JPH0741456A - Oxidation reactor for producing aromatic dicarboxylic acid - Google Patents

Abstract

PURPOSE:To provide a reactor capable of performing the continuous operation for a long period with hardly any recognized sticking of solid substances to the reactor in carrying out the oxidizing reaction of aromatic dialkyl compound. CONSTITUTION:This oxidation reactor for producing aromatic dicarboxylic acid is obtained by polishing the surface of a wall in contact with a reactional solution or a reactional gas in a part at a level higher than 30% in the upper part of a cylindrical part in a cylindrical and vertical type pressure-resistant vessel and/or the surface of an inner structure thereof and the rear surfaces of stirring blades in the rotational direction to a mirror surface of >=No.200 buffing. Thereby, the frequency of the operation to stop the operation of the apparatus for producing aromatic dicarboxylic acid to remove deposits is reduced to afford a high operating efficiency of the apparatus for producing aromatic dicarboxylic acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxidation reactor for producing a corresponding aromatic dicarboxylic acid by liquid-phase oxidation of an aromatic alkyl (hereinafter, simply referred to as a reactor), and particularly para-xylene in a liquid phase. It relates to a reactor for oxidation to produce terephthalic acid.

[Prior art]

In order to produce a corresponding aromatic dicarboxylic acid by liquid-phase oxidation of an aromatic dialkyl such as metaxylene or paraxylene, generally, the starting aromatic alkyl and a catalyst are mixed in a solvent of hydrous acetic acid and heated at a high temperature. The liquid phase oxidation reaction is performed by blowing molecular oxygen gas under high pressure. Heavy metals such as cobalt and manganese, and bromine compounds as catalysts, or acetaldehyde, methyl ethyl ketone and the like as oxidation promoters are used.

What is common to these oxidation reactions is that the aromatic dicarboxylic acid formed as a result of the reaction is partially or mostly precipitated as a solid matter under the reaction conditions, and particularly paraxylene is oxidized. In the case of producing terephthalic acid in this way, since terephthalic acid is poorly soluble in the solvent, most of the terephthalic acid produced precipitates as crystals in the reactor.

Therefore, as one of the basic requirements of such a reactor, the precipitated terephthalic acid crystal is made into a uniform slurry without being locally present in the reactor, and is taken out of the system through the reaction product outlet. It can be mentioned. If the reactor is continuously operated for a long time without performing this completely, a solid deposition phenomenon mainly consisting of terephthalic acid mainly occurs at the bottom of the reactor. Since the accumulation of solids will reduce the effective internal volume of the oxidation reactor, if the amount of deposition reaches a certain limit, the operation must be stopped to remove the deposits. The series of operations involved would significantly impair the overall economic efficiency of the terephthalic acid production equipment. In order to solve this problem, first of all, it is necessary to increase the stirring efficiency of the liquid and maintain the fluid linear velocity sufficient to prevent the precipitation of terephthalic acid crystals.
Secondly, it is necessary to prevent the solid matter (hereinafter, simply referred to as solid matter) substantially consisting of terephthalic acid from adhering to the inner wall of the reactor or the internal structure.

Regarding increasing the first stirring efficiency,
For example, as shown in Japanese Patent Publication No. 61-21217, it has been proposed to devise the shape of the stirring blade and the stirring power. Further, as for the prevention of the second solids from adhering, it has been proposed to use a double structure reactor as shown in Japanese Patent Publication No. 46-5140. In addition, JP-A-50-1
No. 26633 proposes to install a rotary scraper at the bottom of the reactor to prevent the accumulation phenomenon of solid matter.

[0006]

Various measures have been proposed in order to reduce the accumulation of solids in the aromatic dialkyl oxidation reactor as described above. However, even if it has any function, it does not react. If a structure is made inside the vessel, a biased flow (dead space) is likely to occur in the liquid flow, and the chances of solids adhering obviously increase, so there is a great risk of causing the opposite result. Further, preheating the reactor wall as a dual structure reactor complicates the reactor and makes it expensive, and its effect is not clear.

