DE1248029B - Process for the production of pure benzene dicarboxylic acid esters of low molecular weight primary alcohols - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C07c

German: 12 ο-14

Number: 1 248 029

File number: M 58357IV b / 12 ο

Filing date: September 27, 1963

Opened on: August 24, 1967

It is necessary that a terephthalic acid or isophthalic acid ester with a low molecular weight ester component, as it is used as a raw material for polyester production, is extremely pure because disadvantages even in the presence of minor impurities, e.g. B. a delay in the polycondensation reaction, a reduction in the degree of polycondensation or a discoloration of the polyester occur. It is known that low molecular weight formylbenzoic acid or acetylbenzoic acid esters, which are used as intermediates in the oxidation of a dialkylbenzene occur after intermediate esterification, particularly noticeable disadvantageous.

Various cleaning methods such as rectification, Recrystallization, sublimation, or oxidation, attempted either alone or in combination been. Cleaning by oxidation is e.g. B. from British Patent 837,936 has become known. The purification of a terephthalic acid or isophthalic acid ester or a mixture is there in the liquid phase with oxygen or oxygen-containing gases in the presence of copper or Manganese compounds or a mixture of these carried out, the reaction time at a Reaction temperature of over 200 ° C is less than 5 hours. This patent specification shows that in the terephthalic and isophthalic esters small amounts of ketone are used as impurities are included, for example, acetylbenzoic acid methyl ester, and that these impurities too Monomethyl terephthalate can be oxidized and then easily separated by distillation, wherein the proportion of the catalyst is expediently 0.1 to 0.5 percent by weight of the ester.

Terephthalic acid or isophthalic acid, which is produced by the oxidation of dialkylbenzenes with a tertiary carbon atom, for example diisopropylbenzene, contains acetylbenzoic acid, with the result that the ester obtained therefrom, e.g. B. the dimethyl ester, as described in the aforementioned British patent, contains the methyl ester of acetylbenzoic acid as an impurity. In contrast, it contains terephthalic acid or isophthalic acid, which can be obtained by oxidation of dialkylbenzenes with a primary carbon atom, ζ. Β. Xylene is not given an acid with a ketone function, such as acetylbenzoic acid, but formylbenzoic acid, so that the corresponding ester, e.g. B. contains the dimethyl ester, methyl formylbenzoate as the main impurity. It has now been found that when the process of obtaining pure
Benzene dicarboxylic acid esters of low molecular weight
primary alcohols

Applicant:

Mitsui Petrochemical Industries, Ltd., Tokyo

Representative:

R. Kremers, lawyer,
Hamburg 36, Neuer Jungfernstieg 7/8

Named as inventor:
Yasuhiro Fujita, Hiroshima-ken;
Osamu Morita, Yamaguchi-ken (Japan)

Claimed priority:

Japan December 13, 1962 (55 066),
dated July 5, 1963 (34 487),
dated July 10, 1963 (35 375, 35 376)

two previously mentioned dimethyl esters of terephthalic or isophthalic acid can be purified by oxidation with molecular oxygen, which is achieved The cleaning effect is different in each case and depends on the type of contamination, d. h. whether it is in the case of contamination by methyl acetylbenzoate or methyl formylbenzoate acts. If, as described in the aforementioned British patent, a dimethyl phthalate, which contains methyl acetylbenzoate as an impurity, with molecular oxygen in Presence of a catalyst containing 0.1 to 0.5 percent by weight of a manganese or copper compound treated, then acetylbenzoic acid methyl ester can easily be oxidized to monomethyl phthalate and thus separated from the product to be manufactured. But if, on the other hand, a dimethyl phthalate, which contains methyl formylbenzoate as an impurity, according to the same, d. h., the in the process described in the British patent, this contamination cannot are oxidized to such an extent that a cleaning effect can be recognized.

It has now been shown that the oxidative separation of the formylbenzoic acid ester from the to The following conditions must be observed when producing benzene dicarboxylic acid esters:

709 638/565

1. The treatment with molecular oxygen must be carried out carefully;

2. the treatment with molecular oxygen can be carried out without a catalyst;

3. The treatment with molecular oxygen is preferably in the presence of one particular low concentration of a manganese or copper compound soluble in the reaction system perform.

The invention relates to a process for obtaining pure benzene dicarboxylic acid esters of low molecular weight primary alcohols from crude benzene dicarboxylic acid esters containing appropriate formylbenzoic acid esters and possibly contaminated by iron compounds, which is characterized in that the crude esters, if necessary, after reducing their iron content to; <j 20 ppm by distillation, in the liquid phase, optionally in the presence of manganese or copper compounds which ^{are soluble in the reaction system in an amount of less than 1 · 10 ~ a} gram atom of manganese or copper per gram of ester, at 140 to 300 ° C with Treated oxygen or an oxygen-containing gas and then rectified or this treatment is carried out at the same time as the rectification.

