Catalysts for the production of aromatic polycarboxylic acids by liquid-phase oxidation and their applications

Abstract

This invention discloses a catalyst for the liquid-phase oxidation production of aromatic polycarboxylic acids and its application. The catalyst comprises Co salts, Mn salts, Group IVB salts, hydroxycarboxylate salts, and bromine-containing compounds; by weight, the ratio of Co:Mn:Group IVB element:hydroxycarboxylate salt:Br is 500:(200-300):(5-20):(10-50):(500-2000). When used for the liquid-phase oxidation production of aromatic polycarboxylic acids, the catalyst provided by this invention reduces the metal impurity content of CTA products and improves product selectivity.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to a catalyst for the liquid-phase oxidation of aromatic polycarboxylic acids and its application. Background Technology

[0002] Crude terephthalic acid (CTA) can be purified by hydrogenation to obtain purified terephthalic acid, commonly known as PTA, which is a basic raw material for the synthesis of polyethylene terephthalate (PET). Its demand continues to grow, with global PTA demand projected to reach 100 million tons in 2023. Currently, the main production technology for terephthalic acid is the two-step process developed by Amoco-MC, involving the oxidation and hydrogenation of p-xylene (PX). The oxidation step uses a Co-Mn-Br catalyst system with acetic acid as the solvent. The hydrogenation process primarily converts p-aldehyde benzoic acid (4-CBA) into p-methylbenzoic acid (p-TA), which is then removed by centrifugation and water washing.

[0003] In the synthesis of terephthalic acid, the homogeneous catalysts used contain metal components such as Co and Mn, which weakly interact with the terephthalic acid product. This leads to the residue of metal components in the PTA product, resulting in decreased product quality, darker color, and severely affecting subsequent polyester polymerization and product quality. Currently, industrial methods address this by increasing the number of washing cycles and the washing ratio, which increases energy consumption. For example, the oxidation process disclosed in US7985875B2 (Process for preparing aromatic polycarboxylic acid by liquid phase oxidation), despite multiple separations, still results in high Co and Mn content in CTA. Summary of the Invention

[0004] To address the technical problem of high metal content in crude terephthalic acid (CTA) products produced by oxidation in existing technologies, this invention provides a catalyst for the liquid-phase oxidation production of aromatic polycarboxylic acids and its application. The catalyst provided by this invention features reduced metal impurity content in CTA products and improved product selectivity.

[0005] The first aspect of the present invention provides a catalyst for the liquid-phase oxidation production of aromatic polycarboxylic acids, comprising Co salt, Mn salt, group IVB salt, hydroxycarboxylate, and bromine-containing compound; by weight, Co:Mn:group IVB element:hydroxycarboxylate:Br is 500:(200-300):(5-20):(10-50):(500-2000).

[0006] Furthermore, the Co salt is cobalt acetate.

[0007] Furthermore, the Mn salt is manganese acetate.

[0008] Furthermore, the group IVB salt is at least one of zirconium acetate or hafnium acetate, preferably zirconium acetate and hafnium acetate.

[0009] Further, the hydroxycarboxylate is at least one selected from tartrate, heptodrine, gluconate, and alginate; preferably tartrate. Further, the hydroxycarboxylate is a potassium salt, sodium salt, or potassium-sodium salt.

[0010] Furthermore, the bromine-containing compound is selected from at least one of inorganic bromides and bromine hydrocarbons.

[0011] Furthermore, the inorganic bromide is selected from hydrogen bromide or alkali metal bromides.

[0012] Further, the bromoalkane is selected from at least one of tetrabromoethane, tetrabromopropane, and tetrabromobutane. The specific substitution position of bromine in the bromoalkane is not particularly limited. The bromoalkane is, for example, but not limited to, at least one selected from 1,1,2,2-tetrabromoethane, 1,1,1,2-tetrabromoethane, 1,1,2,2-tetrabromopropane, and 2,2,3,3-tetrabromobutane.

[0013] Furthermore, in the catalyst, when Co is 500 parts by weight, the weight parts of the group IVB elements can be selected from 210, 220, 230, 240, 250, 260, 270, 280, and 290; the weight parts of the hydroxycarboxylate can be selected from 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19; and the weight parts of Br can be selected from 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, and 1900.

