CN112876702B

CN112876702B - One-step polymerization method for preparing super absorbent resin and preparation method thereof

Info

Publication number: CN112876702B
Application number: CN202110067090.6A
Authority: CN
Inventors: 王晓; 丁明强; 马吉全; 郝超; 姜云翔; 马磊; 纪学顺; 孙家宽
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2021-01-19
Filing date: 2021-01-19
Publication date: 2022-07-12
Anticipated expiration: 2041-01-19
Also published as: CN112876702A

Abstract

The invention discloses a one-step polymerization method for preparing super absorbent resin and a preparation method thereof. Comprises the following steps: a) and one-step polymerization: mixing a water phase containing a monomer and an oil phase, and initiating polymerization to obtain a one-step polymerization suspension; b) and particle agglomeration: adding the polyacrylate emulsion into the step a) under the stirring state to realize particle agglomeration; c) and post-treatment: and (3) performing azeotropic dehydration and surface crosslinking on the system after the particles are agglomerated, separating an oil phase from the obtained super absorbent resin in a filtering mode, and drying to obtain the product. Two-stage feeding polymerization is not needed, frequent temperature rise and drop can be effectively avoided, the production efficiency is effectively improved, and the energy consumption is reduced. Can be used in the field of health care.

Description

One-step polymerization method for preparing super absorbent resin and preparation method thereof

Technical Field

The invention relates to the field of preparation of super absorbent resin, in particular to a method for preparing super absorbent resin by a one-step polymerization method based on an inverse suspension process.

Background

Super Absorbent Polymer (SAP), which is a crosslinked polymer compound having very strong water absorption and retention capacity, is a synthetic polymer material capable of absorbing about 500 to about 1000 times its own weight of water, and can be widely used in sanitary products, such as diapers for children, feminine hygiene products, adult diapers, and the like. In the future, as the trend of global aging is further enhanced, the market demand thereof has a large space.

The current manufacturing processes of the SAP are roughly divided into two types, wherein about 95 percent of the SAP is prepared by adopting an aqueous solution polymerization process, and the other about 5 percent of the SAP is prepared by adopting an inverse suspension process. Although the current production occupancy of the reversed phase suspension process is low, the water-absorbent resin prepared by reversed phase suspension polymerization forms a unique competitive advantage in the domestic composite core 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 conventional reverse phase suspension polymerization is usually smaller (less than 150 microns), which can not meet the requirement of the water-absorbent resin in the field of physiological hygiene (150-850 microns, preferably 150-710 microns), so that the particle size needs to be further enlarged. CN101410419A SAP particles with particle size of 200-2000um can be obtained by adding hydrophilic solvent such as alcohol into the slurry obtained by phase one-step reverse suspension polymerization. The process is complicated and includes polymerization, coagulation, fusion, recovery, drying and heating. The solid content cannot be improved by using a solvent, the particle size stability also has a problem due to the compatibility of alcohol solvent bonding, and the particle size distribution of SAP particles is wide. CN1053796A discloses that polymerization by adding monomer solution twice can further increase the particle size obtained by the first polymerization to the required range in the hygiene field, but before the second polymerization, the system needs to be cooled to make the dispersant of the system ineffective, thereby realizing the process of adhering the droplets added twice to a section of polymerized particles and realizing the particle size growth. However, frequent temperature reduction and rise can have extremely high requirements on equipment, and meanwhile, the production energy consumption is huge and the economical efficiency is poor.

Therefore, the development of a simple and low-energy-consumption preparation method of the super absorbent resin and the realization of more focusing the particle size of the product in a desired particle size range become the focus of the invention.

Disclosure of Invention

The invention provides a one-step polymerization method for preparing super absorbent resin and a preparation method thereof. The preparation of the super absorbent resin is realized through one-step polymerization of reversed-phase suspension, the polyacrylate emulsion with excellent compatibility with the super absorbent resin is used for adhesion, two-stage feeding polymerization is not needed, frequent temperature rise and fall can be effectively avoided, the production efficiency is effectively improved, and the energy consumption is reduced.

In order to achieve the above purpose, the invention provides the following technical scheme:

the method for preparing the super absorbent resin by the one-step polymerization method comprises the following steps:

a) and one-step polymerization: mixing a water phase containing a monomer and an oil phase, and initiating polymerization to obtain a one-step polymerization suspension;

b) and particle agglomeration: adding the polyacrylate emulsion into the step a) under the stirring state to realize particle agglomeration;

c) and post-treatment: and (3) performing azeotropic dehydration and surface crosslinking on the system after the particles are agglomerated, separating an oil phase from the obtained super absorbent resin in a filtering mode, and drying to obtain the product.

