JP2003128600A - Method for producing terephthalic acid from waste bottle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which high-purity dimethyl terephthalate (DMT) is obtained from waste polyethylene terephthalate (PET) bottle if other bottles than the PET without contamination with impurities and highly-pure terephthalic acid suitable as a raw material for PET for bottles can be obtained. SOLUTION: The waste PET bottle as the principal component and other bottles different from PET are subjected to pretreatment such as pulverization, washing and removal of foreign materials. The pretreated wastes are subsequently depolymerized with ethylene glycol and then subjected to transesterification with methanol to recover high-purity DMT. The DMT is subsequently treated by a hydrolysis reaction to afford powder of terephthalic acid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a chemical reaction treatment after a resin bottle waste containing polyethylene terephthalate (PET) as a main component and a component different from that is subjected to pretreatments such as crushing, washing and removing foreign substances. Is added to recover high-purity dimethyl terephthalate as an active ingredient to obtain high-purity terephthalic acid by a chemical reaction, that is, terephthalate, which is used as a polymer raw material for PET bottles, is recovered from used PET bottles. It relates to a method for producing an acid.

[0002]

2. Description of the Related Art Polyethylene terephthalate (PET)
The polyalkylene terephthalate represented by is excellent in its chemical stability, so it is produced and used in large quantities in the food field such as life related materials such as fibers, films, resins, and bottles for drinking water and carbonated drinks. Has been done.

However, the processing costs of waste of fiber / film / resin products and polyester of nonstandard products which are generated in large quantities with the increase of production / usage amount are not only related to the manufacturing cost. These treatments have become a very big social problem at present, and various proposals have been made for their recycling methods.

Among the wastes, the processing of PET bottles is becoming more serious due to its bulkiness. Nevertheless, as the recycling method, as material recycling, only the recycling to the extent that the collected used PET bottles are melted again to be fiberized is carried out. It cannot be used again as a PET bottle due to the deterioration of its physical properties.

On the other hand, in the refill method of cleaning and refilling PET bottles, the cost of collection, the safety and hygiene viewpoint, the number of reuses is limited, and the PET bottles are eventually discarded. However, there is a problem that it cannot be a permanent measure.

Further, PET bottle scraps include foreign resins such as labels, shrink films, base cups and caps, different polymers such as polyvinyl chloride and polyolefin resins, aluminum derived from caps, adhesives, pigments and dyes. May be mixed. It is unavoidable to mix foreign materials into the PET bottle packing bale that has been separated and collected.

Also in chemical recycling in which such PET bottle waste is decomposed into a monomer constituting a PET polymer using water, a solvent such as methanol or ethylene glycol, and reused, the foreign material is subjected to heating operation and reaction operation. When various decomposition gases (such as hydrogen chloride gas) are generated in the process, or melted and solidified in the recovery device to damage the equipment or significantly deteriorate the quality of the monomer (DMT) recovered by the chemical reaction. There is.

As an example of chemical recycling, a method of hydrolyzing polyester waste in the presence of an alkaline compound to obtain terephthalic acid, which is described in JP-A-11-21374, and WO-97 / 24310, the alkali is also used. Method of hydrolyzing polyester waste in the presence of compound and further neutralizing with acid to obtain terephthalic acid, US Pat.
There is a method for obtaining dimethyl terephthalate and ethylene glycol by vapor-phase methanol decomposition in methanol described in Japanese Patent No. 952520. But these are all
Since high-temperature reaction conditions of 200 ° C or higher are required, 19
There is a problem that the decomposition starts at 0 ° C., and the decomposition product has a very low tolerance for inclusion of polymers different from polyesters such as polyvinyl chloride, which deteriorates the quality of the final product.

Further, in Japanese Patent Laid-Open No. 2000-169623, polyethylene terephthalate waste is decomposed with ethylene glycol, and recovered bis-β-hydroxyethyl terephthalate (BHET) is purified by a thin film evaporator, and then BHET is melt polycondensed. A process for obtaining a polyethylene terephthalate polymer has been proposed, but in this case as well, there is a step of imposing a thermal history of 200 ° C. or higher, and the tolerance of incorporation of thermally decomposing different polymers such as polyvinyl chloride is low. That is, although chemical recycling has a higher tolerance of mixing impurities than material recycling, it was necessary to almost completely remove impurities in the pretreatment process.

