JP2001261598A - Method for purifying alkylene glycol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying an alkylene glycol containing chlorine compounds as impurities by a simple method. SOLUTION: The alkylene glycol containing the chlorine compounds as impurities is distilled in the coexistence of at least one of metallic compound selected from the group composed of carbonate, oxide and hydroxide of an alkaline metal and carbonate, oxide and hydroxide of an alkaline earth metal and the impurities are collected in the residue of the distillation to obtain the high purity alkylene glycol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying an alkylene glycol, and more particularly to a method for purifying an alkylene glycol containing a chlorine compound as an impurity by distillation.
The present invention relates to a method for obtaining a highly pure alkylene glycol.

[0002]

2. Description of the Related Art Polyalkylene terephthalate is excellent in chemical stability, and thus is useful for fibers, films,
It is produced and used in large quantities in resins and other products. These used and discarded polyalkylene terephthalates (hereinafter sometimes abbreviated as polyester waste) are depolymerized to alkylene glycol, dimethyl terephthalate (hereinafter abbreviated as DMT), terephthal. There are various proposals regarding chemical recycling that decomposes into monomers such as acids or derivatives thereof.

The chemical recycling involves reacting the collected polyester waste with methanol (hereinafter sometimes abbreviated as MeOH) to recover DMT and alkylene glycol, and converting the recovered polyester waste to an alkali compound. There is known a method of hydrolyzing in the presence and recovering terephthalic acid and alkylene glycol.

[0004] However, polyester waste discharged from the distribution industry and households sometimes contains chlorine-containing resins such as polyvinyl chloride, and a part of the chlorine contained therein is decomposed in the course of heating and reaction operations. However, the quality of DMT or alkylene glycol to be recovered may be reduced.

In order to solve this kind of foreign matter mixing problem,
In US Pat. No. 5,504,122, assuming that a chlorine compound is mixed, hydrogen chloride generated by thermal decomposition of a chlorine-containing resin is captured by adding an alkali compound, and then polyalkylene terephthalate is decomposed with MeOH to form DMT and Methods for recovering alkylene glycol have been proposed.

When recycling the recovered alkylene glycol, it is preferable to remove impurities to the same extent as the reagent. Most of the impurities can be removed by distillation, but the polarity, molecular weight, Since the specific volatility varies widely, it is difficult to separate and purify the alkylene glycol and these impurities only by distillation.However, since the alkylene glycol containing the impurity loses its commercial value, the alkylene glycol after the distillation is difficult to obtain. Further purification is required.

However, various methods have been proposed for removing chlorine compounds from aqueous solutions, but there are few patents relating to the removal of chlorine compounds contained in organic solvents such as alkylene glycol. For example, US Pat.
No. 0778 proposes passing ethylene glycol recovered from polyester waste through a plurality of columns containing an adsorbent such as activated carbon and alumina to remove polar and non-polar impurities. In addition to the time and cost required, compounds having properties similar to ethylene glycol, such as 2-chloroethanol, which is a chlorine compound, have a molecular structure similar to that of ethylene glycol. Removal is also difficult. Such ethylene glycol containing impurities,
Even if the distillation is simply performed or the number of distillation stages is increased, it is often inevitable that a small amount (on the order of tens of ppm) of a chlorine compound is mixed.

In Japanese Patent Application Laid-Open No. 2000-15088, in order to decompose an organic halide, an organic compound is dispersed in a liquid in which an alkali metal such as metallic sodium is dispersed in an aliphatic or aromatic hydrocarbon such as kerosene or trans oil. It has been proposed to charge a halide and thermally decompose it. However, since an alkali metal having high activity is used, there is a problem in terms of safety and also a problem that a step of removing the alkali metal remaining in the solvent is required.

[0009]

SUMMARY OF 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 purifying an alkylene glycol containing a chlorine compound as an impurity by a simple method. It is in.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that, when distilling an alkylene glycol containing a chlorine compound as an impurity, a specific metal compound is allowed to coexist with the above prior art. The present inventors have found that the problem that has been solved can be solved, and have completed the present invention.

That is, an object of the present invention is to purify an alkylene glycol containing a chlorine compound as an impurity by converting the alkylene glycol into an alkali metal carbonate, oxide, hydroxide, alkaline earth metal carbonate, It can be achieved by a method for purifying alkylene glycol, which is characterized in that it is purified by distillation in the presence of at least one metal compound selected from the group consisting of oxides and hydroxides.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an alkali metal carbonate, oxide, hydroxide, alkaline earth metal carbonate, oxide, water It is necessary to coexist at least one metal compound selected from the group consisting of oxides.

