JPH11343264A - Production of aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing attachment of an oxidation catalyst to a product in precise oxidation terephthalic acid process. SOLUTION: This method for producing an aromatic carboxylic acid comprises (1) a main liquid phase oxidation step for oxidizing an alkylbenzene with an oxygen- containing gas in the presence of a catalyst in a lower aliphatic acid carboxylic acid solvent in a first reaction area to provide slurry containing an aromatic carboxylic acid, (2) a step for additionally oxidizing the reaction mixture from the step 1 with an oxygen-containing gas without feed of the alkylbenzene in a second reaction area to provide crude slurry containing the aromatic carboxylic acid, (3) a step for additionally oxidizing crude slurry from the step 2 with oxygen-containing gas without feed of the alkylbenzene in a third reaction area having a temperature higher than that of the second reaction area to provide purified slurry containing the aromatic carboxylic acid, (4) a crystallization step for lowering purified slurry from the step 3 to proper temperature and pressure, (5) a separation step of the aromatic carboxylic acid for feeding the purified slurry from the step 4 onto a horizontal filtration face filter, (6) a step for washing the aromatic carboxylic acid from the step 5 with a lower carboxylic acid solvent and (7) a step for drying purified aromatic carboxylic acid from the step 6 to provide a product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the production of aromatic carboxylic acids. More specifically, the present invention relates to a method for producing oxidized purified terephthalic acid (precise terephthalic acid) obtained through main oxidation, re-oxidation, and re-re-oxidation.

[0002]

2. Description of the Related Art Oxidized and purified terephthalic acid (precise terephthalic acid) obtained through main oxidation, superoxidation, and repostoxidation in a reaction medium containing acetic acid usually becomes a product through a separation, washing, and drying process. . Processes after this separation have conventionally been performed through complicated procedures of separation, washing, reslurry, separation, washing, dewatering, and drying. This is because the reaction medium contains the catalysts cobalt, manganese, and bromine, and the separation and washing using only a commonly used centrifugal separator or rotary drum filter can reduce the residual amount of adhered impurities. In many cases, the quality required for the product cannot be satisfied. Therefore, there is a problem that the construction cost of the equipment is high and the operation is complicated.

On the other hand, there has been proposed a method of separating and cleaning terephthalic acid using a belt filter, which is an industrial technique for horizontal filtration and cleaning. JP-T-7-507291 is characterized in that crude terephthalic acid obtained by oxidation of para-xylene and terephthalic acid obtained by hydrogenating and purifying crude terephthalic acid are separated under pressure. The hydrorefining is an operation in which crude terephthalic acid is brought into contact with hydrogen under a high temperature and a high pressure to reduce at least a part of impurities to chemically reduce the impurities. This is intended to prevent components dissolved in the reaction medium after hydrogenation purification from becoming supersaturated at the time of separation and to prevent precipitation, thereby reducing product quality and preventing filter clogging. Then, a centrifugal decanter is used to separate the crude terephthalic acid used in the hydrogenation purification from the reaction medium. Therefore, it is not intended to remove an adhering catalyst component such as an oxidation reaction catalyst from the product terephthalic acid.

Japanese Patent Publication No. Hei 8-508194 describes that a slurry containing hydrogenated and purified terephthalic acid is subjected to two-stage high-temperature pressure separation, and that the separated filtrate is recovered and circulated. . This is characterized in that the load on the effluent can be reduced, the processing process can be saved, and the contamination by by-products can be reduced. However, there is no effect of reducing the adhesion catalyst component of the oxidation reaction catalyst system of terephthalic acid.

Further, in Japanese Patent Application Laid-Open No. 5-65246,
The crude terephthalic acid after the main oxidation reaction is separated using a belt filter, washed with an aqueous medium, the separated reaction medium is recycled to the main oxidation reaction, and the crude terephthalic acid crystals are mixed with the aqueous medium again to form a reslurry. It is characterized by: The use of the aqueous medium for the washing liquid is disadvantageous for a method of performing separation, washing, and drying processes without reslurrying. Because the heat of evaporation of acetic acid is 4
Heat of evaporation of water is 2260 kJ / k against 07 kJ / kg
In g, the use of an aqueous medium requires a greater amount of heat for drying than the use of acetic acid for washing.

