The present invention relates to a method for recovery of an oxidation catalyst.
The present invention relates to a method for high-yield recovery of an oxidation catalyst typified by cobalt, manganese and bromine from a mother liquor used in the oxidation of alkyl aromatic compounds in the manufacture of aromatic carboxylic acids typified by terephthalic acid.
In the manufacturing process of terephthalic acid, which is well known as an SD method, p-xylene is oxidized with air under the conditions that a cobalt compound, a manganese compound, a bromine compound or like is used as an oxidation catalyst and an aquous acetic acid solution is used as a reaction solvent, to prepare terephthalic acid. After the reaction, the resulting terephthalic acid slurry is subjected to centrifugal separation for solid-liquid separation. The separated terephthalic acid cake is dried to obtain a crude terephthalic acid. On the other hand, the mother liquor used in the oxidation is recycled to an oxidation reactor and is recycled. The oxidation of p-xylene is performed in any one of a batch mode, a

semicontinuous mode and a continuous mode, but is generally performed in the continuous mode in view of productivity.
The oxidation of p-xylene produces a colored polymer typified by dicarboxyfluorenone, in addition to an unreacted intermediate derived from p-xylene, such as p-toluic acid and 4-carboxybenzaldehyde. As a result, these impurities are also contained in the crude terephthalic acid to cause deterioration in quality. Therefore, in a known manufacturing method, a portion of the oxidation mother liquor recycled to the oxidation reactor is continuously removed via a catalyst recovery process outside the oxidation reaction system to the outside of the manufacturing process and thus the accumulation of impurities in the reaction system is controlled to a constant level or less.
As disclosed in JP-B-53-28420/1978, when an oxidation catalyst is recovered by a continuous process, a portion of a filtrate is recycled to the oxidation reaction system, but the other part of the filtrate is brought into contact under stirring with water in a proportion of 2 to 5 folds in mass, based on the amount of the residue obtained by concentration, the catalyst is extracted and organic impurities such as benzole acid in the molten state are solidified and granulated by rapidly cooling from 50 to 20°C, and then an

aqueous catalyst solution is separated from the granulated organic impurities to recycle the obtained aqueous catalyst solution to the oxidation reaction system. However, in the recovery process of the catalyst according to JP-B-53-28420/1978, the recovery rate of the catalyst is low because extraction of the catalyst and granulation of the residue are simultaneously performed in one stirring tank and the extraction temperature is limited to low temperature suitable for granulation.
On the other hand, as disclosed in JP-A-2004-321889 and USP 2,964,559, when an oxidation catalyst is recovered by a batch process, extraction of the catalyst in a high temperature field and granulation of the residue in a low temperature field are consecutively performed in one stage-stirring tank. At this time, it can be shown that it is advantageous for the extraction of the catalyst to raise the temperature of a hot water slurry obtained by suspending the residue with water at high temperature. In USP 2,964,559, it is recommended to employ the temperature conditions of 100°C or higher. Water is further added to the hot water slurry and then the resulting mixture is slowly cooled to 60°C or less, preferably 50°C or less under stirring, but granulated particles formed by these processes are likely to form fine powders by fragmentation or abrasion. Therefore,

this method has defects that solid-liquid separability of the granulated slurry is not good and the loss of the aqueous catalyst solution into the solid residue is increased. Further, the large-scale production of terephthalic acid is mostly performed in a continuous mode in view of productivity and thus the catalyst recovery process is often performed in the above-mentioned continuous mode than a batch mode.
Further, the aqueous catalyst solution is also subjected to a pretreatment by various methods before recovering to an oxidation process of p-xylene. Most simply, the aqueous catalyst solution is concentrated under heating and the heavy metal catalyst and the bromine catalyst are recovered to the oxidation process. Furthermore, as disclosed in JP-A-5-15788/1993 and JP-B-56-25195/1981, only the heavy metal catalyst contained in the aqueous catalyst solution is recovered as carbonates.
SUMMARY OF THE INVENTION
However, even in the case of the above-mentioned continuous mode catalyst recovery method, during the granulation treatment,- a portion of an oxidation catalyst becomes captured in the inside of solid residue particles, i.e., captured catalyst species and cannot be physically

