JPH08157415A - Production of high-purity terephthalic acid - Google Patents

Abstract

PURPOSE: To stably produce high-purity terephthalic acid by adding formic acid at a stage having strong initial catalytic activity after the exchange of a catalytic hydrogenation catalyst in a terephthalic acid production process, thereby generating CO to temporarily poison the catalyst and control the catalytic activity. CONSTITUTION: Crude terephthalic acid (containing 4-carboxybenzaldehyde as an impurity) is produced by the liquid-phase oxidation of a p-phenylene compound having carboxyl groups or carboxyl-forming oxidizable substituents at p-sites. The crude terephthalic acid is dissolved in hot water at >=230 deg.C and subjected to catalytic hydrogenation in the presence of a group 8 noble metal catalyst to obtain high-purity terephthalic acid. In the above process, a part or total of the catalytic hydrogenation catalyst having lowered activity is removed from the reactor, a new catalyst is filled in the reactor and the catalyst is maintained in stationary state by adding formic acid to the system when the catalyst has high catalytic activity. Terephthalic acid having stable quality can be produced over a long period from the initial stage after the exchange of the catalytic hydrogenation catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-purity terephthalic acid, which is a main raw material for polyester resins widely used for fibers, films, industrial members, general molded articles and the like.

[0002]

BACKGROUND OF THE INVENTION Terephthalic acid usually uses acetic acid as a solvent, a bromine compound is used as a cocatalyst for cobalt and manganese catalysts, or a promoter such as acetaldehyde is added to the cobalt catalyst to make p-xylene under high temperature and high pressure. Manufactured by air oxidation. The crude terephthalic acid obtained by this liquid phase air oxidation usually has poor whiteness and contains a large amount of impurities such as 4-carboxybenzaldehyde (referred to as 4CBA) and paratoluic acid. As it is, it is not suitable for reacting with glycol to form polyester. Also, a method has been proposed in which terephthalic acid is produced by liquid phase oxygen oxidation using acetic acid as a solvent and a cobalt catalyst under high temperature and high pressure as in the above method. Since there are many by-products, this crude terephthalic acid is not immediately suitable for reaction with glycol etc. as in the case of the above method.

As a method for producing high-purity terephthalic acid from such crude terephthalic acid containing impurities such as 4CBA, a method such as a reaction such as oxidation or reduction, or a purification treatment by simply recrystallization (noble metal of Group 8 at high temperature) Catalytic hydrogenation treatment or catalytic treatment in the presence of a catalyst, recrystallization treatment, oxidation treatment, reslurry treatment, or a combination thereof is known, but currently the main practice is catalytic treatment. A hydrotreating method, for example, Japanese Patent Publication No.
No. 16860 describes a method of catalytic hydrotreating an aqueous solution of crude terephthalic acid in a high temperature solvent at 230 ° C. or higher in the presence of a Group 8 noble metal catalyst, and JP-B-47-4.
No. 9049 describes the improved method.

It is known that in the production of high-purity terephthalic acid by the above catalytic hydrotreating method, the treatment efficiency of impurities represented by 4CBA decreases with time. That is, if attention is focused on 4CBA as a representative index of impurities, there is a phenomenon that the content of 4CBA in high-purity terephthalic acid increases with time. This decrease in treatment efficiency is mainly due to the decrease in activity of the catalytic hydrogenation catalyst. There is a method of increasing the amount of hydrogen supplied to the reaction column as one method for suppressing the increase of 4CBA with time and obtaining highly pure terephthalic acid of more stable quality. In other words, by increasing the hydrogen partial pressure, the 4CBA annihilation (hydrogenation) reaction is accelerated. However, in this method, hydrogen cannot be supplied over the upper limit of the total pressure determined by the apparatus, and therefore the catalytic hydrogenation catalyst Need to be replaced regularly.

Since the catalytic hydrogenation catalyst generally has a high initial activity, the content of 4CBA in the high-purity terephthalic acid is so low that it cannot be detected by a usual analytical method when the catalytic hydrogenation catalyst is replaced. That is, the purpose of maintaining stable quality cannot be achieved, and it becomes difficult to keep the 4CBA content in the high-purity terephthalic acid within a certain allowable range for a few days immediately after the fresh catalyst is charged. Furthermore, since the initial activity of the catalyst is too strong, a by-product is generated due to excess reaction, and the stability of the purity of high-purity terephthalic acid is impaired.