On the other hand, PET polymers for bottles are dimethyl terephthalate (DMT) or terephthalic acid (T
It is generally known that A) is used as a starting material to obtain an oligomer by a transesterification reaction or an esterification reaction with ethylene glycol (EG), followed by a polycondensation reaction. Is not sufficiently purified to obtain a PET polymer usable for PET bottles.

Due to such various restrictions, the method of recovering an active ingredient from a used PET bottle by a chemical recycling method and obtaining terephthalic acid which can be used again as a PET polymer raw material for a PET bottle has hitherto been known. In reality, there is no proposal for practical use.

[0012]

SUMMARY OF THE INVENTION The present invention has been made against the background of the above-mentioned prior art, and its object is to remove impurities from resin bottle waste containing PET as a main component and a component different from PET as impurities. It is an object of the present invention to provide a method capable of obtaining a high-purity monomer (DMT) without being contaminated by the contamination of the above, and then efficiently producing terephthalic acid suitable as a raw material for PET for bottles from the high-purity DMT. .

[0013]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned conventional objects, the present inventors have found that resin bottle waste containing PET as a main component and a component different from PET After pretreatment such as crushing, washing, and removal of foreign substances, chemical reaction treatment is added to recover high-purity dimethyl terephthalate, which can be further hydrolyzed to obtain high-purity PET polymer suitable for bottles. Of terephthalic acid is obtained, that is, for example, from collected plastic bottle waste such as used PET bottles, P for bottles can be obtained.
The inventors have found that high-purity terephthalic acid, which is a raw material for ET polymer, can be efficiently obtained, and completed the present invention.

Thus, according to the present invention, "a resin bottle waste containing polyethylene terephthalate (PET) as a main component and a component different from that,
A method for producing terephthalic acid from a resin bottle waste, which is sequentially provided in the following steps (1) to (19). (1) The step of unpacking the resin bottle waste packing bale containing the separated and collected PET as a main component and a different component, (2) the unpacked resin bottle waste is 2 to 30 mm Crushing process to make flakes of corners, (3) PET such as label thin film made of polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), etc. from flaky resin bottle pieces
The process of separating the component polymers different from
(4) A decanter step that also serves to wash foreign substances inside and outside the resin bottle and / or the content residue inside the resin bottle with water and to separate the heterogeneous polymer such as PE or PP having a specific gravity smaller than that of water ( 5) A step of feeding the recovered PET flakes to the flakes storage tank by air feeding, and (6) charging the recovered PET flakes into ethylene glycol (EG) containing a PET depolymerization catalyst at a temperature of 175 ° C. to 190 ° C.
Treated under a pressure of 1 to 0.5 MPa, bis-β-
P to obtain hydroxyethyl terephthalate (BHET)
ET depolymerization step, (7) solid-liquid separation step of components not soluble in EG, (8) concentration step of distilling off EG components in crude BHET in the liquid, (9) transesterification catalyst of concentrated crude BHET To obtain crude dimethyl terephthalate (DMT) and EG by transesterification with methanol (MeOH), (10) after cooling the liquid, DMT cake and EG / M
solid-liquid separation step for separating the eOH mixture, (11) DM
A distillation step for distilling MeOH from the T-cake and purifying DMT, (12) storing the purified purified DMT in a molten state,
A step of sending a liquid, (13) a step of adding water in a weight ratio of 1: 1 to 1: 4 to the recovered and purified DMT, and mixing and holding the mixture at 180 ° C., (14) DMT and water which are held by mixing and melting And the step of carrying out a hydrolysis reaction at 230 to 250 ° C.,
(15) A step of cooling the generated water slurry of terephthalic acid (TA), (16) a step of dehydrating the TA water slurry by a centrifuge, (17) a step of drying the water-containing TA, (18) a TA powder Step of crushing the body, (19) TA
The step of storing powder. Is provided.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. In the manufacturing method of the present invention, the steps from step (1) to step (5) before the step involving the chemical reaction are referred to as the pretreatment step. In this pretreatment step, resin bottle waste (for example, the recovered PET bottle) containing polyethylene terephthalate (PET) as a main component and a component different from that is pulverized into flakes of 2 to 30 mm square. The crushed diameter is more preferably 2
It is 20 mm. The depolymerization reactivity is improved by the operation,
The processing capacity of PET bottle waste is improved. This effect is particularly effective for a portion having a wall thickness of a crystallized and whitened portion for increasing the strength and dimensional stability of the PET bottle. Polymers different from polyesters such as polyethylene, polypropylene, polystyrene and polyvinyl chloride, which are materials of bottle caps or labels, are often mixed in the pulverized products. In the present invention, the reaction conditions are selected such that the contamination of these foreign polymers does not degrade the purity of the recovered monomer by being decomposed in the subsequent reaction step. Adhered to the surface of the filter, it may have an unfavorable effect on handling such as clogging of the filter, so remove the foreign plastics in the pretreatment step,
It is important to suppress the mixture into the reaction process as much as possible for the reaction to proceed smoothly. However, it does not require a wide variety of steps for completely removing the different polymers as in the case of carrying out material recycling, and requires only the minimum necessary steps.

