JP3993832B2 - Regeneration method of reaction solvent - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention mainly relates to a method for regenerating a reaction solvent in which a reaction solvent as an organic solvent is recovered from an aqueous urethane resin dispersion and regenerated.
[0002]
[Prior art and problems to be solved by the invention]
An aqueous urethane resin dispersion is obtained by polymerizing a polyol and a polyisocyanate in a reaction solvent and emulsifying (dispersing) the obtained polymerization product in water. The remaining reaction solvent has a problem of deteriorating the user's environment and is conventionally separated and removed from the dispersion and recovered.
Conventionally, as a method of recovering this type of reaction solvent, a method of evaporating and recovering the reaction solvent by heating the dispersion containing the reaction solvent under reduced pressure has been employed (see Patent Document 1, Reference). .)
[0003]
[Patent Document 1]
JP-A-5-132567 (columns [0044] to [0046])
[0004]
By the way, although the reaction solvent removed by such a method has been recovered and discarded, in recent years, it has been demanded to reuse the recovered reaction solvent due to problems such as environmental conservation.
However, in the reaction solvent recovered by such a conventional method, the basic reaction initiator used in the polymerization of urethane remains, and azeotropic water is also contained. The solvent has a problem that it is not suitable for reuse.
For example, when it is reused as a reaction solvent for polymerizing a urethane resin, it becomes difficult to control the polymerization reaction due to the remaining basic reaction initiator, and the contained water causes a side reaction with the polyisocyanate. It becomes difficult to adjust the desired urethane.
[0005]
By the way, generally, as a method of removing impurities from an organic solvent containing impurities and regenerating the organic solvent, a method of distillation or a method of gasifying the organic solvent and separating and removing the impurities with a gas separation membrane (see Patent Document 2) It has been known.
[0006]
[Patent Document 2]
Japanese Patent Laid-Open No. 2001-219025
However, as a method for regenerating the reaction solvent recovered by the above conventional method, when the method by distillation as described above is adopted, water or a basic reaction initiator is distilled together with the reaction solvent. It becomes difficult to obtain a high purity reaction solvent.
In addition, when a method of gasifying the recovered reaction solvent and separating it with a gas separation membrane is adopted, even if water can be separated and removed, the basic reaction initiator cannot be removed, and it is still sufficiently high. It becomes difficult to obtain a pure reaction solvent.
[0008]
Therefore, in view of the above-mentioned conventional problems, the present invention recovers a reaction solvent from an aqueous urethane resin dispersion and can regenerate it to a high-purity one containing almost no basic reaction initiator or water. it is an object of the present invention to provide a playback how.
[0009]
[Means for Solving the Problems]
In view of the above problems, the present invention recovers and regenerates a reaction solvent from an aqueous urethane resin dispersion in which a urethane resin polymerized by the presence of a basic initiator in the reaction solvent is dispersed in water. A method for regenerating a reaction solvent comprising:
A recovery step of evaporating and recovering the reaction solvent from the dispersion;
A neutralization step of neutralizing and fixing the basic reaction initiator contained in the recovered reaction solvent by adding an acid to the recovered reaction solvent;
A distillation step of distilling the reaction solvent that has undergone the neutralization step to distill the reaction solvent and to take out water contained in the reaction solvent;
There is provided a method for regenerating a reaction solvent, comprising a membrane separation step of separating and removing water contained in the distilled reaction solvent by a gas separation membrane.
[0010]
According to such a method, after fixing the basic reaction initiator in the neutralization step, the reaction solvent containing almost no basic reaction initiator is distilled by distilling the reaction solvent in the distillation step. Furthermore, by separating and removing the water contained in the reaction solvent in the membrane separation step, it is possible to regenerate a high-purity reaction solvent that hardly contains water.
Since the reaction solvent that has undergone the distillation step contains almost no basic reaction initiator or a fixed product (neutralized product) obtained by neutralization of the basic reaction initiator, the basic reaction initiator is gasified. There is almost no fear that it will remain on the reaction solvent side, and there is no possibility that the immobilized product or urethane resin will block the pores of the gas separation membrane.
