JP4459402B2 - Method for recovering active ingredients from polyester waste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for recovering an active ingredient from polyester waste, and more specifically, poly (ethylene-2,6-naphthalenedicarboxylate) (hereinafter sometimes abbreviated as PEN) and polyalkylene terephthalate. The present invention relates to a method for easily and efficiently recovering bishydroxyalkyl terephthalate as an active ingredient, or a terephthalic acid component and an alkylene glycol from a polyester waste consisting essentially of a mixture.
[0002]
[Prior art]
Polyalkylene terephthalate is produced and used in large quantities in fibers, films, resins and the like because of its excellent chemical stability. In order to effectively use these used polyalkylene terephthalates (hereinafter sometimes abbreviated as polyester waste) after being used, ethylene glycol (hereinafter sometimes abbreviated as EG) by depolymerization, There are various proposals regarding chemical recycling that decomposes into monomers such as dimethyl terephthalate (hereinafter sometimes abbreviated as DMT), terephthalic acid or its derivatives.
[0003]
In the chemical recycling, a recovered polyester waste and methanol (hereinafter sometimes abbreviated as MeOH) are reacted to recover DMT and alkylene glycol (JP-A-9-012713, etc.), recovery A method (such as Japanese Patent Publication No. 32-8068) in which the polyester waste is hydrolyzed in the presence of an alkali compound and recovered as terephthalic acid and alkylene glycol is known.
[0004]
However, as polyester waste discharged from distribution businesses and households, PEN may be mixed into polyalkylene terephthalate, and PEN may also be depolymerized at the time of recovery, and may be abbreviated as dimethyl naphthalenedicarboxylate (hereinafter, NDCE) )) And may be mixed into DMT, and particularly when depolymerization is performed at a high temperature exceeding 260 ° C., NDCE formation becomes remarkable.
[0005]
Conventionally, distillation separation and purification have been studied for separation of a mixture of NDCE and DMT obtained by depolymerizing a mixture of polyalkylene terephthalate and PEN, and Japanese Patent Publication No. 3-504379 discloses PEN and A mixture consisting of polyethylene terephthalate (hereinafter sometimes abbreviated as PET) is depolymerized using MeOH under high temperature and high pressure conditions using a depolymerization catalyst, and the resulting product is cooled, precipitated and recovered. Describes a method for fractional distillation of a mixture of NDCE and DMT.
[0006]
However, such a cooled precipitation mixture of the depolymerization product contains various inorganic compounds such as a polymerization catalyst and an added depolymerization catalyst in addition to NDCE and DMT, and a part of NDCE is decomposed to become a side product. The produced methyl 2-naphthoate and the like may cause a decrease in purity of the recovered product.
[0007]
[Problems to be solved by the invention]
The object of the present invention is to solve the above-mentioned problems of the prior art and to efficiently recover bishydroxyalkyl terephthalate or terephthalic acid component and alkylene glycol as active ingredients from polyester waste containing PEN. Is to establish.
[0008]
[Means for Solving the Problems]
As a result of intensive studies in view of the above prior art, the present inventors have preferentially dissolved polyalkylene terephthalate in a temperature range in which PEN is not susceptible to depolymerization reaction with alkylene glycol, and then removed unreacted PEN. As a result, it was found that NDCE mixed in a small amount in DMT can be recovered efficiently by separating it under appropriate distillation conditions, and the present invention has been completed.
[0009]
That is, the object of the present invention is to
Polyester waste comprising a mixture of poly (ethylene-2,6-naphthalene dicarboxylate) and polyalkylene terephthalate, poly (ethylene-2,6-naphthalene dicarboxylate based on the weight of the polyester waste ) And polyalkylene terephthalate is a method for separating and recovering active ingredients from polyester waste, which accounts for 80% or more , and sequentially passes the waste through the following steps (a) to (d) It can be achieved by a method for recovering active ingredients from polyester waste.
(A) A step of introducing polyester waste into alkylene glycol containing a depolymerization catalyst at a temperature of 120 to 210 ° C.
(B) A step of removing unreacted poly (ethylene-2,6-naphthalenedicarboxylate) by solid-liquid separation in a solid state after passing through step (a).
(C) A transesterification catalyst and methanol are added and charged to the residue after the solid is taken out in step (b) to perform transesterification, and dimethyl terephthalate containing dimethyl 2,6-naphthalenedicarboxylate and A process of separating and recovering both after obtaining alkylene glycol.
(D) A step of separating and recovering dimethyl terephthalate from dimethyl terephthalate containing dimethyl 2,6-naphthalenedicarboxylate obtained through step (c).