Further, Japanese Patent Publication No. Hei 8-506049 discloses that terephthalic acid is filtered and washed using a movable filter material, and a solvent such as acetic acid is removed in a first zone of the filter material. The solvent and the cleaning agent are removed with a cleaning agent such as water in two zones, and in the second zone and / or a region downstream thereof,
By supplying gas so as to penetrate through the filter medium, under such conditions that the degree of gas contamination in the direction of movement of the filter medium is reduced, the cake contamination by impurity vapors such as solvents present in the gas is reduced. Features. It does not describe a method for reducing the catalyst component attached to the terephthalic acid cake.

[0007]

SUMMARY OF THE INVENTION The present inventors have proposed a method of separating and washing precision terephthalic acid using a horizontal filtration washing method, preferably a belt filter, and using a lower aliphatic carboxylic acid solvent for washing. It has been found that impurities such as cobalt used as a catalyst in the acid are significantly reduced as compared with the case where other filtration methods are used. This is an effect produced by combining the horizontal filtration washing method with a washing mechanism that can wash the cake uniformly, and the feature that the fine terephthalic acid particles have small pores and a smooth surface. It is considered to be. In other words, the horizontal filtration washing method such as a belt filter applies a washing liquid on a cake formed horizontally,
In the washing section, the washing liquid spreads over the entire surface of the cake, and unevenness in washing of the cake is greatly reduced. The coarse terephthalic acid particles have many pores and the particle surface has many irregularities. When a series of precision oxidation processes such as additional oxidation, re-addition oxidation, and crystallization are performed, the particles are dissolved and recrystallized to form smooth particles with few pores, and the catalyst and reaction medium attached to the surface are removed. It is easy to fall. Moreover, since the inside of the particles has a dense structure, the reaction medium taken in the inside of the particles is removed, and the content of the catalyst component inside the particles is also reduced. Therefore, the use of a belt filter that can perform horizontal filtration washing enables cake washing to be performed homogeneously.As a result, when removing adhered impurities, differences due to differences in particle properties become remarkable, and precision terephthalic acid is removed. Has the effect of reducing deposits to very low levels compared to crude terephthalic acid and compared to other filtration methods.

As a result, the separation step can be omitted with a limited amount of washing liquid while maintaining the quality. In other words, while the conventional separation process involved complicated operations such as separation, washing, reslurry, separation, washing, dewatering, and drying, a simplified process such as separation, washing, dewatering, and drying was performed. It has become possible. Furthermore, it has become possible to reduce the load on incidental equipment by reducing the amount of washing liquid used, and to reduce costs by reducing the accompanying catalyst.

[0009]

That is, the gist of the present invention resides in a method for producing an aromatic carboxylic acid, comprising the following steps: In the first reaction zone, a main oxidation step of subjecting alkylbenzene to liquid phase oxidation with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid solvent in the presence of a catalyst to obtain a slurry containing an aromatic carboxylic acid. In the second reaction zone, the reaction mixture obtained by the reaction is superoxidized with a molecular oxygen-containing gas without supplying alkylbenzene, to obtain a crude slurry containing a crude aromatic carboxylic acid. In the third reaction zone at a temperature higher than the second reaction zone, without additional alkylbenzene, to re-oxidize the reaction mixture with a molecular oxygen-containing gas to obtain a purified slurry containing a purified aromatic carboxylic acid. The re-supplementation step of obtaining the purified slurry obtained by the re-post-oxidation reaction, the crystallization step of lowering the temperature to an appropriate temperature and pressure, the purified slurry after the crystallization step, The purified aromatic carboxylic acid separated on the filter is supplied to a filter having a filtration surface in a substantially horizontal direction, and the purified aromatic carboxylic acid is separated from the purified slurry by a lower carboxylic acid solvent. Washing step of washing The drying step of drying the washed purified aromatic carboxylic acid to obtain a product aromatic carboxylic acid

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, the alkylbenzene used as a raw material is an alkylbenzene such as a mono-, di-, or trialkylbenzene that is converted into an aromatic carboxylic acid such as an aromatic monocarboxylic acid, an aromatic dicarboxylic acid, or an aromatic tricarboxylic acid by liquid phase oxidation. And those in which a part of the alkyl group is oxidized. In particular, the method of the present invention is preferably applied to the production of terephthalic acid. In this case, the starting material alkylbenzene includes para-xylene.

