JP2000297178A - Method for recovering dimethyl terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently recovering dimethyl terephthalate and an alkylene glycol from a mixture of a chlorine-containing resin with a polyalkylene terephthalate. SOLUTION: A mixture of a chlorine-containing resin with a polyalkylene terephthalate is melted in the presence of dimethyl terephthalate and a zinc composition at a temperature of 275-400 deg.C, and the formed methyl chloride is removed and then, methanol depolymerization is conducted to recover dimethyl terephthalate and an alkylene glycol. Preferably, the polyalkylene terephthalate is a polyethylene terephthalate, and the chlorine-containing resin is preferably a poly(vinyl chloride).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering dimethyl terephthalate and alkylene glycol from a mixture of a chlorine-containing resin and a polyalkylene terephthalate. More specifically, the present invention relates to a method of pretreating the mixture to obtain a chlorine-containing resin. After removing the resulting chlorine atom as methyl chloride,
The present invention relates to a method for recovering dimethyl terephthalate and alkylene glycol by methanol depolymerization.

[0002]

2. Description of the Related Art Polyalkylene terephthalate is excellent in chemical stability, and thus is useful for fibers, films,
The use in daily life related materials such as resins, and in the food field such as drinking water and carbonated beverage bottles is rapidly increasing.

[0003] However, 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 (hereinafter referred to as waste polyalkylene terephthalate) Is a major social problem.

In order to solve the above-mentioned problem, so-called chemical recycling, in which the recovered waste polyalkylene terephthalate is converted into a monomer, and the monomer is used as a raw material to produce and reuse the polyalkylene terephthalate by a polymerization reaction, is being studied. . This method basically enables loss-free recycling of compounds and resource recycling.

[0005] These recovered waste polyalkylene terephthalates are generally reacted with methanol and simultaneously distilled to be recovered as dimethyl terephthalate (hereinafter abbreviated as DMT) and alkylene glycol. And the total cost of recycling waste polyalkylene terephthalate is reduced.

However, waste polyalkylene terephthalate often contains foreign substances other than polyalkylene terephthalate, and when it contains a chlorine-containing resin such as polyvinyl chloride or polyvinylidene chloride as a foreign substance, it is difficult to recover raw material monomers. In addition, the resin is thermally decomposed to generate hydrogen chloride, which corrodes the reactor, lowers the reactivity, and is dispersed in the raw material monomer to be recovered, causing a great problem in quality.

In order to solve this problem, US Pat.
Japanese Patent No. 04122 discloses a method in which hydrogen chloride generated by thermal decomposition of a chlorine-containing resin is trapped by adding an alkali compound, and then polyalkylene terephthalate is decomposed with methanol to recover raw material monomers.

Japanese Patent Application Laid-Open No. Hei 8-259728 discloses that a mixture of a chlorine-containing resin and waste polyalkylene terephthalate is hydrolyzed in the presence of an alkali compound to produce terephthalic acid and ethylene glycol (hereinafter, also referred to as EG). Is also proposed, but a method is also employed in which an alkali compound is added to capture hydrogen chloride generated by thermal decomposition of the chlorine-containing resin.

Although the above-mentioned methods all achieve the purpose of recovering DMT or terephthalic acid and ethylene glycol, it is necessary to remove chlorine compounds trapped by an alkali compound. In order to remove it, additional steps such as distillation, washing and ion exchange are required, and there is a disadvantage that the steps become complicated.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for simply recovering DMT and alkylene glycol containing no chlorine compound from a mixture of a chlorine-containing resin and polyalkylene terephthalate.

[0011]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned prior art, and as a result, have found that a chlorine-containing resin and a polyalkylene can be used in the presence of a specific compound and under a specific temperature condition. It has been found that chlorine atoms can be effectively removed from the system by melting a mixture with terephthalate, and the present invention has been completed.

