Title of Invention	A PROCESS FOR PREPARING A CATALYST FOR PURIFICATION OF TEREPHTALIC ACID
Abstract	Heretofore problems were encountered in preparing selective and stable catalysts for purifying terephthalic acid with high content of p - CBA. The present invention attempts to overcome the foregoing problem and relates to a process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodical Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of - i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor. ii) drying said precursor, and iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material.

Title of Invention

A PROCESS FOR PREPARING A CATALYST FOR PURIFICATION OF TEREPHTALIC ACID

Abstract

Heretofore problems were encountered in preparing selective and stable catalysts for purifying terephthalic acid with high content of p - CBA. The present invention attempts to overcome the foregoing problem and relates to a process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodical Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of - i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor. ii) drying said precursor, and iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material.

Full Text	The present invention relates to a process for preparing a catalyst for purification of terephthalic acid. More particularly the invention pertains to a catalyst and a process for their production, which catalysts have been found to be highly effective in purifying tereptithalic acid employed in the synthesis of polyester polymers and copolymers, used in the production of textile fibers. It is important that terephthatic add used as the monomer for the production of polymer fibers has high purity. The main controlled parameter of terephthalic acid quality is the content of p-carboxybenzaldehyde and colored impurities. The purified terephthalic acid is produced from less pure, technical or "crude" terephthalic acid by hydropurification of the latter (by treatment in the presence of hydrogen) over the catalysts containing metals of Group VIII. The crude terephthalic acid is dissolved in water at high temperatures and the produced solution is hydrogenated in a shaking reactor within a fixed bed reactor, preferably in the presence of the catalysts containing metals of Group VIII. The purification methods, catalysts and the methods for the production of those catalysts are described in many patents. Activity and selectivity of the catalyst for hydropurification of terephthalic acid depend on many factors, such as content of VIII group metal or metals in the catalyst, support type, method used for the supporting of metal or metals of Group, VIII, as well as on distribution of metal or metals on the support granule. There is a known method for hydropurification of crude terephthalic acid [GB patent No. 994769,19651, wherein catalyst composition "Palladium on active carbon" shows high activity in the reaction of purification of terephthalic acid from p-carftoxybenzaldehyde impurities. Other compounds, such as SiO2, A12O3 were studied as supports for palladium. Besides, it was found that carbon supports are the best, since they are not subjected to quick decomposition in the corrosive hot water solutions of terephthalic acid unlike oxide supports. The effects of the nature of carbon support have been studied. It is known that active carbons prepared from the plant, animal or mineral precursors, preferably from coconut active carbon, are feasible for the production of palladium catalysts for hydropurification of terephthalic acid, it is desirable that the surface area of such active carbon is not tower than 600m2/g, and granule size is 3-6mm. Additional characteristics of such active carbon, namely the value of pH of water suspension is introduced in [US patent No. 4728693, 19881. The possibility to use porous carbon material modified with pyrocarbon as a feasible support is 1A shown in [USSR patent No. 1660282. 1997]. It was shown in [US patents NoNo.4415479. 1983; 4421676. 1983, and 4791226. 1988] that for a more effective process of hydropurification of terephthalic acid from p-carboxybenzaldehyde, it is important to prepare the catalysts with a definite size of the supported palladium. Such panicles should have a size not bigger than 35A. Authors [US patents No.No.4394299. 1983 and 4791226. 1988] also shows the positive effect of such a distribution of the palladium particles in the carbon granule, when they prevail on the external surface of the granule. It is noticed in many patents, that along with the monometallic catalyst, introduction of Ni, Co. Cu. Fe. Mn. U, Cr to the catalyst composition, as well as Ir, Rh, Pt and Ru. may have a positive effect on the catalytic efficiency of the palladium. According to other groups of patents [US patents NoNo.4629715, 1986 and 4892972. 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. Authors [US patent No.4892972. 1990] have even patented the process using multilayered catalyst, for example, Ru/C + Rh/C + Pd/C. Typically catalysts containing VIII group metals, in particular, palladium catalysts, are prepared by adsorption of the palladium salt from solution onto the support. In one of the methods [US patent No.2857337, 1967], the salt is treated with a water-soluble metal hydroxyde or basic carbonate with further reduction to metallic palladium with a reducing agent like formaldehyde, glucose, glycerin, etc. According to Keit et al. [US patent No.3138560, 1967], at the addition of the sodium tetrachlloropallodoate or palladium chloride to many of the carbon supports, most of the palladium is immediately deposited in the form of a glittering 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 such functional groups as aldehydes on the carbon surface. Before the reduction stage, palladium catalysts are usually prepared by fixing palladium in the form of an insoluble compound to avoid the problem of palladium particles migration and crystallites growth, which may arise at the reduction of the palladium from the solution. P-carboxybenzaldehyde is the most toxic impurity which determines the quality of terephthalic acid which is used for the production of the plastics. P-toluic acid (p-TA) is also an undesirable impurity that should be removed from the water solution of the terephthalic acid produced as the result of hydropurification. Although such a removal may be achieved mainly due to higher solubility of p-toluic acid in water compared to terephthalic acid. significant amounts of p-toluic acid are entrapped in the crystals of purified terephthalic acid in the stage of its crystallization from solution. 2 To avoid this accompanying disadvantage in seperating p-tniuic acid, it was proposed to conduct decarbonylation of p-CBA to benzoic acid in water solutions in the presence of the catalyst "palladium on carbon", because benzoic acid is more soluble in water than p-toluic acid [US patent no.3456001, 1969]. However, the above mentioned decarbonylation of p-CBA to benzoic acid produces equimolar amounts of carbon oxide, which is a known poison for noble metals like palladium [US patent No.4201872, 1980]. To minimize the catalyst poisoning in the above mentioned patent, it is proposed to conduct decarbonylation at a relatively lower process" pressure to reduce to the minimum the concentration of the dissolved carbon oxide in the liquid phase. The process pressure should be also controlled within a narrow range of pressures. Liberated carbon oxide is removed from the reactor in the form of a gas. It is known [US patent No.4892972. 1990] that use in the above mentioned process for the purification of terephthalic acid of the catalytic system including the first catalyst layer, containing VIII group metal fixed on the carbon support, and the second layer of the "palladium on carbon" catalyst, and passing the water solution of crude terephthaiic acid through the above mentioned first layer of the "rhodium on carbon" catalyst, and then through the second layer of the "palladium on carbon" catalyst, minimizes the quantity of p-toluic acid produced in course of the purification of crude terephthalic acid. This method of using of the above mentioned catalytic system does not facilitate hydrogenation of p-CBA to p-toluic acid, but it does facilitate decarbonylation of p-CBA to benzoic acid, which is more soluble in water than p-toluic acid. It, therefore, is more easily separated from terephthalic acid at its crystallization than p-toluic acid. This allows to purify the terephthalic acid solution with higher content of p-CBA at higher economic effect. The closest method of purification is described in [GB patent No.1578725, 1980], where authors propose to use a catalyst comprising two or more metals, such as Pt, Pd. Rh, Ru, Os, Ir, Fe, Ni, Co, Cr, Mn and U. where 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 onto the carbon support - active carbon (granules of from 3 to 6mm). Hydropurification is carried out by treating the solution of terephthalic acid with hydrogen in the presence of the mentioned catalysts at high a temperature (280°C) and pressure (~100atm). The rate of the hydrogenation in the presence of bimetallic catalyst (0.4%Pd-0.1%Pt)/C referred to Ig catalyst, is 20% higher than when 0.5%Pd/C is used. Thus, the crude terephthalic acid, containig p-CBA and other impurities, may be purified by hydrogenation over traditionally prepared catalysts on the base of VIII group supported on carbon. The invention solves the problem of the creation of selective and stable catalysts and processes wherein the crude terephthalic acid with high content of p-CBA may be selectively 3 hydrogenated to p-toluic acid or/and decarbonylated to benzoic acid with low content of the residual p- CBA. The foregoing problems are solved by. the present invention which relates to a process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodic Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of - i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor. ii) drying said precursor, and iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material having an average mesopore size in the range of 40 - 400 A, the ratio of mesopores volume in total pore volume at least 0.5,. and graphite-likeness no less than 20%. The catalyst of this invention includes crystallites of palladium and rhodium or palladium and rhuthenium or palladium and platinum; total content of metals varies from 0.1 to 0.3 % wt, mass ratio of palladium to other metals varies from 0.1 to 10.0. 4 The problem is solved also by the development of the process for the production of a catalyst for purification of terephthalic acid by supporting catalytically active palladium or palladium and at least one of the Group VIII metals upon a carbon material, at the contact of said granules with water solution of salts of palladium or salts of palladium and at least one metal of the Group VIII, with the production of the precusor metal salt - porous carbon, wherein the precusor is dried and treated with reducing agent in the amount sufficient to reduce surface metal salts to metal crystallites, wherein said carbon material is used as mesoporous graphite-like material having an average size of mesopores 40 - 400 A, a share of mesopores in total pore volume not less than 0.5 and degree of graphite-likeness not less than 20%, to produce a metal or bimetal catalyst. The said catalyst is prepared from one of the following, metal precursors : H2PdCl4 or Pd(NO3)2 ; H2PdCl4 and RuOHCl3 or RuNO(NO3)3 ; pd(NO3)2 and RuOHCl3 or RuNO(NO3)3 For the production of said catalyst the nitrate solutions of palladium and/ or ruthenium salts are used with the concentration of the free nitric acid of from 37 to 170 g/1. Bimetallic catalysts are prepared by co-deposition of the metal precursors or by sequent deposition of the metal precursors. We have found that such a catalyst may be produced if mono- or bimetallic particles of metals of Group VIII are supported on the carbon material having an average pore size of from 40 - 400 A and a significant (from 20 to 60%) degree of graphite-likeness. The said metallic particles are distributed in bulk of the carbon support so that the maximums of their distribution are at a distance from the external surface of said granule equal to 1-30% of 4A the radius thereof. The above mentioned carbon materials are the supports prepared by thermal processing of plastics, as well as those symhesized by specia technology from gaseous hydrocarbons (V.A. Likholobov et al., React.Kin.Cat.Lett.. v.54. 2 (1995) 381-411), namely Sibunit, KVU and various composites on their base.' Physical-chemical characteristics for some carbons are given in the table l.