Hereinafter, the present invention will be described in detail using a method for producing terephthalic acid using para-xylene as an example.
Acetic acid is preferred as the lower aliphatic carboxylic acid solvent,
The amount of the solvent to be used is usually 2 to para-xylene starting material.
6 times the weight. The acetic acid solvent may contain a small amount of water, specifically, 10% by weight or less. The water concentration in the reaction system is usually 5 to 25% by weight, preferably 7 to 25% by weight.
The water concentration can be adjusted by a conventional method, that is, by purging a part of the condensed reflux liquid obtained by condensing the gas volatilized from the reactor out of the system.

As the molecular oxygen-containing gas, air, dilution air, oxygen-enriched air and the like are used, but air is desirable from the viewpoint of equipment and cost. As a catalyst,
A catalyst containing cobalt, manganese, and bromine as constituent elements, and specific compounds of the catalyst component include, for example, cobalt acetate, cobalt naphthenate, and cobalt bromide. Examples of the manganese compound include manganese acetate, manganese naphthenate, and manganese bromide. Examples of the bromine compound include hydrogen bromide, sodium bromide, cobalt bromide, manganese bromide, and bromoethane. These compounds may be used in combination as a compound of each component. Further, other metal components may be present in the acetic acid solvent. For example, when the sodium component is present in the reaction system in an amount of 1 ppm or more and 100 ppm or less, there is an effect of preventing precipitation of a manganese component, and an effect of improving the transmittance, which is one of the evaluation methods of the obtained product terephthalic acid. .

The amount of the catalyst used is such that the cobalt component is 100 ppm by weight or more relative to the solvent,
0 ppm by weight or less, preferably 200 ppm by weight or more,
It is 1000 ppm by weight or less. The amount of the manganese component to be used is 1 to 1000 ppm by weight, preferably 5 to 500 ppm by weight. The used amount of the bromine component is 400 ppm or more and 2000 ppm or less.

Further, a co-oxidizing agent can be used in combination to promote the reaction. Examples of the co-oxidizing agent include aldehyde compounds such as acetaldehyde, ketone compounds such as methyl ethyl ketone, and ester compounds such as propyl acetate. The reaction mother liquor contains reaction intermediates such as 4-carboxybenzaldehyde, paratoluic acid, and paratolualdehyde, and impurities such as benzoic acid.

Further, in order to increase the partial pressure of oxygen in the gas phase of the reaction system in the oxidation reaction in the first reaction zone, the oxidation exhaust gas obtained by condensing and removing condensable components from the gas extracted from the reactor is separated into two parts. It is also possible to use a method of branching into a stream, discharging one to the outside of the system, and continuously circulating the other to the reactor. In the oxidation reaction of the first reaction zone, 140 ° C. in an acetic acid solvent in the presence of a catalyst containing cobalt, manganese, and bromine.
95% or more of para-xylene is oxidized while continuously supplying a molecular oxygen-containing gas at a temperature of from 230 to 230C, preferably from 150 to 210C. The reaction pressure is at least a pressure at which the mixture can maintain a liquid phase at the reaction temperature, and is usually 0.2 to 5 MPa. The oxidation reaction time (average residence time) is usually 30 to 300 minutes.

Next, at 130 ° C. to 240 ° C., preferably 14 ° C.
0 ° C to 220 ° C, more preferably 160 ° C to 200 ° C
In the second reaction zone, low-temperature re-oxidation is performed with molecular oxygen without adding para-xylene. The reaction time (average residence time) of the low temperature additional oxidation is usually 20 to 90 minutes. Then, a temperature of 150 to 300 higher than the second reaction zone is used.
In the third reaction zone at a temperature of 200 ° C., preferably 200 ° C. to 280 ° C., the re-postoxidation is carried out with molecular oxygen without adding para-xylene. Re-oxidation reaction time (average residence time)
Is usually 5 to 120 minutes.

