A palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid and its preparation method

Abstract

This invention provides a palladium-on-carbon catalyst for the hydrogenation refining reaction of terephthalic acid and its preparation method. The catalyst composition satisfies the chemical formula, with 0.03–0.05, 0.01–0.04, 0.02–0.1, and 0.01–0.02, representing the number of oxygen atoms required for the valence of each element. When used in the hydrogenation refining reaction of crude terephthalic acid, the catalyst of this invention exhibits superior catalytic performance, good 4-CBA conversion activity and activity stability, and good sulfur resistance and wear resistance, which is beneficial for long-term stable use and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more specifically to a palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid and its preparation method. Background Technology

[0002] High-purity terephthalic acid (PTA) is an important raw material for manufacturing polyester fibers, films, and insulating varnishes, and is also used as a dye intermediate. PTA production units are the leading units in the entire chemical fiber industry, and the production process mainly includes oxidation and refining units. The main impurity in crude terephthalic acid (CTA) obtained from the oxidation process is p-carboxybenzaldehyde (4-CBA), which not only forms eutectic during crystallization, causing pollution, but also affects the polymerization reaction in downstream product production. Its content is a crucial indicator of PTA quality. The main task of the hydrorefining process is to reduce the 4-CBA content in crude terephthalic acid; the core technology lies in the catalyst used in the process and its application.

[0003] Currently, the heterogeneous catalyst used in the industrial hydrogenation refining process of crude terephthalic acid is the palladium-on-carbon catalyst, as exemplified by US Patent 4476242. Directly loading palladium-containing compounds onto activated carbon often results in very low dispersion of metallic palladium in the prepared catalyst. Converting palladium ions in the palladium-containing impregnation solution into insoluble compounds before the reduction process can achieve better results, preventing palladium migration and grain growth. For example, US Patent 4138560 adds hydrogen peroxide to the impregnation solution to hydrolyze water-soluble palladium compounds into insoluble compounds, but this may affect other physicochemical properties of the catalyst. US Patent 4476242 proposes using organic solvents such as methanol or pyridine to prepare the impregnation solution containing palladium compounds, which is claimed to be very effective in preventing palladium migration and grain growth. However, methanol or pyridine are harmful organic compounds, which are detrimental to environmental protection and human health. Chinese patent CN103028398A uses citric acid, tartaric acid, maleic acid, oxalic acid and lactic acid to adjust the pH value, and loads the resulting impregnation solution onto an activated carbon carrier to solve the problem of low 4-CBA conversion rate in the industrial production of PTA hydrogenation refining.

[0004] Chinese patent CN120920060A utilizes a composition of modified carbon material with oxygen-containing functional groups, a covering agent, and an aqueous solution of palladium precursor. This catalyst significantly improves catalytic efficiency and effectively reduces the residual amount of 4-CBA in the PTA hydrorefining reaction. The Chinese patent also utilizes enzyme solution treatment to improve the palladium-on-carbon catalyst, resulting in a catalyst with high activity in the PTA hydrorefining reaction. Chinese patent CN103157464A discloses a method for grinding, washing, acid treatment, and redox treatment of supported activated carbon, selecting dispersants and reducing agents with competitive adsorption and stabilizing effects to improve dispersibility and reduce particle size, obtaining a high-performance catalyst with a particle size of less than 2 nanometers.

[0005] Because the hydrogenation purification of terephthalic acid is a first-order reaction with a rapid reaction rate, reactants have difficulty penetrating into the catalyst particles to react, preventing the active components inside the particles from functioning effectively. To fully utilize precious metals, palladium-on-carbon catalysts are typically made in an eggshell shape, so that the active precious metal components are mainly supported on the surface of the support. Since the hydrogenation reaction takes place on the surface of metallic palladium, for catalysts with the same palladium loading, higher palladium dispersion or higher palladium crystallite content results in better thermal stability, higher catalyst activity, and a longer service life.

[0006] For example, Chinese patent CN119318955A discloses a palladium-on-carbon catalyst with a protein-like palladium content distribution. Less than 5% of the palladium is distributed in the surface layer (0-5 micrometers), 80-95% in the protein-like layer (5-50 micrometers), and the remainder in the inner layer (50-200 micrometers). This catalyst, when used in PTA purification reactions, features reduced palladium loss, high activity, and long lifespan. In contrast, US patent US6066589, using Na₂PdCl₄ as a precursor and adding hydrogen peroxide, produces a catalyst in which the palladium loading in the surface layer (0-20 micrometers) is less than half of the total loading, which may negatively impact the conversion efficiency of 4-CBA.

