JP2000001456A - Production of high purity terephthalic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a method for producing high purity terephthalic acid by accelerating the separation of bubbles to homogeneously disperse powder crude terephthalic acid (CTA), forming a highly concentrated aqueous slurry and subsequently efficiently hydrogenating the slurry, capable of efficiently producing the terephthalic acid (PTA). SOLUTION: This method for producing highly pure terephthalic acid (PTA) 16 comprises preliminarily mixing powder crude terephthalic acid (CTA) 1 with a part of water 2a in a kneading device 3 to form the preliminary mixture having a concentration of 55-75 wt.%, mixing the preliminary mixture with the remaining part of water in a slurr-preparing tank 5 to form a slurry, and further subjecting the product to a hydrogenation process 8, a crystallization process 10, a solid-liquid separation process 12, and a drying process 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-purity terephthalic acid (hereinafter sometimes referred to as PTA) obtained by subjecting crude terephthalic acid (hereinafter sometimes referred to as CTA) obtained by liquid phase oxidation of para-xylene to hydrogenation treatment. And a method for producing the same.

[0002]

2. Description of the Related Art When para-xylene is oxidized in a liquid phase with a molecular oxygen-containing gas, in addition to terephthalic acid (hereinafter sometimes referred to as TA), 4-carboxybenzaldehyde (hereinafter referred to as 4-CBA) is a main impurity. CTA) is generated. However, since PTA is required as a raw material for the production of polyester fibers, the above-mentioned CTA must be purified.

[0003] As a method for producing PTA, there is known a method in which CTA is subjected to a hydrogenation treatment in the presence of a hydrogenation catalyst (for example, JP-A-4-66553). In this method, 4-CBA is reduced to water-soluble paratoluic acid even at a low temperature by hydrogenation, and PTA is produced by separating paratoluic acid from terephthalic acid by crystallization, solid-liquid separation or the like.

The above-mentioned hydrogenation treatment is carried out by forming a fixed layer of a solid catalyst in a reactor and supplying hydrogen while passing a CTA aqueous solution through the catalyst layer. In this case, C
The TA aqueous solution is prepared by forming a slurry in which CTA powder is dispersed in water and heating the slurry to dissolve CTA in water. At this time, in order to carry out the reaction efficiently, it is required to form a slurry having a concentration corresponding to the solubility of terephthalic acid during heating.

[0005] The conventional CTA slurry is generally prepared by adding water and powder CT to a water slurry preparation tank having a rotary stirring blade.
The slurry is formed by introducing and stirring A. This method is a method of dispersing powder CTA in water by continuously supplying water and powder CTA while stirring the liquid filled in the slurry preparation tank.

However, since powdered CTA does not have a high affinity for water, it may be dispersed in a state containing air bubbles, and it is difficult to separate the air bubbles. In the state containing bubbles, powder CT
A flows as a lump, does not melt even when heated, flows into the hydrogenation reactor as a lump, is captured by the hydrogenation catalyst layer, and causes clogging.

[0007] In order to prevent this, conventionally, the amount of powdered CTA dispersed in water is reduced, and a low-concentration water slurry is formed to reduce the amount of bulky CTA including bubbles. Can be dissolved by heating. However, there is a problem that the efficiency of the hydrogenation reaction is reduced when a slurry having a low concentration is supplied.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to promote the separation of air bubbles to uniformly disperse powdered CTA, to form a high-concentration water slurry, and to efficiently perform a hydrogenation reaction.
It is an object of the present invention to propose a method for producing high-purity terephthalic acid, which enables efficient production of PTA.

[0009]

The present invention is the following method for producing high-purity terephthalic acid. (1) Crude terephthalic acid obtained by liquid phase oxidation of para-xylene is mixed with water to form a slurry, and this slurry is heated to form a crude terephthalic acid solution, which is subjected to a hydrogenation treatment in the presence of a hydrogenation catalyst. Then, in the method for producing high-purity terephthalic acid, the powdery crude terephthalic acid and a part of water are premixed in a kneading apparatus to form a premix having a concentration of 55 to 75% by weight, and this premix is mixed with the remainder. A method for producing high-purity terephthalic acid, comprising mixing with water to form a slurry and performing a hydrogenation treatment. (2) The method according to the above (1), wherein the premixing is performed by a continuous kneading apparatus. (3) Powder CT by rotating disk arranged horizontally
The method according to the above (1), wherein the water is mixed while A is fed in the radial direction, and the mixture is premixed by a rotating disk-type kneading device which homogenizes the mixture by moving it through a narrow zigzag resistance path.

