferably, the hydroxyl-containing compound is ethylene glycol, propylene glycol, glycerol, One or more of pentaerythritol, polyglycerol, polyvinyl alcohol or trimethylolaminomethane, and the epoxy group-containing compound is ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl One or more of glycerol ether, 1,6-hexanediol diglycidyl ether, allyl glycidyl ether, and the double bond-containing compound is ethylene glycol diacrylate, propylene glycol diacrylate, N , N'-methylenebisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, One or more of pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate. The amount of the internal crosslinking agent is 0.005-1% of the mass of the water-soluble ethylenically unsaturated monomer, preferably 0.01-0.5%, for example: 0.04%, 0.06%.

In the present invention, in step (1), the mixing of the water-phase mixed solution and the oil-phase solution can be performed in a conventional manner in the art. However, as a preference, the aqueous mixed solution is obtained by in-situ acid-base neutralization, namely: adding a water-soluble ethylenically unsaturated monomer and an alkaline solution such as sodium hydroxide solution to the petroleum oil containing a dispersant It is obtained by adding an initiator and an internal crosslinking agent to the hydrocarbon solvent after cooling to 40° C. or lower. The dissolving of the dispersant is assisted by the temperature rise generated by the heat of neutralization, thereby effectively utilizing the heat of neutralization and avoiding the waste of energy caused by conventional cooling methods; in some preferred embodiments, an alkaline solution such as hydrogen is used. The mass concentration of the sodium oxide solution is 10-50%, preferably 20-40%, more preferably 21%, 32%.

In the present invention, in step (1), the petroleum hydrocarbon solvent of the oil phase solution and the water phase mixed solution (including water, water-soluble ethylenically unsaturated monomer, initiator and internal crosslinking agent) The mass ratio is 0.1-10, preferably 1-5, for example: 1.5, 2.5.

In the present invention, in step (2), considering the ease of operation and particle size control, the removal ratio of the solvent is 50-100%, preferably 70-90%; 0.8-1.25 times the amount.

In the present invention, the mass ratio of the aqueous phase mixed solution added in step (3) and step (1) can be controlled between 0.5-5, and from the perspective of improving production efficiency and effective particle size control, it is more preferably 1- 2, for example: 1.2, 1.6.

In the present invention, in the step (3), since the dispersant will also be partially removed when the solvent is removed in the preceding steps, the dispersant should be supplemented again before the second-stage polymerization, and the ratio of the added dispersant is the one that is removed by filtration. 60-150% of dispersant, preferably 80-120%.

In a specific embodiment, the present invention achieves the purpose of particle size control by adjusting the replacement ratio of the solvent in the first stage, the stirring rate and the amount of the added dispersant. In some preferred embodiments, the cooling temperature of the first suspension is 0-100°C when cooling down. From the perspective of energy consumption, efficiency and preventing polymerization and blocking in the dispersion process, it is preferably 30-60°C. The solvent replacement ratio is easy to achieve; the adjustment of the stirring rate is related to the quality of multiple feedings and the expected particle size of the final product. Generally speaking, the whole polymerization process system is in a stirring state, and the stirring rate should be increased significantly, such as once The feeding speed is 200 rpm, the second feeding is 300 rpm, the third feeding is 400 rpm, and so on. Preferably, the polymerization stirring speed of the first stage is 100-300 rpm, and the polymerization stirring speed of the second stage is 200-600 rpm.

The reversed-phase suspension polymerization of the first stage and the second stage mentioned in the present invention all adopt methods known in the art, for example, in step (1), the aqueous phase mixed solution is mixed with the oil phase solution, and the temperature is raised to 50 °C under stirring. -100 °C, such as 50 °C, 60 °C, carry out the first-stage water-in-oil reversed-phase suspension polymerization, the polymerization reaction is 1-3h, such as 1.5h, 2.0h, wherein nitrogen can be used to replace before the reaction starts; Replace and cool down to 30-60 ° C, such as 50 ° C, in step (3), continue to add the aqueous phase mixture to the first suspension, repeat the above steps to carry out the second-stage water-in-oil reversed-phase suspension polymerization reaction to obtain agglomeration The colloidal particle suspension containing the second stage polymerization.

