JPH07196578A - Recovery of dimethyl naphthalenedicarboxylate and dimethyl terephthalate - Google Patents

Abstract

PURPOSE:To recover dimethyl naphthalenedicarboxylate and dimethyl terephthalate from a raw material consisting of a mixture of dimethyl naphthalenedicarboxylate and dimethyl terephthalate and containing dyes, flame retardants, glass fibers, dusts, etc., by carrying out methanolysis of the raw material and distilling the product. CONSTITUTION:A polymer and/or oligomer containing an alkylene-2,6- naphthalenedicarboxylate unit, a polymer and/or oligomer containing an alkylene terephthalate unit and their mixture are supplied to a reactor while keeping the materials in molten state. The polymers and mixture are depolymerized preferably at 265-320 deg.C under 1-10kg/cm<2>G pressure while introducing methanol into the reactor and the produced dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol are evaporated together with unreacted methanol to recover the objective compounds.

Description

Detailed Description of the Invention

[0001]

The present invention relates to polyalkylene-2,
It relates to a method for recovering dimethyl 2,6-naphthalenedicarboxylate and dimethyl terephthalate by methanolysis from a polyester waste containing a polymer containing 6-naphthalene dicarboxylate units and polyalkylene terephthalate.

More specifically, mainly polyalkylene-
Dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene by simultaneous distillation from methanolysis from polymers containing 2,6-naphthalenedicarboxylate units, polyalkylene terephthalates or / and mixtures thereof containing low polymers thereof. A method for recovering glycol.

[0003]

Polyethylene-2,6-naphthalenedicarboxylate and polybutylene-2,6-naphthalenedicarboxylate have excellent heat resistance and mechanical properties as compared with polyethylene terephthalate and polybutylene terephthalate, and fiber, Used as a highly functional material for films, bottles and industrial resins. On the other hand, the raw material is expensive 2,6-naphthalenedicarboxylic acid (including dimethyl ester) compared to terephthalic acid (including dimethyl ester). Therefore, it is economically and economically important to collect defective products, scraps, and other products that are generated during the polymerization process or in the process of molding into chips, threads, films, bottles, etc. Is also desirable. However, dyes, flame retardants, reinforcing materials such as glass fibers, general waste and other plastics, especially polyethylene terephthalate, are mixed in these recovered materials, and it is difficult to melt-mold and reuse them as they are. Often. The range of reuse is limited in the recovery from waste products.

Against this background, the recovered polyester scraps are distilled at the same time as the methanolysis reaction to separate most of the impurities which are the residues thereof, and then dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol. If separated and collected, the subsequent separation and purification will be easy, which is desirable from the viewpoint of protecting the global environment, and each resource can be effectively used, leading to a reduction in manufacturing cost.

As a method for recovering and using the naphthalenedicarboxylic acid component from polyalkylene-2,6-naphthalenedicarboxylate waste as a raw material for the production of fibers, films, bottles and industrial resins, (1) Japanese Patent Publication No. 50-11381. In the publication, a material containing polyethylene naphthalate scrap as a main constituent is subjected to a heat depolymerization reaction together with ethylene glycol and a depolymerization reaction catalyst,
A method for recovering naphthalenedicarboxylic acid bisglycol ester and a method for reacting the bisglycol ester with methanol to give naphthalenedicarboxylic acid dimethyl ester are described.

(2) Japanese Patent Laid-Open No. 3-504379 describes a method of depolymerizing with an alcohol and a depolymerization reaction catalyst at high temperature and high pressure to recover it as a naphthalenedicarboxylic acid dialkyl ester.

(3) Japanese Patent Publication No. 58-20951 and Japanese Patent Laid-Open No. 4-316541 disclose a method of treating polyethylene terephthalate with methanol vapor to recover dimethyl terephthalate.