The oil phase in step a) of the present invention comprises a hydrocarbon solvent and a dispersant useful for dispersion of the aqueous monomer solution.

The aqueous phase in step a) of the present invention comprises water, water-soluble ethylenically unsaturated monomers and salts thereof, an initiator and an internal cross-linking agent.

The hydrocarbon solvent can be 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 dispersing agent is selected from one or more of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate and octadecyl monophosphate.

The dispersants of the invention are used in an amount of from 0.02 to 5%, preferably from 0.5 to 3%, by mass of the water-soluble ethylenically unsaturated monomers in step a), such as: 1% and 2%.

In the invention, the water-soluble ethylenically unsaturated monomer is one or more of acrylic acid and salts thereof, acrylamide or N, N-dimethylacrylamide.

The mass concentration of the monomers in the aqueous phase according to the invention is 25 to 50%, preferably 30 to 40%, such as 32%, 34%, 36%.

In some embodiments, the initiator is preferably a thermal initiator, and may be one or more of sodium persulfate, potassium persulfate, or ammonium persulfate, and may also be one or more of a water-soluble azo compound such as 2,2 '-azobisisobutylamidine dihydrochloride (AIBA) or 2,2' -azabis (2-imidazolium) dihydrochloride (AIBI).

The initiators described in the present invention are used in an amount of 0.01 to 1%, preferably 0.05 to 0.2% by mass of the water-soluble ethylenically unsaturated monomers.

In some embodiments, the internal crosslinking agent may be a multifunctional compound containing double bonds or epoxy groups, and the multifunctional compound containing double bonds 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, dipentaerythritol hexaacrylate; the multifunctional compound containing the epoxy group is one or more of ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, 1, 6-hexanediol diglycidyl ether and allyl glycidyl ether.

The internal crosslinking agents of the present invention are used in an amount of 0.01 to 1%, such as 0.05%, 0.08% by mass of the water-soluble ethylenically unsaturated monomer.

The polyacrylate emulsion has Tg of-50 deg.c to 30 deg.c and solid content of 30-50%. Preferably, the polyacrylate emulsion has a Tg of-15 ℃ to 10 ℃ and a solid content of 35-45%.

The stirring speed for the particle agglomeration in the step b) of the invention is 300-600 rpm.

In step b) of the present invention, the resin of the polyacrylate emulsion accounts for 1-10% by mass of the one-step polymerization suspension, preferably 2-5%, such as 3% or 4%.

The preparation method of the polyacrylate emulsion comprises the following steps:

(1) adding sodium dodecyl sulfate and water into a reaction kettle, starting stirring and heating, and heating to 85 ℃;

(2) uniformly mixing sodium dodecyl sulfate, water, butyl acrylate, methyl methacrylate and acrylic acid to prepare a pre-emulsion;

(3) and (3) dropwise adding the pre-emulsion and initiator ammonium persulfate into the reaction kettle for 3-5 h. (ii) a Preserving the heat for 0.5-2h after the dropwise adding is finished;

(4) the temperature of the system is reduced to below 45 ℃, and the system is filtered and discharged after neutralization.

In the preparation method of the polyacrylate emulsion, the mass ratio of butyl acrylate (soft segment) to methyl methacrylate (hard segment) is 60:1-2: 1. This ensures that the Tg of the resulting polyacrylate emulsion is in the desired range, and effective bonding of the SAP polymeric particles is achieved.

The mass ratio of the using amount of the acrylic acid to the sum of the soft segment monomers is 1:60-1: 40.

In some embodiments, the agglomeration of the particles in step b) is preferably carried out by dropwise addition of the polyacrylate emulsion over a period of from 15min to 2h, preferably from 0.5 to 1 h.

The temperature of azeotropic dehydration in the step c) is 80-130 ℃, and the water removal amount is 60-85% of the total mass of the added water; the drying temperature is 100-150 ℃, and the drying time is 1-2 h.