In order to remove the thin film (polyethylene, polypropylene, polyvinyl chloride, etc.), which is different from polyester, used for labels, etc., from the crushed flaky resin bottle pieces, these are first subjected to air separation. Remove. At this time, if the air volume is too large, PET flakes, which is an active ingredient, will be removed together with it, so it is necessary to appropriately adjust the air volume. By this air force selection, a label containing polypropylene, polystyrene, or polyvinyl chloride as a main component can be almost completely removed.

Next, in order to remove foreign matters such as caps which cannot be removed by air force selection, the wind-selected flakes are placed on a decanter, and different polymers such as polypropylene and polyethylene having a lower specific gravity than water are centrifuged. Remove to obtain recovered PET flakes. Since the decanter step also serves as washing the impurities (soy sauce, soft drink, etc.) derived from the edible residue remaining in the polyester resin bottle with water, there is no problem even if the contents remain in the bottle. The washing water separated by centrifugation is recycled again to the decanter, and a part of it is purged for wastewater treatment.

The recovered PET flakes discharged from the decanter are transported to the reactor in the reaction step by pneumatic transportation. In the previous crushing process, the size after crushing is 30 to
When it is specified to be relatively large as 150 mm, problems such as deterioration of transportation efficiency in this air transportation process and blockage of the rotary valve occur, so that in the present invention, 2 to 30.
It is important to grind to mm. In the recovered PET flakes before air transportation, about 0.5% of the water used during the centrifugal separation in the decanter process remains based on the weight of the recovered PET flakes. These waters may adversely affect the reaction rate in the successive depolymerization step, but if they are pneumatically transported, they are dried during transportation and can be finally reduced to 0.1% or less. ,
There is no problem in reaction progress.

Most of the components other than PET can be removed by the above pretreatment process, and the pretreatment process can be completed in a significantly smaller number of steps than when material recycling is performed. This is because even if a small amount of impurities remain, the impurities can be separated by a physical / chemical separation method in the next reaction step. In addition,
In material recycling, colored bottles become impurities,
Although it has to be removed by a sorter, in the present invention, the pigment contained in the colored bottle can also be removed in the subsequent reaction step, and therefore the removal in the pretreatment step is not necessary.

Next, as the depolymerization catalyst used in the step (6), sodium carbonate and carboxylic acid Na are used.
A salt containing at least one metal compound selected from the group consisting of manganese acetate and zinc acetate, and the addition amount thereof is 0.1 to 10 of the weight of PET flakes to be subjected to the step (6).
It is preferably in the range of wt%. The amount of EG used in step (6) is preferably in the range of 0.5 to 20 times the weight of PET flakes used in step (6). The conditions for the depolymerization reaction include:
The temperature is 175 to 190 ° C. and the pressure is 0.1 to 0.5 MPa.

In the solid-liquid separation step of step (7), after the depolymerization reaction, undissolved components that could not be removed in the pretreatment step are separated and removed. When passing through the step (7), PET is converted into bis-ω-hydroxyethyl terephthalate (BHET), and the reaction liquid is a mixed liquid of BHET and EG (crude BHET).

In the concentration step of step (8), in order to efficiently proceed the transesterification reaction of step (9) which is the next step, from the above crude BHET, preferably EG and PE.
The weight ratio with T is based on the raw material charging ratio and the former is 0.5 of the latter.
Evaporate EG to ~ 2.0 times and concentrate. The distillation / concentration operation at this time is 1.33 kPa to 0.133 MP.
It is preferable to carry out under the pressure of a. The distilled EG can be recycled to the step (6) again.

