BRPI0714962B1 - palladium / carbon catalysts and their preparations - Google Patents

Abstract

patent for "palladium / carbon catalysts and their preparations". The present invention relates to a palladium / carbon catalyst, in which palladium maintained on activated carbon support is present as crystallites, wherein crystallites with particle size of less than 2.5 nm comprise at least 80% by weight of the total. palladium crystallites. The present invention further relates to a process for preparing the palladium / carbon catalyst, wherein a solution used to impregnate or spray the activated carbon support contains a palladium compound and a compound of formula i, wherein n and m are independently. 0 or an integer from 1 to 5; and r1, r2 and r3 are independently selected from the group consisting of h, ch3, nh2, oh and cooh.

Description

Patent Descriptive Report for "PALADIUM / CARBON CATALYSTS AND THEIR PREPARATIONS" Cross Reference of Related Applications This application claims the benefit of Chinese Patent Application No. 200610029964.4 filed August 11, 2006, incorporated herein by reference in its integrity and for all purposes.

Field of the Invention The present invention relates to the metallic palladium kept on the activated carbon catalyst (referred to as palladium / carbon catalyst) and to a process for its preparation, and in particular to a palladium / carbon catalyst used. in the refinement of crude terephthalic acid by selective hydrogenation and a process for preparing it.

Description of the art Palladium / carbon catalysts are widely used in the selective hydrogenation of unsaturated organic compounds. In particular, palladium / carbon catalysts are useful in refining crude terephthalic acid, where some impurities in crude terephthalic acid such as 4-carboxybenzaldehyde (4-CBA) are converted by hydrogenation to other compounds, and the terephthalic acid product. It can then be isolated by crystallization. Since palladium / carbon catalysts typically contain an individual active component, known prior art research to improve these catalysts has primarily emphasized the support structure and the distribution of metallic Pd [palladium] on the support, and these aspects actually considerably affect properties of catalysts.

As the terephthalic acid hydro-refinement reaction is a first order reaction and the reaction rate is rapid, the reactants are difficult to diffuse into the catalyst particles during the reaction, so the active component within the Catalyst particles may not work well. Thus, to make full use of the noble metal, catalysts are generally prepared as one of the types of eggshell in which the active component, ie the noble metal, is kept mainly on the surface of the support.

As the hydrogenation reaction is performed on the surface of metallic Pd, as a rule for catalysts containing the same amount of metallic Pd charge, the greater the degree of dispersion of metallic Pd in a catalyst and / or the higher the metallic Pd content. maintained in the catalyst and / or the better the thermal stability of the catalyst, the greater the catalyst activity and the longer the catalyst life.

If the solution containing a Pd compound (such as sodium chloropaladate or palladium chloride) is loaded directly onto an activated carbon, a very thin, shiny layer of metallic palladium will appear quickly on the surface of activated carbon. The reason is mainly due to the fact that the surface of activated carbon has reduction groups such as aldehyde group and free electrons, which will easily reduce the Pd ion to the zero valence metallic Pd. As a result, the catalysts thus prepared have very low degrees of dispersion of metallic Pd. One method to overcome this problem is to convert the Pd ion into the impregnating liquid containing Pd compound into an insoluble compound prior to impregnation. For example, a water-soluble Pd compound may be hydrolyzed at room temperature to insoluble Pd (OH) 2 or PdO H20, which is then kept in an activated carbon and then reduced with a reducing agent such as formaldehyde, sodium formate, glucose, formic acid and hydrogen gas. Thus, Pd migration and growth of palladium crystallites can be prevented. For example, US 3,138,560 demonstrates that hydrogen peroxide is added in an impregnation liquid to hydrolyze a water-soluble Pd compound to an insoluble compound, and impregnation is then performed. US 4,476,242 suggests the preparation of an impregnating liquid containing Pd compound using an organic solvent such as methanol, pyridine and the like. It is reported that this is also effective in preventing Pd migration and the increase of palladium crystallites. In addition, there are patents reporting that a chloropaladic acid solution is converted to a colloidal solution containing Pd by adjusting the pH value, and it is said that this can prevent reducing groups on the surface of an activated carbon from directly reducing Pd ions to a zero valence metal Pd. CN1698952A discloses the addition of nitrogen-containing polycarboxylic acids in an impregnation liquid used to prepare a palladium / carbon catalyst.