Here, specifically, as the metal compound,
Sodium carbonate, potassium carbonate, sodium hydroxide, calcium carbonate and the like can be used. These may be used alone or in combination of two or more. Among them, sodium carbonate is preferred from the viewpoint of cost performance. It is preferable to use

Further, in the purification method of the present invention, the alkylene glycol containing the impurities is distilled in advance at any stage before the distillation in the presence of the metal compound, and then the distillation is carried out in the presence of the metal compound. Is preferred. By performing this operation, the amount of sodium carbonate required for the purification operation can be reduced.

The amount of the metal compound to be added may be arbitrarily set as long as the effects of the present invention can be obtained. 1 based on moles
It is preferable to set within the range of 100 to 100 times mol.

In the present invention, as the alkylene glycol to be treated, any one may be used as long as it contains a chlorine compound to be removed, and those recovered through depolymerization of polyester waste may also be used. it can.

Here, as for the above depolymerization operation, any conventionally known depolymerization operation can be employed as long as alkylene glycol is produced or produced as a by-product. It is most preferable from the viewpoint of effective use of resources that the target is an alkylene glycol obtained by depolymerizing a polyalkylene terephthalate waste containing a chlorine-containing compound as an impurity.

When the above-mentioned waste is subjected to a depolymerization operation, for example, the crushed waste is charged into a depolymerization tank, and then ethylene glycol and sodium carbonate as a depolymerization catalyst are mixed. , Respectively, based on the weight of the polyester waste, 50 to 2000 wt% (ethylene glycol input) and 0.1 to 10 wt% (sodium carbonate input), and then the waste may be depolymerized. The residence time in the depolymerization tank may be set to about 4 hours, and the internal temperature may be set to around 185 ° C. When the depolymerization treatment is performed, sand accompanying the waste in advance,
It is preferable to remove foreign substances such as dust by washing.

Next, ethylene glycol is distilled off from the waste depolymerized solution obtained by the depolymerization by distillation, and recovered. This distillation may be performed under reduced pressure.

Next, the concentrated polyester waste depolymerized solution is supplied to a transesterification reaction tank, and MeOH and sodium carbonate as a transesterification catalyst are each added to 200 to 400% (M) based on the weight of the waste.
The amount of the depolymerized polyester waste is converted into DMT and ethylene glycol by supplying 1 to 10% (amount of sodium carbonate). At this time, the temperature inside the transesterification reaction tank may be set at about 75 ° C. and the residence time may be set to about 2 hours at normal pressure.

The mixture of DMT and ethylene glycol produced by the above operation is cooled together with an excess of MeOH, and then separated into a mixture of ethylene glycol and MeOH and a cake of DMT using a solid-liquid separator. MeOH is distilled off from the mixture to obtain a bottom containing ethylene glycol. Further, the residue is supplied to a distillation column to recover ethylene glycol.

In the above-mentioned recovery operation, when ethylene glycol is distilled, if the temperature is too high, side reactions such as dehydration reaction of the ethylene glycol may occur at the same time. Therefore, the pressure is reduced under a reduced pressure of 13.3 to 26.7 kPa. , 14
The distillation is preferably performed at 0 to 160 ° C., and the distillation operation may be performed in any of a batch system and a continuous system.

[0023]

According to the present invention, it is possible to provide a method for purifying an alkylene glycol containing a chlorine compound as an impurity by a simple method. Particularly, it is possible to dissolve a polyalkylene terephthalate waste containing a chlorine compound as an impurity. The alkylene glycol recovered from the polymerization step can be purified to high purity, and its industrial value is great.

[0024]

EXAMPLES Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited by these examples. In addition, each numerical value in an Example was calculated | required by the following method. In the examples, “parts” means “parts by weight” unless otherwise specified. Chlorine Content in Ethylene Glycol (ppm): The chlorine content in ethylene glycol can be measured by using a sample of ethylene glycol as a neat solution or by diluting it with MeOH. "TOX100" manufactured by Kagaku Co., Ltd.).

