Hydrotreating method of crude terephthalic acid

Abstract

The invention relates to a hydrotreating method of crude terephthalic acid, which comprises the step of reacting crude terephthalic acid with hydrogen in the presence of a hydrogenation catalyst, a solvent and fatty acid, and the fatty acid is selected from one or more of C1-C6 carboxylic acids. The C1-C6 carboxylic acid is introduced into the hydrotreating of the crude terephthalic acid, so that the problem of serious decarboxylation in the process of purifying the crude terephthalic acid to produce the refined phthalic acid is solved to a great extent. The method provided by the invention is used for the purification reaction of crude terephthalic acid, and has the characteristic of low impurity benzoic acid after hydrogenation purification.

Description

Technical Field

[0001] This application relates to a method for hydrogenating crude terephthalic acid. Background Technology

[0002] Purified terephthalic acid (PTA) is one of the basic raw materials for the synthesis of polyethylene terephthalate (PET). Demand for PTA continues to grow, and global PTA demand is projected to reach 90 million tons by 2024. Currently, the main PTA production technology is the two-step process developed by Mid-Century (acquired by Amoco-BP), involving the oxidation and hydrogenation of p-xylene (PX). In this process, the oxidation step uses acetic acid as a solvent and a Co-Mn-Br catalyst system; hydrogenation mainly occurs under high temperature and pressure with a palladium-on-carbon catalyst, converting p-aldehyde benzoic acid (4-CBA) to p-methylbenzoic acid (p-TA), which is then removed by centrifugation and washing with water. Many indicators affect PTA quality; currently, polyester-grade PTA requires a 4-CBA content of less than 25 ppmw and a p-methylbenzoic acid (p-TA) content of less than 150 ppmw.

[0003] The main difference between various hydrogenation processes lies in the oxidation reaction temperature (ranging from 160℃ to 225℃), resulting in variations in process conditions, reactor type, and flow design. ICI and Amoco have the highest reaction temperatures, Mitsui-Amoco is in the middle, and Eastman has the lowest, referred to as high-temperature oxidation, medium-temperature oxidation, and low-temperature oxidation processes, respectively. However, the hydrogenation process itself remains largely unchanged, with temperatures ranging from 250 to 290℃ and pressures from 6.5 to 9.0 MPa. Due to the stringent hydrogenation conditions, the decarboxylation of the carboxyl group on the benzene ring to form benzoic acid (BA) is unavoidable, leading to the loss of terephthalic acid (TA). 4-CBA is hydrogenated to form p-hydroxymethylbenzoic acid (HMBA), and p-TA can be returned to the oxidation system via centrifugation.

[0004] To reduce decarboxylation during hydrogenation, the reaction temperature and pressure are minimized, or the hydrogen partial pressure is lowered. However, this increases the concentration of colored impurities in 4-CBA, reducing the quality of the PTA product. US Patent 4626598 (Purification of Terephthalic Acid) discloses a method to reduce the PTA b-value by increasing the hydrogen partial pressure or the hydrogenation reaction temperature. This method increases energy and material consumption, but also increases the decarboxylation side reaction of terephthalic acid. Summary of the Invention

[0005] The technical problem to be solved by this application is the severe decarboxylation problem in the purification of crude terephthalic acid to produce refined terephthalic acid. A new method for hydrogenating crude terephthalic acid is provided. This method is used for the purification reaction of crude terephthalic acid and has the characteristic of low benzoic acid impurity after hydrogenation purification.

[0006] Specifically, the hydrogenation treatment method for crude terephthalic acid provided in this application includes reacting crude terephthalic acid with hydrogen gas in the presence of a hydrogenation catalyst, a solvent, and a fatty acid, wherein the fatty acid is selected from one or more C1-C6 carboxylic acids.

[0007] In this application, by introducing C1-C6 carboxylic acid into the hydrogenation treatment of crude terephthalic acid, on the one hand, the C1-C6 carboxylic acid and the solvent can be used as a mixed solvent to reduce the decarboxylation of terephthalic acid; on the other hand, the addition of C1-C6 carboxylic acid can effectively reduce the content of impurity 4-CBA in the hydrogenation product.

