JP2000212117A - Recovery of highly pure terephthalic acid from recovered polyester bottle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for effectively recovering terephthalic acid and ethylene glycol from a recovered PET in a short time by using a carbonic acid salt having a cost lower than a hydroxide without using a special inert gas. SOLUTION: A crushed product obtained by crushing a recovered polyethylene terephthalate is brought into contact with a carbonic acid salt at the temperature of 120-190 deg.C in the presence of a solvent to degrade the polyethylene terephthalate into a terephthalic acid salt, and ethylene oxide and/or ethylene glycol. The produced terephthalic acid salt is separated from the solvent by a solid-liquid separation, and the separated solid of the terephthalic acid salt is dissolved in water. The solution is neutralized by an acid, and the obtained terephthalic acid is separated, washed and dried to provide the objective highly pure terephthalic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering high-purity terephthalic acid from a recovered polyester (PET) bottle, and more particularly, to a method in which a recovered PET bottle is pulverized, and flakes and powders are carbonated. The present invention relates to a method for recovering high-purity terephthalic acid by pyrolysis.

[0002]

2. Description of the Related Art There are three known methods for recycling recycled PET bottles: (1) material recycling, (2) thermal recycling, and (3) chemical recycling. Is being used. Also, it is said that thermal recycling is not suitable for heat recovery alone because it generates less heat than other petroleum-based plastics. In chemical recycling, PET is decomposed into constituent monomers and is intended to be reused as a raw material. For example, many proposals have been made on the recovery of terephthalic acid.

The recovery of terephthalic acid from terephthalic acid alkali salt is disclosed in Japanese Patent Publication No. 5-64133.
A waste liquid containing an alkali salt of terephthalic acid (excluding a waste liquid from a process for reducing the weight of polyester fiber) is subjected to acid precipitation to precipitate terephthalic acid crystals. A method for recovering terephthalic acid, which is carried out at a temperature of ° C., is described.

The recovery of terephthalic acid from recovered polyethylene terephthalate by alkali decomposition has already been proposed, and Japanese Patent Application Laid-Open No. Hei 4-322550 discloses an alkali metal or alkaline earth metal salt of terephthalic acid or terephthalic acid itself. A process for producing a polyterephthalic acid polyol with an alkali metal or alkaline earth metal hydroxide, the reaction being carried out in the absence of water or by weight of an alkali metal or alkaline earth metal. Performed at 130-190 ° C. in the presence of an amount of water at most equal to the amount of metal hydroxide, the proportion of alkali metal or alkaline earth metal hydroxide is terephthalic acid completely converted to salt. Of the stoichiometry for polyterephthalate calculated to yield
A method is described which is characterized in that, after this reaction, if necessary, if terephthalic acid is the desired product, acidification is carried out.

Japanese Patent Application Laid-Open No. Hei 9-286744 discloses that polyethylene terephthalate granules, powders, small pieces, or aggregates thereof, or a mixture of two or more of them are mixed with an excess of caustic soda in ethylene glycol. And stirring the mixture between room temperature and 195 ° C., and contacting the mixture to separate the generated sodium terephthalate as a solid, and describes a method for recovering terephthalic acid and ethylene glycol from polyethylene terephthalate.

[0006]

The alkaline decomposition method of the recovered PET shown in the above proposal is based on the method of P under relatively mild conditions.
It has the advantage that ET can be decomposed into terephthalate and ethylene glycol, but in order to prevent oxidation during decomposition, the decomposition reaction must be performed in an atmosphere of an inert gas. There's a problem.

[0007] In the above proposal, separation of decomposed sodium terephthalate and ethylene glycol is not easy, and in order to realize the chemical recycling of recovered PET, the cost of decomposition, separation and purification must be reduced. This is an important issue, and it is required that these processing operations are not complicated.

Conventionally, all of the alkali agents used in the alkali decomposition method are hydroxides such as caustic soda, and examples using carbonates have not yet been known. this is,
It is believed that decomposition of carbonate was believed to occur only at high temperatures (eg, 320 ° C. or higher for sodium carbonate).

