JP4183548B2 - Depolymerization method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for depolymerizing polyalkylene terephthalate. More specifically, the present invention relates to a depolymerization method for obtaining dimethyl terephthalate and diol from polyalkylene terephthalate in a high yield with a one-stage reaction.
[0002]
[Prior art]
Once a new synthetic fiber business or synthetic resin business occurs, the amount of fiber waste, polymer waste, used fiber waste, and product waste generated in the manufacturing stage becomes enormous. Therefore, it is necessary to establish recycling technology for fiber waste, product waste, etc. from the viewpoint of reducing manufacturing costs. In particular, it is indispensable to establish a so-called chemical recycling technique in which miscellaneous collected fiber waste and product waste are chemically decomposed and recycled to useful raw materials.
[0003]
In the synthetic fiber business and synthetic resin business, the most used polymers are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polytrimethylene terephthalate (PTT) that has recently been commercialized with resins and fibers. Representative polyalkylene terephthalates. In particular, PET has already been industrially chemically recycled. Specifically, after PET is reacted with ethylene glycol in the presence of a transesterification catalyst, bis (2-hydroxyethyl) terephthalate is once generated (glycolysis). Reaction), and further reacting with methanol to recover dimethyl terephthalate and ethylene glycol (methanolysis reaction), a two-stage reaction method has been put into practical use.
[0004]
-(OC-Ph-COCH ₂ CH ₂ O) n- + HO-CH ₂ CH ₂ -OH →
HOCH ₂ CH ₂ OOC-Ph-COOCH ₂ CH ₂ OH (Glycolysis reaction)
HOCH ₂ CH ₂ OOC-Ph-COOCH ₂ CH ₂ OH + CH ₃ OH →
H ₃ COOC-Ph-COOCH ₃ + HOCH ₂ CH ₂ OH (Methanolysis reaction)
Further, although not industrialized, there is known a one-step method for recovering dimethyl terephthalate or terephthalic acid together with ethylene glycol by directly reacting PET with methanol or water (for example, Patent Documents 1 and 2). ).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 49-041329 [Patent Document 2]
JP-A-48-068537
[Problems to be solved by the invention]
The above two-stage method is a very effective method because there are few by-products and the recovered monomer purity is high. However, since both the glycolysis reaction and the methanolysis reaction are equilibrium reactions, it has been substantially impossible to increase the yield to 90% or more unless the amount of glycol or methanol used is extremely increased. The PET oligomer that could not be completely decomposed into the monomer remained in the reaction product and had to be discarded as a distillation residue of dimethyl terephthalate or ethylene glycol. In such a state, of course, the recycling rate cannot approach 100%.
[0007]
On the other hand, the one-step method is superior to the two-step method in that the purity of the recovered monomer is high, less reaction solvent and catalyst are used, and the equipment is simple. However, the fact that the reaction yield is not quantitative is the same for the one-step method. Although depending on the reaction conditions, it is usually difficult to achieve a yield of 80%, and a low recovery rate is a problem. In this case, the remaining 20% is an oligomer in which polyalkylene terephthalate is partially depolymerized. If the reaction yield can be significantly increased by the one-step method, it can be the most suitable method for chemical recycling technology of polyalkylene terephthalate typified by PET, but it can be recovered without applying special equipment or depolymerization conditions. A method for significantly increasing the rate has not been proposed.
The problem to be solved by the present invention is to provide a method for depolymerizing polyalkylene terephthalate in methanol by a high-yield one-stage reaction.
[0008]
[Problems to be solved by the invention]
The present inventors have studied in detail a method for depolymerizing polyalkylene terephthalate using methanol at high temperature and pressure. As a result, the end point of this reaction was found to be an equilibrium mixture of dimethyl terephthalate, glycol depolymerization product and methanol, and further alkylene terephthalate oligomer. Therefore, using the fact that the reaction is an equilibrium reaction and that high-temperature methanol above the boiling point dissolves dimethyl terephthalate and glycol at a high concentration, but hardly dissolves oligomers, a high temperature is obtained after a one-step reaction. Take out the methanol layer containing dimethyl terephthalate and glycol as it is, add new methanol to the reaction tank, add a new polymer, and repeat depolymerization with the remaining oligomers to recover the overall depolymerization reaction step. It was found that can be greatly improved.
[0009]
That is, the present invention is a depolymerization method in which polyalkylene terephthalate and methanol are reacted at 150 to 200 ° C. to produce dimethyl terephthalate, and (1) terephthalic acid is continuously or discontinuously formed from the reaction product. The methanol layer at 100 to 200 ° C. containing dimethyl is taken out, and dimethyl terephthalate, methanol and glycol are separated from the taken out methanol layer. (2) Remaining reaction product after taking out the methanol layer containing dimethyl terephthalate This is a method for depolymerizing polyalkylene terephthalate, characterized in that after adding methanol and adding polyalkylene terephthalate as necessary, a depolymerization reaction is performed to form dimethyl terephthalate again.
