JP4080720B2 - How to recycle PET bottles - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a resin bottle waste containing polyethylene terephthalate (PET) as a main component and further containing a different component, and after performing pretreatment such as grinding, washing, foreign matter removal, etc., a chemical reaction treatment is added, A method of recovering high-purity dimethyl terephthalate as an active ingredient, obtaining terephthalic acid by a chemical reaction, and further obtaining a PET polymer for PET bottles, that is, a polymer for PET bottles is again obtained from the collected used PET bottles. On how to get.
[0002]
[Prior art]
Since polyalkylene terephthalate is excellent in chemical stability, it is produced and used in large quantities in food-related fields such as life-related materials such as fibers, films and resins, drinking water and bottles for carbonated beverages. However, disposal of fiber, film, resin product waste, non-standard PET, which is generated in large quantities with the increase in production and usage, is currently becoming a major social problem, such as material recycling, chemical recycling, Various proposals have been made regarding thermal recycling and the like. On the other hand, especially among the wastes, the processing of PET bottles is becoming more serious due to its bulkiness. Nonetheless, as a recycling method, only material recycling is performed to the extent that the collected used PET bottles are melted again to form a fiber. It is impossible to use it again as a PET bottle due to a decrease in the above.
[0003]
Also, in the refilling method of cleaning and refilling PET bottles, there is a limit to the cost of collection costs, safety and hygiene, limited number of reuses, and eventually disposal. It cannot be an appropriate measure. In addition, foreign matter resin such as labels, shrink films, base cups and caps, foreign plastics such as polyvinyl chloride and polyolefin resins, aluminum derived from caps, adhesives, pigments, dyes, etc. are mixed in PET bottle waste. Sometimes. It is difficult to avoid mixing foreign material into the PET bottle bale that has been separated and collected, and in chemical recycling that decomposes and reuses the monomer that constitutes the PET polymer using a solvent such as water, methanol, or ethylene glycol. Foreign material generates various decomposition gases (eg, hydrogen chloride gas) during the heating and reaction operations, or melts and solidifies in the recovery device, damages the equipment or recovers the monomer ( The quality of DMT) may be significantly reduced. Examples of the above chemical recycling include a method of hydrolyzing polyester waste in the presence of an alkali compound described in JP-A No. 11-21374 to obtain terephthalic acid, and in methanol described in US Pat. No. 5,952,520. There is a method of obtaining dimethyl terephthalate and ethylene glycol by gas phase methanol decomposition. However, since these all require high temperature reaction conditions of 200 ° C. or higher, the decomposition starts from 190 ° C., and the decomposition product is a different plastic from polyester such as polyvinyl chloride, which deteriorates the quality of the final product. There is a problem that the tolerance for the contamination is very low.
[0004]
Furthermore, Japanese Patent Application Laid-Open No. 2000-169623 proposes a process for decomposing polyethylene terephthalate waste with ethylene glycol, purifying the recovered BHET with a thin film evaporator, and then melt polycondensating BHET to obtain a polyethylene terephthalate polymer. However, in this case as well, there is a step of imposing a thermal history of 200 ° C. or higher, and the admissibility of foreign plastics such as polyvinyl chloride that decomposes thermally is low. That is, even in chemical recycling, although the tolerance for mixing impurities is higher than in material recycling, it is necessary to remove impurities almost completely in the pretreatment process. In addition, it is generally known that PET polymers for bottles are obtained by an ester exchange reaction or esterification reaction with EG using DMT or TA as a starting material, and subsequently obtained by a polycondensation reaction. However, the obtained PET polymer cannot be used for PET bottles unless the raw material DMT or TA is highly purified with sufficiently few impurities. Under such circumstances, there are no examples of a method for recovering an active ingredient from a used PET bottle by a chemical recycling method and obtaining a PET polymer that can be used again for a PET bottle.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to obtain a high-purity monomer (DMT) without contaminating even contamination of impurities, and to efficiently produce a PET polymer suitable for PET bottles from the high-purity DMT. To propose a process.
[0006]
[Means for Solving the Problems]
According to the present invention, high-purity dimethyl terephthalate (DMT) as an active ingredient is recovered from a resin bottle waste containing polyethylene terephthalate (PET) as a main component and a component different from that. A method for obtaining an acid (TA) and further obtaining a PET polymer for a PET bottle is characterized in that the resin bottle waste is sequentially subjected to the following steps (1) to (23).
