KR20190078381A - Preparation method of super absorbent polymer - Google Patents

Abstract

The present invention relates to a method for preparing a super absorbent polymer. The method for preparing a super absorbent polymer according to the present invention lowers the penetration probability of impurities in the drying step of a hydrogel polymer, facilitates control of humidity, and enables energy saving. The method comprises the steps of forming a hydrogel polymer; obtaining a dried polymer; obtaining pulverized polymer particles; and surface-crosslinking the pulverized polymer particles.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a superabsorbent resin,

The present invention relates to a method for producing a superabsorbent resin.

A super absorbent polymer (SAP) is a synthetic polymer material capable of absorbing moisture of about 500 to 1,000 times its own weight. It is also called a super absorbency material (SAM), an absorbent gel material (AGM) have.

The superabsorbent resin has begun to be put to practical use as a sanitary article and is now widely used in a variety of fields such as hygiene articles for infant diapers and the like, soil repair agents for gardening, index materials for civil engineering, seats for seedlings, freshness preservatives in the field of food distribution .

In most cases, such a superabsorbent resin is widely used in the field of sanitary materials such as diapers and sanitary napkins. For this purpose, it is necessary to exhibit a high absorption capacity for moisture and the like, In addition, there is a need to exhibit excellent permeability by keeping the form well even when the water is absorbed and expanded in volume (swollen).

In recent years, as the demand for a thin diaper increases, the proportion of the absorbent resin in the diaper tends to increase. Therefore, there is a need for the absorbent resin to combine the performance of the fiber material of the diaper. For this, the absorbent resin should have a high absorption rate as well as a high absorption rate and a liquid permeability.

In the process of producing the water absorbent resin, a process of drying the hydro gel polymer prepared by polymerizing the monomer of the water absorbent resin is required.

Drying of the hydrogel polymer is typically carried out using a hot air dryer.

For example, FIG. 1 is a schematic view showing a general drying method of hydrogel polymer using a hot-air dryer.

Referring to Fig. 1, the hydrogel polymer ( _Pw ) is dried by hot air passing through the dryer (100) and discharged into the dried polymer ( _Pd ). At this time, as the hot air, external air (A) is supplied to the heater (H) using a fan (F), and the temperature is raised to a temperature of 120 to 200 ° C. After the drying, the vapor (W _s ) generated from the hydrogel polymer (P _w ) and the wetted air (A _w ) containing the vapor (W _s ) are discharged to the outside of the dryer (100).

However, such a conventional drying method may cause various problems because the external air (A) continuously injected into the dryer (100) is an open system which is released into the wetted air (A _w ).

For example, in the drying method as shown in FIG. 1, there is a possibility that impurities penetrate with the external air supplied to the dryer 100, which may affect the physical properties of the hydrogel polymer.

The efficiency of the drying process may be influenced by wind speed, temperature, and humidity. 1, it is difficult to precisely control the humidity inside the dryer 100, so that unstable drying efficiency can be exhibited.

1, the steam (W _s ) and the wetted air (A _w ) are discharged from the dryer (100) after the drying, so that the amount of heat remaining after drying the hydrous gel polymer (P _w ) There is a problem that it is continuously lost to the outside of the dryer.

The present invention is to provide a method of manufacturing a superabsorbent resin which lowers the probability of impurity penetration in the drying step of the hydrous gel polymer, facilitates the control of humidity, and enables energy saving.

According to the present invention,

(i) thermally polymerizing or photopolymerizing a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator to form a hydrous gel polymer,

(ii) drying the hydrogel polymer in a drier to obtain a dried polymer,

(iii) pulverizing the dried polymer to form pulverized polymer particles, and

(iv) surface cross-linking the pulverized polymer particles;

The step (ii)

ii) a step of adding dry air to the hydrogel polymer passing through the dryer to recover the wetted air containing moisture evaporated in the hydrogel polymer and the dried polymer, respectively,

ii-b) feeding the recovered dried polymer to step (iii)

ii-c) supplying the recovered wet air to a heat pump system to obtain a vapor separated from the wetted air by heat exchange and phase separation, respectively, and dry air, and

ii-d) a step of supplying the dry air obtained from the heat pump system as a drying medium for the dryer

Absorbent resin. The present invention also provides a method for producing a superabsorbent resin.

Hereinafter, a method of manufacturing a superabsorbent resin according to an embodiment of the present invention will be described in detail.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. And, the singular forms used herein include plural forms unless the phrases expressly have the opposite meaning.

Means that a particular feature, region, integer, step, operation, element, or element is specified, and that any other feature, region, integer, step, operation, element, It does not exclude addition.

In this specification, terms including ordinals such as "first" and "second" are used for the purpose of distinguishing one element from another, and are not limited by the ordinal number. For example, within the scope of the present invention, a first component may also be referred to as a second component, and similarly, a second component may be named as a first component.

The term "superabsorbent resin" used in the present invention means a base resin powder comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic groups; And a surface cross-linked layer formed on the base resin powder, wherein the first cross-linked polymer comprises a second cross-linked polymer that is additionally cross-linked via a surface cross-linking agent.