The surface cross-linking agent used for surface cross-linking in the present invention is a compound capable of forming a covalent bond or an ionic bond with a carboxyl group: the compound capable of forming a covalent bond includes one or more of 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, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin, 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 cross-linking agent of the present invention is added in an amount of 0.01 to 0.7%, preferably 0.02 to 0.2% by mass based on the mass of the water-soluble ethylenically unsaturated monomer.

In the invention, the particles with the particle size distribution of 150-710 mu m of the prepared water-absorbent resin product account for 70-95 percent of the total product, thereby greatly meeting the requirements of the field of sanitary products on the resin particles.

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

(1) by introducing the polyacrylate emulsion with lower Tg and utilizing the adhesiveness of the polyacrylate emulsion and the compatibility of the water-absorbent resin particles, the resin particle size required by a sanitary product can be obtained by one-step polymerization.

(2) Compared with the prior art that the polymerization is carried out by adding the two-stage monomer, the high requirement of temperature rise and drop in the reaction process on equipment is avoided, meanwhile, the production energy consumption is reduced, and the production risk is reduced.

(3) The final particle size of the product can be effectively regulated and controlled by regulating and controlling the dosage of the polyacrylate emulsion with corresponding Tg, and the proportion of the particle size range within the expected range (150-710 mu m) is higher.

Detailed Description

In order that the technical features and contents of the present invention can be understood in detail, preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.

Source of raw materials

Acrylic acid, tabasheer chemical, purity more than 99.5%;

32% of caustic soda water solution with mass concentration, and Wanhua chemical of a fuming platform;

sucrose fatty acid ester (S370), syneresis, white powder;

n-heptane, Chinese medicine, purity over 99.5%;

ethylene glycol diglycidyl ether, Anhui Xin far, with purity more than 95%;

polyethylene glycol diacrylate (PEGDA), Changxing material, purity more than 95%;

sodium Persulfate (SPS), Chinese medicine, the purity is more than 99%;

the other reagents used in the examples and comparative examples of the present invention are conventional in the art and will not be described herein.

The Tg tester for the polyacrylate emulsion was a Mettler-Torledo DSC-3 instrument.

Preparation of polyacrylate emulsion 1 (solid content 30%, Tg ═ 46 ℃):

(1) adding 1g of sodium dodecyl sulfate and 1000g of water into a reaction kettle, starting stirring and heating, and heating to 85 ℃;

(2) uniformly mixing 1g of sodium dodecyl sulfate, 400g of water, 578g of butyl acrylate, 10g of methyl methacrylate (the mass ratio of the butyl acrylate to the methyl methacrylate is 57.8: 1) and 12g of acrylic acid to prepare a pre-emulsion;

(3) dropwise adding the pre-emulsion and 0.5g of initiator ammonium persulfate into the reaction kettle for 4 hours;

(4) keeping the temperature for 1h after the dropwise addition is finished;

(5) and (4) after the heat preservation is finished, reducing the temperature of the system to be below 45 ℃, and filtering and discharging after neutralization.

Preparation of polyacrylate emulsion 2 (solid content 40%, Tg ═ 9 ℃):

(1) adding 1g of sodium dodecyl sulfate and 720g of water into a reaction kettle, starting stirring and heating, and heating to 85 ℃;

(2) uniformly mixing 1g of sodium dodecyl sulfate, 180g of water, 440g of butyl acrylate, 148g of methyl methacrylate (the mass ratio of the butyl acrylate to the methyl methacrylate is 3: 1) and 12g of acrylic acid to prepare a pre-emulsion;

(4) keeping the temperature for 1h after the dropwise addition is finished;

(5) and after the heat preservation is finished, the temperature of the system is reduced to be below 45 ℃, and the system is neutralized, filtered and discharged.

Preparation of polyacrylate emulsion 3 (solid content 50%, Tg ═ 28 ℃):

(1) adding 1g of sodium dodecyl sulfate and 450g of water into a reaction kettle, starting stirring and heating, and heating to 85 ℃;

(2) uniformly mixing 1g of sodium dodecyl sulfate, 150g of water, 412g of butyl acrylate, 178g of methyl methacrylate (the mass ratio of the butyl acrylate to the methyl methacrylate is 2.3: 1) and 10g of acrylic acid to prepare a pre-emulsion;

(4) preserving the heat for 1h after the dropwise adding is finished;

Comparative example: preparation of polyacrylate emulsion 4 (solid content 40%, Tg 80 ℃):