(1) The process of unpacking the PET bottle packing bale collected and collected separately
(2) The crushing process of making the unpacked PET bottle into a 2-30mm square flake shape
(3) Separating component polymer different from PET of label thin film film made of polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), etc. from flaky PET bottle pieces by wind sorting.
(4) A decanter process that combines washing of foreign matter inside and outside of a PET bottle piece and / or contents inside the PET bottle with water and separating different component plastics such as PE and PP having a specific gravity smaller than that of water.
(5) Air transport process for sending recovered PET flakes to the flake storage tank
(6) The recovered PET flakes were put into an EG containing a PET depolymerization catalyst, treated at a temperature of 175 ° C. to 190 ° C. and a pressure of 0.1 to 0.5 MPa, and bis-β-hydroxyethyl terephthalate (BHET PET depolymerization step to obtain
(7) Solid-liquid separation process of components not dissolved in EG
(8) Concentration step for distilling off the EG component in the crude BHET in the liquid
(9) A step of transesterifying the concentrated crude BHET in a transesterification catalyst and MeOH to obtain crude DMT and EG
(10) Cooling and solid-liquid separation of DMT cake and EG / MeOH mixed solution
(11) Distillation step for purifying DMT by distilling MeOH from DMT cake
(12) A step of storing recovered refined DMT in a molten state and feeding the solution.
(13) The weight ratio of 1: 1 to 1: 4 with respect to recovered and purified DMT ₂ A process of mixing and holding O at 170 to 190 ° C. by adding O
(14) DMT and H that were mixed and melted ₂ A step of feeding O and hydrolyzing at 230 to 250 ° C.
(15) Generated TA and H ₂ Step of cooling the O slurry
(16) H of cooled TA ₂ EG is mixed with O slurry in line, and TA H ₂ The process of making EG slurry containing O
(17) TA H ₂ Obtaining TA cake from O / EG slurry by centrifugation
(18) A step of preparing a slurry from TA cake and EG at a molar ratio of TA / EG of 1: 1 to 1: 3.
(19) Step of obtaining a PET oligomer by esterifying TA and EG
(20) An initial melt polymerization step in which a polycondensation catalyst is added to a PET oligomer, and EG is distilled off by a melt polycondensation reaction at 260 ° C. to 280 ° C. under a weak vacuum of 10 to 30 Torr to increase the degree of polymerization.
(21) Further, a late melt polymerization step in which EG is distilled off by a melt polycondensation reaction at 270 ° C. to 290 ° C. under a high vacuum of 0.5 Torr to 5 Torr to further increase the degree of polymerization.
(22) Solid phase polymerization step for adjusting the degree of polymerization in order to obtain PET suitable for bottles
(23) Storage process
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a resin bottle waste containing polyethylene terephthalate (PET) as a main component and further containing a different component, and after performing pretreatment such as grinding, washing, foreign matter removal, etc., a chemical reaction treatment is added, A method of recovering high-purity dimethyl terephthalate as an active ingredient, obtaining terephthalic acid by a chemical reaction, and further obtaining a PET polymer for PET bottles, that is, a polymer for PET bottles is again obtained from the collected used PET bottles. How to get.
[0008]
Hereinafter, this invention is demonstrated according to a process.
Here, the process before the process accompanied by the chemical reaction from the process (1) to the process (5) is referred to as a pretreatment process. In this pretreatment step, it is preferable to unpack the PET bottle packing bale that has been separately collected and collected, and then pulverize the collected PET bottle into 2 to 30 mm squares. The pulverized diameter is more preferably 2 to 20 mm. By this operation, depolymerization reactivity improves and the processing capacity of PET bottle waste improves. This effect is particularly effective for a portion where the thickness of the portion subjected to crystallization treatment and whitening is increased in order to increase the strength and dimension stability of the PET bottle. The pulverized material often contains different plastics different from polyester such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride, which are cap and label materials contained as impurities in the polyester resin. In the present invention, although the reaction conditions are selected so as not to degrade the purity of the recovered monomer by decomposing in the subsequent reaction step with respect to the mixing of the above different plastics, It may cause undesirable effects on handling such as adhering to the filter or causing clogging of the filter. Therefore, it is necessary to remove the different plastics in the pretreatment process and to suppress contamination to the reaction process as much as possible. It is important for smooth progress. However, various processes for completely removing the above-mentioned different plastics as in the case of material recycling are not required, and only the minimum necessary processes are required.
[0009]
In order to remove the thin film (polyethylene, polypropylene, polyvinyl chloride, etc.) used for the label etc. which is different from polyester from the pulverized product, the label is first removed by wind sorting. At this time, if the air volume is too large, the polyester resin, which is an active ingredient, will be removed together with the air volume, so it is necessary to adjust the air volume appropriately. By this wind sorting, labels mainly composed of polypropylene, polystyrene, and polyvinyl chloride can be almost completely removed.
