JPH1121374A - Chemical treating method for pet resin waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with or markedly decrease the step of separating and removing foreign matters, as a pretreatment step, from a resin waste mainly comprising polyethylene terephthalate contg. foreign matters mixed therein, to simultaneously carry out chemical separation of foreign matters and chemical recycling, and to recover high-purity terephthalic acid in a high yield by hydrolyzing the waste at a specified temp. in the presence of an alkali. SOLUTION: A polyethylene terephthalate resin waste, such as bottles, audio tapes, and prepaid cards, is pref. ground and then is hydrolyzed at a temp. of 140-200 deg.C in an autoclave pref. equipped with a stirrer and having a proof pressure of about 10-20 kg/cm<2> in the presence of an aq. alkali soln. of a 10-50 wt.% concn. The amt. of an alkali used is at least equimolar to that of terephthalic acid-derived carboxyl group contained in polyethylene terephthalate in the waste.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a chemical waste which can be suitably used for resin waste mainly composed of polyethylene terephthalate mixed with foreign substances (hereinafter referred to as "PET resin waste"), especially for PET bottles collected separately. The method relates to a general treatment method.

[0002]

2. Description of the Related Art As a method for regenerating PET resin waste, especially PET bottles collected separately, mechanical methods include gravity separation methods represented by specific gravity separation using water or wind as a medium, static electricity and electromagnets. Separation method such as powder, iron, aluminum, etc. by generating a magnetic field by eddy current or eddy current, optical separation method by color tone, physicochemical separation method by X-ray or near infrared ray, etc. . Examples of the chemical method include a method of cleaning and separating foreign substances such as dirt and an adhesive adhered to the PET bottle with a chemical, and a method of performing reaction separation.

On the other hand, as foreign substances to be separated adhered to PET bottles, those derived from contents such as foods,
Foreign resin such as labels, shrink films, base cups, caps, etc., aluminum derived from caps, adhesives, pigments, dyes, etc. In addition, metal cans, glass bottles,
Different kinds of containers such as bottles made of different kinds of plastics (polyvinyl chloride resin, polyolefin resin, etc.) and their fragments, foreign matter other than bottles, earth and sand, and the like may be mixed.

[0004] Therefore, as a practical method of separating foreign matter from a PET bottle, it is common to combine the above-described various principles and a separation method using an applied device. For example, when separating a vinyl chloride bottle from a PET bottle, the bottle is separated as it is using X-rays, the bottle is wet-pulverized into small pieces, and then immersed and stirred in an alkaline cleaning solution, and a polyolefin having a low specific gravity is used. A method of separating a system resin is employed. In addition, a separation step or an auxiliary step for separation may be required depending on the part or material of the foreign matter to be separated, and even when the same foreign matter is removed, the separation step is often performed a plurality of times. The number of steps may reach 10 to 20 steps. After these separation steps, PET
The bottles are recycled and flaked or powdered recycled P
Reused as ET resin (recycling method by "material recycling").

[0005] On the other hand, there is also a case where the monomer constituting the PET resin is decomposed and reused by using a solvent such as water, methanol or ethylene glycol (recycling method by "chemical recycling").

In any of the above-mentioned material recycling and chemical recycling, in order to reuse the PET resin as a material, it is important how to separate and remove the contaminants. The separation and removal process is generally complicated, and it is necessary to perform the same separation operation a plurality of times in order to increase the accuracy of the separation, or there is a problem that a useful PET resin is removed when separating and removing foreign substances. I do.

However, in PET resin waste,
There are PET bottles with a small proportion of foreign substances mixed, such as separately collected PET bottles, and composites of magnetic powder and PET resin, such as audio tapes and prepaid cards. Particularly in the latter case, it is often very difficult to completely separate and remove foreign matter. In material recycling, accumulation of foreign matter and deterioration of various physical properties of the PET resin occur each time the material is recycled. The reality is that the quality is one rank lower than that of PET resin, and it can only be reused as a cascade. Also, in the case of chemical recycling, some types of PET resin waste can be relatively easily decomposed into monomers, but usually various side reactions occur in the process, foreign substances are decomposed, or The purity of the recovered monomer and the recovery efficiency are greatly reduced due to side reactions with the monomer. For this reason, in the chemical recycling that has been carried out conventionally, the actual situation is that the decomposition treatment is usually performed in a high temperature region exceeding 200 ° C under the equipment and management of the petrochemical plant scale. As described above, in any of the material recycling and the chemical recycling, the separation and removal of the foreign matter can be said to control the life of the plant.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem, and the number of steps of separating and removing foreign substances as a pretreatment step is eliminated or markedly reduced. Simultaneous separation and chemical regeneration improve the purity and recovery rate of terephthalic acid recovered from PET resin waste, and at the same time reduce the amount of industrial waste associated with regeneration, and use simple equipment to reduce PET. The present invention provides a method for chemically treating resin waste.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies there, and as a result, the PET resin
It has been found that the above problem can be solved by hydrolysis in the presence of an alkali at a relatively low temperature range, and the present invention has been achieved.