However, both of the above methods (1) and (2), dye, flame retardant,
Reinforcing materials such as glass fiber, other plastics, and general waste are mixed in, and a complicated separation process is required to remove them. Furthermore, in the method (1), the residual polymerization catalyst, which cannot be completely removed in the recrystallization step, acts when the crude bis (β-hydroxyethyl) naphthalate is rectified under reduced pressure, and conversely the polymerization reaction proceeds to increase the yield. It has the drawback of significantly reducing it. Further, the above method (2) is a reaction under high pressure under severe conditions, and further, according to the study by the present inventor, the crude dimethyl naphthalene dicarboxylate is decompressed by a residual polymerization catalyst which cannot be removed as in the case of the above (1). When rectifying, a considerable amount of dimethyl naphthalene dicarboxylate undergoes a deterioration reaction to produce methyl 2-naphthoate. As a result, it became clear that a decrease in yield and a deterioration in the quality of recovered products cannot be avoided. In addition, when an aromatic hydrocarbon solvent unrelated to the reaction is used as a recrystallization solvent, a solvent separation and recovery step separate from methanol is required, and the efficiency of the equipment and the product of the used solvent, dimethyl 2,6-naphthalenedicarboxylate, are reduced. It is not preferable in terms of reverse contamination.

On the other hand, bisβ obtained by depolymerizing the polyethylene terephthalate prepared by the above method (3) with ethylene glycol.
Even if the method of distilling dimethyl terephthalate by blowing methanol gas into hydroxyethyl terephthalate and its polymer and recovering it is directly applied to the depolymerization of polyethylene naphthalate, its rate is extremely slow and not practical. The behavior of dimethyl terephthalate and dimethyl 2,6-naphthalenedicarboxylate produced by depolymerization by this method is not well known.

[0010]

DISCLOSURE OF THE INVENTION The present invention relates to dimethyl 2,6-naphthalenedicarboxylate and dimethyl terephthalate from polyalkylene-2,6-naphthalenedicarboxylate scraps containing miscellaneous impurities mainly composed of polyalkylene terephthalate. For the purpose of separately collecting and separately collecting alkylene glycol and alkylene glycol, separation from dyes, flame retardants, reinforcing materials such as glass fibers, other plastic materials, and general waste, which was difficult by the conventional method, is carried out simultaneously with the reaction. It is intended to solve the problem that dimethyl terephthalate and dimethyl 2,6-naphthalenedicarboxylate, which were not in the prior art, are separately purified to such a quality that they can be used as raw materials for polymers such as fibers.

[0011]

In order to solve such a difficult problem, the present inventor has found that polyalkylene-2,6
-From naphthalene dicarboxylate, polyethylene terephthalate and mixtures with other impurities, 2,6-
We have earnestly conducted research on a method for recovering and separately purifying dimethyl naphthalenedicarboxylate and dimethyl terephthalate. As a result, dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol produced by depolymerization by introducing methanol into these molten mixtures under appropriate conditions were co-evaporated with unreacted methanol to react. At the same time, it is separated from the residue that does not evaporate,
A method for recovering dimethyl 6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol and separately purifying by the following means was found.

(B) The distilled methanol-entrained fraction is cooled to an appropriate temperature for precipitating crystals, and then separated into crystals and a filtrate, dimethyl 2,6-naphthalenedicarboxylate is obtained from the crystals, and dimethyl terephthalate is obtained from the filtrate. And a method for separating and purifying alkylene glycol. (B) The distilled methanol-entrained vapor is separated into methanol and a high-boiling point component, and the methanol is used again in the depolymerization reaction, and the high-boiling point component is distilled to obtain alkylene glycol, dimethyl terephthalate and 2,6-naphthalenedicarboxylic acid. A method of separating and purifying into dimethyl. (C) The above-mentioned reactive distillation is carried out in a batch system to recover the components mainly containing dimethyl terephthalate and alkylene glycol, and then recover the components mainly containing dimethyl 2,6-naphthalenedicarboxylate and alkylene glycol, A method of separately purifying each of the above (a) or (b).

[0013]

The present invention is directed to a polymer (high polymer) containing a polyalkylene-2,6-naphthalenedicarboxylate unit and a polyalkylene terephthalate polymer, or a low polymer thereof or a low polymer thereof and a low weight polymer thereof. While maintaining at least a part of the combined mixture in a molten state, these polymers or their low polymers or their mixtures are fed to a reactor (depolymerization device) and depolymerized while introducing methanol. And generated 2,6
A method of recovering dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol by evaporating dimethyl naphthalenedicarboxylate, terephthaldimethyl and alkylene glycol together with unreacted methanol and separating them from a residue that does not evaporate.