[0010]
Next, in order to remove the cap that cannot be removed by wind sorting, the pulverized material is placed in a decanter, and different plastics such as polypropylene and polyethylene having a specific gravity lighter than water are removed by centrifugation to obtain a recovered flake. . The decanter also serves as a facility for washing impurities derived from food and the like (soy sauce, soft drinks, etc.) remaining in the polyester resin, so there is no problem even if the contents remain in the resin. The washing water separated by centrifugation is recycled again to the decanter, and a part thereof is purged and subjected to waste water treatment.
[0011]
The recovered flakes discharged from the decanter are transported by pneumatic transportation to the reactor in the reaction process via the flake storage tank. If the size after pulverization is defined as 30 to 150 mm in the previous pulverization step, problems such as deterioration in transport efficiency and blockage of the rotary valve occur in the pneumatic transport step. Thus, it is effective to grind to about 2 to 30 mm. Further, in the recovered flake before air transportation, about 0.5% of the water used in the previous centrifuging by the decanter remains based on the weight of the recovered flake. These water contents may adversely affect the reaction rate in the depolymerization process, but since they are dried during air transportation, the water content is finally reduced to 0.1% or less based on the weight of the recovered flakes. There is no problem in the progress of the reaction.
[0012]
Although most of the components other than polyester can be removed by the above pretreatment process, the pretreatment process is completed with significantly fewer processes than when material recycling is performed. This is because even if impurities remain, the impurities can be separated by a physical / chemical separation method in the next reaction step. In material recycling, the colored bottle becomes an impurity and must be removed by a sorter. However, in the method of the present invention, the pigment contained in the colored bottle can also be removed in the subsequent reaction step, so that it is removed in the pretreatment step. Is unnecessary.
[0013]
Next, the depolymerization catalyst used in the step (6) contains at least one metal compound selected from the group consisting of sodium carbonate, Na carboxylate, manganese acetate, and zinc acetate, and the amount of addition thereof Is preferably 0.1 to 10% by weight based on the weight of the PET flakes used in the step (6). Moreover, it is preferable to make the quantity of EG used at this process (6) into 0.5 to 20 weight times the weight of the PET flakes used for a process (6). As the reaction conditions, a reaction at a temperature of 175 ° C. to 190 ° C. and a pressure of 0.1 to 0.5 MPa is preferable. Thereby, bis-β-hydroxyethyl terephthalate (BHET) is obtained.
In step (7), impurities that are not dissolved in EG are solid-liquid separated.
In step (8), the EG component in the crude BHET in the liquid is distilled off. In this step, the distillation / concentration operation is preferably performed under a pressure of 1.33 kPa to 0.133 MPa.
[0014]
The transesterification reaction catalyst used in the step (9) contains at least one metal compound selected from the group consisting of sodium carbonate, Na carboxylate, manganese acetate, and zinc acetate, and the amount added is the step (9). It is preferable to set it as 0.1 to 10 weight% of the weight of PET flakes used for 6). In addition, the amount of MeOH used in this step (9) is preferably 0.5 to 20 times the weight of the PET flakes used in the step (6). A reaction under a pressure of ˜0.3 MPa is preferred.
[0015]
In step (10), the obtained crude DMT, EG and MeOH mixture is cooled, and the DMT cake and EG / MeOH mixture are separated into solid and liquid.
In step (11), MeOH is distilled from the obtained DMT cake to purify DMT.
In step (12), the recovered purified DMT is stored in a molten state and fed.
[0016]
In step (13), the weight ratio of 1: 1 to 1: 4 with respect to the recovered and purified DMT is H. ₂ It is preferable to introduce O and to use in the hydrolysis step of step (14). Moreover, it is preferable that a process (13) is mixed-melting-maintaining at 170 to 190 degreeC.
In step (14), the provided DMT and H ₂ It is preferable to hydrolyze O under conditions of 230 to 250 ° C. and about 4 MPa.
TA and H generated in step (15) ₂ Cool the O slurry.
In step (16), the H of the cooled TA ₂ The amount of EG mixed in line with O slurry is H ₂ It is preferable that it is 25 to 75 times by weight with respect to O. ₂ O slurry can be replaced by TA EG slurry.
In step (17), TA H ₂ TA cake is obtained from the O / EG slurry by centrifugation.