That is, an object of the present invention is to recover dimethyl terephthalate from a mixture of a chlorine-containing resin and a polyalkylene terephthalate by methanol depolymerization, and to prepare the mixture from the mixture prior to methanol depolymerization. This is achieved by a method for recovering dimethyl terephthalate, which comprises melting at a temperature of 275 to 400 ° C. in the presence of dimethyl acid and a zinc compound to remove generated methyl chloride.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the recovery method of the present invention, chlorine atoms originating from a chlorine-containing resin are removed and separated from a mixture of a chlorine-containing resin and polyalkylene terephthalate in advance. As the removal / separation method, first, a mixture of a chlorine-containing resin and a polyalkylene terephthalate is subjected to 275-275 in the presence of DMT and a zinc compound.
It is necessary to melt at a temperature of 400 ° C.

If the melting temperature is too low, chlorine is not sufficiently desorbed from the chlorine-containing resin, and the effect of removing chlorine from the mixture is low. On the other hand, if the temperature is too high, more energy is used, which is not preferable in terms of cost. The melting temperature is preferably from 280 to 350 ° C.

Here, any of the zinc compounds can be used.
The use of at least one compound selected from the group consisting of zinc oxide, zinc hydroxide, zinc carbonate, zinc oxalate, zinc chloride, zinc nitrate, zinc sulfate, and zinc sulfide makes it possible to increase the catalytic activity of the compound. It is particularly preferable from the viewpoint of the size.

By the above operation, methyl chloride is generated from the chlorine atom in the chlorine-containing resin and DMT, and since the methyl chloride is in a gaseous phase, it can be easily removed from the system. When the mixture of the chlorine-containing resin and the polyalkylene terephthalate is melted, the mixture is preferably stirred.

In the recovery method of the present invention, the amount of the zinc compound is determined to be 0.01 to 1 based on the chlorine-containing resin.
It is preferable to set the weight range. When the amount is within the above range, the balance between the effect of removing chlorine atoms and the cost is further improved. The abundance is 0.05
It is particularly preferred that it is in the range of -0.8 equivalents.

In the recovery method of the present invention, DMT present in the system depolymerizes polyalkylene terephthalate to reduce its melt viscosity, and reacts with hydrogen chloride generated by thermal decomposition of chlorine-containing resin. To form methyl chloride.

The amount of DMT is 0.1 to 10 times mol based on the amount of chlorine atoms contained in the chlorine-containing resin in the mixture, or 0.01 to 10 times by weight based on polyalkylene terephthalate. Is preferred. When it is in the above range, the melt viscosity of the polyalkylene terephthalate is more easily reduced, and the dispersibility of the zinc compound to be present in the system is also improved, and the chlorine atom contained in the chlorine-containing resin is converted to methyl chloride. The transformation of the project will be further improved.

In the recovery method of the present invention, the gaseous methyl chloride generated from the molten mixture is an alcohol such as methanol, ethanol, ethylene glycol, or the like.
It is dissolved in a chlorine compound such as chloroform, water, benzene, etc. and trapped or removed, or alkali hydrolysis is performed using an aqueous alkali solution such as sodium hydroxide or potassium hydroxide. Methyl chloride has a boiling point of −24 ° C. Therefore, removal from the molten mixture is very easy, and efficient chlorine atom removal becomes possible.

Next, the mixture remaining in the system is introduced into a reactor together with methanol to depolymerize methanol.
The separated DMT, alkylene glycol, and unreacted methanol can be reused as respective components by separately collecting them.

Incidentally, any of the known methods can be adopted as each of the separation and collection methods. For example, in the case of DMT, distillation, centrifugation and filtration may be performed.
In the case of unreacted methanol or EG, a distillation operation may be performed.

The pressure at which DMT and the zinc compound are present in the mixture of the chlorine-containing resin and the polyalkylene terephthalate to be melted is not particularly limited. Either method may be used, but it is preferable to perform the reaction under atmospheric pressure, which does not require special equipment.

In addition, the system for causing the mixture to undergo a melt reaction may be any of a batch system and a continuous system without any problem. In this case, the residence time or average residence time of the molten mixture in the system is determined. Regarding the time, the longer the residence time, the higher the chlorine removal effect, but on the other hand, the energy loss increases and the equipment efficiency decreases. , 1
Preferably, it is 5 hours.

In the recovery method of the present invention, the reaction conditions for depolymerizing the polyalkylene terephthalate present in the residue after separating and removing the organic chlorine compound generated in the system using methanol include: Any of the known reaction conditions can be employed. For example, the amount of methanol used may be about 1 to 10 times by weight based on the polyalkylene terephthalate after removing the organic chlorine compound, and particularly 2 to It is preferably about 5 times by weight.