Example 1 As polyester waste,
200 parts (three to 10 mm square) of a polyethylene terephthalate bottle to which the contents such as soy sauce remain and adhere, and 800 parts of a special grade reagent, ethylene glycol
And 6 parts of sodium carbonate were charged into a separable flask, and the temperature was raised at a stirring speed of 100 rpm to an internal temperature of 185 ° C. While maintaining this state for 4 hours, the polyester was dissolved and the depolymerization reaction was completed to obtain a concentrated solution. The concentrated solution was mixed with 6 parts of sodium carbonate as a transesterification catalyst and M
400 parts of OH was added, and then, the transesterification reaction was further performed while maintaining the liquid temperature at 75 ° C. and stirring at 100 rpm for 1 hour under normal pressure.

The obtained mixture of DMT, ethylene glycol and MeOH was cooled to 40 ° C.
-4. The obtained filtrate was charged into a three-necked flask, and the contained MeOH was distilled off at normal pressure and 65 ° C. in a 10-column distillation column. 590 pp was added to the distillation still containing ethylene glycol after the MeOH was distilled off.
m of chlorine.

Three parts of 100 parts of ethylene glycol having a chlorine concentration of 590 ppm and 0.5 parts (2.8 times mol of chlorine atom) of sodium carbonate for distillation in the presence of the ethylene glycol. Into the flask,
Batch distillation was performed at a pressure of 13.3 kPa, a temperature of 145 ° C., and a distillation column having 10 stages, and 80 parts of ethylene glycol was recovered as a fraction. The chlorine concentration was 2 ppm, and a product having approximately the same purity as that of the special grade ethylene glycol was obtained.

[Example 2] In Example 1, MeOH was used.
To the kettle containing ethylene glycol after distilling off
Distillation was carried out without adding sodium carbonate, and then 0.5 part (83 times mol with respect to chlorine atom) of sodium carbonate was added to 100 parts of ethylene glycol after the distillation, under the same conditions as in Example 1. Was distilled again. The chlorine concentration in ethylene glycol obtained as a fraction was 1 ppm or less, and had a purity comparable to that of the special grade reagent.

Example 3 50 parts of ethylene glycol containing impurities (chlorine concentration: 1230 ppm) and 1 part of potassium carbonate (4.2 moles per mol of chlorine atom) were recovered by performing the same operation as in Example 1. Was placed in a three-necked flask, and distillation was performed under the conditions of a pressure of 13.3 kPa, a temperature of 145 ° C., and 10 stages. As a result, the chlorine concentration in ethylene glycol obtained as a fraction was 2 ppm.

[Comparative Example 1]
Was distilled under the conditions of a pressure of 13.3 kPa, a temperature of 145 ° C., and 10 stages without adding sodium carbonate to a residue (ethylene chloride: 590 ppm) containing ethylene glycol after distilling off water. 20 ppm of chlorine was mixed in the ethylene glycol.

Comparative Example 2 50 parts of ethylene glycol containing impurities (chlorine concentration: 1230 ppm) and sodium carbonate 0.02 were collected by performing the same operation as in Example 1.
5 parts (0.1 times mol with respect to chlorine atom) were charged into a three-necked flask, and the pressure was 13.3 kPa, the temperature was 145 ° C.,
When distillation was carried out under the conditions of 10 stages, 33 ppm of chlorine was mixed in ethylene glycol obtained as a fraction. Table 1 shows the results of Examples 1 to 3 and Comparative Examples 1 and 2.
Shown in

[0032]

[Table 1]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Sato 77 Kitayoshida-cho, Matsuyama-shi, Ehime Pref. BE10 BE11 BE12 BE13 FE12 FG24

Claims (4)

[Claims] When purifying an alkylene glycol containing a chlorine compound as an impurity, the alkylene glycol is converted into an alkali metal carbonate, oxide, hydroxide, alkaline earth metal carbonate, oxide, hydroxide. A method for purifying an alkylene glycol, which comprises purifying by distillation in the presence of at least one metal compound selected from the group consisting of: 2. The purification method according to claim 1, wherein the alkylene glycol containing a chlorine compound as an impurity is distilled in an arbitrary stage before the distillation in the presence of the metal compound in the absence of the metal compound. . 3. The purification method according to claim 1, wherein the addition amount of the metal compound is 1 to 100 times mol per 1 mol of chlorine atom in the alkylene glycol. 4. The method for purifying an alkylene glycol according to claim 1, wherein the alkylene glycol is obtained from a depolymerization step of a polyalkylene terephthalate waste containing a chlorine-containing resin.