JP3232700B2 - Method for producing high-purity terephthalic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing high-purity terephthalic acid. More specifically, the present invention relates to an industrially advantageous method for producing high-purity terephthalic acid, which is capable of efficiently dissolving and purifying a trace amount of insolubles in an aqueous solution and purifying it.

[0002]

2. Description of the Related Art In order to further purify terephthalic acid obtained by a liquid phase oxidation reaction of para-xylene, a crude terephthalic acid crystal is dissolved in water at high temperature and high pressure. A purification method for treating with hydrogen in the presence of a platinum group metal catalyst such as palladium / carbon is known (Japanese Patent Publication No. 41-16860, etc.). When this purification method is carried out industrially, usually, in advance, by a tube heater, the crude terephthalic acid crystals are dissolved in a predetermined proportion of water under high pressure, for example, at a high temperature of 260 ° C. or higher,
From the relation of the dissolution rate of terephthalic acid, the dissolution may be insufficient depending on the crystal particle diameter of the crude terephthalic acid. If undissolved terephthalic acid crystals flow into the packed bed of the platinum group metal catalyst, stable continuous operation becomes impossible.

[0003] Therefore, as a conventional method for completely dissolving crude terephthalic acid, a buffer dissolving tank is separately provided between a tube-type heater and a reactor comprising a packed bed of a catalyst. (Tokubosho 51-3)
No. 2618). The residence time in this buffer dissolution tank is usually about several minutes to several tens of minutes. In this case, the terephthalic acid aqueous solution is converted to 260
It will be kept excessively at a high temperature of not less than ° C., which is not preferable in terms of the quality problem of the finally obtained purified terephthalic acid.

[0004]

DISCLOSURE OF THE INVENTION In view of the above circumstances, the present invention reliably dissolves crude terephthalic acid in a short time without providing a buffer dissolving tank, and allows undissolved crystals to pass through the catalyst packed layer. An object of the present invention is to provide a method for dissolving terephthalic acid crystals which is not performed, and to provide a method for producing high-quality terephthalic acid of excellent quality with as little heat history as possible.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and as a result, the aqueous solution obtained by dissolving crude terephthalic acid with a tube-type heater is used to fill a packed tower having a specific structure. The present invention has been completed by finding that a small amount of insolubles in a crude terephthalic acid aqueous solution can be efficiently dissolved by directly supplying the solution to the reactor, and the throughput can be increased.

That is, the gist of the present invention is to dissolve the crude terephthalic acid obtained by the oxidation reaction of para-xylene in water at a high temperature and a high pressure, and then convert the aqueous solution of the crude terephthalic acid to a platinum group metal under a supply of hydrogen. In the method for producing high-purity terephthalic acid by passing through a packed column reactor having a catalyst layer containing, a retention zone formed by being separated by an overflow wall at an upper inlet portion of the packed column reactor is provided. A method for producing high-purity terephthalic acid, characterized in that a crude terephthalic acid aqueous solution is supplied to a zone, and overflows an overflow wall to flow through a packed bed located below the retention zone.

Hereinafter, the present invention will be described in detail. As the oxidation reaction of para-xylene, usually, para-xylene is reacted with molecular oxygen in an acetic acid solvent, for example, in the presence of a catalyst containing cobalt, manganese, and bromine, usually at a temperature of 170 to 230 ° C. The so-called SD method is adopted.
Crude terephthalic acid obtained by such a reaction refers to 4-carboxybenzaldehyde (hereinafter referred to as “4CB”) as an impurity.
A ") is usually 1000 to 5000 pp on a weight basis.
It is crystalline containing m.

[0008] Terephthalic acid has low solubility at normal temperature and normal pressure, and it is necessary to increase the temperature and pressure to increase the solubility of terephthalic acid. As a general method for obtaining an aqueous solution of crude terephthalic acid, the following method is exemplified. The crude terephthalic acid is mixed at a ratio of 10 to 40% by weight with respect to water,
Slurry. Next, the slurry was pressurized to a reaction pressure plus α pressure (plus α is a pressure in consideration of a pressure loss until reaching the reactor) by a pressurizing pump, and combined with a multitubular heat exchanger. It is supplied to the heating and melting step. The temperature increase by heating is carried out up to a predetermined reaction temperature, preferably stepwise by a plurality of heat exchanger groups. The residence time of the slurry in the heating and dissolving step is usually designed to be necessary and sufficient to completely dissolve the crystal particles of the crude terephthalic acid. The residence time in the heater varies depending on the heating method, but is usually 60 to 60. 90 seconds.

