THE STABLE CATALYST FOR HYDROPURIFICATION Background of the Invention The present invention is related to the catalyst compositions for the purification of aromatic carboxylic acid on the base of Group VIII metals including palladium and ruthenium, to the methods for their production and to the process of purification of aromatic carboxylic acid, further used for the synthesis of polyester polymers and copolymers that are used in the production of textile fibers and films.

Field of the Invention The aromatic carboxylic acid used as monomer for the production of polymer fibers should have high purity. The main parameter of aromatic carboxylic acid quality is the content of aromatic aldehyde such as 4-carboxybenzaldehyde (4- CBA) and colored impurities.

The catalyst of the present invention showed much higher activity, especially after aging, than the added activities of each metal component. In other words, the present invention claims the optimum concentration of components in a bimetallic catalyst.

Description of the Related Art The purified aromatic carboxylic acid is produced from less pure, technical or "crude"aromatic carboxylic acid by hydropurification (by treatment in the presence of hydrogen) of the latter over the catalysts containing Group VIII metals. The crude aromatic carboxylic acid is dissolved in water at high temperature and the produced solution is hydrogenated in a stirred reactor or in a fixed bed reactor, preferably in the presence of the catalysts containing Group VIII metals. The purification methods, catalyst composition and the methods for the production of those catalysts are described in several patents.

Activity and selectivity of the catalyst for hydropurification of aromatic carboxylic acid depend on many factors, such as content of Group VIII metal (s) in the catalyst, support type, method used for the supporting of Group VIII metal (s) and size and distribution of metal (s) on the support granule.

There is known the method for hydropurification of crude aromatic carboxylic acid (GB patent No. 994769,1965), wherein catalyst composition"palladium on active carbon"shows high activity in the reaction of purification of terephthalic acid from 4-carboxybenzaldehyde impurities.

It was shown (US patents No. 4,415,479 (1983) ; 4,421,676 (1983), and 4,791,226 (1988)) that for more effective process of hydropurification of terephthalic acid from 4-carboxybenzaldehyde, it is important to prepare the catalysts with definite size of the supported palladium. Such particles should have the size of not bigger than 35 A. Some authors (US patents No. 4,394,299 (1983) and 4,791,226 (1988)) also show the positive effect of such distribution of the palladium particles in the carbon granule when they exist mainly on the external surface of the granule.

It is noticed in many patents that, along with the mono-metallic catalyst, introduction of Ni, Co, Cu, Fe, Mn, U, Cr, Ir, Rh and Pt etc. to the catalyst composition, may have a positive effect on the catalytic efficiency of the palladium.

According to other group of patents (US patents No. 4,629,715 (1986) and 4,892,972 (1990)), the most effective bimetallic catalyst is achieved when the catalysts in the reactor are placed in layers, for example, Pd/C and Rh/C instead of one layer (Rh+Pd)/C. Some authors (US patent No. 4,892,972 (1990)) even patented the process using multi-layered catalyst, for example, Ru/C + Rh/C + Pd/C.

Typically catalysts containing Group VIM metals, in particular, palladium

catalysts, are prepared by deposition of the palladium salts from solution onto the support. In one of the methods (US patent No. 2,857,337 (1967)), the salt is treated with water-soluble metal hydroxide or basic carbonate with further reduction to metallic palladium with reducing agent such as formaldehyde, glucose, glycerin, etc.

According to Keit et al. (US patent No. 3,138,560 (1967)), at the addition of the sodium tetrachloropalladate or palladium chloride to the many carbon supports, most of the palladium is immediately deposited in the form of a shining film of metallic palladium. Catalysts prepared in such a way typically have low activity.

It was supposed that palladium is directly reduced to metal due to free electrons or due to the presence of functional groups such as aldehydes on the carbon surface. Before reduction stage, palladium catalysts are usually prepared by fixing palladium in the form of insoluble compound to avoid the problem of palladium particle migration and crystallites growth, which may arise at the reduction of the palladium from solution.

The most close method of purification is described in GB patent No. 1578725 (1980), where authors propose to use the catalyst comprising two or more metals, such as Pt, Pd, Rh, Ru, Os, Ir, Fe, Ni, Co, Cr, Mn and U, wherein one of the metals is Pd or Pt. In the mentioned catalysts the metals are present in the form of alloy, physical mixture or supported metals on the carbon support, active carbon (granules of from 3 to 6mm). Hydropurification is carried out by treating the solution of aromatic carboxylic acid with hydrogen in the presence of the mentioned catalysts at high temperature (-280°C) and pressure (-lOOatm). The rate of the hydrogenation in the presence of bimetallic catalyst (0.4% Pd- 0.1% Pt)/C is higher than with the catalyst of 0.5% Pd/C by 20%.