In the step (9), the crude BHET concentrated in the above step (8) is transesterified with methanol (MeOH) in the presence of a transesterification catalyst. The transesterification catalyst used here contains at least one metal compound selected from the group consisting of sodium carbonate, Na salt of carboxylic acid, manganese acetate and zinc acetate,
And, the addition amount thereof is preferably in the range of 0.1 to 10% by weight based on the weight of PET flakes used in the step (6). The amount of MeOH used here is 0.5 to 20 of the weight of PET flakes used in the step (6).
It is preferable to set the range to the weight times. The reaction conditions are preferably a temperature of 65 to 85 ° C. and a pressure of 0.1 to 0.3 MPa.

The reaction products obtained (DMT, EG, Me
After cooling the mixture of OH), solid-liquid separation is preferably carried out by solid-liquid separation means such as centrifugation to obtain a DMT cake (crude DM).
T) is obtained.

In step (11), the DMT cake obtained in step (10) is first distilled to remove MeOH and then purified by distillation to separate and collect highly purified DMT. The recovered and purified DMT is stored in a molten state and, if necessary, sent to the next step of water and DMT melt mixing step.

In the step (13), water is added to the recovered and purified DMT at a weight ratio of 1: 1 to 1: 4, and 170-
Mix and hold under stirring at 190 ° C.

Next, in step (14), step (13)
The molten mixture of DMT and water provided by the above is heated in a batch or continuous hydrolysis reaction tank at a temperature of 230 to 250.
It is preferable to carry out the hydrolysis reaction while stirring under a pressure condition of ° C and a pressure of about 2.8 to 4 MPa. At this time, the low-boiling-point reaction by-product mainly composed of methanol generated by the hydrolysis reaction is preferably discharged from the reaction vessel head to the outside of the system together with the vapor of the reaction water.

The water slurry of terephthalic acid (TA) obtained by cooling the above reaction product in the step (15) is dehydrated in the centrifuge in the step (16), and preferably has a water content of about 10 to 20. Separated and collected as a water-containing TA cake of 100%.

The obtained water-containing TA cake is subjected to the step (17).
In the above, the powder is treated with a vibratory fluidized bed type or an inert gas flow type dryer to obtain TA powder having a water content of 0.5% or less. Further, in the step (18), in order to adjust the particle size of TA which affects the reactivity when the PET polymer is obtained from the esterification through the polycondensation reaction by the reaction with EG, pulverization may be performed by a pulverizer. Further, in the step (19), the obtained TA powder is mixed with P
It is a storage process for delivering to the ET polymer manufacturing facility.

By passing through these steps, D
The total amount of MT and monomethyl terephthalic acid (MMT) is 0.1 to 1000 ppm with respect to terephthalic acid, and further 4-carboxybenzaldehyde (4-CB).
A), paratoluic acid (p-TA), benzoic acid (B
A) and high-purity terephthalic acid having a total content of dimethyl hydroxyterephthalate (HDT) of 1 ppm or less can be efficiently recovered from the waste of the resin bottle. Such TA can be reused for resin applications such as fibers, films, PET bottles and the like, and is particularly suitable for PET for bottles, so that the collected PET bottles can be effectively reused.

Hereinafter, referring to FIG. 1, which shows one embodiment of the process for producing terephthalic acid from the waste resin bottle of the present invention,
A more specific description will be given.

From the source 11, the recovered PET flakes treated by the pretreatment step (not shown in FIG. 1) of the steps (1) to (5), and the depolymerization catalyst from the supply tank 10,
Further, EG is simultaneously charged into the depolymerization tank 1 from the supply line 10a, and the PET flakes are depolymerized in the depolymerization tank 1.

The depolymerized mixture is a solid-liquid separator 2
Sent to. Components that do not dissolve in the depolymerization tank 1 are separated in the solid-liquid separator 2 and removed outside the system as solids. The solid matter is further cleaned by EG in the cleaning tank 3, and the adhered matter on the surface of the solid matter is circulated to the depolymerization tank 1 if necessary. Further, the solid matter itself is separated and removed into the solid matter tank 16b. Here, the depolymerization tank 1 has a residence time of 1 to 10 hours and an internal temperature of 175 to 190 ° C.
And it is sufficient.

Next, the depolymerization reaction product after the depolymerization reaction is sent to the distillation / concentration tank 4, and EG is added so that the ratio of the weight ratio of EG to the depolymerization reaction product is 0.5 to 2. Distill and evaporate. The distilled EG can be circulated and supplied to the depolymerization tank 1.