contacted with an aqueous phase to thus inevitably result in loss in the catalyst recovery. It was not always set to the temperature suitable for the catalyst recovery since the treatment temperature conditions are limited to those suitable for granulation. Therefore, in the granulation treatment, the granulated slurry is stirred over a long period of time and the pulverization of the residue particle group is facilitated and thus the contactability of captured catalyst species with the aqueous phase can be improved. However, it has been a problem that this pulverization of the residue particle group deteriorates the solid-liquid separability of the granulated slurry, and hence the amount of the aqueous catalyst solution contained in the solid residue increases and the recovery rate of the oxidation catalyst is not improved. Further, of bromine catalysts contained in the oxidation mother liquor, an organic bromine compound constituting most thereof is almost not dissolved in the aqueous phase of the granulated slurry. Therefore, in the case of recovering to the oxidation process of p-xylene after concentrating the aqueous catalyst solution under heating, it has been a problem that the recovery rate of the bromine catalyst in the catalyst recovery process is extremely low as about 30% as compared to the recovery rate of the heavy metal catalyst such as cobalt and manganese of

approximately 80% or more.
The present inventors have studied intensively various measures to solve the above-mentioned problems of the catalyst recovery process. As a result, they have found that a method for recovery of an oxidation catalyst from a concentrate (residue) obtained by concentrating under heating an oxidation mother liquor in the manufacture of aromatic carboxylic acids comprising liquid phase oxidation of alkyl aromatic compounds with molecular oxygen in a reaction solvent containing a lower aliphatic carboxylic acid in the presence of the oxidation catalyst, said method comprising the steps of:a hot water treatment of the concentrate with stirring, and then
a granulation treatment of the hot water slurry obtained with stirring to obtain a granulated slurry,
wherein the hot water treatment and the granulation treatment are carried out in separate stirring tanks, and
a solid-liquid separation of the granulated slurry obtained so as to recover an aqueous catalyst solution containing the oxidation catalyst,
thereby greatly improving the recovery rate of the oxidation catalyst, and thus have reached the present invention.
In the method for recovery of the oxidation catalyst, a

stirring tank for a hot water treatment (hereinafter, sometimes abbreviated to a hot water treatment stirring tank) and a stirring tank for a granulation treatment (hereinafter, sometimes abbreviated to a granulation treatment stirring tank) are arranged in tandem.
Further in the invention, other hot water treatment stirring tanks, the granulation treatment stirring tanks or the like may be used if necessary, in addition to the above-mentioned hot water treatment stirring tank and the above-mentioned granulation treatment stirring tank.
More specifically, the invention provides a method for recovery of an oxidation catalyst using a continuous hot water treatment/granulation process with the use of at least two stage continuous stirring tanks in tandem, which comprises continuously feeding the concentrate and water to the hot water treatment stirring tank to carry out a hot water treatment and then continuously feeding the slurry obtained after carrying out the hot water treatment and water to the granulation treatment stirring tank to carry out a granulation treatment.
Furthermore, other recovery systems may be arranged in parallel, in addition to a recovery system comprising the above-mentioned hot water treatment stirring tank and the above-mentioned granulation treatment stirring tank which

are arranged in tandem.
According to the invention, the hot water treatment is carried out under strong stirring at the temperature of 65 to 300°C, preferably 70 to 150°C, more preferably 80 to 150°C, particularly preferably 80 to 120°C for 10 to 300 minutes, preferably 10 to 150 minutes, more preferably 15 to 150 minutes, even more preferably 30 to 100 minutes in a hot water treatment stirring tank to which water is fed in a proportion of 0.1 to 10 folds in mass, preferably 0.25 to 5 folds in mass, more preferably 0.5 to 5 folds in mass, and even more preferably 0.5 to 1 fold in mass, based on the amount of the concentrate.
Further, the granulation treatment is carried out by stirring at 20 to 60°C, preferably 30 to 50°C for 5 to 120 minutes, preferably 10 to 30 minutes while adding water in a proportion of 0.1 to 10 folds in mass, preferably 0.2 to 8 folds in mass, and more preferably 0.5 to 5 folds in mass, based on the amount of the slurry obtained after carrying out the hot water treatment. The granulated slurry continuously obtained is subjected to solid-liquid separation and an aqueous solution containing a catalyst is recovered.
Furthermore, the oxidation catalyst is a liquid phase oxidation catalyst of alkyl aromatic compounds.