-Data in the table certify that said carbon materials of such parameters as Vmeso/VE and K are sharply different from traditional active carbons typically used for the production of the catalysts for hydropurification of terephthalic acid produced from plant, animal or mineral precursors, preferably coconut active carbons used for the production of traditional catalysts for hydropurification of terephthalic acid. We also found that at such distribution of the palladium and rhuthenium particles in the granule of mesoporous carbon material, some of palladium may be substituted by rhuthenium. which results in not only lower catalyst cost (because rhuthenium is cheaper than palladium), but also in the change of the ratio of p-toluic and benzoic acids to the latter, that is favorable for reaching the higher quality of the produced crystalline terephthalic acid. For the production of the said catalysts, i.e. catalysts containing mono- or bimetallic particles of palladium and rhuthenium supported on carbon support, the well known in the literature methods, 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 feasible carbon support is used with further treatment of the supported metal precursors with hydrogen. The given below examples 1-35 characterize catalytic compositions and the methods for their production. Examples 7, 30~34 are given for comparison, and examples 8 and 35 are given as prototypes. Examples 36-39 describe the methods for terephthalic acid purification. Analysis results of the character of metal particles distribution in the support granule and of the quality of terephthalic acid purified using proposed catalytic compositions, are given in tables 2-6. Example 1 50g carbon support Sibunit 1 (data on its physical-chemical and texture properties are given in table 1) are loaded to the cylindric rotating reactor. Hereinafter the support is preliminarily purified from the dust by boiling it in distilled water. Then it is discharged to the screen with the cell size of lmm, washed with distilled water and dried at 120°C to the constant weight. Water solutions of Na2CO3 (0.364mole/l; 13ml) and H2PdCl4 (0.182mole/l; 13ml) at the same flow rate (2.5ml/min) at mole ratio of Na2CO3H2PdCl4=2:1 are fed to the injector and the produced mixture is sprayed into the reactor. The catalyst is discharged and dried in a vacuum at 75°C to the constant weight. The next stage of reduction is conducted in the tubular reactor in a hydrogen stream at a temperature of 250°C for 2hr. The temperature is 5 reduced from 250°C to 40°C, and at 110°C the hydrogen is substituted by nitrogen. The catalyst is washed with distilled water till there is no reaction of AgNO3 with chlorine ions in the washing water, and dried in vacuum at 75°C till the constant weight. Pd/Sib.l catalyst is produced with palladium content of 0.5wt%. Electron microsonding of the catalyst granules is conducted by scanning the cut of granule by diameter on microanalyzer MAP-3 with probe of l~2µm diameter at an accelerating voltage of 20kV and current of 20~30nA. Parameter ? characterizing the thickness of the active layer of metal in µn per 1/2 peak height, is used as the characteristics of distribution of active component in catalyst grain. The data on the distribution of Pd and Ru particles in the catalytsts was prepared in accordance with the given examples, are given in table 2. Example 2 The catalyst is prepared using the procedure of example 1, except RuOHCb (0.191 mole/1; 13ml) is used as the water solution instead of H2PdCl4, and concentration of Na2CO3 solution (13ml) corresponds to 0.382mole/l; Na:CO3 ; H2PdCl4 = 2:1. Ru/Sib.l catalyst is produced with Ru content of 0.5wt%. Example 3 The catalyst is prepared by co-deposition of Ru and Pd using water solutions of RuOHCb and H2PdCl4 correspondingly as metal precursors. For this purpose, 50g of carbon support Sibunit 1 are loaded to the cylindric rotating reactor. 13ml of Na2CO2 water solution (0.371mole/l) and 13ml of H2PdCl4(0.109mole/l) + RuOHCb (0.076mole/l) are fed to the injector at the same flow rate (2.5ml/min) at the mole ratio Na2CO3 : (Ru+Pd) = 2:1, and sprayed into the reactor. The catalyst is discharged and dried under vacuum at 70°C till the constant weight. Further stages of reduction, washing and drying are similar to those of the example 1. (Ru-Pd)/Sib.l catalyst is produced with 0.2wt% Ru and 0.3wt%Pd content. Example 4 50g of carbon support Sibunit 1 are loaded to the cylindric rotating reactor. 26ml of nitric acid - water solution of Pd(NO3) (0.091mole/l) with concentration of free HNO3 of 170g/l are fed to the injector and a produced mixture is sprayed to the reactor at the rate of 51m/min. The sample is placed into the tubular reactor and dried in an air stream for 1hr while the temperature is increased to 120°C and held at this temperature for 2hr. Then the air is substituted by nitrogen and the temperature is increased to 250°C (at this temperature Pd(NO3)2 is decomposed to Pd oxide). At these conditions the sample is held for 3hr, then cooled to 150°C. Then at this temperature the nitrogen is substituted with hydrogen and the catalyst is reduced for lhr at 150°C with further increase of temperature to 250°C and held at this temperature for 2hr. The temperature is reduced from 250°C to 40°C. since at 110°C the hydrogen is substituted with nitrogen. Pd/Sib.l catalyst is produced with a palladium content 6 of 0.5wt%. Thus the prepared catalyst is used in examples 24, 25 in the synthesis of bimetallic catalysts. Example 5 The catalyst is prepared using the procedure of example 4, except 26ml nitric acid -water solution of RuNO(NO3)3 (0.091 mole/1) with free HNO3 concentration of 170g/l is used instead of nitric acid - water solution of Pd(NO3)2- Ru/Sib.l catalyst is produced with Ru content of 0.5wt%. Example 6 The catalyst is prepared by co-deposition of Ru and Pd using as a metal precursor the nitric acid - water solutions of RuNO(NO3)3 and Pd(NO3) correspondingly. For this purpose, 50g of carbon support Sibunit I are loaded to the cylindric rotating reactor. 26ml of nitric acid - water solution of RuNO(NO3)3 (0.038mole/n - Pd(NO3): (0.054mole/l) with free HNO3 concentration of l70g/l are fed to the injector and sprayed to the reactor at the rate of 5mo/min. Further stages of drying, calcination, and reduction are simitar to those of the example 4. (Ru-Pd)/Sib.I catalyst is produced with 0.2wt% Ru and 0.3wr% Pd contents. Example 7 (comparative) The catalyst is prepared using the procedure of example 4. except coconut carbon CG-5 is used instead of the carbon support Sibunit I. Pd/CG-5 catalyst is produced with Pd content of 0.5 wt%. Example 8 (prototype) The catalyst is prepared using the procedure of example 3, except coconut carbon CG-5 is used instead of the carbon support Sibunit I. (Ru+Pd)/CG-5 catalyst is produced with 0.2wt% Ru and 0.3wt% Pd content. Example 9 The catalyst is prepared using the procedure of example 3, except 13 ml water solution of Na3CO3 (0.366moie/l) and 13ml of H:PdCL, (0.145 mole/l) + RuOHCb (0.038 mole/l) are fed to the injector; Na2CO3 : (Ru+Pd) = 2:1. (Ru-Pd)/Sib.l catalyst is produced with 0.lwt% Ru and 0.4wt% Pd contents. Example 10 The catalyst is prepared using the procedure of example 3, except 13ml of water solution of Na2CO3 (0.367 mole/l) and 13ml of H2PdCl4 (0.073 moJe/l)+RuOHCI:. (0.115 mole/l) are fed to the injector; Na2CO3: (Ru+Pd)~2:l. The catalyst (Ru-Pd)/Sib.l is produced with 0.3wt% Ru and 0.2wt% Pd contents. Example 11 The catalyst is prepared using the procedure of example 6, except 26ml of nitric acid water solution of RuNO(NO3)3 (0.019mole/l)+Pd(NO3)2 (0.073 mole/l) are fed to the injector with concentration of free HNO3 of 170g/l. The catalyst (Ru-Pd)/Sib.l is produced 7 with 0.1 wt% Ru and 0.4wt% Pd contents. Example 12 The catalyst is prepared using the procedure of example 6. except 26rnl of nitric acid - water solution of RuNO(NO5)3 {0.057mole/l)+Pd(NO3)2 (0.036 mole/1) are fed to the injector with concentration of free HNO3 of 170g/l. The catalyst (Ru-Pd)/Sib.l is produced with 0.3wt% Ru and 0.2wt% Pd contents. Example 13 The catalyst is prepared using the procedure of example 5. except 26ml of nitric acid - water solution of RuNO(NO3)3 (0.038mole/I) are fed to the injector with concentration of free HN03 of 53g/1. The catalyst Ru/Sib.l is produced with Ru content of 0.2wt%. Thus produced catalyst is used in the example 18 in the synthesis of bimetallic catalysts. Example 14 The catalyst is prepared using the procedure of example 13, except 26ml of nitric acid - water solution of RuNO(NO3)3 (0.038mole/l) with concentration of free HNO3 of 170g/l are used. The catalyst Ru/Sib.l is produced with Ru content of 0.2wt%. Thus produced catalyst is used in the example 19in the synthesis of bimetallic catalysts. Example 15 The catalyst is prepared using the procedure of example 4. except 26ml of nitric acid water solution of Pd(NO3)2 (0.054mole/l) with concentration of free HN03 of 53g/l. The catalyst Pd /Sib. 1 is produced with Pd content of 0.3wt%. Thus produced catalyst is used in the example 20. 22 in the synthesis of bimetallic catalysts. Example 16 The catalyst is prepared using the procedure of example 15. except 26ml of nitric acid - water solution of Pd(NO3)2 (0.054mole/l) with concentration of free HNO3 of l70g/l. The catalyst Pd /Sib. 1 is produced with Pd content of 0.3wt%. Thus produced catalyst is used in the example 21 in the synthesis of bimetallic catalysts. Example 17 The catalyst is prepared using the procedure of example 1. except water solutions of Na2CO3 (0.218mole/l; 13ml) and H2PdCI4 (0.109 mole/1; 13ml) is fed to the injector at the same rate (2.5ml/min) at mole ratio of Na2CO3:H2PdCl4=2:l. The catalyst Pd/Sib.l is produced with Pd content of 0.3wt%. Thus produced catalyst is used in the example 23 in the synthesis of bimetallic catalysts. Example 18 The catalyst is prepared using the procedure of example 17, except Ru/Sib.l of example 13 is used instead of Sibunit 1. The catalyst Pd/Ru/Sib.l is produced with 0.2wt%Ru and 0.3 wt% Pd contents. Example 19 8 The catalyst is prepared using the procedure of example 15, except Ru/Sib.l of example 14 is used instead of Sibunit 1. The catalyst Pd/Ru/Sib.l is produced with 0.2wt%Ru and 0.3wt% Pd contents. Example 20 The catalyst is prepared using the procedure of example 2, except water solutions of Na2CO3 (0.152mole/l; 13ml) and H2PdCl4 (0.076 mole/1; 13ml) is fed to the injector at the same rate (2.5ml/min) at mole ratio of Na2CO3:H2PdCl4::=2:l, and Pd/Sib.1 of example 15 is used instead of Sibunit I. The catalyst Ru/Pd/Sib. 1 is produced with 0.2wt% Ru nd 0.3 wt%Pd content. Example 21 The catalyst is prepared using die procedure of example 13, except Ru/Sib.l of example 16 is used instead of Sibunit 1. The catalyst Ru/Pd/Sib. 1 is produced with 0.2wt%Ru and 0.3wt% Pd contents. Example 22 The catalyst is prepared using the procedure of example 14, except Ru/Sib.l of example 15 is used instead of Sibunit 1. The catalyst Ru/Pd/Sib.l is produced with 0.2wt%Ru and 0.3wt% Pd contents. Example 23 The catalyst is prepared using the procedure of example 13. except Pd/Sib.l of . example 17 is used instead of Sibunit 1. The catalyst Ru/Pd/Sib. I is produced with 0.2wt%Ru and 0.3wt% Pd contents. Example 24 50g Pd/Sib.l prepared in the example 4 is loaded to the cylindric rotating reactor. Water solution of H2PtCl6 (0.0099mole/l; 26ml) is fed to injector and sprayed into the reactor at the rate of 5ml/min. Further stages of reduction, washing and drying and similar to those of the example 1. The catalyst Pt/Pd/Sib.l is produced with 0.1 wt%Pt and 0.5wt%Pd contents. Example 25 The catalyst is prepared using the procedure of example 24, except water solution of RhCl3 (0.0l9mole/l; 26ml) is used instead of H2PtCl6. The catalyst Rh/Pd/Sib.l is produced with 0.1 wt%Rh and 0.5wt% Pd contents. Examples 26-27 The catalyst is prepared using the procedure of example 4, except the concentration of free HNO3 is 37g/l (example 26) and !47g/l (example 27). Ru/Sib.l catalysts are produced with Pd content of 0.5wt%. Example 28 The catalyst is prepared using the procedure of example 1. except 13ml water 9 solution of Na2CO3 (0.727mole/l) and 13ml H2PdCI4 (0.363mole/1) are fed to injector; Na2CO3:Pd=:2:l. Pd/Sib.l catalyst is produced with palladium content of 1 .0wt%. Example 29 The catalyst is prepared using the procedure of example 1. except 13ml water solution of Na2CO3 (1.453mo!e/l) and 13ml H2PdCI4 (0.727mole/l) are fed to injector; Na2CO3:Pd=2:l. Pd/Sib.l catalyst is produced with palladium content of 2.0wt%: Example 30 (comparative) The catalyst is prepared using the procedure of example 4, except active carbon ARES is used instead of carbon support Sibunit 1. Pd/ AR-B catalyst is produced vvith palladium content of 0.5wt%. Example 31 (comparative) The catalyst is prepared using the procedure of example 4, except active carbon L-2702 is used instead of carbon support Sibunit 1. Pd/L-2702 catalyst is produced with palladium content of 0.5wt%. Example 32 (comparative) The catalyst is prepared using the procedure of example 4. except active carbon FB-4 is used instead of carbon support Sibunit 1. Pd/FB-4 catalyst is produced with palladium content of 0.5wt%. Example 33 (comparative) The catalyst is prepared using the procedure of example 1, except active carbon KVU-1 is used instead of carbon support Sibunit 1. Pd/ KVU-1 catalyst is produced with palladium content of 0.5wt%. Example 34 (comparative) The catalyst is prepared using the procedure of example 1, except coconut carbon CG-5 is used instead of carbon support Sibunit 1. Pd/ CG-5 catalyst is produced with palladium content of 0.5wt%. Example 35 (prototype) The catalyst is prepared by co-deposition of Pt and Pd using as metal precursors the water solutions fo H2PtCl6 and H2PdCl4 correspondingly. For this purpose, 50g of coconut carbon CG-5 are loaded to the cylindric rotating reactor. 