Next, the crystallization step involves lowering the re-oxidized purified slurry to an appropriate temperature and pressure to obtain a purified aromatic carboxylic acid slurry. The number of crystallization stages is preferably 1
To 6 stages, more preferably 2 to 4 stages, for example, 3 stages. Next, in the present invention, the aromatic carboxylic acid slurry obtained through the crystallization step is supplied to a filter having a filtration surface in a substantially horizontal direction, and after the reaction mother liquor is separated, further lower aliphatic Washed with carboxylic acid solvent. This separation and washing step can be achieved, for example, by using a Buchner funnel or a belt filter. In particular, it is suitable for continuous commercial operation,
Preferably, a belt filter is used.

Hereinafter, the separation and washing steps when a belt filter is used will be described with reference to FIG. In addition,
FIG. 1 is only an example, and the belt filter is a driven endless belt or a filter medium (10), a suction tray installed below the filter medium (first zone: 14, second zone: 17,
Third zone: 20), slurry supply nozzle (13), cleaning liquid supply nozzle (16), sealed housing (1)
9) and a device (not shown) for driving the equipment.

In the present invention, the filter used for separation and washing has a filtration surface substantially in the horizontal direction. However, even if the filter is displaced from the horizontal direction as long as separation and washing are not extremely impaired. good. For example, if it is about ± 10 degrees from the horizontal direction, there is no big problem. The belt or filter material is preferably a metal gauze (thin metal such as gauze) or a woven fabric made of an organic material such as, for example, polyester fibers or polypropylene fibers. Belt or filter media,
It is preferably a continuous belt or a filter medium, which moves continuously or intermittently to form a cake mainly composed of terephthalic acid,
The signal is conveyed from the first band to the third band through the second band.
Then, a pressure difference is provided between the front surface and the back surface of the belt or the filtering material by the suction tray, and the pressure on the surface of the belt on which the slurry is deposited is made higher than that of the back surface of the belt. Preferably, the differential pressure should be at least 0.005 MPa (absolute pressure) and should not exceed the pressure at which additional oxidation is performed, for example, 5 MPa (absolute pressure). Preferably, the pressure difference is 0.01-1.5 MPa in absolute pressure, more preferably 0.02
To 0.7 MPa, particularly preferably 0.03 to 0.3 MPa
a, for example, 0.06 MPa. The actual pressure on the low pressure side of the belt or filter media is maintained at a pressure such that the reaction medium and the wash media removed through the belt or filter media remain in the liquid phase in effect. In addition, it is also possible to further divide the suction tray as necessary and change the pressure of each.

The slurry supply temperature is at least 60 ° C.
The temperature is preferably from 70 ° C to 200 ° C, particularly preferably from 80 ° C to 150 ° C. Feed slurries are advantageous because at elevated temperatures the viscosity of the reaction medium is reduced, allowing for improvements in filtration rate and impurity deposition. The transfer speed of the belt or the filter medium is determined by the throughput and the cake thickness. However, if it is too fast, the operation of the device will be inefficient,
Preferably it is 10 cm / s or less. If the cake thickness is too thin, cracks are liable to occur, and if the cake thickness is too thick, transfer by a belt or a filtering material becomes impossible by its own weight. Therefore, the cake thickness is preferably 10 to 90 mm, particularly preferably 3 to 90 mm.
0 to 70 mm.

The housing is hermetically sealed and filled with an inert gas. The inert gas is preferably nitrogen or the inert gas used in the reaction. An example of the progress of the separation and washing process using such a belt filter is as follows. The purified slurry whose temperature and pressure have been appropriately adjusted is discharged to the first zone of the belt filter, and separated for removing the reaction medium. The separated wet cake is transferred to the second zone of the belt filter, and a reaction medium such as acetic acid is supplied to the wet cake as a washing liquid, and at the same time, the washing liquid is removed by filtering. The washed wet cake is transferred to the third zone of the belt filter and drained. The removal of the reaction medium, the removal of the washing liquid, and the drainage are performed by the pressure difference between the front and back surfaces of the belt or the filter.
The liquid content of the wet cake by draining in the third zone is
0.05 to 0.20 in weight ratio to the cake after drying,
Desirably, it is adjusted to 0.05 to 0.15, for example, about 0.10.