[0010]
In the present invention, polyalkylene terephthalate is a polycondensate of terephthalic acid or its lower alcohol ester and glycol, and examples thereof include PET, PBT, and PTT. Further, the polyalkylene terephthalate may be a copolymer of ternary or higher, such as 5-sodium sulfoisophthalic acid, tetrabutylphosphonium 5-sulfoisophthalate, isophthalic acid, 1,4-butanediol, adipic acid, polyalkylene. Glycol or the like may be copolymerized, for example, 0.05 to 98 wt%. A plurality of polyalkylene terephthalates may be mixed. The intrinsic viscosity is generally 0.2 to 1.5 dl / g.
[0011]
Polyalkylene terephthalate forms include unused and used chip waste, extruder drain polymer, yarn (multifilament, sufu, tow, side-by-side yarn, monofilament, etc.), film, waste resin products, clothing, industrial materials, non-woven fabric There are no particular restrictions on carpets. Moreover, processing agents processing, such as dyeing | staining and a surface treating agent, may be given, Furthermore, an emulsion, suspension, a solution, etc. may be sufficient. When depolymerizing polyalkylene terephthalate, nylon, polyacrylonitrile, polyethylene, polypropylene, polymethylpentene, polybutylene, ABS resin, modified polyphenylene ether, polycarbonate, phenol resin, urea resin, polyurethane, melamine resin, aramid, aromatic Known polymers such as polyester, natural rubber, carbon fiber, polynaphthalene terephthalate, polylactic acid, and cellulose, metals such as iron, copper, and stainless steel, food, glass products, paper, food, sand, stones, etc. In order to improve the recovery efficiency of the depolymerized monomer, it is preferable that these inclusions are less than 30 wt%.
[0012]
The depolymerization method of the present invention is a depolymerization method in which polyalkylene terephthalate and methanol are reacted to produce dimethyl terephthalate and glycol. The amount of methanol used with respect to the polyalkylene terephthalate is at least three times the total terephthalate units of the reaction product (for example, in the case of PET, 192 is considered to be 1 mol because it has one terephthalate unit as a repeating unit) The amount is preferably 3 to 100 times mol, more preferably 5 to 30 times mol, particularly preferably 7 to 25 times mol in order not to excessively increase the recovery yield and use amount of methanol. In order to accelerate the depolymerization reaction, it is preferable to use a catalyst. Examples of the catalyst include sodium acetate, potassium acetate, calcium acetate, zinc acetate, magnesium acetate, sodium carbonate, magnesium carbonate, potassium carbonate, barium carbonate, lithium carbonate, sodium formate, potassium formate, calcium formate, zinc formate, magnesium formate, etc. Acetate, carbonate and formate. Although there is no restriction | limiting in particular as the usage-amount of these metal salts, Preferably it is 0.01-5 wt% from the speed of 0.001-20 wt% of the weight of the polyalkylene terephthalate mixture to depolymerize, and the speed of a depolymerization rate.
[0013]
The reaction temperature is preferably 100 ° C. or higher, the reaction rate is high, and from the viewpoint of improving the recovery yield, 120 to 300 ° C., particularly preferably, the equipment cost is not excessively increased due to the high pressure, and the reaction rate and the recovery rate. It is 140-250 degreeC from height, Most preferably, it is 150-200 degreeC. The reaction time is a function of temperature, but is 10 minutes to 25 hours in the above temperature range.
In the present invention, a methanol layer containing dimethyl terephthalate containing dimethyl terephthalate continuously or discontinuously from the reaction product obtained after the depolymerization reaction is taken out, and dimethyl terephthalate, methanol and glycol are taken out from the taken-out methanol layer. Is necessary to increase the monomer recovery yield. The depolymerization reaction in which polyalkylene terephthalate reacts with methanol does not proceed quantitatively. After completion of the reaction, in addition to dimethyl terephthalate and glycol, oligomers that have not been completely depolymerized, garbage that cannot be decomposed, and the like remain. Although dimethyl terephthalate is not very soluble in methanol at room temperature, it is completely mixed with methanol at 100 ° C., preferably 120 ° C. or higher, more preferably 145 ° C. or higher. At such temperatures, the glycol is also completely mixed with methanol.
[0014]
In contrast, polyalkylene terephthalate oligomers, dusts and the like hardly dissolve in methanol. Therefore, by removing only the methanol layer after the completion of the depolymerization reaction, it can be physically separated from the oligomers and dust. For example, when the stirring is stopped after completion of the depolymerization reaction, oligomers and dust settle. If a methanol layer at 100 ° C. or higher is taken out from the upper part of the settled portion, and then dimethyl terephthalate, glycol, and methanol are separated and purified from the methanol layer, it becomes possible to efficiently recover a high-purity monomer. The methanol layer to be taken out is preferably 10 to 90% of the charged amount and 50 to 90% from the viewpoint of increasing the recovery rate.