[0009] The present inventors have found that the decomposition of carbonate occurs in the presence of PET at a much lower temperature than the decomposition temperature of itself, and the use of carbonate allows PET to be combined with terephthalate and ethylene. It has been found that the compound can be effectively decomposed into oxide and / or ethylene glycol.

That is, an object of the present invention is to use terephthalic acid from recovered PET using a carbonate which is less expensive than hydroxide and without using a special inert gas.
Another object of the present invention is to provide a method capable of effectively recovering ethylene glycol by a short-time treatment.

[0011]

According to the present invention, a carbonate and a pulverized or crushed product of recovered polyethylene terephthalate are brought into contact with each other at a temperature of 120 to 190 ° C. in the presence of a solvent to form terephthalate and ethylene. The terephthalate generated by decomposition into oxides and / or ethylene glycol is solid-liquid separated from the solvent, the terephthalate solid is dissolved in water, the aqueous solution is neutralized with an acid, separated, washed and dried. To obtain high-purity terephthalic acid. In the method of the present invention: 1. the carbonate is sodium carbonate; 2. contacting the carbonate in a state of being dissolved or dispersed in a solvent with a ground or crushed product of the recovered polyethylene terephthalate; 3. the solvent is a polyhydric alcohol; It is preferred that the carbonate contains a small amount of alkali hydroxide. The method of the present invention has a temperature of
The carbonate and the pulverized or crushed product of the recovered polyethylene terephthalate are continuously charged into a reaction device at a temperature of 190 ° C. in a volume ratio that produces terephthalate, decomposed, and the terephthalate containing the solvent is reacted. It is preferably carried out by continuously taking out from the apparatus, and in this case: 1. performing the decomposition at a temperature of 140 ° C. to 180 ° C. and substantially at atmospheric pressure; 2. the carbonate is sodium carbonate containing 0 to 20% of an alkali hydroxide, and the solvent is ethylene glycol; 3. centrifuging the solvent-containing terephthalate to obtain a solvent and terephthalate solids; The terephthalate solid is dissolved in 5 to 10 times the amount of water, and the solution is placed in an activated carbon tower at 5 to 10 mm / cm ² · mi.
4. pass through at a linear flow rate of n to adsorb impurities and recover a pure terephthalate aqueous solution; It is preferable that the activated carbon tower further includes a layer of an ion exchange resin.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a carbonate and a crushed or crushed product of recovered polyethylene terephthalate are subjected to a temperature of 120 to 190 ° C., preferably 140 to 180 ° C.
Temperature. That is, decomposition of carbonate does not occur in the above temperature range when it is present alone, but when polyethylene terephthalate is present,
It occurs in the above low temperature range, which is a completely unexpected finding.

The decomposition reaction of polyethylene terephthalate by carbonate is presumed to be as shown in the following formula (1) or (2).

Embedded image

Embedded image That is, due to metathesis of carbonate and polyethylene terephthalate, terephthalate and ethylene oxide and / or ethylene glycol are generated, and at the same time, carbon dioxide gas is generated. That is, in the present invention, the reaction system is maintained in an inert gas atmosphere by carbon dioxide gas generated during decomposition, oxidation during thermal decomposition is suppressed, and the carbon dioxide gas generated from the reaction system is dissolved in the reaction system or Since it acts to purge the adsorbed oxygen, it is very advantageous in suppressing oxidation. That is, when water does not exist in the reaction system, ethylene oxide is generated by metathesis as shown in formula (1), and when water in some form exists in the reaction system, formula (2) As shown in the above, ethylene glycol is produced by metathesis. Of course, the reaction of the formula (1) and the reaction of the formula (2) sometimes proceed in parallel.