In step (4), the temperature of azeotropic water removal is 90-150°C, and the amount of azeotropic water removal is 50-90% of the total mass of the added water; the drying temperature is 100-160°C, and the time is 0.5-3h;

The surface crosslinking agent used for surface crosslinking is a compound that can form covalent bonds or ionic bonds with carboxyl groups: compounds that can form covalent bonds include polyol compounds, epoxy compounds and polyvalent amines such as polyethyleneimine, preferably Ethylene glycol, propylene glycol, 1,4-butanediol, ethylene carbonate, propylene carbonate, (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, glycerin, trimethylol One or more of aminomethane and pentaerythritol; compounds that can form ionic bonds include inorganic salts of multivalent metals such as calcium, magnesium, aluminum, iron, copper, and zinc. The added amount of the surface crosslinking agent is 0.01-2% of the total mass of the water-soluble ethylenically unsaturated monomer, preferably 0.02-0.2%.

Another object of the present invention is to provide the water-absorbent resin prepared by the above method, and the appearance of the obtained product is an agglomerated "grape bunch" shape.

In the present invention, the particle size distribution of the water-absorbent resin product obtained by the preparation method of the present invention is about 70-90% of the total product.

In the present invention, it is different from the conventional cooling and cooling of the suspension obtained in the first stage, so that the dispersant is separated out and loses the protective effect due to the decrease in solubility, and the oil phase is removed and replaced. The high-temperature oil phase solution (dissolving most of the dispersant) in the stage suspension is replaced with a new low-temperature pure oil phase without dispersant, which reduces the concentration of dispersant and the temperature of the system in disguise, which is helpful for subsequent The particle size is controlled by the secondary feeding, so that a single spherical particle is swollen to obtain an agglomerated particle morphology. This can not only avoid the waste of energy and the decline of production stability caused by severe cooling, but also improve the operation efficiency and repeatability.

Compared with the prior art, the present invention has the following advantages:

(1) the present invention adopts the mode of in-situ acid-base neutralization, effectively utilizes the neutralization heat temperature rise while realizing the preparation of the monomer phase, assists in the completion of the dissolving process of the dispersant in the oil phase, and reduces the waste of neutralization heat ;

(2) the present invention adopts high/medium-low temperature type initiation system to reduce initiation temperature, reduce energy consumption required for heating and cooling, and improve production efficiency;

(3) the present invention adopts the mode of solvent replacement, which can easily realize the continuous change of the dispersant concentration and the efficient control of the system temperature, reduce energy consumption, and the dispersant supplemented subsequently can assist in completing the control of the final product particle size, Improve operational stability.

Description of drawings

FIG. 1 is a SEM image of the water-absorbent resin prepared in Example 1. FIG.

Detailed ways

The present invention will be described in detail below with specific embodiments.

Example 1:

6.9g of sucrose fatty acid esters (Hetang Technology, S-370) and 2000g of technical grade n-heptane were added to the 10L stainless steel polymerization kettle, the jacket was heated to 35°C and uniformly dispersed at a stirring speed of 200rpm to obtain oil. Phase to spare. 600g of sodium hydroxide solution whose mass concentration is 32% and 860g of acrylic acid aqueous solution whose mass concentration is 53.5% are simultaneously added into the polymerization kettle by two feeding ports in a certain proportion, so that acid-base neutralization reaction occurs in the polymerization kettle, The dispersant S-370 in the oil phase is gradually dissolved and dispersed by neutralization heat. When the temperature of the system drops below 40°C, add 0.46g potassium persulfate, 0.23g 2,2'-azobisisobutylamidine dihydrochloride (AIBA) and 0.1g ethylene glycol diglycidyl ether to it 30 g of the aqueous solution, fully dissolved and mixed to obtain a mixed solution of an aqueous phase solution and an oil phase solution. While stirring, it was replaced with nitrogen for 30 minutes, then the temperature was raised to 60°C, and the reaction was carried out for 2 hours under this condition to carry out a stage of W/O reversed-phase suspension polymerization to obtain a stage of suspension containing polymerized SAP colloidal particles;

