JP2004300115A - Method for recovering valuable component from waste polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To establish a method for stably recovering a pure valuable component from waste polyesters of various forms without causing process troubles. <P>SOLUTION: Recovered monomers having high purity can be produced in high efficiency by crushing waste polyesters to give crushed products having different bulk density (apparent density), supplying the crushed product to a granulator while controlling the supplying rate to keep the operation load within a prescribed range and supplying the produced granules to a chemical recycling process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention, after crushing polyester waste of various forms, forms granules stably without causing process troubles, further performs a chemical reaction treatment on the granules, and as an active ingredient The present invention relates to a method for recovering high purity bishydroxyl terephthalate or terephthalic acid component and alkylene glycol.
[0002]
[Prior art]
Polyester, for example, polyethylene terephthalate, is widely used as a fiber, film, resin, etc. due to its excellent properties. It has become a major problem not only from the aspect but also environmental issues, and various proposals have been made as a method of treating it by material recycling, thermal recycling, and chemical recycling.
[0003]
In material recycling, polyester resin waste such as PET bottles is collected mainly by local governments and actively recycled, but fiber waste is mixed with various additives to impart functionality. Therefore, it is extremely difficult to adopt the recycling method.
[0004]
In addition, thermal recycling, which converts polyester waste to fuel, has the advantage of reusing the combustion heat of polyester waste, but it has a relatively low calorific value and burns a large amount of polyester waste. There is a problem of loss, which is not preferable in terms of resource saving.
[0005]
On the other hand, in chemical recycling, since polyester waste is regenerated into raw material monomers, there is little deterioration in quality due to regeneration, and it is suitable for closed-loop recycling. In the chemical recycling, resin waste and film waste are mostly used.
[0006]
As a method of recycling polyester fiber waste, after depolymerizing polyester waste with an excess of ethylene glycol (hereinafter sometimes abbreviated as EG), the obtained bis-β-hydroxyethyl terephthalate (hereinafter referred to as BHET) is used. Is abbreviated to obtain a regenerated polyester by direct polycondensation (for example, see Patent Document 1). However, this method involves a depolymerization reaction between polyester waste and EG in a depolymerization step. Since the depolymerization is performed by batch charging into the system, the charged polyester waste is solidified inside the reactor and cannot be stirred.
[0007]
Therefore, the depolymerization reaction system becomes non-uniform and the depolymerization time is prolonged.Moreover, the amount of EG used is not only economically disadvantageous, but also impurities such as diethylene glycol are produced as by-products in the reaction product. There were drawbacks in that the physical properties of the resulting polyester, particularly the softening point, were remarkably reduced, and only low-grade polyesters could be obtained. In such conventional techniques, a technique for efficiently treating polyester fiber waste has not been completed.
[0008]
When fibers outside the polyester production process are to be collected, polyethylene (hereinafter may be abbreviated as PE), polypropylene (hereinafter may be abbreviated as PP), nylon (hereinafter abbreviated as Ny). In some cases, mixing of fibers different from polyester such as cotton may be unavoidable. Further, even if the material is polyester, those containing a dye are decomposed during a series of reactions such as depolymerization, and are dispersed in the recovered monomer to significantly deteriorate the quality.
[0009]
Therefore, the present inventors have previously proposed a method of crushing and granulating polyester fiber waste and separating and recovering dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) and EG (see Patent Document 2). ). In this method, DMT and EG are recovered by crushing and granulating a polyester waste containing a foreign substance component, depolymerizing with an alkylene glycol, and then performing a transesterification reaction with methanol. However, for example, when fiber wastes having different thicknesses are mixed, the bulk specific gravity (apparent specific gravity) of the crushed material constantly changes, and in the granulation, the melting proceeds excessively in the granulator, causing the motor to stop overloading. There was a concern that a process trouble might occur.
[0010]
[Patent Document 1]
JP-A-48-61447 (claims)
[0011]
[Patent Document 2]
JP-A-2002-167341 (Claims)
[0012]
[Problems to be solved by the invention]
An object of the present invention is to solve the problems of the prior art and to establish a method for stably recovering a high-purity active ingredient from various forms of polyester waste without causing any process trouble. .
