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CN111978436B - High-efficiency and low-consumption reverse suspension polymerization preparation process of water-absorbing compound - Google Patents

High-efficiency and low-consumption reverse suspension polymerization preparation process of water-absorbing compound Download PDF

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CN111978436B
CN111978436B CN202010876190.9A CN202010876190A CN111978436B CN 111978436 B CN111978436 B CN 111978436B CN 202010876190 A CN202010876190 A CN 202010876190A CN 111978436 B CN111978436 B CN 111978436B
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water
stage
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dispersant
mixed solution
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CN111978436A (en
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丁明强
赵帅
王晓
姜云翔
马磊
纪学顺
孙家宽
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Wanhua Chemical Group Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/12—Polymerisation in non-solvents
    • C08F2/16—Aqueous medium
    • C08F2/18—Suspension polymerisation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F120/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
    • C08F120/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F120/04—Acids; Metal salts or ammonium salts thereof
    • C08F120/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
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    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
    • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
    • C08F20/52—Amides or imides
    • C08F20/54—Amides, e.g. N,N-dimethylacrylamide or N-isopropylacrylamide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
    • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
    • C08F20/52—Amides or imides
    • C08F20/54—Amides, e.g. N,N-dimethylacrylamide or N-isopropylacrylamide
    • C08F20/56—Acrylamide; Methacrylamide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F4/00—Polymerisation catalysts
    • C08F4/04—Azo-compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F4/00—Polymerisation catalysts
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    • C08F4/30—Inorganic compounds

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Abstract

The invention provides a high-efficiency low-consumption reverse suspension preparation process of a water-absorbing compound, which comprises the following steps: a. mixing the first-stage water phase mixed solution (in-situ neutralization) and the oil phase solution, and then carrying out reversed-phase suspension polymerization reaction in the first stage to obtain a first suspension; b. filtering the oil phase dissolved with most of the dispersant and replacing the oil phase with a new oil phase without the dispersant, continuously adding a second-stage water phase mixed solution into the first suspension to perform a second-stage reversed phase suspension polymerization reaction to obtain a second suspension, and adding a corresponding amount of dispersant before the second-stage polymerization; c. and (4) carrying out azeotropic dehydration and surface crosslinking on the second suspension, and then filtering and drying to obtain the water-absorbent resin.

Description

High-efficiency and low-consumption reverse suspension polymerization preparation process of water-absorbing compound
Technical Field
The invention relates to a reversed phase suspension preparation process of water-absorbent resin.
Background
Super Absorbent Polymers (SAP) are slightly crosslinked polymer compounds, and are widely used in the field of sanitary materials such as paper diapers and sanitary napkins due to their strong water absorption and retention capacities, water-blocking materials for cables and optical cables, and water-retaining agents special for agriculture, forestry and horticulture. 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 graft polymers, saponified products of vinyl acetate-acrylic ester copolymers, and the like are known.
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. The water-absorbent resin prepared by inverse suspension polymerization forms unique competitive advantages in the domestic composite core body market under the trend of a light and thin diaper market due to the unique product appearance and the extremely fast liquid absorption rate, and occupies a great part of market share. Although the inverse suspension polymerization does not need to go through a crushing and granulating process and the polymerization heat is easy to remove, the polymerization process is complex and has more processes and higher requirements on processes and equipment, and only Japanese Sumitomo Seiko Kaisha has the industrial production capacity at present.
