JP4601223B2 - Degradation method of polyurethane - Google Patents

Description

表１の結果から、本発明の方法によれば、ポリオール化合物、イソシアネート化合物の双方が良好な状態で回収されることが分かる。
【００５１】
一方、比較例１では分解温度が低いためにウレタンの分解反応が十分進行しておらず、回収率は低いものであった。比較例２ではフォームに水分が残留しているため、また比較例３では炭酸ガスに含まれる水分のために、いずれもＴＤＩが該水分と反応してトルエンジアミン（ＴＤＡ）となってしまい、ＴＤＩは回収されなかった。比較例４は、分解温度は高いが、圧力が低く、ＴＤＩが第１分離槽に抽出されずに分解槽に残り、ポリオール化合物と再結合するために、ＴＤＩは回収されず、ポリオール回収率も大きく低下している。また比較例５においては、分解温度が高く、ウレタン結合の解離に加えて原料化合物の熱分解も起こる。その結果、ＰＰＧの分解によりポリオール回収率が低下し、ＰＰＧの分解生成物が超臨界炭酸ガスに抽出されて第１分離槽に移動し、ＴＤＩと反応したためにＴＤＩの回収率も低いものであった。
【図面の簡単な説明】
【図１】ポリウレタンの分解に使用する装置の例を示した構成図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a decomposition method for decomposing polyurethane such as flexible polyurethane foam, rigid polyurethane foam, and polyurethane elastomer into reusable components.
[0002]
[Prior art]
From the viewpoint of environmental protection by reducing industrial waste, a technique for decomposing and reusing resins is desired. The following techniques are known as methods for decomposing and reusing polyurethane.
[0003]
(1) Technology for producing a recycled polyol that can be used again as a raw material for a rigid polyurethane foam by heating and decomposing the rigid polyurethane foam in the presence of alkanolamine using a high-boiling glycol (Japanese Patent Publication No. 53-34000).
(2) Technology for producing a recycled polyol that can be used again as a raw material for a flexible polyurethane foam by heating and decomposing the flexible polyurethane foam using a high-boiling glycol in the presence of alkanolamine (Japanese Patent Publication No. 53-259359).
(3) A technique of hydrolyzing polyurethane at 200 to 370 ° C. and 3 to 30 MPa using high-temperature and high-pressure water and recovering it as a polyamine compound derived from a polyol component and a polyisocyanate (JP-A-10-310663).
[0004]
[Problems to be solved by the invention]
The techniques (1) and (2) are techniques for cleaving polyurethane molecules by the urethane group exchange reaction shown in the following (Chemical Formula 1) to form a hydroxyl group-terminated regenerated polyol component.
[0005]
[Chemical 1]
-R1-NHCOO-R2- + HO-R3-OH
→ -R1-NHCOO-R3-OH + HO-R2-
R1 is an organic group of the polyisocyanate compound, R2 is an organic group of the polyol compound, and R3 is an organic group of glycol.
[0006]
As is apparent from this reaction formula, the regenerated polyol obtained by the above-mentioned known techniques (1) and (2) contains a urethane bond having a large cohesive energy, and has a high viscosity due to the presumed reason for this. is there. Moreover, the color tone is also blackish brown due to the presumed cause due to oxidation, condensation and the like of the aromatic amine produced by the side reaction. For this reason, the obtained regenerated polyol cannot be used as a raw material for polyurethane as it is, but it can only be reused by adding an amount limited to virgin polyol.
[0007]
Further, according to the technique (3), the polyol compound does not contain a urethane bond, and a compound closer to the raw material can be obtained. Therefore, this technique can be said to be a decomposition method with a wide range of reuse.
[0008]
However, according to this known technique (3), the polyisocyanate component is decomposed to diamine, and for example, toluenediamine is recovered from polyurethane using toluene diisocyanate. For this reason, in order to reuse this, it is necessary to use diamine as an isocyanate compound, and for this purpose, for example, an isocyanate step such as reaction of diamine, polyamine, etc. with phosgene is required, and special equipment and reaction steps are required. This is a costly recovery method.