[0013]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have completed the present invention.
[0014]
That is, the purpose of the present invention is to
The polyester waste is put into a crusher as a lump and the waste is first crushed to 30 to 150 mm, and then the crushed product is further crushed to 2 to 30 mm, and the crushed product is continuously put into a granulator. After solidifying into a cylindrical solid having a diameter of 2 to 10 mm and a length of 10 to 60 mm to a bulk density of 0.20 to 1.2 g / cm ³ , the solid is pneumatically transported to a reaction step described below. In combining the pretreatment step of transporting and the following reaction steps (a) to (f), the input amount of the pulverized material per unit time is adjusted so that the operating load of the granulator is within a predetermined range. The method can be achieved by a method for recovering a high-purity active ingredient from polyester waste, characterized in that the granulated material is cooled while controlling the temperature of the granulator within a predetermined range.
(A) A depolymerization reaction step in which the crude polyester obtained through the pretreatment step is introduced into an alkylene glycol containing a depolymerization catalyst to obtain bis-β-hydroxyalkyl terephthalate (BHAT).
(B) A foreign matter removing step of removing foreign plastics other than polyester, such as polyethylene, polystyrene, polypropylene, and polyvinyl chloride, during or after the depolymerization reaction step.
(C) a filtration separation step of filtering and separating undissolved components after the depolymerization reaction.
(D) a BHAT concentration step of subjecting the mixture of BHAT and alkylene glycol obtained through the above-mentioned filtration and separation step to distillation and evaporation to distill and evaporate the alkylene glycol to obtain a concentrated BHAT.
(E) A transesterification reaction step in which a transesterification catalyst and methanol are added and charged into a mixture of the crude BHAT and the crude alkylene glycol obtained in the BHAT concentration step to carry out transesterification.
(F) a purification step of separating and recovering purified dimethyl terephthalate and purified alkylene glycol from a mixture of crude dimethyl terephthalate, crude methanol and crude alkylene glycol obtained in the transesterification step.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the method of the present invention will be described in detail.
In the method for recovering an active ingredient of the present invention, it is necessary to pulverize the polyester waste into an appropriate size from the viewpoint of handling the waste. The size of the pulverized product is preferably 2 to 30 mm. If the crushed diameter is large, a problem that solidification is insufficient in the next granulation step occurs. As an embodiment of the pulverization, it is preferable to use a two-stage pulverizer in order to improve the pulverization processing capacity. That is, the polyester fiber waste is roughly pulverized to 30 to 50 mm by a primary pulverizer, and then pulverized to 2 to 30 mm by a secondary pulverizer. If the size of the pulverized material is specified directly at 2 to 30 mm in the primary pulverizer, the load applied to the pulverizer becomes excessive, which is rather inefficient.
[0016]
Next, the pulverized material is put into a granulator, and the pulverized material is solidified into a cylindrical granulated material, which will be described below with reference to the drawings.
[0017]
The crushed product 1 of the polyester waste is continuously supplied into the main body of the granulator through the crushed material hopper 12 and the feeder 13. The rotation speed of the feeder 13 is driven at a variable speed via a motor 14 by an inverter 15 or a device (not shown) having a speed change mechanism. The crushed material 1 thus supplied into the granulator is compressed between the inner peripheral surface of the rotary die 3 and the outer peripheral surface of the roller 4 having a pore diameter defined in the granulator, and the crushed material 1 is compressed. A part of the surface of the crushed material is solidified and compressed by the frictional heat generated by the compression while being partially melted, cut into granules by the cutter 5, and then sent downstream through the discharge chute 16. Here, the rotary die 3 is a cylindrical one having a large number of through-holes 2 for extruding granulated materials, and a pair of rollers 4 is provided in the rotary die 3 in this embodiment. Numeral 4 is adapted to roll on the inner surface of the rotary die 3 with a predetermined clearance. The crushed material 1 supplied between the inner surface of the rotary die 3 and the roller 4 is compressed, and the compressed crushed material 1 is sequentially extruded from the through-hole 2 for extruding the granulated material, and granulated to a predetermined length by the cutter 5. The object 6 is cut.