The crude terephthalic acid (CTA) to be subjected to the hydrogenation treatment in the present invention is crude terephthalic acid obtained by the liquid phase oxidation of para-xylene. Such terephthalic acid generally contains 4-CBA as a major impurity in 0.1%.
About 1 to 0.4% by weight is contained.

The liquid phase oxidation of para-xylene is carried out using a solvent and a catalyst. Examples of the solvent in the liquid-phase oxidation of para-xylene include fatty acids such as acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, trimethylacetic acid, and caproic acid, or a mixture of these with water. Among them, acetic acid or acetic acid containing water as described below is preferable.

As a liquid phase oxidation catalyst for para-xylene, a heavy metal compound and / or a bromine-containing compound is generally used, and the former is nickel, cobalt, iron, chromium, manganese or the like. , Preferably in a form dissolved in the reaction system. In a preferred embodiment, a cobalt compound, a manganese compound and a bromine compound are used, and the amount of the cobalt compound used is usually 10 to 1 as cobalt with respect to the solvent.
0,000 ppm, preferably 100 to 3000p
pm. The manganese compound has an atomic ratio of manganese to cobalt of 0.001 to 2, and the bromine compound has an atomic ratio of cobalt to cobalt of 0.1 to 5.

The liquid phase oxidation of para-xylene is performed using a molecular oxygen-containing gas. As such an oxygen-containing gas, oxygen diluted with an inert gas is generally used, and for example, air or oxygen-enriched air is used. The temperature of the oxidation reaction is usually from 150 to 270 ° C., preferably from 170 to 220 ° C., and the pressure is at least a pressure at which the mixture can maintain a liquid phase at least at the reaction temperature, and is usually at least 0.5.
To 4 MPa (gauge pressure). Further, the reaction time depends on the size of the apparatus and the like, but is usually about 20 minutes to 180 minutes as the residence time. The water concentration in the reaction system is usually 3 to 30% by weight, preferably 5 to 15% by weight.

CTA obtained by the above liquid phase oxidation reaction
Is introduced into a reactor, and hydrogenation treatment is performed in the presence of a hydrogenation catalyst to produce PTA. In this case, CTA separated from the mother liquor in the liquid phase oxidation reaction is turned into a water slurry, and the obtained water slurry is The mixture is heated and pressurized and introduced into a reactor as an aqueous terephthalic acid solution, followed by hydrogenation treatment. Generally, the CTA concentration of the slurry is 10 to 40% by weight, preferably 20 to 30% by weight, but is preferably a concentration corresponding to the solubility when heated and pressed.

In the present invention, in order to form this slurry, powder CTA and a portion of water are premixed by a kneading device to form a slurry.
A premix having a concentration of 5 to 75% by weight, preferably 60 to 70% by weight, is formed, and the premix is mixed with the remaining water to uniformly disperse the powdered CTA so as to obtain a slurry having less bubbles and agglomerates. To form

The premixing of the powdered CTA and a part of water is performed by a kneading apparatus. The kneading device is a device for kneading powder CTA in the presence of water, and a general kneading device can be used. Such kneading devices include a ball mill type as a container rotating type; a horizontal axis rotating type blade type, a roll type, a screw type, a disk type, a vertical axis rotating type blade type, a wheel type, and a high speed as a container rotating type. Fluid type, rotating disk type, rough type; vibrating mill and the like as a container vibrating type, but a continuous type is preferable.

A particularly preferred kneading apparatus is a rotating circle which mixes water while feeding powder CTA in a radial direction by a rotating disk arranged in a horizontal direction, and homogenizes the mixture by moving it through a narrow zigzag resistance path. A plate type mixing device can be used.

With such a kneading apparatus, the powder CTA concentration is 5
By mixing the powdered CTA and a part of water so as to be 5 to 75% by weight, preferably 60 to 70% by weight,
Bubbles adhering to the powdered CTA are separated and the powdered CTA and water are uniformly mixed to form a homogenized premix.

Since the premix obtained in this way is a state in which bubbles are removed and water and CTA are uniformly mixed, the mixture is introduced into a slurry preparation tank together with the remaining water and mixed by stirring, whereby powder CTA is uniformly mixed. And a homogenized slurry is formed. In this case, as the mixing means, a means conventionally used for adjusting a slurry, such as a mixing tank having a rotary stirring blade, can be used.

The CTA concentration of the slurry at this time is as described above. In this case, since bubbles in the pre-mixture are removed and lumps are reduced, dissolution is easy even if the slurry concentration is increased. Yes, the slurry concentration can be set to a value close to the solubility.