The method of spraying the cleaning liquid includes a co-current flow and a counter-current flow, but the co-current flow is desirable because the apparatus is simplified. The cleaning liquid is uniformly sprayed in a direction perpendicular to the traveling direction of the belt or the filter medium. The spraying method includes a method in which the cleaning liquid overflows from a cleaning liquid tray provided above the belt or the filtering material, a method in which the cleaning liquid is sprayed from a spray nozzle, and the like. The spraying of the cleaning liquid is performed in one or a plurality of rows in a direction perpendicular to the traveling direction of the belt or the filtering material, but is preferably performed in two to three rows in order to improve the cleaning effect.
The amount of the washing liquid is preferably 0.2 or more, more preferably 0.4 to 1.2, for example, 0.8 in weight ratio to the dry cake. If the amount of the cleaning solution is small, the effect of the cleaning is sharply reduced. As a cleaning liquid, a liquid mainly containing a reaction solvent (for example, acetic acid) recovered by reducing the water content (up to a water content of about 7%) of the exhaust gas of the oxidation reactor by distillation, or condensation of the exhaust gas from the process of the present invention. For example, a reaction medium recovered by the above method, for example, a recovered liquid of the evaporation solvent from the reaction tank and the crystallization tank is used.

From the purified slurry that has undergone the crystallization step, the reaction medium is separated and recovered, and this is divided into two streams, one of which is led to a distillation step, and the reaction medium and catalyst are recovered. The other is reused again as the reaction medium for the oxidation reaction. The washing liquid was separated and collected after spraying on the wet cake.
One is directed to a distillation step to recover the washing liquid and the catalyst, and the other is reused as a reaction medium. However, the recovered liquid of the washing liquid is smaller than the recovered liquid from the crystallization step.
Because of the small amount of impurities contained, more can be reused as the reaction medium.

The wet cake that has passed through the third zone of the belt filter is separated and recovered from the belt or the filter. If necessary, it can be scraped off by a scraper. The collected wet cake was transferred to a dryer, and the liquid content was 0.01% by weight based on the dry cake.
Hereinafter, it is dried to preferably 0.00001 to 0.005, more preferably 0.00005 to 0.001, for example 0.0007.

[0025]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the examples unless it exceeds the gist thereof. In the examples, “parts” means “parts by weight based on the dry cake”.

Example 1 In a liquid phase oxidation reactor, para-xylene, acetic acid, cobalt acetate, manganese acetate 3.7 times by weight of para-xylene,
Supply hydrogen bromide, temperature 175 ° C, pressure 14.0kgf
The oxidation reaction was performed at a rate of G / cm ² and a reaction time (average residence time) of 125 minutes (main oxidation reaction). In order to simulate a method in which the ratio of the exhaust gas returned to the reactor to the exhaust gas discharged outside the system after separating the condensed components from the exhaust gas extracted from the oxidation reactor is 1: 1, 82.7 Nm ³ / air of air is used. hr,
Nitrogen 64.0 Nm ³ / hr was supplied to the oxidation reactor. The amount of the catalyst used is such that the amount of the cobalt component is equivalent to 850 ppm by weight of the solvent, the amount of the manganese component is 26 ppm by weight, and the amount of the bromine component is 850 ppm by weight, based on the weight of the solvent. . In addition, air is used as the molecular oxygen-containing gas, and the oxygen concentration in the reactor exhaust gas is 6%.
% Was fed into the reactor.