Inverse suspension polymerization is itself a thermodynamically unstable system that requires a large amount of dispersant and vigorous stirring to maintain the metastable state. The particle size of the water-absorbent resin product prepared by the traditional reversed phase suspension polymerization is usually smaller (less than 150 microns), and cannot meet the particle size requirement of the water-absorbent resin in the field of physiological hygiene (150-. In this way, the newly added monomer droplets, lacking the protective effect of the dispersant, will swell and adhere to the water-absorbent resin particles obtained by the first-stage polymerization, so that the particle size becomes larger, and the product changes from single spherical particles to aggregated grape string-like particles. However, this method (see patent CN104507565B, CN 101466740B) requires lowering the temperature of the system from the polymerization temperature to room temperature, otherwise the product with desired particle size cannot be obtained (see patent CN 100439425C), so there is a huge loss in production efficiency and production stability besides wasting a lot of energy; mitsubishi chemistry (application publication No. CN 1146997A) adopts a two-step polymerization process, and a surfactant with HLB more than 7 is added into a second-stage acrylic acid neutralized liquid, so that after the first-stage polymerization is finished, a second-stage monomer liquid drop is added, and large-particle SAP particles can be obtained without cooling to a lower temperature. In the patent (JP 62310108), SAP fine powder with the particle size of less than 100 meshes is added into a second polymerization kettle for surface treatment by a W/O type reversed phase suspension polymerization process, and the obtained resin has good strength, high water absorption speed and narrow particle size distribution, wherein the particle size of 42-100 meshes can reach 99%; SAP particles having a particle size of 200-2000um can be obtained by adding a hydrophilic solvent such as alcohol to a slurry obtained by a one-phase reverse-phase suspension polymerization in Asahi chemical industry (application publication No. CN 101410419A).
How to effectively remove the reaction heat in the polymerization process and reduce the energy loss and efficiency reduction in the multi-stage polymerization process (frequent temperature rise and drop) is a difficulty limiting the large-scale industrialization of the reversed-phase suspension polymerization. Therefore, there is still a need to develop a particle size control process for preparing water-absorbent resins by reverse phase suspension polymerization with higher efficiency, lower cost and simplicity.
Disclosure of Invention
In view of the above, the main object of the present invention is to provide a method for preparing water-absorbent resin by inverse suspension polymerization, which adopts a solvent replacement method to replace the traditional severe cooling process, thereby reducing the waste of heat exchange external cold source and the requirement of heat exchange equipment; in a preferred embodiment, on one hand, a high/medium-low temperature type initiating system is adopted to reduce the initiating temperature and reduce the energy consumption required by temperature rise and temperature reduction; on the other hand, an in-situ acid-base neutralization mode is adopted, the neutralization heat temperature rise is effectively utilized, the preparation of the monomer phase is realized, the dissolution process of the dispersing agent in the oil phase is completed in an auxiliary mode, and the waste of an external heat source is reduced. In conclusion, the decrease in stability, the loss of energy consumption and the decrease in efficiency caused by the drastic temperature decrease can be avoided in the multiple polymerization, and the controllable preparation of the particle diameter of the water-absorbent resin is realized by the replacement of the solvents in different proportions.
In order to realize the purpose, the invention adopts the following technical scheme:
a method for preparing a water-absorbing compound with controllable particle size by reversed phase suspension polymerization 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;
(2) solvent replacement and particle agglomeration: filtering the first suspension to remove part or all of the oil phase solvent, adding fresh oil phase solvent, and maintaining the temperature of the system;
(3) second-stage polymerization: continuously adding a 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, wherein a dispersing agent is supplemented again before the second-stage polymerization;
(4) and (3) post-treatment: and (4) carrying out azeotropic dehydration and surface crosslinking on the second suspension, and then filtering and drying to obtain the water-absorbent resin.
Wherein the oil phase solution in the step (1) contains a dispersant and a petroleum hydrocarbon solvent (oil phase solvent);
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.
In the invention, the petroleum hydrocarbon solvent in the oil phase solution 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.
