A palladium-on-carbon catalyst, its preparation method and application

Abstract

This invention provides a palladium-on-carbon catalyst, its preparation method, and its application. The palladium-on-carbon catalyst comprises: an activated carbon support and palladium supported on the activated carbon support, wherein, based on the mass of the activated carbon support (100%), the mass fraction of palladium is 0.2–0.9%; the palladium content exhibits a protein-like distribution, with less than 5% palladium distributed in a 0–5 μm surface layer, 80–95% palladium distributed in a 5–50 μm protein-like layer, and the remainder distributed in an inner layer of 50–200 μm. The palladium-on-carbon catalyst provided by this invention is used in the purification reaction of crude terephthalic acid, and features reduced palladium loss, high catalyst activity, and long catalyst lifetime.

Description

Technical Field

[0001] This invention belongs to the field of palladium-on-carbon catalyst preparation, specifically relating to a palladium-on-carbon catalyst, its preparation method, and its application. Background Technology

[0002] Currently, in the production of crude terephthalic acid through hydrogenation refining, to increase the contact area between the reactants and the active palladium component in the catalyst, thereby improving catalytic activity, the selected supported palladium-on-carbon catalysts typically exhibit a higher palladium content closer to the outer layer, displaying a typical eggshell-shaped distribution. However, in actual production, the palladium in the top 5 μm layer is easily washed away by the reaction fluid and enters the ash along with the wear of the activated carbon surface, leading to a decrease in catalyst activity. Summary of the Invention

[0003] To address the problem of low catalyst activity caused by palladium loss during use in existing palladium-on-carbon catalysts, this invention provides a palladium-on-carbon catalyst, its preparation method, and its application. The palladium-on-carbon catalyst provided by this invention is used in the purification reaction of crude terephthalic acid, and features reduced palladium loss, high catalyst activity, and long catalyst life.

[0004] In a first aspect, the present invention provides a palladium-on-carbon catalyst, comprising: an activated carbon support and palladium supported on the activated carbon support, wherein, based on the mass of the activated carbon support as 100%, the mass percentage of palladium is 0.2-0.9%; the palladium content is distributed in a protein-like manner, with less than 5% of palladium distributed in a surface layer of 0-5 μm, 80-95% of palladium distributed in a protein-like layer of 5-50 μm, and the remainder of palladium distributed in an inner layer of 50-200 μm.

[0005] In some embodiments, the mass fraction of palladium is 0.45% to 0.55%, for example 0.45%, 0.48%, 0.51%, or 0.54%.

[0006] In a second aspect, the present invention provides a method for preparing a palladium-on-carbon catalyst, comprising:

[0007] S1: The activated carbon support loaded with palladium precursor is washed with a rinsing solution.

[0008] S2: The activated carbon carrier treated in S1 is then subjected to reduction treatment.

[0009] In some embodiments, in S1, the activated carbon support for the palladium precursor is prepared by a method comprising the following steps:

[0010] (1) Pre-treat activated carbon to obtain activated carbon carrier;

[0011] (2) The palladium precursor solution is adsorbed onto the activated carbon support;

[0012] In some embodiments, S1 also includes aging after washing.

[0013] In some embodiments, in step (2), the palladium precursor solution can be adsorbed onto the activated carbon support by an equal-volume impregnation method.

[0014] In some embodiments, the palladium precursor solution comprises a palladium salt and a buffer solution.

[0015] In some embodiments, the pH of the palladium precursor solution is 4 to 7, for example, pH 4, 5, 6, or 7.

[0016] In some embodiments, the palladium salt is selected from one or more of palladium sulfate, palladium chloroacetic acid, or palladium phosphate.

[0017] In some embodiments, the palladium precursor solution is in a colloidal state.

[0018] In some embodiments, the rinsing solution is a buffer solution or deionized water.

[0019] In some embodiments, the buffer solution has a buffer pH range of 4 to 7, for example, pH 4, 5, 6, or 7.

[0020] In some embodiments, the buffer solution includes anionic surfactant, tartaric acid, glacial acetic acid, and citric acid. The synergistic effect of the anionic surfactant and the three acids in the buffer solution has a slow-release effect on the washing process, which is more conducive to the washing of the surface 0-5 μm palladium. The catalyst obtained by rinsing with the buffer solution loses less palladium after the reaction.