[0008] In some embodiments, the fatty acid is selected from one or more C1-C4 monocarboxylic acids. In some embodiments, the fatty acid is selected from one or more formic acid, acetic acid, propionic acid, and butyric acid.

[0009] In some embodiments, the mass ratio of the fatty acid to the solvent is (0.001-0.05):1, for example, 0.003:1, 0.005:1, 0.007:1, 0.009:1, 0.01:1, 0.011:1, 0.013:1, 0.015:1, 0.017:1, 0.019:1, 0.02:1, 0.021:1, etc. The ratios are 0.023:1, 0.025:1, 0.027:1, 0.029:1, 0.03:1, 0.031:1, 0.033:1, 0.035:1, 0.037:1, 0.039:1, 0.04:1, 0.041:1, 0.043:1, 0.045:1, 0.047:1, 0.049:1, or any value between them. A high fatty acid-to-solvent ratio, i.e., a high fatty acid content, will inhibit the hydrogenation reaction; a low fatty acid-to-solvent ratio, i.e., a low fatty acid content, will not significantly reduce the 4-CBA impurity.

[0010] In some embodiments, the mass ratio of the fatty acid to the solvent is (0.005-0.02):1. In some embodiments, the mass ratio of the fatty acid to the solvent is (0.009-0.013):1.

[0011] In some embodiments, the solvent is selected from water.

[0012] In some embodiments, the reaction temperature is 250°C-300°C, for example, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, 285°C, 290°C, 295°C, or any value between them. In some embodiments, the reaction temperature is 270°C-290°C.

[0013] In some embodiments, the reaction pressure is 5 MPaG-10 MPaG, for example, 5.5 MPaG, 6 MPaG, 6.5 MPaG, 7 MPaG, 7.5 MPaG, 8 MPaG, 8.5 MPaG, 9 MPaG, 9.5 MPaG, or any value between them. In some embodiments, the reaction pressure is 6.5 MPaG-8.5 MPaG.

[0014] In some embodiments, the reaction time is 10 min to 150 min, for example, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, or any value between them. In some embodiments, the reaction time is 30 min to 100 min.

[0015] In some embodiments, the partial pressure of the hydrogen gas is 3 MPaG-10 MPaG, for example, 3.5 MPaG, 4 MPaG, 4.5 MPaG, 5 MPaG, 5.5 MPaG, 6 MPaG, 6.5 MPaG, 7 MPaG, 7.5 MPaG, 8 MPaG, 8.5 MPaG, 9 MPaG, 9.5 MPaG, or any value between them. In some embodiments, the partial pressure of the hydrogen gas is 4 MPaG-7 MPaG.

[0016] In some embodiments, the mass ratio of crude terephthalic acid to solvent is 1:(3-50), for example, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, or 1:45. In some embodiments, the mass ratio of crude terephthalic acid to solvent is 1:(5-30).

[0017] In some embodiments, the mass ratio of the hydrogenation catalyst to the solvent is (0.05-5):100, for example, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, or 4.5:100. In some embodiments, the mass ratio of the hydrogenation catalyst to the solvent is (0.1-3):100.

[0018] In some embodiments, the hydrogenation catalyst has a mesh size of 3-10 mesh, for example, 5 mesh, 6 mesh, 7 mesh, 8 mesh, or 9 mesh. In some embodiments, the hydrogenation catalyst has a mesh size of 4-8 mesh.

[0019] In some embodiments, the hydrogenation catalyst is selected from palladium-on-carbon catalysts, which include the active component palladium and the supported activated carbon.

[0020] In some embodiments, the mass content of the active component palladium is 0.2%-0.6%, for example, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or 0.55%. In some embodiments, the mass content of the active component palladium is 0.45%-0.55%.

[0021] In some embodiments, the specific surface area of ​​the activated carbon is 900 m². 2 / g-1200m 2 / g, for example, 950m 2 / g, 1000m 2 / g, 1050m 2 / g、1100m 2 / g or 1150m 2 / g.

[0022] In some embodiments, the activated carbon has a pore volume of 0.45 μm. 3 / g-0.70m 3 / g, for example, 0.50mL / g, 0.60mL / g or 0.70mL / g.

[0023] In some embodiments, the activated carbon is selected from one or more of coal-based carbon, wood-based carbon, and fruit shell carbon, preferably coconut shell carbon.