Further, the oxidation catalyst is a cobalt compound, a manganese compound and a bromine compound.
The aromatic carboxylic acid is terephthalic acid.
According to the invention, the oxidation catalyst, which is captured in the inside of the solid residue particles and thus cannot be extracted in the aqueous phase in a known continuous mode catalyst recovery method, can be dissolved in a hot aqueous phase by the hot water treatment which is carried out in the temperature range capable of melting the solid residue. Further, of organic bromine
compounds contained in the concentrate, a-bromomethylbenzoic acid constituting most thereof is hydrolyzed by contacting with a hot aqueous phase to convert into inorganic bromine. Specifically, an essentially water-insoluble organic bromine compound can be converted into a water-soluble one and therefore most of the organic bromine compound can be dissolved in the hot aqueous phase as an inorganic bromine compound. Most of the heavy metal catalyst or bromine catalyst dissolved in the hot aqueous phase is also transferred to an aqueous phase during the granulation treatment and thus the recovery rate of the oxidation catalyst can be comprehensively improved.
In a conventional continuous mode catalyst recovery process, the recovery of the catalyst and granulation are

simultaneously carried out and hence a long period of time is required for improving the recovery rate of the oxidation catalyst, and thus the granulation time is also increased. By contrast, according to the invention, the granulation process takes a short time because the extraction of the oxidation catalyst to the aqueous phase is completed by a hot water treatment which is carried out at 65 to 300°C before the granulation of the solid residue.
Further, in a conventional batch mode recovery process, the catalyst-extracted hot slurry is cooled up to the temperature carrying out the granulation in one stage-stirring tank and thus the cooling time is relatively long and granulated particles in the form of fine powders are likely to be formed by pulverization or abrasion during cooling.
By contrast, according to the invention, the slurry subjected to the hot water treatment at 65 to 300°C in the hot water treatment stirring tank is then transferred to the granulation treatment stirring tank and the temperature is instantaneously dropped and thus the pulverization of the granulated particles is minimized during cooling. As a result, the pulverization of the granulated slurry particle group is suppressed as much as possible, the granulated slurry having less fine particles and excellent solid-liquid

separability can be prepared, and the accompanying loss of the aqueous catalyst solution into the solid residue can be reduced and therefore the recovery rate of the catalyst can be improved synergically together with the catalyst recovery effects described in the preceding paragraph.
According to the invention, in the method for the production of aromatic carboxylic acids comprising liquid phase oxidation of alkyl aromatic compounds with molecular oxygen in a reaction solvent containing a lower aliphatic carboxylic acid in the presence of the heavy metal catalyst and the bromine catalyst, the loss of the oxidation catalyst due to the oxidation catalyst contained in the solid residue can be greatly reduced and environment load in the residue treatment can be reduced by decreasing the content of harmful matters such as heavy metal and halogen in the residue, thereby providing an extremely economic, low environment load and industrially advantageous method.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing the outline of a conventional
catalyst recovery method;, and
Fig 2 is a view showing the outline of a catalyst
recovery method according to the present invention.

(Reference Numerals) 1: Oxidation mother liquor; 2: Evaporator; 3: Mixing gas of acetic acid and water; 4: Concentrate; 5: Stirring tank; 6: Water; 7: Hot water slurry; 8: Stirring tank; 9:Water; 10: granulated slurry; 11: Solid-liquid separator; 12: Aqueous catalyst solution; 13: Solid residue DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be specifically explained. In the invention, an aromatic compound having an alkyl-substituted group or partially oxidized alkyl-substituted group is used as raw materials. Examples of the alkyl-substituted group used include one having usually about 1 to 8 carbon atoms, preferably 1 to 3 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group and an isopropyl group. Examples of the partially oxidized alkyl-substituted group include one having usually 1 to 8 carbon atoms, such as a formyl group, a carboxyl group and a hydroxyl group. These alkyl-substituted groups may be substituted not only with one substituent but also with two or more substituents. In addition, each substituent may be the same or different when the alkyl-substituted groups have plural substituents. The aromatic nucleus includes not only a monocyclic aromatic nucleus such as a benzene ring but also a polycyclic aromatic nucleus such as naphthalene.

Examples of the aromatic compound containing the alkyl group or partially oxidized alkyl-substituted group include an aromatic compound having an alkyl-substituted group, such as toluene, ethylbenzene, isopropylbenzene, 4,4'-dimethylbiphenyl, o-, m- or p-xylene, 1,2,4-trimethylbenzene or 2,6-dimethylnaphthalene, or a mixture thereof, but are not limited to these.
Of methods for the production of aromatic carboxylic acids at which the invention is aimed, the most typical example thereof is a process for producing terephthalic acid through liquid phase oxidation of p-xylene using an oxidation catalyst such as cobalt, manganese and bromine.
Hereinafter, the invention will be particularly explained with reference to the production of terephthalic acid, but the invention itself can be applied in the production of aromatic carboxylic acids using other raw material compounds, except that reaction conditions are suitably set.
Terephthalic acid is produced by liquid phase oxidation of p-xylene with a molecular oxygen-containing gas (namely air for industrial scale) using, as a catalyst, a cobalt compound or a manganese compound, or a mixture thereof, and preferably halogen, in particular a bromine compound as a co-catalyst. Examples of the cobalt compound and the