An object of the present invention is to provide an innovative palladium maintained on an activated carbon catalyst. The metal Pd in the catalyst has a high degree of dispersion, a higher crystallite content and better thermal stability. When used in the crude refinement of crude terephthalic acid, the catalyst can provide a greater conversion of 4-carboxybenzaldehyde (4-CBA).

Another object of the invention is to provide a process for preparing the palladium / carbon catalyst.

DETAILED DESCRIPTION OF THE INVENTION In the first aspect, the present invention provides a palladium / carbon catalyst in which palladium held on an activated carbon support is present as nanometer size crystals, and in which crystallites with particle size of less than 2 µm. 5 nm constitutes at least 80 wt%, preferably at least 85 wt%, more preferably at least 88 wt% and more preferably at least 90 wt% of the total palladium crystallites.

In the palladium / carbon catalyst according to the invention, a metallic Pd content preferably is in the range of 0.05 to 5% by weight, and more preferably in the range of 0.2 to 3.5% by weight based on total weight of catalyst.

In a preferred embodiment, the maintained palladium is enriched in an activated carbon support surface layer such that, in the case where the palladium / carbon catalyst has a Pd content of 0.50 ± 0.10 wt%. Palladium crystallites in a 5 nm depth layer under the surface of the activated carbon support comprise at least 30 wt.%, preferably at least 40 wt.% and more preferably at least 50 wt. total weight of all atoms in this layer; and palladium crystallites in a layer at 300 nm depth under the surface of the activated carbon support comprise at least 5 wt%, preferably at least 10 wt%, more preferably at least 15 wt% and more preferably at least 20% by weight of the total weight of all atoms in this layer.

In the palladium / carbon catalyst according to the invention, the maintained palladium is highly dispersed on the surface of the activated carbon support, with a minimum dispersion degree of 5%, preferably at least 10%, more preferably at least 15% and more. preferably at least 20%. After calcining the catalyst in a nitrogen stream, which bubbled in water (at 25 ° C) at 500 ° C for 10 hours, the maintained palladium has an average particle size of at most 10 nm, preferably at most 8, 0 nm, more preferably at most 7.0 nm, and more preferably at most 7.0 nm.

In the second aspect, the present invention provides a process for preparing the palladium / carbon catalyst, the process of which comprises the following steps: a) washing an activated carbon with an aqueous solution of an inorganic acid, and then with water to neutralize, and then then dry the washed activated carbon to obtain an activated carbon support; b) impregnating or spraying the activated carbon support with an aqueous solution containing a Pd compound and an additive to support the Pd compound on an activated carbon support to provide a catalytic precursor, where a molar ratio of the additive with Pd in the Pd compound in the solution is in the range 0.01: 1 to 2.0: 1; the additive is selected from the compounds represented by the general formula I: wherein n, m and I are independently 0 or an integer from 1 to 5; and R 1, R 2 and R 3 are independently selected from the group consisting of H, CH 3, NH 2, OH and COOH; and the palladium containing solution is adjusted to a pH value of 7 + 3; and c) treating the catalytic precursor with a reducing agent to provide the palladium / carbon catalyst.

In a preferred embodiment, the above process further comprises catalytic precursor aging at a temperature of 0 to 80 ° C for 1 to 50 hours prior to catalytic precursor reduction treatment. There are no specific limitations on the activated carbon used in the invention. An example of activated carbon is coconut shell activated carbon with a specific surface area above 900 m2 / g and particle size in the range of 4 to 8 mesh. The aqueous inorganic acid solution useful in the process according to the invention may have an acid concentration of 0.01 to 5 M (mole / liter), preferably 0.01 to 3.0 M. Examples of inorganic acid include, but are not limited to, hydrochloric acid, nitric acid and phosphoric acid. The time period for acid washing is not crucial, but preferably within a range of 0.5 to 8 hours, and more preferably within a range of 0.5 to 4 hours.

After washing with the aqueous inorganic acid solution, the activated carbon is washed with water to neutrality and then allowed to dry. Drying is generally performed at a temperature of 80 to 150 ° C for 0.5 to 10 hours, and preferably for 0.5 to 6 hours.