The reaction temperature for carrying out the depolymerization reaction is preferably in the range of 200 to 300 ° C., and when it is in this range, the entrained evaporation of the produced DMT and alkylene glycol with methanol is carried out. Well done. Further, the reaction pressure of the depolymerization reaction is 0 to 3
The pressure is preferably in the range of 0 kg / cm ² G, and in this range, the depolymerization reaction is sufficiently performed. In addition,
The depolymerization time is preferably from 30 minutes to 4 hours.

[0027]

EXAMPLES The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited by these examples.

(1) Percentage of chlorine in gas (%): contained in a solvent (methanol) trapping an organic chlorine compound based on the chlorine atom content contained in the chlorine-containing resin in the mixture, which was determined in advance. The amount of chlorine atoms measured was measured with a trace chlorine analyzer (TNCL02 manufactured by Mitsubishi Chemical Corporation), and the ratio of the captured chlorine atom amount was calculated.

(2) Chlorine concentration in EG (ppm): EG
The amount of chlorine atoms contained therein was measured using a trace chlorine analyzer (TNCL02 manufactured by Mitsubishi Chemical Corporation).

(3) Chlorine content ratio (%) in the molten mixture:
The amount of chlorine atoms contained in the molten mixture was determined using a fluorescent X-ray analyzer (using a 3270 chromium tube manufactured by Rigaku Denki System) based on the previously determined amount of chlorine atoms contained in the chlorine-containing resin in the mixture. It measured and calculated the ratio of the contained chlorine atom weight.

(4) Chlorine concentration in DMT (ppm):
The amount of chlorine atoms contained in DMT was measured using a fluorescent X-ray analyzer (using a 3270 chrome tube manufactured by Rigaku Corporation).

Example 1 240 g of polyethylene terephthalate, 160 g of DMT and 2 g of zinc acetate as a zinc compound were provided with a condenser, a stirrer, and a thermometer.
After melting at 300 ° C. in a 00 ml three-necked flask and thoroughly stirring and mixing, 16 g of DMT and 4 g of polyvinyl chloride
And melting at 300 ° C. for 5 hours,
The gas was passed through the flask at a flow rate of ml / min, and the gas discharged from the flask was passed through a methanol solution to capture methyl chloride. After the completion of the melting, the chlorine content ratio in the gas component and the melt was determined based on the chlorine atom content contained in the added polyvinyl chloride.
6.1% and 3.9%. The molten mixture 100
g and 640 g of methanol in an autoclave.
The reaction was performed at 5 ° C. and 5 kg / cm ² G for 2 hours to obtain a crude product. The depolymerization to DMT and EG proceeds almost quantitatively,
These obtained products were separated by distillation, and the chlorine content of the obtained DMT was measured to be 0.28 ppm.
When the chlorine content of EG was measured, it was 14.6 pp.
m.

Example 2 The same operation as in Example 1 was carried out except that the amount of polyvinyl chloride was changed to 20 g. After the completion of the melting, the chlorine content in the gas component and the chlorine content in the melt were determined on the basis of the chlorine atom content contained in the added polyvinyl chloride.
2%. 100 g of the molten mixture and methanol 64
0 g in an autoclave at 265 ° C., 5 kg /
The reaction was performed at cm ² G for 2 hours to obtain a crude product. The depolymerization into DMT and EG proceeded almost quantitatively. The obtained product was separated by distillation, and the chlorine content of DMT was measured to be 0.44 ppm. The chlorine content of EG was measured and found to be 22.5 ppm.

Example 3 The same operation was performed as in Example 1, except that zinc oxide was added instead of zinc acetate as the zinc compound. After the completion of the melting, the chlorine content in the gas component and the chlorine content in the melt were determined based on the chlorine atom content in the added polyvinyl chloride, and were found to be 95.3% and 4.7%, respectively. 100 g of the molten mixture and 640 g of methanol were reacted in an autoclave at 265 ° C. and 5 kg / cm ² G for 2 hours to obtain a crude product. The depolymerization into DMT and EG proceeded almost quantitatively, and the obtained product was separated by distillation to obtain DMT.
Was 0.34 ppm. When the chlorine content of EG was measured, it was 17.4.
ppm.