In the present invention, the dispersant described in step (1) is selected from one or more of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate and stearyl monophosphate. Preferably, the dispersant is used in an amount of 0.01 to 5%, preferably 0.5 to 3%, by mass of the water-soluble ethylenically unsaturated monomer in step (1), such as: 1.25% and 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 mass concentration of the water-soluble ethylenically unsaturated monomer in the aqueous mixture is 20 to 50%, preferably 30 to 40%, such as: 34% and 36%;
the initiator is selected from a high-temperature initiation initiator persulfate and a medium-low temperature initiation initiator water-soluble azo compound, wherein the initiator in the step (1) is preferably a mixed system of the high-temperature initiation initiator persulfate and the medium-low temperature initiation initiator 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 one or more of 2,2 '-azobisisobutylamidine dihydrochloride (AIBA) or 2,2' -azabicyclo (2-imidazolium) dihydrochloride (AIBI); the mass ratio of the high-temperature initiation initiator to the medium-low temperature initiation initiator is 1-5, such as: 1.0 and 2.0. By adopting the mixed initiator system, on one hand, initiators with different activities are reasonably matched to carry out accumulation force initiation polymerization, and the initiation temperature is reduced; and the subsequent heat transfer and heat transfer are facilitated, and the energy consumption is saved. The initiator is used in an amount of 0.005 to 5%, preferably 0.01 to 0.5%, by mass of the water-soluble ethylenically unsaturated monomer, such as: 0.15 percent and 0.2 percent;
the internal crosslinking agent is one or more of a hydroxyl-containing compound, an epoxy-containing compound or a double-bond-containing compound, 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-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, poly (hydroxymethyl) triacrylate, poly (propylene glycol) diacrylate, poly (ethylene glycol) diacrylate, poly (propylene glycol) diacrylate, poly (ethylene glycol) triacrylate, poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (propylene glycol acrylate, poly (ethylene glycol acrylate, poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (, One or more of pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate. The internal crosslinking agent is used in an amount of 0.005 to 1%, preferably 0.01 to 0.5%, based on the mass of the water-soluble ethylenically unsaturated monomer, such as: 0.04% and 0.06%.
In the present invention, in the step (1), the mixing of the aqueous phase mixture and the oil phase solution may be performed by a conventional method in the art. Preferably, however, the aqueous mixture is obtained by in situ acid-base neutralization, namely: adding water-soluble ethylenic unsaturated monomer and alkaline solution such as sodium hydroxide solution into petroleum hydrocarbon solvent containing dispersant, cooling to below 40 deg.C, and adding initiator and internal cross-linking agent. The dissolution of the dispersing agent is realized by the aid of the temperature rise caused by the neutralization heat, so that the neutralization heat is effectively utilized, and the energy waste caused by a conventional cooling mode is avoided; in some preferred embodiments, the alkaline solution, such as sodium hydroxide solution, is used in a concentration of 10 to 50% by mass, preferably 20 to 40% by mass, more preferably 21% by mass or 32% by mass.
In the present invention, in step (1), the mass ratio of the petroleum hydrocarbon solvent of the oil phase solution to the aqueous phase mixed solution (including water, water-soluble ethylenically unsaturated monomer, initiator and internal crosslinking agent) is 0.1 to 10, preferably 1 to 5, such as: 1.5 and 2.5.
In the present invention, in step (2), the solvent removal ratio is 50 to 100%, preferably 70 to 90%, from the viewpoint of ease of operation and particle size control; the amount of fresh oil phase added is 0.8-1.25 times the amount removed.
In the present invention, the mass ratio of the aqueous phase mixed liquid added in step (3) and step (1) can be controlled between 0.5 and 5, and from the viewpoint of improving production efficiency and controlling effective particle size, more preferably 1 to 2, such as: 1.2 and 1.6.
In the invention, in the step (3), because the dispersant is also partially removed when the solvent is removed in the previous step, the dispersant is supplemented again before the second-stage polymerization, and the proportion of the added dispersant is 60-150 percent, preferably 80-120 percent of the dispersant removed by filtration.
In a specific embodiment, the 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 dosage of the added dispersant. In some preferred embodiments, the cooling temperature of the first suspension is 0-100 ℃ when the temperature of the first suspension is reduced, and is preferably 30-60 ℃ from the viewpoints of energy consumption, efficiency and prevention of polymerization and adhesion in the dispersion process, which can be conveniently realized by replacing the solvent at different temperatures according to the proportion; the stirring rate is adjusted according to the quality of multiple feeding 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 is obviously increased, such as the rotation speed of one feeding is 200rpm, the rotation speed of the second feeding is 300rpm, the rotation speed of the third feeding is 400rpm and the like. Preferably, the first stage polymerization agitation rate is 100-300rpm and the second stage polymerization agitation rate is 200-600 rpm.