[0018]
When the pore size is large, the frictional heat becomes very small, so that the surface of the solidified product is not sufficiently solidified. Insufficient solidification in this manner causes the solids to collapse in the subsequent pneumatic transportation process due to collisions with the pipes, resulting in a structure that is easy to form a bridge in the storage tank at the destination, which makes it extremely difficult to discharge from the storage tank. Become. The size of the hole diameter is preferably 2 to 10 mm, more preferably 4 to 6 mm. The length is preferably set to 10 to 60 mm.
[0019]
The granulator is provided with a temperature sensor 7, which is set to accurately measure the temperature of the granulated material 6. In the granulation method, it is necessary to operate at a temperature equal to or higher than the glass transition point of the polyester and lower than the melting point. That is, as a granulation method, there is a method in which the fiber waste is heated to a temperature equal to or higher than the melting point of the polyester, completely melted, and then cooled and solidified. However, in the granulation method, impurities such as Ny are decomposed and collected. Deterioration of monomer quality. Further, if the solidification is completely solidified to the inside of the solid in the granulation method, there is also a problem that the reaction rate is greatly reduced due to a decrease in the contact efficiency between the solvent and the granulated solid in the reaction step. In the present invention, it is necessary that only a part of the fiber waste surface is melted and solidified at an operating temperature equal to or higher than the glass transition point of the polyester and lower than the melting point. The granulation method can improve the handleability while suppressing the decomposition of impurities and the decrease in the reaction rate.
[0020]
On the other hand, the control device 11 receives a signal from the recorder 10 that records the current value or the electric energy of the granulator motor, and adjusts the rotation speed of the feeder 13 to the inverter 15 or an appropriate value so that the detected value becomes a predetermined value. A variable speed drive is controlled by a device (not shown) having a suitable transmission mechanism. Further, the detected value of the temperature sensor 7 is input to the control device 11 of the feeder 13, and the temperature is allowed to rise until the temperature reaches a predetermined temperature determined by the physical properties of the crushed material. Controlling starts watering from the watering nozzle 9 and stops the watering by controlling the valve 8 based on the detection value of the temperature sensor 7.
[0021]
By the above control, the crushed material 1 is granulated in an optimum state without reaching the temperature at which melting starts to occur, so that machine troubles are prevented from occurring, and unnecessary stoppage is avoided, thereby reducing the production efficiency. Can be maximized.
[0022]
The bulk density of the pulverized product before the granulation treatment is about 0.05 g / cm ^{3. When the} pulverized product is put into the reactor in this state, the pulverized product becomes very bulky and absorbs the solvent alkylene glycol. This makes it very difficult to stir the reaction tank.
[0023]
In order for this reaction to proceed smoothly, it is necessary to increase the bulk density along with granulation and solidification. The final bulk density is 0.20 to 1.20 g / cm ³ , preferably 0.40 to 1. It is necessary to increase to 20 g / cm ³ to improve the handling property.
[0024]
The granulated product after granulation is transported to the reaction step by pneumatic transport. Hereinafter, each of the reaction steps will be described.
[0025]
In the step (a), the polyester fiber solid that has passed through the pretreatment step is subjected to a depolymerization reaction in a known depolymerization catalyst, in an excess of alkylene glycol at a known catalyst concentration at a temperature of 120 to 210 ° C. Here, if the temperature of the alkylene glycol is lower than 120 ° C., the depolymerization time becomes extremely long, and the efficiency becomes inefficient. On the other hand, when the temperature exceeds 200 ° C., thermal decomposition of the oil agent and the like contained in the fiber waste becomes remarkable, and nitrogen compounds and the like generated by the decomposition are dispersed in the recovered monomer, making it difficult to separate them in the subsequent purification step. The temperature is preferably between 140 and 190C.
[0026]
Further, when the polyester fiber waste to be treated in the present invention is colored with a dye, the dye may be decomposed in the reaction step to reduce the molecular weight, and may be dispersed in the recovered monomer to significantly lower the quality. Therefore, when handling the colored fiber waste, it is effective to incorporate a step of discharging the dye before the step (a). In this step, the granulated solid containing the dye is put into a solvent such as water, alkylene glycol, dimethylformamide, para-xylene, or 2-heptanone, and optionally heated at 100 to 190 ° C. while applying pressure to extract the dye. I do. The discharge method may be a batch method or a continuous extraction method such as a countercurrent multistage extraction method. The solid after dye extraction is washed with alkylene glycol, and then transported to the step (a) in the same manner as the fiber waste not containing dye.