manganese compound include organic acid salts such as acetate, propionate and naphthenate; organic complexes such as acetylacetonate complexes, carbonyl complexes and ammine complexes; a halide such as chloride and bromide; a hydroxide; and an inorganic acid salt such as borate, nitrate and carbonate. Among these, the most suitable catalyst is acetate. The bromine compound is usually used as the co-catalyst. As a reaction accelerator, acetaldehyde, methyl ethyl ketone, p-aldehyde or like may be used or may be used in combination with the bromine compound. Examples of the bromine compound include bromine, hydrogen bromide, ammonium bromide, an alkali metal bromide such as sodium bromide, lithium bromide and potassium bromide, and an organic bromine compound such as tetrabromoethane, bromoacetate and benzyl bromide. Among these, the most suitable co-catalyst is hydrogen bromide.
The amount of each of the cobalt compound and the manganese compound to be used is adjusted in the range of usually 10 to 5000 ppm, preferably 20 to 2000 ppm, more preferably 50 to 1000 ppm, based on the solvent. The amount of the bromine compound to be used is adjusted in the range of usually 10 to 10000 ppm, preferably 20 to 5000 ppm, more preferably 50 to 2000 ppm, based on the solvent.
As the oxidation mode of p-xylene, any one of a batch

mode, a semicontinuous mode and a continuous mode may be used. In general, the continuous mode is used in view of productivity. The reaction conditions employed in the invention include temperatures of usually 160 to 260°C, preferably 170 to 220°C and pressures of 0.4 to 5 MPa (gauge pressure), preferably 0.5 to 2 MPa (gauge pressure). The residence time used is 10 to 200 minutes, preferably 30 to 120 minutes. Examples of the molecular oxygen-containing gas used include pure oxygen, air or a mixture of oxygen with an inert gas, but usually air is used for molecular oxygen-containing gas, which is fed in the range of 0.1 to 5 Nm3 (reduced value at 0°C and 1 atm) per 1 kg of p-xylene.
The reaction solvent used in the invention is preferably a lower aliphatic carboxylic acid, particularly preferably acetic acid or a mixture of acetic acid and water. Further, when the reaction solvent contains water, the water content in the reaction solvent is preferably 20% by mass or less. Furthermore, the reaction solvent is preferably used in a proportion so that the concentration of alkyl aromatic compounds as raw materials is 1 to 50% by mass, based on the amount of the reaction solvent.
The terephthalic acid produced by oxidation is usually solid-liquid separated by crystallization and centrifugation from the oxidation mixture, is dried and then is recovered

as a product. Further, an unreacted intermediate may be further subjected to an oxidation treatment prior to crystallization and subjected to a purification treatment to produce terephthalic acid. The separated oxidation mother liquor contains the catalyst component and therefore is circulated to the oxidation reactor and is recycled. Herein, a portion of the oxidation mother liquor is removed as the solid residue from the oxidation reaction system via the process for recovery of the catalyst to the outside of the process.
Hereinafter, the outline of the known continuous mode catalyst recovery method will be explained with reference to the accompanying drawing (Fig. 1).
The oxidation mother liquor (1) is concentrated in an evaporator (2) under atmosphere pressure at 105 to 230°C, preferably 110 to 130°C. The resulting mixture gas (3) of acetic acid and water is cooled and then is recycled in the oxidation process as the aqueous acetic acid solution. This concentration process may be carried out in single-stage or in multi-stages for improving the recovery rate of acetic acid. The concentrate (4) is fed to a continuous stirring tank (5) to which water is added, and thus the solid residue is granulated. The stirring tank (5) is usually provided with a temperature-controlling jacket and the granulation

temperature is controlled by the temperature or flow rate of a heat medium fed to the jacket, or the temperature or flow rate of water (6). In this case, the flow rate of water (6) may be the minimum required for obtaining a sufficient catalyst extraction rate and is suitable in a proportion of 0.1 to 10 folds in mass, preferably 0.5 to 5 folds in mass, based on the amount of the concentrate (4). The type of the stirring blade used in the stirring tank (5) is not limited as long as it is suitable for mixing the slurry. Further, in order to improve stirring effects, the stirring tank (5) may be equipped with a baffle plate or it is also effective to increase the stirring speed. The granulation temperature is controlled to 20 to 60°C, preferably to 30 to 50°C that an aromatic organic acid (benzoic acid) mainly constituting the concentrate (4) is completely solidified and the slurry having good properties is obtained. In the granulation treatment, an oxidation catalyst contained in the concentrate (4) is extracted to an aqueous phase, but a portion of the oxidation catalyst becomes captured in the inside of solid residue particles, i.e., captured catalyst seed species and thus is difficult to be extracted to the aqueous phase. Therefore, the granulated slurry is stirred over a long period of time of 10 minutes or more, preferably 30 minutes or more and the particularization of the residue