The reversed-phase suspension polymerization reaction of the first stage and the second stage mentioned in the invention adopts a method known in the art, for example, in the step (1), the water-phase mixed solution and the oil-phase solution are mixed, the temperature is raised to 50-100 ℃ such as 50 ℃ and 60 ℃ under stirring, the first-stage water-in-oil reversed-phase suspension polymerization is carried out for 1-3 hours such as 1.5 hours and 2.0 hours, wherein, nitrogen can be adopted for replacement before the reaction; and (3) continuously adding the aqueous phase mixed solution into the first suspension in the step (3) by replacing the solvent and reducing the temperature to 30-60 ℃, such as 50 ℃, and repeating the steps to perform a second-stage water-in-oil reversed-phase suspension polymerization reaction to obtain the aggregation colloidal particle suspension containing second-stage polymerization.
In the step (4), the temperature of azeotropic dehydration is 90-150 ℃, and the azeotropic dehydration amount is 50-90% of the total mass of the added water; the drying temperature is 100-160 ℃, and the drying time is 0.5-3 h;
the surface cross-linking agent used for surface cross-linking is a compound that can form a covalent bond or an ionic bond with a carboxyl group: the compounds capable of forming covalent bonds include polyol compounds, epoxy compounds, and polyvalent amines such as polyethyleneimine, and preferably one or more of ethylene glycol, propylene glycol, 1, 4-butanediol, ethylene carbonate, propylene carbonate, (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, glycerol, tris (hydroxymethyl) aminomethane, and pentaerythritol; the compound capable of forming an ionic bond includes inorganic salts of polyvalent metals such as calcium, magnesium, aluminum, iron, copper, zinc, and the like. The surface-crosslinking agent is added in an amount of 0.01 to 2%, preferably 0.02 to 0.2% by mass based on the total mass of the water-soluble ethylenically unsaturated monomer.
Another object of the present invention is to provide a water-absorbent resin prepared by the above method, wherein the obtained product is in the form of an agglomerated grape bunch.
In the present invention, the water-absorbent resin product obtained by the preparation method of the present invention has a particle size distribution of 150-710. mu.m in a proportion of about 70 to 90% of the total product.
According to the invention, compared with the conventional method of cooling the suspension obtained in the first stage, the method is different from the conventional method of cooling the suspension obtained in the first stage, so that the dispersant is separated out due to the reduction of the solubility and loses the protection effect, the method adopts the oil phase removal and replacement mode to replace the high-temperature oil phase solution (dissolving most of the dispersant) in the suspension obtained in the first stage after the first-stage polymerization is finished with the new low-temperature pure oil phase without the dispersant, the concentration of the dispersant and the temperature of the system are reduced by phase change, the control of subsequent multiple feeding on the particle size is facilitated, and the single spherical particle is swelled to obtain the particle morphology of an agglomerated state. Therefore, energy waste and reduction of production stability caused by severe cooling can be avoided, and the operation efficiency and repeatability can be improved.
Compared with the prior art, the invention has the following advantages:
(1) the method adopts an in-situ acid-base neutralization mode, effectively utilizes the temperature rise of neutralization heat to realize the preparation of the monomer phase, and simultaneously assists in completing the dissolution process of the dispersing agent in the oil phase, thereby reducing the waste of neutralization heat;
(2) the invention adopts a high/medium-low temperature type initiation system to reduce the initiation temperature, reduce the energy consumption required by temperature rise and temperature reduction and improve the production efficiency;
(3) the invention adopts a solvent replacement mode, can simply and conveniently realize the continuous change of the concentration of the dispersing agent and the high-efficiency control of the system temperature, reduces the energy consumption, and can assist in completing the control of the particle size of the final product and improve the operation stability by subsequently supplementing the dispersing agent.