[0014] The second aspect of the present invention provides a method for producing aromatic polycarboxylic acids by liquid-phase oxidation, the method comprising reacting a polyalkyl-substituted aromatic hydrocarbon with an oxidant in the presence of a catalyst provided in the first aspect, using acetic acid as a solvent, to obtain aromatic polycarboxylic acids.

[0015] Furthermore, the oxidant is a gas containing elemental oxygen, such as, but not limited to, oxygen, air, oxygen-nitrogen mixtures, oxygen-air mixtures, oxygen-nitrogen mixtures, etc.

[0016] Furthermore, the aromatic hydrocarbon in the polyalkyl substituted aromatic hydrocarbon is preferably benzene or naphthalene.

[0017] Furthermore, the polyalkyl-substituted aromatic hydrocarbons are preferably dialkyl-substituted aromatic hydrocarbons.

[0018] Furthermore, the alkyl group in the polyalkyl-substituted aromatic hydrocarbon is preferably a C1 to C4 alkyl group, such as, but not limited to, methyl, ethyl, or propyl.

[0019] Furthermore, as examples, but not limited to, the polyalkyl aromatic hydrocarbons mentioned above include p-xylene and m-xylene.

[0020] Furthermore, the reaction temperature is preferably 160–250°C.

[0021] Furthermore, the pressure of the reaction is preferably 0.8 to 2.0 MPa.

[0022] Furthermore, the reaction time is preferably 1 to 5 hours.

[0023] Furthermore, the oxidant in the reaction is preferably air, and the space velocity (the ratio of gas volume flow rate to the volume of the liquid raw material mixture) is 2 to 5 h⁻¹. -1 .

[0024] Furthermore, in the reaction, the mass ratio of the polyalkyl-substituted aromatic hydrocarbon, solvent, and catalyst (calculated as Co) is 1:(2-10):(1×10⁻⁶). -4 ~1×10 -3 ).

[0025] Furthermore, the crude terephthalic acid (CTA) obtained from the reaction can be purified by hydrogenation to obtain purified terephthalic acid (PTA).

[0026] Furthermore, the crude terephthalic acid (CTA) obtained from the reaction has a Co content of no more than 1 ppmw, more preferably less than 0.8 ppmw, and a Mn content of no more than 1.5 ppmw, preferably less than 0.9 ppmw.

[0027] Those skilled in the art will readily understand that the number of alkyl groups in the aromatic polycarboxylic acids obtained by the above method is the same as the number of alkyl groups in the polyalkyl-substituted aromatic molecule.

[0028] Compared with the prior art, the beneficial effects of this invention are as follows:

[0029] In the catalysts for the conventional liquid-phase oxidation to produce aromatic polycarboxylic acids in this field, due to the weak interaction between Co salts, Mn salts and terephthalic acid products, metal components remain in the PTA products. The catalyst for the liquid-phase oxidation to produce aromatic polycarboxylic acids provided by the present invention includes Co salts, Mn salts, Group IVB salts, hydroxycarboxylates, and bromine-containing compounds. By the mutual cooperation of each component, the selectivity of crude terephthalic acid (CTA) is improved, the generation of by-products 4-CBA and p-TA is reduced, and the content of metal impurities (Co salts, Mn salts, Group IVB salts) in the CTA products is also significantly reduced. In particular, the mass content of Co is below 0.8 ppmw, and the mass content of Mn is below 0.9 ppmw, which is much lower than the metal impurity content in the products of the existing technologies in this field. Detailed Embodiments

[0030] The following examples will further illustrate the technical solutions provided by the present invention, but the protection scope of the present invention is not limited by these examples.

[0031] For the products of the examples and comparative examples of the present invention, the samples to be analyzed are first completely dissolved in dimethyl sulfoxide. PX is analyzed by gas chromatography, and other substances are analyzed by high performance liquid chromatography (HPLC).

[0032]

Example 1

[0033] The reaction is carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery pipe, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed is 400 rpm, and it is heated by circulating hot oil. The reaction steps are as follows:

[0034] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ , 15 ppmw Zr 4+ ), as well as 0.44 g of 1,1,2,2-tetrabromoethane (the bromine is 800 ppmw based on the whole solution), and 0.10 g of sodium potassium tartrate. Mix them evenly and then add them to the autoclave and seal it.