That is, the gist of the present invention is as follows. (1) A method for chemically treating PET resin waste, comprising maintaining the reaction temperature in the range of 140 to 200 ° C. when hydrolyzing the PET resin waste in the presence of an alkali. (2) The chemical treatment method according to the above (1), wherein after the pulverization is performed without performing pre-separation as a pretreatment, hydrolysis is performed in the presence of an alkali.

The low-temperature keeping in the present invention has two purposes. Firstly, hydrolysis is carried out at a low temperature so that the decomposition of the contaminants can be suppressed as much as possible so that the contaminants can be separated and removed chemically. Second, PE
The point is that high-purity terephthalic acid can be obtained at a high recovery rate by simultaneously performing hydrolysis of the T resin.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

[0013] PET resin waste in the present invention includes PET bottles separated by local governments, composites of PET resin and foreign matter such as audio tape and prepaid cards, or PET resin waste as industrial waste. The use of a separately collected PET bottle is preferable in that higher purity terephthalic acid can be obtained. Further, it is more preferable to use PET resin waste that has been pulverized into flakes or chips by a method such as a dry method or a water-cooling method prior to hydrolysis in the presence of an alkali.

In the present invention, when the above-mentioned PET resin waste is hydrolyzed in the presence of an alkali, the reaction temperature is increased.
It is necessary to maintain the temperature in the range of 140 to 200 ° C. If the reaction temperature is lower than 140 ° C., the time required for hydrolysis of the PET resin becomes long, and it is difficult to obtain terephthalic acid at a high recovery rate. On the other hand, when the reaction temperature exceeds 200 ° C,
The contaminants are easily decomposed, making it difficult to recover high-purity terephthalic acid.

As a reaction vessel for carrying out the hydrolysis, an autoclave equipped with a stirrer is used.
An autoclave having a pressure resistance of about m ² can be suitably used.

The alkali used for hydrolysis in the presence of an alkali includes sodium hydroxide, potassium hydroxide, calcium hydroxide and the like. The form of use of these alkalis may be either a flake form or a liquid form, but when hydrolysis is performed, water is usually added, so that even if a flake form is used, Sometimes, it is dissolved in water and becomes a liquid, so using a liquid is more preferable from the viewpoint of handling. Any alkali concentration for hydrolysis can be used as long as it is 50% by weight or less, but an alkali aqueous solution having a concentration of 10 to 50% by weight is more preferable. When the concentration exceeds 50% by weight, the viscosity of the aqueous solution increases, and it is necessary to devise the shape of the stirrer.

The ratio between the PET resin waste and the alkali charged in the autoclave is as follows, assuming that all the PET resin waste is polyethylene terephthalate.
If the number of moles is equal to or more than the number of moles corresponding to the carboxyl group of the terephthalic acid component contained in the polyethylene terephthalate, the hydrolysis proceeds. It is preferable that the number of moles of alkali is somewhat larger than the carboxyl group of the terephthalic acid component because the reaction proceeds quickly, but the excess alkali amount is preferably 10 mol% or less.

In the present invention, the hydrolysis may be carried out in such a manner that hydrolysis is carried out until all of the PET resin waste and alkali charged in the autoclave are completely reacted, and then the reaction product and unreacted residue are removed. It can be carried out by any method of the formula or a continuous method in which hydrolysis is performed while taking out a part of the reaction in a state where the reaction in the autoclave has partially proceeded.

The foreign substances mixed in the PET resin waste include metal components such as iron and aluminum, earth and sand, glass, silicon-containing components of pottery, other types of synthetic resins, and adhesives and papers. Polymer components, PET bottle contents, deposits,
Alternatively, there are components such as dyes and pigments, but in the present invention, any of them can be separated. For example, even if a vinyl chloride resin, a polyethylene resin, a polystyrene resin, or the like is mixed as a foreign substance, all of these resins can be separated in the present invention because they do not undergo hydrolysis or thermal decomposition.

