JPH1112223A - High-purity terephthalic acid and its recovery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide terephthalic acid of high purity that is obtained from PET resin waste and can be used at the equal level to the virgin terephthalic acid. SOLUTION: Resin waste mainly comprising polyethylene terephthalate and contains foreign contaminants is hydrolyzed in the presence of an alkali. An acid is added to the resultant hydrolyze aqueous solution to adjust its pH to 3.5-9 to precipitate foreign substances, further the pH is lowered less than 3 to precipitate terephthalic acid whereby high-purity terephthalic acid is obtained that has 97% or higher purity according to high-performance liquid chromatography.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a resin waste containing polyethylene terephthalate as a main component mixed with foreign substances (hereinafter referred to as "PET resin waste"), in particular, a PET bottle collected and sorted by recycling. And a method for recovering the same.

[0002]

2. Description of the Related Art As a method of regenerating PET resin waste, especially industrial waste represented by separately collected PET bottles, a material recycling process mainly for flakes for various uses and a chemical treatment are carried out. There is chemical recycling to reuse as monomers.

[0003] Chemical recycling consists of water, methanol,
This is a method of solvolysis to a monomer using a solvent such as ethylene glycol. In this method, the ester group of the PET resin is decomposed to generate a monomer, which is then dissolved in a solvent and separated. However, when a foreign substance is contained, it reacts with the solvent depending on the type of the foreign substance. Or it may not always be separated from the monomer by dissolution in a solvent.

The same applies to the case where PET resin waste is hydrolyzed in the presence of an alkali using water as a solvent.
At this time, the PET resin is decomposed into sodium terephthalate and ethylene glycol and dissolved in water, but the one mixed as a foreign substance is directly dissolved in water, or dissolved in water by reacting with an alkali, or It decomposes with the heat of hydrolysis and dissolves in water. For this reason, the monomer to be recovered and the foreign matter are mixed, and the monomer cannot be separated and separated in some cases.

Taking PET bottles collected separately, for example, those which dissolve in water as they are attached, those which dissolve in water by reacting with alkali such as aluminum caps, dyes for labels Examples thereof include those that dissolve in water or disperse in fine powder like pigments and pigments, and those that dissolve in water by causing thermal decomposition such as some adhesives.
Therefore, the degree of removal of these foreign substances greatly affects the purity and recovery rate of the monomer.

[0006] In the chemical recycling of PET resin waste by the above-mentioned hydrolysis, it is common practice to carry out hydrolysis after removing foreign substances which are soluble in water by hydrolysis in advance. There is a problem that the separation operation for removing the foreign matter becomes very complicated.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to solve such problems, and it is intended to obtain high-purity terephthalic acid obtained from PET resin waste and usable at the same level as terephthalic acid of pergin. And a method for recovering the same.

[0008]

Means for Solving the Problems The inventor of the present invention has conducted intensive studies, and as a result, obtained by adding an acid to an aqueous solution of sodium terephthalate obtained by hydrolyzing PET resin waste in the presence of an alkali, adding terephthalate. It has been found that when precipitating as an acid, the pH of the aqueous solution is adjusted in advance to a weakly acidic to neutral range to remove foreign substances, and then, when the pH of the aqueous solution is adjusted to an acidic range, terephthalic acid of high purity can be recovered.

That is, the gist of the present invention is as follows. (1) Terephthalic acid recovered from PET resin waste and having a purity determined by high performance liquid chromatography of 97
% Of high-purity terephthalic acid. (2) Acid is added to an aqueous solution obtained by hydrolyzing PET resin waste in the presence of alkali to adjust the pH to 3.5 to 9 to precipitate and separate foreign substances, and the pH is further reduced to 3 or less. The method for recovering high-purity terephthalic acid according to the above (1), characterized in that terephthalic acid is precipitated by adjustment.

[0010]

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

The PET resin waste according to the present invention includes PET bottles collected separately by local governments, composites of PET resin and foreign matter such as audio tapes and prepaid cards, or PET resin waste as industrial waste. Although it is preferable to use a separately collected PET bottle, terephthalic acid with higher purity can be obtained.

Next, a method for recovering high-purity terephthalic acid will be described. In the method of the present invention, first, P
ET resin waste is hydrolyzed in the presence of an alkali to form an aqueous solution. Here, the hydrolysis in the presence of an alkali means
The hydrolysis is carried out using caustic soda or potassium hydroxide as an alkaline agent. And in the obtained aqueous solution, sodium terephthalate, ethylene glycol,
In addition to the residual water and alkali remaining in the reaction, they usually contain dissolved substances of foreign substances, and in some cases, may contain finely divided suspensions such as pigments that are difficult to filter. .