Examples of the Pd compound useful in the invention include, but are not limited to, palladium halides, palladium acetate, palladium nitrate, chloropaladic acid, basic chloropaladic acid salts, palladium amino complexes and mixtures thereof. Preferably the Pd compound is chloropaladic acid or palladium acetate. The solution containing the compound Pd and the additive preferably has a pH value between 4 and 9. The concentration of compound Pd in terms of Pd in the solution is preferably in the range 0.01 to 20% by weight, more preferably. in a range of 0.1 to 10% by weight and more preferably in a range of 0.2 to 3.6% by weight. The amount of additive used in the solution containing Pd may vary depending on the compound Pd used as well as the additive used. In general, however, a molar ratio of the additive to Pd in the Pd compound in the solution in the range of 0.01: 1 to 2: 1 is feasible, and the molar ratio of the additive to Pd in the compound Pd is preferably in the ranges. from 0.05: 1 to 1.5: 1, and more preferably in a range from 0.1: 1 to 1.0: 1.

Examples of the compound of general formula I useful in the invention include: Examples of reducing agent used to reduce catalyst precursor include, but are not limited to, formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose, hydrogen gas and mixtures of these. Preferably, the reducing agent is sodium formate or hydrazine hydrate. The amount of reducing agent used is determined according to the amount of active component, Pd, and is generally in the range of 1 to 10 times, and preferably 2 to 5 times of the theoretical amount required by the reduction reaction. The catalytic precursor reduction treatment may be performed according to procedures and under conditions well known to those skilled in the art. For example, the reduction treatment may be performed at a temperature of from 0 to 200 ° C, preferably from 20 to 120 ° C for 0.5 to 24 hours, preferably for 1 to 10 hours and more preferably for 1 to 4 hours. .

In a preferred embodiment, the process for preparing the palladium / carbon catalyst according to the invention consists of the following steps: i) washing an activated carbon support of particulate or particulate material with an aqueous solution of an acid by 5 to 8 hours, the aqueous acid solution having an acid concentration of 0.01 to 3.0 mole / liter, and at least the acid selected from the group consisting of hydrochloric acid, nitric acid and phosphoric acid; ii) washing the acid washed activated carbon support with water to neutral, and then drying at a temperature of 80 to 150 ° C for 0.5 to 10 hours to provide a treated activated carbon support; iii) impregnating or spraying the activated carbon support treated with an aqueous solution containing a water-soluble Pd compound and an additive of the general formula I: wherein n, m and I are independently 0 or an integer from 1 to 5; and R 1, R 2 and R 3 are independently selected from the group consisting of OH, H, CH 3, NH 2 and COOH to support the Pd compound on the treated activated carbon support to provide a catalytic precursor, where a content of the compound of Pd in terms of Pd in the aqueous solution is in the range 0.1 to 10% by weight, a molar ratio of the additive to Pd is in the range 0.05: 1 to 1.5: 1, and the aqueous solution is adjusted at a pH value of 7 + 3; iv) aging the catalytic precursor obtained from step iii) at a temperature of 0 to 80 ° C for 1 to 50 hours; and v) treating the aged catalytic precursor with a reducing agent, thereby reducing the Pd ion in the Pd compound to the metallic Pd to obtain the palladium carbon catalyst.

Compared to the state of the art, the present invention has advantages that the prepared catalyst has a higher degree of metallic Pd dispersion and a higher crystallite content, and that the catalyst exhibits a high activity and a long service life.

Examples: The following examples are provided to further illustrate the invention, but without limitation of the invention.