[0017]
In the step (18), it is preferable to prepare a slurry from TA cake and EG at a molar ratio of TA: EG of 1: 1 to 1: 3.
In the step (19), when esterifying TA and EG to obtain a PET oligomer, the esterification temperature is preferably set to 260 ° C to 270 ° C.
In the step (20), the polycondensation catalyst used for the PET oligomer is a catalyst selected from the group consisting of Ge, Sb, and Ti catalysts typified by germanium oxide, antimony trioxide, and trimellitic acid titanium, and the step (19). It is preferable to set it as 0.002 weight%-0.1 weight% of TA weight supplied to. The reaction conditions are preferably 260 ° C. to 280 ° C. under a weak vacuum of 10 Torr to 30 Torr.
[0018]
In the step (21), the reaction conditions are preferably 270 ° C. to 290 ° C. under a high vacuum of 0.5 Torr to 5 Torr.
In the step (22), the solid phase polymerization reaction for adjusting the degree of polymerization and removing the cyclic oligomer is N ₂ You may carry out under either airflow or a vacuum.
In step (23), the obtained solid-phase polymerized PET is stored.
[0019]
The present invention will be described more specifically with reference to FIG. 1 showing one embodiment of the PET bottle recycling method of the present invention.
The recovered PET bottle flakes processed in the pretreatment step (not shown in FIG. 1) of step (1) to step (5) are supplied from the supply source 11 and the depolymerization catalyst is supplied from the supply tank 10 to the EG. Are simultaneously fed 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 sent to the solid-liquid separator 2. Components that do not dissolve in the depolymerization tank 1 are separated in the solid-liquid separation device 2 and removed out of the system as solids. In addition, this solid substance is further washed by EG in the washing tank 3, and the deposit on the surface of the solid substance is circulated to the depolymerization tank 1 as necessary. Further, the solid material itself is separated and removed to the solid material tank 16b. Here, the residence time of the depolymerization tank 1 may be 1 to 10 hours, and the internal temperature may be 175 to 190 ° C.
[0020]
Next, the depolymerization reaction product after the depolymerization reaction is completed is sent to the distillation / concentration tank 4, and the EG is distilled / distilled so that the ratio of the EG to the depolymerization reaction product is 0.5 to 2 in the charged weight ratio. Leave. The distilled EG can be circulated and supplied to the depolymerization tank 1.
Subsequently, the concentrated depolymerization reaction product liquid is supplied to the transesterification reaction tank 5, and by supplying the transesterification reaction catalyst from the supply source 13 and MeOH from the supply source 12, the depolymerization reaction solution liquid is supplied. To DMT and EG. In this case, the internal temperature of the transesterification reaction tank is preferably 65 to 85 ° C. and an internal pressure of 0.1 to 0.3 MPa, and the residence time is preferably treated for 0.5 to 5 hours. The resulting mixture of DMT and EG is cooled together with an excess of MeOH, which is supplied to the solid-liquid separator 6 and separated into a DMT cake and a mixture of EG and MeOH.
[0021]
Here, since the separated DMT cake contains MeOH as a mother liquid, it is again slurried with MeOH and solid-liquid separated again. Further, this DMT cake is supplied to the DMT distillation column 7, and the purified DMT is recovered in the DMT recovery tank 14. A part of the remaining liquid at the bottom of the distillation column 7 is returned to the depolymerization tank 1 through the line 7 a and the rest is discarded to the outside of the system 18.
On the other hand, the mixed liquid of EG and MeOH separated in the solid-liquid separator 6 is supplied to the MeOH distillation column 9 and the EG distillation column 8 to distill off MeOH and EG. This distilled MeOH can be used as a part of MeOH supplied to the transesterification reaction tank 5. Further, the residual liquid at the bottom of the MeOH distillation column 9 is supplied to the EG distillation column 8 to distill off the EG. A part of the distilled EG is used as EG to be supplied to the depolymerization tank 1 through the line 10a, and the remaining EG is recovered and taken out to the outside of the system 15.
A part of the remaining liquid in the EG distillation column 8 is returned to the depolymerization tank 1 and the rest is withdrawn to the outside of the system 17 as waste.
[0022]
Subsequently, a process of obtaining TA by hydrolyzing DMT will be described with reference to FIG.
The purified DMT stored in the recovered DMT tank 14 remains in a molten state, ₂ H in the O supply line ₂ H heated by O heater 26 ₂ Both O are fed to the mixing tank 19. DMT in mixing tank 19: H ₂ The O weight ratio is preferably in the range of 1: 1 to 1: 4.
