JP2004224940A - Method for recovering effective component from polyester waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably and efficiently recovering an effective component from a polyester waste mainly containing a polyalkylene terephthalate. <P>SOLUTION: The method comprises controlling the concentration of sodium in a depolymerization reaction concentrate when a depolymerization reaction liquid resulting from the depolymerization of the polyester waste is concentrated to produce the depolymerization reaction concentrate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for recovering an active ingredient from a polyester waste mainly containing polyalkylene terephthalate.
[0002]
[Prior art]
Polyalkylene terephthalate typified by polyethylene terephthalate has excellent chemical stability, so it can be used in daily life-related materials such as fibers, films and resins, and in the food field such as drinking water and carbonated beverage bottles. It is growing rapidly.
[0003]
However, the treatment of used polyalkylene terephthalate, which is generated in large quantities with the increase in the amount of use as described above, or an unqualified product generated in the production stage of polyalkylene terephthalate, is a major social problem.
[0004]
In order to solve the above-mentioned problem, so-called chemical recycling in which polyester waste is converted and collected into a monomer, and this monomer is used as a raw material to produce and reuse polyethylene terephthalate by a polymerization reaction again is being studied. This method is basically free of loss, enables cyclic recycling of compounds, and can realize resource recycling.
[0005]
Specifically, a depolymerization reaction is performed with ethylene glycol, followed by a transesterification reaction using methanol, followed by separation and purification to obtain dimethyl terephthalate (hereinafter, sometimes abbreviated as DMT) and ethylene glycol (hereinafter, referred to as DMT). , EG.), Which leads to effective use of resources and a reduction in total cost.
[0006]
As a chemical recycling method of polyethylene terephthalate, for example, an excess of EG is added to polyethylene terephthalate, heated, and a mixture of bis (β-hydroxyethyl) terephthalate and a low polymer containing a β-hydroxyethyl ester group at a terminal is obtained by a depolymerization reaction. A method of recovering DMT by adding an excess of methanol (hereinafter sometimes abbreviated as MeOH) to the mixture and subjecting the mixture to a transesterification reaction in the presence of a catalyst is known (for example, Patent Document 1). 1).
[0007]
Further, a polyester waste containing polyvinyl chloride (hereinafter sometimes abbreviated as PVC) as a foreign substance component is subjected to a depolymerization reaction under conditions in which PVC does not substantially melt and / or thermally decompose, followed by esterification. A method of performing an exchange reaction to recover DMT and EG is also known (for example, see Patent Document 2).
[0008]
Since such polyester waste contains various kinds of foreign substances, it is necessary to set the upper limit of the depolymerization reaction temperature to a low temperature, for example, 190 ° C. or lower, so that the foreign substances do not thermally decompose and deteriorate the quality of the active ingredient. . Then, in order to compensate for the decrease in the rate of the depolymerization reaction due to the low depolymerization reaction temperature, an excessive amount of the depolymerization reaction catalyst must be added.
[0009]
However, if a large amount of catalyst, especially inexpensive sodium compound, is used in excess, the concentration of sodium compound in the distillation residue or the like will increase beyond the solubility, causing clogging of heat exchangers and pipes, and stable and efficient operation. Has been difficult to maintain.
[0010]
[Patent Document 1]
JP-B-43-2088 (Claims)
[0011]
[Patent Document 2]
WO 01/30729 pamphlet (claims)
[0012]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for stably and efficiently recovering an active ingredient.
[0013]
Still other objects and advantages of the present invention will become apparent from the following description.
[0014]
[Means for Solving the Problems]
According to one embodiment of the present invention, a polyalkylene terephthalate comprising the following steps (a) and (b), wherein the sodium concentration of the depolymerization reaction concentrated solution in step (b) is controlled to be 1% by weight or less. For recovering active ingredients from polyester waste mainly containing
[0015]
(A) a step of subjecting a polyester waste mainly containing polyalkylene terephthalate to a depolymerization reaction in the presence of an alkylene glycol and a depolymerization reaction catalyst to obtain a depolymerization reaction solution;
[0016]
(B) a step of separating at least a portion of water and / or alkylene glycol from the depolymerization reaction solution obtained in step (a) by distillation to concentrate the depolymerization reaction solution to obtain a depolymerization reaction concentrated solution;
[0017]
Thereby, it is possible to stably and efficiently recover the active ingredient from the polyester waste mainly containing polyalkylene terephthalate.