In order to suppress the excessively strong initial activity of these catalytic hydrogenation catalysts and to prolong the life of the catalytic hydrogenation catalysts, the total amount of the catalytic hydrogenation catalysts whose activity has decreased is not replaced all at once. It is known that only part of the catalyst is replaced with fresh catalyst and the rest is recharged with the catalyst whose activity has decreased (East German Patent 212,162). It is said that this method can extend the catalyst life, but after replacing some catalysts, it takes a long time for the product terephthalic acid to reach a steady state with an acceptable low content of 4CBA. Therefore, the production of nonstandard products and the loss of time are large in industrial production.

Another method is to reduce the amount of hydrogen supplied to the reaction column at the beginning when a part or all of the catalytic hydrogenation catalyst is replaced with a fresh catalyst. This method is effective after a certain amount of time has passed since the catalyst was exchanged, but in a phenomenological sense, it was effective after the content of 4CBA in high-purity terephthalic acid was detected at about 1 ppm or more, but before that, the initial activity of the catalyst was suppressed. It is not possible (see the comparative example described later). It is also possible to operate by reducing the amount of hydrogen to almost stop the hydrogen supply, but if the reaction is carried out with the hydrogen supply amount extremely reduced, the activity of the catalytic hydrogenation catalyst will significantly decrease, It becomes impossible to restore activity.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems in the conventional catalytic hydrotreating process in the production process of terephthalic acid, and to replace the catalytic hydrogenation catalyst with lowered activity. It is intended to provide a method for producing high-purity terephthalic acid, which can quickly reach a steady state in which high-purity terephthalic acid containing 4CBA in a certain allowable low content range is stably obtained.

[0009]

Means for Solving the Problems As a result of intensive studies for achieving the above object, the present inventor has found that when the catalytic hydrogenation catalyst is replaced and the catalytic activity is high, formic acid is added to remove carbon monoxide. The present inventors have found that the catalytic activity can be controlled by generating and temporarily poisoning the catalyst, and high-purity terephthalic acid can be stably produced, and the present invention has been accomplished.

That is, according to the present invention, a p-phenylene compound having a carboxyl group and / or a carboxyl group-forming oxidizable substituent at the para position is subjected to liquid phase oxidation to obtain 4-
In a method for producing high-purity terephthalic acid by dissolving crude terephthalic acid containing carboxybenzaldehyde as a main impurity in high-temperature water at 230 ° C. or higher and subjecting it to catalytic hydrogenation in the presence of a Group 8 noble metal catalyst, a method for producing high-purity terephthalic acid is used. The method for producing high-purity terephthalic acid is characterized in that a part or all of the catalytic hydrogenation catalyst having a reduced amount is extracted, a fresh catalyst is charged, and then formic acid is added until a steady state is reached.

The crude terephthalic acid used to produce the high purity terephthalic acid of the present invention is obtained by liquid phase oxidation of p-phenylene compounds. The p-phenylene compound used has a carboxyl group at the para position and / or an oxidizable substituent that forms a carboxyl group by liquid phase air oxidation, and the substituent is a methyl group, an ethyl group or a propyl group. , Isopropyl group, formyl group, acetyl group and the like. These substituents may be the same or different from each other. Para-xylene is the most common of the p-phenylene compounds used to produce crude terephthalic acid.

Water or acetic acid or a mixture thereof is used as a solvent for the liquid phase oxidation. Transition metal compounds such as manganese, cobalt, iron, chromium, and nickel are used as catalysts for liquid-phase oxidation, and bromine compounds are usually used as co-catalysts, which promotes cobalt catalysts when bromine catalysts are not used. Acetaldehyde and methyl ethyl ketone are used together as agents. The catalyst used is cobalt ion, manganese ion, iron ion in the oxidation reactor,
There is no particular limitation as long as it produces chromium ions, nickel ions, and bromide ions.