Drawings
FIG. 1 is an SEM photograph of a water-absorbent resin prepared in example 1.
Detailed Description
The present invention will be described in detail below with reference to specific examples.
Example 1:
6.9g of sucrose fatty acid ester (sugar-synthesizing technology, S-370) and 2000g of technical-grade n-heptane were charged into a 10L stainless polymerization vessel, and the temperature was raised to 35 ℃ by a jacket and uniformly dispersed at a stirring speed of 200rpm to obtain an oil phase for use. 600g of sodium hydroxide solution with the mass concentration of 32% and 860g of acrylic acid aqueous solution with the mass concentration of 53.5% are synchronously added into a polymerization kettle through two feed inlets according to a certain proportion, so that acid-base neutralization reaction is carried out in the polymerization kettle, and the dispersant S-370 in the oil phase is gradually dissolved and dispersed by utilizing neutralization heat. When the temperature of the system is reduced to below 40 ℃, 30g of aqueous solution containing 0.46g of potassium persulfate, 0.23g of 2,2' -azobisisobutylamidine dihydrochloride (AIBA) and 0.1g of ethylene glycol diglycidyl ether is added into the system, and the mixture is fully dissolved and mixed to obtain a first-stage mixed solution of aqueous phase solution and oil phase solution. Replacing with nitrogen gas for 30min while stirring, heating to 60 deg.C, reacting for 2h under the condition to perform a section of W/O reversed phase suspension polymerization to obtain a section of suspension containing polymerized SAP particles;
under the condition of cooling and stirring, 600g of sodium hydroxide solution with the mass concentration of 32% is dropwise added into a mixing device dissolved with 460g of acrylic acid monomer and 400g of deionized water, when the temperature is reduced to below 30 ℃, 30g of aqueous solution containing 0.69g of potassium persulfate and 0.1g of ethylene glycol diglycidyl ether is added, and after full dissolution and mixing, a two-stage aqueous phase mixed solution (the total mass is 1490g) is obtained for later use;
the first stage suspension was filtered while stirring hot to remove 1600g (80% of the initial charge) of n-heptane (containing about 4.5g of dispersant tested inside) and replaced with 1600g of n-heptane, at which time the temperature of the system was controlled at 45 ℃, the rotation speed was increased to 300rpm, the prepared second stage aqueous phase was added and stirred at this temperature for 30min to complete the particle agglomeration process. Then, adding 4.5g of sucrose fatty acid ester (from the angle of facilitating quick dispersion, a dispersing agent is dissolved in a small amount of n-heptane in advance) into the system, heating to 80 ℃, reacting for 1h under the condition, and carrying out two-stage W/O reversed-phase suspension polymerization to obtain two-stage suspension containing polymerized SAP particles with aggregation;
the temperature was further raised to 120 ℃ to remove water from the system and to allow n-heptane to reflux continuously. Then the temperature of the system is reduced to 80 ℃, 36.8g of ethylene glycol diglycidyl ether aqueous solution with the mass concentration of 2 percent is added, and the surface crosslinking is carried out for 1 hour. And finally filtering and centrifuging to obtain SAP particles with aggregation, and drying and screening to obtain a final finished product.
Example 2:
example 1 was repeated with the difference that: the n-heptane filtered off was replaced by 1800g of fresh n-heptane and the dispersant addition was 5.0 g.
Example 3:
example 1 was repeated with the difference that: the n-heptane filtered out was replaced with 2000g of fresh n-heptane, and the dispersant addition amount was 5.5g, and the two-stage aqueous phase mixture addition amount was 2085g (1.4 times as much as the two-stage aqueous phase mixture in example 1).
Example 4:
example 1 was repeated with the difference that: 1200g of n-heptane (60% of the initial charge, containing about 4.2g of dispersant inside by the test) was removed and replaced with 1400g of fresh n-heptane, and the dispersant addition was 3.0g, and the two-stage aqueous phase monomer solution addition was changed to 1190g (0.8 times that of the two-stage aqueous phase mixture in example 1).