[0018]
Controlling the concentration of sodium in the depolymerization reaction concentrate in step (b) by the amount of sodium compound added in the depolymerization reaction catalyst, comprising the following steps (c) and (d); It is preferable to control the concentration of sodium in the distillation residue in (1) to be 1% by weight or less.
[0019]
(C) a cake separation step of subjecting the concentrated depolymerization reaction obtained in step (b) to a transesterification reaction with methanol in the presence of a transesterification catalyst to separate the reaction product into a cake and a mixed solution;
[0020]
(D) A methanol recovery step of subjecting the mixed solution obtained in the step (c) to a distillation treatment to separate it into distilled methanol and a distillation residue.
[0021]
Further, it is preferable to include the following steps (e) and (f).
[0022]
(E) an alkylene glycol recovery step of subjecting the distillation residue obtained in step (d) to distillation to distill alkylene glycol.
[0023]
(F) A DMT recovery step in which the cake obtained in step (c) is subjected to a washing treatment with methanol, and further subjected to distillation and purification to distill out DMT.
[0024]
Further, the control of the sodium concentration in the methanol distillation residue in the step (d) is controlled by the addition amount of the sodium compound in the depolymerization reaction catalyst and / or the addition amount of the sodium compound in the transesterification reaction catalyst. Wherein the glycol is ethylene glycol, and as a depolymerization reaction catalyst, a group consisting of alkali metal carbonates, hydrogen carbonates, hydroxides, alcoholates, alkaline earth metal carbonates, hydrogen carbonates, hydroxides and alcoholates Use of at least one metal compound selected from the group consisting of: a transesterification catalyst, an alkali metal carbonate, a hydrogen carbonate, a hydroxide, an alcoholate, an alkaline earth metal carbonate, a hydrogen carbonate, or a hydroxide It is preferable to use at least one metal compound selected from the group consisting of alcoholates. Arbitrariness.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described using examples and the like. It should be noted that these examples and the like and the description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments can also belong to the category of the present invention as long as they conform to the gist of the present invention.
[0026]
In the recovery method according to the present invention, polyester waste mainly containing polyalkylene terephthalate, such as used polyalkylene terephthalate or an unqualified product generated in the production stage of polyalkylene terephthalate (hereinafter referred to as polyalkylene terephthalate as described above) Is mainly referred to simply as polyester waste.). The range of “polyester waste mainly containing polyalkylene terephthalate” can be specifically determined depending on whether the recovery method according to the present invention can be applied regardless of whether or not the waste is actually treated as waste. In this case, a polyalkylene terephthalate production intermediate or a decomposition product can be included in the polyalkylene terephthalate.
[0027]
In the recovery method of the present invention, the polyester waste is passed through any of the above-described steps (a) to (f). Hereinafter, each step will be described. Note that these steps do not need to be clearly recognized as manufacturing steps. Depending on the actual situation, these steps may be complex steps, include circulating steps, or have other steps between them. May be.
[0028]
In step (a), the polyester waste is subjected to a depolymerization reaction in the presence of an alkylene glycol and a depolymerization catalyst to obtain a depolymerization reaction solution. For example, the polyester waste is put into an alkylene glycol containing a polyester depolymerization catalyst to be depolymerized. The temperature at this time is preferably 175 to 190 ° C.
[0029]
When the reaction temperature in the step (a) is lower than 175 ° C., the required depolymerization reaction time is prolonged, and the tendency for production efficiency to decrease often becomes remarkable. On the other hand, when the temperature exceeds 190 ° C., thermal decomposition of foreign components such as PVC becomes remarkable, and the quality of the target recovery component is often deteriorated.
[0030]
Here, the metal compound used as the depolymerization catalyst is preferably selected from alkali metal, alkaline earth metal, titanium, manganese, cobalt, zinc, antimony, lead and cerium compounds. Examples thereof include carbonates, bicarbonates, hydroxides, and alcoholates of these metals. More specifically, at least one metal selected from the group consisting of alkali metal carbonates, bicarbonates, hydroxides, alcoholates, alkaline earth metal carbonates, bicarbonates, hydroxides and alcoholates Preferably, a compound is used.