[0024] In some embodiments, the crude terephthalic acid contains p-carboxybenzaldehyde at a mass content of less than or equal to 4000 ppmw and p-methylbenzoic acid at a mass content of less than or equal to 1000 ppmw.

[0025] In some embodiments, the hydrogenation treatment method for crude terephthalic acid includes the following specific steps:

[0026] Using water as a solvent, in the presence of fatty acids and a hydrogenation catalyst, hydrogen gas is used to purify crude terephthalic acid in the liquid phase to produce refined terephthalic acid. Preferably, the purification temperature is 270–290°C, the purification pressure is 6.5–8.5 MPaG, and the purification time is 30–100 min.

[0027] In the above technical solution, the hydrogenation catalyst is preferably a 0.45-0.55 wt% Pd / C catalyst with a mesh size of 4-8, and the BET specific surface area of ​​the activated carbon support is preferably 900-1200 m². 2 / g, with a preferred pore volume of 0.48–0.70m³. 3 / g; The activated carbon carrier is preferably coal-based carbon, wood-based carbon, or fruit shell carbon. The fruit shell carbon is preferably coconut shell carbon.

[0028] In the above technical solution, the fatty acid is at least one of acetic acid, propionic acid, and butyric acid, and the mass ratio of water to fatty acid is 100:(0.01-10); the preferred fatty acid is acetic acid.

[0029] In the above technical solution, the hydrogen partial pressure is preferably 3 to 10 MPaG.

[0030] In the above technical solution, the mass ratio of crude terephthalic acid to solvent is preferably 100:(5-30).

[0031] In the above technical solution, the mass ratio of the catalyst to the solvent is preferably (0.1-5):100.

[0032] In the above technical solution, the crude terephthalic acid has a concentration of 5-35 wt%, the main impurity p-carboxybenzaldehyde (4-CBA) has a mass content of no more than 4000 ppmw, and p-methylbenzoic acid (p-TA) has a mass content of no more than 1000 ppmw.

[0033] The beneficial technical effects of this application are as follows:

[0034] This application largely solves the problem of severe decarboxylation in the purification of crude terephthalic acid to refined terephthalic acid by introducing C1-C6 carboxylic acids during the hydrogenation treatment of crude terephthalic acid. The method provided in this application, used for the purification reaction of crude terephthalic acid, features low levels of benzoic acid impurities after hydrogenation purification. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and technologies have also been described in numerous publications.

[0036] The endpoints and any values in the ranges disclosed herein are not limited to the exact 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 each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered as specifically disclosed herein.

[0037] In the examples and comparative examples of this application, the impurities 4-CBA (p-carboxybenzaldehyde), p-TA (p-toluic acid), BA (benzoic acid), and HMBA (p-hydroxymethylbenzoic acid) in the raw materials and products were analyzed by high performance liquid chromatography (HPLC). First, the sample to be analyzed was completely dissolved in ammonia water before analysis.

[0038] Unless otherwise specified, the pressures described in the following examples and comparative examples are gauge pressures.

[0039] The following will describe this application in detail through examples and comparative examples.

[0040] Example 1

[0041] The purification reaction was carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disc. The stirring speed was 400 rpm and it was heated electrically. The process was as follows:

[0042] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 10 g of acetic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g, pore volume of 0.62 m 3 / g) into the autoclave and seal it.

[0043] 2) Add nitrogen at 8.0 MPa for a 30-minute airtight test. If the pressure drop is not more than 0.1 MPa within 30 minutes, it is qualified.

[0044] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, the pressure is 7.5 MPa, the stirring rate is 400 rpm, maintain the reaction conditions, and react for 60 minutes.

[0045] 4) After the reaction, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure, completely dissolve the hydrogenated and purified product in ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0046] The product analysis results are shown in Table 1.

[0047] Example 2

[0048] The purification reaction is carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disk. The stirring speed is 400 rpm, and it is heated electrically. The process is as follows:

[0049] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 5 g of acetic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g and pore volume of 0.62 m 3 / g) into the autoclave and seal it.

[0050] 2) Add nitrogen at 8.0 MPa for a 30-minute airtight test. It is qualified if the pressure drop is no more than 0.1 MPa within 30 minutes.