According to the invention, the content of formylbenzoic acid ester in the benzene dicarboxylic acid ester to less than 40 millionth parts, in particular to 10 millionth parts. Of the Reasonable content of methyl formylbenzoate in a for the production of polyester as a starting material Dimethyl terephthalate or dimethyl isophthalate used is generally included 40 millionth parts. If this content is over 40 millionths of a part, that's 5 hours one Dimethyl terephthalate or dimethyl isophthalate exposed to a temperature of 200 ° C yellow and causes in the production of polyester a delay in the polycondensation reaction, a decrease the degree of polycondensation and a color of the product.

The process according to the invention can be carried out in various ways. The source material can on the one hand be treated with molecular oxygen in the liquid state and the reaction mixture can then be rectified, and on the other hand can be oxidized and distilled at the same time when molecular oxygen is introduced will.

To keep the ester to be cleaned in a liquid state, it can be heated and melted or optionally in a solvent composed of hydrocarbons, carboxylic acids, carboxylic acid esters and halogenated hydrocarbons. However, the inventive method will preferably carried out with molten ester.

The molecular oxygen used is pure oxygen, air or a gas containing molecular oxygen. Preferably pure oxygen or a gas containing more than 50% oxygen is used. The treatment temperature is between 140 and 300 ^° C. and preferably between 200 and 280 ^° C. The process, which is normally carried out at atmospheric pressure, can also be carried out under 6 g excess pressure or reduced pressure. It is likewise also possible to carry out the process batchwise or continuously and also as part of the process for the preparation of lower phthalic acid ester by esterification of phthalic acid, as described below.

In order to determine the relationship between the proportion of catalyst and the amount of the remaining in the reaction product To determine contamination, the following investigation was carried out:

Samples of dimethyl terephthalate with a 10% proportion of p-formylbenzoic acid methyl ester and of dimethyl terephthalate with a 10% proportion of p-acetylbenzoic acid methyl ester were each oxidized for one hour with molecular oxygen in the presence of a manganese compound (manganese naphthenate) as a catalyst. The results are shown in the drawing, in which the abscissa indicates the proportion of metallic manganese, based on the crude dimethyl terephthalate in millionths of parts, and the ordinate indicates the content of acetylbenzoic acid ester or formylbenzoic acid ester in the reaction product in percent. Curve A shows the result obtained by oxidizing crude dimethyl terephthalate containing 1% methyl acetylbenzoate for one hour at a temperature of 250 ° C. with oxygen, and curve B shows the result obtained by oxidizing crude dimethyl terephthalate containing 1% methyl formylbenzoate at a temperature of 250 for one hour ° C result obtained with oxygen.

These results show that for the purification of methyl acetylbenzoate as an impurity containing dimethyl terephthalate a catalyst content of more than 100 millionth parts is necessary, whereas in the purification of formylbenzoic acid methyl ester as an impurity containing dimethyl terephthalate a catalyst content of more than 100 millionth parts shows the tendency to oxidize To inhibit contamination, and that in the purification of dimethyl terephthalate, which contains methyl formylbenzoate as an impurity, a satisfactory result can be achieved if less than 100 millionth part of the catalyst are used, which in the purification of dimethyl terephthalate, which contains methyl acetylbenzoate as an impurity, without Effect remains. The same results were also achieved with a copper compound (copper naphthenate) as a catalyst. Compared to the catalyst content used in the aforementioned British patent, the amount of catalyst used according to the invention is very small, namely less than 10 " ^G gram-atom per 1 g ester. Since the catalyst is used in the form of a soluble salt, such as manganese naphthenate, the The proportion of metallic manganese in the catalyst is about 10% by weight, which corresponds to a proportion by weight of the catalyst of 0.06% per 1 g of the ester to be treated the catalyst content is 0.1 to 0.5 percent by weight per gram of the ester to be treated, thus it is not possible to sufficiently purify a phthalic acid ester containing formylbenzoic acid ester as an impurity by the method of the British patent specification.

The process according to the invention can be used as part of the known processes for the production of terephthalic

acid or isophthalic acid alkyl esters carried out will. For example, the method according to the invention can be applied to the evaporation residue Mother liquor can be applied, which can be obtained by esterification of terephthalic acid or isophthalic acid obtained by a conventional process. The resulting ester is crystallized and then the crystals formed and / or a fraction containing formylbenzoic acid methyl ester, the one as a lower boiling fraction by the rectification of the crude ester of separated in crystal form Terephthalic or isophthalic acid is removed, whereupon the treated material then goes back to the first Can be returned to the esterification stage.