In the examples, the following test methods are used: (1) Degree of dispersion of metallic palladium: The degree of dispersion of metallic palladium was measured by the hydrogen-oxygen titration method using chemical adsorption equipment. The degree of dispersion was calculated according to the following equation: Degree of dispersion = ((2xVadS · X MPd) / (3 x 22400 x Wamostra x Cpd)) x 100% Where: Vads- Represents the amount of adsorbed hydrogen gas by the sample, Mpd represents the atomic weight of Pd, Wamostra represents the weight of the sample and Cpd represents the content of Pd in the sample. (2) Crystallite content: As used herein, the term "crystallite content" is intended to mean a crystallite content with a particle size of less than 2.5 nm. The palladium content in the catalysts was measured by X-ray fluorescence spectrograph, and the particle sizes of the metallic Pd crystallites by X-ray diffractometer (XRD). Then the crystallite content was calculated as: Crystallite content = ((Weight of metallic Pd crystallites with particle size below 2.5 nm) / (Total weight of metallic Pd)) x 100%. (3) Thermal Stability: An average particle diameter of Pd crystallites from a palladium / carbon catalyst was measured by X-ray diffractometer (XRD). After calcining the catalyst in a nitrogen stream, which bubbled in water (at 25 ° C) at 500 ° C for 10 hours, an average particle diameter of the Pd crystallites was measured again by X-ray diffractometer. (XRD). The average particle diameter of Pd crystallites after calcination as well as the change in mean particle diameter of Pd crystallites before and after calcination indicate the thermal stability of the catalyst. The smaller the average particle diameter of Pd crystallites, the better the thermal stability of the catalyst. And the smaller the change in mean particle diameter of Pd crystallites before and after calcination, the better the thermal stability of the catalyst. (4) Pd content in layers of various depths under the surface of the catalysts: The surface of a catalyst was etched with argon. After recording at a certain depth, the surface layer Pd content revealed by the recording was measured by X-ray photoelectron spectrometry (XPS) and Auger electron spectroscopy (AES), and thus the Pd content was obtained. in the layers at various depths below the catalyst surface.

Example 1: A 100 g volume of activated carbon from the coconut shell, which was passed through a 4 mesh screen but retained in an 8 mesh screen and with a specific surface area of 1100 m2 / g, was washed with 200 ml of 0.4 M aqueous nitric acid solution for 2 hours. After removing the acidic solution, the activated carbon was washed with deionized water to neutrality and then dried at 120 ° C for 6 hours.

To 3.2 g of aqueous chloropaladic acid solution containing 16 wt% palladium, deionized water was added to a total volume of 40 ml. Then, 2.16 g of 10 wt% solution of additive A in water was added, followed by the addition of deionized water until the total volume of the solution reached 60 ml. Aqueous 3% NaOH solution was added to adjust the pH value of the Pd-containing solution to approximately 7. After aging for 180 minutes, the Pd-containing solution was used to impregnate the activated carbon treated above for 3 hours to provide a precursor. catalytic The catalytic precursor was aged at room temperature for 24 hours, and then soaked in a reducing liquid consisting of 20 g of 5% by weight aqueous hydrazine hydrate solution and 200 g of pure water at 20 ° C for 3 hours. After removing the liquid by filtration, the solids were washed with pure water to neutrality and then dried to provide a catalyst product.

Examples 2 to 24: The procedure as described in Example 1 was followed, but different Pd compounds and different additives were used to prepare the Pd containing solution. The Pd compounds used, Pd compound content in terms of Pd in the Pd-containing solution, the additives used and the molar ratios of the Pd additives are shown in Table 1 below.

Examples 25 to 30: The procedure as described in Example 1 was followed except that different additives (the additives used are shown in Table 1) were used to prepare the Pd containing solution, the Pd containing solutions were sprayed on carbon. catalyst precursors, and inorganic acids, inorganic acid concentrations, acid washout times, drying times, temperatures, pH values of the additive-containing solutions and Pd compound, reducing agents, reduction treatment temperatures and time periods for reduction treatment as shown in Table 2 below.

Comparative Example: The procedure as described in Example 1 was followed except that no additives were used in the preparation of the solution containing Pd.

The degrees of dispersion, crystallite content, thermal stability and Pd content of the layers at various depths below the catalyst surface were measured on the catalysts prepared in the Examples and Comparative Example. Catalysts were better evaluated under the evaluation conditions as shown below. Results are shown in Tables 3 and 4 below.

Catalyst evaluation conditions: Amount of catalyst: 2.0 g Amount of crude terephthalic acid: 30.0 g Amount of 4-CBA: 1.0 g Reaction pressure: 70 kg Partial gas pressure 5.0 kg : Reaction time: 1.0 hour Reaction temperature: 270 ° C

4-CBA conversion = quant. of 4-CBA added - quant. Residual x 100% Amount of 4-CBA added ________________________________ Table 3 ________________________________ ι _______________________________ Table 4 ____________________________ Patents, patent applications, non-patent literature, and test methods cited in the report are incorporated herein by reference.

While the invention has been described with respect to embodiments of the examples, it will be understood by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. Therefore, the invention is not limited to the particular embodiments disclosed as the best contemplated embodiment of this invention, but will include all embodiments within the scope of the appended claims.