[0051] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, the pressure is 7.5 MPa, the stirring rate is 400 rpm, maintain the reaction conditions, and react for 60 minutes.

[0052] 4) After the reaction, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure, completely dissolve the hydrogenated and purified product with ammonia water, and analyze the dissolved product by high-performance liquid chromatography.

[0053] The product analysis results are shown in Table 1.

[0054] Example 3

[0055] The purification reaction is carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disk. The stirring speed is 400 rpm, and it is heated electrically. The process is as follows:

[0056] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 8 g of acetic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g and pore volume of 0.62 m 3 / g) into the autoclave and seal it.

[0057] 2) Add nitrogen at 8.0 MPa for a 30-minute airtight test. It is qualified if the pressure drop is no more than 0.1 MPa within 30 minutes.

[0058] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, the pressure is 7.5 MPa, the stirring rate is 400 rpm, maintain the reaction conditions, and react for 60 minutes.

[0059] 4) After the reaction is completed, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure. Completely dissolve the hydrogenated and purified product with ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0060] The product analysis results are shown in Table 1.

[0061] Example 4

[0062] The purification reaction is carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed is 400 rpm and it is heated electrically. The process is as follows:

[0063] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 12 g of acetic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area is 1100 m 2 / g, pore volume 0.62 m 3 / g) into the autoclave and seal it.

[0064] 2) Add nitrogen at 8.0 MPa for a 30-minute airtight test. If the pressure drop is no more than 0.1 MPa within 30 minutes, it is qualified.

[0065] 3) Replace with hydrogen 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, the pressure is 7.5 MPa, the stirring rate is 400 rpm, maintain the reaction conditions, and react for 60 minutes.

[0066] 4) After the reaction is completed, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure. Completely dissolve the hydrogenated and purified product with ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0067] The product analysis results are shown in Table 1.

[0068] Example 5

[0069] The purification reaction is carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed is 400 rpm and it is heated electrically. The process is as follows:

[0070] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 15 g of acetic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area is 1100 m 2 / g, pore volume 0.62 m 3 / g) into the autoclave and seal it.

[0071] 2) Add nitrogen at 8.0 MPa for a 30 - minute airtight test. It is qualified if the pressure drop is no more than 0.1 MPa within 30 minutes.

[0072] 3) Add hydrogen for 5 replacements, then add hydrogen to 5 MPa, heat up to 280 °C, with a pressure of 7.5 MPa and a stirring rate of 400 rpm. Maintain the reaction conditions and react for 60 minutes.

[0073] 4) After the reaction, switch to nitrogen again and cool to room temperature. Release the pressure of the reaction kettle to atmospheric pressure. Completely dissolve the product after hydrogenation and purification with ammonia water, and analyze the dissolved product by high - performance liquid chromatography.

[0074] The product analysis results are shown in Table 1.

[0075] Example 6

[0076] The purification reaction is carried out in a 2000 - mL titanium high - pressure kettle equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disk. The stirring speed is 400 rpm and it is heated by electricity. The process is as follows:

[0077] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4 - CBA and 450 ppmw of p - TA), 15 g of acetic acid, 900 g of pure water, and 4 g of commercial 4 - 8 - mesh CTP - IV type palladium - carbon catalyst (specific surface area is 1100 m 2 / g, pore volume 0.62 m 3 / g) into the high - pressure kettle and seal it.

[0078] 2) Add nitrogen at 8.0 MPa for a 30 - minute airtight test. It is qualified if the pressure drop is no more than 0.1 MPa within 30 minutes.

[0079] 3) Add hydrogen for 5 replacements, then add hydrogen to 5 MPa, heat up to 280 °C, with a pressure of 7.5 MPa and a stirring rate of 400 rpm. Maintain the reaction conditions and react for 60 minutes.

[0080] 4) After the reaction, switch to nitrogen again and cool to room temperature. Release the pressure of the reaction kettle to atmospheric pressure. Completely dissolve the product after hydrogenation and purification with ammonia water, and analyze the dissolved product by high - performance liquid chromatography.

[0081] The product analysis results are shown in Table 1.