In the conventional alkali decomposition, it is essential to introduce an inert gas into the reaction system to maintain a non-oxidizing atmosphere, and it is difficult to separate the reaction system from ethylene glycol. Such an operation is unnecessary, which is advantageous in terms of operation and cost. In particular,
In a reaction in a system in the absence of moisture, ethylene oxide is generated in the form of a gas. By collecting this in water or sulfuric acid, ethylene glycol can be recovered in a relatively pure form. Further, the use of carbonate has an advantage that the material cost can be considerably reduced as compared with the case where hydroxide is used. For example, in the case of sodium carbonate, it will be apparent that the price is almost half that of sodium hydroxide, which can significantly reduce the cost of decomposition.

In the present invention, the carbonate and the pulverized or crushed product of the recovered polyethylene terephthalate are allowed to stand in the presence of a solvent at 120 to 190 ° C., preferably 140 to 180 ° C.
It is also important to make contact at a temperature of ° C. That is, when the carbonate and the pulverized or crushed material of PET are brought into contact with each other by powder, the decomposition reaction does not substantially proceed, but by contacting both via a solvent, the decomposition reaction proceeds smoothly. become. It is also important that the temperature at the time of contact be in the above range. That is, when the temperature is lower than the above range, the decomposition reaction speed is considerably reduced compared to the case where the temperature is within the above range, which is not practical, and the higher the temperature, the higher the decomposition speed.
Exceeding the above range is not preferred because side decomposition reactions, solvent decomposition, isomerization, decomposition of impurities, and the like are likely to occur, and the burden on the purification operation increases.

The coexistence of a small amount of alkali hydroxide with the carbonate used is preferred from the viewpoint of accelerating the reaction and lowering the reaction temperature. That is, in the present invention, although carbonate is consumed in the decomposition of PET, it is recognized that the coexisting alkali hydroxide acts as a catalyst or accelerator for the decomposition reaction. However, if the amount of the alkali hydroxide is too large, separation from the solvent tends to be difficult.

According to the present invention, the recovery P
Since the pulverized or crushed ET can be decomposed into terephthalate and ethylene oxide and / or ethylene glycol by carbonate, the terephthalate produced is separated from the solvent by solid-liquid separation, and the terephthalate solid is separated from water. And the aqueous solution is neutralized with an acid, and separated, washed and dried to obtain high-purity terephthalic acid.

[Decomposition reaction] The recovered PET bottle is
In order to be able to disassemble in a compact reactor, it is necessary to make the bulk as small as possible, for which purpose it is ground or crushed. It is generally desirable that the size of the pulverized or crushed product is generally within 5 mm square. Although not generally necessary, the crushed or crushed material can be subjected to a washing treatment with water or hot water in order to avoid contamination with impurities.
The PET pulverized or crushed material used may inevitably contain other plastics such as vinyl chloride resin, polyethylene, polypropylene and polystyrene, but these other plastics are not decomposed. Since it remains as a residue, it can be separated by post-decomposition treatment.

As the carbonate, an alkali metal salt or an alkaline earth metal salt of carbonic acid is used. Particularly, alkali metal salts such as sodium salt and potassium salt are preferable, and sodium carbonate is most preferable. Sodium carbonate includes monohydrate, heptahydrate, decahydrate and the like in addition to anhydrides. All of them can be used for the purpose of the present invention, but anhydrides are preferred. In addition, the carbonate includes sodium hydrogen carbonate, which can be used for the purpose of the present invention.

As the solvent, the aforementioned 120 to 190 ° C.
Any of those which exist in a stable liquid state at the decomposition temperature can be used. Generally, it is preferred that this solvent does not substantially dissolve the terephthalate formed by decomposition. Suitable examples of solvents are by no means limited to polyhydric alcohols such as ethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, diethylene glycol, triethylene glycol, Tetraethylene glycol, glycerin, cyclohexanedimethanol and the like. Of these, ethylene glycol is particularly preferred. Because ethylene glycol is PE
This is because it is recovered by decomposition of T, and by using this, solvent cost can be reduced. Further, ethylene glycol is particularly suitable for the purpose of the present invention in that it promotes the decomposition reaction between carbonate and PET and does not substantially dissolve terephthalate.