[0031]
As a metal compound for a depolymerization catalyst, a sodium compound, particularly sodium carbonate, has been often used in the past because of its excellent depolymerization reactivity, low cost and easy availability. As the depolymerization reaction catalyst, for example, potassium carbonate or the like can be used in combination. In addition, the total amount of the depolymerization catalyst added may be about 1 to 10% by weight based on the amount of the polyester waste, and the sodium compound is preferably 0.2% by weight or less.
[0032]
Further, the weight ratio of the alkylene glycol to the polyester waste to be supplied to the step (a) may be about 0.5 to 20: 1, preferably 1 to 5: 1.
[0033]
The alkylene glycol used at this time may be a plurality of types, and may contain other compounds.The amount of the oligomer component of the polyester, the metal compound, and other impurities that do not affect the depolymerization reaction is reduced. May be included.
Which alkylene glycol is used can be determined according to the actual situation. By using such an alkylene glycol, the purification cost of the alkylene glycol can be reduced.
[0034]
The time of the depolymerization reaction in step (a) is not particularly limited, but is usually 1 to 10 hours under the above conditions.
[0035]
In addition, the depolymerization reaction of the polyester waste with the alkylene glycol and the temperature rise at that time, by using together operations such as stirring in the depolymerization tank, circulation of the liquid in the tank by an external pump, and the like, the depolymerization reaction time and Although the effect of shortening the heating time can be obtained, excessive stirring or the like wastes power, so it is sufficient that the liquid in the tank is flowing. The reaction system may be either a continuous reaction system or a batch system.
[0036]
In the step (b), at least a part of water and / or alkylene glycol is separated from the depolymerization reaction solution obtained in the step (a) by distillation, and the depolymerization reaction solution is concentrated. obtain. Distilled alkylene glycol can be recycled in the process if there is no problem in quality.
[0037]
The distillation / concentration means in the step (b) is not limited, and a conventional distillation / concentration apparatus, for example, a vacuum continuous distillation apparatus, a vacuum batch distillation apparatus, or the like can be used. The concentration of the concentrated solution in step (b) is preferably performed at 140 to 180 ° C. More preferably, it is 150 to 170 ° C.
[0038]
The distillation / concentration operation in the step (b) may be performed under normal pressure or under reduced pressure. However, a typical alkylene glycol, EG, has a boiling point of 198 ° C. In consideration of the fact that the thermal decomposition of the compound becomes remarkable at 195 ° C. or higher, the pressure is preferably 1.33 to 100 kPa. It is more preferable to perform the vacuum distillation operation at 6.65 to 26.6 kPa. In this distillation / concentration operation, it is preferable that the concentration is adjusted so that the concentration of the alkylene glycol in the depolymerization reaction concentrated liquid is 20 to 50% by weight. If the alkylene glycol concentration is less than 20% by weight, the polymerization reaction proceeds, the degree of polymerization of the depolymerized product increases, and the next transesterification reaction does not proceed. Conversely, if the alkylene glycol concentration exceeds 50% by weight, the rate of the next transesterification reaction decreases, and the DMT recovery rate decreases.
[0039]
In the step (b), it is necessary to specially consider the blocking problem caused by the depolymerization catalyst. This consideration is particularly important when a sodium compound is used. That is, when the concentration of sodium in the depolymerization reaction concentrated solution in step (b) exceeds 1% by weight and is concentrated beyond the solubility, precipitation of a sodium compound causes blockage of a heat exchanger, piping, and the like, It is difficult to maintain stable and efficient operation. For this reason, it is important that the sodium concentration in the depolymerization reaction concentrate in the step (b) be 1% by weight or less. As described above, a depolymerization reaction catalyst other than sodium, such as potassium carbonate having high solubility, can be used in combination as the depolymerization reaction catalyst, but the sodium concentration in the depolymerization reaction concentrated solution is still 1 wt. It is important to keep it below%.
[0040]
The requirement that the concentration of sodium in the depolymerization reaction concentrated solution be 1% by weight or less is controlled by controlling the addition amount of the sodium compound in the depolymerization reaction catalyst in step (a), or by controlling the concentration condition of the depolymerization reaction solution. May be changed by any method. When controlling the amount of the sodium compound in the depolymerization reaction catalyst in step (a), a method in which another metal compound is used in combination as the depolymerization reaction catalyst is practical and preferable.