Under the condition of stirring while cooling, 600g of sodium hydroxide solution with a mass concentration of 32% was added dropwise to a mixing device in which 460g of acrylic monomer and 400g of deionized water were dissolved. Add the aqueous solution 30g containing 0.69g potassium persulfate and 0.1g ethylene glycol diglycidyl ether, after fully dissolving and mixing, obtain two-stage water phase mixed solution (total mass is 1490g) for subsequent use;

While stirring, filter a section of the suspension while hot, remove 1600g (80% of the initial charge) of n-heptane (the interior contains about 4.5g of dispersant after testing), and replace it with 1600g of n-heptane, which can be controlled at this time. The temperature of the system is 45° C., the rotation speed is increased to 300 rpm, the second-stage water phase prepared above is added, and stirred for 30 minutes at this temperature to complete the particle agglomeration process. Subsequently, 4.5g of sucrose fatty acid ester was added to the system (from the point of view of being conducive to rapid dispersion, the dispersant was dissolved in a small amount of n-heptane in advance), the temperature was raised to 80°C, and the reaction was carried out under this condition for 1h to carry out two-stage W/O reverse phase Suspension polymerization to obtain a second-stage suspension containing polymerized SAP colloidal particles with agglomeration;

Continue to raise the temperature to 120°C, remove the water of the system and make the n-heptane reflux continuously. Then, the temperature of the system was lowered to 80° C. and 36.8 g of an aqueous solution of ethylene glycol diglycidyl ether with a mass concentration of 2% was added to carry out surface cross-linking for 1 h. Finally, the agglomerated SAP particles are obtained by filtration and centrifugation, and the final product can be obtained after drying and sieving.

Example 2:

Example 1 was repeated, except that the filtered n-heptane was replaced with 1800 g of fresh n-heptane, and the additional amount of dispersant was 5.0 g.

Example 3:

Repeat embodiment 1, the difference is: replace the n-heptane filtered out with the fresh n-heptane of 2000g, and the additional amount of dispersant is 5.5g, and the second-stage aqueous phase mixed solution addition amount becomes 2085g (embodiment 1.4 times that of the second-stage aqueous phase mixture in 1).

Example 4:

Example 1 was repeated with the following differences: 1200 g of n-heptane (60% of the initial addition, with about 4.2 g of dispersant inside tested) was removed and replaced with 1400 g of fresh n-heptane, and the additional amount of dispersant was 3.0 g, and the addition amount of the second-stage water-phase monomer solution was changed to 1190 g (0.8 times the second-stage water-phase mixed solution in Example 1).

Example 5:

Repeat Example 1, the difference is: the composite initiator during one-stage polymerization was changed to 0.46g potassium persulfate, 0.23g 2,2'-azabis(2-imidazoline) dihydrochloride (AIBI), and Sucrose fatty acid ester was replaced with octadecyl monophosphate.

Comparative Example 1:

6.9g of sucrose fatty acid ester (Sucrose Technology, S-370) and 2000g of technical grade n-heptane were added to the 10L stainless steel polymerization kettle, heated to 50°C and uniformly dissolved and dispersed at a stirring speed of 200rpm, then cooled to 50°C to obtain an oil phase for later use.

Under the condition of stirring while cooling, 1200 g of sodium hydroxide solution with a mass concentration of 32% was added dropwise to a mixing device in which 920 g of acrylic monomer and 800 g of deionized water were dissolved. 60 g of an aqueous solution containing 1.4 g of potassium persulfate and 0.1 g of ethylene glycol diglycidyl ether was added, fully dissolved and mixed to obtain an aqueous phase mixture for later use.

Half of the prepared aqueous phase mixture was added to the oil phase, and the mixture was replaced with nitrogen for 30 minutes while stirring. Then the temperature was raised to 75°C, and the reaction was carried out for 2 h under this condition to carry out a stage of water-in-oil reversed-phase suspension polymerization to obtain a stage of suspension containing polymerized SAP colloidal particles.

Cool the suspension obtained in the above paragraph to 25°C, increase the rotation speed to 300rpm, then add the other half of the prepared aqueous phase mixture, and stir at this temperature for 30min to complete the particle agglomeration process. The temperature was raised to 75° C. and the reaction was continued for 2 h under this condition to carry out the second-stage water-in-oil reversed-phase suspension polymerization to obtain a second-stage suspension containing polymerized SAP colloidal particles that had undergone agglomeration.