Recently, it is claimed that the crude terephthalic acid can be purified over the supported Group VDI metals such as Pd, Pt, Rh, Ru on mesoporous carbon materials with graphite-likeness. (International publication No. W000108798Al, "Catalytic composition, method for manufacturing thereof and method for the

purification of terephthalic acid", 2001.2.8) Thus, the crude aromatic carboxylic acid, containing aromatic aldehyde such as 4- CBA and other impurities, may be purified by hydrogenation over traditionally prepared catalysts on the base of Group VIII metals supported on carbon.

But the lifetime of a catalyst known until now is about one year in an actual plant.

To increase the lifetime of a catalyst is extremely important in the viewpoint of economics such as the period of plant shut down and the cost of a catalyst.

Nevertheless, the case is not known in which one or more than one of Group Vm metal components are added to the palladium to increase the stability of a catalyst for hydropurification of aromatic carboxylic acid. In other words, the lifetime of catalyst for hydropurification should be increased because it is merely about one year.

Therefore, it is very important to develop a purification method of aromatic carboxylic acid with catalyst components with high activity and especially with high stability. The inventors completed the invention of very stable catalyst by optimizing the composition of palladium and ruthenium in a bimetallic catalyst.

Summary of the Invention As a result of research for resolving the above problems of activity and stability, the inventors herein substituted ruthenium metal components for some part of palladium supported on a support such as a carbon. The inventors found that a decline in activity after aging could be decreased and the activity of palladium- ruthenium catalyst was larger than the added activities of palladium catalyst and ruthenium catalyst in a specific concentration. In other words, the palladium and ruthenium showed a synergetic effect in activity and stability. Based on such findings, the present invention has been perfected.

In view of the foregoing, the present invention relates to a method of producing an hydropurification catalyst for aromatic carboxylic acid, the method comprising supporting simultaneously palladium and ruthenium on a support.

In another aspect, the present invention relates to a method of purification of aromatic carboxylic acid, the method utilizing the supported palladium-ruthenium catalyst.

Description of the Preferred Embodiments The present invention solves the problem of the creation of active and stable catalysts and processes wherein the crude aromatic carboxylic acid with high content of aromatic aldehyde such as 4-CBA may be selectively hydrogenated to purified aromatic carboxylic acid with low content of aromatic aldehydes.

The problem is solved by the purification of aromatic carboxylic acid with the catalyst composition comprising crystallites of catalytically active palladium and ruthenium metal, supported on a solid support such as carbon material, wherein the weight ratio of said metal, Pd/Ru, is from 0.2 to 5.0. The total content of metals including palladium and ruthenium varies from 0.1 to 3.0 wt%.

The said carbon material can be any carbon material including a mesoporous graphite-like material having an average size of mesopores from 40 to 400A, the share of mesopores in total pore volume not less than 0.5, and degree of graphite- likeness no less than 20%, wherein said crystallites of metals are distributed in the bulk of the carbon material granule so as the maxima of those crystallites distribution being at a distance from the external surface of said granule equal to 1-30% of the radius thereof.

The said catalyst composition is prepared using one of the following metal precursors, but similar precursors containing palladium and/or ruthenium can be used instead: PdCl2, H2PdC14 or Pd (N03) 2 ; RuCIs, RuCl3 hydrates, RuOHCl3 or

RuNO (NO3) 3.

For the production of the said catalysts, i. e. catalysts containing bimetallic particles of palladium and rhuthenium supported on a support, the well known methods in a literature, like impregnation of the support with the solutions of various salts of Pd and Ru, may be used. However, as was found, the best catalysts are produced if the method of spraying of acidic salts of Pd and Ru on a support is used with further treatment of the supported metal precursors with hydrogen.

It was found that the catalyst containing both palladium and ruthenium in a specific concentration showed higher activity than the added activities of palladium and ruthenium. The difference of activity increased more after the aging of catalysts with 4-CBA. With the present invention more active and stable catalyst can be manufactured. With this catalyst a crude aromatic carboxylic acid can be purified effectively and cheaply because the catalyst showed a synergetic effect in activity and stability and the ruthenium is much cheaper than palladium.

Above mentioned catalysts, supported Pd and Ru on carbon, can be prepared by any known method to impregnate solution of various salts of Pd and Ru. The wet or solution impregantion and gas or dry impregnation can be used to impreganate the metal compounds on a support, and the gas phase impregnation including spraying method was effective.