[0007] However, the precious metal elements on the outer layer are also prone to loss during the reaction process, requiring improvements to reduce this loss. For example, CN103769210A discloses modified organosilicon based on polydimethylsiloxane, such as ammonia-modified organosilicon, epoxy-modified organosilicon, or polyether-modified organosilicon, which is sprayed onto a dry, fresh catalyst and then dried under an inert gas atmosphere; this improves the wear resistance of the palladium-carbon catalyst for the hydrogenation refining of crude terephthalic acid; the invention disclosed in CN104549241A is similar.

[0008] However, the precious metal elements in the outer layer are also easily lost during the reaction, requiring improvements to reduce this loss. For example, Chinese patent CN103769210A discloses modified organosilicon based on polydimethylsiloxane, such as ammonia-modified, epoxy-modified, or polyether-modified organosilicon, which is sprayed onto a fresh, dry catalyst and then dried under inert gas protection, improving the wear resistance of the palladium-on-carbon catalyst used in the hydrogenation refining of crude terephthalic acid. The invention disclosed in Chinese patent CN104549241A is similar.

[0009] In addition to single-palladium active component catalysts, Chinese patent CN104549255A also discloses a method for modification using alkaline earth metal elements and lanthanide elements to solve the problems of poor sulfur resistance and easy growth of palladium grains in the industrial production of terephthalic acid hydrogenation refining catalysts. Chinese patent CN119215887A discloses a palladium-ruthenium bimetallic catalyst supported on activated carbon, in which the proportion of exposed Pd(111) crystal atoms is 25% to 75%. When applied to the PTA hydrogenation refining process, it can effectively reduce the residual 4-CBA content.

[0010] Furthermore, Chinese patent CN103721706A improves the reduction and washing method of the palladium-on-carbon catalyst in PTA hydrorefining by setting a gas distributor or porous plate in the reduction and washing container. Chinese patent CN103028422A also discloses a regeneration method for the palladium-on-carbon catalyst in PTA hydrorefining after deactivation due to palladium grain growth.

[0011] In summary, in the existing technology, the manufacturing and use costs of catalysts are high due to the high price of palladium; the contradictory distribution structure of palladium can easily lead to reduced efficiency or loss of active components, thus affecting the activity and stability of the catalyst; in addition, the catalyst's sulfur resistance and wear resistance can also affect its stable use and lifespan. Summary of the Invention

[0012] This invention aims to solve the problems of low conversion activity, poor stability, insufficient sulfur resistance, insufficient use intensity, and high manufacturing and use costs of catalysts in the preparation and use of existing technologies, and provides a palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid and its preparation method.

[0013] The technical method of the present invention is as follows: A palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid, wherein the catalyst has a composition satisfying the chemical formula , The value is 0.03 to 0.05. The value ranges from 0.01 to 0.04. The value is 0.02 to 0.1. The value is between 0.01 and 0.02. The number of oxygen atoms required to satisfy the valence of each element.

[0014] This invention also provides a method for preparing a palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid, comprising the following steps: S1. Based on the chemical formula of the catalyst, weigh the acid-washed activated carbon, the nickel soluble salt solution, the ruthenium soluble salt solution, the palladium soluble salt solution, and the silicone resin solution. S2. Impregnate the acid-washed activated carbon with an equal volume of nickel soluble salt solution and ruthenium soluble salt solution and dry it, then impregnate it with an equal volume of palladium soluble salt solution and dry it. S3. Spray the impregnated material treated in step S2 with silicone resin solution, dry it until the resin is completely cured, and then slurry it with deionized water to obtain catalyst slurry. S4. Neutralize the catalyst slurry treated in step S3 with an alkaline solution, wash and dry to obtain the palladium-on-carbon catalyst.