13ml of water solution of Na2CO3 (0.330mole/l) and 13ml H2PdCl4(0.145mole/l)+H:PtCl6('0.020mole/l).are fed to injector and sprayed into reactor at the same rate (2.5ml/min) at mole rntio of Na2CO3:(Pt+Pd)=2:l. The catalyst is discharged and dried under vacuum at 700°C till the constant weight. Further stages of reduction, washing and drying are similar to those of the example 1. Produced catalyst (Pt-Pd)/CG-5 contains 0.1 wt% Pt and 0.4wt%Pd. Example 36 150ml distilled water and 12.9g crude terephthalic acid, containing 8-000ppm p-CBA. 10 and 126pprn p-to!uic acid are loaded to the reactor (4561 Mini Parr Reactor) made of stainless steel. The anchor of the reactor has the form of a net basket intended for loading catalyst granules thereto. The granules of the catalyst, prepared in accordance with example I. in the amount of 0.170a. are loaded to the basket bottom. The basket is fixed to the stirrer shaft. After that the cover is put on the vessel and carefully screwed-up. The reactor is connected with the system. The system is purged with nitrogen, then with hydrogen, and the pressure is set at 14atm using hydrogen. The temperature of 250°C is set on the control pannel and the furnace is turned on. When the temperature in the reactor reaches the prescribed temperature, the stirrer equipped with magnetic gear (~240rpm) is turned on. The time the stirrer is turned on is considered the beginning of the experiment. Experiment time is 3hr. The reactor is opened, the basket with the catalyst is removed from the stirrer shaft and the catalyst is discharged. The content of the autoclave (suspension of terephthalic acid in water) is transferred to the glass filter, filtered, washed with distilled water (50ml) and dried under vacuum at 75°C for 2hr. The produced terephthalic acid powder,is analyzed for impurities content. Content of p-CBA in purified terephthalic acid is determined using universal polarograph ON-105 by voltammetering method in differential mode of polarization on Hg-graphite electrode by the analytical signal with the maximum at the potential of -1.07V proportional to the concentration of p-CBA in terephthalic acid. Concentration of p-toluic acid in purified terephthalic acid is determined by high pressure LC method on liquid chromatograph Milichrom-4. The sample of terephthalic-acid is dissolved in 0.3M NH4H2PO4 and analyzed on 2xS0mm column,with fixed phase - anion exchange resin Partisil, 10 SAX (Watman). Color (transparency) of the purified terephthalic acid is determined by direct measuring of optical density of water-alkaline solutions at 340 and 400nm. For this purpose, 1.5g of purified terephthalic acid are dissolved in 10ml of 2M KOH solution. The solution is preliminary centrifuged during 15min at 3000rpm. Optical density is measured on spectrophotometer (we used Specord M40) in quartz cells of 10mm thickness reffering to 2M KOH solution at 340 and 400nm. Analysis data on the quality of terephthalic acid, purified by this method over the catalyst, prepared in accordance with'the below given examples, are given in table 3. Example 2 The method for the purification of terephthalic acid is similar to that descirbed in example 3. except 0.340g catalyst are loaded to the reactor. Besides the catalyst after the experiment (cycle) is washed directly in the basket with distilled water and used in the next cycle. The experiment time for one sample is from 4 to 5 cycles. Similar data on the quality of terephthalic acid, purified by this method over the 11 catalysts prepared in accordance with the above given examples, are given in table -4 Example 3 The method for the purification of terephthalic acid is similar to that of example except the purification is conducted over the catalysts produced in examples 5 and 34, at the initial content of p-CBA of 30,000ppm, Analysis data on the quality of terephthalic acid purified by this method are given in table 5, Example 4 500ml distilled water H2O and 25g crude terephthalic acid, containing 3,552ppm p- CBA and I26ppm p-colucid acid, are loaded to the stainless vessel of 750ml volume (dissolver). After that the cover is put on the vessel and carefully screwed-up. 2.0g catalyst, prepared in.the example 1 are placed on the reactor grid, in the form of the stainless tube with inner diameter of 10mm and discharge hole on the distance of 110mm from the tower grid. and the cover fixed with the second grid. The reactor is connected with the dissolver, Reactor's discharge hole is hermetically connected with the crystailizer via rhermostafed still capillary. The said crystallizer is an autoclave made of stainless still of 750ml volume. The dissolver, reactor and crystallizer are placed in the heated thermostat. The system is purged with nitrogen, then with hydrogen at H2 bubbling throught the water suspension of terephthalic acid in dissolver. and the pressure is set at lOatm with hydrogen. The temperature of 250°C is set on the control pannef and the thermostat is turned on. When the temperature in the system reaches the prescribed temperature the hydrogen is fed to the dissolver at the constant mote rate using flow mater. Constant pressure in the system is maintained by a pressure regulator situated at the crystallizer outlet The gas substitutes ihe solution of terephthalic acid from dissolver to reactor. The solution of terephthalic acid is pumped over upward through the catalyst level at i constant rate and discharged via a discharge hole to the crystallizer. "Pumping over" time of the solution throught the reactor is 8hr. The reaction mass is cooled and the installation is purged with nitrogen. The content of the crystallizer (suspension of terephthalic acid in water) is transferred to the glass filter, filtered, washed with distilled water (100ml) and dried under vacuum at 75OC for 2hr. The produced powder of terephthalic acid is analyzed for impurities content Analysis data on the quality of ferephthalic acid, purified by this method over the catalyst, which is prepared in accordance with the above given examples, are given in table 6. As may be seen from the examples and tables, the invention proposed allows purification of terephthalic acid till low content of p-CBA and allows to this method to ftnd wide application in the chemical industry. 12 Table 1, Main characteristics of some granulated porous carbon materials ite m Grade Origine (source) Shape Size, mm AHET11 . m2/g Vmacro 21 cm3/g Vmeso31 cm3 /g Vmeso41 cm3/g Vmeso D 51 A K61 1 AR-B Charcoal grip 4-5 438 , 0.192 0.027 0.219 0.12 20 5 10 2 CG-5 Coconut carbott crushed 3-6 1024 0.438 0,047 0 185 0.10 19 3 L-2702 Charcoal grip 4-8 1024 0.453 0.046 0 499 0.03 19 4 FB-4 Charcoal grip 4-6 606 0.222 0.144 0.366 0.39 24 5 KVU-I Hydrocarbons granule 3-5 120 0.010 0.310 0.32 u.97 107 40 6 Sibunit I Hydrocarbons granule 2-3 440 0.015 0.665 0.680 0.98 62 60 11ABET(m2/g) - specific suriace area by BET, Surfucc urea was calculated on the isotherm scctions, where P/P0-0.05-0,20; the value of the section of the nitrogen molecule in the filled monomolecualr layer was considered equal to w-0. 162 nm2; 21Vmicro (cm3/g) - volume of microporcs. It was calculated using comparative method on the isotherm sections, corresponding to the range between fillilng of micropores and beginning of the capillary condensation;; value VMHKPO corresponds to the total volume of ultramicro- and supermicropores, i.e. to the volume of micropores having the size below 20A, 31Vmesow(cm3/g) = VE-Vmicro; 41 VE (cm3/g) - volume of pores having the size below 5000 A . It was calculated from nitrogen adsorption at P/P0=0.98; 51Dav (A) - an average size of pores calculated us Dav. - 4-104 - VE-/ ABEI 61K (%) - degree of cryslallinity, calculated from the integral intensity of the peak (002); difratograms of the samples were recorded on difractometer IIZG-4C (CuKw graphite monochromator). Table 2. Properties of the catalysts Example No. Catalyst composition. wt% Distribution of metal in granule, u ?llRu ?md Ru ? Pd ?mcl Pd 1 0.5%Pd/Sib.l 27-75 38 0.5%Ru/Sib.l 18-45 32 3 (0.2%Ru-0.3%Pd)/Sib.l 30-91 44 19-82 38 4 0.5%Pd/Sib.l 58-410 302 5 0.5%Ru/Sib.i 220-384 293 6 (0.2%Ru-0.3%Pd)/Sib.l 90-339 240 90-298 249 7 0.5%Pd/CG-5 18-75 41 3 (0.2%Ru-0.3%Pd)/CG-5 12-48 26 9-42 10 (0.3%Ru-0.2%Pd)/Sib.l 22-79 44 14 0.2%Ru/Sib.l fuzzy =475 15 0.3%Pd/Sib.l 261-597 371 16 0.3%Pd/Sib.l 477-1530 988 17 0.3%Pd/Sib.l 17-123 46 18 0.3%Pd/0.2%Ru/Sib.l 34-716 285 fuzzy =580 19 0.3%Pd/0.2%Ru/Sib.l fuzzy =766 56-183 134 20 0.2%Ru/0.3%Pd/Sib.l 28-206 92 14-597 211 21 0.2%Ru/0.3%Pd/Sib.l 178-505 286 322-1533 739 22 0.2%Ru/0.3%Pd/Sib.l 64-673 396 56-1150 200 23 0.2%Ru/0.3%Pd/Sib.l 159-430 302 17-239 90 26 0.5%Pd/Sib.l 51-232 121 30 0.5%Pd/AR-B 45-250 128 31 0.5%Pd/L-2702 58-287 150 32 0.5%Pd/FB-4 7-29 17 34 0.5%Pd/CG-5 6-40 18 Parameter A characterizes the thickness of the active layer in µm per 1/2 of the height of the peak of metal distribution in subsurface layer of the granule; _md - a mean average of parameter=? 14 Tablet: Characteristics of TPA purified by method described m example36 Example No. Catalyst composition, wt. % Characteristics of purified TPA Transmission of alkaline solutions, % Impurities content. ppm 340 nm 400 nm p-CBA p-+TA 1 0.5%Pd/Sib.l 95.51 98.83 9 3620 2 0.5%Ru/Sib.l S4.51 96.27 25 520 5 (0.2%Ru-0.3%Pd)/Sib ! 93.21 98.42 12 2620 4 0.5%Pd/Sib. 1 84.57 96.86 455 729 5 0.5%Ru/Sib.I 75.78 97.43 851 138 6 (G.2%Ru~d.3%Pd)/Sib.l 89.31 98.47 345 524 7 0.5%Pd/CG-5 66.14 81.65 16 760 8 (0.2%Ru-0.3%Pd)/CG-5 89.90 95.50 10 3696 9 (0.1%Ru-0.4%Pd)/Sib.l 95.79 99.1 5 9 2830 10 (0.3%Ru-G.2%PdySib. 1 94.18 98.56 10 1640 11 (0.1 °/oRu-0.4%Pd)/Sib. 1 91.98 100.00 340 602 12 (0.3%Ru-G.2%Pd)/Sib.I 90.82 100.00 336 394 13 0.2%Ru/Sib. I 69,76 98.16 1265 79 15 0.3%Pd/Sib,l 77.0S 95.96 842 138 16 0.3%Pd/Sib.i 78.22 96.99 772 15! I8 0.3%Pd/0.2%Ru/Sib,l 97.03 99.70 1402 197 19 0.3%Pd/0.2%Ru/Sib.l 93.08 100.00 131 914 20 0.2%Ru/0.3%Pd/Sib.l 86.52 98.67 446 743 21 0.2%Ru/0.3%Pd/Sib. 1 77.66 97.51 . 973 284 23 0.2%Ru/0.3%Pd/Sib. 1 77.80 97.51 1303 201 24 0,I%Pt/0.5%Pd/Sib.l 75.54 97.56 200 689 25 0.1%Rh/0.5%Pd/Sib.S 52.57 96.30 494 176 26 0,5%Pd/Ssb. I 92.88 97.17 56 2251 27 0.5%Pd/Sib.l 95.00 98.90 83 3662 28 1%Pd/Sib,l 89.50 94.23 6 6048 29 2%Pd/Sib.l 100.00 100.00 15 5443 30 0.5%Pd/AR-B 72.65 94.28 432 235 31 0.5%Pd/L-2702 56.28 99.00 676 184 32 0.5%Pd/FB-4 59.84 92.57 412 230 33 0.5%Pd/KVU-l 94.79 94.44 6 1020 15 Table 3 continued Example* No, Catalyst composition, wt. % Characteristics of purified TPA Transmission of alkaline Impurities content, solutions. % ppm 340 nm 400 nm P-CBA p-TA 34 0.5%Pd/CG-5 98.6 100.00 6 559 35 (0.1%Pt-0.4%Pd)/CG-5 87.57 98.41 18 1200 16 Table 4. Characteristics of TPA purified by the method described in example 2 Example No. Catalyst composition. wt% Cycle No. Characteristics of purified TPA Transmittance of alkaline solutions, % Impurities content, ppm 340 nm 400 nm p-CBA p-TA 1 0.5%Pd/Sib.l I 96.52 98.85 6 249 2 97.18 99.52 5 6955 3 94.25 98.35 5 4534 4 89.90 95.92 6 2688 5. 88.55 95.63 4 1058 2 0.5%Ru/Sib.l 1 89.86 97.79 24 1067 2 88.39 98.60 23 546 3 84.81 100.00 25 269 4 80.46 96.16 23 297 5 82.44 97.12 25 199 (0.2%Ru-0.3%Pd)/Sib.l 1 95.80 99.17 11 1873 2 96.64 100.00 10 1528 3 97.50 100.00 9 1218 4 89.19 96.25 14 974 5 84.46 94.30 15 907 6 (0.2%Ru-0.3%Pd)/Sib.l 1 93.80 99.08 6 1890 2 92.06 97.08 8 1033 3 90.51 97.42 53 949 4 88.76 97.47 85 1117 5 82.00 97.85 206 1151 7 0.5%Pd/CG-5 I 98.11 100.00 5 4402 2 97.74 100.00 7 1381 3 94.78 99.08 12 748 4 91.95 99.22 52 882 8 (0.2%Ru-0.3%Pd)/CG-5 1 99.27 100.00 9 5275 2 99.30 100.00 40 1613 3 96.53 100.00 34 3142 4 91.38 98.26 60 511 17 Table 4 continued Example No. Catalyst composition, wt% Cycle No, Characteristics of purified TPA Transmmance of alkaline solutions. % Impurities content. ppm 340 nm 400 nm p-CBA p-TA 5 90.91 99.46 202 442 19 0.3%Pd/0.2%Ru/Sib.l 1 93.84 99.18 12 7200 2 90.67 97.65 88 6200 94.78 \| 100.00 279 756 4 83.80 96.18 366 873 5 79.52 95.06 297 672 20 0.2%Ru/0.3%Pd/Sib.l 1 97.13 100.00 8 1267 2 90.87 100.00 219 571 3 82.48 100.00 865 549 4 76.62 100.00 1213 477 5 68.24 96.39 1312 319 23 0.2%Ru/0.3%Pd/Sib. 1 1 96.80 100.00 255 899 2 83.89 97.13 405 168 3 75.50 94.09 778 124 4 70.48 93.70 814 155 5 67.61 94.70 1003 286 26 0.5%Pd/Sib.l 1 97.87 100.00 10 2612 2 98.71 100.00 10 2352 3 95.33 100.00 6 361 4 92.26 99.44 72 470 5 86.55 97.88 198 655 34 0.5%Pd/CG-5 1 94,85 96.84 8 2 95,41 100,00 11 3 93,72 98.87 71 4 91,28 97,72 . 360 89,16 97,24 739 18 Tabie 5. Characteristics of TPA purified by method described in example 3 (intial content of p-CBA 30,00ppm) Example No. Catalyst composition, wt% Cycle No- Characteristics of purified TPA Transmittance of alkaline solutions, % p-CBA content 340 nm 400 nm (0.2%Ru-0.3%Pd)/Sib.l 1 92,22 97,00 10 2 94,34 98,33 20 3 93,93 97,46 31 4 79,58 93,73 41 5 77,89 93,46 156 34 0.5%Pd/CG-5 1 97,95 98,54 9 2 91,15 97,67 37 3 88,29 97,68 434 4 72,85 97,52 1607 5 41,71 92,83 3447 19 Table 6. Characteristics of TPA purified by method described in example 4 Example No. Catalyst composition, wt% Experiment time (t), hr Catalyst weight (Pwt.). g Lw11 Characteristics of purified TPA Tratismittance of alkaline solutions. % Impurities content. 340 nm 400 nm P-CBA p-IA 1 0.5%Pd/Sib. 1 8 2,00 29.5 90.7 97.1 15 460 '3 0.2%Ru-0,3%Pd/Sib.l 10 2.00 4,2 92,17 99.21 32 1930 3 0.2%Ru-0.3%Pd/Sib.l 10 2,00 18.8 83.01 9 1.88 80 116 4 0.5%Pd/Sib.l 10 2.00 1.2 55 1242 4 0.5%Pd/Sib.l 10 2.00 20.3 86.6 99.3 189 10 10 7 0.5%Pd/CG-5 10 2.00 22.4 88.75 97.19 164 8 0.2%Ru-0.3%Pd/CG-5 10 2.00 17.3 92.13 99.27 100 152 33 10 2.00 20.1 87.81 98.46 80 162 34 0.5%Pd/CG-5 10 2.00 20.2 89.7 95 3 15 162 ^ Volumetric load on catalyst 1.w=WIPA/(Pwt-t) wherein WTPA-volumeof TPA solution passed though the catalyst layer during time. WE CLAIM ; 1. A process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodic Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being, at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of - i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor. ii) drying said precursor, and iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material having an average mesopore size in the range of 40 - 400 A, the ratio of mesopores volume in total pore volume at least 0.5 and graphite-likeness no less than 20%. 2. A process as claimed in Claim 1, wherein the metal crystallites are palladium and rhodium. 3. A process as claimed in Claim 1, wherein the metal crystallites are palladium and ruthenium. 4. A process as claimed in Claim 1, wherein the metal crystallites are palladium and platinum. 5. A process as claimed in Claim 1, wherein a total of metal content is in the range of 0.1 to 3.0 wt %. 21 6. A process as claimed in Claim 1, wherein the weight ratio of palladium to the other constituent metals is in the range of 0.1 to 10. 7. A process as claimed in Claim 1, wherein the said catalyst composition is prepared from one of the following metal precursors : H2PdCl4 or Pd(NO3)2 ; H2PdCl4 and RuOHCl3 or RuNO(NO3)3 ; Pd(NO3)2 and RuOHCl3 or RuNO(NO3)3 8. A process as claimed in Claim 1, wherein nitric acid solutions of palladium and/or ruthenium salts with the concentration of the free acid within the range 37 to 170 g/1.are used for the preparation of the said catalyst composition. 9. A process as claimed in Claim 1, wherein bimetal catalysts are prepared by co-depositing the metal precursors. 10. A process as claimed in Claim 1, wherein catalysts are prepared by successively depositing the metal precursors. 11. A method for preparing a catalyst for purification of terephthalic acid, substantially as hereinbefore described particularly with reference to the appended examples. DATED THIS 27TH DAY OF JULY, 2000. Dr. A. Basu. of D. SEN & CO. Attorney for the Applicant. 22 Heretofore problems were encountered in preparing selective and stable catalysts for purifying terephthalic acid with high content of p - CBA. The present invention attempts to overcome the foregoing problem and relates to a process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodical Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of - i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor. ii) drying said precursor, and iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material.