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the recovery method of the present invention, it is necessary to sequentially pass the polyester waste substantially consisting of the mixture of PEN and polyalkylene terephthalate to each of the above-mentioned steps (a) to (d).
Here, “substantially” means that the total of PEN and polyalkylene terephthalate accounts for 80% or more based on the weight of the polyester waste.
[0011]
Hereinafter, each process of (a)-(d) is demonstrated in detail.
In the step (a), it is necessary to put the polyester waste into the alkylene glycol containing the depolymerization catalyst at a temperature of 120 to 210 ° C. Here, when the temperature of the alkylene glycol is less than 120 ° C., the depolymerization time becomes very long and it is not efficient. On the other hand, when the temperature exceeds 210 ° C., depolymerization of PEN becomes remarkable, and the amount of by-product NDCE increases. The temperature is preferably 140 to 190 ° C., and may be heated and held under these conditions for 1 to 10 hours.
[0012]
Furthermore, the weight ratio of the alkylene glycol and polyalkylene terephthalate supplied to the step (a) is preferably set to about 0.5 to 20, and when the ratio is within this range, it does not depend on the shape of the polyester waste. In addition, the depolymerization time is not significantly changed, and the purification cost of the alkylene glycol to be finally reused can be suppressed. The weight ratio is preferably 1-5.
[0013]
Here, the depolymerization catalyst used in step (a) is at least one selected from the group consisting of alkali metal carbonates, oxides, alkaline earth metal carbonates, oxides, manganese acetate, and zinc acetate. It is preferable to use this compound and to add 0.1 to 10% based on the weight of the polyester waste. When the addition amount is within this range, the reaction proceeds economically and efficiently.
[0014]
In the recovery method of the present invention, examples of the polyalkylene terephthalate include polyethylene terephthalate, polytrimethylene terephthalate, polytetramethylene terephthalate, and the like, but usually polyethylene terephthalate.
[0015]
Furthermore, examples of the alkylene glycol used in the recovery method of the present invention include ethylene glycol and diethylene glycol. Among them, ethylene glycol produced as a by-product when polymerized again from recycled raw materials is used. Is preferred.
[0016]
PEN partially depolymerizes under the reaction conditions to produce bishydroxyalkyl naphthalate and dissolves in alkylene glycol. However, some PEN remains unreacted as a solid without being depolymerized. In the step (b), the polyester waste that has passed the step (a) is passed through a solid-liquid separator. Since the polyester waste after passing through the step (a) forms a slurry state with PEN in a solid state, a normal solid-liquid separation operation may be performed. Here, various solid-liquid separation devices can be used for the solid-liquid separation operation, and when there is little mixing of PEN, a filter intended to remove foreign substances may be used.
[0017]
The PEN obtained by the operation in the step (b) may be separated and recovered as a valuable material or as a waste, but the surface of the PEN obtained by solid-liquid separation contains an alkylene containing a polyalkylene terephthalate component. Since glycol adheres, when recovering this as a valuable material, it is preferable to wash the PEN surface with alkylene glycol before being supplied to step (a). The washing method may be performed by charging the PEN that has been subjected to solid-liquid separation into a tank in which the EG to be supplied to the step (a) is stored, stirring and washing, and performing solid-liquid separation operation again for separation.
[0018]
The polyester waste obtained by the operation of the step (b) is depolymerized with alkylene glycol and converted into oligomers of repeating units 1 to 4. It is possible to obtain DMT even if a transesterification reaction is carried out at 65 to 85 ° C. by directly adding the solution containing the oligomer to the step (c) described later, but when a large amount of alkylene glycol is present, Since the recovery rate of DMT can be kept low, it is preferable to distill and concentrate the residue after taking out the solid in step (b). That is, it is preferable to concentrate the liquid containing the oligomer until the weight ratio of the alkylene glycol to the polyester waste is 0.5 to 2.0 based on the raw material charge ratio.
[0019]
The concentration can be easily carried out by distillation operation, and can be carried out at normal pressure or under reduced pressure. However, the progress of PEN depolymerization becomes remarkable at 210 ° C. Taking into account the leaked PEN and the like, it is preferable to carry out a vacuum distillation operation at 1.33 to 100 kPa, preferably 6.67 to 26.6 kPa.
[0020]
Next, in step (c), the ester exchange reaction catalyst and MeOH are added and charged into the separated solution of step (b), preferably a solution in which the oligomer is concentrated to the above-mentioned ratio, to perform the ester exchange reaction, After obtaining DMT containing NDCE and alkylene glycol, both are separated and recovered.