[0015] Optionally, the acid-washing activated carbon step includes: soaking activated carbon powder in 0.05 wt% to 0.1 wt% inorganic acid for 2 to 8 hours, washing, and drying to obtain acid-washed activated carbon; wherein the inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and phosphoric acid; the drying step includes: drying the washed product at 80 to 130°C for 1 to 10 hours under nitrogen protection; the activated carbon powder is selected from one or more of wood charcoal powder, bamboo charcoal powder, coal-based charcoal powder, fruit shell charcoal powder, petroleum coke powder, and resin-based charcoal powder, with a particle size of 2 to 5 mm and a surface area of ​​500 to 1300 m². 2 / g, pore volume is 0.3~0.9ml / g.

[0016] Optionally, the palladium-containing soluble salt is selected from one or more of palladium halides, acetates, oxalates, and nitrates, wherein the palladium halides include palladium chloride and / or chloropalladium acid; the nickel-containing soluble salt is selected from one or more of nickel halides, nitrates, sulfates, and acetates. The ruthenium-containing soluble salt solution is selected from one or more of ruthenium halides, nitrates, and oxides.

[0017] Optionally, the silicone resin solution includes a silicone resin and a solvent; wherein the silicone resin is selected from one or more of methyl silicone resin, phenyl silicone resin, methylphenyl silicone resin, and epoxy-modified silicone resin; and the solvent includes one or more of acetone, toluene, xylene, methyl ethyl ketone, dichloromethane, trichloroethane, ethyl acetate, butyl acetate, petroleum ether, and ethanol.

[0018] Optionally, the drying conditions after impregnating the acid-washed activated carbon with an equal volume of nickel soluble salt solution and ruthenium soluble salt solution are drying at 100~140℃ under nitrogen protection for 0.5~5 hours, and the drying conditions after impregnating the carbon with an equal volume of palladium soluble salt solution are drying at 100~140℃ under nitrogen protection for 2~6 hours.

[0019] Optionally, in step S3, the step of atomizing and spraying the silicone resin solution includes: transferring the impregnated material treated in step S2 onto a rotating turntable and atomizing and spraying the silicone resin solution; the curing method is air drying at room temperature and / or heat curing; wherein the curing conditions are drying at 40-50°C for 1-3 days under nitrogen protection, and then drying at 100-130°C for 1-10 hours.

[0020] Optionally, in step S4, the alkaline solution is a 5wt% to 10wt% ammonium bicarbonate solution, and the neutralization is carried out to a pH value of 7.0 to 7.4; the drying is airflow drying, and the airflow drying conditions are an exhaust gas temperature of 130 to 160°C.

[0021] The present invention also provides a method for hydrogenating and refining terephthalic acid, comprising using crude terephthalic acid as raw material, reducing the catalyst in the presence of the above-mentioned catalyst and the catalyst obtained by the above-mentioned preparation method, and then carrying out a hydrogenation reaction to obtain high-purity terephthalic acid, wherein the p-carboxybenzaldehyde content is less than 2 wt%; the hydrogenation reaction is carried out at a temperature of 270-290°C, a pressure of 7-8.5 MPa, a hydrogen partial pressure of 0.5-1 MPa, and a reaction time of 5-30 minutes.

[0022] Optionally, the reduction process employs gas-phase reduction or liquid-phase reduction; the molar ratio of reducing agent to palladium is 5 to 40 times; the gas-phase reducing agent is selected from hydrogen or a mixture of hydrogen and nitrogen or argon; the gas-phase reduction temperature is 130 to 220°C, and the reduction time is 1 to 10 hours; the liquid-phase reducing agent is selected from one or more of formic acid, formaldehyde, ascorbic acid, hydrazine hydrate, and glucose; the liquid-phase reduction temperature is 80 to 100°C, and the reduction time is 0.1 to 1.5 hours per kilogram of catalyst.

[0023] The beneficial effects of this invention are: I. When the catalyst of the present invention is used in the hydrogenation refining reaction of crude terephthalic acid, it can exhibit superior catalytic performance, with good 4-CBA conversion activity and activity stability, as well as good sulfur resistance and wear resistance, which is conducive to the long-term stable use of the catalyst and is suitable for industrial production.

[0024] II. The catalyst preparation method of the present invention uses widely available raw materials, simplifies the preparation steps, reduces the requirements for harsh conditions, and relatively reduces the preparation cost, making it convenient for the production and use of catalysts. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In a first aspect, the present invention provides a palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid, wherein the composition of the catalyst satisfies the chemical formula , The value is 0.03 to 0.05. The value ranges from 0.01 to 0.04. The value is 0.02 to 0.1. The value is between 0.01 and 0.02. The number of oxygen atoms required to satisfy the valence of each element.