Next, in order to increase the recovery yield, it is necessary to depolymerize the oligomer remaining in the depolymerization reaction tank again. Of course, a new polyalkylene terephthalate may be added in order to proceed with a new methanol, a catalyst, or a further depolymerization reaction. These amounts and ratios are not particularly limited, but it is preferable to keep the amounts and ratios at the start of the reaction described above.
[0015]
As described above, a depolymerization method in which polyalkylene terephthalate is reacted with methanol to produce dimethyl terephthalate, (1) containing dimethyl terephthalate continuously or discontinuously from the reaction product, Take out the above methanol layer, separate dimethyl terephthalate, methanol and glycol from the taken out methanol layer. (2) Add methanol to the remaining reactant after removing the methanol layer containing dimethyl terephthalate. Then, after adding polyalkylene terephthalate as necessary, it is possible to recover the monomer in an extremely high yield by repeatedly performing a depolymerization reaction for generating dimethyl terephthalate again.
The hot methanol layer taken out from the depolymerization reaction tank once distills dimethyl terephthalate, glycol and methanol after cooling to 95 ° C or lower, preferably 0 to 60 ° C, more preferably 0 to 30 ° C or without cooling. Etc., and can be separated and purified. In this case, the method is preferably a method of once cooling, since dimethyl terephthalate is precipitated from the methanol layer by crystallization and is easily separated from the methanol layer containing glycol.
[0016]
In the case of cooling, the method for separating dimethyl terephthalate from the methanol layer is not particularly limited, such as filtration and centrifugation. The centrifuge used for centrifugation is not particularly limited, and may be a continuous type or a batch type. When performing centrifugation, the rotation speed and time are important, and the rotation speed is preferably 300 rpm or more. When the rotational speed is less than 300 rpm, separation is insufficient, and PDO and other glycols contained in the crude dimethyl terephthalate increase, and further, microcrystalline dialkyl terephthalate remains in the liquid layer, resulting in poor recovery. . Preferably, it is 500 rpm or more. The centrifugation time is preferably 10 minutes or longer. The temperature at the time of centrifugation does not need to be particularly controlled, but is preferably set to 30 ° C. or less from the viewpoint of safety.
[0017]
The separated methanol layer contains glycol and a small amount of dimethyl terephthalate, but each component can be purified by distillation. Preferably, the methanol can be recovered by substantial atmospheric distillation and then the glycol can be isolated by vacuum distillation.
On the other hand, the isolated crude dimethyl terephthalate is preferably purified by distillation under reduced pressure, and is preferably distilled at 120 to 250 ° C. and 2.7 to 33 kPa in order to suppress decomposition and increase the recovery yield. . When the pressure exceeds 33 kPa, the boiling point is increased, and problems such as dialkyl terephthalate being colored during the distillation process and an acid value being increased are caused. On the other hand, if the pressure is less than 2.7 kPa, the temperature can be set low, but the degree of vacuum is too high, so that it is sucked into the vacuum pump and the recovery rate becomes low. Preferably, it is 120-220 degreeC and 4-20 kPa.
[0018]
【Example】
Hereinafter, the present invention will be specifically described in detail. Various measured values used in the examples of the present invention were measured by the following measuring methods.
(1) Monomer purity Purity was calculated from the peak area ratio using the following gas chromatography. Column: DURABOND DB-WAX 0.25 mmI. D. × 30m
Film thickness: 0.25 μm
Temperature raising method: After holding at 50 ° C. for 5 minutes, the temperature was raised to 230 ° C. at a temperature raising rate of 20 ° C./min and then kept at 230 ° C. as it was. The detector used was FID.
(2) Intrinsic viscosity Intrinsic viscosity [η] is a value determined based on the definition of the following equation.
[Η] = lim (ηr−1) / C
C → 0
Ηr in the definition formula is a value obtained by dividing the viscosity of a diluted solution of PTT or PET dissolved in o-chlorophenol having a purity of 98% at 35 ° C. by the viscosity of the solvent itself measured at the same temperature. It is defined as viscosity. C is the solute weight value in grams in 100 ml of the solution.