Next, the concentrated depolymerization reaction product liquid is supplied to the transesterification reaction tank 5, to which the transesterification reaction catalyst is supplied, and MeOH is supplied from the supply source 12.
The depolymerization reaction product liquid is converted into DMT and EG by supplying from the above. At this time, it is preferable that the temperature in the transesterification reaction tank is treated at 65 to 85 ° C. and an internal pressure of 0.1 to 0.3 MPa for a residence time of 0.5 to 5 hours.

The produced mixture of DMT and EG is cooled together with excess MeOH, and this is supplied to the solid-liquid separator 6 to separate it into a cake of DMT and a mixture of EG and MeOH. Here, since the separated DMT cake contains EG as the mother liquor, it is again slurried with MeOH and solid-liquid separated again.

Next, the cake of DMT is supplied to the DMT distillation column 7, and the purified DMT is recovered in the DMT recovery tank 14. A part of the residual liquid at the bottom of the distillation column 7 is returned to the depolymerization tank 1 through the line 7a, and the rest is discarded outside the system 18.

On the other hand, the mixed liquid of EG and MeOH separated in the solid-liquid separation device 6 is supplied to the MeOH distillation column 9 and EG.
Supply to the distillation column 8 to distill off MeOH and EG. The distilled MeOH is supplied to the transesterification reaction tank 5 as Me.
It can be used as part of OH. Furthermore, Me
The residual liquid at the bottom of the OH distillation column 9 is supplied to the EG distillation column 8 to
Distill off. Part of the distilled EG was used as EG supplied to the depolymerization tank 1 via the line 10a, and the remaining E
G is collected and taken out of the system 15. The EG distillation tower 8
Part of the residual liquid of (1) is returned to the depolymerization tank 1, and the rest is discharged as waste to the outside of the system 17.

Subsequently, DMT is hydrolyzed to give TA.
The process of obtaining the above will be described with reference to FIG. The purified DMT stored in the recovery DMT tank 14 is sent to the mixing tank 19 together with the water heated by the heater 26 in the water supply line in the molten state. The weight ratio of DMT: water in the mixing tank 19 is 1: 1.
To 1: 4, preferably 1: 2 to 1: 3.

Next, the mixed solution of DMT and water is supplied from the mixing tank 19 to the first hydrolysis reaction tank 20. The reaction temperature in the first hydrolysis reaction tank 20 is preferably 230 to 250 ° C., more preferably 240 ° C. or higher, and the reaction pressure at that time is about 30 to 40 kg / cm ² (gauge pressure).
Is. Me generated in the hydrolysis reaction from the upper part of the reaction tank
The pressure is applied to the first hydrolysis reaction tank 20 when the reaction temperature is maintained when OH and excess water are distilled off by a predetermined reaction. The residence time is preferably 1 to 5 hours.

Next, TA generated in the first hydrolysis reaction tank 20, residual water and unreacted DMT, and TA from DMT
Monomethyl terephthalate (MM
The mixed water slurry of T) is supplied to the second hydrolysis reaction tank 21. The reaction conditions in the second hydrolysis reaction tank 21 are the same as those in the first hydrolysis reaction tank 20. However, 90% of the hydrolysis reaction from DMT to TA is usually carried out in the second hydrolysis reaction tank.
It is provided to achieve a reaction conversion rate close to 100% from the advanced state.

Next, the high temperature TA / water slurry obtained in the second hydrolysis reaction tank 21 is supplied to a cooling tank 22 for cooling. The cooled TA / water slurry is supplied from the cooling tank 22 to the centrifuge 23, and separated into a centrifugal water-containing TA cake and a water mother liquor.

The water-containing TA cake obtained by the centrifuge 23 usually has a moisture content of about 10 to 20%, and is dried by the dryer 24 to reduce the moisture content in TA to 0.5% or less. The particle size of the powder TA after drying is adjusted by a pulverizer / granulator 25 if necessary. The product TA powder is stored in the silo 33 and supplied to the PET process.

Here, the water / MeOH mixed liquid generated from the first hydrolysis reaction tank 20 is stored in the MeOH tank 28 and then distilled and separated into MeOH and water in the MeOH distillation column 27, and the MeOH is distilled in the previous MeOH distillation. It is supplied to the column 9 and subjected to distillation again. In addition, the generated water is disposed of. Further, the water / MeOH mixed liquid generated in the second hydrolysis reaction tank 21 is heated with water 26 and is circulated and supplied again to the mixing tank 19.