Continue to raise the temperature to 120°C, remove the water of the system and make the n-heptane reflux continuously. Then, the temperature of the system was lowered to 80° C. and 36.8 g of an aqueous solution of ethylene glycol diglycidyl ether with a mass concentration of 2% was added to carry out surface cross-linking for 1 h. Finally, the agglomerated SAP particles are obtained by filtration and centrifugation, and the final product can be obtained after drying and sieving.

Comparative Example 2:

Comparative Example 1 was repeated, except that the cooling temperature of the suspension obtained by the one-stage polymerization was changed to 35°C.

Comparative Example 3:

Example 1 was repeated, with the difference that the amount of n-heptane removed by filtration was changed to 1000 g (with 3.0 g of dispersant inside tested), replaced with 1000 g of fresh n-heptane, and 3.0 g of dispersant was added subsequently.

Comparative Example 4:

Example 1 was repeated, with the difference that the amount of dispersant added after particle agglomeration and before the second-stage polymerization was changed to 2.0 g.

Comparative Example 5:

The follow-up operation of Example 1 was repeated except that no dispersant was added after the particle agglomeration and before the second-stage polymerization. As a result, when the temperature of the second-stage polymerization was raised to about 60 °C, the polymerization failed, and the colloids were bonded into large pieces and adhered to the stirring paddle. .

The basic properties of the SAP prepared above are shown in Table 1:

Table 1. Basic properties of the above water-absorbent resins

It can be seen from the examples that the method of solvent replacement can easily and efficiently obtain a water-absorbent resin with a suitable particle size and its distribution in an agglomerated state, and the size of the particle size is controllable: by adjusting the ratio of dissolving replacement and adding suitable In addition, the temperature can be directly achieved by low-temperature solvent replacement, saving energy and improving efficiency. From the comparative example, it can be seen that only when the temperature is lowered to 25°C after the first stage of polymerization, can a particle size distribution that is closer to the example can be obtained. Insufficient, can not obtain products with ideal particle size distribution. In addition, the present invention adopts a high/medium-low temperature type initiation system to reduce the initiation temperature and reduce the energy consumption required for heating and cooling; At the same time as the preparation of the phase, it assists the dissolving process of the dispersant in the oil phase and reduces the waste of external heat sources.

In a word, the present invention provides a method for preparing a water-absorbent resin with a controllable particle size distribution by adopting a solvent replacement process to replace the traditional cooling temperature, using in-situ acid-base neutralization and a high/medium-low temperature type composite initiation system, which can It avoids the waste of energy and the decrease of production stability caused by severe cooling, and improves the operation efficiency and repeatability.

The above are only preferred embodiments of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Any improvement to the present invention, including equivalent replacement and addition of raw materials, etc., fall within the scope of the present invention. , which should be known to those skilled in the art. The scope of patent protection of the present invention should be defined by the claims.

Claims (10)

1. A process for preparing water-absorbent resin by inverse suspension polymerization is characterized in that: the method comprises the following steps:

(1) one-stage polymerization: mixing the first-stage water phase mixed solution and the oil phase solution, and then carrying out reversed-phase suspension polymerization reaction in a first stage to obtain a first suspension; wherein the oil phase solution contains a dispersant and a petroleum hydrocarbon solvent;

(2) solvent replacement and particle agglomeration: filtering the first suspension to remove part or all of the solvent, adding fresh solvent, and maintaining the temperature of the system;

(3) second-stage polymerization: continuously adding the second-stage aqueous phase mixed solution into the first suspension to perform a second-stage reversed-phase suspension polymerization reaction to obtain a second suspension, and supplementing the dispersing agent again before the second-stage polymerization;

(4) and (3) post-treatment: dehydrating and surface-crosslinking the second suspension, and then filtering and drying to obtain the water-absorbent resin;

the composition of the aqueous phase mixed solution in the step (1) and the step (3) comprises water, water-soluble ethylenically unsaturated monomer, initiator and internal crosslinking agent.