[0041]
After step (b), step (c) can be performed. In the step (c), the depolymerization reaction concentrate obtained in the step (b) is subjected to a transesterification reaction with methanol in the presence of a transesterification catalyst, and the reaction product is separated into a cake and a mixed solution; The cake is subjected to distillation and purification to distill DMT, and DMT is recovered. For example, the concentrated solution of the depolymerization reaction obtained in the step (b) is put into a liquid comprising a transesterification catalyst and methanol to carry out a transesterification reaction, and further subjected to a centrifugal separation treatment to give a DMT cake and a mixed solution. Then, as a step (f), the cake is subjected to washing treatment with, for example, methanol if necessary, followed by distillation and purification to distill out DMT, which is recovered. The transesterification reaction temperature is preferably from 65 to 85 ° C.
[0042]
The metal compound used as the transesterification catalyst is preferably selected from alkali metal, alkaline earth metal, titanium, manganese, cobalt, zinc, antimony, lead and cerium compounds. Examples thereof include carbonates, bicarbonates, hydroxides, and alcoholates of these metals. More specifically, at least one metal selected from the group consisting of alkali metal carbonates, bicarbonates, hydroxides, alcoholates, alkaline earth metal carbonates, bicarbonates, hydroxides and alcoholates Preferably, a compound is used.
[0043]
As the metal compound for the transesterification reaction catalyst, a sodium compound, particularly sodium carbonate, has conventionally been used because the same catalyst as the depolymerization reaction catalyst is used. As the transesterification catalyst, for example, potassium carbonate or the like can be used in combination. The amount of the transesterification catalyst added is preferably 0.3 to 10% by weight based on the amount of polyester waste.
[0044]
The amount of methanol supplied to the step (c) is preferably 1.5 to 4 parts by weight based on 1 part by weight of the polyester waste. In addition, other compounds such as an alkylene glycol, dimethyl terephthalate, an oligomer component, and a metal compound may coexist in the methanol used at this time as long as the ester exchange reaction is not adversely affected.
[0045]
The transesterification reaction is usually completed in 0.5 to 5 hours, and a slurry in which solid DMT is dispersed in a mixed solution of methanol and alkylene glycol is obtained. In recovering DMT from this slurry, a known solid-liquid separator can be applied, but other methods may be employed.
[0046]
Since DMT is dissolved to some extent in a mixed solution of methanol and alkylene glycol, it is preferable to cool the slurry to 30 to 60 ° C. and then supply the slurry to a solid-liquid separator. Since the cake of DMT obtained by this solid-liquid separation operation contains MeOH and alkylene glycol as a mother liquor, the cake is poured into fresh MeOH, stirred to re-slurry, and DMT is washed. Useful. The obtained slurry is again supplied to a solid-liquid separation device, where it is separated into a DMT cake and a filtrate containing methanol as a main component.
[0047]
The number of repetitions of this washing operation can be determined depending on the required quality of the DMT to be recovered, but usually, the operation may be performed 2 to 4 times. In addition, the filtrate MeOH in each washing step can be recycled. Further, the washing operation may be performed in a continuous manner or in a batch manner.
[0048]
The mixed solution obtained in the step (c) contains dissolved DMT, oligomers, and various metal compounds, and is separated and purified to reuse alkylene glycol, MeOH, and the like. This purification operation is preferably performed by distillation, but need not be limited to the distillation operation.
[0049]
In the case of performing the distillation, in the step (d), the mixed solution obtained in the step (c) is subjected to a distillation treatment, separated into distilled methanol and a distillation residue, and methanol is recovered. Next, in step (e), the distillation residue obtained in step (d) is subjected to a distillation treatment to distill and collect the alkylene glycol. That is, in step (d), MeOH having a low boiling point is first distilled off, and the liquid remaining at the bottom of the distillation column is subjected to step (e) to distill off the alkylene glycol. At this time, DMT dissolved in alkylene glycol, a catalyst, and a polyester oligomer having about 1 to 3 repeating units are present at the bottom of the tower. Therefore, for the purpose of reducing the amount of catalyst used and improving the recovery rate of the active ingredient, a part of the bottom liquid after methanol and / or alkylene glycol distillation is returned to the depolymerization tank (step (a)). You may.