particle group is facilitated, and thus the contactability of captured catalyst seed species with the aqueous phase can be improved to obtain the granulated slurry (10) having an average particle size of 0.8 to 1.4 mm. The granulated slurry (10) continuously extracted from the stirring tank (5) is continuously fed to a solid-liquid separator (11) . The solid residue (13) after separation is burned or embedded as industrial wastes. On the other hand, the separated aqueous catalyst solution (12) is recovered to the oxidation process of p-xylene via a concentration process under heating. Further, as described above, only the heavy metal catalyst contained in the aqueous catalyst solution may be recovered as carbonates.
Hereinafter, the outline of the continuous mode catalyst recovery method according to the invention will be explained with reference to the accompanying drawing (Fig. 2) .
Also in the invention, the process in which the oxidation mother liquor (1) is concentrated in an evaporator (2) under atmosphere pressure to obtain a mixing gas (3) of acetic acid and water and the concentrate (4), is the same as that of the known method described above. However, in the invention, the concentrate (4) is fed to a continuous stirring tank (5) to be subjected to a hot water treatment

while adding water (6) in a proportion of 0.1 to 10 folds in mass, preferably 0.25 to 5 folds in mass, more preferably 0.5 to 5 folds in mass, and even more preferably 0.5 to 1 fold in mass, based on the amount of the concentrate (4). The hot water treatment is preferably carried out at high temperature in which, of bromine compounds contained in the
concentrate (4), a-bromomethylbenzoic acid as a main component is rapidly hydrolyzed and the hot water slurry has good handling properties. However, if the hot treatment is carried out at the temperature greatly exceeding 100 to 110°C as the boiling temperature of the hot water slurry, the setup cost regarding the pressure-resistant design of the stirring tank (5) increases and thus it is not economic. For this reason, the hot water treatment is carried out under strong stirring at 65 to 300°C, preferably 70 to 150°C, more preferably 80 to 150°C, and particularly preferably 80 to 120°C. Further, the hot water treatment is preferably
carried out for the time in which most of a-bromomethylbenzoic acid contained in the concentrate (4) is hydrolyzed. However, when the hot water treatment time is set to too long, the stirring tank (5) becomes large and the equipment cost becomes high. Therefore, the hot water treatment is carried out for 10 to 300 minutes, preferably 10 to 150 minutes, more preferably 15 to 150 minutes, and

even more preferably 30 to 100 minutes. The stirring tank (5) is equipped with an insulating jacket and the hot water treatment temperature is controlled by the temperature or flow rate of a heat medium fed to the stirring tank. The type of the stirring blade used in the stirring tank (5) is not limited as long as it is suitable for mixing the slurry. Further, in order to improve stirring effects, the stirring tank (5) may be equipped with a baffle plate or it is also effective to increase the stirring speed.
The hot water slurry (7) obtained is fed to a continuous stirring tank (8) to carry out the granulation in the same temperature range as that of the known method described above while adding water (9) in a proportion of 0.1 to 10 folds in mass, preferably 0.2 to 8 folds in mass, and more preferably 0.5 to 5 folds in mass, based on the amount of the hot water slurry (7). Herein, in the catalyst recovery method according to the invention, unlike the known method described above, the granulation conditions for positively extracting the oxidation catalyst are not required because the hot water treatment is carried out. Therefore, the time for the granulation treatment carried out in the stirring tank (8) is sufficient even for taking an extremely short time. The granulation treatment is carried out for 5 to 120 minutes, preferably 10 to 30

minutes to thereby obtain the granulated slurry (10) having an average particle size of 1.4 to 2.0 mm and relatively less fine particles. The granulated slurry (10) is fractionated into the aqueous catalyst solution (12) and the solid residue (13) in a solid-liquid separator (11) and the oxidation catalyst is recovered to the oxidation process of p-xylene, as in the known method described above.
Hereinafter, the present invention will be further specifically explained with reference to Examples and Comparative Examples, while the invention shall not be limited to these Examples.
Hereinafter, measurements used in Examples and Comparative Examples will be explained.
Quantitation of the concentration of cobalt, manganese and bromine contained in the oxidation mother liquor and the aqueous catalyst solution was carried out using an energy-dispersing X-ray fluorescence spectrometer (Model 100F manufactured by OURSTEX Corporation).
Quantitation of the concentration of cobalt and manganese contained in the concentrate and the solid residue was carried out using an TCP emission spectrometer (ICPS-7500 manufactured by Shimadzu Corporation). The analysis sample was prepared by dry carbonizing the solid residue under an acidic condition with sulfuric acid, melting the