[0027]
Further, when Ny is mixed into the polyester waste, Ny is decomposed in the reaction step, and mixed as a nitrogen compound such as ε-caprolactam in the recovered monomer, making separation difficult. Therefore, it is effective to incorporate the step of dissolving and removing Ny in the solidified substance containing Ny before the step (a). In this step, a solidified substance containing Ny is introduced into a solvent such as an alkylene glycol and heated to 100 to 190 ° C. to dissolve and remove Ny. This step may be performed in the discharge printing step.
[0028]
In the step (b), a different fiber from polyester such as PE or PP is floated and separated in the depolymerization reaction layer. Since the specific fibers have a lower specific gravity than the alkylene glycol which is a solvent for the depolymerization reaction and float on the liquid surface, they are separated into layers as a eutectic mixed floating mass of different fibers, and then the eutectic mixing is performed. The suspended matter layer is extracted from the depolymerization and removed.
[0029]
In the step (c), after the depolymerization reaction, different fibers such as cotton are filtered and separated. The foreign fiber to be removed in the step (c) is a component having a higher specific gravity than the alkylene glycol and cannot be separated by the removal method in the step (b). At the time of passing through the step (c), the polyester is converted into bis-β-hydroxyalkyl terephthalate (hereinafter sometimes abbreviated as BHAT), and the reaction solution is a mixture of BHAT and alkylene glycol.
[0030]
In the step (d), the weight ratio of the alkylene glycol and the polyester fiber waste is determined from the mixture of the BHAT and the alkylene glycol passed through the step (c) in order to efficiently advance the transesterification reaction in the step (e). The alkylene glycol is distilled off until the raw material charge ratio becomes 0.5 to 2.0 times. The alkylene glycol distilled off at this time is recycled to the step (a) again.
[0031]
In the step (e), the mixture of BHAT and the alkylene glycol, from which the alkylene glycol has been distilled off in the step (d), is subjected to a transesterification reaction with methanol in the presence of a known ester exchange catalyst and a known concentration, followed by centrifugation. Solid-liquid separation is performed by solid-liquid separation means.
[0032]
In step (f), the crude DMT and crude alkylene glycol obtained in step (e) are purified by a purification method such as distillation to obtain high-purity purified DMT and purified alkylene glycol. At this time, the impurities that have passed through the reaction step are also captured at the bottom of the column, so that the recovered monomers contain no impurities and have high purity.
[0033]
【Example】
Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited by the examples.
[0034]
[Example 1]
For 600 kg of polyethylene terephthalate fiber waste mixed with various thicknesses and containing no dye generated from the polyester production process, the entire amount of the fiber waste was put into the primary pulverizer, and the screen diameter of the pulverizer was set to 75 mm to make the primary pulverizer. Pulverization was performed, and then the pulverized material was put into a secondary pulverizer, and a secondary pulverization was performed by setting the screen diameter of the pulverizer to 20 mm. Thereafter, the pulverized product was put into a granulator that was operated with a die having a diameter of 4 mm for a through-hole for extruding the granulated product under conditions that the cut length of the granulated product was 45 mm. At this time, the current value of the motor that drives the granulator is set to 130 A, the rotation speed of the supply conveyor to the granulator is adjusted so that the current value is constant, and the temperature of the granulated material is 130 ° C. A control system that adjusts the amount of water injected was adopted. Although the bulk specific gravity of the polyester crushed material to be fed to the granulator during operation varies between 0.02g ^/ cm ³ ~0.06g / cm 3 is confirmed, the rotation following the change in the bulk density The speed was changed and a granulated product was obtained without any trouble. The average bulk density of the obtained granules was 0.45 g / cm ³ .