[0023]
Next, DMT and H from the mixing tank 19 ₂ A mixed solution of O is supplied to the first hydrolysis reaction tank 20. The reaction temperature in the first hydrolysis reaction tank 20 is preferably 230 to 250 ° C., and the reaction pressure is about 30 to 40 kg / cm. ² (Gauge pressure), MeOH generated by hydrolysis reaction from the upper part of the reaction tank and excess H ₂ When O is distilled off for a predetermined amount of reaction, the pressure applied to the first hydrolysis reaction tank 20 is maintained when the reaction temperature is maintained. The residence time is preferably 1 to 5 hours.
[0024]
Next, TA produced in the first hydrolysis reaction tank 20 and residual H ₂ O and unreacted DMT, as well as a mixture of DMT and TA intermediate MMT (monomethyl terephthalate) H ₂ The O slurry 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, the second hydrolysis reaction tank is usually provided in order to achieve a reaction conversion rate close to almost 100% from the state where the hydrolysis reaction from DMT to TA has progressed 90% or more.
[0025]
Next, the high-temperature TA / H obtained in the second hydrolysis reaction tank 21 ₂ It supplies to the cooling tank 22 for cooling O slurry. Cooled TA / H ₂ In order to make the O slurry into the TA / EG slurry, EG is supplied from the cooling tank 22 to the TA slurry feed line between the centrifuge 23 and the TA / H ₂ EG is line mixed with the O slurry. The amount of EG to be supplied is TA / H ₂ H of O slurry ₂ The weight is preferably 25 to 75 times the weight of O.
TA / H obtained by line mixing ₂ The O / EG slurry is centrifuged in a centrifuge 23 and TA cake and H ₂ Separated into O / EG mother liquor.
The TA cake obtained by the centrifugal separator 23 is supplied to the TA slurry preparation tank 24, and is prepared to a slurry having an EG: TA slurry molar ratio of 1: 1 to 1: 3 by the EG supplied from the EG supply source 25. .
[0026]
Here, H generated from the first hydrolysis reaction tank 20 ₂ After the O / MeOH mixed solution is stored in the MeOH tank 28, the MeOH and H in the MeOH distillation column 27 are stored. ₂ It is separated by distillation into O, and MeOH is supplied to the previous MeOH distillation column 9 and again distilled. Also generated H ₂ O is discarded. In addition, H produced in the second hydrolysis reaction tank 21 ₂ O / MeOH mixture is H ₂ It is heated by the O heater 26 and is circulated again to the mixing tank 19.
Further, the mother liquor of the centrifuge 23 is H. ₂ After the O / EG mixed solution is stored in the filtrate tank 31, EG and H are mixed in the EG distillation column 30. ₂ EG is redistilled in the previous EG distillation column 8 and H ₂ O is H ₂ It is circulated again through the O tank 29.
[0027]
Next, a process of obtaining a PET polymer from the obtained TA slurry will be described with reference to FIG. A TA / EG slurry whose molar ratio is adjusted in the TA slurry tank 24 is supplied to the esterification tank 33, and a PET oligomer is obtained by an esterification reaction. The reaction temperature of the esterification tank 33 is preferably 260 ° C. to 270 ° C., and the residence time is preferably 1 to 5 hours.
During this time, EG / H ₂ The reaction product mixture of O was distilled, and EG and H were ₂ Separate into O. The EG is redistilled in the EG distillation column 30 and further in the EG distillation column 8.
[0028]
The PET oligomer obtained in the esterification tank 33 is supplied to the initial polymerization tank 34, vacuumed by the vacuum device 44, and a polycondensation reaction is carried out under a condition of 260 ° C. to 280 ° C. under a weak vacuum of 10 Torr to 30 Torr. . Further, the obtained initial polycondensate is supplied to the late polymerization tank 35 and is vacuumed by the vacuum device 44, and the polycondensation reaction is carried out at 270 ° C. to 290 ° C. under a high vacuum of 0.5 Torr to 5 Torr. EG generated by the polycondensation reaction from the polymerization tank 34 and the polymerization tank 35 is both distilled through the EG tank 30 and in the EG distillation column 8.
[0029]
The PET polymer obtained in the late polymerization tank 35 is taken out from the late polymerization tank in a plate shape or a strand shape, cooled in the cooling water bath 36, and then cut into pellets by the cutter 37. The obtained PET pellet is subjected to a polycondensation reaction in the form of a solid pellet in order to obtain a predetermined degree of polymerization of a PET polymer suitable for PET bottles in a solid phase polymerization reaction tank 38 equipped with a dryer and a pre-crystallization machine. . This solid state polymerization reactor can be used for vacuum reaction even with N ₂ A reaction under an air current is also possible. The final product PET is stored in the storage tank 39. This PET polymer is used as a polymer suitable for PET bottles.