The ratio of the carbonate to the pulverized or crushed material of the recovered PET is desirably in a stoichiometric amount to a slightly excessive amount.
The amount is preferably 1.5 to 1.5 times, particularly 1.1 to 1.3 times. On the other hand, the amount of the solvent is not particularly limited, but it is recommended to use 1.5 to 5.5 times by weight, particularly 2 to 4 times by weight, based on the weight of the carbonate. When the amount of the solvent is smaller than the above range, the wettability of the PET pulverized or crushed material becomes insufficient, and the reaction tends to not proceed smoothly. On the other hand, even when the amount is larger than the above range, the decomposition reaction is particularly excellent. It is disadvantageous because it has no advantage and the volume of the reaction vessel is increased, and is disadvantageous for the separation step.

When an alkali is present in the carbonate as a catalyst or a reaction accelerator, sodium hydroxide or the like is preferably present in an amount of 2 to 20% by weight, particularly 5 to 10% by weight, based on the carbonate.

The sub-decomposition reaction between the carbonate and the PET pulverized or crushed product can be carried out continuously or batchwise under stirring. The reaction temperature is 120 to 190 ° C.
In this range, the pressure is sufficient at atmospheric pressure, but of course, the pressure may be slightly higher than atmospheric pressure. The reaction time is not particularly limited, but a short time of about 10 to 30 minutes is generally sufficient.

In the case of a continuous reaction, a reactor equipped with a screw is used, a raw material is charged from one side, and a decomposition product is taken out from the other side. In a preferred embodiment of the present invention, a temperature of 120
A carbonate and a crushed or crushed product of the recovered polyethylene terephthalate in a solvent at a temperature of from 0 ° C. to 190 ° C. are continuously introduced into a reactor at an amount ratio that yields terephthalate, and decomposed.
The solvent-containing terephthalate is continuously removed from the reactor.

Since the decomposition product contains terephthalate in a solid state, the terephthalate can be separated from the solvent by subjecting it to a solid-liquid separation operation such as filtration or centrifugation. Can be.

Ethylene oxide generated in the form of gas during the metathesis reaction can be separated from carbon dioxide gas by passing it in water or sulfuric acid water and collected in the form of relatively pure ethylene glycol. . By subjecting the separated ethylene glycol to precision distillation, pure ethylene glycol can be recovered. Further, when ethylene glycol is produced by metathesis, it remains in the solvent, so that pure ethylene glycol can be recovered by subjecting the solvent to the above-mentioned precision distillation. When ethylene glycol is used as a solvent, ethylene oxide may be added to the solvent to form an adduct such as diethylene glycol. These components can also be separated by distillation.
Furthermore, ethylene carbonate obtained by adding carbon dioxide to ethylene oxide may be by-produced.

The terephthalate separated as a solid is dissolved in water and the solution is filtered. As a result, unreacted PET and solid impurities are separated from the terephthalate solution. Of course, vinyl chloride resin, polyethylene,
Contaminants such as other plastics such as polypropylene and polystyrene are also separated. In order to dissolve the terephthalate in water, if 5 to 20 times by weight, especially 7 to 12 times by weight of water is used with respect to the terephthalate, purification of the solution and subsequent acid precipitation can be easily performed. It is.

The terephthalate solution recovered by the solid-liquid separation still contains dispersed fine particles such as ionic impurities and colorants. Preferably, a purification treatment is performed to remove these impurities. In this purification treatment, an adsorbent such as activated carbon, an ion exchange resin, or the like can be used.

As a preferred example of the purification operation, the terephthalate solid is dissolved in 5 to 10 times the amount of water, and this solution is passed through an activated carbon tower at a linear flow rate of 5 to 10 mm / cm ² · min. The impurities are adsorbed, and a pure terephthalate aqueous solution is recovered. At this time, it is convenient to further include a layer of an ion exchange resin in the activated carbon tower, because the trapping of ionic impurities can be effectively performed.