[0019]
[Example 1]
10.3 g of polytrimethylene terephthalate having an intrinsic viscosity of 0.9 dl / g (corresponding to 0.05 mol as a terephthalate unit), 32 g (1 mol) of methanol, 0.13 g of sodium carbonate (1.3 wt% / polymer, this unit Represents wt% relative to the mass of the polymer.) Was charged into an autoclave and allowed to react with stirring at a temperature of 150 ° C. and a pressure of 1.3 MPa for 8 hours. After the reaction, stirring was stopped and the methanol layer was taken out from the autoclave at 150 ° C. and 0.5 MPa, and cooled to 10 ° C. without releasing the pressure as it was. After cooling, the crystallized crude dimethyl terephthalate was filtered off, and the crude dimethyl terephthalate was purified by distillation under reduced pressure at 220 ° C. and 6.7 kPa. Moreover, about the methanol solution containing 1, 3- propanediol, methanol was distilled off completely at 70 degreeC and 13 kPa, and PDO was then isolated at 150 degreeC and 6.7 kPa.
[0020]
On the other hand, the autoclave after taking out a part of the methanol layer contained a trimethylene terephthalate oligomer. While maintaining 150 ° C. and 1.3 MPa again, 5.9 g of polytrimethylene terephthalate, 24.0 g of methanol, and 0.10 g of sodium carbonate were added, and depolymerization under the same conditions and removal of the methanol layer at 150 ° C. Separation and purification were performed. Such depolymerization reaction, removal, and separation and purification were repeated 10 times. The recovery rate of dimethyl terephthalate was 98%, and the recovery rate of 1,3-propanediol was 97%. The recovered dimethyl terephthalate had a purity of 99.9% and PDO had a purity of 98.4%.
[0021]
[Example 2]
Example 1 was repeated by using polyethylene terephthalate having an intrinsic viscosity of 0.65 dl / g instead of polytrimethylene terephthalate and changing the depolymerization reaction temperature from 150 ° C. to 200 ° C. The recovery rate of dimethyl terephthalate was 97%, and the recovery rate of ethylene glycol was 95%. The recovered dimethyl terephthalate had a purity of 98.5% and ethylene glycol had a purity of 98.1%.
[Example 3]
Example 1 was repeated by using polybutylene terephthalate having an intrinsic viscosity of 1.20 dl / g instead of polytrimethylene terephthalate and changing the depolymerization reaction temperature from 150 ° C. to 200 ° C. The recovery rate of dimethyl terephthalate was 94%, and the recovery rate of 1,4-butanediol was 95%. The recovered dimethyl terephthalate had a purity of 95.0% and 1,4-butanediol had a purity of 86.3%.
[0022]
[Comparative Example 1]
10.3 g of polytrimethylene terephthalate with an intrinsic viscosity of 0.9 dl / g (corresponding to 0.05 mol as a terephthalate unit), 32 g (1 mol) of methanol, 0.13 g of sodium carbonate (1.3 wt% / polymer, this unit Represents wt% relative to the mass of the polymer. After the reaction, stirring was stopped and the mixture was cooled to 25 ° C. without releasing the pressure. After cooling, the crystallized crude dimethyl terephthalate was filtered off, and the crude dimethyl terephthalate was purified by distillation under reduced pressure at 220 ° C. and 6.7 kPa. Moreover, about the methanol solution containing 1, 3- propanediol, methanol was distilled off completely at 70 degreeC and 13 kPa, and PDO was then isolated at 150 degreeC and 6.7 kPa.
The recovery rate of dimethyl terephthalate was 71%, and the recovery rate of 1,3-propanediol was 68%.
[Comparative Example 2]
Comparative Example 1 was repeated using polyethylene terephthalate having an intrinsic viscosity of 0.65 dl / g instead of polytrimethylene terephthalate and changing the depolymerization reaction temperature from 150 ° C. to 200 ° C. The recovery rate of dimethyl terephthalate was 75%, and the recovery rate of ethylene glycol was 73%.
[0023]
【The invention's effect】
By utilizing the present invention, high-purity raw material monomers can be efficiently recovered from fibers, films, resin products using polyalkylene terephthalate, and scrap polymers discharged in the production stage.
By using the present invention, it is possible to recover a high-quality monomer similar to or higher than a commercially available product in a high yield, and the present invention can be used without waste in terms of environmental protection and manufacturing cost reduction. Is a very useful technique. The recovered monomer is useful as an intermediate material for various chemical products and pharmaceuticals in addition to fibers, films and molded products.

Claims (2)

Polyalkylene telephthalate with terephthalate and methanol are reacted at 150 to 200 ° C., a solution polymerization process to produce dimethyl terephthalate, including continuously or batchwise dimethyl terephthalate from (1) the reaction product, 100 Take out the methanol layer at 200 ° C and separate dimethyl terephthalate, methanol and glycol from the taken out methanol layer. (2) Add methanol to the remaining reactants after taking out the methanol layer containing dimethyl terephthalate. And then depolymerizing the polyalkylene terephthalate again to generate a dimethyl terephthalate.   2. The method for depolymerizing polyalkylene terephthalate according to claim 1, wherein polyalkylene terephthalate is also added when methanol is newly added.