[0035]
In the reaction step, 500 kg of the solidified product was charged into a mixture of 700 kg of EG and 3 kg of sodium carbonate which had been heated to 185 ° C. in advance, and reacted at normal pressure for 4 hours.
[0036]
After completion of the reaction, a mixture of BHET and EG was sent to a distillation column, and 200 kg of EG was distilled off under the conditions of a bottom temperature of 140 to 150 ° C and a pressure of 13.3 kPa. Next, 3 kg of sodium carbonate and 200 kg of methanol were added to 200 kg of a mixture of BHET and EG after the EG was distilled off, and reacted at 75 to 80 ° C. for 1 hour at normal pressure.
[0037]
After completion of the reaction, the reaction solution was cooled to 40 ° C., and subjected to centrifugal separation to solid-liquid separation into a cake mainly composed of crude DMT and a filtrate mainly composed of methanol and crude EG. Next, the crude DMT was purified by distillation under the conditions of a pressure of 6.7 kPa and a bottom temperature of 180 to 200 ° C., and the crude EG was purified by distillation under the conditions of a pressure of 13.3 kPa and a bottom temperature of 140 to 150 ° C., and finally DMT and EG were collected. 85%. The recovered DMT is comparable to the commercial product in the appearance, acid value, melting color, and sulfated ash test items, and the recovered EG is comparable to the commercial product in the diethylene glycol concentration, water content, and melt colorimetric test items. In each case, a high-purity recovered monomer was obtained.
[0038]
[Example 2]
About 600 kg of polyethylene terephthalate uniform containing dye recovered from the city, the entire amount of the uniform was put into a primary pulverizer, a primary pulverizer was set by setting a screen diameter of the pulverizer to 75 mm, and then the pulverized product was subjected to primary pulverization. It was put into a secondary pulverizer, and the secondary pulverization was performed by setting the screen diameter of the pulverizer to 20 mm. Thereafter, the pulverized product was put into a granulator operated by using a die having a through-hole for extruding the granulated material having a diameter of 4 mm and a cut length of the granulated material of 45 mm and an internal temperature of the granulator of 130 ° C. At this time, the current value of the motor that drives the granulator was set to 130 A, and the granulator was operated in a control system that adjusted the rotation speed of the supply conveyor to the granulator so that the current value was constant. Although the bulk specific gravity of the polyester crushed material to be fed to the granulator during operation varies between 0.03g ^/ cm ³ ~0.08g / cm 3 is confirmed, the rotation following the change in the bulk density The speed was changed and a granulated product was obtained without any trouble. The average bulk density of the obtained granules was 0.50 g / cm ³ .
[0039]
500 kg of the granulated product was charged into a reactor containing 4000 kg of para-xylene which had been heated to 130 ° C. in advance, and heated and stirred at normal pressure for 30 minutes to extract a dye contained in the granulated product. Thereafter, solid-liquid separation was performed with a pressure filter, and solid-liquid separation was performed on the granules from which the dye was extracted and paraxylene containing the dye. After removing the paraxylene remaining in the granules from which the dye was extracted by drying, the paragylene was removed from the granules, 700 kg of EG and 3 kg of sodium carbonate, which had been heated to 185 ° C. in advance, were charged into the reactor, and 4 kg at normal pressure. Allowed to react for hours.
[0040]
After completion of the reaction, a mixture of BHET and EG was sent to a distillation column, and 200 kg of EG was distilled off under the conditions of a bottom temperature of 140 to 150 ° C and a pressure of 13.3 kPa. Next, 3 kg of sodium carbonate and 200 kg of methanol were added to 200 kg of a mixture of BHET and EG after the EG was distilled off, and reacted at 75 to 80 ° C. for 1 hour at normal pressure.
[0041]
After completion of the reaction, the reaction solution was cooled to 40 ° C., and subjected to centrifugal separation to solid-liquid separation into a cake mainly composed of crude DMT and a filtrate mainly composed of methanol and crude EG. Next, the crude DMT was purified by distillation under the conditions of a pressure of 6.7 kPa and a bottom temperature of 180 to 200 ° C., and the crude EG was purified by distillation under the conditions of a pressure of 13.3 kPa and a bottom temperature of 140 to 150 ° C., and finally DMT and EG were collected. 85%. The recovered DMT is comparable to the commercial product in the appearance, acid value, melting color, and sulfated ash test items, and the recovered EG is comparable to the commercial product in the diethylene glycol concentration, water content, and melt colorimetric test items. In each case, a high-purity recovered monomer was obtained.