[0021] In some embodiments, the buffer solution comprises 0.05–0.1 wt% anionic surfactant, 0.15–0.25 wt% tartaric acid, 0.15–0.25 wt% glacial acetic acid, and 0.35–0.5 wt% citric acid.

[0022] In some embodiments, the buffer solution comprises 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt%, or 0.1 wt% anionic surfactant, 0.15 wt%, 0.17 wt%, 0.19 wt%, 0.21 wt%, 0.23 wt%, or 0.25 wt% tartaric acid, 0.15 wt%, 0.17 wt%, 0.19 wt%, 0.21 wt%, 0.23 wt%, or 0.25 wt% glacial acetic acid, and 0.35 wt%, 0.37 wt%, 0.39 wt%, 0.41 wt%, 0.43 wt%, or 0.45 wt% citric acid.

[0023] In some embodiments, the anionic surfactant is selected from one or more of sodium hexadecyl sulfate, potassium dodecyl polyoxyethylene ether phosphate, and sodium dodecylbenzene sulfonate.

[0024] In some embodiments, the pretreatment includes: washing the activated carbon with water to remove activated carbon powder; then adding an oxidant solution to carry out an oxidation reaction to obtain an oxidized carrier; and washing and drying the oxidized carrier to obtain the activated carbon carrier.

[0025] In some embodiments, the oxidant is selected from one or more of nitric acid, hydrogen peroxide, and potassium permanganate.

[0026] In some embodiments, the concentration of the oxidant solution is 0.1 to 1 mol / L, for example 0.15 mol / L, 0.2 mol / L, 0.26 mol / L, 0.31 mol / L, 0.36 mol / L, 0.39 mol / L, 0.45 mol / L, 0.58 mol / L, 0.67 mol / L, 0.74 mol / L, 0.88 mol / L, 0.92 mol / L, or 0.99 mol / L.

[0027] In some embodiments, the equivalence ratio of the oxidant solution to the activated carbon is 5 to 50:1, for example, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1.

[0028] In some embodiments, the oxidation reaction is carried out at a temperature of 20–80°C, for example, 22°C, 27°C, 32°C, 37°C, 41°C, 46°C, 50°C, 57°C, 63°C, 70°C, 72°C, or 79°C.

[0029] In some embodiments, drying can be carried out by baking at a temperature of 100-200°C, such as 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C.

[0030] In some embodiments, the activated carbon is selected from one or more of coal-based carbon, wood-based carbon, and fruit shell carbon.

[0031] In some embodiments, the activated carbon is fruit shell carbon, and more preferably, the activated carbon is coconut shell carbon.

[0032] In some embodiments, the activated carbon has a specific surface area of ​​1000–1300 m². 2 / g, for example, 1000m 2 / g、1020m 2 / g、1080m2 / g、1150m 2 / g、1200m 2 / g、1240m 2 / g or 1270m 2 / g.

[0033] In some embodiments, more than 90% of the activated carbon particles are in the 4-8 mesh size.

[0034] In some embodiments, the reducing agent used in the reduction treatment is selected from one or more of sodium oxalate, sodium sulfite, sodium formate, formic acid, and sodium nitrite.

[0035] In some embodiments, the reducing agent is a sodium formate solution with a mass fraction of 1-5%.

[0036] In a third aspect, the present invention provides the application of the palladium-on-carbon catalyst described in the first aspect or the palladium-on-carbon catalyst prepared by the preparation method described in the second aspect in the hydrogenation refining reaction of crude terephthalic acid.

[0037] This invention uses activated carbon as a support to prepare a supported palladium-carbon catalyst. By adding a rinsing process between the impregnation and aging processes, the surface palladium salt is recovered. The palladium-carbon catalyst provided by this invention is used in the purification reaction of crude terephthalic acid and has the characteristics of reducing palladium loss, high catalyst activity, and long life. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0039] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0040] The present invention will be described in detail below through embodiments.

[0041] Evaluation of palladium loss rate: Add 20g of catalyst and 200mL of water to a centrifuge tube, place it in a shaking incubator and shake at high speed for 1 hour, then filter and dry.