[0009]
An object of the present invention is to provide a method for decomposing a polyurethane capable of recovering a polyisocyanate compound and a polyol from the polyurethane.
[0010]
[Means for Solving the Problems]
The present inventors dissolved polyisocyanate compounds and polyol compounds having a relatively low molecular weight used as raw materials for rigid polyurethane foams in supercritical carbon dioxide (supercritical carbon dioxide), and adjusted the conditions after extraction. For example, the present inventors have found that a polyol compound and a polyisocyanate compound can be separated from each other, thereby completing the present invention.
[0011]
The method for decomposing a polyurethane according to the present invention includes a drying step for drying the polyurethane , the polyurethane being heated and decomposed in an inert gas at a temperature of 200 to 350 ° C. , and a decomposition product containing a polyol component and a polyisocyanate component; And a separation step of extracting and separating at least one of a polyol component and a polyisocyanate component in the decomposition product by contacting the decomposition product with a supercritical carbon dioxide gas using dry carbon dioxide gas. And
[0012]
As shown in the following chemical formula (Chemical Formula 2), the urethane bond is dissociated by heat to generate an isocyanate group and a hydroxyl group.
[0013]
[Chemical 2]
-NHCOO---NCO + HO-
That is, when the polyurethane is heated to 200 ° C. or more, the urethane group is dissociated to produce a polyisocyanate compound and an active hydrogen compound such as a polyol compound, which are decomposed products existing in an equilibrium state. When carbon dioxide gas in a supercritical state is brought into contact in this state, at least the polyisocyanate compound and, depending on the molecular weight, the polyol compound are extracted from the decomposition product into carbon dioxide gas in the supercritical state. When only the polyisocyanate compound is extracted, the polyisocyanate compound is recovered simply by removing the carbon dioxide gas. The decomposed product after the extraction has a low urethane bond content or a polyol having no urethane bond. The active hydrogen compound remains.
[0014]
The pressure in the decomposition reaction vessel in the decomposition step is preferably from 0.1 to 80 MPa (1 atm to 800 atm) in consideration of the cost required for the decomposition reaction vessel or incidental equipment.
[0015]
The decomposition step is appropriately set in the range of 200 ° C. to 350 ° C. in consideration of the characteristics of each component constituting the polyurethane. When the decomposition temperature is less than 200 ° C., the decomposition reaction does not occur sufficiently, and when it exceeds 350 ° C., the decomposition of the polyol component or the polyisocyanate component itself occurs, which is not preferable. The decomposition temperature is more preferably 230 ° C to 330 ° C, still more preferably 260 to 300 ° C.
[0016]
The inert gas used in the decomposition process is not particularly limited as long as it does not react with oxygen, active hydrogen groups, or isocyanate groups, and carbon dioxide, nitrogen, helium, etc. can be used, but substances used in the separation process Since is a supercritical carbon dioxide, it is more preferably carbon dioxide.
[0017]
The separation step preferably includes a polyol component recovery step and a polyisocyanate component recovery step.
[0018]
The separation step is performed by bringing the decomposition product obtained in the decomposition step into contact with supercritical carbon dioxide. That is, in a temperature range of 200 ° C. to 350 ° C., at a pressure of 7.3 MPa (73 atm) or more, the carbon dioxide gas is in a supercritical state, and a polyisocyanate compound, a polyol having a low molecular weight, and the like are extracted from the supercritical carbon dioxide gas.
[0019]
When the polyol compound has a high molecular weight and does not dissolve in the supercritical carbon dioxide, the supercritical carbon dioxide layer containing the isocyanate compound is taken out into the separation tank, the temperature is 30 ° C. or less, and the pressure is less than 7.3 MPa (73 atm). Then, the polyisocyanate compound is separated and recovered.