On the other hand, as a result of continuous research by the inventors of the present invention, it has been found that the wet air discharged to the outside of the dryer in the drying step of the hydrogel polymer is regenerated by the dry air using the closed system heat pump system, By recycling to the drying medium it has been found that it is possible to reduce the possibility of impurities penetration and provide stable drying efficiency.

Further, in the drying step according to the present invention, steam can be incidentally obtained together with the dry air from the heat pump system, and it has been confirmed that energy can be saved in comparison with the conventional drying step.

According to one embodiment of the invention,

(i) thermally polymerizing or photopolymerizing a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator to form a hydrous gel polymer,

(ii) drying the hydrogel polymer in a drier to obtain a dried polymer,

(iii) pulverizing the dried polymer to form pulverized polymer particles, and

(iv) surface cross-linking the pulverized polymer particles;

The step (ii)

ii) a step of adding dry air to the hydrogel polymer passing through the dryer to recover the wetted air containing moisture evaporated in the hydrogel polymer and the dried polymer, respectively,

ii-b) feeding the recovered dried polymer to step (iii)

ii-c) supplying the recovered wet air to a heat pump system to obtain a vapor separated from the wetted air by heat exchange and phase separation, respectively, and dry air, and

ii-d) a step of supplying the dry air obtained from the heat pump system as a drying medium for the dryer

Absorbent resin. The present invention also provides a method for producing a superabsorbent resin.

Hereinafter, each step that can be included in the method for producing a superabsorbent resin will be described.

(i) Function gel  Step of forming polymer

The step (i) is a step of producing a hydrogel polymer. Specifically, it is a step of thermally or photopolymerizing a monomer composition containing a water-soluble ethylenically unsaturated monomer and a polymerization initiator to form a hydrous gel polymer.

The water-soluble ethylenically unsaturated monomer may be any monomer conventionally used in the production of a superabsorbent resin. Specifically, the water-soluble ethylenically unsaturated monomer may be a compound represented by the following Formula 1:

[Chemical Formula 1]

R ¹ -COOM ¹

In Formula 1,

R ¹ is an alkyl group having 2 to 5 carbon atoms containing an unsaturated bond,

M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group or an organic amine salt.

Preferably, the water-soluble ethylenically unsaturated monomer may be at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts of these acids. When acrylic acid or a salt thereof is used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a highly water-absorbent resin having improved water absorption. (Meth) acryloyl ethane sulfonic acid, 2- (meth) acryloyl propane sulfonic acid, or 2- (meth) acryloyl propane sulfonic acid. The monomer may be selected from the group consisting of maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2- Meth) acrylamide-2-methylpropanesulfonic acid and salts thereof; (Meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol Non-ionic hydrophilic-containing monomer of (meth) acrylate; And at least one member selected from the group consisting of an unsaturated monomer containing an amino group of (N, N) -dimethylaminoethyl (meth) acrylate or (N, N) -dimethylaminopropyl (meth) Can be used.

The water-soluble ethylenically unsaturated monomer has an acidic group, and at least a part of the acidic group may be neutralized. Preferably, the monomer is partially neutralized with an alkali substance such as sodium hydroxide, potassium hydroxide, ammonium hydroxide or the like.

At this time, the neutralization degree of the monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The degree of neutralization may vary depending on the final physical properties. However, if the degree of neutralization is too high, the neutralized monomer may precipitate and polymerization may not proceed smoothly. On the other hand, if the degree of neutralization is too low, It can exhibit properties similar to elastic rubber which is difficult to handle.

The monomer composition may include a polymerization initiator generally used in the production of a superabsorbent resin.

As the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator may be used depending on the polymerization method. However, even with the photopolymerization method, a certain amount of heat is generated by ultraviolet irradiation or the like, and a certain amount of heat is generated as the polymerization reaction, which is an exothermic reaction, proceeds, so that a thermal polymerization initiator may further be included.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal ( Benzyl dimethyl ketal, acyl phosphine, and a-aminoketone may be used. As a specific example of the acylphosphine, a commonly used lucyrin TPO, i.e., 2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide can be used . For a broader range of photopolymerization initiators, see Reinhold Schwalm, "UV Coatings: Basics, Recent Developments and New Application (Elsevier, 2007)

As the thermal polymerization initiator, at least one compound selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specific examples of persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ ), and the like. Azo-based initiators include 2,2-azobis (2-amidinopropane) dihydrochloride, 2,2-azobis- (N, N-dimethylene isobutyramidine dihydrochloride, 2- (carbamoylazo) isobutylonitrile, 2,2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride, Azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride), 4,2-diazabicyclo [ 4-azobis- (4-cyanovaleric acid), and the like. More thermal polymerization initiators are described in the Odian book, " Principle of Polymerization (Wiley, 1981), " page 203, which is incorporated herein by reference.

Such a polymerization initiator may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, if the concentration of the polymerization initiator is too low, the polymerization rate may be slowed and the remaining monomer may be extracted in the final product in a large amount, which is not preferable. On the contrary, when the concentration of the polymerization initiator is too high, the chain of the polymer forming the network is shortened, and the physical properties of the resin may be lowered, such that the content of the water-soluble component is increased and the pressure absorption capacity is lowered.