After the impregnation, the metal compounds can be reduced by the reducing properties of carbon such as free electron or aldehyde, and additional reduction can be accomplished by hydrogen, formaldehyde, hydrazine, sodium formate, glucose and sodium hypophosphite etc., if necessary. The reduction by hydrogen in gas phase or aqueous solution of sodium hypophosphite in liquid phase was effective. However, the simplest method of preparation of catalyst can be accomplished by an impregnation and consequent autogenous reduction by carbon without any additional reduction.

The most effective catalyst was obtained by simultaneous spraying of the acidic solutions of Pd and Ru on carbon and subsequent reduction by hydrogen.

The present invention is explained in detail by examples below. Nevertheless, the examples are illustrative only and should not be deemed to limit the present invention.

Examples Example 1 Catalyst with the composition of 0.3% Pd-0.2% Ru/Sibunit was manufactured similar to the method of example 3 of Int ernational publication No. W000108798A1 ("Catalytic composition, method for manufacturing thereof and method for the purification of terephthalic acid", 2001.

2.8). Namely, 20g of carbon support Sibunit (V. A. Likholobov et al., React. Kin. Cat. Lett., v. 54,2 (1995) 381-411) was loaded to a cylindric rotating reactor after the support was purified from the dust by boiling in distilled water and dried at 120°C to a constant weight. Solutions of PdCl2 (0.3mole/1 in HC1 solution, 1.88ml) and RuCl3 (0.25mole/1 in HC1 solution, 1. 58ml) and 1.44ml of distilled water were loaded in a syringe. Water solutions of Na2C03 (0.60 mole/1, 3.2ml) and 1.7ml of distilled water were loaded in another syringe. Two solutions were fed simultaneously, at the same flow rate of 1. Oml/min, into a nozzle and sprayed, with the help of flowing air, into the reactor containing Sibunit support, and the reactor was rotated with the speed of 60-80 rpm. The catalyst was discharged and dried in vacuum at 70 °C to a constant weight. The reduction was conducted in a tubular reactor in hydrogen stream at the temperature of 250 °C for 2hr. The temperature was increased to 250 °C in 1. 5hr. The catalyst was washed, after cooling, with distilled water till no reaction of AgNO3 with chlorine ions in the washing water, and dried in vacuum at 70 °C till the constant weight.

The fresh activity of manufactured catalyst was determined after the hydropurification of terephthalic acid containing 3% of 4-CBA at 250 °C for 5 to 30 min. The kinetic constant was calculated by the assumption of the first order kinetics of removal of 4-CBA with the concentration of 4-CBA. The activity of aged catalyst was determined by similar hydropurification for 20 to 40 min after aging of catalyst. The aging was carried out by the method described in Korean patent application no. 10-2000-0032736 ("Rapid aging method of hydropurification catalyst", 2000.6.14). Namely, four catalysts were aged simultaneously for 44hr in the hydrogen and 4-CBA solution.

The determined activities of fresh and aged catalyst were 0.119 and 0.116/min, and larger by 127.2 and 217.3%, respectively, than the activities (O. 094 and 0.053/min) calculated by arithmetic summation of 0.3% Pd/Sibunit and 0.2% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst shows a synergetic effect in fresh and aged activities. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Example 2 Catalyst with the composition of 0.2% Pd-0.3% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of PdCl2, RuC13 and Na2CO3 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.098 and 0.069/min, and larger by 138. 1 and 173.3%, respectively, than the activities (O. 071 and 0.040/min) calculated by arithmetic summation of 0.2% Pd/Sibunit and 0.3% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from

comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst shows a synergetic effect in fresh and aged activities. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Example 3 Catalyst with the composition of 0.15% Pd-0.35% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of PdCl2, RuC13 and Na2C03 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activity of fresh catalyst was 0.088/min, and larger by 147.5% than the activity of 0.059/min calculated by arithmetic summation of 0.15% Pd/Sibunit and 0.35% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst shows a synergetic effect in fresh activity. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Example 4 Catalyst with the composition of 0.256% Pd-0.244% Ru/Sibunit was manufactured similar to the method of example i, except the amount of PdCl2, RuCl3 and Na2C03 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activity of fresh catalyst was 0.104/min, and larger by 124.3% than the activity of 0.084/min calculated by arithmetic summation of 0.256% Pd/Sibunit and 0.244% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst shows a synergetic effect in fresh activity. The

detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Example S Catalyst with the composition of 0. 4% Pd-0.1% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of PdCl2, RuC13 and Na2CO3 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.101 and 0.095/min, and were 87. 0 and 141.6%, respectively, of the activities (O. 116 and 0.067/min) calculated by arithmetic summation of 0.4% Pd/Sibunit and 0. 1% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst shows a synergetic effect in aged activities even though the fresh activity is decreased somewhat. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Example 6 Catalyst with the composition of 0.1% Pd-0.4% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of PdCl2, RuCl3 and Na2CO3 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.044 and 0.042/min, and were 91.8 and 161.5%, respectively, of the activities (O. 048 and 0.026/min) calculated by arithmetic summation of 0.1% Pd/Sibunit and 0.4% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst shows a synergetic effect in aged

activities even though the fresh activity is decreased somewhat. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Comparative example 1 Catalyst with the composition of 0.5% Pd/Sibunit was manufactured similar to the method of example 1, except the amount of PdClz and Na2C03 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.139 and 0.081/min, and showed that the aged activity was about 58% of fresh activity and the aged activity was smaller than that of catalyst of example 1 even though the fresh activity was quite high. In other words, the catalyst showed very poor stability after aging. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Comparative example 2 Catalyst with the composition of 0.5% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of RuCIs and Na2C03 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.025 and 0.012/min, and showed that the fresh and aged activities were very low. The aged activity was about 48% of fresh activity and showed very poor stability after aging. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Comparative example 3

Catalyst with the composition of 0.45% Pd-0.05% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of PdCl2, RuCIs and Na2C03 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.120 and 0.077/min, and were 93.9 and 104.1%, respectively, of the activities (O. 127 and 0.074/min) calculated by arithmetic summation of 0.45% Pd/Sibunit and 0.05% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst with the composition of 0.45% Pd-0.05% Ru/Sibunit does not show a remarkable synergetic effect in fresh and aged activities. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2.

Comparative example 4 Catalyst with the composition of 0.05% Pd-0.45% Ru/Sibunit was manufactured similar to the method of example 1, except the amount of PdCl2, RuCl3 and Na2C03 was adjusted for catalyst composition. The activities of the catalyst were determined by the method of example 1.

The determined activities of fresh and aged catalyst were 0.036 and 0. 018/min, and were 97.2 and 94.0%, respectively, of the activities (O. 037 and 0. 019/min) calculated by arithmetic summation of 0.05% PdlSibunit and 0.45% Ru/Sibunit of which were derived from the activities of 0.5% Pd/Sibunit (from comparative example 1) and 0.5% Ru/Sibunit (from comparative example 2). Therefore, it can be known that the palladium-ruthenium catalyst with the composition of 0.05% Pd-0.45% Ru/Sibunit does not show a remarkable synergetic effect in fresh and aged activities. The detailed data including the kinetic constants are given in table 1 and figures 1 and 2. <Table 1> Kinetic constants of fresh and aged catalyst with various concentration of palladium and ruthenium supported on Sibunit. Ex. No. Pd (%) Ru (%) Fresh catalyst Aged catalyst Kcalculated @ Kmeasured Ratio Kcalculated Kmeasured Ratio * * 1 0. 30 0.20 0. 094 0. 119 127. 2 0. 053 0. 116 217.3 2 0. 20 0.30 0. 071 0. 098 138. 1 0. 040 0. 069 173.3 3 0. 15 0.35 0. 059 0. 088 147. 5 0.033 4 0.256 0.244 0.084 0.104 124.3 0. 047 5 0. 40 0.10 0. 116 0. 101 87. 0 0. 067 0. 095 141.6 6 0.10 0. 40 0. 048 0. 044 91. 8 0. 026 0. 042 161.5 Comp. 1 0. 50 0.00 0. 139 0. 139 100. 0 0. 081 0. 081 100. 0 Comp. 2 0. 00 0. 50 0. 025 0. 025 100. 0 0. 012 0. 012 100. 0 Comp.3 0. 45 0. 05 0. 127 0. 120 93. 9 0. 074 0. 077 104. 1 Comp.4 0.05 0.45 0.037 0.036 97.2 0.019 0.018 94.0

* First order kinetic constant in/min. Kcaicuiated was calculated by the arithmetic summation of kinetic constants of each component.

** Ratio Of Kmeasured/Kcalcu, ated in % Kinetic constant(/min) <Figure 1> Effect of Ru substitution for the Pd on the fresh activity of the 0.5%-Pd/Sibunit catalyst in the hydropurification of terephthalic acid.

Kinetic constant(/min <Figure 2> Effect of Ru substitution for the Pd on the aged activity of the 0.5%-Pd/Sibunit catalyst in the hydropurification of terephthalic acid.