Next, the main oxidation reaction slurry was continuously transferred to a low-temperature post-oxidation reactor, at a temperature of 177 ° C. and a pressure of 12.
At 5 kgfG / cm ² and reaction time (average residence time) of 64 minutes, air is supplied as a molecular oxygen-containing gas so that the oxygen concentration in the exhaust gas becomes 6% by volume, and a mixture of crude terephthalic acid and the reaction medium is used. A crude slurry was obtained. This crude slurry was continuously transferred to the re-oxidation reactor, and the temperature was 255 ° C.
Pressure 55 kgfG / cm ² , reaction time (average residence time)
30 minutes, air 3Nm ³ / h as molecular oxygen-containing gas
Then, a re-supply oxidation reaction was carried out to obtain a purified slurry sample which was a mixture of precisely terephthalic oxide and a reaction medium.

The purified slurry sample was filtered by the following two-step parallel flow washing method and the procedure simulating the filtration method, and the washing property was evaluated. (See FIG. 2) A filter cloth was spread and fixed on a Buchner funnel over which the support grid was inserted, and this was attached to a filter bottle and connected to a vacuum pump.
A sample of the slurry warmed to 90 ° C. was fed to a Buchner funnel and filtered under reduced pressure (). A cylindrical container was mounted on the funnel over the filter cloth to hold the solid material deposit (). 0.4 parts of acetic acid heated to 90 ° C. was supplied to the sample () and filtered under reduced pressure (). Subsequently, an additional 0.4 parts of acetic acid was supplied (), and the liquid was drained (). This was placed in a dryer to remove volatile components, and the concentration of the cobalt catalyst remaining on the surface was analyzed.

Comparative Example 1 A part of the crude slurry after the post-oxidation in Example 1 was extracted, and filtered and washed in the same procedure as in Example 1 to simulate a two-stage cocurrent washing method and a filtration method. The sex was evaluated. The obtained cake was put into a dryer to remove volatile components, and the concentration of the cobalt catalyst remaining on the surface was analyzed. The results of Example 1 and Comparative Example 1 are summarized in Table 1 below. As a result, it is clear that the cleaning of the combination of the belt filter of the present invention and the precision terephthalic acid oxide is excellent, as is clear from the comparison of the cobalt adhering to TPA and the residual ratio.

[0030]

[Table 1] * Residual rate = 100 × (Cobalt adhering to TPA / (Cobalt in reaction medium × Liquid content / 100))

Example 2 In a liquid phase oxidation reactor, para-xylene, acetic acid, cobalt acetate, manganese acetate 5.5 times by weight of para-xylene were continuously added.
Supply hydrogen bromide, temperature 197 ° C, pressure 14.5kgf
The oxidation reaction was performed at G / cm ² and a reaction time (average residence time) of 90 minutes (main oxidation reaction). The amount of the catalyst used is such that the amount of the cobalt component is 28
0 weight ppm, the amount of manganese component used is 280 weight pp
m, the amount of bromine component used corresponds to 700 ppm.
Air was used as the molecular oxygen-containing gas and supplied into the reactor such that the oxygen concentration in the reactor exhaust gas became 5% by volume. Next, the main oxidation slurry was continuously transferred to a low-temperature post-oxidation reactor, and at a temperature of 190 ° C., a pressure of 13 kgfG / cm ² , and a reaction time (average residence time) of 35 minutes, air was used as oxidizing gas and the oxygen concentration in the exhaust gas was 6% by volume. And subjected to low temperature additional oxidation. The low temperature reoxidation slurry was continuously transferred to the reoxidation reactor, and the temperature was 255 ° C and the pressure was 46 kgfG / c.
Air was supplied as a molecular oxygen-containing gas at m ² and a reaction time (average residence time) of 30 minutes to perform a re-oxidation reaction.