[0050]
In the above, when a sodium compound is used as the transesterification catalyst, when the concentration of sodium in the distillation residue in step (d) exceeds 1% by weight and exceeds the solubility, it is concentrated in a heat exchanger or a pipe. In many cases, it becomes difficult to stably and efficiently operate and maintain the air conditioner. For this reason, it is important that the sodium concentration of the distillation residue in step (d) be 1% by weight or less.
[0051]
The requirement that the sodium concentration in the distillation residue be 1% by weight or less controls the amount of the sodium compound in the transesterification catalyst in step (c) or changes the concentration conditions in the subsequent steps. For example, any method may be used. When controlling the amount of the sodium compound in the transesterification reaction catalyst in the step (c), a method in which another metal compound is used in combination as the transesterification reaction catalyst is practical and preferable. For example, potassium carbonate or the like having high solubility can be used in combination. In addition, the sodium compound added before the step (c) can also function as a transesterification catalyst, but can also contribute to clogging of heat exchangers and pipes. Therefore, the sodium concentration in the distillation residue is reduced to 1% by weight. In order to satisfy the requirement of the following, it is preferable to control in consideration of these factors. That is, it is preferable that the control of the sodium concentration in the methanol distillation residue in the step (d) is controlled by the addition amount of the sodium compound in the depolymerization reaction catalyst and / or the addition amount of the sodium compound in the transesterification reaction catalyst. .
[0052]
In step (c), the recovered DMT may contain trace solids such as dust, sand, and metal salts, acid components, unreacted oligomers, and the like contained in the polyester waste. Depending on the required quality of the DMT, if necessary, the DMT may be purified by distillation under reduced pressure, or a part of the bottom liquid in the purification operation may be returned to the depolymerization tank in step (a).
[0053]
The DMT recovered in the separation method of the present invention can be used as a raw material for producing terephthalic acid. DMT recovered in the separation method of the present invention can also be used as a raw material for producing bis (β-hydroxyethyl) terephthalate. Further, the DMT recovered in the separation method of the present invention can be used as a raw material for producing a polyester. The effect of the present invention is particularly large when the above-mentioned alkylene glycol is EG.
[0054]
【Example】
Hereinafter, the contents of the present invention will be described more specifically with reference to examples. In the examples, “parts” means “parts by weight” unless otherwise specified. In addition, each value in an Example was calculated | required according to the following method.
[0055]
(1) Na, K metal concentration (% by weight)
A 0.1N hydrochloric acid solution was added to the obtained depolymerization reaction concentrated solution and the distillation residue to perform a pretreatment, and the solution was analyzed by an atomic absorption spectrophotometer (apparatus: Z-8100 manufactured by Hitachi, Ltd.). , Na, and K were determined.
[0056]
[Example 1]
50 parts of polyethylene terephthalate as a model of the polyester waste according to the present invention, 200 parts of EG as an alkylene glycol according to the present invention, and 1.5 parts of potassium carbonate as a depolymerization catalyst were charged into a depolymerization tank, and stirred for 185 minutes. When the temperature was maintained at 4 ° C. for 4 hours, the polyethylene terephthalate was dissolved and the depolymerization reaction was completed. From the obtained depolymerization reaction solution, 150 parts of EG was collected as a distillate by distillation under reduced pressure of 20 kPa, and the depolymerization reaction solution was concentrated.
[0057]
At the time of this vacuum distillation operation, there was no undissolved component in the depolymerization reaction concentrated solution, and the concentration operation could be performed stably without problems such as clogging of the heater. When the concentrated solution of the depolymerization reaction after the concentration was analyzed, K was detected at 0.85% by weight and Na was not detected.
[0058]
[Example 2]
50 parts of polyethylene terephthalate, 200 parts of EG, and 1.5 parts of sodium carbonate as a depolymerization catalyst were charged into a depolymerization tank and kept at 185 ° C. for 4 hours with stirring. As a result, the polyethylene terephthalate was dissolved and the depolymerization reaction was completed. did. From the obtained depolymerization reaction solution, 150 parts of EG was collected as a distillate by distillation under reduced pressure of 20 kPa, and the depolymerization reaction solution was concentrated.