[0042] Catalyst activity evaluation conditions:

[0043] Sample loading and evaluation in autoclave

[0044] Catalyst dosage: 2.0g

[0045] Crude terephthalic acid content: 30.0g

[0046] Solvent: Deionized water, 850g

[0047] CBA dosage: 1.0g

[0048] Reaction pressure: 7.5 MPa

[0049] Reaction temperature: 280℃

[0050] Samples were taken after 1000 hours and analyzed by high-performance liquid chromatography.

[0051]

[0052] The weight percentage of Pd was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), and the palladium distribution was determined by electron probe microanalysis (EPMA).

[0053] The present invention will be further illustrated below through examples.

[0054] Example 1

[0055] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtering to remove activated carbon powder, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker and oxidized at 50℃ for 2h. Then it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.05g of glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including aqueous solution of 0.05g tartaric acid, 0.05g glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid) was prepared for later use. Palladium colloid solution was sprayed onto the activated carbon support in a rotary kiln to ensure thorough impregnation. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then aged in a beaker at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0056] Example 2

[0057] The catalyst preparation process is the same as in Example 1, except that sodium dodecylbenzenesulfonate is used instead of potassium dodecyl polyoxyethylene ether phosphate. Details are as follows:

[0058] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtering to remove activated carbon powder, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker and oxidized at 50℃ for 2h. Then it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.05g of glacial acetic acid, 0.02g of sodium dodecylbenzenesulfonate and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including aqueous solution of 0.05g tartaric acid, 0.05g glacial acetic acid, 0.02g sodium dodecylbenzenesulfonate and 0.10g citric acid) was prepared for later use. Palladium colloid solution was sprayed onto the activated carbon support in a rotary kiln to ensure thorough impregnation. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then aged in a beaker at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0059] Example 3

[0060] The catalyst preparation process is the same as in Example 1, except that deionized water is used instead of the buffer solution in the rinsing process. Details are as follows:

[0061] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtering to remove activated carbon powder, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker and oxidized at 50℃ for 2h. Then it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.05g of glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including aqueous solution of 0.05g tartaric acid, 0.05g glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid) was prepared for later use. Palladium colloid solution was sprayed onto the activated carbon support in a rotary kiln to ensure thorough impregnation. The solid was placed in a filter screen, sprayed with 24.5 mL of deionized water, and then aged in a beaker at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100°C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120°C to obtain the catalyst product.

[0062] Example 4

[0063] The catalyst preparation process was the same as in Example 1, except that potassium dodecyl polyoxyethylene ether phosphate was not added during the rinsing process. Details are as follows:

[0064] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtration to remove activated carbon powder, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker and oxidized at 50℃ for 2h. Then it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.05g of glacial acetic acid and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including aqueous solution of 0.05g tartaric acid, 0.05g glacial acetic acid and 0.10g citric acid) was prepared for later use. The palladium gel solution was sprayed into the activated carbon carrier in a rotary pan to fully impregnate it. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then placed in a beaker for aging at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0065] Example 5

[0066] The catalyst preparation process was the same as in Example 1, except that citric acid was not added during the rinsing process. Details are as follows:

[0067] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtering to remove floating powder from activated carbon, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker, and oxidation was carried out at 50℃ for 2h. Then, it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.05g of glacial acetic acid, and 0.02g of potassium dodecyl polyoxyethylene ether phosphate were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including 0.05g of tartaric acid, 0.05g of glacial acetic acid, and 0.02g of potassium dodecyl polyoxyethylene ether phosphate) was prepared for later use. The palladium gel solution was sprayed into the activated carbon carrier in a rotary kiln to ensure thorough impregnation. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then placed in a beaker for aging at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0068] Example 6

[0069] The catalyst preparation process was the same as in Example 1, except that tartaric acid was not added during the rinsing process. Details are as follows:

[0070] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtering to remove floating powder from activated carbon, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker and oxidized at 50℃ for 2h. Then it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including aqueous solution of 0.05g glacial acetic acid, 0.02g potassium dodecyl polyoxyethylene ether phosphate and 0.10g citric acid) was prepared for later use. The palladium gel solution was sprayed into the activated carbon carrier in a rotary kiln to fully impregnate it. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then placed in a beaker for aging at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0071] Example 7