[0020]
When the molecular weight of the polyol compound is low, the supercritical carbon dioxide gas in which the polyisocyanate compound and the polyol compound are dissolved is taken out into the first separation tank, the temperature is 31 ° C. to 200 ° C., and the pressure is 0.1 to 30 MPa (1 to 30 MPa). 300 atm). Even in this range, carbon dioxide is still in a supercritical state. By this operation, the polyol compound does not dissolve in the supercritical carbon dioxide gas and is separated. The polyisocyanate compound remains dissolved in the remaining supercritical carbon dioxide gas. When this is taken out to the second separation tank and the temperature is set to 30 ° C. or less and the pressure is less than 7.3 MPa (73 atm), the carbon dioxide gas is removed. The polyisocyanate compound is separated and recovered.
[0021]
In the supercritical carbon dioxide gas in which the polyisocyanate compound and the polyol compound are dissolved, the isocyanate group and the hydroxyl group are used because the supercritical carbon dioxide gas is a diluent and the temperature is close to the temperature at which the urethane bond is dissociated. Reaction to become polyurethane again is inhibited.
[0022]
The decomposition step preferably uses a catalyst.
By using the catalyst, the decomposition reaction is completed in a short time at a lower decomposition temperature, and a decomposition product can be generated.
[0023]
In the method for decomposing a polyurethane according to the present invention, it is preferable to provide a drying step for preliminarily drying the polyurethane that is the decomposition target.
[0024]
If water is present, the isocyanate group produced in the decomposition step reacts irreversibly with this moisture to become an amino group and carbon dioxide gas, and the recovery rate of the polyisocyanate compound decreases.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The decomposition method of the present invention will be described using the apparatus schematically shown in FIG.
The polyurethane decomposition apparatus illustrated in FIG. 1 is for supplying a decomposition reaction vessel 1 for carrying out a decomposition step, a first separation tank 3 for carrying out a separation step, a second separation tank 5 and a supercritical carbon dioxide gas. And a carbon dioxide gas storage tank 7.
[0026]
The polyurethane to be decomposed and regenerated is put into the container from the hopper 11 of the decomposition reaction container 1, decomposed by heating, and a decomposed product in which a polyisocyanate component and a polyol component are generated by dissociation of urethane bonds and exist in an equilibrium state. 17 (decomposition step).
[0027]
At the time of decomposition, the inside of the decomposition reaction vessel is set to an atmosphere containing no oxygen or water, preferably an inert gas atmosphere, more preferably a carbon dioxide gas atmosphere. Such an operation prevents undesirable side reactions such as oxidation. Moreover, it is preferable that the polyurethane to be decomposed and regenerated is provided with a drying step to remove water in advance.
[0028]
Carbon dioxide gas in a supercritical state is sent from the storage tank 7 to the decomposition reaction vessel 1 in which the decomposition product 17 exists through the pipe 20 and stirred. By mixing the decomposition product 17 and the supercritical carbon dioxide gas 15, the polyisocyanate compound or the polyisocyanate compound and the polyol compound are extracted from the decomposition product 17 into the supercritical carbon dioxide gas 15.
[0029]
The separation step may be a method in which supercritical carbon dioxide gas is sent to the decomposition reaction vessel 1 in a batch manner and separated, or a method in which it is continuously fed and separated.
[0030]
When the polyurethane to be decomposed is one using a relatively high molecular weight polyol compound such as a flexible polyurethane foam or polyurethane elastomer, the resulting polyol compound remains in the decomposition product and the polyisocyanate compound is extracted. . When the decomposition target is a rigid polyurethane foam, the polyol compound used as a raw material has a relatively low molecular weight, and the polyol compound is also extracted. The extraction conditions are appropriately set in consideration of the solubility of the polyol compound in supercritical carbon dioxide.
[0031]
The apparatus shown in FIG. 1 is an apparatus suitable for disassembling a rigid polyurethane foam. For this purpose, a first separation tank 3 and a second separation tank 5 are provided.