[0082] Example 7

[0083] The purification reaction is carried out in a 2000 - mL titanium high - pressure kettle equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disk. The stirring speed is 400 rpm and it is heated by electricity. The process is as follows:

[0084] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 15 g of acetic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g, pore volume of 0.62 m 3 / g) into an autoclave and seal it.

[0085] 2) Add nitrogen at 8.0 MPa for a 30-minute airtight test. A pressure drop not exceeding 0.1 MPa within 30 minutes is considered qualified.

[0086] 3) Add hydrogen for replacement 5 times, then add hydrogen to 8 MPa, heat up to 280 °C, with a pressure of 7.5 MPa and a stirring rate of 400 rpm. Maintain the reaction conditions and react for 60 minutes.

[0087] 4) After the reaction, switch to nitrogen again, cool to room temperature, relieve the pressure of the autoclave to atmospheric pressure, completely dissolve the hydrogenated and purified product with ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0088] The product analysis results are shown in Table 1.

[0089] Example 8

[0090] The purification reaction is carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disk, with a stirring speed of 400 rpm and heated by electricity. The process is as follows:

[0091] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 10 g of formic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g, pore volume of 0.62 m 3 / g) into an autoclave and seal it.

[0092] 2) Add nitrogen at 8.0 MPa for a 30-minute airtight test. A pressure drop not exceeding 0.1 MPa within 30 minutes is considered qualified.

[0093] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, with a pressure of 7.5 MPa and a stirring rate of 400 rpm. Maintain the reaction conditions and react for 60 minutes.

[0094] 4) After the reaction, switch to nitrogen again, cool to room temperature. Relieve the pressure of the autoclave to atmospheric pressure, completely dissolve the hydrogenated and purified product with ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0095] The product analysis results are shown in Table 1.

[0096] Example 9

[0097] The purification reaction was carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and heating was by electricity. The process was as follows:

[0098] 1) 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 10 g of n-propionic acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g and pore volume of 0.62 m 3 / g) were placed in the autoclave and sealed.

[0099] 2) Nitrogen at 8.0 MPa was added for a 30-minute airtight test. A pressure drop of no more than 0.1 MPa within 30 minutes was considered qualified.

[0100] 3) Hydrogen was added for replacement 5 times, then hydrogen was added to 5 MPa, the temperature was raised to 280 °C, the pressure was 7.5 MPa, the stirring rate was 400 rpm, and the reaction conditions were maintained for 60 minutes. <00e0240>4) After the reaction, it was switched to nitrogen again and cooled to room temperature. The autoclave was depressurized to atmospheric pressure, and the hydrogenated and purified product was completely dissolved with ammonia water, and the dissolved product was analyzed by high performance liquid chromatography.

[0102] The product analysis results are shown in Table 1.

[0103] Example 10

[0104] The purification reaction was carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and heating was by electricity. The process was as follows:

[0105] 1) 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 10 g of n-butyric acid, 900 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g and pore volume of 0.62 m 3 / g) were placed in the autoclave and sealed.

[0106] 2) Nitrogen at 8.0 MPa was added for a 30-minute airtight test. A pressure drop of no more than 0.1 MPa within 30 minutes was considered qualified.

[0107] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, the pressure is 7.5 MPa, the stirring rate is 400 rpm, maintain the reaction conditions, and react for 60 min.

[0108] 4) After the reaction is completed, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure, completely dissolve the product after hydrogenation purification with ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0109] The product analysis results are shown in Table 1.

[0110] Comparative Example 1

[0111] The purification reaction was carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disc. The stirring speed was 400 rpm and it was heated by electricity. The process is as follows:

[0112] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 1000 g of pure water, and 2 g of commercial 4-8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g, pore volume of 0.62 m 3 / g) into the autoclave and seal it.

[0113] 2) Add nitrogen at 8.0 MPa for a 30 min airtight test. If the pressure drop is not more than 0.1 MPa within 30 min, it is qualified.

[0114] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, the pressure is 7.5 MPa, the stirring rate is 400 rpm, maintain the reaction conditions, and react for 60 min.

[0115] 4) After the reaction is completed, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure, completely dissolve the product after hydrogenation purification with ammonia water, and analyze the dissolved product by high performance liquid chromatography.

[0116] The product analysis results are shown in Table 1.