concentrate in potassium hydrogensulfate and dissolving the resulting melt into water.
Quantitation of the concentration of bromine contained in the concentrate and the solid residue was carried out using an ion chromatography analyzer (DX-500 Series, a set of transfer pump, column oven and electric conductivity detector, auto suppressor model, manufactured by DIONEX Corporation). An ion-exchange column (lonPac AS14A, 4 mm
(inner diameter) x 250 mm (length), manufactured by DIONEX) was used as the column, and an aqueous mixed solution of 8.0 mM-sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and 1.0 mM-sodium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) was used as a carrier. The flow rate of the transfer pump was set to 1.0 ml/min and the temperature of the column oven was set to 40°C. The analysis sample was prepared by combusting the solid residue in an oxygen flask and absorbing the combusted exhaust gas in an aqueous hydrazine solution.
Quantitation of the concentration of acetic acid in the oxidation mother liquor and the concentrate was carried out using a potentiometric titrator (COM-500, manufactured by Hiranuma Sangyo Co., Ltd.) with an aqueous sodium hydroxide solution as a titrant.

Quantitation of the moisture concentration in the oxidation mother liquor, the concentrate and the solid residue was carried out using a Karl Fischer moisture meter (MKS-510, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) with a Karl Fischer reagent (SS3mg, manufactured by Mitsubishi Chemical Corporation) as a titrant.
Quantitation of the aromatic organic acid in the concentrate was carried out using a liquid chromatography analyzer (transfer pump: LC-10A, column oven: CTO-10A, infrared absorption detector: SPD-10A, manufactured by Shimadzu Corporation). A reversed-phase ion-exchange column
(Simpack WAX-1, 4 mm (inner diameter) x 150 mm (length), manufactured by Shimadzu Corporation) was used as the column, and an aqueous mixed solution of 0.2 M-ammonium dihydrogen phosphate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) and 3% acetonitrile (manufactured by Wako Pure Chemical Industries, Ltd., liquid chromatography grade) was used as a carrier. The flow rate of the transfer pump was set to 1.2 ml/min, the temperature of the column oven was set to 40°C, and the absorption wavelength of the detector was set to 235 nm. The analysis sample was prepared by mixing the concentrate in an aqueous ammonia solution and an aqueous phosphoric acid solution. The quantitation was carried out by an absolute calibration

method.
The average particle size of the granulated slurry was determined by extracting directly the granulated slurry with a test sieve made of stainless steel (200 mm (inner diameter) x 45 mm (height), opening of sieve: 0.15 mm, 0.30 mm, 0.50 mm, 0.81 mm, 1.40 mm, 2.00 mm, 2.80 mm and 4.00 mm, manufactured by lida Kogyo Co., Ltd.) and separating the residue particle group.
(Example 1)
The process of Example 1 will be explained using reference numerals in Fig. 2.
In a continuous tank type reactor, p-xylene was oxidized with air under the conditions of the mass ratio of solvent/p-xylene of 5.0, the reaction temperature of 190°C, the reaction pressure of 1.1 MPa and the residence time of 60 minutes, in a 90% aqueous acetic acid solution containing a cobalt acetate tetrahydrate (700 ppm in terms of cobalt atom, purity: 98% or more, manufactured by Osaki Industry Co., Ltd.), a manganese acetate tetrahydrate (300 ppm in terms of manganese atom, purity: 99% or more, manufactured by Wako Pure Chemical Industries, Ltd.) and an aqueous hydrobromic acid solution (1200 ppm in terms of bromine atom, aqueous solution having the hydrogen bromide concentration of 47 to 49%, manufactured by Tosoh Corporation) to obtain a

terephthalic acid slurry. The terephthalic acid slurry obtained was subjected to solid-liquid separation by a vertical centrifugal separator (rotation number: 4500 rpm) to thus obtain an oxidation mother liquor and a terephthalic acid cake.
The oxidation mother liquor (1) was concentrated under heating at a rate of 6000 parts by mass per hour at 110°C at normal pressures in a thin-film evaporator (2) to obtain the mixing gas (3) of acetic acid and water at a rate of 5600 parts by mass per hour and the concentrate (4) at a rate of 400 parts by mass per hour. The concentrate (4) had a composition comprising 1.9% of cobalt, 0.9% of manganese, 2.5% of bromine, 7.1% of moisture, 4.3% of acetic acid, 29% of benzole acid and 14% of p-toluic acid. The concentrate
(4) and water (6) were continuously fed to the stirring tank
(5) equipped with a warming jacket at respective rates of
400 parts by mass per hour and 200 parts by mass per hour to
carry out the hot water treatment (100°C, 40 min, 300 rpm).
Two-stage blades at upper and lower sides were used as the
stirring blade, which the upper stage thereof comprises six
turbine blades and the lower stage thereof comprises two
paddle blades. The stirring tank (5) was equipped with six
baffle plates on its inner wall. Herein, the hot water
slurry (7) formed and water (9) were continuously fed to the