Comparative Example 1 The same operation as in Example 1 was carried out except that zinc acetate as a zinc compound was not added. After the completion of melting, the chlorine content ratio in the gas component and the melt was determined based on the chlorine atom content contained in the added polyvinyl chloride, and was found to be 14.0% and 86.0%, respectively. 100 g of the molten mixture and 640 g of methanol were placed in an autoclave at 265.degree.
The reaction was performed at kg / cm ² G for 2 hours to obtain a crude product. These obtained products were separated by distillation, and the chlorine content of DMT was measured to be 6.3 ppm. The chlorine content of EG was measured and found to be 321.1 ppm.

Comparative Example 2 The same operation as in Example 1 was performed except that the amount of polyethylene terephthalate was changed to 400 g and DMT was not added. After the completion of the melting, the chlorine content ratio in the gas component and in the melt was determined based on the chlorine atom content contained in the added polyvinyl chloride, and was 0.5% and 99.5%, respectively. 100 g of the molten mixture and 640 g of methanol were placed in an autoclave and reacted at 265 ° C. and 5 kg / cm ² G for 2 hours to obtain a crude product. These obtained products were separated by distillation, and the chlorine content of DMT was measured.
m. The chlorine content of EG was measured and found to be 369.1 ppm.

Comparative Example 3 The same operation as in Example 1 was carried out except that the melting temperature was changed to 250 ° C. After the completion of the melting, the chlorine content in the gas component and the chlorine content in the melt were determined on the basis of the chlorine atom content in the added polyvinyl chloride, and were found to be 0.0% and 100.0%, respectively. 100 g of the molten mixture and 640 g of methanol were placed in an autoclave at 265 ° C. and 5 kg / cm ² G for 2 hours.
After reacting for hours, a crude product was obtained. These obtained products were separated by distillation, and the chlorine content of DMT was measured to be 7.3 ppm. The chlorine content of EG was measured and found to be 374.2 ppm.

[0038]

According to the recovery method of the present invention, when polyalkylene terephthalate containing a chlorine-containing resin is chemically recycled, DMT and alkylene glycol can be separated without being affected by a chlorine compound generated from the chlorine-containing resin. It can be simply and efficiently recovered.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideo Hasegawa 77 Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Limited Matsuyama Plant F-term (reference) 4F301 AA16 AA25 CA09 CA23 CA26 CA71 CA72 4J029 AA03 AB05 AB07 AC01 BA03 CB06A JA061 JA091 JA121 JA161 JA201 JB171 JB183 JF181 KD01 KD02 KG01 KG02 KG03 KH01

Claims (8)

[Claims] When recovering dimethyl terephthalate from a mixture of a chlorine-containing resin and polyalkylene terephthalate by methanol depolymerization, the mixture is treated with dimethyl terephthalate and a zinc compound prior to methanol depolymerization. In existence, 2
A method for recovering dimethyl terephthalate, which comprises melting at a temperature of 75 to 400 ° C. and removing generated methyl chloride. 2. The method according to claim 1, wherein the polyalkylene terephthalate is polyethylene terephthalate. 3. The chlorine-containing resin is polyvinyl chloride.
The method according to claim 1. 4. The method according to claim 1, wherein the chlorine-containing resin is polyvinylidene chloride. 5. The zinc compound is at least one selected from the group consisting of zinc acetate, zinc oxide, zinc hydroxide, zinc carbonate, zinc oxalate, zinc chloride, zinc nitrate, zinc sulfate, and zinc sulfide. The recovery method according to claim 1, wherein the compound is 6. The recovery method according to claim 1, wherein the amount of the zinc compound is 0.01 to 1 times by weight based on the weight of the chlorine-containing resin. 7. The amount of dimethyl terephthalate is 0.1 to 0.1 based on the amount of chlorine atoms contained in the chlorine-containing resin.
The recovery method according to claim 1, wherein the molar amount is 10-fold. 8. An amount of dimethyl terephthalate in a range of 0.01 to 10 based on polyalkylene terephthalate.
The recovery method according to claim 1, wherein the weight is doubled.