On the other hand, the polymerization of the monomer composition is carried out in the presence of a crosslinking agent (so-called "internal crosslinking agent") in order to improve the physical properties of the resin by polymerization of the water-soluble ethylenically unsaturated monomer. The cross-linking agent is for cross-linking the hydrogel polymer, and can be used separately from the "surface cross-linking agent"

As the internal crosslinking agent, any compound can be used as long as it allows introduction of crosslinking in the polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent may be selected from the group consisting of N, N'-methylenebisacrylamide, trimethylolpropane tri (meth) acrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) (Meth) acrylate, diethylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, butylene glycol di (meth) acrylate, (Meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, dipentaerythritol pentaacrylate, glycerin tri , Pentaerythritol tetraacrylate, triallylamine, allyl (meth) acrylate, ethylene glycol di Receiving ether, a multifunctional crosslinking agent, such as propylene glycol, glycerin, or ethylene carbonate can be used in combination than alone or two.

Such an internal cross-linking agent may be added at a concentration of about 0.001 to 1% by weight based on the monomer composition. That is, when the concentration of the internal cross-linking agent is too low, the absorption rate of the resin may be lowered and the gel strength may be weakened. On the other hand, if the concentration of the internal cross-linking agent is too high, the absorption power of the resin may be lowered, which may be undesirable as an absorber.

On the other hand, the crosslinking polymerization of the monomer composition can be carried out in the presence of a foaming agent. The foaming agent may form pores by decomposition upon polymerization and crosslinking reaction of step 1).

Non-limiting examples of the foaming agent include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, calcium bicarbonate, calcium carbonate (calcium carbonate), calcium carbonate bicarbonate, magnesium bicarbonate, magnesium carbonate, azodicarbonamide (ADCA), dinitroso pentamethylene tetramine (DPT), p, p'-oxybis (Benzenesulfonyl hydrazide, OBSH), p-toluenesulfonyl hydrazide (TSH), sucrose stearate, water May include one or more compounds selected from the group consisting of sucrose palmitate, sucrose laurate, The.

The foaming agent is preferably present in the monomer composition at a concentration of 1000 to 3000 ppm during the step (i). Specifically, the foaming agent may be added to the monomer composition in an amount of 1000 ppm or more, or 1100 ppm or more, or 1200 ppm or more; And 3000 ppm or less, or 2500 ppm or less, or 2000 ppm or less.

In addition, the monomer composition may further contain additives such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

Such a monomer composition may be prepared in the form of a solution in which a raw material such as the above-mentioned water-soluble ethylenically unsaturated monomer, a polymerization initiator, an internal cross-linking agent, a foaming agent, etc. is dissolved in a solvent.

At this time, usable solvents may be used without limitation of the constitution as long as they can dissolve the above-mentioned raw materials. Examples of the solvent include water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate Methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, N, N-dimethylacetamide, or a mixture thereof.

The formation of the hydrogel polymer through polymerization of the monomer composition can be carried out by a conventional polymerization method, and the process is not particularly limited.

As a non-limiting example, the polymerization method is divided into thermal polymerization and photopolymerization depending on the type of polymerization energy source. In the case of conducting the thermal polymerization, the polymerization may proceed in a reactor having a stirring axis such as a kneader, It is possible to proceed in a reactor equipped with a movable conveyor belt.

For example, the hydrogel polymer can be obtained by charging the monomer composition into a reactor such as a kneader equipped with a stirring shaft, supplying hot air thereto, or heating the reactor by heating. At this time, the hydrogel polymer discharged to the reactor outlet depending on the shape of the stirring shaft provided in the reactor can be obtained as particles of several millimeters to several centimeters. Specifically, the hydrogel polymer to be obtained can be obtained in various forms depending on the concentration and the injection rate of the monomer composition to be injected, and a hydrogel polymer having a particle diameter of 2 to 50 mm (weight average) can be obtained.

And, as another example, a hydrogel polymer in the form of a sheet can be obtained when photopolymerization is carried out on the monomer composition in a reactor equipped with a movable conveyor belt. At this time, the thickness of the sheet may vary depending on the concentration and the injection rate of the monomer composition to be injected. In general, the thickness of the sheet is adjusted to 0.5 to 10 cm in order to ensure uniform polymerization of the entire sheet, desirable.

The hydrogel polymer formed in such a manner can exhibit a water content of 40 to 80% by weight.

Here, the water content may be the weight of water in the total weight of the hydrogel polymer, which is the weight of the hydrogel polymer minus the weight of the polymer in the dry state. Specifically, it can be defined as a value calculated by measuring weight loss due to moisture evaporation in the polymer in the process of raising the temperature of the polymer through infrared heating. In this case, the drying condition may be set to a temperature of from about 180 ° C to about 180 ° C, and then maintained at 180 ° C. The total drying time may be set to 20 minutes including 5 minutes of the temperature rising step.

(ii) drying step

The step (ii) is a step of drying the hydrogel polymer in a dryer to obtain a dried polymer.

At this time, prior to carrying out the step (ii), it may be necessary to further crush the so-called hydrogel polymer (so-called "coarse pulverization") to increase the efficiency of the drying.