[0030]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, the measurement of IV performed in the following example was obtained by dissolving an appropriate amount of a PET sample in orthochlorophenol, measuring the flow time of the solution in an Ostwald viscosity tube, and obtaining the solution viscosity.
[0031]
Example 1
Separately collected and collected PET bottle veils (veil dimensions: 900 mm x 1,000 mm x 550 mm 120 kg bale) were unpacked and then put into a pulverizer and pulverized by setting the screen diameter of the pulverizer to 10 mm. . After that, this pulverized product is applied to a wind power sorter to remove the label attached to the bottle mainly composed of polyethylene, polystyrene and polypropylene, and then centrifuged with a decanter to wash and remove the contents of the bottle with water. Then, a cap mainly composed of polyethylene and a label that was not removed by wind sorting were removed to obtain recovered PET flakes. The recovered PET flakes were transported for storage in a recovered PET flake supply tank by pneumatic transport. Next, 100 parts by weight of the 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 are supplied to the depolymerization tank. And kept at 180 ° C. for 4 and a half hours.
[0032]
The above-described depolymerization reaction treatment solution using EG was put into a filtration device surrounded by a heater heated to 170 ° C. and equipped with a 100-mesh wire mesh as a filter medium, and filtered while hot. The residue on the filter was washed with 90 parts by weight of EG heated to 170 ° C., and the washing solution was stored in a washing solution receiving tank.
The depolymerization reaction solution obtained by hot filtration was concentrated by distillation under reduced pressure at 6.65 kPa, and 270 parts by weight of EG was recovered as a fraction.
[0033]
2.7 parts by weight of sodium carbonate and 180 parts by weight of MeOH are added to the transesterification reaction tank from this concentrated liquid and transesterification catalyst tank, and the transesterification reaction is carried out by maintaining the liquid temperature at 75 ° C. for 1 hour with stirring at normal pressure. did. The resulting mixture of DMT, EG and MeOH was cooled to 40 ° C., and a DMT cake was obtained by a subsequent solid-liquid separator. This DMT cake was once put in a MeOH washing tank, 180 parts by weight of MeOH was put in, stirred and washed at 40 ° C., and solid-liquid separated again by a centrifugal separator to obtain a DMT cake. The obtained DMT cake was put into the MeOH washing tank again, and this time, DMT was melted at 160 ° C. and at the same time, the remaining MeOH was distilled off. Molten DMT was charged into a DMT distillation column, and DMT was distilled as a fraction by vacuum distillation at a pressure of 6.65 kPa, and 83 parts by weight could be obtained as recovered DMT. This DMT was fed to the DMT collection tank.
[0034]
Next, molten DMT is removed from the DMT recovery tank at a rate of 100 parts by weight / hour, and H ₂ O tank was continuously fed to the mixing tank at a rate of 200 parts by weight / hour, and DMT and H were mixed at 180 ° C. in the mixing tank. ₂ While stirring O, the mixed solution was supplied to the first hydrolysis reaction tank at a rate of 300 parts by weight / hour. While stirring the liquid temperature of the first hydrolysis reaction tank at 250 ° C., a reaction time is ensured with a residence time of 2 hours, and MeOH generated in the hydrolysis reaction is H from the tank head. ₂ Distilled with O. Distillation rate is MeOH and H ₂ The mixed solution of O was about 76 parts by weight / hour, and the internal pressure at this time was about 4 MPa. TA, H obtained ₂ The mixed slurry of O 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., and the reaction was performed while ensuring a residence time of 1 hour with stirring. ₂ Distilled with O. Distillation rate is MeOH and H ₂ The mixed liquid of O was about 58 parts by weight / hour, and the internal pressure at this time was about 4 MPa. TA, H obtained ₂ The O slurry was fed to the rejection tank at a rate of about 166 parts by weight / hour. TA / H in this cooling tank ₂ TA / H in O slurry ₂ The O weight ratio is about 1/1. High TA / H temperature of about 250 ° C ₂ The O slurry was cooled to about 70 ° C. and held with a vent condenser, a cooling inner pipe, and a cooling jacket. TA / H at a rate of 166 parts by weight / hour from this cooling bath ₂ When the O slurry was fed to the centrifuge, EG was introduced into the line between the cooling tank and the centrifuge at a rate of 4,150 parts by weight / hour and mixed with the slurry. TA / H ₂ The weight ratio of O / EG was 1: 1: 50, and the TA EG slurry was processed by a centrifuge to obtain a TA cake. TA / H of this TA cake ₂ The weight ratio of O / EG is about 83: 0.4: 14.3, and the TA slurry tank is dumped at a rate of about 97.6 parts by weight / hour, and at the same time, about 35.3 parts by weight from the EG supply tank. EG was supplied to the TA slurry tank at a supply rate of / hour. The EG / TA weight ratio in the TA slurry tank is about 49.6: 83, but a slurry circulation line is provided in the TA slurry tank to stabilize the reaction in the subsequent process, and the slurry specific gravity is measured online. The amount of EG supplied from the EG supply tank to the TA slurry tank was adjusted so that the slurry had a weight ratio of 49.6: 83 as accurately as possible.