[0059]
During the concentration operation in this vacuum distillation, there was no undissolved component in the depolymerization reaction concentrated solution, and the concentration operation could be performed stably without problems such as clogging of the heater. Analysis of the concentrated solution of the depolymerization reaction after concentration revealed that Na was detected at 0.65% by weight and K was not detected.
[0060]
[Example 3]
50 parts of polyethylene terephthalate, 200 parts of EG, and 1.2 parts of potassium carbonate and 0.3 parts of sodium carbonate as depolymerization catalysts were charged into a depolymerization tank, and the mixture was kept at 185 ° C. for 4 hours with stirring. Upon dissolution, the depolymerization reaction was completed.
[0061]
From the obtained depolymerization reaction solution, 150 parts of EG was collected as a distillate by distillation under reduced pressure of 20 kPa, and the depolymerization reaction solution was concentrated.
[0062]
During the concentration operation in this vacuum distillation, there was no undissolved component in the depolymerization reaction concentrated solution, and the concentration operation could be performed stably without problems such as clogging of the heater. When the concentrated solution of the depolymerization reaction after this concentration was analyzed, 0.13% by weight of Na and 0.68% by weight of K were detected.
[0063]
[Comparative Example 1]
When 50 parts of polyethylene terephthalate, 200 parts of EG, and 5 parts of sodium carbonate as a depolymerization catalyst were charged into the depolymerization tank and kept at 185 ° C. for 4 hours with stirring, the polyethylene terephthalate was dissolved and the depolymerization reaction was completed.
[0064]
From the obtained depolymerization reaction solution, 150 parts of EG was collected as a distillate by distillation under reduced pressure of 20 kPa, and the depolymerization reaction solution was concentrated.
[0065]
During the concentration operation of this vacuum distillation, undissolved components considered to be derived from sodium carbonate were generated in the concentrated solution of the depolymerization reaction, and solids adhered to the heat transfer portion of the heater. Analysis of the concentrated depolymerization reaction solution after concentration revealed that Na was detected at 2.17% by weight and K was not detected.
[0066]
[Example 4]
100 parts of the depolymerization reaction concentrated liquid obtained in Example 1, 0.35 part of potassium carbonate, and 85 parts of MeOH were charged into a transesterification tank, and the liquid was circulated under a condition of a liquid temperature of 70 to 75 ° C. at normal pressure. The reaction was performed for 1 hour, and a transesterification reaction was performed.
[0067]
The resulting mixture (reactant) containing DMT, EG and MeOH as main components is cooled to 40 ° C., and a solid-liquid separation operation is performed to obtain a solid component (cake) of DMT and a liquid component containing MeOH and EG as main components. (Mixed solution).
[0068]
MeOH was distilled and separated from the resulting liquid component by atmospheric distillation. At the time of the atmospheric distillation, the MeOH distillation residue (distillation residue) did not contain any undissolved components, and the concentration operation could be performed stably without problems such as blockage of the heater. When the distillation residue after the concentration was analyzed, K was detected at 1.4% by weight and Na was not detected.
[0069]
[Example 5]
100 parts of the concentrated depolymerization reaction solution obtained in Example 3, 0.35 part of sodium carbonate, and 85 parts of MeOH were charged into a transesterification tank. The liquid was circulated at a liquid temperature of 70 to 75 ° C. under normal pressure for 1 hour, and a transesterification reaction was performed.
[0070]
The resulting mixture containing DMT, EG and MeOH as main components was cooled to 40 ° C., and a solid-liquid separation operation was performed to separate solid components into DMT and a liquid component containing MeOH and EG as main components.
[0071]
MeOH was distilled and separated from the resulting liquid component by atmospheric distillation. At the time of the atmospheric distillation, the MeOH distillation residue had no undissolved components, and the concentration operation could be performed stably without problems such as clogging of the heater. Analysis of the distillation residue after concentration showed that K was 0.8 and Na was 0.33% by weight.
[0072]
[Comparative Example 2]
100 parts of the depolymerization reaction concentrate obtained in Example 2, 0.7 part of sodium carbonate, and 85 parts of MeOH were charged into a transesterification tank. The liquid circulation was carried out at normal pressure and at a liquid temperature of 70 to 75 ° C. for 1 hour to carry out a transesterification reaction.