stirring tank (8) at respective rates of 600 parts by mass per hour and 1800 parts by mass per hour to carry out the granulation treatment (40°C, 10 min, 600 rpm) . Further, two-stage blades at upper and lower sides were used as the stirring blade, which the upper stage thereof comprises six turbine blades and the lower stage thereof comprises two paddle blades. The stirring tank (8) was also equipped with six baffle plates on its inner wall. The granulated slurry (10) was fed to the solid-liquid separator (11) through vertical centrifugation (rotation number: 4500 rpm) to fractionate into the aqueous catalyst solution (12) and the solid residue (13). As a result, the granulated slurry (10) obtained had an average particle size of 1.4 to 2.0 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 95% of cobalt, 95% of manganese and 87% of bromine. The results are shown in Table 1.
(Comparative Example 1)
The process of Comparative Example 1 will be explained using reference numerals in Fig. 1.
The concentrate (4) prepared in the same manner as in Example 1 and water (6) were continuously fed to the stirring tank (5) at respective flow rates of 400 parts by

mass per hour and 2000 parts by mass per hour to carry out the stirring treatment (40°C, 30 min, 600 rpm) and granulation of the residue. The after treatment of the granulated slurry was carried out in the same manner as in Example 1 above. Specifically, Comparative Example 1 was carried out under the conditions that the hot water treatment carried out in the stirring tank (5) of Fig. 2 was omitted and the granulation time in the stirring tank (8) of Fig. 2 was extended, with respect to Example 1. Further, the total flow rate of water used in Example 1, i.e., water (6) and water (9) of Fig. 2 was the same as the flow rate of water used in Comparative Example 1, i.e., water (6) of Fig. 1. As a result, the granulated slurry (7) obtained in Comparative Example 1 had an average particle size of 0.81 to 1.40 mm and the solid residue (13) after separation had the moisture concentration of 25%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 85% of cobalt, 85% of manganese and 30% of bromine. The results are shown in Table 1.
(Comparative Example 2)
The concentrate (4) prepared in the same manner as in Example 1 and water (6) were fed to the stirring tank (5) at respective flow rates of 400 parts by mass per hour and 800 parts by mass per hour to carry out the hot water treatment

(100°C, 40 min, 300 rpm) . Then, the hot water slurry (7) obtained was cooled to 50°C with stirring for 30 minutes. To 1200 parts by mass of the hot water slurry was added 1200 parts by mass (1 fold) of water (9) and the granulation temperature was adjusted to 40°C with stirring at 600 rpm. As a result, the granulated slurry (10) obtained had an average particle size of 0.15 to 0.30 mm and the solid residue (13) after separation had the moisture concentration of 40%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 91% of cobalt, 91% of manganese and 83% of bromine. The results are shown in Table 1.
(Example 2)
The concentrate (4) prepared in the same manner as in Example 1 and water (6) were continuously fed to the stirring tank (5) equipped with a warming jacket at respective rates of 400 parts by mass per hour and 200 parts by mass per hour to carry out the hot water treatment (74°C, 40 min, 500 rpm). Herein, the hot water slurry (7) formed and water (9) were continuously fed to the stirring tank (8) at respective rates of 600 parts by mass per hour and 1800 parts by mass per hour to carry out the granulation treatment (40°C, 20 min, 700 rpm). The aftertreatment of the granulated slurry was carried out in the same manner as

in Example 1. As a result, the granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 93% of cobalt, 93% of manganese and 75% of bromine. The results are shown in Table 1. (Example 3)
The granulated slurry (10) was obtained by carrying out the treatment in the same manner as in Example 2 except that the hot water treatment temperature in Example 2 was changed from 74°C to 88°C. The granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 94% of cobalt, 94% of manganese and 85% of bromine. The results are shown in Table 1.
(Example 4)
The granulated slurry (10) was obtained by carrying out the treatment in the same manner as in Example 2 except that the hot water treatment temperature in Example 2 was changed from 74°C to 104°C. The granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid

residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 95% of cobalt, 95% of manganese and 88% of bromine. The results are shown in Table 1.
(Example 5)
The concentrate (4) prepared in the same manner as in Example 1 and water (6) were continuously fed to the stirring tank (5) equipped with a warming jacket at respective rates of 400 parts by mass per hour and 100 parts by mass per hour to carry out the hot water treatment (100°C, 40 min, 500 rpm). Herein, the hot water slurry (7) formed and water (9) were continuously fed to the stirring tank (8) at respective rates of 600 parts by mass per hour and 1800 parts by mass per hour to carry out the granulation treatment (40°C, 20 min, 700 rpm). The aftertreatment of the granulated slurry was carried out in the same manner as in Example 1. As a result, the granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 93% of cobalt, 93% of manganese and 77% of bromine. The results are shown in Table 1.