[0072] The catalyst preparation process was the same as in Example 1, except that glacial acetic acid was not added during the rinsing process. Details are as follows:

[0073] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtering to remove activated carbon powder, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker and oxidized at 50℃ for 2h. Then it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, 24.5g of buffer solution (including aqueous solution of 0.05g tartaric acid, 0.02g potassium dodecyl polyoxyethylene ether phosphate and 0.10g citric acid) was prepared for later use. The palladium gel solution was sprayed into the activated carbon carrier in a rotary pan to fully impregnate it. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then placed in a beaker for aging at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0074] Comparative Example 1

[0075] The catalyst preparation process does not involve a rinsing process; other processes are the same as in Example 1. Details are as follows:

[0076] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, after washing and filtration to remove activated carbon powder, 500mL of 0.5mol / L hydrogen peroxide solution was added to a beaker, and oxidation was carried out at 50℃ for 2h. Then, it was washed with deionized water and dried at 120℃. 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%) was weighed, 10mL of deionized water was added, and then 0.05g of tartaric acid, 0.05g of glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid were added. The pH was adjusted to 6.5 with 10% sodium carbonate solution, and deionized water was added to a final volume of 24.5g to obtain palladium gel solution. The palladium gel solution was sprayed into the activated carbon carrier in a rotary kiln to fully impregnate it. After 24h, 200mL of 2% sodium formate solution was added, and reduction was carried out at 100℃ for 1h. Then, it was washed three times with deionized water, filtered, and dried at 120℃ to obtain the catalyst product.

[0077] Comparative Example 2

[0078] The catalyst preparation process is the same as in Example 1, except that the support is not pre-oxidized with an oxidant. Details are as follows:

[0079] Weigh 50g of 4-8 mesh coconut shell activated carbon, with a specific surface area of ​​1020m². 2 / g, pore volume 0.49mL / g, washed and filtered to remove floating powder from activated carbon. Then washed with deionized water and dried at 120℃. Weigh 1.67g of chloropalladium acid aqueous solution (palladium mass fraction 15%), add 10mL of deionized water, then add 0.05g of tartaric acid, 0.05g of glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid, adjust the pH to 6.5 with 10% sodium carbonate solution, and add deionized water to a final volume of 24.5g to obtain palladium gel solution. At the same time, using the same method, without adding chloropalladium acid aqueous solution, prepare 24.5g of buffer solution (including aqueous solution of 0.05g tartaric acid, 0.05g glacial acetic acid, 0.02g of potassium dodecyl polyoxyethylene ether phosphate and 0.10g of citric acid) for later use. Spray the palladium gel solution into the activated carbon carrier in a rotary kiln to fully impregnate it. The solid was placed in a filter screen, sprayed with 24.5 mL of buffer solution, and then placed in a beaker for aging at room temperature. After 24 hours, 200 mL of 2% sodium formate solution was added, and reduction was carried out at 100 °C for 1 hour. The solution was then washed three times with deionized water, filtered, and dried at 120 °C to obtain the catalyst product.

[0080] The content and distribution of palladium, the active component of the catalyst, in each embodiment and comparative example, as well as the evaluation results of the catalyst under the above-described activity evaluation conditions, are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from Table 1, the palladium-carbon catalysts prepared in each embodiment of the present invention have a palladium mass fraction of 0.2-0.9%; the palladium content is distributed in a protein-like manner, with less than 5% palladium distributed in the 0-5 μm surface layer, 80-95% palladium distributed in the 5-50 μm protein-like layer, and the remainder distributed in the 50-200 μm inner layer.

[0084] After evaluation by palladium loss rate experiment, the content and distribution of palladium, the active component of catalyst in each example and comparative example, and the evaluation results of catalyst under the above-mentioned activity evaluation conditions are shown in Table 2.

[0085] Table 2

[0086]

[0087]

[0088] According to Tables 1 and 2, compared with Examples 1-7, Comparative Example 1 had a higher palladium loss rate and a lower 4-CBA conversion rate because there was no rinsing process and more palladium elements were distributed in the 0-5 μm surface layer. In Comparative Example 2, the palladium loading in the catalyst was lower because no oxidant was used to pre-oxidize the support, resulting in a lower 4-CBA conversion rate.