[0042]
[Comparative example]
A total of 600 kg of polyester fiber waste similar to that in Example 1 was put into the primary pulverizer, the screen diameter of the pulverizer was set to 75 mm, and the primary pulverization was performed. It was put into a pulverizer, and a secondary pulverization was performed by setting the screen diameter of the pulverizer to 20 mm. Thereafter, the pulverized product was put into a granulator operated by a die having a through-hole for extruding the granulated material having a diameter of 4 mm and a cut length of the granulated material of 45 mm and an internal temperature of the granulator of 130 ° C. At this time, the current value of the motor for driving the granulator was initially set to 130 A, but thereafter no particular control was performed. Although the bulk specific gravity of the polyester crushed material to be fed to the granulator during operation varies between 0.02g ^/ cm ³ ~0.06g / cm 3 has been confirmed, the change control of the temperature of the bulk density of the raw material And the temperature reached 160 ° C. during operation, and as a result, a problem occurred in which the crushed material supplied to the granulator in the granulator melted into a sticky state and the motor stopped.
[Brief description of the drawings]
FIG. 1 is a schematic diagram schematically showing an apparatus for performing a granulation method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Crushed material 2 Granulated material extrusion through hole 3 Rotary die 4 Roller 5 Cutter 6 Granulated material 7 Temperature sensor 8 Valve 9 Watering nozzle 10 Recorder 11 Controller 12 Crushed material hopper 13 Feeder 14 Motor 15 Inverter 16 Discharge chute

Claims (5)

The polyester waste is put into a crusher as a lump and the waste is first crushed to 30 to 150 mm, then the crushed product is further crushed to 2 to 30 mm, and the crushed product is continuously put into a granulator. After solidifying into a cylindrical solid having a diameter of 2 to 10 mm and a length of 10 to 60 mm to a bulk density of 0.20 to 1.2 g / cm ³ , the solid is pneumatically transported to a reaction step described below. In combining the pretreatment step of transporting with the following reaction steps (a) to (f),
Cooling the granulated material so that the temperature of the granulator is within the predetermined range while controlling the amount of the pulverized material per unit time so that the operation load of the granulator is within the predetermined range. A method for recovering high-purity active ingredients from polyester waste.
(A) A depolymerization reaction step in which the crude polyester obtained through the pretreatment step is introduced into an alkylene glycol containing a depolymerization catalyst to obtain bis-β-hydroxyalkyl terephthalate (BHAT).
(B) A foreign matter removing step of removing foreign plastics other than polyester, such as polyethylene, polystyrene, polypropylene, and polyvinyl chloride, during or after the depolymerization reaction step.
(C) a filtration separation step of filtering and separating undissolved components after the depolymerization reaction.
(D) a BHAT concentration step of subjecting the mixture of BHAT and alkylene glycol obtained through the above-mentioned filtration and separation step to distillation and evaporation to distill and evaporate the alkylene glycol to obtain a concentrated BHAT.
(E) A transesterification reaction step in which a transesterification catalyst and methanol are added and charged into a mixture of the crude BHAT and the crude alkylene glycol obtained in the BHAT concentration step to carry out transesterification.
(F) a purification step of separating and recovering purified dimethyl terephthalate and purified alkylene glycol from a mixture of crude dimethyl terephthalate, crude methanol and crude alkylene glycol obtained in the transesterification step. The method for recovering an active ingredient according to claim 1, wherein the supply of the crushed material to the granulator is performed by a supply conveyor, and the amount of the crushed material is controlled by a transport speed of the supply conveyor. The method for recovering an active ingredient according to claim 1, wherein the detection of the operation load of the granulator is performed based on a current value or an electric energy of a granulator motor. The method for recovering an active ingredient according to claim 1, wherein cooling for controlling the temperature of the granulated material is performed by pouring water. The method of claim 1, wherein the polyester waste is polyester fiber waste.

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