Full Text

The present invention relates to a process for preparing a catalyst for purification of terephthalic acid. More particularly the invention pertains to a catalyst and a process for their production, which catalysts have been found to be highly effective in purifying tereptithalic acid employed in the synthesis of polyester polymers and copolymers, used in the production of textile fibers.
It is important that terephthatic add used as the monomer for the production of polymer fibers has high purity. The main controlled parameter of terephthalic acid quality is the content of p-carboxybenzaldehyde and colored impurities.
The purified terephthalic acid is produced from less pure, technical or "crude" terephthalic acid by hydropurification of the latter (by treatment in the presence of hydrogen) over the catalysts containing metals of Group VIII. The crude terephthalic acid is dissolved in water at high temperatures and the produced solution is hydrogenated in a shaking reactor within a fixed bed reactor, preferably in the presence of the catalysts containing metals of Group VIII. The purification methods, catalysts and the methods for the production of those catalysts are described in many patents.
Activity and selectivity of the catalyst for hydropurification of terephthalic acid depend on many factors, such as content of VIII group metal or metals in the catalyst, support type, method used for the supporting of metal or metals of Group, VIII, as well as on distribution of metal or metals on the support granule.
There is a known method for hydropurification of crude terephthalic acid [GB patent No. 994769,19651, wherein catalyst composition "Palladium on active carbon" shows high activity in the reaction of purification of terephthalic acid from p-carftoxybenzaldehyde impurities. Other compounds, such as SiO2, A12O3 were studied as supports for palladium. Besides, it was found that carbon supports are the best, since they are not subjected to quick decomposition in the corrosive hot water solutions of terephthalic acid unlike oxide supports.
The effects of the nature of carbon support have been studied. It is known that active carbons prepared from the plant, animal or mineral precursors, preferably from coconut active carbon, are feasible for the production of palladium catalysts for hydropurification of terephthalic acid, it is desirable that the surface area of such active carbon is not tower than 600m2/g, and granule size is 3-6mm. Additional characteristics of such active carbon, namely the value of pH of water suspension is introduced in [US patent No. 4728693, 19881. The possibility to use porous carbon material modified with pyrocarbon as a feasible support is
1A