The minimum internal structure required for the reactor is
An oxidizing gas blowing pipe, a baffle, a stirrer, a raw material supply pipe, a reaction product take-out pipe, a reflux liquid return pipe, and a supporting tool for them are required, but solid substances also tend to adhere to these. Among these internal structures, some proposals have been made for preventing solids from adhering to the oxidant gas blowing section and baffles, but few proposals have been made to prevent solids from adhering to other structures. As mentioned above, when the amount of solid deposits reaches a certain limit, the operation must be stopped to remove the deposits, and the series of operations associated with this removal is economically feasible with equipment such as terephthalic acid production equipment. Will be significantly impaired. An object of the present invention is to provide a reactor which can prevent the deposition and accumulation of solid matter in such an aromatic dialkyl oxidation reactor and can be continuously operated for a long time.

[0008]

Means for Solving the Problems The inventors of the present invention have made extensive studies on an aromatic dialkyl oxidation reactor having the above-mentioned problems, and as a result, solid deposition is higher than the upper 30% of the reactor in the liquid phase portion. It is easy to occur in the upper part from the vicinity of the gas-liquid interface where the gas phase and the gas phase part come into contact with each other, and by buffing the inner wall surface and structure of this part to a high degree, solid matter can be prevented from adhering significantly, and the solid behind the stirring blade. The present invention has been completed, and it has been found that it is effective to carry out a high degree of buffing for the object to be easily attached and grown in a conical shape.

That is, according to the present invention, the wall surface in contact with the reaction liquid or the reaction gas in a portion higher than 30% of the upper portion of the cylindrical portion of the cylindrical vertical pressure vessel and / or the surface of the internal structure is buffed to a mirror surface of 200 or more. Is an oxidation reactor for producing an aromatic dicarboxylic acid, which is ground to the interior of the reactor, and further has therein an agitator having one or more agitating blades installed on the longitudinal axis, and the rear surface in the rotating direction of the agitating blades is buffed to 200. It is an oxidation reactor for producing an aromatic dicarboxylic acid, which is polished to a mirror surface of No. 1 or more.

The oxidation reactor for producing an aromatic dialkyl in the present invention is a reactor for producing a corresponding aromatic dicarboxylic acid by liquid-phase oxidation of an aromatic dialkyl, and as described above, the raw material aromatic dialkyl and the catalyst are used. It is mixed in a solvent of hydrous acetic acid, and molecular oxygen gas is blown into it at high temperature and high pressure to carry out a liquid phase oxidation reaction. Examples of the aromatic dialkyl as a raw material include dimethylbenzene such as metaxylene and paraxylene, diethylbenzene and the like, and the corresponding dicarboxylic acid is produced. In particular, the present invention is terephthalic acid which is hardly soluble and easily causes adhesion of solid matter. It is suitable for use in a production oxidation reactor. When producing terephthalic acid from paraxylene, the reaction temperature is usually 180 to 210 ° C, and the pressure is about 16 to 20 atm.

A cylindrical vertical pressure vessel is used in the reactor of the present invention, and the internal structure includes an oxidizing gas blowing pipe, a baffle, a stirrer, a raw material supply pipe, a reaction product take-out pipe, and a reflux liquid return pipe. And their supports. According to the present inventors' experience of operating an oxidation reactor for many years, increasing the stirring efficiency of the first liquid to prevent the precipitation of terephthalic acid crystals can be achieved by combining many known techniques to improve the dispersion of the liquid. However, it was almost achieved by eliminating the liquid flow drift (dead space) and maintaining the required fluid linear velocity.

As a result of repeated observations of an experiment for preventing solids from adhering to the inner wall of the reactor and internal structures with an experiment of an experimental autoclave and an actual apparatus, the biggest problem was that the liquid phase above the reactor was This is the adhesion of solids from the vicinity of the gas-liquid interface where the part and the gas phase part contact each other to the upper part. This is because the oxidizing gas is directly injected into the reactor and vigorous stirring is performed on it, and it is assumed that the vicinity of the gas-liquid interface is always in a state similar to boiling due to the characteristics of the oxidation reaction. According to the autoclave experiment, solid matter adhesion from the vicinity of the gas-liquid interface to the upper part tends to occur when the stirring efficiency in the reaction vessel is good, and when the stirring efficiency of the liquid is increased and the fluid linear velocity is increased. ,
We face the complication of sometimes accelerating the phenomenon of solids deposition.

