JPS6056698B2 - Recovery method for dimethyl terephthalate and its intermediates - Google Patents

Description

Detailed Description of the Invention The present invention is disclosed in Japanese Patent No. 235515 (Japanese Patent Publication No. 32-276
(See Publication No. 5), Patent No. 286284 (Special Publication No. 1973-
70η Publication) is produced when dimethyl terephthalate is produced by oxidizing p-xylene and/or methyl p-toluate and then methyl esterifying it. The present invention relates to a method for recovering dimethyl terephthalate and its intermediates from boiling point byproducts.

These intermediates include, for example, methyl p-toluate, p-toluic acid, methyl p-formylbenzoate, monomethyl terephthalate, and terephthalic acid, which readily forms dimethyl terephthalate by oxidation and/or methyl esterification. means compounds that can Various methods have already been proposed for recovering active ingredients such as dimethyl terephthalate and its intermediates from such high-boiling byproducts.

First, as a treatment method using an oxygen-containing gas such as air, for example, a method of oxidizing in the presence of chloride (see Japanese Patent Publication No. 45-30814), a method of oxidizing in the presence of heavy metals and bromine (see Japanese Patent Publication No. 45-30814), (see Kosho Shoichi 4 Osu No. Publication) and the method of oxidizing in the presence of a manganese compound (Japanese Unexamined Patent Publication No. 48
-76830). In addition, a method of treating in the presence of methanol (for example, JP-A-48-965
(see Japanese Patent Application Laid-Open No. 12041/1982) or a method using water (see Japanese Patent Application Laid-open No. 48-965).
(Refer to Publication No. 41). Furthermore, a simple heat treatment method (
For example, Japanese Patent Publication No. 46-6412, Japanese Patent Publication No. 49-93
(See Publication No. 332). Therefore, the present inventors conducted intensive research to find an even better method, and found that the high-boiling by-product was heated to 140 to 3
It has been found that dimethyl terephthalate and its intermediates can be easily recovered industrially in good yield and with a simple device by contacting with molecular oxygen or molecular oxygen-containing gas at a temperature of 5CfC, and the present invention This conclusion was reached based on these findings.

That is, the present invention oxidizes p-xylene and/or methyl p-toluate with molecular oxygen or molecular oxygen-containing gas in the presence of a heavy metal catalyst, and then esterifies it with methanol to produce dimethyl terephthalate. A by-product with a boiling point higher than that of dimethyl terephthalate, which is produced as a by-product during the production, is heated to 140 to 3 ml in the presence of methanol and a manganese compound in the substantial absence of a halogen compound.
A method for recovering dimethyl terephthalate and its intermediates from the high-boiling by-products, characterized in that the method is brought into contact with molecular oxygen or a molecular oxygen-containing gas in the liquid phase at a temperature of 50°C. The method of the present invention is characterized in that the high-boiling by-product is brought into contact with the molecular oxygen-containing gas in the presence of a manganese compound as well as methanol. Methods of oxidizing substances with molecular oxygen-containing gases or treating them with methanol are already known.

However, the method of the present invention achieves extremely superior effects compared to the aforementioned oxidation or methanol treatment methods, as will be clear from the following explanation. That is, Special Publication No. 45-30814 or Special Publication No. 4
The oxidation method described in Publication No. 8-43340 uses chloride and bromine, which causes severe corrosion of the reaction equipment, requires the use of equipment made of expensive materials such as titanium, and has a short service life, making it difficult for industrial use. It cannot be said that it is a preferable method.

Furthermore, since the method described in JP-A-48-7 Seki (9) uses a manganese compound as a catalyst, it is relatively easy to implement industrially in that it does not require expensive equipment such as titanium. However, the amount of active ingredients recovered is still not sufficient, and most of the products obtained by processing high-boiling byproducts are obtained as carboxylic acids. Difficult to separate and recover components. Furthermore, this method requires methyl esterification of the oxidized product in order to facilitate separation and recovery, and a separate esterification device is required for methyl esterification, making the overall equipment cost very high. It has the disadvantage of becoming. On the other hand, when the method of the present invention is carried out, most of the active ingredients obtained as a reaction product by oxidation in the presence of methanol are obtained as dimethyl terephthalate, which is subsequently separated without the need for esterification. Easy to collect.