(2) uniformly mixing 1g of sodium dodecyl sulfate, 180g of water, 50g of butyl acrylate, 538g of methyl methacrylate (the mass ratio of the butyl acrylate to the methyl methacrylate is 0.1: 1) and 12g of acrylic acid to prepare a pre-emulsion;

(4) preserving the heat for 1h after the dropwise adding is finished;

Example 1

0.7g of sucrose fatty acid ester and 180g of n-heptane were charged into a 1-L round-bottom flask and uniformly dispersed at a stirring speed of 300rpm to obtain an oil phase. 60g of sodium hydroxide solution with the mass concentration of 32% and 85g of acrylic acid aqueous solution with the mass concentration of 52% are neutralized to obtain a monomer aqueous solution, when the temperature of the neutralized solution is reduced to 40 ℃, 3g of aqueous solution containing 0.06g of sodium persulfate and 0.01g of ethylene glycol diglycidyl ether is added, and the mixture is fully dissolved and mixed to obtain a mixed solution of a water phase and an oil phase. The nitrogen was bubbled for 15min with stirring, then the temperature was raised to 70 ℃ and the reaction was carried out for 1.5h under these conditions to give a one-step polymerized SAP particle suspension.

And (3) cooling the suspension obtained by the one-step polymerization to 50 ℃, keeping stirring at 400rpm, dropwise adding 40g of polyacrylate emulsion 2 by using a peristaltic pump, keeping the dropwise adding time for 0.5 hour, and continuously stirring for 15 min.

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 ℃, 3.6g of ethylene glycol diglycidyl ether aqueous solution with the mass concentration of 2% is added, and the surface crosslinking is carried out for 1 hour. And finally filtering to obtain the SAP particles with agglomeration, and drying and screening to obtain the final finished product.

Example 2

Example 1 was repeated with the difference that: adding 30g of polyacrylate emulsion 3, dropwise adding for 15min, and keeping the stirring speed at 500 rpm.

Example 3

Example 1 was repeated with the difference that: 80g of polyacrylate emulsion 1 is added, the dropping time is 2 hours, the internal crosslinking agent is replaced by polyethylene glycol diacrylate instead of ethylene glycol diglycidyl ether, and the using amount is changed to 0.19 g.

Example 4

Example 1 was repeated with the difference that: 12g of polyacrylate emulsion 1 is added, the dropping time is 0.5h, the mass of 32 percent sodium hydroxide is adjusted to be 50g, and the adding amount of the dispersing agent is changed to be 2.2 g.

Example 5

Example 1 was repeated with the difference that: the amount of the dispersant added was changed to 0.1g, the amount of the initiator used was adjusted to 0.4g, and the amount of the 2% concentration surface-crosslinking agent used was adjusted to 1 g.

Comparative example 1

The polyacrylate emulsion was not added during particle agglomeration and the conditions were otherwise the same as in example 1.

Comparative example 2

40g of polyacrylate emulsion 4 were added during the agglomeration of the particles, the other conditions being the same as in example 1.

Comparative example 3

The polyacrylate emulsion was added at one time during particle agglomeration, and the rest of the conditions were the same as in example 1.

Comparative example 4

And (2) cooling the system to 25 ℃, adding 40g of a monomer aqueous solution obtained by neutralizing a 32% sodium hydroxide solution and 56g of a 52% acrylic acid aqueous solution in mass concentration and 2g of an aqueous solution containing 0.06g of sodium persulfate and 0.01g of ethylene glycol diglycidyl ether after the dispersant is invalid, fully stirring and agglomerating for 0.5h, blowing nitrogen, further heating to 70 ℃, continuing to initiate second-stage polymerization, and continuing to keep the temperature for 1.5h to obtain a two-stage polymerized SAP particle suspension.

The particle size distribution data of the SAP obtained above are shown in table 1:

TABLE 1 particle size distribution ratio (%) of each group of samples

Sample numbering	＞710μm	500-710μm	300-500μm	150-300μm	＜150μm
						Example 1	10.2	18.9	35.6	27.2	8.1
Example 2	14.2	25.6	28.7	20.9	10.6
						Example 3	10.3	28.9	30.2	19.8	10.8
Example 4	9.3	18.9	37.5	20.4	13.9
						Example 5	11.1	25.6	28.3	22.8	12.2
Comparative example 1	0	0	0.5	1.9	97.6
						Comparative example 2	0.2	0.3	1.1	7.9	90.5
Comparative example 3	48.5	20.2	21.8	7	2.5
						Comparative example 4	19.6	29.2	23.4	17.7	10.1

It is obvious from the particle size distribution of the samples in the examples and the comparative examples that after one-step polymerization, the added proper polyacrylate emulsion can effectively realize the growth of particles, has good adhesion effect, and can be regulated to the particle size required by the application of the high water-absorbent resin in the field of sanitary products.