As a non-limiting example, the pulverizers usable for the above coarse grinding include a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutter mill, Examples thereof include a cutter mill, a disc mill, a shred crusher, a crusher, a chopper, and a disc cutter.

At this time, the coarse pulverization may be performed such that the diameter of the hydrogel polymer is 1 to 10 mm. That is, in order to increase the drying efficiency, the hydrogel polymer is preferably pulverized into particles of 10 mm or less. However, since excessive agglomeration may occur during pulverization, the hydrogel polymer is preferably pulverized into particles of 1 mm or more.

And, when the coarse pulverization step is performed before the drying step of the hydrous gel polymer, the polymer may have a phenomenon that the polymer sticks to the surface of the pulverizer because the water content is high. In order to minimize such a phenomenon, the crude pulverization step may include, if necessary, steam, water, a surfactant, an anti-flocculation inhibitor such as clay or silica; A crosslinking agent comprising a hydroxyl group-containing initiator, an azo-based initiator, an azo-based initiator, hydrogen peroxide and a thermal polymerization initiator such as ascorbic acid, an epoxy crosslinking agent, a diol crosslinking agent, an acrylate of a bifunctional group or a polyfunctional group having three or more functional groups, A crosslinking agent such as a compound of a monofunctional group may be added.

On the other hand, the drying of the functional gel polymer immediately after the above coarse pulverization or polymerization may be carried out at a temperature of 120 to 250 ° C, or 150 to 200 ° C, or 160 to 180 ° C. The temperature can be defined as the temperature of the drying medium supplied for drying or the temperature inside the drying reactor comprising the drying medium and the polymer in the drying process.

That is, if the drying temperature is low and the drying time is long, the physical properties of the final resin may be deteriorated. Therefore, the drying temperature is preferably 120 ° C or higher.

However, when the drying temperature is too high, only the surface of the hydrogel polymer is dried, and the amount of the fine powder generated in the subsequent milling step may become large, and the physical properties of the final resin may be deteriorated. Therefore, the drying temperature is preferably 250 DEG C or less.

The drying time in the drying step is not particularly limited. However, considering the process efficiency, the drying can be adjusted to 20 to 90 minutes under the temperature range.

In particular, according to an embodiment of the invention,

ii) a step of adding dry air to the hydrogel polymer passing through the dryer to recover the wetted air containing moisture evaporated in the hydrogel polymer and the dried polymer, respectively,

ii-b) feeding the recovered dried polymer to step (iii)

ii-c) supplying the recovered wet air to a heat pump system to obtain a vapor separated from the wetted air by heat exchange and phase separation, respectively, and dry air, and

ii-d) a step of supplying the dry air obtained from the heat pump system as a drying medium for the dryer

.

2 is a schematic view showing a drying method of the hydrogel polymer according to an embodiment of the present invention.

When Fig. 2, the dryer 100, the hydrogel polymer (P _w), wet air containing the moisture evaporated from the hydrogel polymer (P _w) was added to dry air (A _d) on (A passing through the _w ) and the dried polymer (P _d ), respectively.

The dried polymer (P _d ) recovered in the dryer (100) is fed to the subsequent step (iii).

The wet air A _w recovered in the dryer 100 is supplied to the heat pump system 200. In the heat pump system 200, the humid air A _w is recovered by the heat exchange and the phase separation, respectively, into the vapor W _s and dry air A _d separated from the humid air A _w .

The dry air A _d obtained from the heat pump system 200 is supplied as a drying medium for the dryer 100.

According to an embodiment of the invention, the dryer 100 may be a hot air dryer with a circulating conveyor belt.

The hydrogel polymer (P _w ) may be conveyed on the circulating conveyor belt provided in the dryer (100) and dried.

According to an embodiment of the invention, the heat pump system 200 interconnected with the dryer 100 regenerates the wet air A _w discharged from the dryer 100 into the dry air A _d , To form a closed system.

The drying step using the dryer 100 and the heat pump system 200 can reduce the possibility of impurities permeating from the outside and prevent the deterioration of physical properties of the hydrogel polymer due to impurities in the drying process. In addition, in the drying step, the humidity inside the dryer 100 can be precisely controlled, and more stable drying efficiency can be provided.

In addition, in the heat pump system 200, the steam W _s can be obtained incidentally together with the dried air A _d . The obtained steam (W _s ) can be used as an energy source in another process for producing a superabsorbent resin. That is, in the method of manufacturing a superabsorbent resin according to the embodiment of the present invention, facility investment for providing the heat pump system 200 is required. However, in terms of overall process operation, advantages Respectively.

On the other hand, the heat pump system 200 to play a humid air (A _w) discharged from the dryer 100 in the dry air (A _d) and recycled to the dryer 100, the steam (W _s) in the process, Can be obtained.