Furthermore, compared to the method described in JP-A No. 48-768 (To), the method of the present invention surprisingly produces less carbon dioxide as a by-product during the reaction, and also increases the amount of active ingredients recovered. . Therefore, when the method of the present invention is carried out, it is better than JP-A-48-7683 in terms of both the amount of active ingredients recovered and the equipment cost.
This method is superior to the method described in the official publication. Moreover, the present invention
Since it is carried out substantially in the absence of halogen, there is no risk of corrosion of the equipment. Furthermore, when comparing the methanol treatment described in JP-A-48-9653 Wani Publication etc. with the method of the present invention, the amount of active ingredients such as dimethyl terephthalate recovered is much greater with the method of the present invention. It is excellent in that there are many As described above, according to the present invention, dimethyl terephthalate and its intermediates can be industrially advantageously recovered with a higher yield than conventionally proposed methods and with a simple device.

In the present invention, the high-boiling byproducts with a boiling point higher than dimethyl terephthalate, which are the target of active ingredient recovery, are, for example, oxidized p-xylene and/or methyl p-toluate as shown below, and then esterified. When dimethyl terephthalate is produced by a method such as distillation, it is a high-boiling byproduct with a boiling point higher than that of dimethyl terephthalate contained in the residue that remains after separating and purifying dimethyl terephthalate by distillation, etc. . (a) When dimethyl terephthalate is produced from p-xylene by the so-called four-step process described in Patent No. 235515, p-xylene is first subjected to liquid phase oxidation using an oxygen-containing gas in the presence of a heavy metal catalyst. This was then esterified with methanol to obtain an oxidation product containing p-toluic acid as the main component, and the resulting methyl p-toluate was again oxidized and esterified in the same manner as above to yield dimethyl terephthalate. How to get it.

(b) When dimethyl terephthalate is produced from p-xylene by the so-called two-step process described in Japanese Patent No. 286284, which is an improved method of (a) above, first, p-xylene and methyl p-toluate are produced. The mixture was subjected to liquid phase oxidation with oxygen-containing gas in the presence of a heavy metal catalyst to obtain an oxidation product mainly composed of p-toluic acid and monomethyl terephthalate, which was then esterified with methanol to give methyl p-toluate. and a method of obtaining an ester mixture containing dimethyl terephthalate as a main component and separating this into dimethyl terephthalate and methyl p-toluate.

The crude dimethyl terephthalate obtained by these methods is usually further purified by a method such as distillation, and in this case, high-boiling byproducts having a boiling point higher than that of dimethyl terephthalate remain as a distillation residue.

This distillation residue still contains some dimethyl terephthalate, so if it is further distilled to recover dimethyl terephthalate, a high-boiling byproduct concentrate containing almost no dimethyl terephthalate can be obtained. It will be done. Traditionally, this was discarded as an unavoidable loss or used as fuel, but with the present invention, these high-boiling by-products can be converted into active ingredients in good yields and easily recovered. . The high-boiling byproducts targeted by the present invention are not only those concentrated during the distillation of dimethyl terephthalate as described above, but also those separated and concentrated from dimethyl terephthalate by other known methods. or dimethyl terephthalate, as long as it contains a high-boiling byproduct with a boiling point higher than that of dimethyl terephthalate.

Furthermore, as mentioned above, not only concentrates containing almost no active ingredients such as dimethyl terephthalate, but also concentrates containing some active ingredients can be used in the same way without any problems. In the present invention, high boiling point byproducts include those obtained by the methods (a) and (b) above, as well as those obtained by the method described in Patent No. 31838, which is an improved method of (b). When producing dimethyl terephthalate, high-boiling by-products can also be used.

Further, the present invention is disclosed in, for example, Japanese Patent Publication No. 49-27574,
It can also be advantageously applied to high-boiling by-products produced during the production of dimethyl terephthalate according to the method described in JP-A-48-9654.