Claims (8)

Process for preparing a palladium / carbon catalyst, consisting of the operations of: (a) washing an activated carbon with an aqueous solution of an inorganic acid, and then with water to neutralize, and then drying the washed activated carbon to get an activated carbon support; (b) impregnating or spraying the activated carbon support with an aqueous solution containing a Pd compound and an additive to support the Pd compound on an activated carbon support to provide a catalytic precursor, wherein a molar ratio of Pd additive in the Pd compound in solution is in the range 0.01: 1 to 2.0: 1; the additive is selected from the compounds represented by general formula I; Where n, m and 1 are independently 0 or an integer from 1 to 5; and R1, R2 and R3 are independently selected from the group consisting of H, CH3, NH2, OH and COOH; and the palladium containing solution is adjusted to a pH value of 7 + 3; and (c) treating the catalytic precursor with a reducing agent to provide the palladium / carbon catalyst. Process according to Claim 1, characterized in that the inorganic acid is at least that selected from the group consisting of hydrochloric acid, nitric acid and phosphoric acid; the acid wash time is in the range of 0.5 to 8 hours; the inorganic acid solution has an acid concentration of 0.01 to 5.0 moles / liter; and drying is performed at a temperature of 80 to 150 ° C for 0.5 to 10 hours. Process according to Claim 1 or 2, characterized in that the Pd compound is selected from palladium halide groups, palladium acetate, palladium nitrate, doropaladic acid, doropaladic acid basic salts, amino acid complexes. palladium and mixtures thereof; the palladium concentration in the solution containing Pd is in the range 0.01 to 20% by weight; and a molar ratio of the palladium additive to compound Pd in solution is in the range 0.01: 1 to 2.0: 1. Process according to Claim 3, characterized in that the compound Pd is chloropaladic acid or palladium acetate, the solution containing the compound Pd and the additive has a pH value of 4 to 9; the palladium concentration in the solution is in the range 0.1 to 10% by weight; and the molar ratio of the palladium additive to the Pd compound in the solution is in the range 0.05: 1 to 1.5: 1. A process according to any one of claims 1 to 4, further comprising aging the catalytic precursor at a temperature of from 0 to 80 ° C for 1 to 50 hours prior to the reduction treatment. Process according to any one of Claims 1 to 5, characterized in that the reducing agent is selected from the group consisting of thermal acid, sodium formate, formaldehyde, hydrazine hydrate, glucose, hydrogen gas and mixtures thereof. ; and the reduction treatment is performed at a temperature of 0 to 200 ° C for 0.5 to 24 hours. Process according to claim 6, characterized in that the catalytic precursor is aged at a temperature of from 0 to 80 ° C for 1 to 24 hours before carrying out the reduction treatment; the reducing agent is sodium formate or hydrazine hydrate and the reducing treatment is conducted at a temperature of 20 to 120 ° C for 1 to 10 hours. Process for preparing palladium on the carbon catalyst according to claim 1, characterized in that it consists of the following steps: (i) Washing an activated carbon support of particulate or particulate material with an aqueous solution of an acid for 0.5 to 8 hours, the aqueous acid solution having an acid concentration of 0.01 to 3.0 moles / liter, and at least the acid is selected from the group consisting of hydrochloric acid, nitric acid and acid phosphoric; (ii) washing the acid-washed activated carbon support with water to neutral, and then drying at a temperature of 80 to 150 ° C for 0.5 to 10 hours to provide a treated activated carbon support; impregnate or spray the activated carbon support treated with an aqueous solution containing a water-soluble Pd compound and an additive of the general formula I: wherein n, m and I are independently 0 or an integer from 1 to 5, and R 1 R2 and R3 are independently selected from the group consisting of OH, H, CH3, NH2 and COOH to support the Pd compound on the treated activated carbon support to provide a catalytic precursor, where a content of the Pd compound in terms of Pd in the aqueous solution is in the range 0.1 to 10 wt.%, a molar ratio of the additive to Pd is in the range 0.05: 1 to 1.5: 1, and the aqueous solution is adjusted to a pH value of 7 ± 3, (iv) aging the catalytic precursor obtained from operation (iii) at a temperature of 0 to 80 ° C for 1 to 50 hours, and (v) treating the aged catalytic precursor with a reducing agent, thereby reducing the Pd ion in the Pd compound to the metallic Pd to provide palladium on the carbon catalyst.