[0009] The crude terephthalic acid aqueous solution obtained as described above is passed through a packed tower reactor having a catalyst layer containing a platinum group metal, and the crude terephthalic acid is purified by a hydrogenation reaction treatment in the reactor. As a catalyst containing a platinum group metal,
It is selected from palladium, ruthenium, rhodium, osmium, iridium, platinum and the like or metal oxides thereof. These metals or metal oxides can be used as a catalyst as they are, but they can be used as carriers such as activated carbon.
Usually, those loaded with 0.5 to 10% by weight are particularly effective. As the reaction conditions, the temperature is usually 200 to 400.
℃, preferably 250-350 ℃, the pressure is usually 70k
g / cm ² G or more, preferably 80-100 kg / cm
Is a ² G. Hydrogen is supplied to the reactor after being pressurized into the reactor at a pressure higher than the reaction pressure.

The present invention is characterized in that a packed tower reactor having a specific structure is used in the purification of the above crude terephthalic acid. The packed tower type reactor used in the present invention has a structure in which a retention zone for a crude terephthalic acid aqueous solution partitioned by an overflow wall is provided at an upper inlet portion, and a reaction zone having a catalyst packed layer is provided below the retention zone. . This crude terephthalic acid aqueous solution, which may contain some undissolved crystal particles, is first pressurized and supplied to the upper residence zone, flows downward from the upper part of the reactor, and flows out from the bottom of the reactor. Hydrogen is also supplied from above and dissolves in the liquid phase. Inside the reactor, a vapor phase portion of water vapor and hydrogen gas is present above, and most of the lower portion, including the entire catalyst packed bed, becomes a liquid phase portion. The average residence time of the terephthalic acid aqueous solution in the liquid phase in the reactor is usually 5 to 30 minutes.

The structure of the above-mentioned reactor, particularly the structure of the upper part of the reactor, will be further described with reference to the drawings. FIG. 1 shows the structure of an example of the reactor used in the present invention. 1 is a hydrogen supply port, 2 is a crude terephthalic acid aqueous solution supply port, 3 is an overflow wall, 4 is a partition plate, 5 is a catalyst packed layer, 6 is a terephthalic acid aqueous solution outlet, and 7 is a terephthalic acid aqueous solution flow path. When the reaction is performed, an interface between the liquid phase and the gas phase exists between the partition plate 4 and the catalyst packed layer 5.

[0012] Hydrogen is supplied from a supply port 1 near the top of the tower. Hydrogen is sufficiently dissolved in the terephthalic acid aqueous solution in the high temperature and high pressure column, but in order to increase the dissolving efficiency, hydrogen gas is supplied along the flow path of the terephthalic acid aqueous solution that overflows and descends, Preferably, it is easy to get involved. The crude terephthalic acid aqueous solution is supplied from the supply port 2. The position of the supply port 2 is set at 0.2 to 0.4 times the height of the overflow wall 3 from the partition plate 4, and a portion surrounded by the overflow wall 3 and the partition plate 4 forms a stagnation zone. Therefore, the height of the overflow wall 3 is appropriately set in consideration of the residence time of the aqueous solution in the retention zone, and the temperature of the retention zone is usually set in the same manner as in the reaction zone. The main significance of this residence zone is to supply the crude terephthalic acid aqueous solution to the reaction zone in as short a time as possible, and
The purpose is to make undissolved relatively large crystal particles slightly mixed in the aqueous solution stay in the staying zone, where they are completely dissolved.

The aqueous solution supplied into the retention zone rises along the overflow wall 3 and finally overflows, and is supplied to the lower reaction zone of the partition plate 4. Therefore, even if there are undissolved crystal particles, the particles settle to the lower part of the stagnation zone without overflowing and stagnate, where they are subjected to mixing by the supply liquid or the flow of hydrogen and are rapidly dissolved. Becomes Since the retention of the undissolved particles occurs due to the relationship between the rising flow of the solution and the sedimentation due to the action of gravity, it is preferable to reduce the speed of the rising flow of the solution as much as possible and to reduce the volume of the retention zone as much as possible. The residence time in the retention zone varies depending on the size of the apparatus, but is, for example, about 0.5 to 5 minutes.