[0073]
The resulting mixture containing DMT, EG and MeOH as main components was cooled to 40 ° C., and a solid-liquid separation operation was performed to separate solid components into DMT and a liquid component containing MeOH and EG as main components.
[0074]
MeOH was distilled and separated from the resulting liquid component by atmospheric distillation. During the atmospheric distillation, undissolved components considered to be derived from sodium carbonate were generated, and solids adhered to the heater heat transfer portion. When the distillation residue after concentration was analyzed, 1.1% by weight of Na was detected and K was not detected.
[0075]
[Example 6]
The solid content (cake) obtained in Example 4 was washed three times with 2 parts by weight of methanol, and distilled under the conditions of a pressure of 6.65 kPa and a reflux ratio of 1 to distill DMT. The purity of the obtained DMT was 99.99%.
[0076]
[Example 7]
The MeOH distillation residue (distillation residue) obtained in Example 4 was distilled under normal pressure conditions to distill EG. At this time, no clogging of the piping or the like occurred.
[0077]
[Comparative Example 3]
The MeOH distillation residue (distillation residue) obtained in Comparative Example 2 was distilled under normal pressure under normal pressure conditions to distill EG, and clogging occurred in the reboiler portion of the methanol distillation column. .
[0078]
【The invention's effect】
According to the method for recovering active ingredients from polyester waste of the present invention, it is possible to stably and efficiently recover active ingredients.

Claims (8)

Including the following steps (a) and (b),
Controlling the sodium concentration of the depolymerization reaction concentrate in step (b) to be 1% by weight or less;
A method for recovering active ingredients from polyester waste mainly containing polyalkylene terephthalate.
(A) a step of subjecting a polyester waste mainly containing polyalkylene terephthalate to a depolymerization reaction in the presence of an alkylene glycol and a depolymerization reaction catalyst to obtain a depolymerization reaction solution;
(B) a step of separating at least a portion of water and / or alkylene glycol from the depolymerization reaction solution obtained in step (a) by distillation to concentrate the depolymerization reaction solution to obtain a depolymerization reaction concentrated solution; The method for recovering an active ingredient according to claim 1, wherein the control of the sodium concentration in the depolymerization reaction concentrated solution in the step (b) is controlled by the amount of a sodium compound added in the depolymerization reaction catalyst. Including the following steps (c) and (d),
The method for recovering an active ingredient according to claim 1 or 2, wherein the sodium concentration of the distillation residue in the step (d) is controlled to be 1% by weight or less.
(C) a cake separation step of subjecting the concentrated depolymerization reaction obtained in step (b) to a transesterification reaction with methanol in the presence of a transesterification catalyst to separate the reaction product into a cake and a mixed solution;
(D) A methanol recovery step of subjecting the mixed solution obtained in the step (c) to a distillation treatment to separate it into distilled methanol and a distillation residue. 4. The method for recovering an active ingredient according to claim 3, comprising the following steps (e) and (f).
(E) an alkylene glycol recovery step of subjecting the distillation residue obtained in step (d) to distillation to distill alkylene glycol.
(F) A dimethyl terephthalate recovery step in which the cake obtained in step (c) is subjected to a washing treatment with methanol, and further subjected to distillation and purification to distill dimethyl terephthalate. The control of the sodium concentration in the methanol distillation residue in the step (d) is controlled by the addition amount of the sodium compound in the depolymerization reaction catalyst and / or the addition amount of the sodium compound in the transesterification reaction catalyst. 5. The method for recovering an active ingredient according to 4. The method for recovering an active ingredient according to claim 1, wherein the alkylene glycol is ethylene glycol. As the depolymerization reaction catalyst, at least one metal selected from the group consisting of alkali metal carbonates, hydrogen carbonates, hydroxides, alcoholates, alkaline earth metal carbonates, hydrogen carbonates, hydroxides and alcoholates The method for recovering an active ingredient according to claim 1, wherein a compound is used. As a transesterification catalyst, at least one metal selected from the group consisting of alkali metal carbonates, hydrogen carbonates, hydroxides, alcoholates, alkaline earth metal carbonates, hydrogen carbonates, hydroxides, and alcoholates The method for recovering an active ingredient according to claim 3, wherein a compound is used.