Water, which is the mother liquor of the centrifuge 23, is stored in the filtrate tank 31 and is then filtered by the filter 30 into water and TA contained in the mother liquor from the centrifuge. Water is aquarium 2
9 is supplied to the mixing tank 19 via the water heater 26 or is treated for drainage.

[0046]

The present invention will be described in more detail with reference to the following examples. Each value in the examples can be measured by various methods, but here, it was determined according to the following method. 4-Carboxybenzaldehyde (4-CBA) weight concentration: After dissolving the obtained terephthalic acid in 2N-ammonia water, Shimadzu liquid chromatograph system (LC-6)
A), separated measurement with STRφDS-H column. Paratoluic acid (p-TA) weight concentration: same as 4-CBA. Dimethyl hydroxyterephthalate (HDT) Weight concentration:
Same as 4-CBA. Dimethyl terephthalate (DMT) Weight concentration: High performance liquid chromatography (apparatus: Hitachi HPLC D-70)
00, packed column: RP-18; 2). Monomethyl terephthalate (MMT) Weight concentration: similar to DMT Benzoic acid (BA) concentration: After esterification with diazomethane,
Using n-tridecane as an internal standard, 10% SE-30 is used for the separation column for quantification by gas chromatography. 250 ° C heat-resistant alkali permeability of terephthalic acid: After terephthalic acid is treated at 250 ° C for 2 hours and dissolved in 2N-KOH, UV transmittance at 400 nm is measured with a spectrophotometer (equivalent to JASCO UVIDEC660). It is a measure of the influence on the hue of the PET polymer obtained from terephthalic acid.

[Example 1] Separately collected and collected PET bottle veils (veil size: 900 mm x 1000 mm)
After unpacking (120 kg bale of x550 mm), it was put into a crusher and crushed by setting the screen diameter of the crusher to 10 mm. Then, the pulverized product is subjected to an air sorter, polyethylene, polystyrene, and after removing the label attached to the bottle containing polypropylene as the main component, centrifugation is performed by a decanter, while washing and removing the contents of the bottle with polypropylene, The cap containing polyethylene as a main component and the label that was not removed by the wind screening were removed to obtain recovered PET flakes. The collected PET
The flakes were transported by air transportation for storage in a recovered PET flakes supply tank. Next, 100 parts by weight of recovered PET flakes from the recovered PET flakes supply tank, 360 parts by weight of EG from the EG supply line, and 2.7 parts by weight of sodium carbonate from the polymerization catalyst supply tank were supplied to the depolymerization tank,
The mixture was kept under stirring at 180 ° C. for 4 hours and a half.

The above depolymerization reaction solution by EG is put into a filtration device which is surrounded by a heater which is heated to 170 ° C. and which is equipped with a 100-mesh wire mesh as a filter medium, to perform hot filtration. Carried out. The residue on the filter was washed with 90 parts by weight of EG heated to 170 ° C., and the washing liquid was stored in the washing liquid receiving tank.

The depolymerization reaction solution obtained by hot filtration was concentrated by vacuum distillation at 6.65 kPa, and 270 parts by weight of EG was recovered as a fraction.

This concentrated liquid, 2.7 parts by weight of sodium carbonate from the transesterification catalyst tank, and further 180 parts by weight of MeOH were charged into the transesterification reaction tank, and the liquid temperature was kept at 75 ° C. under normal pressure for 1 hour with stirring to conduct transesterification. The reaction was carried out. The produced mixture of DMT, EG and MeOH was cooled to 40 ° C., and a DMT cake was obtained by the subsequent solid-liquid separation device. Once the DMT cake was put into a MeOH cleaning tank,
180 parts by weight was added, the mixture was stirred and washed at 40 ° C., and solid-liquid separation was performed again by a centrifugal separator to obtain a DMT cake. The obtained DMT cake was put into the MeOH washing tank again, this time to 1
At the same time as melting DMT at 60 ° C., the residual MeOH was distilled off. Molten DMT was charged into a DMT distillation column, and DMT was distilled as a fraction by vacuum distillation under a pressure of 6.65 kPa, and 83 parts by weight could be obtained as recovered DMT. This DMT was sent to the DMT recovery tank. In this process, the total amount of 4-carboxybenzaldehyde (4-CBA), paratoluic acid (p-TA), benzoic acid (BA), and dimethyl hydroxyterephthalate (HDT) as impurities was 1 ppm or less. It was a high-purity DMT of.