The slurry thus obtained is heated to form C
TA is dissolved to form a terephthalic acid solution, which is introduced into a reactor for hydrogenation treatment. The shape, structure, and the like of the reactor for performing the hydrogenation treatment are not limited as long as the reactor is filled with a catalyst and can supply hydrogen in contact with the CTA aqueous solution.

As a preferred reactor, a solid catalyst is filled to form a fixed bed, and an inlet and an outlet for passing a CTA aqueous solution therethrough. Those having a path are preferred. CTA
The solution may flow upward, but it is preferable that the introduction path communicates with the upper part of the reactor and the discharge path communicates with the lower part so that the liquid flows downward.Hydrogen is connected to the upper part of the reactor so that hydrogen is supplied from the upper part. Is preferred.

As the hydrogenation catalyst, those conventionally used can be used. For example, palladium, ruthenium, rhodium, osmium, iridium, platinum, platinum black, palladium black, iron, cobalt-nickel and the like are used. A solid catalyst in which these are supported on a carrier, preferably an adsorptive carrier such as activated carbon, so that a fixed layer can be formed is preferred.

In the hydrogenation treatment in a steady state, CT
A water slurry at a temperature of 230 ° C. or higher, preferably 240 ° C.
~ 300 ° C, pressure 1 ~ 11MPa, preferably 3 ~ 9M
While heating and pressurizing to Pa (gauge pressure) to dissolve terephthalic acid, the resulting CTA aqueous solution is supplied to the reactor and passed through the catalyst layer, and hydrogen gas is passed through the crude terephthalic acid aqueous solution while passing through the catalyst layer. Hydrogenation is carried out by supplying at a flow rate of at least 0.5 times mol, preferably at least 2 times mol. The reaction temperature for hydrogenation is 230 ° C or higher, preferably 255 to 300 ° C,
The pressure is 1 to 11 MPa, preferably 3 to 9 MPa (gauge pressure), and the hydrogen partial pressure is 0.05 MPa or more, preferably about 0.05 to 2 MPa.

By the hydrogenation treatment, 4-CB in CTA
Since A is reduced to water-soluble paratoluic acid, 300
Crystallization is performed at a temperature of 100 ° C. or lower, preferably 100 to 280 ° C., and solid-liquid separation is performed to separate paratoluic acid from the terephthalic acid slurry to obtain purified terephthalic acid. The purified terephthalic acid is re-slurried to transfer foreign substances adhering to the crystals to the water side, and then subjected to solid-liquid separation and drying to produce high-purity terephthalic acid (PTA).

[0026]

According to the present invention, the powder CTA and a portion of water are kneaded to form a premix, and this mixture is mixed with the remaining water to form a slurry. Separation is promoted to uniformly disperse the powdered CTA, and a high-concentration water slurry is formed to efficiently carry out the hydrogenation reaction, whereby PTA can be efficiently produced.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flow sheet showing a method for producing high-purity terephthalic acid according to the embodiment.

In FIG. 1, high purity terephthalic acid (PT
In the production of A), first, powdered terephthalic acid (CTA) 1 is supplied to a kneading apparatus 3 together with a part of water 2a and premixed to form a premix 4 having a concentration of 55 to 75% by weight. The water is supplied to the slurry preparation tank 5 together with the other water 2b, and if necessary, another water (supplementary water) 2c is supplied and stirred to form a slurry. This slurry is heated and pressed to C
The TA is dissolved, and the CTA aqueous solution 6 and the hydrogen 7 are supplied to the hydrogenation reactor 8 to perform a hydrogenation treatment. The reaction solution 9 subjected to the hydrogenation treatment is reduced in pressure, cooled and introduced into a crystallization tank 10 for crystallization.

The resulting slurry 11 is separated into a solid-liquid separation device 12
To perform solid-liquid separation. The solid-liquid separation is usually performed in a plurality of stages, and the separated liquid 13a in the former stage is discharged as waste water, and in the latter solid-liquid separation, water (washing water) 2d is supplied to re-slurry to perform solid-liquid separation. The separated liquid 13b circulates as water 2a, 2b. The separated crystal 14 is dried in a dryer 15 and is made of high-purity terephthalic acid (PTA).
16 is manufactured.