A feature of the present invention is, for example, a polymer containing a polyalkylene-2,6-naphthalene dicarboxylate unit in which a polyalkylene terephthalate is mainly mixed in a reactor equipped with a distillation column, a low polymer thereof, or a mixture thereof. , While maintaining at least a part of it in a molten state, for example, by introducing superheated methanol and contacting it efficiently,
At the same time that the depolymerization reaction proceeds, the produced dimethyl naphthalene dicarboxylate, dimethyl terephthalate and alkylene glycol are distilled out of the reactor through a distillation column together with unreacted methanol on the principle of so-called steam distillation.

Accordingly, a polymer containing a polyalkylene-2,6-naphthalenedicarboxylate unit mainly mixed with polyalkylene terephthalate supplied as a raw material for the present invention, a low polymer thereof or a mixture thereof is a dye or a flame retardant. It may be mixed with reinforcing materials such as glass fiber, other plastic materials, and general waste. The amount of polyalkylene terephthalate mixed is not limited. Further, as another plastic, for example, polyethylene, polypropylene, polyvinyl chloride, or another polyalkylene-2,6-naphthalene dicarboxylate, which has a small difference in specific gravity and is difficult to sort by a mechanical separation method, is mixed. Can also be used as a raw material in the present invention.

The amount of methanol used in the present invention introduced into the reactor is 2 to 15 parts by weight, preferably 3 to 8 parts by weight, relative to 1 part by weight of the raw material waste. That is, if the amount of methanol introduced is less than 2 parts by weight, the production rate of dimethyl 2,6-naphthalenedicarboxylate and the amount of distillate are reduced, which is not preferable in terms of efficiency. On the other hand, if the amount exceeds 15 parts by weight, the amount of energy required for evaporation and heating of the introduced methanol increases, and the operating cost increases, which is not preferable. The temperature of methanol introduced into the reactor may be a temperature at which the melt of the reaction system does not solidify, but is preferably 200 to 300 ° C.

In the present invention, the internal temperature of the reactor, that is, the reaction temperature is preferably 265 to 320 ° C. so that at least a part thereof is in a molten state, and more preferably 280 to 3 ° C.
It is 00 ° C. That is, if the reaction temperature is less than 265 ° C., the fluidity of the contents in the reactor may be lowered, and efficient contact with methanol may be impossible, the reaction rate may be lowered, and dimethyl 2,6-naphthalenedicarboxylate may be reduced. The amount of distillate is reduced. On the other hand, when the reaction temperature exceeds 320 ° C., on the contrary, the polymerization reaction and the thermal deterioration and thermal decomposition of the contents in the reactor are likely to occur, and the quality such as the coloring of dimethyl 2,6-naphthalenedicarboxylate is deteriorated and the alkylene glycol is reduced. The yield of is also reduced.

In the present invention, the reaction pressure is preferably 1 to 10 kg / cm ² G. That is, when it exceeds 10 / cm ² G, it distills out of the reaction system along with unreacted methanol.
-The amount of dimethyl naphthalene dicarboxylate decreases, which is not preferable, and when it is less than 1 kg / cm ² G, the reaction rate of the depolymerization reaction is small, which is not preferable. The effect of the present invention is also obtained by introducing into the reaction system together with an inert gas such as nitrogen gas in order to accelerate the distillation of dimethyl 2,6-naphthalenedicarboxylate and allene glycol.

In the present invention, the polymerization reaction catalyst or the like substantially contained in the polymer or the low polymer thereof acts as a depolymerization reaction / ester exchange reaction catalyst, so that a newly added depolymerization reaction catalyst is not always necessary. Furthermore, in order to make the effect of the present invention remarkable, a depolymerization reaction catalyst can be used. Alkali metal or alkaline earth metal simple substance, hydroxide, oxide, carbonate and acetate effective in the depolymerization reaction of polyethylene naphthalate and ethylene glycol as the depolymerization reaction catalyst; zinc, tin, titanium and antimony , Oxides of manganese, cobalt, or lead, acetates, and the like, and these compounds can be used alone or in combination of two or more kinds.