[0089] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. The application of a palladium-on-carbon catalyst in the hydrogenation refining reaction of crude terephthalic acid, wherein the palladium-on-carbon catalyst comprises: The activated carbon carrier and palladium loaded on the activated carbon carrier, wherein, based on the mass of the activated carbon carrier as 100%, the mass percentage of palladium is 0.2-0.9%; the palladium content is distributed in a protein-like manner, with less than 5% of palladium distributed in the 0-5 μm surface layer, 80-95% of palladium distributed in the 5-50 μm protein-like layer, and the remainder distributed in the 50-200 μm inner layer.

2. A method for preparing a palladium-on-carbon catalyst, comprising: S1: The activated carbon support loaded with palladium precursor is washed with a rinsing solution. S2: Reduce the activated carbon carrier after S1 treatment; In S1, the activated carbon support for the palladium precursor is prepared by a method comprising the following steps: (1) Pre-treat the activated carbon to obtain an activated carbon carrier; (2) The palladium precursor solution is adsorbed onto the activated carbon support; S1 also includes aging after washing; The palladium precursor solution comprises a palladium salt and a buffer solution, and the palladium precursor solution is in a colloidal state. The rinsing solution is a buffer solution, which includes anionic surfactants, tartaric acid, glacial acetic acid, and citric acid.

3. The preparation method according to claim 2, characterized in that, The pH value of the palladium precursor solution is 4-7.

4. The preparation method according to claim 2, characterized in that, The palladium salt is selected from one or more of palladium sulfate, chloropalladium acid, or palladium phosphate.

5. The preparation method according to claim 2, characterized in that, The buffer solution has a buffer pH range of 4 to 7.

6. The preparation method according to claim 2, characterized in that, The buffer solution comprises 0.05-0.1 wt% anionic surfactant, 0.15-0.25 wt% tartaric acid, 0.15-0.25 wt% glacial acetic acid, and 0.35-0.45 wt% citric acid.

7. The preparation method according to claim 2, characterized in that, The anionic surfactant is selected from one or more of sodium hexadecyl sulfate, potassium dodecyl polyoxyethylene ether phosphate, and sodium dodecylbenzene sulfonate.

8. The preparation method according to claim 2, characterized in that, The preprocessing includes: The activated carbon is washed with water, and then an oxidant solution is added to carry out an oxidation reaction to obtain the oxidized carrier; The oxidized carrier is washed with water and dried to obtain the activated carbon carrier.

9. The preparation method according to claim 8, characterized in that, The oxidant is selected from one or more of nitric acid, hydrogen peroxide, and potassium permanganate.

10. The preparation method according to claim 8, characterized in that, The concentration of the oxidant solution is 0.1~1 mol / L.

11. The preparation method according to claim 8, characterized in that, The equivalence ratio of the oxidant solution to the activated carbon is 5~50:

1.

12. The preparation method according to claim 8, characterized in that, The oxidation reaction is carried out at a temperature of 20~80℃.

13. The preparation method according to claim 2, characterized in that, The activated carbon is selected from one or more of coal-based carbon, wood-based carbon, and fruit shell carbon.

14. The preparation method according to claim 2, characterized in that, The activated carbon is fruit shell carbon.

15. The preparation method according to claim 2, characterized in that, The activated carbon is coconut shell carbon.

16. The preparation method according to claim 2, characterized in that, The activated carbon has a specific surface area of ​​1000~1300 m². 2 / g, of which more than 90% of the activated carbon particles are in the 4-8 mesh range.

17. The preparation method according to claim 2, characterized in that, The reducing agent used in the reduction treatment is selected from one or more of sodium oxalate, sodium sulfite, sodium formate, formic acid, and sodium nitrite.

18. The preparation method according to claim 17, characterized in that, The reducing agent is a sodium formate solution with a mass fraction of 1-5%.

19. The application of the palladium-on-carbon catalyst prepared by the method according to any one of claims 2 to 18 in the hydrogenation refining reaction of crude terephthalic acid.

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