[0035] 2) Add nitrogen at 2.0 MPa for a 30-minute airtightness test. If the pressure drop is not more than 0.1 MPa within 30 minutes, it is qualified.

[0036] 3) Add nitrogen with an air velocity of 4 h -1 , start the stirrer with a stirring rate of 400 rpm, and heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0037] 4) Switch to air at 186 °C with an air velocity of 4 h -1, React for 120 min while keeping the temperature constant.

[0038] 5) After the reaction, switch to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is vacuum filtered, and the filtered solid is washed with 1000 ml of pure water, and then the washed solid is filtered continuously. The obtained solid is dried in an oven at 130 °C for 8 h. After cooling to room temperature in a dryer, the solid sample is analyzed for organic impurities and metal impurities.

[0039] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3-6 wt%, and the CO2 content is controlled between 1.0-1.5 wt%. The catalyst formulation is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0040]

Example 2

[0041] The reaction is carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery pipe, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed is 400 rpm, and it is heated by circulating hot oil. The reaction steps are as follows:

[0042] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ , 15 ppmw Hf 4+ ), as well as 0.44 g of 1,1,2,2-tetrabromoethane (bromine is 800 ppmw based on the whole solution), and 0.10 g of potassium sodium tartrate. Mix them evenly and add them to the autoclave, then seal it.

[0043] 2) Add nitrogen at 2.0 MPa for a 30-min airtight test. If the pressure drop is not more than 0.1 MPa within 30 min, it is qualified.

[0044] 3) Add nitrogen with an air space velocity of 4 h -1 , and start the stirrer with a stirring rate of 400 rpm. Heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0045] 4) Switch to air at 186 °C with an air space velocity of 4 h -1 , React for 120 min while keeping the temperature constant.

[0046] 5) After the reaction, switch to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is vacuum filtered, and the filtered solid is washed with 1000 ml of pure water, and then the washed solid is filtered continuously. The obtained solid is dried in an oven at 130 °C for 8 h. After cooling to room temperature in a dryer, the solid sample is analyzed for organic impurities and metal impurities.

[0047] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, the CO2 content is controlled between 1.0 - 1.5 wt%. The catalyst formula is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0048]

Example 3

[0049] The reaction is carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery tube, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed is 400 rpm, and it is heated by circulating hot oil. The reaction steps are as follows:

[0050] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ , 7.5 ppmw Zr 4+ , 7.5 ppmw Hf 4+ ), as well as 0.44 g of 1,1,2,2-tetrabromoethane (calculated based on the whole solution, bromine is 800 ppmw), 0.10 g of potassium sodium tartrate. Mix them evenly and add them to the autoclave, then seal it.

[0051] 2) Add nitrogen at 2.0 MPa for a 30 - minute airtight test. If the pressure drop is no more than 0.1 MPa within 30 minutes, it is qualified.

[0052] 3) Add nitrogen with an air velocity of 4 h -1 , start the stirrer with a stirring rate of 400 rpm, and heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0053] 4) Switch to air at 186 °C with an air velocity of 4 h -1 , and keep the temperature unchanged for a reaction of 120 minutes.

[0054] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is vacuum filtered, and the filtered solid is washed with 1000 ml of pure water. Then the washed solid is filtered again. The obtained solid is dried in an oven at 130 °C for 8 h, and after cooling to room temperature in a dryer, the solid sample is analyzed for organic impurities and metal impurities.

[0055] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, the CO2 content is controlled between 1.0 - 1.5 wt%. The catalyst formula is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0056]

Example 4

[0057] The reaction was carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery tube, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and heating was carried out by circulating hot oil. The reaction steps were as follows:

[0058] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ , 15 ppmw Zr 4+ ), as well as 0.55 g of 1,1,2,2-tetrabromoethane (bromine was 1000 ppmw based on the whole solution), and 0.10 g of sodium potassium tartrate. Mix them evenly and then add them to the autoclave and seal it.

[0059] 2) Add nitrogen at 2.0 MPa for a 30-minute airtightness test. It is qualified if the pressure drop is not more than 0.1 MPa within 30 minutes.

[0060] 3) Add nitrogen with an air velocity of 4 h -1 , start the stirrer with a stirring rate of 400 rpm, and heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0061] 4) Switch to air at 186 °C with an air velocity of 4 h -1 , and keep the temperature constant for 120 minutes of reaction.