The amount of the depolymerization reaction catalyst to be added to the reactor is such that the content of the polymer in the reactor is a polyalkylene-2,6-naphthalenedicarboxylate unit-containing polymer and polyalkylene terephthalate or a low polymer thereof or a polymer thereof. It is preferably 0.1 g to 5.0 g per 1 mol of the mixture of the polymer and the low polymer. The amount of catalyst present is 0.
If it is less than 1 g, its effect is small, and if it exceeds 5.0 g, it causes an operational trouble such as the catalyst itself adhering to the inner wall of the reactor as a scale, which is not preferable.
The depolymerization reaction catalyst is preferably added before the introduction of methanol, but is not particularly limited, but it is preferable to add the depolymerization reaction catalyst at the same time as the feeding of the raw material scraps.

The reactor used in the method of the present invention is, for example, (A) a tank reactor with a stirrer equipped with a distillation column,
Further, for example, a tower reactor in which several stages of multi-stage perforated trays and the like are installed inside (B) can be mentioned.

Further, the evaporation fraction containing methanol obtained by this reactive distillation process is cooled to precipitate crystals, and then it is solid-liquid separated into a cake and a filtrate.
It can be recovered in a cake rich in dimethyl naphthalene dicarboxylate and in a filtrate rich in dimethyl terephthalate and alkylene glycol. Polyalkylene-2,
6-Naphthalene dicarboxylate is polyethylene-
When 2,6-naphthalenedicarboxylate, polyalkylene terephthalate is polyethylene terephthalate, and alkylene glycol is ethylene glycol, for example, the ratio of dimethyl naphthalene dicarboxylate and dimethyl terephthalate in the evaporation fraction obtained by depolymerization is 4 In the case where methanol was present in an amount of 1: 1 in the amount of 1: 1, the evaporation fraction was cooled to 40 ° C. and precipitated,
The concentration of dimethyl terephthalate in the cake of dimethyl 2,6-naphthalenedicarboxylate obtained by solid-liquid separation was set to 0.1.
It can be less than or equal to%. When the ratio of dimethyl naphthalenedicarboxylate and dimethyl terephthalate in the evaporation fraction is 7: 3 and methanol is present in an amount of 10 times the total amount thereof, after cooling the evaporation fraction to 40 ° C. and precipitating it,
By further recrystallizing the cake obtained by solid-liquid separation with 6 times the amount of methanol, the dimethyl terephthalate concentration in dimethyl 2,6-naphthalenedicarboxylate can be made 0.1% or less. On the filtrate side, after recovering methanol by atmospheric distillation, ethylene glycol was recovered at, for example, 200 mmHg / 158 ° C., and thereafter, for example, 5 theoretical plates and a reflux ratio of 0.
Distillation under the condition of 2,40 mmHg / 188 to 190 ° C. can give dimethyl terephthalate with less than 0.1% impurities without coloring.

Further, the evaporation fraction obtained in the reactive distillation process is separated into methanol and a high boiling point component by evaporation, and the methanol is used again in the depolymerization reaction, and the high boiling point component is distilled to obtain alkylene glycol, dimethyl terephthalate and It can be purified by distillation fractionation into dimethyl 2,6-naphthalenedicarboxylate. In this case, since the non-evaporated solid component such as a metal compound involved in the polymerization reaction or the decomposition reaction is not contained in the high boiling point component, there is no fear of the polymerization or the decomposition reaction during the distillation operation. Glycol, dimethyl terephthalate and dimethyl 2,6-naphthalenedicarboxylate can be separated and purified by distillation, respectively, and a fraction free from coloration can be obtained.