(Example 6)
The granulated slurry (10) was obtained by carrying out the treatment in the same manner as in Example 5 except that the hot water treatment in Example 5 was carried out by changing the flow rate of water (6) from 100 parts by mass per hour to 200 parts by mass per hour. The granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 94% of cobalt, 94% of manganese and 87% of bromine. The results are shown in Table 1.
(Example 7)
The granulated slurry (10) was obtained by carrying out the treatment in the same manner as in Example 5 except that the hot water treatment in Example 5 was carried out by changing the flow rate of water (6) from 100 parts by mass per hour to 300 parts by mass per hour. The granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 95% of cobalt, 95% of manganese and 88% of bromine. The results are shown in Table 1.

(Example 8)
The concentrate (4) prepared in the same manner as in Example 1 and water (6) were continuously fed to the stirring tank (5) equipped with a warming jacket at respective rates of 400 parts by mass per hour and 200 parts by mass per hour to carry out the hot water treatment (100°C, 10 min, 500 rpm). Herein, the hot water slurry (7) formed and water (9) were continuously fed to the stirring tank (8) at respective rates of 600 parts by mass per hour and 1800 parts by mass per hour to carry out the granulation treatment (40°C, 20 min, 700 rpm). The aftertreatment of the granulated slurry was carried out in the same manner as in Example 1. As a result, the granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous' catalyst solution (12) was determined as 93% of cobalt, 93% of manganese and 82% of bromine. The results are shown in Table 1.
(Example 9)
The granulated slurry (10) was obtained by carrying out the treatment in the same manner as in Example 8 except that the hot water treatment time in Example 8 was changed from 10 minutes to 20 minutes. The granulated slurry (10)

obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 95% of cobalt, 95% of manganese and 85% of bromine. The results are shown in Table 1.
(Example 10)
The granulated slurry (10) was obtained by carrying out the treatment in the same manner as in Example 8 except that the hot water treatment time in Example 8 was changed from 10 minutes to 40 minutes. The granulated slurry (10) obtained had an average particle size of 1.40 to 2.00 mm and the solid residue (13) after separation had the moisture concentration of 15%. Herein, the catalyst recovery rate to the aqueous catalyst solution (12) was determined as 95% of cobalt, 95% of manganese and 87% of bromine. The results are shown in Table 1.
(Table Removed)

WE CLAIM-;
1. A method for recovery of an oxidation catalyst from a
concentrate obtained by concentrating under heating an oxidation mother liquor in the manufacture of aromatic carboxylic acids comprising liquid phase oxidation of alkyl aromatic compounds with molecular oxygen in a reaction solvent containing a lower aliphatic carboxylic acid the present of oxidation catalyst, said method comprising the steps of:
a hot water treatment of the concentrate with stirring and then
a granulation treatment of the hot water slurry obtained with stirring to obtain a granulated slurry,
wherein the hot water treatment and the granulation treatment are carried out in separate stirring tanks, and
a solid-liquid separation of the granulated slurry obtained so as to recover an aqueous catalyst solution containing the oxidation catalyst,
wherein the hot water treatment is carried out by stirring at 65 to 300°C for 10 to 300 minutes while adding water in a proportion of 0.1 to 10 folds in mass, based on the amount of the concentrate, and the granulation treatment is carried out by stirring at 20 to 60°C for 5 to 120 minutes while adding water in a proportion of 0.1 to 10 folds in mass,

based on the amount of the slurry obtained after carrying out the hot water treatment.
2. The method as claimed in claim 1, wherein a stirring tank for the hot water treatment and a stirring tank for the granulation treatment are arranged in tandem.
3. The method as claimed in claim 1 or 2, wherein the oxidation catalyst is a liquid phase oxidation catalyst of alkyl aromatic compounds.
4. The method as claimed in any one of claims 1 to 3, wherein the oxidation catalyst is a cobalt compound, a manganese compound and a brome compound.
5. The method as claimed in any one of claims 1 to 4, wherein the aromatic carboxylic acid is terephthalic acid.