An acid is added to the aqueous terephthalate solution from which the impurities have been removed to precipitate terephthalic acid as crystals. As the acid, mineral acids such as sulfuric acid, hydrochloric acid, phosphoric acid and nitric acid are used, but sulfuric acid is preferred. For the acid precipitation of terephthalic acid, it is preferable to add an acid so that the pH in the system is on the acidic side of 7 or less. The precipitated terephthalic acid is subjected to solid-liquid separation and washed with water to remove sulfuric acid, sodium sulfate, ethylene glycol and the like adhering to the terephthalic acid crystals. Thus, the recovered terephthalic acid can be dried, granulated if necessary, and effectively reused as a raw material such as polyethylene terephthalate.

[0031]

The present invention will be further described with reference to the following examples.

Example 1 A heating reactor equipped with a 100 mm diameter × 500 mm screw with a 5 mm pitch wing was filled with ethylene glycol, the temperature was raised to 170 ° C., and 20 g of recovered PET (6 to 8 mm square flakes) was carbonated. A mixture of 11 g of soda / min was continuously charged and reacted at a screw rotation of 10 rpm, and after 30 minutes, terrestrial sodium terephthalate containing EG was sufficiently subjected to centrifugal filtration (EG remaining about 5%). After drying in a vacuum oven at 130 ° C. for 2 hours, the liquid component was sufficiently removed to obtain 720 g of a dry solid (Na terephthalate and insoluble PET, solid impurities) and 900 g of a filtrate (EG and dissolved impurities). The filtrate is distilled by a conventional method to recover EG having high purity. On the other hand, the dry solid content is dissolved with 10 times the volume of water and centrifuged to remove water-insoluble solids. Next, the filtrate was passed through an activated carbon tower to adsorb impurities dissolved in water to obtain about 7000 cc of high purity Na terephthalate solution. (The activated carbon tower has a multi-stage structure in which the particle size of the activated carbon is reduced in order from the top, and has a structure in which a cation exchange resin layer is inserted in the middle stage.) The obtained sodium terephthalate solution 7000
Concentrated sulfuric acid in about 3 cc.
10 g was added, and the neutralized terephthalic acid and sodium sulfate were centrifugally filtered to obtain a solid terephthalic acid and a sodium sulfate solution as a filtrate. Wash the solid terephthalic acid thoroughly with water,
After drying, 510 g of terephthalic acid was recovered. Purity 9
9.9% and the recovery was 98.5%. The sodium sulfate solution of the filtrate was heated to remove water, and could be used as sodium sulfate.

Example 2 A mixture of 10 g of sodium carbonate and 2 g of NAOH mixed with 20 g of recovered PET (flakes of 6 to 8 mm square) was reacted in the same apparatus as in Example 1 to obtain sodium terephthalate containing EG after filtration. . Since about 20% of EG was contained, the same operation as in Example 1 was carried out to obtain terephthalic acid having a purity of 99.9%, except that drying was performed in a vacuum oven at 130 ° C. for 12 hours to sufficiently remove liquid components.

Comparative Example 1 Powder N was added to 20 g (6-8 mm square flakes) of recovered PET.
A mixture of 20 g of AOH / min was reacted in the same apparatus as in Example 1 while supplying nitrogen gas as an inert gas, followed by filtration to obtain terephthalic acid NA containing EG.
Since about 35% of EG was contained, except that it was dried in a vacuum oven at 130 ° C. for 24 hours to sufficiently remove liquid components.
By performing the same operation as in Example 1, terephthalic acid having a purity of 99.1% was obtained.

[0035]

According to the present invention, it has been found that PET can be effectively decomposed into terephthalate and ethylene oxide and / or ethylene glycol at a relatively low temperature in a short time by using a carbonate. According to the present invention,
Terephthalic acid and ethylene glycol can be effectively recovered from recovered PET in a short period of time using carbonates that are less expensive than hydroxides and without using any special inert gas. There is an advantage.