In the practice of the invention Process has been found that the presence of a very low level of iron or an iron compound inhibits the oxidation of the formylbenzoic acid ester and thus the inventive method to achieve effect is detrimental. It is therefore necessary that an in the iron compound contained in the ester to be treated proportionally less than 20 millionth parts of metallic Iron stays.

In order to meet this condition, a device with an inner surface made of aluminum or titanium is used. This condition must in particular with the vessel for the oxidation reaction, and if necessary it can also be met in the vessel for the esterification reaction, the separator for alcohol and water, the distillation device for the ester to be treated and the like facilities are met.

The crude ester of terephthalic or isophthalic acid usually quite often contains iron or an iron compound because the iron or the iron compound already in the crude terephthalic or isophthalic acid was contained and / or by the corrosion of the for the esterification reaction The vessel used has been brought into the acid.

The presence of iron or iron compounds prevents the feasibility of the invention Process, even if, for example, the proportion of catalyst increases in the oxidation will. If the ester to be treated contains more than 20 millionth part of iron, it must be before the oxidative treatment of a distillation under atmospheric or reduced pressure, preferably between 40 and 300 mm Hg. This distillation can be done with a simple Distillation device or a film evaporator can be carried out.

The invention is to be explained further using the following examples:

example 1

p-xylene was present in acetic acid solution by cobalt, manganese and bromine compounds oxidized with air to terephthalic acid. The terephthalic acid was esterified with methanol at high temperature and under high pressure in a titanium vessel. The reaction product was heated in a glass vessel to evaporate the methanol and water. as The residue remained crude dimethyl terephthalate, the 5% monomethyl terephthalate, 0.8% methyl formylbenzoate and contained 5 millionths of a part of iron.

The crude dimethyl terephthalate was stirred for 1 hour at 270 ° C in a titanium vessel with oxygen oxidized. The reaction product contained 150 millionth part of formylbenzoic acid ester.

The reaction product was pumped into a 15 tray glass still column under reduced pressure distilled from the Oldershaw type and yielded 50 g of a low boiling fraction and 200 g Dimethyl terephthalate as the main fraction. The dimethyl terephthalate contained 20 millionth parts of formylbenzoic acid ester. The color of the dimethyl terephthalate in the molten state was Scale value of 20 according to APHA, after 4 hours in a tightly closed tube heater 200 ° C had been heated.

In contrast, the proportion of formylbenzoic acid ester in a dimethyl terephthalate that by the same distillation of crude dimethyl terephthalate was obtained without oxidation, 1000 millionths Parts and the color of the molten dimethyl terephthalate had a scale value of 350 according to APHA.

Example 2

A sample of 300 g of crude dimethyl terephthalate according to Example 1 was given 0.015 g of manganese naphthenate with a 10% content of metallic manganese added. The mixture was left at 250 ° C for 30 minutes oxidized in a glass reaction vessel while stirring with oxygen. The content of formylbenzoic acid ester in the reaction product was less than 100 millionths of part.

The content of formylbenzoic acid ester in a dimethyl terephthalate obtained by distillation of the reaction product, as described in Example 1, was less than 10 millionth parts. A coloration of the dimethyl terephthalate could even after 4 hours of heating at 200 ° C in one tightly sealed tube heater cannot be detected.

As the proportion of catalyst to 1.5 g per 300 g of crude dimethyl terephthalate was increased and oxidized as described above in a glass reaction vessel, the formylbenzoic acid ester content found in the reaction product was 1000 millionths Parts.

Example 3

300 g of the crude dimethyl terephthalate used in Example 1 received an addition of 0.0015 g Copper naphthenate with a 10% content of metallic copper and were 1 hour in one glass reaction vessel is oxidized with oxygen while stirring. The content of formylbenzoic acid ester in the reaction product was less than 10 millionths of a part. The content of formylbenzoic acid ester in the dimethyl terephthalate obtained by distilling the reaction product according to Example 1 was less than 10 millionth parts. The dimethyl terephthalate could also be colored after 4 hours Heating at 200 ° C in a tightly closed tube heater cannot be determined.