Oxygen or air is used as the oxidizer used for the oxidation carried out in the liquid phase. Air is sufficient for oxidation in acetic acid solution in the presence of cobalt and manganese catalysts and bromine compounds, and oxygen is preferred for oxidation in acetic acid solution in the presence of cobalt catalyst. In an acetic acid solution, crude terephthalic acid obtained by a liquid phase oxidation method usually contains many impurities such as 4CBA, and the value of OD ₃₄₀ , which is an index of hue, is not at a level at which it can be directly used as a raw material for a polymer for molding. A purification step is usually required. There is no particular upper limit on the 4CBA content or the content of other impurities and OD ₃₄₀ in the crude terephthalic acid used for the purification treatment.

The catalytic hydrogenation treatment is carried out at a high temperature and high pressure in a solution state, and the catalytic hydrogenation temperature is 230 ° C. or higher in the presence of hydrogen.
The range of 240 to 300 ° C. is preferably adopted. On the other hand, the concentration of crude terephthalic acid is preferably in the range of 10 to 40% by weight, and therefore, the pressure is sufficient to maintain the liquid phase, and the pressure which can maintain the hydrogen partial pressure suitable for the catalytic hydrogenation reaction is preferable. Usually, a range of 30-80 atm is preferable.

A noble metal of Group VIII is used as a catalyst for the catalytic hydrogenation reaction, and as the noble metal of Group VIII, palladium, platinum, ruthenium and rhodium are preferable, and palladium is particularly preferably used. The catalytic hydrogenation catalyst is usually used by supporting it on a carrier. A porous material is usually used as this carrier, but a carbon-based carrier is preferable in terms of material.
Activated carbon, especially granular coconut shell charcoal is preferred. The amount of the catalyst loaded on the carrier is effective even if the amount is small, and the range is not particularly limited, but in order to maintain long-term activity, it is 0.1
A supported amount of about 1.0% by weight is suitable.

Water or acetic acid or a mixture thereof is used as the catalytic hydrotreating solvent. The amount of hydrogen for catalytic hydrogenation needs to be at least twice the molar amount of 4 CBA. The catalytic hydrotreating time may be a time sufficient for the hydrogenation reaction to proceed substantially, and in the case of a packed column reaction, it is usually 1 to 60 minutes, preferably 2 to 20 minutes.
It is in the range of minutes. Usually, the catalytic hydrotreatment is carried out continuously.

In the method of the present invention, the steady state means the p
A method for producing high-purity terephthalic acid by treating crude terephthalic acid containing 4CBA as a main impurity obtained by liquid-phase oxidation of a phenylene compound in a reactor in the presence of hydrogen with a catalytic hydrogenation catalyst. , A state in which high-purity terephthalic acid containing a low content of 4CBA within a certain range can be stably obtained. The decrease in the activity of the catalytic hydrogenation catalyst can be known by the increase in the content of 4CBA in the obtained terephthalic acid. In addition, since the quality of terephthalic acid generally obtained as a product also correlates with its transmittance at 340 nm (OD ₃₄₀ ), in the industrial production of terephthalic acid, 4CBA content and OD are usually used.
Purity is determined by ₃₄₀ . In the steady state of the catalytic hydrotreatment, 4CBA and OD ₃₄₀ are thus maintained at a certain control value within a certain range. Therefore, when these control values deviate from the steady state, the catalytic hydrogenation catalyst in the reactor is replaced with fresh catalyst.

At the time when the catalytic hydrogenation reaction of the crude terephthalic acid was restarted after the catalytic hydrogenation catalyst was replaced, the high purity obtained by catalytic hydrogenation of the crude terephthalic acid due to the high activity of the catalyst as described above. Terephthalic acid has a significantly lower 4CBA content. In the method of the present invention, when such catalytic hydrotreating is restarted, formic acid is added to generate carbon monoxide, and the catalytic hydrogenation catalyst is temporarily poisoned to carry out the reaction until a steady state is reached. . By controlling the catalyst activity in this way, the steady state can be reached in a shorter time. The amount of formic acid to be added is determined by feedback while measuring the 4CBA content in high-purity terephthalic acid, but generally speaking, the concentration in the solvent is preferably in the range of 0.0001 to 0.1%. . The poisoning of the catalytic hydrogenation catalyst due to the addition of formic acid is temporary, and the operation of the present invention does not shorten the life of the catalytic hydrogenation catalyst.

