JP2000212326A - Recovery of dimethyl terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently recovering dimethyl terephthalate from a mixture of a chlorine-containing resin with a polyalkylene terephthalate. SOLUTION: This method for recovering dimethyl terephthalate comprises melting a mixture of a chlorine-containing resin with a polyalkylene terephthalate in the presence of dimethyl terephthalate and an alkali metal salt and/or an alkaline earth metal salt at a temperature of 275-400 deg.C, removing the generated organic chlorocompounds, and then depolymerizing the residue to recover the dimethyl terephthalate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering dimethyl terephthalate from a mixture of a chlorine-containing resin and polyalkylene terephthalate, and more particularly, to a method of pretreating the mixture to obtain chlorine atoms originating from the chlorine-containing resin. To remove dimethyl terephthalate by removing methanol as an organic chlorine compound and then depolymerizing methanol.

[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 problem, so-called chemical recycling, in which waste polyalkylene terephthalate is converted and recovered 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.

The recovered waste polyalkylene terephthalate is reacted with methanol and simultaneously distilled to be recovered as dimethyl terephthalate (hereinafter abbreviated as DMT) and alkylene glycol. Leads to a decline.

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.

[0009] According to the above-mentioned methods, although all of the objects have been achieved in terms of the recovery of the target substance, it is necessary to remove the chlorine compound captured by the alkali compound. In addition, additional steps such as washing with water and ion exchange are required, resulting in a disadvantage that the steps are complicated.

[0010]

An object of the present invention is to provide a method for efficiently recovering DMT and alkylene glycol 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. When a mixture with terephthalate is melted, the chlorine-containing resin is thermally decomposed to generate an organic chlorine compound, and since the organic chlorine compound can be easily removed, chlorine atoms can be effectively removed from the reaction system. Thus, 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 polyalkylene terephthalate by methanol depolymerization, and then, prior to the methanol depolymerization, convert the mixture to dimethyl terephthalate. And a method for recovering dimethyl terephthalate, characterized by melting in the presence of an alkali metal salt and / or an alkaline earth metal salt at a temperature of 275 to 400 ° C. to remove an organic chlorine compound generated. Is done.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the recovery method of the present invention, it is necessary to previously remove and separate chlorine atoms originating from a chlorine-containing resin from a mixture of a chlorine-containing resin and polyalkylene terephthalate from the system.

As the removal / separation method, first, a mixture of a chlorine-containing resin and a polyalkylene terephthalate is used.
It is necessary to melt at a temperature of 275 to 400 ° C. in the presence of DMT and an alkali metal salt and / or an alkaline earth metal salt.

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 alkali metal salt and / or the alkaline earth metal salt can be used.
At least one selected from the group consisting of hydroxide, carbonate, bicarbonate, phosphate, sulfite, and carboxylate
It is particularly preferable to use at least one kind of compound in view of its high catalytic ability.

The above operation generates an organic chlorine compound, and since the chlorine compound is in a gaseous state, it can be easily removed into the system. When the mixture of the chlorine-containing resin and the polyalkylene terephthalate is melted, it is preferable to stir the mixture.

In the recovery method of the present invention, the amount of the alkali metal salt and / or the alkaline earth metal salt is determined based on the number of moles of chlorine atoms contained in the chlorine-containing resin. Alternatively, the amount is preferably in the range of 0.5 equivalent to 10 equivalent in terms of cation of the alkaline earth metal salt. When the amount is within the above range, the balance between the effect of removing chlorine atoms and the cost is further improved. The addition amount is particularly preferably in the range of 1 to 3 equivalents.

Further, DMT present in the system serves to depolymerize polyalkylene terephthalate to lower its melt viscosity, and to react with hydrogen chloride generated by thermal decomposition of chlorine-containing resin to react with methyl chloride or the like. It has a function of forming an organic chlorine compound.

The amount of the 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 viscosity of the polyalkylene terephthalate can be further reduced, the dispersibility of the alkali metal salt and / or the alkaline earth metal salt in the system can be improved, and the chlorine contained in the chlorine-containing resin can be improved. The conversion of atoms to organochlorine compounds is further improved.

In the recovery method of the present invention, an apparatus formed from gas components generated from a molten mixture using alcohols such as methanol, ethanol and ethylene glycol, chlorine compounds such as chloroform, water, benzene and the like. The chlorine compound is trapped and removed, and it is preferable that the boiling point of the trapped organic chlorine compound be in the range of -40 to 20 ° C. Organic chlorine compounds having a boiling point within the above range are very easily removed from the molten mixture, and efficient removal of chlorine atoms becomes possible.

Next, the mixture remaining in the system is introduced into a reactor together with methanol, and is subjected to methanol decomposition (depolymerization) to produce DMT and alkylene glycol.
In addition, the unreacted methanol can be separated and recovered, and can be reused as each component.