Next, the molten DMT is collected from the DMT recovery tank.
Is continuously supplied to the mixing tank at a rate of 100 parts by weight / hour and at a rate of 200 parts by weight / hour from the water tank. It was supplied to the first hydrolysis reaction tank at a rate of parts by weight / hour. The liquid temperature of the first hydrolysis reaction tank is set to 250 ° C.,
While stirring, a retention time of 2 hours was secured and the reaction was carried out, and MeOH produced by the hydrolysis reaction was distilled out together with water from the head of the tank. The distillation rate is as a mixture of MeOH and water,
About 76 parts by weight / hour, and the internal pressure at this time is about 4 MPa
Met. The obtained mixed slurry of TA, water and DMT was supplied to the second hydrolysis reaction tank at about 224 parts by weight / hour. The liquid temperature of the second hydrolysis reaction tank was also set to 250 ° C., a residence time of 1 hour was secured while stirring, and the reaction was carried out, and MeOH produced was distilled out together with water from the head of the tank. The distillation rate was about 58 parts by weight / hour as a mixed solution of MeOH and water, and the internal pressure at this time was about 4 MPa.

The resulting water slurry of TA is about 1 in the cooling tank.
The liquid was sent at a rate of 66 parts by weight / hour. The TA / water weight ratio in the slurry in this cooling tank is about 1/1 weight ratio.
The high temperature TA / water slurry of about 250 ° C. was cooled to about 70 ° C. by the vent condenser of the cooling tank, the cooling inner tube, and the cooling jacket and held. The TA / water slurry was sent from the cooling tank to the centrifuge at a rate of 166 parts by weight / hour and treated by the centrifuge to obtain a TA cake. The water-containing TA cake had a TA / water weight ratio of about 83:12, and the cake was dump-supplied to the nitrogen stream dryer at a rate of about 95 parts by weight / hour for drying treatment. The moisture content of the dried TA powder was 0.2%. This TA powder was adjusted to a mean particle size of 150 μm with a continuous granulator and
I sent it to the TA storage tank.

The concentrations of DMT and MMT in the obtained TA were 500 ppm and 50 ppm, respectively, and the 250 ° C. heat-resistant alkali permeability was 99% or more, and TA was suitable as a raw material for PET for bottles.

[Comparative Example 1] The PET bottle veil was unpacked and then put into a crusher to adjust the screen diameter of the crusher to 10
Milling was performed by setting to mm, but the subsequent pulverized product was not subjected to an air separator, and centrifugal separation by a decanter was also performed.
The procedure of Example 1 was repeated, except that the contents of the bottle were not washed and removed, and the flakes that were simply fragmented were used as the recovered PET flakes. DM recovered
T was analyzed in the same manner as in Example 1, but many unidentifiable impurities were detected by liquid chromatography and gas chromatography, and the DMT obtained here could not be called high-purity DMT. . Further, the 250 ° C heat-resistant alkali permeability of TA obtained by hydrolysis was also poor at 93%.

[Comparative Example 2] The same procedure as in Example 1 was carried out except that DMT distillation was omitted in the DMT recovery step. The recovered DMT was analyzed in the same manner as in Example 1, but many unidentifiable impurities were detected by liquid chromatography and gas chromatography, and the DMT obtained here cannot be called high-purity DMT. Met. In addition, the hydrolysis resistance of TA obtained at 250 ° C. is 90% against alkali resistance.
It was bad with%.

[0056]

According to the present invention, the used P recovered is recovered.
High-purity terephthalic acid can be efficiently obtained via DMT from a resin bottle waste waste containing PET as a main component and a component different from PET, such as an ET bottle. This makes it possible to effectively circulate PET bottles, which have become particularly socially problematic due to their bulkiness and are becoming a social problem, and their industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus used for carrying out the present invention.