Specifically, the heat pump system 200 is configured such that,

A first heat exchanger E ₁ for condensing the humid air A _w by heat exchange between the humid air A _w supplied to the heat pump system and the refrigerant,

A separator S for phase-separating the condensate of the wetted air A _w supplied from the first heat exchanger E ₁ into air and water,

A compressor (C) for compressing the refrigerant that has passed through the first heat exchanger (E ₁ )

A second heat exchanger E ₂ for discharging the dry air A _d by heat exchange between the air supplied from the separator S and the refrigerant supplied from the compressor C,

A third heat exchanger E ₃ for discharging the steam W _s by heat exchange between the water supplied from the separator S and the refrigerant supplied from the second heat exchanger E ₂ ,

The expansion valve (V) to the third heat exchanger to expand the refrigerant passing through the (E _3), and

A cooler R for cooling the refrigerant passing through the expansion valve V and supplying the cooled refrigerant to the first heat exchanger E ₁ ,

Lt; RTI ID = 0.0 > a < / RTI >

FIG. 3 is a schematic view illustrating a method of drying a hydrogel polymer according to another embodiment of the present invention, in particular, a heat pump system 200 is embodied.

Referring to FIG. 3, the wet air A _w discharged from the dryer 100 is supplied to the first heat exchanger E ₁ . The said wet air (A _w) is the first heat exchanger and (E ₁₎ rapidly cooled by heat exchange with the refrigerant in, the moisture contained in the air (A _w) of wet in the process is condensed.

The condensate of the wetted air (Aw) is supplied to a separator (S) and separated into air and water by gas-liquid phase separation.

And, while passing through the first heat exchanger (E ₁₎ by the refrigerant absorbing the heat of the wet air (A _w) is compressed to a high temperature even in the compressor (C).

On the other hand, the gas (air) separated in the separator S is supplied to the second heat exchanger E ₂ and heated by heat exchange with the refrigerant compressed and supplied by the compressor C. The gas (air) heated to a sufficient temperature in the second heat exchanger E ₂ is discharged as the dry air (A _d ) which is the drying medium of the dryer 100.

Then, the liquid (water), the phase separation in the separator (S) is being fed to the third heat exchanger (E _3), it is first heated by heat exchange with the heat exchanger 2 through the supply (E ₂₎ refrigerant. The liquid (water) heated to a sufficient temperature in the third heat exchanger E ₃ is discharged as steam W _s .

The refrigerant having passed through the third heat exchanger (E ₃ ) is expanded in the expansion valve (V). The expanded refrigerant is cooled in the cooler R and supplied to the first heat exchanger E ₁ .

As described above, in the heat pump system 200, evaporation, compression, condensation, and expansion of the refrigerant are repeated, and in the course of the heat exchange between the humidified air A _w and the separated air and water is performed.

On the other hand, the dried air (A _d ) supplied to the dryer 100 in the drying step has a temperature of 120 ° C or more, 120 to 250 ° C, 150 to 200 ° C, or 160 to 180 ° C, .

The wet air A _w recovered in the dryer 100 has a temperature of less than 120 캜, 119.9 캜 or 119.5 캜 to ensure condensation efficiency in the heat pump system 200 Do.

And, such drying is preferably performed so that the dried polymer has a water content of 0.1 to 10% by weight. That is, when the water content of the dried polymer is less than 0.1% by weight, an increase in manufacturing cost due to excessive drying and degradation of the cross-linking polymer may occur, which is not preferable. If the water content of the dried polymer exceeds 10% by weight, defects may occur in the subsequent process, which is undesirable.

(iii) Grinding step

The step (iii) is a step for pulverizing the dried polymer obtained in the step (ii), and is a step for optimizing the surface area. The pulverization may be carried out such that the particle size of the pulverized polymer is 150 to 850 mu m.

The pulverizer may be a conventional pulverizer such as a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, .

Further, in order to control the physical properties of the superabsorbent resin to be finally produced, the step of selectively classifying the particles having a particle diameter of 150 to 850 mu m in the polymer particles obtained through the above-mentioned pulverization step may be further performed.

(iv) surface cross-linking step

The step (iv) is a step of surface-modifying the pulverized polymer obtained in the step (iii).

The surface modification induces a crosslinking reaction on the surface of the pulverized polymer in the presence of a second crosslinking agent (surface crosslinking agent). Through such surface modification, a surface modifying layer (surface crosslinking layer) is formed on the surface of the pulverized polymer particles .

The surface modification may be carried out by a conventional method for increasing the cross-linking density of the polymer particle surface. For example, a method of mixing a solution containing a second cross-linking agent (surface cross-linking agent) Lt; / RTI >

The second crosslinking agent is a compound capable of reacting with a functional group contained in the polymer, and is preferably an alkylene carbonate having 2 to 5 carbon atoms. More preferably, ethylene carbonate may be used as the second crosslinking agent. In addition to the second crosslinking agent, it may further include porous silica or clay. In order to control the penetration speed and depth of the second crosslinking agent, an acidic compound or a polymer may be further added if necessary.

At this time, the content of the second crosslinking agent may be appropriately controlled according to the kind of crosslinking agent, reaction conditions, etc., and preferably 0.001 to 5 parts by weight based on 100 parts by weight of the pulverized polymer. If the content of the second crosslinking agent is too low, surface modification may not be performed properly and the physical properties of the final resin may be deteriorated. On the contrary, if an excess amount of the second crosslinking agent is used, the absorption force of the resin may be lowered due to excessive surface crosslinking reaction, which is not preferable.