[0035]
Next, TA EG slurry (slurry in which the weight ratio of TA / water / EG is 83: 0.4: 49.6) is supplied from the TA slurry tank to the esterification tank at a feed rate of 133 parts by weight / hour. EG and H so that the residence time is 2 hours while stirring at a reaction temperature of 270 ° C. ₂ The reaction was carried out while distilling off O. The distilled EG can be used for the depolymerization reaction by being distilled together with the generated EG in this process. H ₂ O was drained along with other generated water. While supplying the PET oligomer obtained in the esterification tank to the initial polymerization tank at 102 parts by weight / hour, Ge ₂ O _Three A (germanium oxide) catalyst was supplied at a supply rate of 0.015 parts by weight / hour, and a polycondensation reaction was performed at 280 ° C. while stirring and distilling off EG under a weak vacuum of about 2 kPa (about 15 Torr). Distilled EG can be used for the depolymerization reaction if it is distilled together with some other EG.
[0036]
The PET oligomer was supplied from the initial polymerization tank to the latter polymerization tank at a feed rate of 97 parts by weight / hour, and the latter polymerization tank was stirred at 280 ° C. under a high vacuum of 0.13 kPa (about 1 Torr) while distilling off the EG. A polycondensation reaction was performed to obtain a PET polymer. This PET polymer had an intrinsic viscosity (IV) of 0.51. The PET polymer was taken out from the late polymerization tank in a molten state, cooled in a cooling bath, cut into pellets with a cutter, and supplied in a pellet state to a solid phase polymerization tank at a supply rate of 96.5 parts by weight / hour. Under a vacuum of 0.65 kPa (about 5 Torr) in a packed column type solid phase polymerization tank having a pre-crystallizer, the jacket temperature is adjusted so that the pellet temperature at the center of the tank is 210 ° C., and the residence time in the tank is about Solid state polymerization was performed under conditions of 8 hours. The obtained PET polymer had an intrinsic viscosity (IV) of 0.76, and was an optimal polymer as a PET bottle polymer. The solid phase polymerization tank is stored in a PET storage tank at 96.4 parts by weight / hour.
[0037]
In addition, the PET oligomer generated in the initial polymerization tank, the late polymerization tank, and the solid phase polymerization tank, and the PET polymer waste are directly supplied to the depolymerization tank depending on the form, and depolymerized or supplied to the pulverizer and pulverized. Can be supplied to the depolymerization reaction tank, and can be reused with as little loss as possible in a series of steps. In addition, H generated from each process ₂ By distillation of O, EG, and MeOH, a significant part can be recycled somewhere in the series of steps, and can be reused with as little loss as possible.
[0038]
【The invention's effect】
From the recovered used PET bottles of the present invention, dimethyl terephthalate is used to obtain high-purity terephthalic acid, and the PET polymer for PET bottles is obtained from it as a raw material. It becomes possible to effectively circulate and use PET bottles that are attracting particular attention and are becoming a social problem.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of the steps of the method of the present invention.
[Explanation of symbols]
1: Depolymerization tank
2: Solid-liquid separator
3: Cleaning tank
4: Distillation concentration tank
5: Transesterification reactor
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: Collected PET flakes supply tank
12: MeOH supply tank
13: Transesterification catalyst tank
14: DMT collection tank
15: EG discharge tank
16a: Cleaning liquid receiving tank
16b: Solid tank
17: EG distillation pot remaining treatment tank
18: DMT distillation pot remaining treatment tank
19: Mixing tank
20: First hydrolysis reactor
21: Second hydrolysis reactor
22: Cooling tank
23: Centrifuge
24: TA slurry tank
25: EG supply tank
26: H ₂ O heater
27: MeOH distillation column
28: MeOH tank
29: H ₂ O tank
30: EG distillation tower
31: Filtrate tank
32: Wastewater treatment equipment
33: Esterification tank
34: Initial polymerization tank
35: Late polymerization tank
36: Cooling water bath
37: Cutter
38: Solid state polymerization reactor
39: PET storage tank
40: EG distillation tower
41: EG condenser 1
42: EG condenser 2
43: Vacuum generator
44: H ₂ O supply tank

Claims (7)

A method for recycling PET bottles, comprising sequentially providing resin bottle waste containing polyethylene terephthalate (PET) as a main component and further different components to the following steps (1) to (23).