shown in [USSR patent No. 1660282. 1997].
It was shown in [US patents NoNo.4415479. 1983; 4421676. 1983, and 4791226. 1988] that for a more effective process of hydropurification of terephthalic acid from p-carboxybenzaldehyde, it is important to prepare the catalysts with a definite size of the supported palladium. Such panicles should have a size not bigger than 35A. Authors [US patents No.No.4394299. 1983 and 4791226. 1988] also shows the positive effect of such a distribution of the palladium particles in the carbon granule, when they prevail on the external surface of the granule.
It is noticed in many patents, that along with the monometallic catalyst, introduction of Ni, Co. Cu. Fe. Mn. U, Cr to the catalyst composition, as well as Ir, Rh, Pt and Ru. may have a positive effect on the catalytic efficiency of the palladium.
According to other groups of patents [US patents NoNo.4629715, 1986 and 4892972. 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. Authors [US patent No.4892972. 1990] have even patented the process using multilayered catalyst, for example, Ru/C + Rh/C + Pd/C.
Typically catalysts containing VIII group metals, in particular, palladium catalysts, are prepared by adsorption of the palladium salt from solution onto the support. In one of the methods [US patent No.2857337, 1967], the salt is treated with a water-soluble metal hydroxyde or basic carbonate with further reduction to metallic palladium with a reducing agent like formaldehyde, glucose, glycerin, etc.
According to Keit et al. [US patent No.3138560, 1967], at the addition of the sodium tetrachlloropallodoate or palladium chloride to many of the carbon supports, most of the palladium is immediately deposited in the form of a glittering 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 such functional groups as aldehydes on the carbon surface. Before the reduction stage, palladium catalysts are usually prepared by fixing palladium in the form of an insoluble compound to avoid the problem of palladium particles migration and crystallites growth, which may arise at the reduction of the palladium from the solution.
P-carboxybenzaldehyde is the most toxic impurity which determines the quality of terephthalic acid which is used for the production of the plastics. P-toluic acid (p-TA) is also an undesirable impurity that should be removed from the water solution of the terephthalic acid produced as the result of hydropurification. Although such a removal may be achieved mainly due to higher solubility of p-toluic acid in water compared to terephthalic acid. significant amounts of p-toluic acid are entrapped in the crystals of purified terephthalic acid in the stage of its crystallization from solution.
2

To avoid this accompanying disadvantage in seperating p-tniuic acid, it was proposed to conduct decarbonylation of p-CBA to benzoic acid in water solutions in the presence of the catalyst "palladium on carbon", because benzoic acid is more soluble in water than p-toluic acid [US patent no.3456001, 1969]. However, the above mentioned decarbonylation of p-CBA to benzoic acid produces equimolar amounts of carbon oxide, which is a known poison for noble metals like palladium [US patent No.4201872, 1980]. To minimize the catalyst poisoning in the above mentioned patent, it is proposed to conduct decarbonylation at a relatively lower process" pressure to reduce to the minimum the concentration of the dissolved carbon oxide in the liquid phase. The process pressure should be also controlled within a narrow range of pressures. Liberated carbon oxide is removed from the reactor in the form of a gas.
It is known [US patent No.4892972. 1990] that use in the above mentioned process for the purification of terephthalic acid of the catalytic system including the first catalyst layer, containing VIII group metal fixed on the carbon support, and the second layer of the "palladium on carbon" catalyst, and passing the water solution of crude terephthaiic acid through the above mentioned first layer of the "rhodium on carbon" catalyst, and then through the second layer of the "palladium on carbon" catalyst, minimizes the quantity of p-toluic acid produced in course of the purification of crude terephthalic acid. This method of using of the above mentioned catalytic system does not facilitate hydrogenation of p-CBA to p-toluic acid, but it does facilitate decarbonylation of p-CBA to benzoic acid, which is more soluble in water than p-toluic acid. It, therefore, is more easily separated from terephthalic acid at its crystallization than p-toluic acid. This allows to purify the terephthalic acid solution with higher content of p-CBA at higher economic effect.
The closest method of purification is described in [GB patent No.1578725, 1980], where authors propose to use a catalyst comprising two or more metals, such as Pt, Pd. Rh, Ru, Os, Ir, Fe, Ni, Co, Cr, Mn and U. where 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 onto the carbon support - active carbon (granules of from 3 to 6mm). Hydropurification is carried out by treating the solution of terephthalic acid with hydrogen in the presence of the mentioned catalysts at high a temperature (280°C) and pressure (~100atm). The rate of the hydrogenation in the presence of bimetallic catalyst (0.4%Pd-0.1%Pt)/C referred to Ig catalyst, is 20% higher than when 0.5%Pd/C is used.
Thus, the crude terephthalic acid, containig p-CBA and other impurities, may be purified by hydrogenation over traditionally prepared catalysts on the base of VIII group supported on carbon.
The invention solves the problem of the creation of selective and stable catalysts and processes wherein the crude terephthalic acid with high content of p-CBA may be selectively
3

hydrogenated to p-toluic acid or/and decarbonylated to benzoic acid with low content of the residual p- CBA.
The foregoing problems are solved by. the present invention which relates to a process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodic Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of -
i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor.
ii) drying said precursor, and
iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material having an average mesopore size in the range of 40 - 400 A, the ratio of mesopores volume in total pore volume at least 0.5,. and graphite-likeness no less than 20%.
The catalyst of this invention includes crystallites of palladium and rhodium or palladium and rhuthenium or palladium and platinum; total content of metals varies from 0.1 to 0.3 % wt, mass ratio of palladium to other metals varies from 0.1 to 10.0.
4

The problem is solved also by the development of the process for the production of a catalyst for purification of terephthalic acid by supporting catalytically active palladium or palladium and at least one of the Group VIII metals upon a carbon material, at the contact of said granules with water solution of salts of palladium or salts of palladium and at least one metal of the Group VIII, with the production of the precusor metal salt - porous carbon, wherein the precusor is dried and treated with reducing agent in the amount sufficient to reduce surface metal salts to metal crystallites, wherein said carbon material is used as mesoporous graphite-like material having an average size of mesopores 40 - 400 A, a share of mesopores in total pore volume not less than 0.5 and degree of graphite-likeness not less than 20%, to produce a metal or bimetal catalyst.
The said catalyst is prepared from one of the following, metal precursors :
H2PdCl4 or Pd(NO3)2 ;
H2PdCl4 and RuOHCl3 or RuNO(NO3)3 ;
pd(NO3)2 and RuOHCl3 or RuNO(NO3)3
For the production of said catalyst the nitrate solutions of palladium and/ or ruthenium salts are used with the concentration of the free nitric acid of from 37 to 170 g/1. Bimetallic catalysts are prepared by co-deposition of the metal precursors or by sequent deposition of the metal precursors.
We have found that such a catalyst may be produced if mono- or bimetallic particles of metals of Group VIII are supported on the carbon material having an average pore size of from 40 - 400 A and a significant (from 20 to 60%) degree of graphite-likeness. The said metallic particles are distributed in bulk of the carbon support so that the maximums of their distribution are at a distance from the external surface of said granule equal to 1-30% of
4A

the radius thereof.
The above mentioned carbon materials are the supports prepared by thermal processing of plastics, as well as those symhesized by specia technology from gaseous hydrocarbons (V.A. Likholobov et al., React.Kin.Cat.Lett.. v.54. 2 (1995) 381-411), namely Sibunit, KVU and various composites on their base.' Physical-chemical characteristics for some carbons are given in the table l.-Data in the table certify that said carbon materials of such parameters as Vmeso/VE and K are sharply different from traditional active carbons typically used for the production of the catalysts for hydropurification of terephthalic acid produced from plant, animal or mineral precursors, preferably coconut active carbons used for the production of traditional catalysts for hydropurification of terephthalic acid.
We also found that at such distribution of the palladium and rhuthenium particles in the granule of mesoporous carbon material, some of palladium may be substituted by rhuthenium. which results in not only lower catalyst cost (because rhuthenium is cheaper than palladium), but also in the change of the ratio of p-toluic and benzoic acids to the latter, that is favorable for reaching the higher quality of the produced crystalline terephthalic acid.
For the production of the said catalysts, i.e. catalysts containing mono- or bimetallic particles of palladium and rhuthenium supported on carbon support, the well known in the literature methods, 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 feasible carbon support is used with further treatment of the supported metal precursors with hydrogen.
The given below examples 1-35 characterize catalytic compositions and the methods for their production. Examples 7, 30~34 are given for comparison, and examples 8 and 35 are given as prototypes. Examples 36-39 describe the methods for terephthalic acid purification. Analysis results of the character of metal particles distribution in the support granule and of the quality of terephthalic acid purified using proposed catalytic compositions, are given in tables 2-6.
Example 1
50g carbon support Sibunit 1 (data on its physical-chemical and texture properties are given in table 1) are loaded to the cylindric rotating reactor. Hereinafter the support is preliminarily purified from the dust by boiling it in distilled water. Then it is discharged to the screen with the cell size of lmm, washed with distilled water and dried at 120°C to the constant weight. Water solutions of Na2CO3 (0.364mole/l; 13ml) and H2PdCl4 (0.182mole/l; 13ml) at the same flow rate (2.5ml/min) at mole ratio of Na2CO3H2PdCl4=2:1 are fed to the injector and the produced mixture is sprayed into the reactor. The catalyst is discharged and dried in a vacuum at 75°C to the constant weight. The next stage of reduction is conducted in the tubular reactor in a hydrogen stream at a temperature of 250°C for 2hr. The temperature is
5