Further, a polymer containing a polyalkylene-2,6-naphthalenedicarboxylate unit mixed with polyalkylene terephthalate, a low polymer or a mixture thereof is depolymerized with methanol to produce 2,6-naphthalene. When carrying out distillation with dimethyl dicarboxylate, dimethyl terephthalate and alkylene glycol entrained in unreacted methanol, it is carried out in a batch reaction, and (a) first, dimethyl terephthalate and alkylene glycol are recovered as fractions of the main component, then (B) Dimethyl 2,6-naphthalenedicarboxylate and alkylene glycol were recovered as main component distillates, and each evaporative distillate was cooled to precipitate crystals, which were then separated into cake and filtrate by solid-liquid separation. For example, (a) is a cake and an almond containing a large amount of dimethyl terephthalate. The filtrate rich in glycol, (b) can be recovered in the filtrate rich in cake and alkylene glycol containing much dimethyl 2,6-naphthalene dicarboxylic acid. Further, when (a) and (b) are obtained, methanol and a high boiling point component are respectively separated by evaporation, and methanol is used again in the depolymerization reaction, and (a) is an alkylene glycol by distillation purification of each high boiling point component. It is possible to efficiently obtain dimethyl terephthalate, (b) alkylene glycol, and dimethyl 2,6-naphthalenedicarboxylate.

Further, the polyalkylene-2,6 of the present invention
-Naphthalenedicarboxylate is a polyethylene-2,6-naphthalenedicarboxylate which is already used as a base polymer for video films but is promising as a base polymer for bottles because of its high gas barrier property. If the polyalkylene terephthalate is a general-purpose polyethylene terephthalate, the effect of the present invention is great.

Further, in the present invention, for example, two reactors are connected in series, and in the first reactor, the purpose is to partially depolymerize with methanol or ethylene glycol to lower the melting temperature, part of which is depolymerized. The second polyalkylene naphthalene dicarboxylate with attached distillation column
The dimethyl naphthalene dicarboxylate and the alkylene glycol produced at the same time as being supplied to the reactor and progressing the depolymerization reaction with methanol are removed from the reactor system along with unreacted methanol through the distillation column attached to the second reaction tank. It can also be distilled.

Hereinafter, the contents of the present invention will be described in more detail with reference to examples.

[0028]

Example 1 5 of polyethylene-2,6-naphthalene dicarboxylate (hereinafter abbreviated as 2,6-PEN) and polyethylene terephthalate (hereinafter abbreviated as PET)
100 g of 0:50 polymer alloy was charged into a 300 ml stirred autoclave and melted at 280 ° C., and 260 was obtained from a blowing nozzle dipped in the melted polymer.
280 ° C, 5.0kg while blowing methanol vapor superheated to ℃ at a rate of 320g per hour
/ Cm ² G It was made to react for 1.5 hours. At the time, 61.9 g of methanol was recovered by distillation from the fraction containing methanol that had been distilled, and 51.9% by weight of dimethyl terephthalate (hereinafter abbreviated as DMT), methyl-, hydroxyethyl-terephthalate (hereinafter referred to as MHET).
3.1% by weight, dimethyl 2,6-naphthalenedicarboxylate (hereinafter abbreviated as NDCE) 10.
A mixture A containing 8% by weight and 34.2% by weight of ethylene glycol (hereinafter abbreviated as EG) was obtained. Thereafter, a part of the recovered methanol was used, and the reaction temperature was raised to 290 ° C., and the reaction was continued for another 1.5 hours under the same conditions. The methanol-containing fraction distilled at this point was cooled to 40 ° C. with stirring, and solid-liquid separation was performed by filtration to obtain a cake and a filtrate. Methanol was evaporated from the cake and the filtrate, and the cake was free of methyl 2-naphthoate and had no color and a purity of 99.9% by weight.
40 g of NDCE was obtained. 7 DMT from the filtrate
18.2 g of a mixture B containing 2.0% by weight, 1.5% by weight of MHET, 0.6% by weight of NDCE and 26.4% by weight of EG was obtained.

Further, the mixture A and the mixture B were combined and separated by distillation to obtain 27 g of EG, 47 g of DMT and 7 g of ND.
CE was obtained.