The obtained purified slurry was continuously guided to a belt filter separator (see FIG. 1), and was subjected to two-stage washing to evaluate the washing property. The used belt filter has a suction tray having a width of 0.25 m and a length of 3.2 m including the first zone, the second zone, and the third zone. The tray is divided into respective zones by partitions. I have. Sealed outer shell (housing: 19), filter cloth (filter material) transfer motor (not shown), vacuum pump (not shown), filtrate recovery pump (not shown), suction tray driving cylinder (shown) ) And a control panel (not shown). 1. The filter cloth (filter material: 10) is moved by a transfer motor.
It is transported at a speed of 3 cm / s. When moving the suction tray in the direction of transport of the filter cloth, increase the friction with the filter cloth under reduced pressure and pull it by the driving force of the filter cloth.When returning, return to normal pressure and return the friction with the filter cloth. And the cylinder is driven in the opposite direction to the filter cloth. The moving distance (stroke) of the suction tray is 30 cm. The slurry is continuously fed onto a filter cloth and filtered by a vacuum suction tray to recover the reaction medium. The degree of pressure reduction was -0.4 bar, and the cake thickness on the filter cloth was 50 mm. The cake on the filter cloth was transferred to the next step together with the transfer of the filter cloth, and acetic acid was supplied from the fixed washing liquid spray tray at a supply rate of 0.4 times the weight of the cake passing per unit time by adjusting the supply rate. . The acetic acid supplied there is filtered by the action of the suction tray under reduced pressure, and the cake is transferred to the next step together with the transfer of the filter cloth. Therefore, acetic acid is again supplied from the fixed cleaning liquid spray tray so as to be 0.4 times the weight of the cake passing per unit time. Acetic acid is filtered by the action of the suction tray under reduced pressure, and the cake is transferred to the next step together with the transfer of the filter cloth. Then, the cake is dewatered by the action of the reduced pressure suction tray. The cake thus obtained was sampled, placed in a dryer to remove volatile components, and analyzed for the concentration of the cobalt catalyst remaining on the surface.

Example 3 In a liquid phase oxidation reactor, para-xylene, acetic acid, cobalt acetate, manganese acetate 5.5 times by weight of para-xylene were continuously added.
Supply hydrogen bromide, temperature 197 ° C, pressure 14.5kgf
The oxidation reaction was performed at G / cm ² and a reaction time (average residence time) of 90 minutes (main oxidation reaction). The amount of the catalyst used is such that the amount of the cobalt component is 28
0 weight ppm, the amount of manganese component used is 280 weight pp
The amount of the m and bromine components is equivalent to 700 ppm. Air was used as the molecular oxygen-containing gas and supplied into the reactor such that the oxygen concentration in the reactor exhaust gas became 5% by volume. Next, the main oxidation reaction slurry was continuously transferred to a low-temperature post-oxidation reactor, and the temperature was 190 ° C. and the pressure was 13 kgfG /
cm ² , the reaction time (average residence time) was 35 minutes, and the oxygen concentration in the exhaust gas was 6% by volume as the molecular oxygen-containing gas.
And subjected to low temperature additional oxidation. The obtained additional oxidation reaction slurry was continuously transferred to the additional oxidation reactor, and air was supplied as a molecular oxygen-containing gas at a temperature of 255 ° C., a pressure of 46 kgfG / cm ² , and a reaction time (average residence time) of 30 minutes to supply the air again. A re-oxidation reaction was performed to obtain a purified slurry sample which was a mixture of precisely terephthalic oxide and a reaction medium.

The same procedure as in Example 1 was repeated on this purified slurry sample to simulate a two-stage co-current washing procedure. The concentration of the cobalt catalyst remaining on the surface of the obtained sample was analyzed in the same manner as in Example 1.

COMPARATIVE EXAMPLE 2 Paraxylene, acetic acid, cobalt acetate, manganese acetate and hydrogen bromide were continuously supplied to a liquid phase oxidation reactor, and the temperature was 195.
An oxidation reaction was performed at a temperature of 1 ° C., a pressure of 14.5 kgfG / cm ² , and a reaction time (average residence time) of 65 minutes (main oxidation reaction). The amount of the catalyst used was such that the amount of the cobalt component was 350 ppm by weight of the solvent in terms of cobalt metal, the amount of the manganese component was 230 ppm by weight, and the amount of the bromine component was 770 p.
pm. Air is used as the molecular oxygen-containing gas, and the oxygen concentration in the exhaust gas from the reactor is 4% by volume.
And fed into the reactor. Next, the main oxidation reaction slurry was continuously transferred to a post-oxidation reactor, and the temperature was changed to 190.
C., pressure 11 kgfG / cm ² , reaction time (average residence time) 15 minutes, air was supplied as a molecular oxygen-containing gas so that the oxygen concentration in the exhaust gas became 2% by volume, and additional oxidation was performed. A sample of a crude slurry that was a mixture of terephthalic acid and the reaction medium was obtained.