[0027] This invention also provides a method for preparing a palladium-on-carbon catalyst for the hydrogenation purification reaction of terephthalic acid, comprising the following steps: S1. Based on the chemical formula of the catalyst, weigh the acid-washed activated carbon, the nickel soluble salt solution, the ruthenium soluble salt solution, the palladium soluble salt solution, and the silicone resin solution.

[0028] In this embodiment, the palladium-containing soluble salt is selected from one or more palladium halides, acetates, oxalates, and nitrates, wherein the palladium halides include palladium chloride and / or chloropalladic acid. Palladium chloride, palladium nitrate, and chloropalladic acid are preferred, with palladium chloride being more preferred.

[0029] In this embodiment, the soluble salt of nickel is selected from one or more of nickel halides, nitrates, sulfates, and acetates. Nickel chloride, nickel nitrate, nickel sulfate, and nickel acetate are preferred, and nickel chloride and nickel nitrate are more preferred.

[0030] In this embodiment, the soluble salt solution of ruthenium is selected from one or more of ruthenium halides, nitrates, and oxides. Preferably, ruthenium chlororuthenic acid, ruthenium nitrate, and ruthenium tetroxide are used, with ruthenium nitrate being more preferred.

[0031] In this embodiment, the silicone resin solution includes silicone resin and a solvent. The silicone resin is selected from one or more of methyl silicone resin, phenyl silicone resin, methylphenyl silicone resin, and epoxy-modified silicone resin; the solvent includes one or more of acetone, toluene, xylene, methyl ethyl ketone, dichloromethane, trichloroethane, ethyl acetate, butyl acetate, petroleum ether, and ethanol.

[0032] S2. Impregnate the acid-washed activated carbon with an equal volume of nickel soluble salt solution and ruthenium soluble salt solution and dry. Then impregnate it with an equal volume of palladium soluble salt solution and dry.

[0033] In this embodiment, the acid-washing activated carbon step includes: soaking activated carbon powder in 0.05 wt% to 0.1 wt% inorganic acid for 2 to 8 hours, washing, and drying to obtain acid-washed activated carbon. The inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and phosphoric acid, preferably hydrochloric acid. The drying step includes: drying the washed product at 80 to 130°C for 1 to 10 hours under nitrogen protection. The activated carbon powder is selected from one or more of wood charcoal powder, bamboo charcoal powder, coal-based charcoal powder, fruit shell charcoal powder, petroleum coke powder, and resin-based charcoal powder, with a particle size of 2 to 5 mm and a surface area of ​​500 to 1300 m². 2 / g, with a pore volume of 0.3–0.9 ml / g. Further, the fruit shell activated carbon powder may include coconut shell activated carbon powder.

[0034] In this embodiment, the drying conditions after the acid-washed activated carbon is impregnated with an equal volume of nickel soluble salt solution and ruthenium soluble salt solution are 0.5 to 5 hours under nitrogen protection at 100 to 140°C, and the drying conditions after the carbon is impregnated with an equal volume of palladium soluble salt solution are 2 to 6 hours under nitrogen protection at 100 to 140°C.

[0035] In this embodiment, the acid-washed activated carbon can be simultaneously impregnated with an equal volume of nickel-soluble salt solution and ruthenium-soluble salt solution.

[0036] S3. Spray the impregnated material treated in step S2 with silicone resin solution, dry it until the resin is completely cured, and then slurry it with deionized water to obtain catalyst slurry.

[0037] In this embodiment, the step of atomizing and spraying the silicone resin solution includes: transferring the impregnated material treated in step S2 onto a rotating turntable and atomizing and spraying the silicone resin solution.

[0038] In this embodiment, the curing method is air drying at room temperature and / or heat curing. For example, the curing conditions are staged drying at 40-50°C for 1-3 days under nitrogen protection, followed by drying at 100-130°C for 1-10 hours.

[0039] S4. Neutralize the catalyst slurry treated in step S3 with an alkaline solution, wash and dry to obtain the palladium-on-carbon catalyst.

[0040] In this embodiment, the alkaline solution is a 5wt% to 10wt% ammonium bicarbonate solution.

[0041] In this embodiment, the pH was neutralized to 7.0–7.4.