Expressing the above results as a yield with the molar amount of the raw material unit present in the charged polymer alloy as the denominator, it reached 93 mol% in the case of NDCE, 93 mol% in the case of DMT and 94% in the case of EG. .

[0031]

Example 2 100 g of scrap PEN was charged into a 300 ml stirred autoclave, melted at 300 ° C., and methanol vapor superheated to 260 ° C. was blown from the molten polymer at a rate of 320 g per hour. While blowing at the same time as nitrogen gas, at 290 ° C. and 5.0 kg / cm ² G,
Reacted for 3.0 hours. The remaining 112.0 g of a mixture containing 79% by weight of NDCE and 21% by weight of EG was obtained by recovering the methanol by distillation from the fraction containing the distilled methanol.

Expressing the above results as a yield with the molar amount of raw material unit present in the charged polymer alloy as the denominator, it reached 89% for NDCE and 93% for EG.

[0033]

Examples 3 to 5 The reaction was carried out under the conditions of Example 2 except that 2 g of anhydrous sodium carbonate, zinc acetate and tin oxide were used as catalysts and the reaction time was changed according to the reaction rate. The results are shown in Table 1.

[0034]

[Table 1]

[0035]

[Examples 6 to 7] The reaction pressure was 2.0 or 8.0 kg.
/ Cm ² G except that the reaction was performed under the conditions of Example 2.
The results are shown in Table 2.

[0036]

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C07C 67/54 67/60 69/82 A 9279-4H

Claims (9)

[Claims] 1. A high polymer and / or low polymer containing an alkylene-2,6-naphthalenedicarboxylate unit,
A high polymer and / or low polymer containing an alkylene terephthalate unit and a mixture thereof are fed to a reactor while keeping at least a part thereof in a molten state, and the polymer and the polymer are introduced while introducing methanol. 2,6-naphthalenedicarboxylic acid, which comprises depolymerizing the mixture and evaporating dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol produced by the reaction together with unreacted methanol to separate a residue that does not evaporate. A method for recovering dimethyl acid dimethyl, dimethyl terephthalate and alkylene glycol. 2. 1 part by weight of a high polymer and a low polymer of alkylene-2,6-naphthalene dicarboxylate, a high polymer and a low polymer of alkylene terephthalate and a mixture thereof (hereinafter referred to as a feed raw material). In contrast, the amount of methanol introduced into the reactor is 2 to 15 parts by weight.
The collection method described in. 3. The method according to claim 1, wherein the depolymerization reaction temperature is 265 to 320 ° C. 4. The depolymerization reaction pressure is 1 to 10 kg / cm.
The method according to claim 1, which is ² G. 5. The method according to claim 1, wherein a depolymerization reaction catalyst is used. 6. The methanol-entrained evaporation fraction obtained by the method according to any one of claims 1 to 5 is cooled and recrystallized, and then solid-liquid separated into a cake and a filtrate, and 2,6-naphthalene is obtained from the cake obtained. A method for separately purifying dimethyl terephthalate and alkylene glycol from dimethyl dicarboxylate and a filtrate. 7. The methanol-entrained evaporative fraction obtained by the method according to any one of claims 1 to 5 is separated by evaporation into methanol and a high-boiling component, and the methanol is used again in the depolymerization reaction, and the high-boiling component is distilled. A method in which alkylene glycol, dimethyl terephthalate and dimethyl 2,6-naphthalenedicarboxylate are fractionated by distillation for purification. 8. The method according to claim 1, wherein the high polymer, the low polymer and the mixture are depolymerized with methanol, and the produced dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and alkylene glycol are unreacted methanol. When carrying out the distillation with, carry out in a batch reaction,
(A) Dimethyl terephthalate and alkylene glycol are recovered as a main component fraction, and then (b) dimethyl 2,6-naphthalenedicarboxylic acid and alkylene glycol are recovered as a main component fraction.
A method for fractionating and purifying by the means described in. 9. The polyalkylene-2,6-naphthalenedicarboxylate is polyethylene-2,6-naphthalenedicarboxylate, the polyalkylene is polyethylene terephthalate and the alkylene glycol is ethylene glycol. the method of.