reduced from 250°C to 40°C, and at 110°C the hydrogen is substituted by nitrogen. The catalyst is washed with distilled water till there is no reaction of AgNO3 with chlorine ions in the washing water, and dried in vacuum at 75°C till the constant weight. Pd/Sib.l catalyst is produced with palladium content of 0.5wt%.
Electron microsonding of the catalyst granules is conducted by scanning the cut of granule by diameter on microanalyzer MAP-3 with probe of l~2µm diameter at an accelerating voltage of 20kV and current of 20~30nA. Parameter ? characterizing the thickness of the active layer of metal in µn per 1/2 peak height, is used as the characteristics of distribution of active component in catalyst grain.
The data on the distribution of Pd and Ru particles in the catalytsts was prepared in accordance with the given examples, are given in table 2.
Example 2
The catalyst is prepared using the procedure of example 1, except RuOHCb (0.191 mole/1; 13ml) is used as the water solution instead of H2PdCl4, and concentration of Na2CO3 solution (13ml) corresponds to 0.382mole/l; Na:CO3 ; H2PdCl4 = 2:1. Ru/Sib.l catalyst is produced with Ru content of 0.5wt%.
Example 3
The catalyst is prepared by co-deposition of Ru and Pd using water solutions of RuOHCb and H2PdCl4 correspondingly as metal precursors. For this purpose, 50g of carbon support Sibunit 1 are loaded to the cylindric rotating reactor. 13ml of Na2CO2 water solution (0.371mole/l) and 13ml of H2PdCl4(0.109mole/l) + RuOHCb (0.076mole/l) are fed to the injector at the same flow rate (2.5ml/min) at the mole ratio Na2CO3 : (Ru+Pd) = 2:1, and sprayed into the reactor. The catalyst is discharged and dried under vacuum at 70°C till the constant weight. Further stages of reduction, washing and drying are similar to those of the example 1. (Ru-Pd)/Sib.l catalyst is produced with 0.2wt% Ru and 0.3wt%Pd content.
Example 4
50g of carbon support Sibunit 1 are loaded to the cylindric rotating reactor. 26ml of nitric acid - water solution of Pd(NO3) (0.091mole/l) with concentration of free HNO3 of 170g/l are fed to the injector and a produced mixture is sprayed to the reactor at the rate of 51m/min. The sample is placed into the tubular reactor and dried in an air stream for 1hr while the temperature is increased to 120°C and held at this temperature for 2hr. Then the air is substituted by nitrogen and the temperature is increased to 250°C (at this temperature Pd(NO3)2 is decomposed to Pd oxide). At these conditions the sample is held for 3hr, then cooled to 150°C. Then at this temperature the nitrogen is substituted with hydrogen and the catalyst is reduced for lhr at 150°C with further increase of temperature to 250°C and held at this temperature for 2hr. The temperature is reduced from 250°C to 40°C. since at 110°C the hydrogen is substituted with nitrogen. Pd/Sib.l catalyst is produced with a palladium content
6

of 0.5wt%. Thus the prepared catalyst is used in examples 24, 25 in the synthesis of bimetallic catalysts.
Example 5
The catalyst is prepared using the procedure of example 4, except 26ml nitric acid -water solution of RuNO(NO3)3 (0.091 mole/1) with free HNO3 concentration of 170g/l is used instead of nitric acid - water solution of Pd(NO3)2- Ru/Sib.l catalyst is produced with Ru content of 0.5wt%.
Example 6
The catalyst is prepared by co-deposition of Ru and Pd using as a metal precursor the nitric acid - water solutions of RuNO(NO3)3 and Pd(NO3) correspondingly. For this purpose, 50g of carbon support Sibunit I are loaded to the cylindric rotating reactor. 26ml of nitric acid - water solution of RuNO(NO3)3 (0.038mole/n - Pd(NO3): (0.054mole/l) with free HNO3 concentration of l70g/l are fed to the injector and sprayed to the reactor at the rate of 5mo/min. Further stages of drying, calcination, and reduction are simitar to those of the example 4. (Ru-Pd)/Sib.I catalyst is produced with 0.2wt% Ru and 0.3wr% Pd contents.
Example 7 (comparative)
The catalyst is prepared using the procedure of example 4. except coconut carbon CG-5 is used instead of the carbon support Sibunit I. Pd/CG-5 catalyst is produced with Pd content of 0.5 wt%.
Example 8 (prototype)
The catalyst is prepared using the procedure of example 3, except coconut carbon CG-5 is used instead of the carbon support Sibunit I. (Ru+Pd)/CG-5 catalyst is produced with 0.2wt% Ru and 0.3wt% Pd content.
Example 9
The catalyst is prepared using the procedure of example 3, except 13 ml water solution of Na3CO3 (0.366moie/l) and 13ml of H:PdCL, (0.145 mole/l) + RuOHCb (0.038 mole/l) are fed to the injector; Na2CO3 : (Ru+Pd) = 2:1. (Ru-Pd)/Sib.l catalyst is produced with 0.lwt% Ru and 0.4wt% Pd contents.
Example 10
The catalyst is prepared using the procedure of example 3, except 13ml of water solution of Na2CO3 (0.367 mole/l) and 13ml of H2PdCl4 (0.073 moJe/l)+RuOHCI:. (0.115 mole/l) are fed to the injector; Na2CO3: (Ru+Pd)~2:l. The catalyst (Ru-Pd)/Sib.l is produced with 0.3wt% Ru and 0.2wt% Pd contents.
Example 11
The catalyst is prepared using the procedure of example 6, except 26ml of nitric acid
water solution of RuNO(NO3)3 (0.019mole/l)+Pd(NO3)2 (0.073 mole/l) are fed to the
injector with concentration of free HNO3 of 170g/l. The catalyst (Ru-Pd)/Sib.l is produced
7

with 0.1 wt% Ru and 0.4wt% Pd contents. Example 12 The catalyst is prepared using the procedure of example 6. except 26rnl of nitric acid
- water solution of RuNO(NO5)3 {0.057mole/l)+Pd(NO3)2 (0.036 mole/1) are fed to the
injector with concentration of free HNO3 of 170g/l. The catalyst (Ru-Pd)/Sib.l is produced
with 0.3wt% Ru and 0.2wt% Pd contents.
Example 13
The catalyst is prepared using the procedure of example 5. except 26ml of nitric acid
- water solution of RuNO(NO3)3 (0.038mole/I) are fed to the injector with concentration of
free HN03 of 53g/1. The catalyst Ru/Sib.l is produced with Ru content of 0.2wt%. Thus
produced catalyst is used in the example 18 in the synthesis of bimetallic catalysts.
Example 14
The catalyst is prepared using the procedure of example 13, except 26ml of nitric acid - water solution of RuNO(NO3)3 (0.038mole/l) with concentration of free HNO3 of 170g/l are used. The catalyst Ru/Sib.l is produced with Ru content of 0.2wt%. Thus produced catalyst is used in the example 19in the synthesis of bimetallic catalysts.
Example 15
The catalyst is prepared using the procedure of example 4. except 26ml of nitric acid water solution of Pd(NO3)2 (0.054mole/l) with concentration of free HN03 of 53g/l. The catalyst Pd /Sib. 1 is produced with Pd content of 0.3wt%. Thus produced catalyst is used in the example 20. 22 in the synthesis of bimetallic catalysts.
Example 16
The catalyst is prepared using the procedure of example 15. except 26ml of nitric acid - water solution of Pd(NO3)2 (0.054mole/l) with concentration of free HNO3 of l70g/l. The catalyst Pd /Sib. 1 is produced with Pd content of 0.3wt%. Thus produced catalyst is used in the example 21 in the synthesis of bimetallic catalysts.
Example 17
The catalyst is prepared using the procedure of example 1. except water solutions of Na2CO3 (0.218mole/l; 13ml) and H2PdCI4 (0.109 mole/1; 13ml) is fed to the injector at the same rate (2.5ml/min) at mole ratio of Na2CO3:H2PdCl4=2:l. The catalyst Pd/Sib.l is produced with Pd content of 0.3wt%. Thus produced catalyst is used in the example 23 in the synthesis of bimetallic catalysts.
Example 18
The catalyst is prepared using the procedure of example 17, except Ru/Sib.l of example 13 is used instead of Sibunit 1. The catalyst Pd/Ru/Sib.l is produced with 0.2wt%Ru and 0.3 wt% Pd contents.
Example 19
8

The catalyst is prepared using the procedure of example 15, except Ru/Sib.l of example 14 is used instead of Sibunit 1. The catalyst Pd/Ru/Sib.l is produced with 0.2wt%Ru and 0.3wt% Pd contents.
Example 20
The catalyst is prepared using the procedure of example 2, except water solutions of Na2CO3 (0.152mole/l; 13ml) and H2PdCl4 (0.076 mole/1; 13ml) is fed to the injector at the same rate (2.5ml/min) at mole ratio of Na2CO3:H2PdCl4::=2:l, and Pd/Sib.1 of example 15 is used instead of Sibunit I. The catalyst Ru/Pd/Sib. 1 is produced with 0.2wt% Ru nd 0.3 wt%Pd content.
Example 21
The catalyst is prepared using die procedure of example 13, except Ru/Sib.l of example 16 is used instead of Sibunit 1. The catalyst Ru/Pd/Sib. 1 is produced with 0.2wt%Ru and 0.3wt% Pd contents.
Example 22
The catalyst is prepared using the procedure of example 14, except Ru/Sib.l of example 15 is used instead of Sibunit 1. The catalyst Ru/Pd/Sib.l is produced with 0.2wt%Ru and 0.3wt% Pd contents.
Example 23
The catalyst is prepared using the procedure of example 13. except Pd/Sib.l of . example 17 is used instead of Sibunit 1. The catalyst Ru/Pd/Sib. I is produced with 0.2wt%Ru and 0.3wt% Pd contents.
Example 24
50g Pd/Sib.l prepared in the example 4 is loaded to the cylindric rotating reactor. Water solution of H2PtCl6 (0.0099mole/l; 26ml) is fed to injector and sprayed into the reactor at the rate of 5ml/min. Further stages of reduction, washing and drying and similar to those of the example 1. The catalyst Pt/Pd/Sib.l is produced with 0.1 wt%Pt and 0.5wt%Pd contents.
Example 25
The catalyst is prepared using the procedure of example 24, except water solution of RhCl3 (0.0l9mole/l; 26ml) is used instead of H2PtCl6. The catalyst Rh/Pd/Sib.l is produced with 0.1 wt%Rh and 0.5wt% Pd contents.
Examples 26-27
The catalyst is prepared using the procedure of example 4, except the concentration of free HNO3 is 37g/l (example 26) and !47g/l (example 27). Ru/Sib.l catalysts are produced with Pd content of 0.5wt%.
Example 28
The catalyst is prepared using the procedure of example 1. except 13ml water
9

solution of Na2CO3 (0.727mole/l) and 13ml H2PdCI4 (0.363mole/1) are fed to injector; Na2CO3:Pd=:2:l. Pd/Sib.l catalyst is produced with palladium content of 1 .0wt%.
Example 29
The catalyst is prepared using the procedure of example 1. except 13ml water solution of Na2CO3 (1.453mo!e/l) and 13ml H2PdCI4 (0.727mole/l) are fed to injector; Na2CO3:Pd=2:l. Pd/Sib.l catalyst is produced with palladium content of 2.0wt%:
Example 30 (comparative)
The catalyst is prepared using the procedure of example 4, except active carbon ARES is used instead of carbon support Sibunit 1. Pd/ AR-B catalyst is produced vvith palladium content of 0.5wt%.
Example 31 (comparative)
The catalyst is prepared using the procedure of example 4, except active carbon L-2702 is used instead of carbon support Sibunit 1. Pd/L-2702 catalyst is produced with palladium content of 0.5wt%.
Example 32 (comparative)
The catalyst is prepared using the procedure of example 4. except active carbon FB-4 is used instead of carbon support Sibunit 1. Pd/FB-4 catalyst is produced with palladium content of 0.5wt%.
Example 33 (comparative)
The catalyst is prepared using the procedure of example 1, except active carbon KVU-1 is used instead of carbon support Sibunit 1. Pd/ KVU-1 catalyst is produced with palladium content of 0.5wt%.
Example 34 (comparative)
The catalyst is prepared using the procedure of example 1, except coconut carbon CG-5 is used instead of carbon support Sibunit 1. Pd/ CG-5 catalyst is produced with palladium content of 0.5wt%.
Example 35 (prototype)
The catalyst is prepared by co-deposition of Pt and Pd using as metal precursors the water solutions fo H2PtCl6 and H2PdCl4 correspondingly. For this purpose, 50g of coconut carbon CG-5 are loaded to the cylindric rotating reactor. 13ml of water solution of Na2CO3 (0.330mole/l) and 13ml H2PdCl4(0.145mole/l)+H:PtCl6('0.020mole/l).are fed to injector and
sprayed into reactor at the same rate (2.5ml/min) at mole rntio of Na2CO3:(Pt+Pd)=2:l. The
catalyst is discharged and dried under vacuum at 700°C till the constant weight. Further stages
of reduction, washing and drying are similar to those of the example 1. Produced catalyst (Pt-Pd)/CG-5 contains 0.1 wt% Pt and 0.4wt%Pd.
Example 36
150ml distilled water and 12.9g crude terephthalic acid, containing 8-000ppm p-CBA.
10