With an increased catalyst content of 5 g copper naphthenate to 300 g crude dimethyl terephthalate was the content of formylbenzoic acid ester in the

7 8

Reaction product after the same treatment 2000 mil terephthalic acid contained 5 millionth part of iron

lionstel parts. and 0.8% formylbenzoic acid. The terephthalic acid

Example 4 was made in a carbon steel reaction vessel

at high temperature and under high pressure with

500 g of crude dimethyl terephthalate esterified according to Example 1 5 of methanol. Methanol and water were

were then evaporated in a 15-tray glass to obtain a crude dimethyl terephthalate

Oldershaw distillation column received under one. The crude dimethyl terephthalate contained 5%

Pressure of 300 mm Hg distilled, while oxygen terephthalic acid monomethyl ester ^{, 0.8 0} Ia formyl

was blown in at the bottom of the column to 100 g of benzoic acid ester and 100 millionth parts of iron,

of the distillate. Blowing in the io A sample of 500 g of crude dimethyl terephthalate

Oxygen was then set and a distillation with an iron content of 100 millionths of a part

lation under a pressure of 50 mm Hg at the head was subjected to a simple distillation to

the column carried out to 300 g of dimethyltereph- 450 g of a 3%> Monomethyl terephthalate

to obtain thalat as the main fraction. The content of and 1 millionth part of iron-containing fraction

Formylbenzoic acid ester in this dimethyltereph- 15 win. The faction was in a titanium

thalat was 30 millionths of a part. The staining of the vessel for 1 hour at 270 ° C with oxygen under

Dimethyl terephthalate had oxidized after stirring for 4 hours. The content of formylbenzoic acid

heating to 200 ° C in a tightly sealed ester in the reaction product was 150 millionths

Tube heater in the molten state the parts.

Scale value 40 according to APHA. 20 If this contains 100 millionth part of iron

In contrast, the content of formyl crude dimethyl terephthalate was oxy-

benzoic acid ester in one by the above, but without the simple distillation

Using the distillation method, but without blowing in, the formylbenzoic acid content

Oxygen obtained dimethyl terephthalate 1000 lactic acid ester in the product 4000 millionth parts,

lionstel parts and the coloring of the latter had in the 25. .

In the molten state, the scale value 350 according to Example 8

APHA. A sample of 300 g of crude dimethyl terephthalate with

Example 5 according to an iron content of 100 millionth part

^v Example 7, received an addition of 0.015 g of manganese

The crude dimethyltereph- 30 naphthenate used in Example 1 with a 10% content of metallic

thalate was in a reaction vessel made of carbon manganese and was then in a glass reactor

stoffstahl 1 hour at 270 ° C with oxygen under ionization vessel at 250 ° C with oxygen while stirring

Stirring oxidizes. The formylbenzoic acid content oxidizes for 30 minutes. The content of formylbenzoic

ester in the reaction product was 3000 million-acid ester in the reaction product was 5000 mil-

stel parts. The reaction product was as in the one-part 35 million.

Game 1 distilled to produce dimethyl terephthalate. The catalyst content was kept at 1.5 g of manganese. The content of formylbenzoic acid ester in naphthenate increases per 300 g of crude dimethyl terephthalate, the dimethyl terephthalate was 200 millionths and this mixture in the same way with Sauer parts. After heating to 200 ° C for 4 hours, it is oxidized in a fabric. The formylbenzoic acid content is dense closed tube heater, the di-4 ° ester in the reaction product was 5000 millionths methyl terephthalate in the molten state one part. In each case this was demonstrated by distillation Color corresponding to the scale value 150 according to APHA from the dimethylterephosphere obtained from the reaction product. thalat a considerable coloring.

^ b Rhdih

Beismel 6 ^ ^as above crude dimethyl terephthalate with

"45 has an iron content of 100 millionths of a part

300 g of crude dimethyl terephthalate according to Example 1 in a glass still of a simple one

received an addition of 0.015 g of manganese naphthenate subjected to distillation. The distillate contained 3 ⁰ Zo

with a 10% proportion of metallic manganese. Terephthalic acid monomethyl ester and 1 millionth

Then the mixture became part of iron in a reaction vessel. The distillate received an addition of

made of carbon steel for 30 minutes at a temperature 50 0.015 g of manganese naphthenate and was then in a

door of 250 ° C, as described in Example 2, with a glass reaction vessel at 250 ° C with stirring

Oxygen is oxidized with stirring. The content of 30 minutes is oxidized with oxygen. The content of

Formylbenzoic acid ester in the reaction product Formylbenzoic acid ester in the reaction product

was 3,000 millionths of a part. was less than 100 millionth parts.