Further, in the recovery process, there is a possibility that the polyurethane resin may be scattered and recovered together with the reaction solvent as the reaction solvent evaporates. By passing through such a distillation process, the reaction solvent contains the polyurethane resin. Therefore, the possibility that the gas separation membrane is blocked by such a polyurethane resin is also reduced.
[0011]
Here, the reaction solvent is an organic solvent used for polymerizing the urethane resin by dissolving the monomer, and the reaction solvent has a lower boiling point than water and a larger molecular weight than water.
Further, immobilization means increasing the molecular weight by neutralization, thereby increasing the boiling point and making it difficult to be distilled off, and the immobilization product means one that has been subjected to such treatment.
The basic reaction initiator is a reaction initiator that exhibits basicity and is immobilized by neutralization with an acid, and the reaction initiator has a molecular weight larger than that of water. When the basic initiator has a boiling point lower than that of water, the basic initiator is usually a substance having a boiling point higher than that of water by immobilization (neutralization).
Furthermore, the gas separation membrane is usually one that allows gaseous water to permeate but does not allow gaseous reaction solvent or basic reaction initiator to permeate.
[0012]
In the present invention, the distillation in the distillation step is preferably simple distillation.
Since the basic reaction initiator is immobilized by the neutralization step, the basic reaction initiator can be sufficiently removed by simple distillation, while the cost of the distillation step is reduced as compared with rectification. Can do.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic flow diagram showing an embodiment of a method for regenerating a reaction solvent in which the reaction solvent is recovered from an aqueous urethane resin dispersion and regenerated.
[0015]
As shown in FIG. 1, the method for regenerating a reaction solvent according to the present embodiment comprises a water-based urethane resin dispersion in which a urethane resin polymerized by the presence of a basic reaction initiator in the reaction solvent is dispersed in water. And recovering the reaction solvent by evaporating the reaction solvent from the dispersion, and adding the acid to the reaction solvent recovered in the recovery process A to thereby leave the basic reaction initiator remaining in the reaction solvent. A neutralization step B for neutralizing and immobilizing, and a distillation step C for distilling the reaction solvent that has passed through the neutralization step B to distill the reaction solvent and to take out water contained in the reaction solvent. And a membrane separation step D for separating and removing water contained in the reaction solvent distilled in the distillation step C by a gas separation membrane, and neutralizing the reaction solvent recovered in the recovery step A Regenerate through process B, distillation process C, membrane separation process D Than it is.
In this embodiment, examples of the reaction solvent include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran, acetate esters such as ethyl acetate and butyl acetate, dimethyl, and the like. Amides such as formamide can be used. Of these, ketones such as acetone and methyl ethyl ketone, and acetates such as ethyl acetate and butyl acetate are preferred.
Moreover, amines, such as a triethanolamine and a trimethanolamine, can be used as a basic reaction initiator.
[0016]
The recovery step A is a step of supplying the aqueous urethane resin dispersion into the distillation vessel 1 and recovering the reaction solvent by distilling (evaporating) it by heating and reducing the pressure inside the distillation vessel 1.
By this recovery step A, the reaction solvent is recovered in a state in which impurities such as water, a basic reaction initiator, a urethane resin, an unreacted material such as isocyanate as a component of the urethane resin, and other additives are included.
[0017]
In the neutralization step B, the reaction solvent recovered in the recovery step A is supplied to the neutralization tank 2, and an acid is supplied to the neutralization tank 2, so that a basic reaction initiator contained in the reaction solvent is added. This is a step of fixing by neutralization.
In this neutralization step B, since the reaction solvent supplied to the neutralization tank 2 contains water, the addition of an acid causes the neutralization reaction to proceed in the water. Forms a salt and is immobilized.
The acid is not particularly limited as long as it forms a salt with the basic initiator to immobilize the basic initiator, and examples thereof include inorganic acids such as sulfuric acid and hydrochloric acid, acetic acid, oxalic acid, and the like. Organic acids can be used.