and 126pprn p-to!uic acid are loaded to the reactor (4561 Mini Parr Reactor) made of stainless steel. The anchor of the reactor has the form of a net basket intended for loading catalyst granules thereto. The granules of the catalyst, prepared in accordance with example I. in the amount of 0.170a. are loaded to the basket bottom. The basket is fixed to the stirrer shaft. After that the cover is put on the vessel and carefully screwed-up. The reactor is connected with the system. The system is purged with nitrogen, then with hydrogen, and the pressure is set at 14atm using hydrogen. The temperature of 250°C is set on the control pannel and the furnace is turned on. When the temperature in the reactor reaches the prescribed temperature, the stirrer equipped with magnetic gear (~240rpm) is turned on. The time the stirrer is turned on is considered the beginning of the experiment. Experiment time is 3hr. The reactor is opened, the basket with the catalyst is removed from the stirrer shaft and the catalyst is discharged. The content of the autoclave (suspension of terephthalic acid in water) is transferred to the glass filter, filtered, washed with distilled water (50ml) and dried under vacuum at 75°C for 2hr. The produced terephthalic acid powder,is analyzed for impurities content.
Content of p-CBA in purified terephthalic acid is determined using universal polarograph ON-105 by voltammetering method in differential mode of polarization on Hg-graphite electrode by the analytical signal with the maximum at the potential of -1.07V proportional to the concentration of p-CBA in terephthalic acid.
Concentration of p-toluic acid in purified terephthalic acid is determined by high pressure LC method on liquid chromatograph Milichrom-4. The sample of terephthalic-acid is dissolved in 0.3M NH4H2PO4 and analyzed on 2xS0mm column,with fixed phase - anion exchange resin Partisil, 10 SAX (Watman).
Color (transparency) of the purified terephthalic acid is determined by direct measuring of optical density of water-alkaline solutions at 340 and 400nm. For this purpose, 1.5g of purified terephthalic acid are dissolved in 10ml of 2M KOH solution. The solution is preliminary centrifuged during 15min at 3000rpm. Optical density is measured on spectrophotometer (we used Specord M40) in quartz cells of 10mm thickness reffering to 2M KOH solution at 340 and 400nm.
Analysis data on the quality of terephthalic acid, purified by this method over the catalyst, prepared in accordance with'the below given examples, are given in table 3.
Example 2
The method for the purification of terephthalic acid is similar to that descirbed in example 3. except 0.340g catalyst are loaded to the reactor. Besides the catalyst after the experiment (cycle) is washed directly in the basket with distilled water and used in the next cycle. The experiment time for one sample is from 4 to 5 cycles.
Similar data on the quality of terephthalic acid, purified by this method over the

11

catalysts prepared in accordance with the above given examples, are given in table -4 Example 3
The method for the purification of terephthalic acid is similar to that of example except the purification is conducted over the catalysts produced in examples 5 and 34, at the initial content of p-CBA of 30,000ppm,
Analysis data on the quality of terephthalic acid purified by this method are given in
table 5,
Example 4
500ml distilled water H2O and 25g crude terephthalic acid, containing 3,552ppm p-
CBA and I26ppm p-colucid acid, are loaded to the stainless vessel of 750ml volume (dissolver). After that the cover is put on the vessel and carefully screwed-up. 2.0g catalyst, prepared in.the example 1 are placed on the reactor grid, in the form of the stainless tube with inner diameter of 10mm and discharge hole on the distance of 110mm from the tower grid. and the cover fixed with the second grid. The reactor is connected with the dissolver, Reactor's discharge hole is hermetically connected with the crystailizer via rhermostafed still capillary. The said crystallizer is an autoclave made of stainless still of 750ml volume. The dissolver, reactor and crystallizer are placed in the heated thermostat. The system is purged with nitrogen, then with hydrogen at H2 bubbling throught the water suspension of terephthalic acid in dissolver. and the pressure is set at lOatm with hydrogen. The temperature of 250°C is set on the control pannef and the thermostat is turned on. When the temperature in the system reaches the prescribed temperature the hydrogen is fed to the dissolver at the constant mote rate using flow mater. Constant pressure in the system is maintained by a pressure regulator situated at the crystallizer outlet The gas substitutes ihe solution of terephthalic acid from dissolver to reactor. The solution of terephthalic acid is pumped over upward through the catalyst level at i constant rate and discharged via a discharge hole to the crystallizer. "Pumping over" time of the solution throught the reactor is 8hr. The reaction mass is cooled and the installation is purged with nitrogen. The content of the crystallizer (suspension of terephthalic acid in water) is transferred to the glass filter, filtered, washed with distilled water (100ml) and dried under vacuum at 75OC for 2hr. The produced powder of terephthalic acid is analyzed for impurities content
Analysis data on the quality of ferephthalic acid, purified by this method over the catalyst, which is prepared in accordance with the above given examples, are given in table 6.
As may be seen from the examples and tables, the invention proposed allows purification of terephthalic acid till low content of p-CBA and allows to this method to ftnd wide application in the chemical industry.
12

Table 1, Main characteristics of some granulated porous carbon materials

ite m
Grade
Origine (source)
Shape
Size, mm
AHET11 .
m2/g
Vmacro 21
cm3/g
Vmeso31 cm3 /g
Vmeso41 cm3/g
Vmeso
D 51
A
K61
1
AR-B
Charcoal
grip
4-5
438
, 0.192
0.027
0.219
0.12
20
5 10
2
CG-5
Coconut carbott
crushed
3-6
1024
0.438
0,047
0 185
0.10
19

3
L-2702
Charcoal
grip
4-8
1024
0.453
0.046
0 499
0.03
19

4
FB-4
Charcoal
grip
4-6
606
0.222
0.144
0.366
0.39
24

5
KVU-I
Hydrocarbons
granule
3-5
120
0.010
0.310
0.32
u.97
107
40
6
Sibunit I
Hydrocarbons
granule
2-3
440
0.015
0.665
0.680
0.98
62
60
11ABET(m2/g) - specific suriace area by BET, Surfucc urea was calculated on the isotherm scctions, where P/P0-0.05-0,20; the value of the section of the nitrogen molecule in the filled monomolecualr layer was considered equal to w-0. 162 nm2;
21Vmicro (cm3/g) - volume of microporcs. It was calculated using comparative method on the isotherm sections, corresponding to the range between fillilng of micropores and beginning of the capillary condensation;; value VMHKPO corresponds to the total volume of ultramicro- and supermicropores, i.e. to the volume of micropores having the size below 20A,
31Vmesow(cm3/g) = VE-Vmicro;
41 VE (cm3/g) - volume of pores having the size below 5000 A . It was calculated from nitrogen adsorption at P/P0=0.98; 51Dav (A) - an average size of pores calculated us Dav. - 4-104 - VE-/ ABEI
61K (%) - degree of cryslallinity, calculated from the integral intensity of the peak (002); difratograms of the samples were recorded on difractometer IIZG-4C (CuKw graphite monochromator).

Table 2. Properties of the catalysts

Example
No.
Catalyst composition.
wt%
Distribution of metal in granule, u

?llRu
?md Ru
? Pd
?mcl Pd
1
0.5%Pd/Sib.l

27-75
38

0.5%Ru/Sib.l
18-45
32

3
(0.2%Ru-0.3%Pd)/Sib.l
30-91
44
19-82
38
4
0.5%Pd/Sib.l

58-410
302
5
0.5%Ru/Sib.i
220-384
293

6
(0.2%Ru-0.3%Pd)/Sib.l
90-339
240
90-298
249
7
0.5%Pd/CG-5

18-75
41
3
(0.2%Ru-0.3%Pd)/CG-5
12-48
26
9-42

10
(0.3%Ru-0.2%Pd)/Sib.l

22-79
44
14
0.2%Ru/Sib.l
fuzzy
=475

15
0.3%Pd/Sib.l

261-597
371
16
0.3%Pd/Sib.l

477-1530
988
17
0.3%Pd/Sib.l

17-123
46
18
0.3%Pd/0.2%Ru/Sib.l
34-716
285
fuzzy
=580
19
0.3%Pd/0.2%Ru/Sib.l
fuzzy
=766
56-183
134

20
0.2%Ru/0.3%Pd/Sib.l
28-206
92
14-597
211
21
0.2%Ru/0.3%Pd/Sib.l
178-505
286
322-1533
739
22
0.2%Ru/0.3%Pd/Sib.l
64-673
396
56-1150
200
23
0.2%Ru/0.3%Pd/Sib.l
159-430
302
17-239
90
26
0.5%Pd/Sib.l

51-232
121
30
0.5%Pd/AR-B

45-250
128
31
0.5%Pd/L-2702

58-287
150
32
0.5%Pd/FB-4

7-29
17
34
0.5%Pd/CG-5

6-40
18
Parameter A characterizes the thickness of the active layer in µm per 1/2 of the height of the peak of metal distribution in subsurface layer of the granule; _md - a mean average of parameter=?
14

Tablet: Characteristics of TPA purified by
method described m example36

Example No.