The treatment of high boiling point byproducts in the present invention is 140 to 350
It is carried out at temperatures in the range of °C.

At temperatures lower than 140°C, the reaction hardly progresses and the yield of the active ingredient is extremely low.

On the other hand, if the reaction temperature exceeds 35 degrees, the equipment cost and operating cost will increase, and the decomposition reaction will be accelerated and the yield of the active ingredient will also decrease. The preferred reaction temperature is 180-33
This is the range of σC. A more preferable temperature is 200 to 300
℃ range. The manganese compound used in the present invention is preferably a compound that is soluble in the reaction system, such as the following organic acids (1), such as formic acid, acetic acid, propionic acid, butyric acid, stearic acid, palmitic acid, etc. having 1 carbon number.
Manganese salts and metallic manganese of (2) aromatic carboxylic acids such as benzoic acid and toluic acid, and (3) alicyclic carboxylic acids such as naphthenic acid are preferably used.

Various inorganic compounds such as manganese carbonates, oxides, and hydroxides can also be used. In addition, when manganese compounds are used as oxidation catalysts when producing dimethyl terephthalate by the method described above, it is extracted from oxidation products or esterification products containing these manganese compounds.

It is also possible to use a manganese compound that has been concentrated or separated by a method such as distillation as it is. Further, even if a cobalt compound, etc., which are similarly used as an oxidation catalyst, are present, there is no problem in the reaction of the present invention. The amount of manganese compound used in the present invention is 0.00% in terms of manganese metal amount based on the raw material containing the high boiling point byproduct.
It is preferably at least 5% by weight, particularly at least 0.01% by weight.

The upper limit is not particularly limited, but for economic reasons, it is usually desirable to have an amount of 2% by weight or less. If the amount of the catalyst is less than this range, the reaction rate will decrease, which is not preferable. In addition, the raw materials used in the present invention include not only the above-mentioned high-boiling byproducts but also co-oxides such as p-xylene, methyl p-toluate, and methyl p-formylbenzoate. Good too.

Similarly, to facilitate the handling of the high-boiling by-products, aromatic compounds which are stable under the reaction conditions of the invention, such as methyl benzoate or biphenyl, may also be added. The amount of methanol used in the present invention varies depending on the composition of the high-boiling byproduct and the methanol preparation method, but is generally based on 1 part by weight of the raw material containing the high-boiling byproduct. 0 as final value
．． It is preferably 0 parts by weight or more, particularly 0.05 to 1 part by weight.

It is industrially advantageous to carry out the reaction while supplying methanol to the reaction system in liquid or gaseous form, preferably in liquid form. Molecular oxygen gas or molecular oxygen-containing gas as an oxidizing agent used in the present invention may be pure oxygen, air with increased oxygen concentration, air diluted with reaction exhaust gas, or inert gas such as carbon dioxide or nitrogen. Mixed gases with oxygen and the like are used, but among these, air is economically most preferred.

These gases are brought into contact with the reaction mixture, such as by blowing into the liquid reaction mixture. Preferred pressure conditions depend on the above-mentioned temperature, but are usually 1 to 250k9/
Clt.G1 is preferably in the range of 2 to 60k9/DG. When carrying out the present invention, the reaction system may be stirred by any suitable method, such as forced mechanical stirring, stirring by blowing gas such as molecular oxygen-containing gas, or a combination of these methods.

The reaction of the present invention can be carried out either batchwise or continuously. The method of the present invention will be described in detail below with reference to Examples.

Example 1 and Comparative Examples 1 to 2 A mixture of p-xylene and methyl p-toluate was oxidized in the liquid phase with air at 165° C. and 4k9/All-G in the presence of cobalt acetate and manganese acetate to produce p-toluic acid. and an oxidation product containing terephthalic monomethyl as the main component, which was then esterified with methanol to obtain an ester mixture containing methyl p-toluate and dimethyl terephthalate as main components (Japanese Patent Publication No. 49-27574) method of writing).

This ester mixture was distilled to separate those having a lower boiling point than dimethyl terephthalate.