(1) Step of unpacking the separately collected and collected PET bottle packing bale (2) Crushing step of making the unpacked PET bottle into a 2-30 mm square flake shape (3) From the PET-shaped PET bottle piece to polyethylene ( Separating component polymer different from PET of label thin film made of PE), polystyrene (PS), polyvinyl chloride (PVC), etc. by wind sorting (4) Foreign matter inside and / or inside PET bottle and / or inside PET bottle A decanter process that doubles the contents residue with water and separates different component plastics such as PE and PP, which have a specific gravity smaller than that of water (5) Air transport process that sends the recovered PET flakes to the flake storage tank (6 ) Put the recovered PET flakes into ethylene glycol (EG) containing a PET depolymerization catalyst PET depolymerization step for obtaining bis-β-hydroxyethyl terephthalate (BHET) by treatment at a temperature of 90 ° C. and a pressure of 0.1 to 0.5 MPa (7) Solid-liquid separation step of components not dissolved in EG (8 ) Concentration step for distilling off EG components in crude BHET in the liquid (9) Step for obtaining crude DMT and EG by transesterification of concentrated crude BHET in transesterification catalyst and methanol (MeOH) (10) Cooling Step of solid-liquid separation of DMT cake and EG / MeOH mixed solution (11) Distillation step of distilling MeOH from DMT cake to purify DMT (12) Step of storing recovered purified DMT in a molten state and sending the solution ( 13) A step of adding water (H ₂ O) at a weight ratio of 1: 1 to 1: 4 with respect to the recovered and purified DMT and mixing and holding at 170 to 190 ° C. (14) Mixing and holding The DMT and H ₂ O were fed and hydrolyzed at 230 to 250 ° C. (15) The produced terephthalic acid (TA) and the H ₂ O slurry were cooled (16) The cooled TA H ₂ O EG is line-mixed with the slurry to obtain an EG slurry containing TA H ₂ O (17) A TA cake is obtained by centrifugation from the H ₂ O / EG slurry of TA (18) TA and EG to TA A step of preparing a slurry at a molar ratio of 1: 1 to 1: 3 (EG) (19) A step of esterifying TA and EG to obtain a PET oligomer (20) A polycondensation catalyst is added to the PET oligomer, An initial melt polymerization step (21) for evaporating EG by performing a melt polycondensation reaction at 260 ° C. to 280 ° C. under a weak vacuum of 10 to 30 torr, and further increasing the degree of polymerization, and further under a high vacuum of 0.5 to 5 torr, 270 ° C to 2 EG is distilled off by melt polycondensation reaction at 0 ° C. Late melt polymerization step for further increasing the degree of polymerization (22) Solid state polymerization step for adjusting the degree of polymerization in order to obtain PET suitable for bottle use (23) Storage process The PET bottle recycling method according to claim 1, wherein the depolymerization catalyst used in step (6) is selected from the group consisting of sodium carbonate, Na carboxylate, manganese acetate, and zinc acetate. The method for recycling a PET bottle according to claim 1, wherein the amount of the depolymerization catalyst used in the step (6) is 0.1 to 10% by weight of the weight of the recovered PET flakes. The method for recycling a PET bottle according to claim 1, wherein the transesterification catalyst used in step (9) is selected from the group consisting of sodium carbonate, Na carboxylate, manganese acetate, and zinc acetate. The method for recycling a PET bottle according to claim 1, wherein the amount of the transesterification catalyst used in step (9) is 0.1 to 10% by weight of the weight of the recovered PET flakes. The PET bottle recycling method according to claim 1, wherein the polycondensation reaction catalyst used in the step (20) is selected from the group consisting of Ge, Sb, and Ti catalysts. The PET bottle recycling method according to claim 1, wherein the amount of the polycondensation reaction catalyst used in the step (20) is 0.002 to 0.1% by weight of the TA weight supplied to the step (19).

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