[0042] In this embodiment, the drying is airflow drying, and the airflow drying condition is an exhaust gas temperature of 130~160℃.

[0043] Thirdly, the present invention also provides a method for hydrogenating and refining terephthalic acid, comprising using crude terephthalic acid as raw material, and in the presence of the above-mentioned catalyst and the catalyst obtained by the above-mentioned preparation method, reducing the catalyst and then carrying out a hydrogenation reaction to obtain high-purity terephthalic acid, wherein p-carboxybenzaldehyde is less than 2 wt%, preferably less than 1 wt%. Further crystallization and separation can then yield fiber-grade high-purity terephthalic acid with p-carboxybenzaldehyde less than 25 ppm.

[0044] In this embodiment, the hydrogenation reaction temperature is 270–290°C, the pressure is 7–8.5 MPa, the hydrogen partial pressure is 0.5–1 MPa, and the reaction time is 5–30 minutes.

[0045] In this embodiment, the reduction process employs either gas-phase reduction or liquid-phase reduction; the molar ratio of reducing agent to palladium is 5–40, preferably 20–30. The gas-phase reducing agent is selected from hydrogen or a mixture of hydrogen and nitrogen or argon, with hydrogen reduction being preferred; the gas-phase reduction temperature is 130–220°C, and the reduction time is 2–10 hours. The liquid-phase reducing agent is selected from formic acid, formaldehyde, ascorbic acid, hydrazine hydrate, and glucose, with formaldehyde reduction being preferred; the liquid-phase reduction temperature is 80–100°C, and the reduction time is 0.1–1.5 hours / kg catalyst.

[0046] In the method for preparing palladium-carbon catalyst for hydrogenation purification of terephthalic acid provided by this invention, the amount of deionized water and solvent involved in the preparation process, the dilution of solutions, slurries and mixtures, and the dissolution of soluble salts to prepare solutions and organic matter are mainly to meet operational requirements and convenience, and depend on the operation process. They have no substantial impact on the performance of the final catalyst.

[0047] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0048] The present invention will be described in detail below through embodiments and experimental examples. However, these are merely examples and do not limit the present invention in any way.

[0049] Example 1 according to The molar ratio in the formula =0.03、 =0.03、 =0.1、 =0.02, the constrained molar ratio, the calculated amount of coconut shell activated carbon powder with a particle size range of 2-5 mm, acid-washed with dilute nitric acid, is impregnated in a mixed solution prepared with ruthenium nitrate and nickel nitrate at room temperature with equal volume, and then dried in an oven under nitrogen protection at 120°C. o Dry at C for 1 hour; then impregnate with an equal volume of palladium chloride solution at 120°C.o After drying under nitrogen protection for 1 hour, the solution of methyl silicone resin dissolved in acetone was atomized and sprayed onto a small laboratory rotating turntable at 40°C. o Air dry at C for two and a half days, then under nitrogen protection at 120°C. o Dry at C for 4 hours; then slurry with deionized water to obtain catalyst slurry; neutralize the catalyst slurry with 6wt% ammonium bicarbonate solution to pH 7.0-7.4, and wash with deionized water until chloride ions are removed; dry in an airflow dryer at a tail gas temperature of 140℃; obtain the palladium-on-carbon catalyst for PTA hydrogenation refining of Example 1 of this invention; the catalyst has a pore volume of 0.52 ml / g and a surface area of ​​741 m². 2 / g.

[0050] Example 2 according to The molar ratio in the formula =0.04、 =0.01、 =0.03、 =0.01, constrained molar ratio; wood charcoal powder acid-washed with dilute hydrochloric acid within the same particle size range as in Example 1; ruthenium chloride, nickel chloride, and palladium nitrate; phenyl silicone resin dissolved in xylene solvent; following the same operating steps as in Example 1, the drying conditions were 110 under nitrogen protection. o Dry at C for 2 hours, then cure and dry under 50°C conditions. o The catalyst was air-dried at C for two days, then dried at 110°C for 6 hours under nitrogen protection, with the exhaust gas temperature at 150°C. This yielded the palladium-on-carbon catalyst for PTA hydrogenation refining described in Example 2 of this invention. The catalyst has a pore volume of 0.51 ml / g and a surface area of ​​729 m². 2 / g.