At this time, substances with boiling points higher than dimethyl terephthalate remained in the distillation residue. Since the distillation residue contained the heavy metal catalyst used in the oxidation reaction, it was recovered by extraction with water. The distillation residue thus obtained was further distilled to remove remaining useful components such as dimethyl terephthalate and methyl p-toluate, and a distillation residue containing almost no useful components was obtained.

The distillation residue contained only 1.1% of dimethyl terephthalate and 1.0% of monomethyl terephthalate as useful components. 200 y of this distillation residue was placed in a 500 cc stainless steel autoclave equipped with a reflux condenser, a stirrer, a methanol inlet, and a gas inlet, and manganese acetate was added to give a concentration of 0.4% by weight in terms of metallic manganese. Temperature 240'C1 Pressure 25k9/d
- While stirring at high speed with G, the flow rate at the outlet is 1500cc/M.
At the same time as oxygen absorption started, methanol was injected at a rate of 1.2 g/min.

The reaction was allowed to proceed in this state for 3 hours. After completion of the reaction, weight and composition analysis of the reaction product revealed dimethyl terephthalate, methyl valatoluate, balatoluic acid, monomethyl terephthalate, terephthalic acid, methyl valatoluate, p-
The content of methyl formylbenzoate was determined. The results are shown in Table-1.

For comparison, an experiment (Comparative Example 1) which was completely the same except that methanol was not injected, and an experiment (Comparative Example 2) which was completely the same except that no air was blown were conducted.

These results are also shown in Table-1. Examples 2 to 4 200y of distillation residue obtained in the same manner as in Example 1 was charged into the same autoclave as in Example 1, and the methanol shown in Table 2 below was prepared using the same amount of catalyst, temperature, pressure, and air flow rate as in Example 1. Methanol was injected at an injection rate and reacted for 3 hours.

The results are shown in Table-2. Examples 5 to 6 200 y of distillation residue obtained in the same manner as in Example 1. The mixture was charged into the same autoclave as in Example 1, and reacted for 3 hours at the same catalyst amount, pressure, air flow rate, and methanol injection rate as in Example 1 at the temperature shown in Table 3 below.

The results are shown in Table-3. Examples 7 to 8 200f of distillation residue obtained in the same manner as in Example 1 was charged into the same autoclave as in Example 1, and manganese acetate was charged in the amount of catalyst shown in Table 4 below. The reaction was carried out for 3 hours at various temperature, pressure, air flow rate, and methanol injection rate.

The results are shown in Table-4. Examples 9-10 An ester mixture was obtained in the same manner as in Example 1.

This ester mixture was distilled to separate those having a lower boiling point than dimethyl terephthalate. The distillation residue thus obtained is further distilled to remove remaining useful components such as dimethyl terephthalate and methyl p-toluate.
A distillation residue was subsequently obtained which contained almost no useful components. The active ingredients contained in this distillation residue were only 1.2% of dimethyl terephthalate and 0.8% of monomethyl terephthalate. The distillation residue also contained the heavy metal catalyst used in the oxidation reaction, of which manganese was contained in an amount of 0.0482% by weight in terms of metallic manganese. This distillation residue (200V) was charged into the same autoclave as in Example 1, and reacted for 3 hours at the same temperature, pressure, air flow rate, and methanol injection rate as in Example 1.

(Example 9) The results are shown in Table 5. In addition, an experiment (Example 10) completely similar to Example 9 was conducted by adding manganese acetate to the distillation residue so that the concentration of manganese was 0.4% by weight in terms of metallic manganese. .

Claims (1)

[Claims] 1 In producing dimethyl terephthalate by oxidizing p-xylene and/or methyl p-toluate with molecular oxygen or molecular oxygen-containing gas in the presence of a heavy metal catalyst, and then esterifying with methanol. A by-product with a boiling point higher than that of dimethyl terephthalate is treated with molecular oxygen or molecular oxygen in the liquid phase at a temperature of 140 to 350°C in the presence of methanol and a manganese compound and in the substantial absence of a halogen compound. A method for recovering dimethyl terephthalate and its intermediates from the above-mentioned high-boiling by-products, the method comprising contacting the high-boiling by-products with a gas containing the same.