In a commercial-scale oxidation reactor, the structures near the gas-liquid interface include, in addition to the inner wall of the reactor, the shaft of the stirrer, the upper part of the baffle, the return pipe of the reflux liquid, and their supports. Etc. are the main ones. As a result of the observation, the solid matter is likely to adhere to all of these structures, and the adhered solid matter often forms not only a film but also a block. The solid matter that has grown in a block shape is in an extremely unstable state, and repeatedly falls and grows due to disturbance such as slight fluctuations in the liquid surface. The falling phenomenon of block-shaped solids often appears as an instantaneous and minute fluctuation of the liquid surface of the reactor, and can be detected by careful observation. A part of the block-shaped solid that has fallen is pulverized by the liquid flow and the shearing force of the stirrer, becoming a slurry and discharged from the reaction product outlet to the outside of the system, but if pulverization remains insufficient, the reactor It appears as a solid deposition phenomenon on the bottom.

As described above, for the purpose of preventing the adherence of solid matter from the vicinity of the boundary between the liquid phase portion and the gas phase portion of the upper part of the reactor, improving the dispersion of the liquid rather promotes the adhesion. There is a troublesome problem of being easy. In this regard, the solid surface is prevented from adhering by mirror-finishing the surface above the portion in contact with gas and liquid. There is no problem with mirror-finishing the lower surface that is always in contact with liquid, but as mentioned above, solid matter can be prevented from adhering by sufficiently increasing the liquid dispersion effect. Therefore, there is no need to dare to make it a mirror surface. Since the liquid level of the reactor is often changed for the purpose of controlling the entire reaction, it is difficult to exactly determine the range of mirror finish, but generally, the surface equivalent to 30% from the top of the cylindrical part is the mirror finish. If it is finished, the purpose can be fully achieved.

That is, as shown in Example 1, a rod-shaped stirrer having a mirror finish was attached near the gas-liquid boundary surface to carry out the oxidation reaction of paraxylene, and then the autoclave was released and checked. Almost no adherence of solid matter was observed, but the effect of mirror finish is confirmed by the large amount of solid matter adhered to the stirrer which was not mirror-finished in Comparative Example 1. Also, as shown in Example 2, the results of an overhaul after a long period of commercial operation when some baffles were buffed in a commercial scale reactor showed that baffles were present in sections without mirror finish. Solids were found on the surface and the inner wall of the reactor, and block-like solids were found at the top of the baffle, whereas almost no solids were found in the mirror-finished section. Also confirmed the effect of mirror finish. In addition, it is necessary that the buff finish is 200 or more.

In the oxidation reactor for producing an aromatic dicarboxylic acid, a stirrer having a longitudinal axis is generally used, but as described above, solid matter is easily attached and grown in a conical shape on the back side of the stirring blade. However, the solid surface can be prevented from adhering by polishing the rear surface of the stirring blade in the rotating direction to a buffed No. 200 or higher mirror surface (see Example 3).

[0017]

EXAMPLES The effects of the present invention will be described more specifically below with reference to examples. However, the present invention is not limited to these examples.

Example 1 A titanium autoclave having an internal volume of 2 L having a stirrer, a reflux condenser, an air blowing port, an exhaust gas outlet, a raw material liquid charging port, and a product slurry withdrawing port was used. In addition, a rod-shaped stirrer consisting of four titanium rod stirring blades was attached. This stirrer and the stirrer shaft above the part where the stirrer was attached were previously buffed with No. 2000 water resistant abrasive paper to a mirror finish of No. 200 or more. Charge acetic acid (water content 10%) and manganese acetate, cobalt acetate, and hydrobromic acid as catalysts to this autoclave,
Air was blown in with vigorous stirring to heat and raise the temperature to 200 ° C. At 200 ° C. and 16 kg / cm ² G,
A raw material liquid prepared by adding paraxylene to a solvent consisting of acetic acid (water content: 10%) and manganese acetate, cobalt acetate, and hydrobromic acid as a catalyst was continuously supplied to carry out an oxidation reaction.
The amount of raw material air blown was adjusted so that the oxygen concentration in the exhaust gas was about 5%. The amount of the product slurry withdrawn was adjusted so that the liquid surface was slightly below the rod-shaped stirring blade attached to the upper part. After continuous operation for 10 hours, stop the reaction after sufficiently lowering the liquid level, open the autoclave and observe the degree of adhesion of solids. As a result, a rod-shaped stirrer with a mirror finish attached to the top and a mirror finish Although a thin film-like solid substance was observed to be attached to the stirring shaft, the block-like solid substance was not observed. The thin, film-like solid could be removed by simply sprinkling it with water.