[0032]
Supercritical carbon dioxide 15 gas obtained by extracting and dissolving the polyisocyanate compound and the polyol compound in the decomposition reaction vessel 1 is sent to the first separation tank 3 through the pipe 22.
[0033]
In the first separation tank 3, the polyol compound 37 is separated by adjusting the temperature and pressure while maintaining the supercritical state of the carbon dioxide gas, and adjusting the extract concentration by removing only the carbon dioxide gas as necessary. The supercritical carbon dioxide gas layer 35 is dissolved only in the polyisocyanate compound.
[0034]
The first separation tank 3 has a temperature of 31 ° C. to 200 ° C. and a pressure of 1 to 800 atm. Adjusted to The recovered polyol compound is discharged from a valve 39 provided at the bottom of the first separation tank, purified as necessary, and reused. The temperature and pressure of the first separation tank are appropriately set within the above range in consideration of the molecular weight and composition of the polyol compound to be recovered, that is, the solubility in supercritical carbon dioxide.
[0035]
The supercritical carbon dioxide layer 35 in which the polyisocyanate compound obtained in the first separation tank 3 is dissolved is sent to the second separation tank 5 through the pipe 24. In the second separation tank, the temperature of the supercritical carbon dioxide gas 55 is increased to 30. The polyisocyanate compound 57 is separated by evaporating carbon dioxide gas from the pipe 26 and recovering it by evaporating the carbon dioxide gas at a pressure of normal temperature to 73 atm or lower. The recovered polyisocyanate compound 57 is discharged through a valve 59 at the lower part of the second separation tank and is reused.
[0036]
The carbon dioxide discharged from the pipe 26 of the second separation tank is compressed again by a compressor (not shown) and sent to the storage tank 7 as supercritical carbon dioxide.
[0037]
If the supercritical carbon dioxide gas brought into contact with the decomposition product 17 contains water, it reacts irreversibly with the polyisocyanate compound to form an amino group and carbon dioxide gas, so that it does not contain water or has a low water content. Use things. In that sense, it is preferable to reuse the carbon dioxide gas discharged from the pipe 26 of the second separation tank. When compressing the commercially available carbon dioxide gas accommodated in the cylinder, it is preferable to use it by drying it through a drying device.
[0038]
In the decomposition reaction of polyurethane, it is preferable to use a catalyst. As the catalyst, a compound that promotes esterification reaction or urethanization reaction can be used. Specifically, alkali metal hydroxide such as potassium hydroxide, tertiary amine, quaternary ammonium compound, alkyl titanate. Etc. are exemplified.
[0039]
It is preferable to pulverize and decompose the polyurethane in advance because the time required for the decomposition reaction can be shortened.
[0040]
As a method for drying the polyurethane to be decomposed and regenerated in the drying process, a general drying method can be used without limitation. For example, after being immersed in an organic solvent such as MEK, the organic solvent is distilled and simultaneously removed by azeotropic distillation. Examples include a method of drying, a method of drying under reduced pressure, a method of heating and drying using hot air or an infrared heater, and a method of drying by blowing dry gas. Two or more drying methods may be used in combination.
[0041]
[Other Embodiments]
In the decomposition of a flexible polyurethane foam or polyurethane elastomer, a high molecular weight polyol having a low solubility in supercritical carbon dioxide gas is generated. In such a case, there is no need to provide a first separation tank. Isocyanate compounds can be recovered. The polyol compound is discharged and collected through a valve 19 provided at the lower part of the decomposition reaction vessel 1.
[0042]
【Example】
Examples and the like specifically showing the configuration and effects of the present invention will be described below. In this example, an example in which a flexible polyurethane foam is decomposed is shown.