[0062] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is vacuum filtered, and the filtered solid is washed with 1000 ml of pure water. Then the washed solid is filtered continuously. The obtained solid is dried in an oven at 130 °C for 8 h, cooled to room temperature in a dryer, and then the solid sample is analyzed for organic impurities and metal impurities.

[0063] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, and the CO2 content is controlled between 1.0 - 1.5 wt%. The catalyst formulation is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0064]

Example 5

[0065] The reaction was carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery tube, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed was 400 rpm, and heating was carried out by circulating hot oil. The reaction steps were as follows:

[0066] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+, 15 ppmw Zr 4+ ), and 0.44 g of 1,1,2,2 - tetrabromoethane (bromine is 800 ppmw based on the whole solution), 0.10 g of sodium heptonate were mixed evenly and then added to the autoclave, which was sealed.

[0067] 2) Nitrogen at 2.0 MPa was added for a 30 - minute airtight test. It was qualified if the pressure drop was no more than 0.1 MPa within 30 minutes.

[0068] 3) Nitrogen was added with an air velocity of 4 h -1 , and the stirrer was started with a stirring rate of 400 rpm. The temperature was raised to 186 °C while maintaining the pressure at 1.0 MPa.

[0069] 4) At 186 °C, it was switched to air with an air velocity of 4 h -1 , and the temperature was kept constant for a reaction of 120 minutes.

[0070] 5) After the reaction, it was switched back to nitrogen again, cooled to room temperature, the pressure in the reaction kettle was released to atmospheric pressure. The oxidized product was vacuum - filtered, and the filtered solid was washed with 1000 ml of pure water. Then the washed solid was filtered continuously. The obtained solid was dried in an oven at 130 °C for 8 h, and after cooling to room temperature in a dryer, the solid sample was analyzed for organic impurities and metal impurities.

[0071] 6) The tail gas was analyzed online by infrared. The tail oxygen content was controlled between 3 - 6 wt%, and the CO2 content was controlled between 1.0 - 1.5 wt%

[0072] between. The catalyst formulation is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0073]

Example 6

[0074] The reaction was carried out in a 1000 - ml titanium autoclave equipped with a magnetic stirrer, a gas delivery pipe, a reflux condenser, a thermocouple, and a rupture disk, with a stirring speed of 400 rpm and heated by circulating hot oil. The reaction steps were as follows:

[0075] 1) Weigh 80 g of p - xylene, 400 g of acetic acid, 20 g of metal acetate (based on the whole solution, containing 50 ppbw Co 2+ , 300 ppmw Mn 2+ , 15 ppmw Zr 4+ ), and 0.44 g of 1,1,2,2 - tetrabromoethane (bromine is 800 ppmw based on the whole solution), 0.10 g of potassium sodium tartrate were mixed evenly and then added to the autoclave, which was sealed.

[0076] 2) Add nitrogen at 2.0 MPa for a 30-min airtight test. It is qualified if the pressure drop is no more than 0.1 MPa within 30 min.

[0077] 3) Add nitrogen with an airspeed of 4 h -1 , and start the stirrer with a stirring rate of 400 rpm. Heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0078] 4) Switch to air at 186 °C with an airspeed of 4 h -1 , and keep the temperature constant for 120 min of reaction.

[0079] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is vacuum-filtered, and the filtered solid is washed with 1000 ml of pure water. Then the washed solid is filtered continuously. The obtained solid is dried in an oven at 130 °C for 8 h. After cooling to room temperature in a dryer, the solid sample is analyzed for organic impurities and metal impurities.

[0080] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, and the CO2 content is controlled between 1.0 - 1.5 wt%. The catalyst formula is shown in Table 1, and the main impurity analysis results of the product are shown in Table 2.

[0081]

Example 7

[0082] The reaction is carried out in a 1000-ml titanium autoclave equipped with a magnetic stirrer, gas delivery pipe, reflux condenser, thermocouple, and rupture disc, with a stirring speed of 400 rpm and heated by circulating hot oil. The reaction steps are as follows:

[0083] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ , 15 ppmw Zr 4+ ), as well as 0.44 g of 1,1,2,2-tetrabromoethane (bromine is 800 ppmw based on the whole solution), and 0.05 g of potassium sodium tartrate. Mix them evenly and add them to the autoclave, then seal it.