[0021]
In the transesterification reaction, 200 to 400% by weight of MeOH is charged based on the polyester waste, and at the same time, 1 to 10% by weight of the transesterification reaction catalyst is charged based on the polyester waste. The reaction may proceed at a transesterification reaction tank pressure near atmospheric pressure and a transesterification reaction temperature of 65 to 85 ° C.
[0022]
The transesterification reaction is completed in 0.5 to 5 hours, and becomes a slurry of NDCE, DMT, MeOH, and alkylene glycol in a solid state. In recovering DMT from the slurry, a solid-liquid separator can be applied as a conventional means, but any method may be adopted.
[0023]
Since a small amount of DMT is dissolved in MeOH and alkylene glycol, the slurry is cooled to 30 to 60 ° C. and then supplied to a solid-liquid separator. The cake of DMT obtained by the solid-liquid separation operation contains MeOH and alkylene glycol as mother liquors, so the cake is put into new MeOH and stirred, and then slurried again to wash DMT. To do. The obtained slurry is supplied again to the solid-liquid separator, and separated into a DMT cake and a mother liquor MeOH.
[0024]
The number of repetitions of this washing operation is uniquely determined by the required quality of the DMT to be recovered, but usually it may be performed 2 to 4 times. Further, as a conventional means, the mother liquor MeOH in each washing step can be circulated. Further, the washing operation may be performed continuously or batchwise.
[0025]
The mixed solution of EG and MeOH solid-liquid separated from DMT contains dissolved DMT, depolymerization catalyst and transesterification catalyst. EG and MeOH are separated and purified separately for use in the process again. The This purification operation is preferably carried out by distillation, but need not be limited to the distillation operation. In the case of performing distillation, MeOH having a low boiling point is first distilled off, and then the liquid remaining at the bottom of the column is supplied to the next distillation column, and EG is distilled off. At this time, since DMT dissolved in alkylene glycol, catalyst, and oligomer having 1 to 3 repeating units are present at the bottom of the tower, the bottom liquid is used for the purpose of reducing the amount of catalyst used and improving the recovery rate of active ingredients. A part of may be returned to the depolymerization tank.
[0026]
In addition, since there is a possibility that a small amount of solids such as dust and sand contained in NDCE and polyester waste produced by depolymerization of PEN may be mixed in the DMT recovered by the above-described solid-liquid separation operation. In the step (d), purification is performed by distillation under reduced pressure. When the distillation temperature exceeds 260 ° C., methyl 2-naphthoate produced by decomposition of NDCE may be mixed into DMT. Therefore, it is desirable to operate the column bottom temperature at 260 ° C. or lower. Also, DMT containing 5 to 10 theoretical plates and not containing NDCE can be recovered by distillation. Rather, if the theoretical plate is larger than 10 plates, the bottom temperature exceeds 260 ° C and becomes unnecessarily high depending on the type of distillation column. Then, methyl 2-naphthoate produced by the decomposition of NDCE is mixed into the recovered DMT.
[0027]
In order to reuse the recovered active ingredient subsequently, the obtained DMT and alkylene glycol may be subjected to a polymerization reaction under known conditions.
[0028]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, each numerical value in an Example was calculated | required with the following method. In the examples, “parts” means “parts by weight” unless otherwise specified.
[0029]
[Example 1]
100 parts of PEN, 100 parts of PET, 800 parts of EG and 6 parts of anhydrous sodium carbonate were charged into a 1000 ml separable flask and reacted under reflux conditions at 185 ° C. for 4.0 hours. After completion of the reaction, hot filtration was performed to separate 47.0 parts of undissolved PEN. Subsequently, after 600 parts of EG were distilled off from the filtrate, 400 parts of MeOH and 6 parts of anhydrous sodium carbonate were added and reacted under reflux conditions at 77 ° C. for 1.0 hour.
[0030]
The reaction product was cooled to room temperature and solid-liquid separated. The obtained filtrate was distilled in a distillation column having a theoretical plate number of 10 to obtain 150 parts of recovered EG.
[0031]
On the other hand, the obtained cake was washed twice with 400 parts of MeOH, dried and distilled, but the composition before distillation was 56.7% by weight of DMT, 38.5% by weight of NDCE, and 4.8% by weight of the other containing inorganic substances. And methyl 2-naphthoate was not included. The mixture of DMT and NDCE was distilled in a distillation column equipped with a regular packing having a theoretical plate number of 10 at a vacuum degree of 6.7 kPa, no reflux, a column top temperature of 180 to 183 ° C, and a column bottom temperature of 180 to 220 ° C. As a result, 81 parts of DMT having a purity of 99.4% or more was obtained. Yield was 81% based on the charged polyester.