In the method of the present invention, what is solubilized by an alkali is an alkali-soluble foreign resin such as aluminum or polyvinyl alcohol used for a cap or the like, and also a part of paper and earth and sand. It is solubilized. Further, substances derived from the contents of PET bottles such as foods are also decomposed. Most of these solubles can be separated when terephthalic acid is precipitated.

In the present invention, separation is basically possible even if the above-mentioned soluble matter is mixed, but it is necessary to reduce the consumption of the alkali agent used for the reaction with the internal volume of the autoclave and foreign substances. Thus, the smaller the amount of foreign matter, the more efficiently hydrolysis can be performed. However, if the foreign substance mixing rate exceeds 20% or the alkali-soluble content is large,
It is more preferable to insert one or two simple foreign matter removing steps between the pulverizing step and the alkaline hydrolysis step from the viewpoint of preventing loss of the medicine.

After the PET resin waste is hydrolyzed in the presence of an alkali, the waste is separated into an unreacted residue and a solubilized aqueous solution. Unreacted residues are substances that have not been hydrolyzed and can be easily removed by operations such as filtration. In addition, foreign substances that react with alkali or heat, for example, aluminum used as a cap or polyvinyl alcohol used as an adhesive are solubilized and present in an aqueous solution. The pH of the aqueous solution can be separated and removed by adjusting the pH to a weakly acidic to neutral range. The acid used at this time is hydrochloric acid, sulfuric acid,
In addition to mineral acids such as nitric acid and phosphoric acid, organic acids such as acetic acid can be suitably used.

Through the above-described steps, foreign substances mixed in the PET resin waste are separated and removed, and useful terephthalic acid can be recovered by adjusting the pH of the aqueous solution to an acidic range of 3 or less. .

[0024]

The present invention will be described more specifically with reference to the following examples. The measuring methods used in Examples and Comparative Examples are as follows. 1. Measurement method (a) Purity of terephthalic acid (%) The purity of terephthalic acid was calculated using a high performance liquid chromatograph (600E, manufactured by Waters). The high-performance liquid chromatograph measurement was performed under the following conditions, and was calculated from the equation. Detector: PDA (photodiode array) Column: Waters μ Bondasphere 5μ C18-100A Column temperature: 40 ° C Target retention time: 0 to 1.9 minutes Terephthalic acid Target peak: Retention time Single peak near 0.9 minutes Impurity: Target Peak during the retention time (excluding negative peaks) Purity (%) = (area of) / (area of + area of)
× 100 (b) Recovery rate of terephthalic acid (%) Calculated from the PET ratio of the composition analysis example in Table 1 below.

Reference Example 1 (Example of composition analysis of PET resin waste) Table 1 shows an example of composition analysis of a PET bottle separated and collected by a local government and wet-crushed so as to pass through a 9 mm screen.

[0026]

[Table 1]

Example 1 500 g of the PET resin waste (A) of Reference Example 1 and 700 g of a 30% by weight aqueous solution of caustic soda were placed in an autoclave having an internal volume of 2 liters, purged with nitrogen, heated, and kept at 150 ° C. for 6 hours. After the hydrolysis, the contents were allowed to cool naturally, and the contents were discharged when the internal temperature reached 40 ° C. or lower. This content was separated by filtration with a filter paper to give an aqueous solution and a residue, and the residue was 52.6 g. Further, while stirring the aqueous solution, 5% by weight of sulfuric acid was added little by little to adjust the pH to 6.5, and a gray-brown precipitate was deposited. When the pH was adjusted to 2.5 by adding sulfuric acid little by little, white terephthalic acid was precipitated. Then
It was isolated after filtration, washing and drying. As a result of measuring the purity of this terephthalic acid by HPLC, the purity was 97.8%. The recovery of terephthalic acid was 97.5%. Furthermore, when polycondensation was carried out using this terephthalic acid by a conventional method, PET at a level equivalent to that obtained when virgin terephthalic acid was used was obtained.