[0018]
In the distillation step C, the reaction solvent containing the basic reaction initiator neutralized and immobilized in the neutralization step B is supplied to the distillation vessel 3 for simple distillation, and the reaction solvent containing water is removed. This is a step of distilling and removing the remaining water together with the immobilized basic reaction initiator. In addition, by such a distillation process, impurities, such as a urethane resin neutralized material, are taken out, and the quantity of impurities, such as a urethane resin contained in the distilled reaction solvent, is also reduced.
Therefore, by this distillation step C, the reaction solvent as the distillate contains almost no impurities other than water.
[0019]
In the membrane separation step D, the reaction solvent containing the water as the distillate in the distillation step C is gasified by heating, and sucked under reduced pressure as necessary, and only the gaseous water permeates the gas separation membrane 4. And separating from the reaction solvent.
In the present embodiment, the gas separation membrane 4 is not particularly limited as long as it is a membrane that allows water molecules to permeate and does not permeate molecules of the reaction solvent. For example, a gas separation membrane 4 that includes a hollow fiber membrane for gas separation. Can be used. Specifically, a polyimide film (manufactured by Ube Industries) or the like can be used.
[0020]
The reaction solvent separated from the water in the membrane separation step D contains almost no water and is usually liquefied and recovered by cooling.
[0021]
Examples of the water-based urethane resin dispersion to be used in the present embodiment include those in which anionic, cationic, and nonionic hydrophilic groups are introduced into the urethane resin skeleton and are self-dispersed in water, or hydrophobic. The thing etc. which are disperse | distributed in water by adding surfactant to a urethane resin can be mentioned.
In addition, as the urethane resin, a resin obtained by polymerizing polyisocyanate and polyol in a reaction solvent is usually used.
As the polyisocyanate, conventionally used aromatic, aliphatic and alicyclic polyisocyanates can be used, for example, naphthalene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, hydrogenated diphenylmethane diisocyanate, diphenylmethane. Polyisocyanates such as diisocyanate and tolylene diisocyanate can be used.
[0022]
As the polyol, known ones can be used, and compounds having two or more hydroxyl groups in the molecule such as polyether, polyester, polyether ester, polythioether, polyacetal, polybutadiene, polysiloxane and the like can be used.
Examples of the polyol include ethylene glycol, diethylene glycol, butanediol, propylene glycol, hexanediol, bisphenol A, bisphenol B, bisphenol S, hydrogenated bisphenol A, dibromobisphenol A, 1,4-cyclohexanedimethanol, dihydroxyethyl. Polyhydric alcohols such as ethyl terephthalate, hydroquinone dihydroxyethyl ether, trimethylolpropane, glycerin and pentaerythritol; alkylene derivatives of these polyhydric alcohols; polyhydric alcohols or alkylene derivatives and polyhydric carboxylic acids and polycarboxylic anhydrides Or an ester compound with a polycarboxylic acid ester; polycarbonate polyol, polytetramethylene glycol, polycap Lactone polyols, polybutadiene polyols, polythioether polyols, polyacetal polyols, fluorine polyol, silicon polyol, castor oil polyol, may be used an acrylic polyol.
[0023]
【Example】
Examples of the present invention will be described below.
Example 1
100 parts by weight (mass) of methyl ethyl ketone (MEK) and 79 parts by weight of cyclohexane diisocyanate (manufactured by Nippon Polyurethane) are mixed and stirred at 50 ° C., 110 parts by weight of polyol (trade name “Uniol”, manufactured by Nippon Oil & Fats) and tri 2 parts by weight of ethanolamine was added to advance the polymerization reaction, thereby preparing a urethane resin. This urethane resin was added to 460 parts by weight of water and emulsified (dispersed) to prepare an aqueous urethane resin dispersion. Methyl ethyl ketone was evaporated from this water-based urethane resin dispersion under the conditions of a pressure of 8 kPa and a temperature of 42 ° C. to recover methyl ethyl ketone (solution) containing 32% by weight of water. The solid content was 33% by weight, and the average particle size of the urethane resin was 1 An aqueous urethane resin dispersion having a recovered reaction solvent of 2 μm was obtained.