[0032]
[Comparative Example 1]
80 parts by weight of 50 to 50 polymer alloy of PEN and PET, 160 parts of EG and 0.8 part of anhydrous sodium carbonate were charged into a 1000 ml stainless steel reactor equipped with a stirrer / cooler and refluxed at 212 ° C. When reacted for 3.3 hours, PEN was also completely depolymerized. The reaction product was cooled to room temperature and the solid-liquid separation was washed with MeOH. Thereafter, MeOH was evaporated and distilled, but the composition before distillation was DMT 47.2% by weight, NDCE 47.0% by weight, EG 1.2% by weight, and other 4.6% by weight including inorganic substances. Methyl 2-naphthoate was not included. Since all PEN was also depolymerized, the composition was richer in NDCE than in Example 1.
[0033]
The mixture of DMT and NDCE was distilled in a plate-type distillation column having a theoretical plate number of 25 at a vacuum degree of 6.7 kPa, a reflux ratio of 0.2, a column top temperature of 185 ° C., and a column bottom temperature of 255 to 265 ° C. , DMT containing 10 ppm of methyl 2-naphthoate was obtained although NDCE was not contained.
[0034]
【The invention's effect】
According to the method of the present invention, bishydroxyalkyl terephthalate as an active ingredient, or DMT and alkylene glycol can be easily recovered from polyester waste containing PEN, and its industrial significance is great.

Claims (11)

Polyester waste comprising a mixture of poly (ethylene-2,6-naphthalene dicarboxylate) and polyalkylene terephthalate, poly (ethylene-2,6-naphthalene dicarboxylate based on the weight of the polyester waste ) And polyalkylene terephthalate is a method for separating and recovering active ingredients from polyester waste, which accounts for 80% or more , and sequentially passes the waste through the following steps (a) to (d) A method for recovering active ingredients from polyester waste, characterized in that:
(A) A step of introducing polyester waste into alkylene glycol containing a depolymerization catalyst at a temperature of 120 to 210 ° C.
(B) A step of removing unreacted poly (ethylene-2,6-naphthalenedicarboxylate) by solid-liquid separation in a solid state after passing through step (a).
(C) A transesterification catalyst and methanol are added and charged to the residue after the solid is taken out in step (b) to perform transesterification, and dimethyl terephthalate containing dimethyl 2,6-naphthalenedicarboxylate and A process of separating and recovering both after obtaining alkylene glycol.
(D) A step of separating and recovering only dimethyl terephthalate from dimethyl terephthalate containing dimethyl 2,6-naphthalenedicarboxylate obtained through step (c).   As the depolymerization catalyst used in step (a), at least one compound selected from the group consisting of alkali metal carbonates, oxides, alkaline earth metal carbonates, oxides, manganese acetate, and zinc acetate is used. The active ingredient recovery method according to claim 1, wherein the addition amount is 0.1 to 10% based on the weight of the polyester waste.   2. The active ingredient recovery method according to claim 1, wherein the amount of alkylene glycol used in step (a) is 0.5 to 20 times by weight based on polyalkylene terephthalate.   The residue after taking out the solid matter in the step (b) is distilled and concentrated, the distilled alkylene glycol is reused in the step (a), and the residue is sent to the next step. Active ingredient recovery method. In the distillation / concentration operation, the weight ratio between the weight of the alkylene glycol and the weight obtained by subtracting the poly (ethylene-2,6-naphthalenedicarboxylate) separated in the step (b) from the polyester waste charged in the depolymerization tank. The active ingredient collection | recovery method of Claim 4 performed until becomes in the range of 0.5-2.   The active ingredient recovery method according to claim 4, wherein the distillation and concentration are performed under a pressure of 1.33 to 100 kPa.   The active ingredient recovery method according to claim 1, wherein the separation and recovery in the step (c) is performed by distillation or solid-liquid separation operation.   The active ingredient recovery method according to claim 1, wherein the separation and recovery in the step (d) is performed by distillation.   The method for recovering an active ingredient according to claim 8, wherein the number of theoretical stages of the distillation operation is 5 to 10 and the bottom temperature of the distillation column is 160 ° C to 260 ° C.   The active ingredient recovery method according to claim 1, wherein the polyalkylene terephthalate is polyethylene terephthalate.   2. The active ingredient recovery method according to claim 1, wherein the alkylene glycol is ethylene glycol.