For this reason, it is preferable to increase the horizontal sectional area of the portion where the solution rises as much as possible. For example, in the case of the residence zone in the reactor of FIG. 1, the diameter of the cylindrical portion where the aqueous solution rises and the diameter of the reaction zone are the same cylinder, and the overflowing and descending flow path has a cylindrical shape concentric with the inner diameter of the reaction zone. When the inner diameter of the reactor is D, the length of the overflow wall 3 is 0.3 to 0.9 times D, and the diameter of the cylindrical portion of the flow channel in which the aqueous solution overflows and descends is 0.2 of D. It is preferable to set it in the range of up to 0.4 times.

If the reactor has a structure based on the above principle, the reactor is not limited to the one shown in FIG. 1. For example, as shown in FIG. A structure in which an acid aqueous solution is supplied and a stagnation zone including the overflow wall 3 and the partition plate 4 may be provided so as to include the leading end of the supply port 2. The terephthalic acid aqueous solution overflowed by the above-mentioned method is purified through a reaction zone, specifically, a catalyst packed bed 5, and flows out of the system from an outlet 6 at a lower portion of the reactor. The effluent is usually recovered as purified terephthalic acid crystals through crystallization and drying steps.

[0016]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto unless it exceeds the gist thereof.
The present invention is not limited to the following embodiments. Terephthalic acid was produced using a reactor having a structure as shown in FIG.

That is, a slurry of raw terephthalic acid (containing 2700 ppm of 4CBA with respect to terephthalic acid) in an aqueous solution concentration of 30% by weight was prepared, and this was subjected to a pressure of 90 kg / c.
The pressure was raised to m ² G, and the temperature was raised to 285 ° C. by a multitubular heat exchanger. The residence time here was about 90 seconds. The slurry was supplied at a flow rate of 45 m ³ / h to the packed column reactor of the present invention. The reactor has a structure as shown in FIG.
m, the height is 10 m, and the height of the catalyst layer is 7 m. The structure of the residence zone is such that the height of the overflow wall is 700 m / m and the diameter of the downcomer is 300 m / m. The residence time here was about 1 minute. The reaction conditions were a pressure of 80 kg / cm ² G, a temperature of 285 ° C., a hydrogen partial pressure of 8 kg / cm ² , and a catalyst of 0.1 kg / cm ² .
5% palladium / carbon was used. The continuous operation was performed for about 170 days under such conditions, but there was no trouble due to clogging in the reactor, and the obtained purified terephthalic acid was
The quality of 6 ppm or less in CBA concentration could be maintained.

[0018]

According to the present invention, high-purity high-purity terephthalic acid can be produced without troubles such as clogging by undissolved coarse terephthalic acid crystal particles.

[Brief description of the drawings]

FIG. 1 is a view showing the structure of an example of a packed reactor used in the present invention.

FIG. 2 is a diagram showing the structure of an example of a packed reactor used in the present invention.

[Explanation of symbols]

 Reference Signs List 1 hydrogen supply port 2 crude terephthalic acid aqueous solution supply port 3 overflow wall 4 partition plate 5 catalyst packed layer 6 terephthalic acid aqueous solution outlet 7 terephthalic acid aqueous solution flow path

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hironori Ogi 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City, Fukuoka Prefecture Inside the Kurosaki Plant of Mitsubishi Chemical Co., Ltd. (56) References JP-A-56-79635 (JP, A) No. 51-32618 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C07C 63/26 C07C 51/487

Claims (1)

(57) [Claims] 1. Crude terephthalic acid obtained by oxidation reaction of para-xylene is dissolved in water at high temperature and high pressure, and then the crude terephthalic acid aqueous solution is charged with a catalyst layer containing a platinum group metal under a supply of hydrogen. In the method for producing high-purity terephthalic acid by passing through a tower reactor, a retention zone formed by an overflow wall is provided at an upper inlet portion of a packed tower reactor, and crude terephthalic acid is provided in the retention zone. A method for producing high-purity terephthalic acid, comprising supplying an aqueous solution, causing the overflow wall to overflow, and then passing the solution through a catalyst packed bed located below the retention zone.