FIG. 2 is a cross-sectional view of the kneading apparatus 3, in which a rotating disk type kneading apparatus of a vertical axis rotation type is used. The kneading device 3 is opposed to the center of a rotating disk 22 arranged in a horizontal direction and rotated by a vertical rotating shaft 21 so as to face the CTA supply path 2.
3 is opened, and a donut-shaped partition plate 25 having a thicker peripheral portion is provided around the distal end portion thereof in parallel with the rotating disk 22 via an annular gap 24, and these peripheral portions are provided below and below the peripheral portion. A zigzag resistance path 28 is formed between the peripheral portions of the guide plates 26 and 27 covering from above. 29 is a water supply path provided so as to surround the CTA supply path 23, and 30 is a casing.

In the kneading device 3, while rotating the rotating disk 22 by the rotating shaft 21, the powder CT
When A1 is supplied and water 2a is supplied from the water supply path 29,
The powder CTA1 coming out of the CTA supply path 23 is
And flows radially and mixes with the water exiting the gap 24 and spirals in the peripheral direction, mixes with the water flowing from above the diaphragm 25 and flows in a zigzag manner through the resistance path 28, thereby forming a powder CTA. And water are premixed to separate air bubbles, whereby the powdered CTA and water are uniformly mixed to form a homogeneous premix 4.

The homogenized pre-mixture 4 is stirred and mixed with the water 2b and 2c in the slurry preparation tank 5, so that the powder CTA is uniformly dispersed in water without forming a lump, and the homogenized slurry is dispersed. It is formed. Therefore, even when the CTA concentration of the slurry is increased, the TA solution is almost completely dissolved when heated and pressurized to obtain a uniform TA aqueous solution, and the reaction efficiency of the hydrogenation treatment in the hydrogenation reactor 8 can be increased.

In the above example, a rotary disk type kneading device is used, but another type may be used. Further, the crystal 14 subjected to solid-liquid separation in the solid-liquid separation device 12 is dried as it is, but water is added to the separated crystal 14 to form a re-water slurry, and the re-water slurry is purified again by solid-liquid separation. Is also good.

[0034]

Embodiments of the present invention will be described below.

REFERENCE EXAMPLE 1 200 kg of powdered CTA and 800 kg of water were introduced into the slurry preparation tank 5 of FIG. 1 having a rotating blade type stirrer and mixed by stirring to form a 20% by weight slurry. The condition was observed.

Examples 1 and 2, Reference Examples 2 and 3 Powder CTA and a portion of water were introduced into a rotary disk-type kneading apparatus 3 shown in FIG. 2 and kneaded. 1 and introduced into the slurry preparation tank 5 of FIG.
A 0% by weight slurry was prepared, and the separation state after similarly standing for 30 minutes was observed. Table 1 shows the above results.

[0037]

[Table 1]

From the results shown in Table 1, the powder CTA and a portion of water were kneaded to form a premix having a concentration of 55 to 75% by weight, particularly 60 to 70% by weight, and this was mixed with the remaining water to form a slurry. It can be seen that the formation of makes it possible to obtain a homogenized slurry with less bubbles and suspended CTA.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing a method for producing high-purity terephthalic acid according to an embodiment.

FIG. 2 is a sectional view of a kneading device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Powder CTA 2a, 2b, 2c, 2d Water 3 Kneading apparatus 4 Premix 5 Slurry preparation tank 6 CTA aqueous solution 7 Hydrogen 8 Hydrogenation reactor 9 Reaction liquid 10 Crystallization tank 11 Slurry 12 Solid-liquid separation apparatus 13a, 13b Separation liquid 14 Crystal 15 Dryer 16 PTA 21 Rotating shaft 22 Rotating disk 23 CTA supply path 24 Gap 25 Separator 26, 27 Guide plate 28 Resistance path 29 Water supply path 30 Casing

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4H006 AA02 AC46 BA14 BA16 BA19 BA20 BA21 BA37 BD10 BD81 BE30 BE60 BJ50 BS30 4H039 CA65 CC30

Claims (3)

[Claims] 1. A crude terephthalic acid obtained by liquid-phase oxidation of para-xylene is mixed with water to form a slurry, and the slurry is heated to form a crude terephthalic acid solution, which is then treated with hydrogen in the presence of a hydrogenation catalyst. In the method for producing high-purity terephthalic acid by adding, premixed crude terephthalic acid and a portion of water in a kneading apparatus to form a premix having a concentration of 55 to 75% by weight. A method for producing high-purity terephthalic acid, comprising mixing with the remaining water to form a slurry and performing a hydrogenation treatment. 2. The method according to claim 1, wherein the premixing is performed by a continuous kneading apparatus. 3. A rotating disk-type kneader for mixing water while feeding powder CTA in a radial direction by a horizontally disposed rotating disk, and homogenizing the mixture by moving it through a narrow zigzag resistance path. The method of claim 1, wherein premixing is performed.