On the other hand, the surface modification step may include a method in which the second crosslinking agent and the pulverized polymer are mixed in a reaction tank, a method in which a second crosslinking agent is injected into the pulverized polymer, a method in which a pulverized polymer and a second crosslinking agent And then the mixture is continuously supplied and mixed.

Further, when adding the second crosslinking agent, water may be added additionally. Thus, the addition of the second crosslinking agent and water together can induce an even dispersion of the second crosslinking agent, prevent the aggregation of the polymer particles, and further optimize the penetration depth of the second crosslinking agent to the polymer particles. In consideration of this purpose and effect, the content of water to be added together with the second crosslinking agent may be adjusted to 0.5 to 10 parts by weight based on 100 parts by weight of the pulverized polymer.

The surface modification step may be performed at a temperature of 100 to 250 ° C. The surface modification may be carried out for 1 minute to 120 minutes, preferably 1 minute to 100 minutes, more preferably 10 minutes to 80 minutes. That is, the surface modification step may be performed under the above-described conditions in order to prevent the polymer particles from being damaged due to excessive reaction while inducing minimal surface cross-linking reaction.

The method of producing a superabsorbent resin according to the present invention lowers the probability of impurities penetration in the drying step of the hydrous gel polymer, facilitates control of humidity, and enables energy saving.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing a general drying method of hydrogel polymer using a hot-air dryer. FIG.
2 is a schematic view showing a drying method of the hydrogel polymer according to an embodiment of the present invention.
3 is a schematic view showing a drying method of the hydrogel polymer according to another embodiment of the present invention.

Best Mode for Carrying Out the Invention Hereinafter, preferred embodiments are shown to facilitate understanding of the present invention. However, the following examples are intended to illustrate the present invention without limiting it thereto.

Example  One

- Step (i) -

0.4 part by weight of polyethylene glycol diacrylate (weight average molecular weight: ~ 500 g / mol), 0.1 part by weight of hexanediol diacrylate and 0.01 part by weight of IRGACURE 819 as a photoinitiator were mixed with 100 parts by weight of acrylic acid as an internal cross- . Subsequently, 160 parts by weight of a 24 wt% aqueous solution of sodium hydroxide was continuously mixed by line mixing while continuously supplying the monomer solution by a metering pump to prepare a monomer aqueous solution. At this time, it was confirmed by the neutralizing heat that the temperature of the aqueous monomer solution rose to about 72 캜 or more, and then the temperature was allowed to cool to 40 캜.

When the temperature was cooled to 40 캜, sodium bicarbonate as a foaming agent was added to the monomer aqueous solution at 2000 ppm, and at the same time, 6 parts by weight of a 2 wt% sodium persulfate aqueous solution was added.

The solution was poured into a Vat-shaped tray (15 cm wide by 15 cm long and 15 cm wide) equipped with a light irradiation device and placed inside a square polymerization reactor preheated at 80 ° C, and light irradiation was performed to initiate light irradiation. After about 25 seconds from the light irradiation, it was confirmed that the gel was generated from the surface and polymerization reaction occurred simultaneously with the foaming after about 50 seconds. Further, the reaction product was reacted for 3 minutes to obtain a hydrogel polymer having a sheet form (water content of 50% by weight).

- step (ii) -

The hydrogel polymer of the sheet form obtained in the above step (i) was cut into a size of 3 cm x 3 cm and then placed in a Meat Chopper (manufactured by SL, mesh hole diameter 10 mm) And chopped.

The pulverized hydrogel polymer was dried in an apparatus having a dryer 100 and a heat pump system 200 of the configuration shown in Fig.

The dryer (100) is equipped with a circulating conveyor belt capable of airflow transfer up and down. The pulverized hydrogel polymer ( _Pw ) was spread on the circulating conveyor belt of the dryer 100 to a thickness of about 30 mm and dried air (A _d ) at 160 ° C was flowed downward for 15 minutes, (Flow rate of dry air (A _d ) at a flow rate of 40,000 kg / hr).

The dried polymer (P _d ) (moisture content 0.2 wt%) recovered in the dryer 100 was transferred to the subsequent step (iii).

The hydrogel polymer by a wet containing evaporated water air (A _w) is the flow rate of the temperature, and 40,000 kg / hr of 119.5 ℃ is withdrawn from dryer 100 groups the first heat exchange of the heat pump system 200 ( E ₁ ).

In the heat pump system 200, the refrigerant (R-22) circulated at a flow rate of 110,000 kg / hr. The refrigerant was supplied to the first heat exchanger E ₁ at a temperature of -42 ° C and heat exchange with the humid air A _w supplied to the first heat exchanger E ₁ was performed. The moisture contained in the air (Aw) wetted by the heat exchange was condensed and separated into air and water by the gas-liquid phase separation in the separator (S).

First refrigerant has absorbed the thermal energy of the wet while passing through the heat exchanger (E ₁₎ air (A _w) was compressed at a high temperature in the compressor (C).