Comparative Example 1 The same experiment as in Example 1 was carried out using the rod-shaped stirrer and the stirring shaft mounted on the upper part as they were machined by a lathe without mirror finishing. After stopping the reaction, the autoclave was opened and the degree of adhesion of the solid matter was observed. As a result, it was found that the film-like solid matter was heavily adhered to the rod-shaped stirrer and the stirring shaft attached to the upper part. Moreover, a ball-shaped block was attached on the rod-shaped stirrer as if it was clinging to the stirring shaft. None of these deposits could be removed by sprinkling water.

Example 2 Terephthalic acid was prepared from para-xylene in a commercial scale oxidation reactor. This reactor has an inner diameter of 3.6 m and a cylindrical height
A 5.1 m cylindrical vertical pressure vessel with a ceiling and bottom consisting of semi-elliptical lids, two agitators installed on the longitudinal axis, and a reflux condenser connected to the top of the tower. Have
The raw material liquid supply port, the oxidizing gas blowing port, and the reaction product extraction port containing solid matter are all in the liquid in the reactor, and vertical baffles close to the side walls are circumferentially distributed in the reactor. Four pieces are installed at intervals. The reactor side wall is evenly divided into four along the circumference around each baffle, and the wall surface in the area higher than the upper 30% of the cylindrical portion for the first and third sections No. 200 buffing was performed on the entire surface of the baffle and the surface of the baffle support. However, the upper limit of wall bubbling was set to about 0.5 m from the upper end of the cylindrical part to the upper part along the semi-elliptical lid part. Using this reactor, terephthalic acid was produced by blowing air into a hydrous acetic acid solvent using paraxylene as a raw material.
Manganese acetate, cobalt acetate, and hydrobromic acid were used as the catalyst, the reaction temperature was about 200 ° C, and the pressure was about 16 kg / cm ^2.
G was set to G, the oxygen concentration in the exhaust gas was set to about 2 to 4%, and terephthalic acid was produced on a commercial scale for about 3 months without any interruption. During this period, the liquid surface of the reactor was in the range of about 10 to 30% above the cylindrical portion. The reaction was stopped after sufficiently lowering the liquid level, and the inside of the reactor was carefully washed so as not to affect the buffed surface and then released, and the degree of adhesion of solid matter was observed. As a result, thin film-like crystals adhered to the first and third compartments that were buffed, but the thin film-like crystals could be removed by simply sprinkling water. It was On the other hand, on the surface of the baffle of the remaining section that was not buffed, a relatively thick layer of solid matter is attached. There was a large block-shaped solid substance that reached about 0.2 m. Further, a relatively thick layer of solid matter was adhered to the side wall in places around the baffle attachment part. None of these solids could be removed by simply sprinkling them with water.

Example 3 In the reactor of Example 2, 2 installed on the longitudinal axis
Among the four stirrers, the upper stirrer was four non-tilted desk turbine type stirrers, and the rear surface of the first and third stirrer blades in the circumferential direction with respect to the rotational direction was subjected to No. 200 buffing. Operating conditions were the same as in Example 2, and terephthalic acid was produced on a commercial scale for about 3 months. As a result of the release inspection after the operation was stopped, the conical solids with the blade surface as the bottom surface were found to be attached to the rear surface of the two stirring blades that were not buffed. Only thin film-like crystals adhered to the rear surface of the blade, and the thin film-like crystals could be removed simply by sprinkling water lightly.

[0022]

As is apparent from each of the examples, in the reactor of the present invention, almost no solid matter is observed during the oxidation reaction of aromatic dialkyl, and long-term continuous operation can be performed. As a result, the number of operations for stopping the operation of the aromatic dicarboxylic acid production apparatus to remove the deposit is reduced, and a high operating rate of the aromatic dicarboxylic acid production apparatus can be obtained.

Claims (2)

[Claims] 1. An upper portion 30 of a cylindrical portion of a cylindrical vertical pressure-resistant container.
% Of the reaction liquid or reaction gas in contact with the reaction gas and / or the surface of the internal structure is buffed and polished to a mirror surface of No. 200 or more to produce an aromatic dicarboxylic acid 2. An agitator having one or more agitating blades installed on the longitudinal axis is installed inside, and the rear surface in the rotating direction of the agitating blades is polished to a buff finish No. 200 or more mirror surface. Oxidation reactor for the production of aromatic dicarboxylic acids