[0051] Example 3 according to The molar ratio in the formula =0.035、 =0.03、 =0.08、 =0.015, the constrained molar ratio; bamboo charcoal powder acid-washed with dilute phosphoric acid within the same particle size range as in Example 1, ruthenium tetroxide, nickel acetate, and palladium chloroacetic acid, and methylphenyl silicone resin dissolved in toluene solvent; following the same operating steps as in Example 1, the drying conditions were 105 under nitrogen protection. o Dry at C for 5 hours, then cure and dry at 45°C. o The catalyst was air-dried at C for two and a half days, then dried at 110°C for 6 hours under nitrogen protection, with the exhaust gas temperature at 150°C. This yielded the palladium-on-carbon catalyst for PTA hydrogenation refining described in Example 3 of this invention. The catalyst has a pore volume of 0.48 ml / g and a surface area of ​​690 m².2 / g.

[0052] Comparative Example 1 Following the steps outlined in patent document US3138560, palladium chloride was used as the active component and acid-washed coconut shell activated carbon powder was used as the carrier. To facilitate comparison with this invention, the palladium content was made similar to that of Example 1 of this invention to obtain a comparative catalyst. The catalyst had a pore volume of 0.57 ml / g and a surface area of ​​753 m². 2 / g.

[0053] Application Example 1 The catalyst performance was evaluated using a small-scale laboratory autoclave reactor. The catalyst dosage was 2 g. Raw materials included 30 g crude terephthalic acid and 10 g 4-CBA, with 800 mL deionized water as the solvent. The reaction pressure was 7.5 MPa, the hydrogen partial pressure was 0.5 MPa, the reaction temperature was 282 °C, and the reaction time was 30 minutes. For ease of comparison, the catalyst reduction conditions were standardized to hydrogen reduction at 200 °C for 1 hour. See Table 1 for the catalyst evaluation results.

[0054] Table 1 shows the evaluation results of the catalysts in Examples 1-3 and the comparative catalysts.

[0055] Table 1 The catalyst's erosion resistance life was simulated by ultrasonic treatment for 1 hour: the catalyst activity reduction rate of Examples 1-3 was less than 3%, while the activity reduction rate of the comparative catalyst was 10%-20%, showing that the PTA palladium-carbon catalyst prepared by the present invention has better activity stability and resistance to loss of precious metal active components.

[0056] By adding 0.1% thiourea to the raw materials to simulate sulfur resistance performance, the decrease rate of 4-CBA conversion activity of the catalysts in Examples 1-3 was only half that of the comparative catalysts, indicating that the PTA palladium-carbon catalyst prepared in this invention has better sulfur resistance performance.

[0057] Because the precious metal content of the PTA palladium-carbon catalyst of the present invention is at a low level, it can bring about 5% to 10% cost savings in the manufacture and procurement of the catalyst.

[0058] This invention demonstrates that the catalyst prepared in this invention exhibits better catalytic performance, activity, and activity stability during the hydrogenation purification of crude terephthalic acid. It also reduces the residual flow of 4-CBA, improves sulfur resistance, and has better erosion resistance and less catalyst loss. This effectively extends the catalyst's lifespan and maintains its stability in industrial applications.

[0059] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A palladium-on-carbon catalyst for the hydrogenation refining reaction of terephthalic acid, characterized in that, The composition of the catalyst satisfies the chemical formula , The value is 0.03 to 0.

05. The value ranges from 0.01 to 0.

04. The value is 0.02 to 0.

1. The value is between 0.01 and 0.

02. The number of oxygen atoms required to satisfy the valence of each element.

2. The method for preparing the palladium-on-carbon catalyst according to claim 1, characterized in that, Includes the following steps: S1. Based on the chemical formula of the catalyst, weigh the acid-washed activated carbon, the nickel soluble salt solution, the ruthenium soluble salt solution, the palladium soluble salt solution, and the silicone resin solution. S2. Impregnate the acid-washed activated carbon with an equal volume of nickel soluble salt solution and ruthenium soluble salt solution and dry it, then impregnate it with an equal volume of palladium soluble salt solution and dry it. S3. Spray the impregnated material treated in step S2 with silicone resin solution, dry it until the resin is completely cured, and then slurry it with deionized water to obtain catalyst slurry. S4. Neutralize the catalyst slurry treated in step S3 with an alkaline solution, wash and dry to obtain the palladium-on-carbon catalyst.