2. The method of claim 1, wherein: the water-soluble ethylenically unsaturated monomer is one or more of acrylic acid or salts thereof, acrylamide or N, N-dimethylacrylamide, and the mass concentration of the water-soluble ethylenically unsaturated monomer in the water-phase mixed solution is 20-50%.

3. The method according to any one of claims 1-2, wherein: the petroleum hydrocarbon solvent in the step (1) is one or more of aliphatic hydrocarbon, alicyclic hydrocarbon or aromatic hydrocarbon; preferably, the aliphatic hydrocarbon is one or more of n-pentane, n-hexane, n-heptane or petroleum ether, the alicyclic hydrocarbon is one or more of cyclopentane, methylcyclopentane, cyclohexane or methylcyclohexane, and the aromatic hydrocarbon is one or more of benzene, toluene or xylene; the mass ratio of the petroleum hydrocarbon solvent to the water phase mixed solution is 0.1-10;

the dispersant is at least one of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate and octadecyl monophosphate, and the dosage of the dispersant is 0.01-5%, preferably 0.5-3% of the mass of the water-soluble ethylenic unsaturated monomer.

4. A method according to any one of claims 1-3, characterized in that: the initiator is selected from a high-temperature initiation type initiator persulfate and a medium-low temperature initiation type initiator water-soluble azo compound, wherein the initiator in the step (1) is a mixed system of the high-temperature initiation type persulfate and the medium-low temperature initiation type water-soluble azo compound, and the persulfate is one or more of sodium persulfate, potassium persulfate and ammonium persulfate; the water-soluble azo compound is 2,2 '-azobisisobutylamidine dihydrochloride (AIBA) and/or 2,2' -azabicyclo (2-imidazolium) dihydrochloride (AIBI); the mass ratio of the high-temperature initiator to the medium-low temperature initiator is 1-5;

the amount of the initiator is 0.005 to 5%, preferably 0.01 to 0.5% by mass of the water-soluble ethylenically unsaturated monomer.

5. The method according to any one of claims 1-4, wherein: the internal crosslinking agent is one or more of a hydroxyl-containing compound, an epoxy-containing compound or a double bond-containing compound, and the amount of the internal crosslinking agent is 0.005-1%, preferably 0.01-0.5% of the mass of the water-soluble ethylenically unsaturated monomer;

preferably, the hydroxyl-containing compound is one or more of ethylene glycol, propylene glycol, glycerol, pentaerythritol, polyglycerol, polyvinyl alcohol or tris (hydroxymethyl) aminomethane, the epoxy group-containing compound is one or more of ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, 1, 6-hexanediol diglycidyl ether and allyl glycidyl ether, the double-bond-containing compound is one or more of ethylene glycol diacrylate, propylene glycol diacrylate, N' -methylene bisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate.

6. The method according to any one of claims 1 to 5, wherein: in the step (1), a water-soluble ethylenically unsaturated monomer and an alkaline solution are added to a petroleum hydrocarbon solvent containing a dispersant, and after cooling to below 40 ℃, an initiator and an internal crosslinking agent are added thereto to obtain the aqueous phase mixed solution.

7. The method according to any one of claims 1-6, wherein: in the step (2), the removal proportion of the solvent is 50-100%, preferably 70-90%; the amount of fresh solvent added is 0.8 to 1.25 times the amount removed.

8. The method according to any one of claims 1 to 7, wherein: the mass ratio of the second-stage aqueous phase mixed solution to the first-stage aqueous phase mixed solution is 0.5-5, preferably 1-2; the amount of dispersant added in step (3) is 60 to 150%, preferably 80 to 120% of the dispersant removed in step (2).

9. The method according to any one of claims 1-8, wherein: the temperature of the polymerization reaction in the steps (1) and (3) is 50-100 ℃, and the polymerization reaction lasts for 1-3 h; adjusting the temperature of the first suspension to 30-60 ℃ before the second-stage polymerization in the step (3); the first-stage polymerization stirring rate was 100-300rpm, and the second-stage polymerization stirring rate was 200-600 rpm.

10. A water-absorbent resin produced by the method according to any one of claims 1 to 9, characterized in that: the shape of the water-absorbent resin product is in an aggregated state of a grape cluster, and the proportion of particles with the particle size distribution of 150-710um is 70-90% of the total product.

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