As the same oxidation in a titanium vessel 55 The content of formylbenzoic acid ester in the

was carried out, the content of formyl- by distillation of this reaction product was as in

benzoic acid ester in the reaction product less than Example 1 obtained dimethyl terephthalate

than 100 millionth parts. The formyl content is less than 10 millionth of a part. When the dimethyl

benzoic acid ester in a by distillation of this terephthalate for 4 hours at a temperature of

Reaction product obtained dimethyl terephthalate 60 200 ° C in a tightly closed tube heater

was less than 10 millionth of a part, as was heated in, no coloration could be determined

game 2. A coloration of the dimethyl terephthalate will be

it could not be detected. Example 9

Example 7 _6s p-xylene was dissolved in acetic acid in the presence

p-Xylene was made in acetic acid solution in the presence of cobalt, manganese and bromine compounds

of cobalt, manganese and bromine compounds oxidized with air to obtain terephthalic acid.

Air oxidizes to produce terephthalic acid. The 1000 g of this terephthalic acid were at high

Esterified temperature and under high pressure with 4000 g of methanol. The resulting reaction product was cooled to 40 ° C. and filtered to obtain 950 g of solid matter and 4050 g of liquid. 100 g of dimethyl terephthalate (reclaimed ester A) was distilled off as a low boiling fraction by distilling the solid under reduced pressure, and 800 g of dimethyl terephthalate was obtained as the main fraction. Methanol and water were evaporated from the liquid, and the liquid was then subjected to simple distillation in a glass still under reduced pressure to obtain 150 g of dimethyl terephthalate (recovered ester B). 250 g of the recovered esters A and B were oxidized hour with oxygen in a titanium vessel at 270 ⁰ C with stirring. The formylbenzoic acid content went down from 3% to 1%. The oxidation product from these recovered esters and crude terephthalic acid were co-esterified with methanol and the product treated as described above. The content of formylbenzoic acid ester in the dimethyl terephthalate obtained as the main fraction by the distillation of the solid matter was 20 millionths of a part and the color of the dimethyl terephthalate in the molten state had a scale value of 20 according to APHA.

Example 10

m-xylene was present in acetic acid solution from cobalt, manganese and bromine compounds oxidized with air to isophthalic acid. Isophthalic acid was esterified with methanol in a titanium vessel at high temperature and under high pressure. That Reaction product was heated in a glass vessel to evaporate methanol and water. The residue was crude dimethyl isophthalate. The crude dimethyl isophthalate contained 5% isophthalic acid monomethyl ester, 0.8% methyl formylbenzoate and 5 millionth part iron.

300 g of the crude dimethyl isophthalate received an addition of 0.015 g of manganese naphthenate with a 10% share of metallic manganese and were placed in a glass reaction vessel at 250 ° C Stir for one hour, oxidized with oxygen. The formylbenzoic acid ester content in the reaction product was less than 100 millionths of a part. Of the Content of formylbenzoic acid ester in the distillation of the reaction product according to Example 1 recovered dimethyl isophthalate was 10 millionth part. As the dimethyl isophthalate in one was heated to 200 ° C in a tightly closed tube heater, no coloration could be detected.

Claims (7)

Patent claims: 1. A process for obtaining pure benzene dicarboxylic acid esters of low molecular weight primary alcohols from crude benzene dicarboxylic acid esters containing corresponding formylbenzoic acid esters and possibly contaminated by iron compounds, characterized in that the crude esters are, if necessary, after reducing their iron content to ^ 20 ppm by distillation, in the liquid phase, optionally rectified in the presence of manganese or copper compounds that are soluble in the reaction system in an amount of less than 1 x 10 ^-6 gram atoms of manganese or copper per gram of ester-treated at 140 to 300 ° C with oxygen or an oxygen-containing gas and subsequently or these Performing treatment at the same time as rectification. 2. The method according to claim 1, characterized in that the benzene dicarboxylic acid ester low molecular weight primary alcohols a low molecular weight dialkyl terephthalate and resp. or isophthalate, in particular dimethyl terephthalate and / or isophthalate, is used. 3. The method according to claim 1, characterized in that the oxidation with the molten benzene dicarboxylic acid ester. 4. The method according to claim 1, characterized in that the oxidation at a Temperature between 200 and 280 ° C performs. 5. The method according to claim 1, characterized in that there is used as molecular oxygen pure oxygen or gases containing at least 50% pure oxygen are used. 6. The method according to claim 1, characterized in that the manganese or copper catalyst Manganese or copper naphthenate is used. 7. The method according to claim 1, characterized in that to carry out the Process devices with internal surfaces made of titanium or aluminum are used. Considered publications:
German interpretative document No. 1082 901. 1 sheet of drawings 709 638/565 8.67 © Bundesdruckerei Berlin