The air phase-separated from the separator S was supplied to the second heat exchanger E ₂ and heated by heat exchange with the refrigerant compressed and supplied at a high temperature in the compressor C. The air heated to a temperature of 160 ° C was discharged from the second heat exchanger E ₂ and supplied to the dry air A _d , which is the drying medium of the dryer 100.

The water phase separated in the separator S was supplied to the third heat exchanger E ₃ and heated by heat exchange with the refrigerant supplied through the second heat exchanger E ₂ . The heated water is the third heat exchanger (E ₃₎ steam (W _s) was recovered in a (steam (recovered flow rate 9200 kg / hr of W _s); generating energy equivalent to 6705 kW).

The refrigerant that has passed through the third heat exchanger E ₃ is expanded in the expansion valve V and then condensed in the cooler R and supplied to the first heat exchanger E ₁ at a temperature of -42 ° C.

The operation of the dryer 100 and the heat pump system 200 consumed 6311 kW of energy.

- Step (iii) -

The dried polymer (P _d ) obtained in the above step (ii) was pulverized by a pulverizer and classified with a standard mesh of ASTM standard to obtain base resin particles having a particle size of 150 to 850 탆.

- Step (iv) -

100 parts by weight of the base resin particles obtained in the above step (iii) were mixed with a crosslinking agent solution in which 3 parts by weight of water, 3 parts by weight of methanol and 0.5 part by weight of ethylene carbonate were mixed, and then surface cross-linking reaction was carried out at 180 ° C for 40 minutes. Then, the obtained product was cooled and classified to obtain surface-crosslinked superabsorbent resin particles having a particle size of 150 to 850 mu m.

Example  2

- Step (i) -

A hydrogel polymer having a water content of 50% by weight was obtained in the same manner as in the step (i) of Example 1 above.

- step (ii) -

The hydrogel polymer of the sheet form obtained in the above step (i) was cut into a size of 3 cm x 3 cm and then placed in a Meat Chopper (manufactured by SL, mesh hole diameter 10 mm) And chopped.

The pulverized hydrogel polymer was dried in an apparatus having a dryer 100 and a heat pump system 200 of the configuration shown in Fig.

The dryer (100) is equipped with a circulating conveyor belt capable of airflow transfer up and down. The pulverized hydrogel polymer ( _Pw ) was spread on the circulating conveyor belt of the dryer 100 to a thickness of about 30 mm and dried air (A _d ) at 170 ° C was flowed downward for 15 minutes, (Flow rate of dry air (A _d ) at a flow rate of 40,000 kg / hr).

The dried polymer (P _d ) (moisture content 0.2 wt%) recovered in the dryer 100 was transferred to the subsequent step (iii).

The hydrogel polymer by a wet containing evaporated water air (A _w) is the flow rate of the temperature, and 40,000 kg / hr of 119.5 ℃ is withdrawn from dryer 100 groups the first heat exchange of the heat pump system 200 ( E ₁ ).

In the heat pump system 200, the refrigerant (R-22) circulated at a flow rate of 110,000 kg / hr. The refrigerant was supplied to the first heat exchanger E ₁ at a temperature of -42 ° C and heat exchange with the humid air A _w supplied to the first heat exchanger E ₁ was performed. The moisture contained in the air (Aw) wetted by the heat exchange was condensed and separated into air and water by the gas-liquid phase separation in the separator (S).

First refrigerant has absorbed the thermal energy of the wet while passing through the heat exchanger (E ₁₎ air (A _w) was compressed at a high temperature in the compressor (C).

The air phase-separated from the separator S was supplied to the second heat exchanger E ₂ and heated by heat exchange with the refrigerant compressed and supplied at a high temperature in the compressor C. The air heated to a temperature of 160 ° C was discharged from the second heat exchanger E ₂ and supplied to the dry air A _d , which is the drying medium of the dryer 100.

The water phase separated in the separator S was supplied to the third heat exchanger E ₃ and heated by heat exchange with the refrigerant supplied through the second heat exchanger E ₂ . The heated water is the third heat exchanger (E ₃₎ steam (W _s) was recovered in a (steam (recovered flow rate 9400 kg / hr of W _s); generating energy equivalent to 6864 kW).

The refrigerant that has passed through the third heat exchanger E ₃ is expanded in the expansion valve V and then condensed in the cooler R and supplied to the first heat exchanger E ₁ at a temperature of -42 ° C.

The operation of the dryer 100 and the heat pump system 200 as described above consumes 6545 kW of energy.

- Steps (iii) and (iv) -

Superfine resin particles having a surface diameter of 150 to 850 mu m cross-linked were obtained in the same manner as in steps (iii) and (iv) of Example 1 above.

Comparative Example

- Step (i) -

A hydrogel polymer having a water content of 50% by weight was obtained in the same manner as in the step (i) of Example 1 above.

- step (ii) -

The hydrogel polymer obtained in the above step (i) was cut into a size of 3 cm x 3 cm and then chopped so as to have a particle size of about 5 mm or less by putting it in Meat Chopper (made by SL; Respectively.

The pulverized hydrogel polymer was dried in the dryer 100 of the configuration shown in FIG.