Example 5:
example 1 was repeated with the difference that: the compound initiator in the first-stage polymerization is changed into 0.46g of potassium persulfate and 0.23g of 2,2' -aza-bis (2-imidazolium) dihydrochloride (AIBI), and sucrose fatty acid ester is replaced by octadecyl monophosphate.
Comparative example 1:
6.9g of sucrose fatty acid ester (syneresis technology, S-370) and 2000g of industrial-grade n-heptane are added into a 10L stainless steel polymerization kettle, the temperature is raised to 50 ℃, the mixture is uniformly dissolved and dispersed at the stirring speed of 200rpm, and then the temperature is lowered to 50 ℃ to obtain an oil phase for later use.
Under the condition of cooling and stirring, 1200g of sodium hydroxide solution with the mass concentration of 32% is dropwise added into a mixing device dissolved with 920g of acrylic acid monomer and 800g of deionized water, when the temperature is reduced to below 30 ℃, 60g of aqueous solution containing 1.4g of potassium persulfate and 0.1g of ethylene glycol diglycidyl ether is added, and after full dissolution and mixing, an aqueous phase mixed solution is obtained for later use.
Adding half of the prepared water phase mixed solution into the oil phase, and replacing with nitrogen for 30min while stirring. Then heating to 75 ℃, reacting for 2h under the condition for primary water-in-oil reversed-phase suspension polymerization, and obtaining primary suspension containing polymerized SAP colloidal particles.
And (3) cooling the suspension obtained in the previous stage to 25 ℃, increasing the rotating speed to 300rpm, then adding the other half of the prepared water phase mixed solution, and stirring for 30min at the temperature to finish the particle agglomeration process. And heating to 75 ℃, and continuously reacting for 2 hours under the condition to perform two-stage water-in-oil reversed-phase suspension polymerization to obtain two-stage suspension containing polymerized SAP particles with aggregation.
The temperature was further raised to 120 ℃ to remove water from the system and to allow n-heptane to reflux continuously. Then the temperature of the system is reduced to 80 ℃, 36.8g of ethylene glycol diglycidyl ether aqueous solution with the mass concentration of 2 percent is added, and the surface crosslinking is carried out for 1 hour. And finally filtering and centrifuging to obtain SAP particles with aggregation, and drying and screening to obtain a final finished product.
Comparative example 2:
comparative example 1 was repeated with the difference that: the cooling temperature of the suspension obtained in the one-stage polymerization was changed to 35 ℃.
Comparative example 3:
example 1 was repeated with the difference that: the amount of n-heptane removed by filtration was changed to 1000g (3.0 g of dispersant in the interior of the test) and replaced with 1000g of fresh n-heptane and subsequently supplemented with 3.0g of dispersant.
Comparative example 4:
example 1 was repeated with the difference that: the amount of the dispersion added after the agglomeration of the particles and before the second polymerization was changed to 2.0 g.
Comparative example 5:
the subsequent operations of example 1 were repeated except that the dispersant was not added after the agglomeration of the particles and before the second-stage polymerization, and as a result, when the temperature of the second-stage polymerization was raised to about 60 ℃, the polymerization became ineffective and the colloids became large masses 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
Figure BDA0002652709070000121
As can be seen from the examples, the solvent replacement method can be used to obtain the agglomerated water-absorbent resin with suitable particle size and distribution simply and efficiently, and the particle size can be controlled: by adjusting the proportion of dissolution replacement and supplementing a proper amount of dispersant; moreover, the purpose of temperature can be directly realized through low-temperature solvent replacement, so that the energy consumption is saved and the efficiency is improved. However, as can be seen from the comparative examples, the particle size distribution relatively close to that of the examples can be obtained only when the temperature is reduced to 25 ℃ after the completion of the first-stage polymerization, and products having the desired particle size distribution cannot be obtained unless the cooling temperature is raised, the solvent replacement ratio is lowered, or the amount of the dispersant to be added is insufficient. In addition, the invention adopts a high/medium-low temperature type initiation system to reduce the initiation temperature and reduce the energy consumption required by temperature rise and temperature reduction; on the other hand, an in-situ acid-base neutralization mode is adopted, the neutralization heat temperature rise is effectively utilized, the preparation of the monomer phase is realized, the dissolution process of the dispersing agent in the oil phase is completed in an auxiliary mode, and the waste of an external heat source is reduced.