Next, an acid is added to the above aqueous solution to adjust the pH.
The pH is adjusted to 3.5 to 9, preferably 4.5 to 7, to deposit foreign matter. In this case, as the acid, an organic acid such as acetic acid can be suitably used in addition to a mineral acid such as sulfuric acid, hydrochloric acid, and nitric acid. In addition, prior to the addition of the acid, by adding a small amount of a polymer flocculant to the aqueous solution, it is possible to efficiently remove aluminum dissolved substances, suspended fine powder, organic foreign substances, and the like contained in the aqueous solution. .

Finally, an acid is further added to the aqueous solution from which the foreign substances have been separated and separated to adjust the pH to 3 or less, preferably to 2 to 2.5 to precipitate terephthalic acid. At this time, as the acid, either the same acid as the acid used for separating and separating the foreign substance or a different acid can be suitably used. Furthermore, mixtures of several acids may be used.

In the above-mentioned recovery step, PET is used.
After an aqueous solution obtained by hydrolyzing resin waste in the presence of alkali is treated with activated carbon, an acid is added to the treated solution to adjust the pH.
Is adjusted to 3.5 to 9 to deposit foreign matter, terephthalic acid with less coloring can be obtained.

The terephthalic acid thus precipitated is separated by a filtration operation, washed with water, dried, and the like to obtain high-purity terephthalic acid with few foreign substances.

The terephthalic acid thus obtained is
The purity determined by high performance liquid chromatography (HPLC) is 97% or more, usually 98% or more, and it can be used at the same level as terephthalic acid of pergin.

[0018]

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 PET bottles collected and sorted by a local government and wet-crushed so as to pass through a 9 mm screen.

[0020]

[Table 1]

Example 1 500 g of the PET resin waste 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, replaced with nitrogen, heated, kept at 150 ° C. for 6 hours, and then naturally cooled. The contents were discharged when the internal temperature became 40 ° C. or less. After the content was filtered off with a filter paper, the residue was removed by filtration, whereby 1130 g of an aqueous solution was obtained. 200 g of this aqueous solution was taken, and 5% by weight of sulfuric acid was added little by little with stirring to adjust the pH to 6.5. At this time, a grey-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 white terephthalic acid was deposited. Next, terephthalic acid 66.3 g through the steps of filtration, washing and drying
Was isolated. 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 2 200 g of the aqueous solution used in Example 1 was taken, and a polymer flocculant Uniflocker UF 105 (manufactured by Unitika) was added thereto with stirring at a concentration of 4 mg / l. The pH was adjusted to 5.0 by adding sulfuric acid little by little. A 5% by weight mixture of sulfuric acid / acetic acid was added little by little to the remaining liquid after separation and removal of the grey-brown components precipitated at this time, and the pH was adjusted to 2.5 by little. As a result, white terephthalic acid was precipitated. . Then, through the steps of filtration, washing and drying, 66.0 g of terephthalic acid
Was isolated. As a result of measuring the purity of this terephthalic acid by HPLC, the purity was 98.8%. The recovery of terephthalic acid was 97.0%. 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 1 200 g of the aqueous solution used in Example 1 was taken, and stirred for 5 minutes.
When the pH was adjusted to 2.5 by gradually adding wt% sulfuric acid, gray terephthalic acid was precipitated. Next, 62.8 g of terephthalic acid was isolated through the steps of filtration, washing and drying. The purity of this terephthalic acid was measured by HPLC. As a result, the purity was 96.6%, and it contained 3.4% of foreign substances. In addition, inorganic components such as aluminum, iron, etc., including silicon, were detected as components of the foreign matter. The recovery of terephthalic acid was 92.4%. 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.

[0024]

According to the present invention, high-purity terephthalic acid which can be used at the same level as terephthalic acid of perzine is made of PE
It can be obtained from T resin waste, and these can be suitably used as bottle raw materials, fiber raw materials, film raw materials, raw material intermediates, and the like.

Claims (3)

[Claims] 1. High-purity terephthalic acid recovered from resin waste containing polyethylene terephthalate as a main component and having a foreign substance content of 97% or more, as determined by high performance liquid chromatography. Terephthalic acid. 2. The high-purity terephthalic acid according to claim 1, wherein the resin waste mainly composed of polyethylene terephthalate mixed with foreign substances is a separately collected PET bottle. 3. An aqueous solution obtained by hydrolyzing a resin waste mainly composed of polyethylene terephthalate mixed with foreign substances in the presence of an alkali is added with an acid to adjust the pH to 3.5 to 9;
The method for recovering high-purity terephthalic acid according to claim 1 or 2, wherein the terephthalic acid is precipitated by further adjusting the pH to 3 or less after precipitating and separating foreign matter by adjusting the pH.