3. The method for preparing the palladium-on-carbon catalyst according to claim 2, characterized in that, The steps of acid washing activated carbon include: soaking activated carbon powder in 0.05 wt% to 0.1 wt% inorganic acid for 2 to 8 hours, washing and drying to obtain acid-washed activated carbon; The inorganic acid is selected from one or more of hydrochloric acid, nitric acid, and phosphoric acid; The drying step includes: drying the washed product at 80-130°C for 1-10 hours under nitrogen protection; The activated carbon powder is selected from one or more of the following: wood-based charcoal powder, bamboo-based charcoal powder, coal-based charcoal powder, fruit shell charcoal powder, petroleum coke powder, and resin-based charcoal powder, with a particle size of 2-5 mm and a surface area of ​​500-1300 m². 2 / g, pore volume is 0.3~0.9ml / g.

4. The method for preparing the palladium-on-carbon catalyst according to claim 2, characterized in that, The palladium-containing soluble salt is selected from one or more palladium halides, acetates, oxalates, and nitrates, and the palladium halides include palladium chloride and / or chloropalladium acid; The soluble salt of nickel is selected from one or more of nickel halides, nitrates, sulfates, and acetates; The ruthenium soluble salt solution is selected from one or more of ruthenium halides, nitrates, and oxides.

5. The method for preparing the palladium-on-carbon catalyst according to claim 2, characterized in that, The silicone resin solution includes silicone resin and solvent; The silicone resin is selected from one or more of methyl silicone resin, phenyl silicone resin, methylphenyl silicone resin, and epoxy-modified silicone resin. The solvent includes one or more of acetone, toluene, xylene, methyl ethyl ketone, dichloromethane, trichloroethane, ethyl acetate, butyl acetate, petroleum ether, and ethanol.

6. The method for preparing the palladium-on-carbon catalyst according to claim 2, characterized in that, The drying conditions after impregnating the acid-washed activated carbon with equal volumes of nickel-soluble salt solution and ruthenium-soluble salt solution are as follows: drying at 100-140°C under nitrogen protection for 0.5-5 hours. The drying conditions after impregnating the palladium-soluble salt solution with an equal volume are as follows: drying at 100-140°C under nitrogen protection for 2-6 hours.

7. The method for preparing the palladium-on-carbon catalyst according to claim 2, characterized in that, In step S3, the step of atomizing and spraying the silicone resin solution includes: Transfer the impregnated material after step S2 to a rotating turntable and spray the silicone resin solution using atomization. The curing method is air drying at room temperature and / or heat curing; wherein the curing conditions are drying at 40-50℃ for 1-3 days under nitrogen protection, and then drying at 100-130℃ for 1-10 hours.

8. The method for preparing the palladium-on-carbon catalyst according to claim 2, characterized in that, In step S4, the alkaline solution is a 5wt%–10wt% ammonium bicarbonate solution. The pH is then neutralized to 7.0–7.4; The drying process is airflow drying, and the airflow drying conditions are an exhaust gas temperature of 130~160℃.

9. A method for hydrogenating and purifying terephthalic acid, characterized in that, The process includes using crude terephthalic acid as a raw material, reducing the catalyst in the presence of the catalyst described in claim 1 and the catalyst obtained by the preparation method according to any one of claims 2 to 8, and then carrying out a hydrogenation reaction to obtain high-purity terephthalic acid, wherein the p-carboxybenzaldehyde content is less than 2 wt%; The hydrogenation reaction is carried out at a temperature of 270–290°C, a pressure of 7–8.5 MPa, a hydrogen partial pressure of 0.5–1 MPa, and a reaction time of 5–30 minutes.

10. The method according to claim 9, characterized in that, The reduction process employs either gas-phase reduction or liquid-phase reduction; the molar ratio of reducing agent to palladium is 5–40; the gas-phase reducing agent is selected from hydrogen or a mixture of hydrogen and nitrogen or argon; the gas-phase reduction temperature is 130–220℃, and the reduction time is 1–10 hours; the liquid-phase reducing agent is selected from one or more of formic acid, formaldehyde, ascorbic acid, hydrazine hydrate, and glucose; the liquid-phase reduction temperature is 80–100℃, and the reduction time is 0.1–1.5 hours / kg catalyst.

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