The catalytic hydrotreated crude terephthalic acid solution is first filtered in series with a filter made of a corrosion-resistant material in order to prevent contamination of fine powder caused by abrasion of, for example, activated carbon used for the catalyst carrier. The terephthalic acid crystals were crystallized by being introduced into a connected 2 to 6-stage crystallizer or a batch-type crystallizer, and sequentially depressurized to lower the temperature to 120 to 220 ° C. by evaporation of the solvent. Become a solution. The slurry solution is sent to a crystal separator, terephthalic acid is separated and taken out, and a high-purity terephthalic acid is obtained through a drying step.

[0020]

The present invention will now be described with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, crude terephthalic acid was used on a commercial scale apparatus with manganese acetate, cobalt acetate and hydrobromic acid as catalysts at a temperature of 205
It was produced by air-oxidizing para-xylene in a water-containing acetic acid solvent under the conditions of ° C and a pressure of 17 atm. 4C in crude terephthalic acid
The BA content was 3090 ppm.

Example 1 A pressure-resistant stainless steel reactor having an inner diameter of 26 mm and a length of 350 mm equipped with an external heating device was charged with 200 ml of a fresh catalyst having 0.5% palladium supported on activated carbon, and the whole system was filled with water. The temperature was controlled at 280 ° C. A raw material tank was charged with 25 parts by weight of crude terephthalic acid and 75 parts by weight of a 0.01% formic acid aqueous solution, and the mixture was stirred to form a slurry, and 800 g of the slurry was sent to the top of the reactor by a slurry sending pump every hour. An oil bath for heating was provided on the way from the discharge port of the slurry feed pump to the top of the reactor, and the slurry liquid was heated to 280 ° C.
In addition, 0.7 normal liters of hydrogen gas was supplied per hour from a hydrogen supply line connected to the top of the reactor. The reaction liquid flowing out from the bottom of the reactor is cooled to room temperature through a buffer tank provided to adjust the difference between the supply rate and the withdrawal rate,
It was extracted as a slurry solution into an external receiver by an intermittent extraction device composed of a three-way valve and an actuator. The extracted slurry solution was held in a hot water bath controlled at about 95 ° C. for 30 minutes while stirring, and then rapidly filtered through a sufficiently heated G3 glass filter to separate into crystals and mother liquor. The cake on the glass filter was rinsed with a small amount of hot water, dried in a nitrogen stream at 115 ° C. for 6 hours, and taken out as high-purity terephthalic acid crystals. When the obtained high-purity terephthalic acid was analyzed, the 4CBA content was 6 ppm.

Comparative Example 1 The same operation as in Example was carried out except that the solvent charged into the raw material tank of the catalytic hydrogenation reactor was changed from 0.01% formic acid aqueous solution to pure water. When the obtained high-purity terephthalic acid was analyzed,
4CBA was not detected.

Comparative Example 2 The amount of hydrogen gas supplied to the catalytic hydrogenation reactor was 0.15 per hour.
The same operation as in Comparative Example 1 was performed except that the normal liter was used. When the obtained high-purity terephthalic acid was analyzed, 4CBA was not detected.

Comparative Example 3 The same operation as in Comparative Example 1 was carried out except that the catalytic hydrogenation catalyst was charged with a palladium carbon catalyst which had been used for one year in a commercial-scale crude terephthalic acid refining apparatus. When the obtained high-purity terephthalic acid was analyzed, the content of 4CBA was 1
It was 0 ppm.

Comparative Example 4 After the experiment of Comparative Example 3 was completed, the solvent was changed from pure water to 0.01
The same operation was performed instead of the% formic acid aqueous solution. When the obtained high-purity terephthalic acid was analyzed, the 4CBA content was 32 ppm.