Catalyst composition, wt. %
Characteristics of purified TPA

Transmission of alkaline
solutions, %
Impurities content. ppm

340 nm
400 nm
p-CBA
p-+TA
1
0.5%Pd/Sib.l
95.51
98.83
9
3620
2
0.5%Ru/Sib.l
S4.51
96.27
25
520
5
(0.2%Ru-0.3%Pd)/Sib !
93.21
98.42
12
2620
4
0.5%Pd/Sib. 1
84.57
96.86
455
729
5
0.5%Ru/Sib.I
75.78
97.43
851
138
6
(G.2%Ru~d.3%Pd)/Sib.l
89.31
98.47
345
524
7
0.5%Pd/CG-5
66.14
81.65
16
760
8 (0.2%Ru-0.3%Pd)/CG-5
89.90
95.50
10
3696
9
(0.1%Ru-0.4%Pd)/Sib.l
95.79
99.1 5
9
2830
10
(0.3%Ru-G.2%PdySib. 1
94.18
98.56
10
1640
11
(0.1 °/oRu-0.4%Pd)/Sib. 1
91.98
100.00
340
602
12
(0.3%Ru-G.2%Pd)/Sib.I
90.82
100.00
336
394
13
0.2%Ru/Sib. I
69,76
98.16
1265
79
15
0.3%Pd/Sib,l
77.0S
95.96
842
138
16
0.3%Pd/Sib.i
78.22
96.99
772
15!
I8
0.3%Pd/0.2%Ru/Sib,l
97.03
99.70
1402
197
19
0.3%Pd/0.2%Ru/Sib.l
93.08
100.00
131
914
20
0.2%Ru/0.3%Pd/Sib.l
86.52
98.67
446
743
21
0.2%Ru/0.3%Pd/Sib. 1
77.66
97.51 .
973
284
23
0.2%Ru/0.3%Pd/Sib. 1
77.80
97.51
1303
201
24
0,I%Pt/0.5%Pd/Sib.l
75.54
97.56
200
689
25
0.1%Rh/0.5%Pd/Sib.S
52.57
96.30
494
176
26
0,5%Pd/Ssb. I
92.88
97.17
56
2251
27
0.5%Pd/Sib.l
95.00
98.90
83
3662
28
1%Pd/Sib,l
89.50
94.23
6
6048
29
2%Pd/Sib.l
100.00
100.00
15
5443
30
0.5%Pd/AR-B
72.65
94.28
432
235
31
0.5%Pd/L-2702
56.28
99.00
676
184
32
0.5%Pd/FB-4
59.84
92.57
412
230
33
0.5%Pd/KVU-l
94.79
94.44
6
1020
15

Table 3 continued

Example*
No,
Catalyst composition, wt. %
Characteristics of purified TPA

Transmission of alkaline Impurities content, solutions. % ppm

340 nm
400 nm P-CBA
p-TA
34
0.5%Pd/CG-5
98.6
100.00
6
559
35
(0.1%Pt-0.4%Pd)/CG-5
87.57
98.41
18
1200
16

Table 4. Characteristics of TPA purified by the method described in example 2

Example No.
Catalyst composition. wt%
Cycle No.
Characteristics of purified TPA

Transmittance of alkaline solutions, %
Impurities content, ppm

340 nm
400 nm
p-CBA
p-TA
1
0.5%Pd/Sib.l
I
96.52
98.85
6
249

2
97.18
99.52
5
6955

3
94.25
98.35
5
4534

4
89.90
95.92
6
2688

5.
88.55
95.63
4
1058
2
0.5%Ru/Sib.l
1
89.86
97.79
24
1067

2
88.39
98.60
23
546

3
84.81
100.00
25
269

4
80.46
96.16
23
297

5
82.44
97.12
25
199

(0.2%Ru-0.3%Pd)/Sib.l
1
95.80
99.17
11
1873

2
96.64
100.00
10
1528

3
97.50
100.00
9
1218

4
89.19
96.25
14
974

5
84.46
94.30
15
907
6
(0.2%Ru-0.3%Pd)/Sib.l
1
93.80
99.08
6
1890

2
92.06
97.08
8
1033

3
90.51
97.42
53
949

4
88.76
97.47
85
1117

5
82.00
97.85
206
1151
7
0.5%Pd/CG-5
I
98.11
100.00
5
4402

2
97.74
100.00
7
1381

3
94.78
99.08
12
748

4
91.95
99.22
52
882
8
(0.2%Ru-0.3%Pd)/CG-5
1
99.27
100.00
9
5275

2
99.30
100.00
40
1613

3
96.53
100.00
34
3142

4
91.38
98.26
60
511
17

Table 4 continued

Example No.
Catalyst composition, wt%
Cycle No,
Characteristics of purified TPA

Transmmance of alkaline solutions. %
Impurities content. ppm

340 nm
400 nm
p-CBA
p-TA

5
90.91
99.46
202
442
19
0.3%Pd/0.2%Ru/Sib.l
1
93.84
99.18
12
7200

2
90.67
97.65
88
6200

94.78 | 100.00
279
756

4
83.80
96.18
366
873

5
79.52
95.06
297
672
20
0.2%Ru/0.3%Pd/Sib.l
1
97.13
100.00
8
1267

2
90.87
100.00
219
571

3
82.48
100.00
865
549

4
76.62
100.00
1213
477

5
68.24
96.39
1312
319
23
0.2%Ru/0.3%Pd/Sib. 1
1
96.80
100.00
255
899

2
83.89
97.13
405
168

3
75.50
94.09
778
124

4
70.48
93.70
814
155

5
67.61
94.70
1003
286
26
0.5%Pd/Sib.l
1
97.87
100.00
10
2612

2
98.71
100.00
10
2352

3
95.33
100.00
6
361

4
92.26
99.44
72
470

5
86.55
97.88
198
655
34
0.5%Pd/CG-5
1
94,85
96.84
8

2
95,41
100,00
11

3
93,72
98.87
71

4
91,28
97,72
. 360

89,16
97,24
739

18

Tabie 5. Characteristics of TPA purified by method described in example 3 (intial content of p-CBA 30,00ppm)
Example
No.
Catalyst composition, wt%
Cycle No-
Characteristics of purified TPA

Transmittance of alkaline
solutions, %
p-CBA
content

340 nm
400 nm

(0.2%Ru-0.3%Pd)/Sib.l
1
92,22
97,00
10

2
94,34
98,33
20

3
93,93
97,46
31

4
79,58
93,73
41

5
77,89
93,46
156
34
0.5%Pd/CG-5
1
97,95
98,54
9

2
91,15
97,67
37

3
88,29
97,68
434

4
72,85
97,52
1607

5
41,71
92,83
3447
19

Table 6. Characteristics of TPA purified by method described in example 4

Example No.
Catalyst composition, wt%
Experiment time (t), hr
Catalyst weight (Pwt.). g
Lw11
Characteristics of purified TPA

Tratismittance of alkaline solutions. %
Impurities content.

340 nm
400 nm
P-CBA
p-IA
1
0.5%Pd/Sib. 1
8
2,00
29.5
90.7
97.1
15
460
'3
0.2%Ru-0,3%Pd/Sib.l
10
2.00
4,2
92,17
99.21
32
1930
3
0.2%Ru-0.3%Pd/Sib.l
10
2,00
18.8
83.01
9 1.88
80
116
4
0.5%Pd/Sib.l
10
2.00
1.2

55
1242
4
0.5%Pd/Sib.l
10
2.00
20.3
86.6
99.3
189
10 10
7
0.5%Pd/CG-5
10
2.00
22.4
88.75
97.19
164

8
0.2%Ru-0.3%Pd/CG-5
10
2.00
17.3
92.13
99.27
100
152
33

10
2.00
20.1
87.81
98.46
80
162
34
0.5%Pd/CG-5
10
2.00
20.2
89.7
95 3
15
162
^ Volumetric load on catalyst 1.w=WIPA/(Pwt-t) wherein WTPA-volumeof TPA solution passed though the catalyst layer during time.

WE CLAIM ;
1. A process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodic Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being, at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of -
i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor.
ii) drying said precursor, and
iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material having an average mesopore size in the range of 40 - 400 A, the ratio of mesopores volume in total pore volume at least 0.5 and graphite-likeness no less than 20%.
2. A process as claimed in Claim 1, wherein the metal crystallites are
palladium and rhodium.
3. A process as claimed in Claim 1, wherein the metal crystallites are
palladium and ruthenium.
4. A process as claimed in Claim 1, wherein the metal crystallites are
palladium and platinum.
5. A process as claimed in Claim 1, wherein a total of metal content is in the
range of 0.1 to 3.0 wt %.
21

6. A process as claimed in Claim 1, wherein the weight ratio of palladium to
the other constituent metals is in the range of 0.1 to 10.
7. A process as claimed in Claim 1, wherein the said catalyst composition is
prepared from one of the following metal precursors :
H2PdCl4 or Pd(NO3)2 ;
H2PdCl4 and RuOHCl3 or RuNO(NO3)3 ;
Pd(NO3)2 and RuOHCl3 or RuNO(NO3)3
8. A process as claimed in Claim 1, wherein nitric acid solutions of palladium
and/or ruthenium salts with the concentration of the free acid within the range
37 to 170 g/1.are used for the preparation of the said catalyst composition.
9. A process as claimed in Claim 1, wherein bimetal catalysts are prepared
by co-depositing the metal precursors.
10. A process as claimed in Claim 1, wherein catalysts are prepared by
successively depositing the metal precursors.
11. A method for preparing a catalyst for purification of terephthalic acid,
substantially as hereinbefore described particularly with reference to the
appended examples.
DATED THIS 27TH DAY OF JULY, 2000.

Dr. A. Basu.
of D. SEN & CO.
Attorney for the Applicant.
22
Heretofore problems were encountered in preparing selective and stable catalysts for purifying terephthalic acid with high content of p - CBA.
The present invention attempts to overcome the foregoing problem and relates to a process for preparing a catalyst for purification of terephthalic acid consisting of crystallites of catalytically active palladium or palladium and at least one metal of Group VIII of the Periodical Table deposited on a carbon material wherein said metal crystallites are distributed through the bulk of granules of said carbon material so as within a layer being at a distance from the outer surface of said granule equal to 1 - 30% of the radius thereof, the said process comprising the steps of -
i) contacting granules of carbon material with an aqueous solution of palladium salts or salts of palladium and at least one metal of Group VIII to produce a "metal salt-porous carbon" precursor.
ii) drying said precursor, and
iii) treating said precursor with a reducing agent like hydrogen to reduce surface metal salts to crystallites of said metal, whereby a catalytically active palladium or palladium and at least one metal of Group VIII is deposited upon the surface of said granules to produce a metal or bimetal catalyst, wherein said carbon material is a mesoporous graphite-like material.

Documents:

00428-cal-2000-abstract.pdf

00428-cal-2000-claims.pdf

00428-cal-2000-correspondence.pdf

00428-cal-2000-description(complete).pdf

00428-cal-2000-form-1.pdf

00428-cal-2000-form-2.pdf

00428-cal-2000-form-3.pdf

00428-cal-2000-form-5.pdf

00428-cal-2000-pa.pdf

00428-cal-2000-priority document.pdf

428-cal-2000-granted-abstract.pdf

428-cal-2000-granted-claims.pdf

428-cal-2000-granted-description (complete).pdf

428-cal-2000-granted-examination report.pdf

428-cal-2000-granted-form 1.pdf

428-cal-2000-granted-form 2.pdf

428-cal-2000-granted-form 3.pdf

428-cal-2000-granted-form 5.pdf

428-cal-2000-granted-letter patent.pdf

428-cal-2000-granted-pa.pdf

428-cal-2000-granted-priority document.pdf

428-cal-2000-granted-reply to examination report.pdf

428-cal-2000-granted-specification.pdf

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Patent Number

195157

Indian Patent Application Number

428/CAL/2000

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

21-Oct-2005

Date of Filing

27-Jul-2000

Name of Patentee

SAMSUNG GENERAL CHEMICALS CO. LTD

Applicant Address

SAN 222-2, DOKGOD-RI, DAESAN-UP, SEOSAN-SI, CHUNGNAM PROVINCE

Inventors:

#	Inventor's Name	Inventor's Address
1	ROMANENKO, ANATOLII VLADIMIROVICH	RU, 630058, NOVOSIBIRSK, UL. SHULUZOVAYA, D.22, KY, 52
2	LIKHOLOBOV, VLADIMIR ALEKSANDROVICH	RU, 630090, NOVOSIBIRSK, UL, DETSKII PROEZD, D.9, KV.8
3	TIMOFEEVA, MARIA NIKOLAEVNA	RU 630090, NOVOSIBIRSK, UL. MORSKOI PROSPEKT, D.48. KV.50
4	JHUNG, SUNG HWA	KR, TAEJEON-SI, UL. CHUNGSOL D.V, KV.1104
5	PARK, YOUN SEOK	KR, TAEJEON-SI, UL. SEJEONG, D.103, KV.302

PCT International Classification Number

B01J 23/40

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	99116348	1999-07-29	Russia