The dryer (100) is equipped with a circulating conveyor belt capable of airflow transfer up and down. The pulverized hydrogel polymer ( _Pw ) was spread on the circulating conveyor belt of the dryer (100) to a thickness of about 30 mm, dried air at 160 캜 was flowed upward from below for 15 minutes, And the hydrogel polymer was dried (flow rate of dry air 40,000 kg / hr).

The dried air was supplied to the heater H at a flow rate of 40,000 kg / hr by heating the air to 160 ° C. by supplying air (A) from the outside to the heater (H) using a fan (F).

The dried polymer (P _d ) (moisture content 0.2 wt%) recovered in the dryer 100 was transferred to the subsequent step (iii).

The function that the wet air containing moisture evaporated from the gel polymer (A _w) was discharged from the vapor (W _s) and with temperature and 40,000 dryer 100 at a flow rate kg / hr of 119.5 ℃.

The operation of the dryer 100 as described above consumes 2603 kW of energy.

- Steps (iii) and (iv) -

Superfine resin particles having a surface diameter of 150 to 850 mu m cross-linked were obtained in the same manner as in steps (iii) and (iv) of Example 1 above.

Review

The method of manufacturing the superabsorbent resin according to the above Examples and Comparative Examples was carried out under the same conditions except that the operating method of the drying step of step (ii) was different.

In the operation of the drying process, in Example 1 (6311 kW) and Example 2 (6545 kW), a larger amount of energy was input than in the comparative example in which 2603 kW of energy was consumed.

By the way, the comparative example in the dryer 100 in the open system at a flow rate of wet air (A _w) is 40,000 kg / hr of 119.5 ℃ is degassed (vent).

Thus compared, in Example 1 and 2, to reproduce the air (A _w), wet from the heat pump system 200 in a closed system with dry air (A _d) and supplied to a drier 100, incidentally 9200 kg / hr (Example 1) and 9400 kg / hr (Example 2) steam (W _s ) can be obtained.

That is, in Examples 1 and 2, a large amount of energy was applied to the operation of the drying process in comparison with the Comparative Example, but 9200 kg / hr (energy corresponding to Example 1, 6705 kW) and 9400 kg / hr , it is possible to recover the steam (W _s) of the energy) is equivalent to 6864 kW, it is possible to use this as a new ten won (heat source), it is consequently possible to save the energy.

100: dryer
200: Heat pump system
P _w : Function gel polymer
P _d : dried polymer
A: air
F: Fan
H: Heater
A _w : wet air
A _d : Dry air
W _s : Steam
E ₁ : first heat exchanger
E ₂ : the second heat exchanger
E ₃ : third heat exchanger
S: Separator
C: Compressor
V: expansion valve
R: Cooler

Claims (5)

(i) thermally polymerizing or photopolymerizing a monomer composition comprising a water-soluble ethylenically unsaturated monomer and a polymerization initiator to form a hydrous gel polymer,
(ii) drying the hydrogel polymer in a drier to obtain a dried polymer,
(iii) pulverizing the dried polymer to form pulverized polymer particles, and
(iv) surface cross-linking the pulverized polymer particles;

The step (ii)
ii) a step of adding dry air to the hydrogel polymer passing through the dryer to recover the wetted air containing moisture evaporated in the hydrogel polymer and the dried polymer, respectively,
ii-b) feeding the recovered dried polymer to step (iii)
ii-c) supplying the recovered wet air to a heat pump system to obtain a vapor separated from the wetted air by heat exchange and phase separation, respectively, and dry air, and
ii-d) a step of supplying the dry air obtained from the heat pump system as a drying medium for the dryer
Absorbent resin.
The method according to claim 1,
The dry air supplied to the dryer has a temperature of 120 ° C or higher,
Wherein the humid air recovered in the dryer has a temperature of less than < RTI ID = 0.0 > 120 C,
A method for producing a superabsorbent resin.
The method according to claim 1,
The hydrogel polymer has a water content of from 40 to 80% by weight,
The dried polymer has a water content of from 0.1 to 10% by weight,
Is a method for producing a superabsorbent resin.
The method according to claim 1,
The dryer comprises a circulating conveyor belt,
The hydrogel polymer is conveyed on the circulating conveyor belt and dried,
A method for producing a superabsorbent resin.
The method according to claim 1,
In the heat pump system,
A first heat exchanger E ₁ for condensing the humid air A _w by heat exchange between the humid air A _w supplied to the heat pump system and the refrigerant,
A separator S for phase-separating the condensate of the wetted air A _w supplied from the first heat exchanger E ₁ into air and water,
A compressor (C) for compressing the refrigerant that has passed through the first heat exchanger (E ₁ )
A second heat exchanger E ₂ for discharging the dry air A _d by heat exchange between the air supplied from the separator S and the refrigerant supplied from the compressor C,
A third heat exchanger E ₃ for discharging the steam W _s by heat exchange between the water supplied from the separator S and the refrigerant supplied from the second heat exchanger E ₂ ,
The expansion valve (V) to the third heat exchanger to expand the refrigerant passing through the (E _3), and
A cooler R for cooling the refrigerant passing through the expansion valve V and supplying the cooled refrigerant to the first heat exchanger E ₁ ,
Wherein the water-absorbing resin is a water-absorbent resin.

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