Comparative Example 5 After the experiment of Comparative Example 4 was completed, the solvent was returned to pure water and the operation of Comparative Example 3 was repeated. When the obtained high-purity terephthalic acid was analyzed, the 4CBA content was 9 ppm. The operating conditions and analytical values of high-purity terephthalic acid in the above Examples and Comparative Examples are shown below.

[Table 1] ──────────────────────────────────── Catalyst solvent Hydrogen supply amount 4CBA concentration [N liters] / Hour] [ppm] ──────────────────────────────────── Example 1 Fresh 0.01% Aqueous formic acid solution 0.7 6 Comparative example 1 Fresh pure water 0.7 Not detected Comparative example 2 Fresh pure water 0.15 Not detected Comparative example 3 Used pure water 0.7 10 Comparative example 4 Used 0.01% formic acid aqueous solution 0.7 32 Comparative Example 5 Used pure water 0.7 9 ──────────────────────────────────── ─

The following points are confirmed from Table 1. Although 4CBA was not detected in high-purity terephthalic acid when a fresh catalytic hydrogenation catalyst was used and pure water was used as a solvent (Comparative Example 1), in the case of using formic acid-added water, high-purity terephthalic acid was detected. 4CBA was 6 ppm (Example 1), and addition of formic acid is effective for controlling the initial activity of the catalyst. In the used catalytic hydrogenation catalyst, 4CBA in high-purity terephthalic acid is stable at 10 ppm when formic acid is not added (Comparative Example 3), whereas when formic acid is added, 4CBA in high-purity terephthalic acid is added. Increase to 32 ppm (Comparative Example 4). After that, when the solvent is returned to pure water again, 4 CBA
Is 9 ppm (Comparative Example 5), returning to the same level as Comparative Example 3. That is, the effect of suppressing the catalytic activity due to the addition of formic acid is temporary, and the catalytic activity is restored when the addition of formic acid is stopped. In Comparative Example 2, the hydrogen supply amount was reduced for the purpose of suppressing the initial activity of the catalytic hydrogenation catalyst, but 4CBA was not detected and there was no suppressing effect. The amount of hydrogen supplied in Comparative Example 2 corresponds to about twice the molar amount of 4CBA in the raw material crude terephthalic acid. It is conceivable to further reduce the hydrogen supply amount, but it is not preferable to continue the reaction in a hydrogen-deficient state because the palladium catalyst is likely to undergo unrecoverable deterioration.

[0028]

As is apparent from the above Examples and Comparative Examples, by the method of the present invention, stable quality high-purity terephthalic acid can be obtained by adding formic acid at a time when the initial activity after catalytic catalytic hydrogenation catalyst replacement is strong. Obtainable. That is, it is difficult to keep the 4CBA content in high-purity terephthalic acid within a certain allowable range for a few days immediately after charging a fresh catalyst in the catalytic hydrogenation device, and the initial activity of the catalyst is too strong. Although it is difficult to maintain the stable quality of high-purity terephthalic acid due to a by-product due to excess reaction, the method of the present invention can provide a stable quality of the catalytic hydrogenation catalyst from the initial stage over a long period of time. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumio Ogoshi, 3-10 Mizushima Kaigan Dori, Kurashiki City, Okayama Prefecture Sanryo Gas Chemical Co., Ltd. Mizushima Plant (72) Inhito Masato, 3 Mizushima Kaigan Dori, Kurashiki City, Okayama Prefecture No. 10 Sanritsu Gas Chemical Co., Ltd., Mizushima Plant

Claims (1)

[Claims] 1. A crude terephthalic acid containing 4-carboxybenzaldehyde as a main impurity obtained by liquid phase oxidation of a p-phenylene compound having a carboxyl group and / or a carboxyl group-forming oxidizable substituent at the para position. In a method for producing high-purity terephthalic acid by dissolving it in high-temperature water at 230 ° C. or higher and subjecting it to catalytic hydrogenation in the presence of a Group 8 noble metal catalyst, a part of the catalytic hydrogenation catalyst whose activity has decreased from the reactor or A method for producing high-purity terephthalic acid, which comprises extracting all of them and filling them with fresh catalyst, and then adding formic acid until a steady state is reached.