Example 2 The same operation as in Example 1 was carried out except that the temperature at the time of hydrolysis was changed to 190 ° C., and the contents were discharged. The contents were filtered off with filter paper and separated into an aqueous solution and a residue.
The residue weighed 51.3 g. Further, while stirring the aqueous solution, 5% by weight of sulfuric acid was added little by little to adjust the pH to 6.5. As a result, a gray-brown precipitate was deposited, which was filtered off. When the pH was adjusted to 2.5 by adding sulfuric acid little by little, white terephthalic acid was precipitated. Next, it was isolated through filtration, washing and drying steps. As a result of measuring the purity of this terephthalic acid by HPLC, the purity was 97.5%. The recovery of terephthalic acid was 97.5%. Furthermore, when polycondensation was carried out using this terephthalic acid by a conventional method, PET at a level equivalent to that obtained when virgin terephthalic acid was used was obtained.

Example 3 The contents were discharged by performing the same operation as in Example 1 except that the PET resin waste (A) was replaced with the PET resin waste (B). The content was separated by filtration with a filter paper and separated into an aqueous solution and a residue, and the residue was 3.5 g. While stirring this aqueous solution, 5 wt% sulfuric acid was added little by little to adjust the pH.
Was adjusted to 6.5, a gray-brown precipitate was deposited. This was filtered off, and 5% by weight of sulfuric acid was added little by little to this aqueous solution to adjust the pH to 2.5, whereby white terephthalic acid was precipitated. . Next, it was isolated through filtration, washing and drying steps. As a result of measuring the purity of this terephthalic acid by HPLC, the purity was 99.8%. The recovery of terephthalic acid was 99.0%. Furthermore, when polycondensation was carried out using this terephthalic acid by a conventional method, PET at a level equivalent to that obtained when virgin terephthalic acid was used was obtained.

Comparative Example 1 The same operation as in Example 1 was carried out except that the conditions for the hydrolysis were changed to 220 ° C. × 3 hours, and the contents were discharged. The content was separated by filtration with a filter paper to obtain an aqueous solution and a residue. The residue was 160 g. While stirring this aqueous solution, 5 wt% sulfuric acid was added little by little to adjust the pH.
Was adjusted to 6.5, a gray-brown precipitate was deposited. This was filtered off, and 5% by weight of sulfuric acid was gradually added to the aqueous solution to adjust the pH to 2.5, whereby gray terephthalic acid was precipitated. . Next, it was isolated through filtration, washing and drying steps. As a result of measuring the purity of this terephthalic acid by HPLC, the purity was 91.1%. The recovery of terephthalic acid was 87.0%. Further, when polycondensation was performed using this terephthalic acid by a conventional method, PET at the same level as when virgin terephthalic acid was used was not obtained.

Comparative Example 2 The same operation as in Example 1 was carried out except that the conditions for the hydrolysis were changed to 130 ° C. × 10 hours, and the contents were discharged. When the content was separated by filtration with a filter paper and separated into an aqueous solution and a residue, unreacted PET resin waste remained in the residue. While stirring this aqueous solution, 5 wt% sulfuric acid was added little by little to adjust the pH to 6.5.
A gray-brown precipitate was deposited, which was filtered off. Further, 5% by weight of sulfuric acid was gradually added to the aqueous solution to adjust the pH to 2.5.
Then, gray terephthalic acid was deposited. Next, it was isolated through filtration, washing and drying steps. As a result of measuring the purity of this terephthalic acid by HPLC, the purity was 97.7.
%Met. The recovery of terephthalic acid was 54.2%. Furthermore, when polycondensation was carried out using this terephthalic acid by a conventional method, PET at a level equivalent to that obtained when virgin terephthalic acid was used was obtained.

[0032]

According to the present invention, the step of separating and removing foreign matter as a pretreatment step is eliminated or markedly reduced, and by simultaneously performing chemical foreign matter separation and chemical regeneration, PET resin waste can be removed. The purity and recovery rate of the recovered terephthalic acid can be increased, and at the same time, the industrial waste associated with the regeneration can be reduced, and the PET resin waste can be chemically treated with simple equipment.

Claims (2)

[Claims] 1. A PET resin waste, characterized in that a reaction temperature is maintained in a range of 140 to 200 ° C. when hydrolyzing a resin waste mainly containing polyethylene terephthalate mixed with foreign substances in the presence of an alkali. Chemical treatment method. 2. The chemical treatment method according to claim 1, wherein pulverization is performed without performing pre-separation as a pretreatment, and then hydrolysis is performed in the presence of an alkali.