[0043]
Example 1
A flexible polyurethane foam comprising a trifunctional polyoxypropylene polyol (PPG) having a molecular weight of 3000 and toluene diisocyanate (TDI-80,2,4- / 2,6-isomer ratio = 80/20) as polymer components. A polyurethane subject to decomposition treatment was used. 5 g of this polyurethane to be decomposed was dried at 85 ° C. for 2 hours under a reduced pressure of about 5 Torr with a rotary vacuum pump.
[0044]
Subsequently, it was accommodated in an autoclave, which is a decomposition reaction vessel, and heated at a temperature of 280 ° C. for 2 hours to obtain a decomposition product. TDI is extracted by continuously supplying supercritical carbon dioxide gas from which moisture has been removed while maintaining the temperature (280 ° C.) and pressure (20 MPa), which are decomposition conditions, to this decomposed product, and supercritical fluid containing TDI is extracted. Carbon dioxide gas was moved to the first separation tank.
[0045]
The supercritical carbon dioxide gas in which TDI was dissolved was vaporized and separated at a temperature of 0 ° C. and a pressure of 0.1 MPa (normal pressure) in the first separation tank, and toluene diisocyanate (TDI) was recovered.
[0046]
Solids were removed by filtration from the liquid remaining in the decomposition reaction vessel, and the polyol compound was recovered. The results are shown in the upper part of Table 1 for the decomposition conditions and in the lower part of Table 1 for the recovery results.
[0047]
The recovery rate is the weight percent of the recovered raw material compound with respect to the raw material compound in the decomposition target polyurethane, and the purity is the content of the target component in the recovered tank. For example, in the decomposition tank, the polyol compound is the target component. Yes,
Purity = polyol compound / (polyol compound + other components)
It is. The other component is, for example, an amine catalyst used for foaming.
[0048]
(Example 2)
Recovery and evaluation were performed in the same manner as in Example 1 except that the decomposition temperature under the decomposition conditions was 230 ° C. The decomposition conditions and recovery results are also shown in Table 1.
[0049]
(Comparative Examples 1-5)
The same decomposition target polyurethane as that used in Example 1 was used, and decomposition and recovery experiments were performed under the decomposition conditions shown in Table 1. The decomposition conditions and recovery results are also shown in Table 1.
[0050]
[Table 1]

From the results in Table 1, it can be seen that according to the method of the present invention, both the polyol compound and the isocyanate compound are recovered in a good state.
[0051]
On the other hand, in Comparative Example 1, since the decomposition temperature was low, the urethane decomposition reaction did not proceed sufficiently, and the recovery rate was low. In Comparative Example 2, water remains in the foam, and in Comparative Example 3, because of the water contained in carbon dioxide gas, TDI reacts with the water to form toluenediamine (TDA). Was not recovered. In Comparative Example 4, although the decomposition temperature is high, the pressure is low, TDI remains in the decomposition tank without being extracted into the first separation tank, and recombines with the polyol compound. It has greatly decreased. In Comparative Example 5, the decomposition temperature is high, and in addition to the dissociation of the urethane bond, the raw material compound is also thermally decomposed. As a result, the polyol recovery rate decreased due to the decomposition of PPG, the decomposition product of PPG was extracted into supercritical carbon dioxide gas, moved to the first separation tank, and reacted with TDI, so the recovery rate of TDI was low. It was.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of an apparatus used for decomposing polyurethane.

Claims (3)

A drying step of drying polyurethane , a decomposition step in which the polyurethane is heated and decomposed in an inert gas at a temperature of 200 to 350 ° C. to form a decomposition product containing a polyol component and a polyisocyanate component , and the decomposition product A method for decomposing a polyurethane, comprising: a separation step in which at least one of a polyol component and a polyisocyanate component in the decomposition product is extracted and separated by contacting with supercritical carbon dioxide using dry carbon dioxide . The method for decomposing a polyurethane according to claim 1, wherein the separation step comprises a polyol component recovery step and a polyisocyanate component recovery step. The method for decomposing a polyurethane according to claim 1 or 2, wherein the decomposing step uses a catalyst.

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