[0117] Comparative Example 2

[0118] The purification reaction was carried out in a 2000 mL titanium autoclave equipped with a magnetic stirrer, reflux condenser, thermocouple, and rupture disc. The stirring speed was 400 rpm and it was heated by electricity. The process is as follows:

[0119] 1) Put 100 g of crude terephthalic acid (containing 3000 ppmw of 4-CBA and 450 ppmw of p-TA), 10 g of methanol, 900 g of pure water, and 2 g of commercial 4 - 8 mesh CTP-IV type palladium-carbon catalyst (specific surface area of 1100 m 2 / g and pore volume of 0.62 m 3 / g) into an autoclave and seal it.

[0120] 2) Add nitrogen at 8.0 MPa for a 30 - minute airtight test. It is qualified if the pressure drop is not more than 0.1 MPa within 30 minutes.

[0121] 3) Add hydrogen for replacement 5 times, then add hydrogen to 5 MPa, heat up to 280 °C, with a pressure of 7.5 MPa and a stirring rate of 400 rpm. Maintain the reaction conditions and react for 60 minutes.

[0122] 4) After the reaction, switch to nitrogen again and cool to room temperature. Release the pressure of the autoclave to atmospheric pressure. Completely dissolve the hydrogenated and purified product with ammonia water, and analyze the dissolved product by high-performance liquid chromatography.

[0123] The product analysis results are shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] The preferred embodiments of the present application are described in detail above. However, the present application is not limited thereto. Within the technical concept scope of the present application, various simple modifications can be made to the technical solutions of the present application, including combining each technical feature in any other suitable way. These simple modifications and combinations should also be regarded as the content disclosed by the present application and all fall within the protection scope of the present application.

Claims

1. A process for the hydroprocessing of crude terephthalic acid, comprising reacting crude terephthalic acid with hydrogen in the presence of a hydrogenation catalyst, a solvent and a fatty acid selected from one or more of C1-C6 carboxylic acids.

2. The hydroprocessing process of claim 1 wherein, the fatty acid is selected from one or more of C1-C4 monocarboxylic acids, preferably from one or more of formic acid, acetic acid, n-propionic acid and n-butyric acid.

3. The hydroprocessing process of claim 1 or 2, wherein, the mass ratio of the fatty acid to the solvent is (0.001-0.05):1, preferably (0.005-0.02):1, more preferably (0.009-0.013):1; and / or the solvent is selected from water.

4. The hydroprocessing process of any of claims 1-3, characterized in that, the temperature of the reaction is 250°C-300°C, preferably 270°C-290°C; and / or the pressure of the reaction is 5 MPaG-10 MPaG, preferably 6.5 MPaG-8.5 MPaG; and / or the time of the reaction is 10 min-150 min, preferably 30 min-100 min.

5. The hydroprocessing process of claim 4, wherein, the partial pressure of the hydrogen is 3 MPaG-10 MPaG, preferably 4 MPaG-7 MPaG.

6. The hydroprocessing process of any of claims 1-5, wherein, the mass ratio of the crude terephthalic acid to the solvent is 1:(3-50), preferably 1:(5-30).

7. The hydroprocessing process of any of claims 1-6, wherein, the mass ratio of the hydrogenation catalyst to the solvent is (0.05-5):100, preferably (0.1-3):

100.

8. The hydroprocessing process of any of claims 1-7, wherein, the mesh number of the hydrogenation catalyst is 3 mesh-10 mesh, preferably 4 mesh-8 mesh; and / or the hydrogenation catalyst is selected from a palladium on carbon catalyst comprising an active component of palladium and a support of activated carbon.

9. The hydroprocessing method according to claim 8, characterized in that, the mass content of the active component of palladium is 0.2%-0.6%, preferably 0.45%-0.55%; and / or The activated carbon has a specific surface area of 900 m 2 / g-1200 m 2 / g, a pore volume of 0.45 m 3 / g-0.70 m 3 / g; and / or the activated carbon is selected from one or more of coal-based carbon, wood-based carbon and nut shell carbon, preferably coconut shell carbon.

10. The hydroprocessing process of any of claims 1-9, wherein, the mass content of p-carboxybenzaldehyde in the crude terephthalic acid is less than or equal to 4000 ppmw, and the mass content of p-toluic acid is less than or equal to 1000 ppmw.

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