The examples compare with comparative examples 1 and 2, if no polyacrylate emulsion is added, or if the added polyacrylate emulsion is "too hard", it is not favorable for the effective agglomeration and adhesion between suspended particles in one-step polymerization, and the particle size distribution is not satisfactory for use in sanitary articles.

The examples compared with comparative example 3, when the addition of a suitable polyacrylate emulsion is too fast, the local blocking is severe, and the ratio of the large particle size is too large, so that the particle size distribution ratio of 150-710 μm is too low, which is not desirable.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the spirit of the invention.

Claims

1. A method for preparing super absorbent resin by a one-step polymerization method comprises the following steps:

a) and one-step polymerization: mixing a water phase containing water-soluble ethylenically unsaturated monomers with an oil phase, and initiating polymerization to obtain a one-step polymerization suspension;

b) and particle agglomeration: dropwise adding a polyacrylate emulsion into the step a) under the stirring state to realize particle aggregation;

c) and post-treatment: carrying out azeotropic dehydration and surface crosslinking on the system after the particles are agglomerated, separating an oil phase from the obtained super absorbent resin in a filtering mode, and drying to obtain a product;

the water-soluble ethylenically unsaturated monomer is one or more of acrylic acid and salts thereof, acrylamide or N, N-dimethylacrylamide; the oil phase in step a) comprises a hydrocarbon solvent and a dispersant; the dispersing agent is selected from one or more of sucrose fatty acid ester, sorbitan monostearate, sorbitan monooleate, triglycerol monostearate and octadecyl monophosphate; the Tg of the polyacrylate emulsion is between-50 ℃ and 30 ℃, and the solid content is 30-50%.

2. The process of claim 1, wherein the aqueous phase in step a) comprises water, water-soluble ethylenically unsaturated monomers and salts thereof, an initiator, and an internal crosslinking agent.

3. The process according to claim 1, wherein the mass concentration of the monomer in the aqueous phase is 25 to 50%.

4. The process according to claim 1, wherein the monomer concentration in the aqueous phase is 30-40% by mass.

5. The process according to claim 1, wherein the dispersant is used in an amount of 0.02 to 5% by mass of the water-soluble ethylenically unsaturated monomer in step a).

6. The process according to claim 5, wherein the dispersant is used in an amount of 0.5 to 3% by mass of the water-soluble ethylenically unsaturated monomer in step a).

7. The method according to claim 2, wherein the internal cross-linking agent comprises a double bond-or epoxy group-containing multifunctional compound, and the double bond-containing multifunctional compound is one or more of ethylene glycol diacrylate, propylene glycol diacrylate, N' -methylenebisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate; the multifunctional compound containing the epoxy group is one or more of ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, 1, 6-hexanediol diglycidyl ether and allyl glycidyl ether; the amount of the internal crosslinking agent is 0.01 to 1% by mass based on the water-soluble ethylenically unsaturated monomer.

8. The method of claim 1 wherein said polyacrylate emulsion has a Tg of from-15 ℃ to 10 ℃ and a solids content of from 35 to 45%.

9. The method of claim 1, wherein in step b), the resin of the polyacrylate emulsion accounts for 1-10% of the mass of the one-step polymerization suspension.

10. The method of claim 1, wherein in step b), the resin of the polyacrylate emulsion accounts for 2-5% of the mass of the one-step polymerization suspension.

11. The method of claim 1, wherein the polyacrylate emulsion is prepared by the steps of:

(3) dropwise adding the pre-emulsion and initiator ammonium persulfate into the reaction kettle for 3-5 h; preserving the heat for 0.5-2h after the dropwise adding is finished;

(4) the temperature of the system is reduced to below 45 ℃, and the system is neutralized, filtered and discharged.

12. The method of claim 11, wherein the mass ratio of butyl acrylate to methyl methacrylate is from 60:1 to 2: 1.

13. A superabsorbent resin prepared according to the method of any one of claims 1 to 12 having particles with a particle size distribution of 150-710 μm in the range of 70 to 95% of the total product.