Next, 25% by weight sulfuric acid was added to the recovered methyl ethyl ketone (solution) to adjust the pH to 5. The methyl ethyl ketone (solution) was subjected to simple distillation to distill off the methyl ethyl ketone, and water was taken out. The distilled methyl ethyl ketone (solution) contained 22% by weight of water. Further, most of the reaction initiator remained in water as the bottoms as a solid. In addition, other impurities remained in the bottom water. Next, the distilled methyl ethyl ketone (solution) is gasified by heating, and led to a gas separation membrane module (UBE organic solvent dehydration system using polyimide membrane, manufactured by Ube Industries), which separates and removes water and contains almost no water. Methyl ethyl ketone (water content 0.01% by weight) was regenerated.
A urethane resin dispersion with the reaction solvent recovered was re-prepared in the same manner as above except that the regenerated methyl ethyl ketone was used and the scale was reduced to half. The resulting dispersion was the same as that originally prepared.
[0024]
Comparative Example 1
Distillation was carried out in the same manner as in Example 1 except that 25% by weight sulfuric acid was not added to the recovered methyl ethyl ketone (solution), and it was led to a separation membrane module to separate and remove water to obtain methyl ethyl ketone.
Using the obtained methyl ethyl ketone, when the urethane resin dispersion was re-prepared with half the scale as in Example 1, the reaction was rapid and the same urethane resin dispersion could not be re-prepared.
As is clear from the results, it can be seen that many initiators remained in methyl ethyl ketone.
[0025]
Comparative Example 2
A gas separation membrane module was introduced in the same manner as in Example 1 except that simple distillation was not performed. A urethane resin or a neutralized product adhered to the gas separation membrane module, and water could not be sufficiently separated and removed.
[0026]
Comparative Example 3
Methyl ethyl ketone (solution) was obtained in the same manner as in Example 1 except that it was not led to the gas separation membrane module.
Using the obtained methyl ethyl ketone, the urethane resin dispersion was re-prepared with half the scale as in Example 1. As a result, the side reaction was the main component, and the same urethane resin dispersion could not be re-prepared.
As is apparent from the results, it can be seen that much water remained in the methyl ethyl ketone.
[0027]
Comparative Example 4
Except that 25% by weight sulfuric acid was not added, it was led to a gas separation membrane module in the same manner as in Example 1, and water was separated and removed to obtain methyl ethyl ketone containing almost no water. Next, equimolar amount of malic acid (equimolar to the amount of sulfuric acid added in Example 1) was added. Next, as in Example 1, when the urethane resin dispersion was re-prepared with half the scale, the reaction was rapid and the same urethane resin dispersion could not be re-prepared.
As is clear from these results, it was confirmed that even when acid was added after separating and removing water, the neutralization reaction did not proceed sufficiently, and a large amount of reaction initiator remained in methyl ethyl ketone. .
[0028]
【The invention's effect】
As described above, according to the method for regenerating a reaction solvent according to the present invention, the reaction solvent is recovered from the aqueous urethane resin dispersion and regenerated to a high purity containing almost no basic reaction initiator or water. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic flow diagram showing a method for regenerating a reaction solvent in the present embodiment.
[Explanation of symbols]
A ... Recovery process, B ... Neutralization process, C ... Distillation process, D ... Membrane separation process

Claims (2)

A reaction solvent regeneration method for recovering and regenerating a reaction solvent from an aqueous urethane resin dispersion in which a urethane resin polymerized by the presence of a basic reaction initiator in the reaction solvent is dispersed in water,
A recovery step of evaporating and recovering the reaction solvent from the dispersion;
A neutralization step of neutralizing and fixing the basic reaction initiator contained in the recovered reaction solvent by adding an acid to the recovered reaction solvent;
A distillation step of distilling the reaction solvent that has undergone the neutralization step to distill the reaction solvent and to take out water contained in the reaction solvent;
And a membrane separation step of separating and removing water contained in the distilled reaction solvent by a gas separation membrane. Play how the reaction solvent according to claim 1 wherein in the distillation is a single distillation to the distillation step.

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