[Explanation of symbols]

1: Depolymerization tank 2: Solid-liquid separator 3: Cleaning tank 4: Distillation concentrator 5: Transesterification reaction tank 6: Solid-liquid separator 6a: MeOH cleaning tank 7: DMT distillation column 8: EG distillation column 9: MeOH distillation column 10: Polymerization catalyst supply tank 10a: EG supply line 11: Recovery PET flakes supply tank 12: MeOH supply tank 13: Transesterification catalyst tank 14: DMT recovery tank 15: EG discharge tank 16a: Cleaning liquid receiving tank 16b: Solid matter tank 17: EG distillation tank residual treatment tank 18: DMT distillation tank residual treatment tank 19: Mixing tank 20: First hydrolysis reaction tank 21: Second hydrolysis reaction tank 22: Cooling tank 23: Centrifuge 24: Dryer 25: Grinding granulator 26: Water heater 27: MeOH distillation column 28: MeOH tank 29: Aquarium 30: Filter 31: Filtrate tank 32: Wastewater treatment device 33: TA silo

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 67:00 C08L 67:00 (72) Inventor Minoru Nakajima 77 Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Stock Exchange F term in company Matsuyama office (reference) 4F301 AA25 BF09 BF12 BF27 BG21 CA09 CA23 CA72 CA73 4H006 AA02 AC46 BA02 BA32 BC10 BC31 BC34 BC35 BC40 BE60 BS30 4H039 CA60 CA66 CE10

Claims (7)

[Claims] 1. Polyethylene terephthalate (PET)
A method for producing terephthalic acid from a resin bottle waste, characterized in that a resin bottle waste containing, as a main component, and a component different from that is sequentially supplied to the following steps (1) to (19). (1) The step of unpacking the resin bottle waste packing bale containing the separated and collected and collected PET as the main component and a different component, (2) the unpacked resin bottle waste is 2 to 30 mm Crushing process to make flakes of corners, (3) PET such as label thin film made of polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), etc. from flaky resin bottle pieces
The process of separating the component polymers different from
(4) A decanter step that also serves to wash foreign substances inside and outside the resin bottle and / or the content residue inside the resin bottle with water and to separate a heterogeneous polymer such as PE or PP having a specific gravity smaller than that of water ( 5) A step of feeding the recovered PET flakes to the flakes storage tank by air feeding, and (6) charging the recovered PET flakes into ethylene glycol (EG) containing a PET depolymerization catalyst at a temperature of 175 ° C. to 190 ° C.
Treated under a pressure of 1 to 0.5 MPa, bis-β-
P to obtain hydroxyethyl terephthalate (BHET)
ET depolymerization step, (7) solid-liquid separation step of components not soluble in EG, (8) concentration step of distilling off EG components in crude BHET in the liquid, (9) transesterification catalyst of concentrated crude BHET To obtain crude dimethyl terephthalate (DMT) and EG by transesterification with methanol (MeOH), (10) after cooling the liquid, DMT cake and EG / M
solid-liquid separation step for separating the eOH mixture, (11) DM
A distillation step for distilling MeOH from the T-cake and purifying DMT, (12) storing the purified purified DMT in a molten state,
A step of sending a liquid, (13) a step of adding water in a weight ratio of 1: 1 to 1: 4 to the recovered and purified DMT, and mixing and maintaining the mixture at 180 ° C .; And the step of carrying out a hydrolysis reaction at 230 to 250 ° C.,
(15) A step of cooling the produced water slurry of terephthalic acid (TA), (16) a step of dehydrating the TA water slurry with a centrifuge, (17) a step of drying the water-containing TA, (18) a TA powder Step of crushing the body, (19) TA
The step of storing powder. 2. The terephthalic acid according to claim 1, wherein the depolymerization catalyst used in the step (6) is at least one catalyst selected from the group consisting of sodium carbonate, Na salt of carboxylic acid, manganese acetate and zinc acetate. Manufacturing method. 3. The addition amount of the depolymerization catalyst used in the step (6) is 0.1% with respect to the weight of the recovered PET flakes.
The method for producing terephthalic acid according to claim 1, which is 1 to 10% by weight. 4. The transesterification catalyst used in step (9) is sodium carbonate or Na of carboxylic acid.
The method for producing terephthalic acid according to claim 1, which is at least one catalyst selected from the group consisting of salts, manganese acetate, and zinc acetate. 5. The method for producing terephthalic acid according to claim 1, wherein the amount of the transesterification reaction catalyst used in step (9) is 0.1 to 10% by weight based on the weight of the recovered PET flakes. 6. The method for producing terephthalic acid according to claim 1, wherein the unreacted impurities (total amount of dimethyl terephthalate and monomethyl terephthalate) in the product terephthalic acid is 1000 ppm or less. 7. An impurity in the product terephthalic acid, which is 4-
The total content of carboxybenzaldehyde (4-CBA), paratoluic acid (p-TA), benzoic acid (BA) and dimethyl hydroxyterephthalate (HDT) is 1p.
The method for producing terephthalic acid according to claim 1, which is pm or less.