Any known method can be used for each of the separation and recovery 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 alkali metal salt and / or alkaline earth metal salt are melted in the mixture of the chlorine-containing resin and the polyalkylene terephthalate is not particularly limited. It may be carried out under atmospheric pressure or under reduced pressure, but it is preferable to carry out under atmospheric pressure where it is not necessary to employ special equipment.

[0025] 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. As for the time, the longer the residence time, the higher the chlorine removing effect, but on the other hand, the energy loss increases and the equipment efficiency decreases, so it may be about 0.1 to 8 hours, and it is 1 to 5 hours. Is preferred.

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 at the time of 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 DMT and alkylene glycol and methanol produced 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.
The depolymerization reaction product can be separated and recovered into methanol, DMT and alkylene glycol by a conventionally known method, for example, distillation.

[0028]

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) Chlorine content ratio 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 A 500 ml three-necked unit equipped with a cooling pipe, a stirrer, and a thermometer was charged with 240 g of polyethylene terephthalate, 160 g of DMT, and 16 g of sodium terephthalate as an alkali metal salt and / or an alkaline earth metal salt. After melting at 300 ° C. in a flask and sufficiently stirring and mixing, 16 g of DMT and polyvinyl chloride 4
and melting at 300 ° C. for 5 hours while adding 5 g of nitrogen.
The gas was allowed to flow through the flask at a flow rate of 0 ml / min, and the gas discharged from the flask was passed through a methanol solution to capture an organic chlorine compound such as methyl chloride. After the completion of the melting, the proportions of chlorine in the gas component and in the melt were determined based on the amount of chlorine atoms contained in the added polyvinyl chloride, and were 94.2% and 5.8%, 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. These obtained products were separated by distillation, and the chlorine content of the obtained DMT was measured to be 0.42 ppm. The chlorine content of EG was measured and found to be 21.7 ppm.

Example 2 The same operation as in Example 1 was performed except that the polyethylene terephthalate was changed to 360 g, the DMT was changed to 40 g, the melting temperature was changed to 330 ° C., and the melting time was changed to 3 hours. 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.
9.3% and 0.7%. The molten mixture 100
g 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. 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 less than 0.1 ppm.

Example 3 The same operation as in Example 1 was carried out except that 8 g of sodium carbonate was added instead of sodium terephthalate as the alkali metal salt and / or the alkaline earth metal salt. After melting,
The chlorine content in the gas component and the chlorine content in the melt were calculated based on the chlorine atom content in the added polyvinyl chloride, and were found to be 89.7% and 10.3%, 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. The obtained product was separated by distillation, and the chlorine content of DMT was measured.
pm.

Comparative Example 1 The same operation as in Example 1 was performed except that sodium terephthalate as an alkali metal salt and / or an alkaline earth metal salt 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. D
Depolymerization into MT and EG proceeded almost quantitatively, and the obtained product was 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 carried out 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. The depolymerization into DMT and EG proceeds almost quantitatively, and the obtained products are separated by distillation,
When the chlorine content of DMT was measured, it was 7.2 ppm.

Comparative Example 3 The same operation was performed as in Example 1, 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. The depolymerization into DMT and EG proceeded almost quantitatively. The obtained product was separated by distillation, and the chlorine content of DMT was measured.
pm.

[0039]

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 easily converted without being affected by chlorine compounds generated from the chlorine-containing resin. In addition, it can be efficiently collected.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hideo Hasegawa 77 Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Limited Matsuyama Office F-term (reference) 4D004 AA07 AB06 AC05 BA07 CA22 CA34 CC11 DA03 DA06 DA10 4F301 AA16 AA17 AA25 CA23 CA24 CA71

Claims (8)

[Claims] 1. When recovering dimethyl terephthalate from a mixture of a chlorine-containing resin and polyalkylene terephthalate by methanol depolymerization, the mixture is mixed with dimethyl terephthalate and an alkali metal salt prior to the methanol depolymerization. Alternatively, a method for recovering dimethyl terephthalate, which comprises melting at a temperature of 275 to 400 ° C. in the presence of an alkaline earth metal salt to remove generated organic chlorine compounds. 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. Alkali metal salts and / or alkaline earth metal salts, hydroxides, carbonates, bicarbonates, phosphates, sulphite and carboxylates of alkali metals and / or alkaline earth metals The recovery method according to claim 1, wherein at least one compound selected from the group consisting of: is used. 6. The amount of the alkali metal salt and / or alkaline earth metal salt in terms of cation of the alkali metal salt and / or alkaline earth metal salt based on the amount of chlorine atoms contained in the chlorine-containing resin. The recovery method according to claim 1, wherein the amount is 0.5 to 10 equivalents. 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.