The sample was filtered by the same procedure as in Example 1 simulating a two-stage co-current washing and filtration method. This was placed in a dryer in the same manner as in Example 1 to remove volatile components, and the concentration of the cobalt catalyst remaining on the surface was analyzed.
The results of Examples 2 and 3 and Comparative Example 2 are shown in Table 2 below.
It is summarized and shown. As a result, it is shown that the combination of precision terephthalic acid and horizontal filtration and washing such as a belt filter or a Buchner has a much better effect than the combination of crude terephthalic acid and a horizontal line.

[0037]

[Table 2]

[0038]

According to the present invention, it has been found that when the horizontal separation washing method is used for precision terephthalic acid, superior washing can be performed as compared with crude terephthalic acid. According to the present invention, the use of, for example, a belt filter in the precision terephthalic acid oxidizing process makes it possible to greatly simplify the equipment and reduce construction costs and operation costs. In addition, it is possible to reduce the load on incidental equipment by reducing the amount of washing liquid used, and to reduce costs by reducing the accompanying catalyst. This is a special effect resulting from the combination of separating the precision oxide terephthalic acid slurry by the horizontal separation washing method.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a belt filter that can be suitably used in horizontal filtration and washing in the present application. The belt filters used in Examples 2 and 3 and Comparative Example 2 are also of this type.

FIG. 2 is a diagram schematically showing a procedure for simulating a two-stage co-current cleaning method and a filtration method adopted in Example 1 and Comparative Example 1.

[Explanation of symbols]

10: filter medium (filter cloth), 11: filter medium drive roller,
13: slurry supply nozzle, 16: cleaning liquid supply nozzle,
14: suction tray (first zone), 17: suction tray (second zone), 20: suction tray (third zone), 19: housing, 21: suction nozzle (first zone), 22: suction nozzle (first zone) 2), 23: suction nozzle (3rd zone), 2
5: Cake collection port

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C07C 51/487 C07C 51/487 // C07B 61/00 300 C07B 61/00 300

Claims (5)

[Claims] 1. A method for producing an aromatic carboxylic acid comprising the following steps: In the first reaction zone, a main oxidation step of subjecting alkylbenzene to liquid phase oxidation with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid solvent in the presence of a catalyst to obtain a slurry containing an aromatic carboxylic acid. In the second reaction zone, the reaction mixture obtained by the reaction is superoxidized with a molecular oxygen-containing gas without supplying alkylbenzene, to obtain a crude slurry containing a crude aromatic carboxylic acid. In the third reaction zone at a temperature higher than the second reaction zone, without additional alkylbenzene, to re-oxidize the reaction mixture with a molecular oxygen-containing gas to obtain a purified slurry containing a purified aromatic carboxylic acid. The re-supplementation step of obtaining the purified slurry obtained by the re-post-oxidation reaction, the crystallization step of lowering the temperature to an appropriate temperature and pressure, the purified slurry after the crystallization step, The purified aromatic carboxylic acid separated on the filter is supplied to a filter having a filtration surface in a substantially horizontal direction, and the purified aromatic carboxylic acid is separated from the purified slurry by a lower carboxylic acid solvent. Washing step of washing The drying step of drying the washed purified aromatic carboxylic acid to obtain a product aromatic carboxylic acid 2. The method for producing an aromatic carboxylic acid according to claim 1, wherein the separation step and the washing step are performed using a belt filter. 3. The method for producing an aromatic carboxylic acid according to claim 1, wherein the alkylbenzene is para-xylene. 4. The method for producing an aromatic carboxylic acid according to claim 1, wherein the lower aliphatic carboxylic acid solvent is acetic acid. 5. The method for producing an aromatic carboxylic acid according to claim 1, wherein the molecular oxygen-containing gas supplied to the oxidation step is air.