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[Procedure amendment]

[Submission date] February 3, 1999 (1999.2.3)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

[0011]

According to the present invention, a carbonate and a pulverized or crushed product of recovered polyethylene terephthalate are brought into contact with each other at a temperature of 120 to 190 ° C. in the presence of a solvent to form terephthalate and ethylene. The terephthalate generated by decomposition into oxides and / or ethylene glycol is solid-liquid separated from the solvent, the terephthalate solid is dissolved in water, the aqueous solution is neutralized with an acid, separated, washed and dried. To obtain high-purity terephthalic acid. In the method of the present invention: 1. the carbonate is sodium carbonate; 2. contacting the carbonate with the pulverized or crushed product of the recovered polyethylene terephthalate in a state of being dispersed in the solvent; 3. the solvent is a polyhydric alcohol; It is preferred that the carbonate contains a small amount of alkali hydroxide. The method of the present invention has a temperature of
The carbonate and the pulverized or crushed product of the recovered polyethylene terephthalate are continuously charged into a reaction device at a temperature of 190 ° C. in a volume ratio that produces terephthalate, decomposed, and the terephthalate containing the solvent is reacted. It is preferably carried out by continuously taking out from the apparatus, and in this case: 1. performing the decomposition at a temperature of 140 ° C. to 180 ° C. and substantially at atmospheric pressure; 2. the carbonate is sodium carbonate containing 0 to 20% of an alkali hydroxide, and the solvent is ethylene glycol; 3. centrifuging the solvent-containing terephthalate to obtain a solvent and terephthalate solids; The terephthalate solid is dissolved in 5 to 10 times the amount of water, and the solution is placed in an activated carbon tower at 5 to 10 mm / cm ² · mi.
4. pass through at a linear flow rate of n to adsorb impurities and recover a pure terephthalate aqueous solution; It is preferable that the activated carbon tower further includes a layer of an ion exchange resin.

Continued on the front page F term (reference) 4F301 AA25 CA03 CA04 CA09 CA24 CA32 CA65 CA68 CA72 4H006 AA02 AC41 AC46 AD15 AD17 AD32 BA72 BB14 BC10 BC31 BD82 BE10 BE12 BS30

Claims (10)

[Claims] [Claim 1] A carbonate and a pulverized or crushed product of recovered polyethylene terephthalate are mixed with each other in the presence of a solvent at 120 to 19%.
Contacting at a temperature of 0 ° C. to decompose terephthalate into ethylene oxide and / or ethylene glycol,
The resulting terephthalate is separated from the solvent by solid-liquid separation, the terephthalate solid is dissolved in water, the aqueous solution is neutralized with an acid, and separated, washed and dried to obtain high-purity terephthalic acid. Features method. 2. The method according to claim 1, wherein the carbonate is sodium carbonate. 3. The method according to claim 1, wherein the solvent is a polyhydric alcohol. 4. The method according to claim 1, wherein the carbonate contains a small amount of alkali hydroxide. 5. A method in which a carbonate and a crushed or crushed product of recovered polyethylene terephthalate are continuously charged in a solvent at a temperature of 120 ° C. to 190 ° C. at a ratio by which terephthalate is produced, to be decomposed. 5. The method according to claim 1, wherein the terephthalate containing the solvent is continuously removed from the reactor. 6. The method according to claim 5, wherein the decomposition is carried out at a temperature of 140 ° C. to 180 ° C. and substantially at atmospheric pressure. 7. The carbonate contains 0 to 20% of an alkali hydroxide.
The method according to claim 5 or 6, wherein sodium carbonate is contained in a proportion of 0.1%, and the solvent is ethylene glycol. 8. The method according to claim 7, wherein the solvent-containing terephthalate is centrifuged to obtain a solvent and a terephthalate solid. 9. A terephthalate solid is dissolved in 5 to 10 times the amount of water, and the solution is placed in an activated carbon tower at 5 to 10 mm / cm.
Impregnated by passing at a linear flow rate of ² min,
The method according to claim 5, wherein an aqueous terephthalate solution having a high purity is recovered. 10. The method of claim 9, wherein the activated carbon tower further comprises a layer of an ion exchange resin.