In conclusion, the invention provides a method for preparing the water-absorbent resin with controllable particle size distribution by adopting a solvent replacement process to replace the traditional cooling temperature, adopts in-situ acid-base neutralization and adopts a high/medium-low temperature type composite initiation system, can avoid energy waste and production stability reduction caused by severe temperature reduction, and can improve the operation efficiency and the repeatability.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, and any modifications to the present invention, including equivalent substitutions and additions of various materials, are within the scope of the present invention as would be understood by a person skilled in the art. The scope of the invention is defined by the appended claims.

Claims (15)

1. A method for preparing water-absorbent resin by reversed phase suspension polymerization, which 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 while the first suspension is hot, removing 60-100% of the solvent in the first suspension, adding fresh solvent, and maintaining the temperature of the system, wherein the amount of the added fresh solvent is 0.8-1.25 times of the removal amount;
(3) and (2) secondary polymerization: continuously adding the two-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 a dispersant again before the second-stage polymerization, wherein the amount of the supplemented dispersant is 60-150% of that of the dispersant removed in the step (2);
(4) and (3) post-treatment: dehydrating and surface-crosslinking the second suspension, and then filtering and drying to obtain the agglomerated grape bunch-shaped 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; the water-soluble ethylenically unsaturated monomer is one or more of acrylic acid or a salt thereof, acrylamide or N, N-dimethylacrylamide.
2. The method of claim 1, wherein: 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; the mass ratio of the petroleum hydrocarbon solvent to the water phase mixed solution is 0.1-10;
the dispersing agent is at least one of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate and octadecyl monophosphate, and the using amount of the dispersing agent is 0.01-5% of the mass of the water-soluble ethylenic unsaturated monomer.
4. The method of claim 3, wherein: 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 amount of the dispersant is 0.5-3% of the mass of the water-soluble ethylenically unsaturated monomer.
5. The method according to any one of claims 1-2, wherein: 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 mass ratio of the high-temperature initiator to the medium-low temperature initiator is 1-5;
the amount of the initiator is 0.005-5% by mass of the water-soluble ethylenically unsaturated monomer.
6. The method of claim 5, wherein: the persulfate is one or more of sodium persulfate, potassium persulfate or ammonium persulfate; the water-soluble azo compound is 2,2 '-azobisisobutylamidine dihydrochloride (AIBA) and/or 2,2' -azabicyclo (2-imidazolium) dihydrochloride (AIBI);
the amount of the initiator is 0.01 to 0.5% by mass of the water-soluble ethylenically unsaturated monomer.
7. The method according to any one of claims 1-2, 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 using amount of the internal crosslinking agent is 0.005-1% of the mass of the water-soluble ethylenically unsaturated monomer.
8. The method of claim 7, wherein: the amount of the internal crosslinking agent is 0.01 to 0.5% by mass of the water-soluble ethylenically unsaturated monomer.
9. The method of claim 7, wherein: 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.
10. The method of claim 1, 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.
11. The method of claim 1, wherein: in the step (2), the removal ratio of the solvent is 70-90%.
12. The method of claim 1, wherein: the mass ratio of the second-stage water phase mixed solution to the first-stage water phase mixed solution is 0.5-5; the amount of the dispersant supplemented in the step (3) is 80-120% of the dispersant removed in the step (2).
13. The method of claim 12, wherein: the mass ratio of the second-stage aqueous phase mixed solution to the first-stage aqueous phase mixed solution is 1-2.
14. The method of claim 1, 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.
15. A water-absorbent resin produced by the method according to any one of claims 1 to 14, 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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