[0084] 2) Add nitrogen at 2.0 MPa for a 30-min airtight test. It is qualified if the pressure drop is no more than 0.1 MPa within 30 min.

[0085] 3) Add nitrogen with an airspeed of 4 h -1 , and start the stirrer with a stirring rate of 400 rpm. Heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0086] 4) Switch with air at 186°C, with an air space velocity of 4 h -1 , and keep the temperature constant for a reaction of 120 min.

[0087] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure, filter the oxidized product by vacuum filtration, wash the filtered solid with 1000 ml of pure water, then continue to filter the solid after water washing, and dry the obtained solid in an oven at 130°C for 8 h. After cooling to room temperature in a dryer, analyze the organic impurities and metal impurities of the solid sample.

[0088] The tail gas is analyzed online by infrared, the tail oxygen content is controlled between 3-6 wt%, the CO2 content is controlled between 1.0-1.5 wt%, the catalyst formulation is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0089]

Comparative Example 1

[0090] The reaction is carried out in a 1000 ml titanium high-pressure kettle equipped with a magnetic stirrer, a gas delivery pipe, a reflux condenser, a thermocouple, and a rupture disc. The stirring speed is 400 rpm, and it is heated by circulating hot oil. The reaction steps are as follows:

[0091] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ .), and 0.44 g of 1,1,2,2-tetrabromoethane (the bromine is 800 ppmw based on the whole solution), mix evenly and add it to the high-pressure kettle, and seal it.

[0092] 2) Add nitrogen at 2.0 MPa for a 30-min airtight test. If the pressure drop is not more than 0.1 MPa within 30 min, it is qualified.

[0093] 3) Add nitrogen, with a space velocity of 4 h -1 , start the stirrer, with a stirring rate of 400 rpm, heat up to 186°C, and at the same time keep the pressure at 1.0 MPa.

[0094] 4) Switch with air at 186°C, with a space velocity of 4 h -1 , and keep the temperature constant for a reaction of 120 min.

[0095] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure, filter the oxidized product by vacuum filtration, wash the filtered solid with 1000 ml of pure water, then continue to filter the solid after water washing, and dry the obtained solid in an oven at 130°C for 8 h. After cooling to room temperature in a dryer, analyze the organic impurities and metal impurities of the solid sample.

[0096] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, the CO2 content is controlled between 1.0 - 1.5 wt%. The catalyst formulation is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2. The catalyst of this comparative example is equivalent to the composition of the existing conventional catalyst. According to the results in Table 2, the selectivity of its product is low, and the contents of metal Co and Mn impurities are also high, affecting the product quality.

[0097]

Comparative Example 2

[0098] The reaction is carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, gas delivery pipe, reflux condenser, thermocouple, and rupture disk. The stirring speed is 400 rpm, and it is heated by circulating hot oil. The reaction steps are as follows:

[0099] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (calculated based on the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ , 15 ppmw Zr 4+ ), and 0.44 g of 1,1,2,2-tetrabromoethane (bromine is 800 ppmw based on the whole solution). After mixing evenly, add them to the autoclave and seal it.

[0100] 2) Add nitrogen at 2.0 MPa for a 30 - minute airtight test. If the pressure drop is not more than 0.1 MPa within 30 minutes, it is qualified.

[0101] 3) Add nitrogen with an air velocity of 4 h -1 , start the stirrer with a stirring rate of 400 rpm, and heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0102] 4) Switch to air at 186 °C with an air velocity of 4 h -1 , and keep the temperature unchanged for a reaction of 120 minutes.

[0103] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is filtered by vacuum filtration, and the filtered solid is washed with 1000 ml of pure water. Then the washed solid is filtered continuously, and the obtained solid is dried in an oven at 130 °C for 8 h. After cooling to room temperature in a dryer, the solid sample is analyzed for organic impurities and metal impurities.

[0104] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, the CO2 content is controlled between 1.0 - 1.5 wt%. The catalyst formulation is shown in Table 1, and the analysis results of the main impurities in the product are shown in Table 2.

[0105]

Comparative Example 3

[0106] The reaction was carried out in a 1000 ml titanium autoclave equipped with a magnetic stirrer, a gas delivery tube, a reflux condenser, a thermocouple, and a rupture disk. The stirring speed was 400 rpm, and the reaction was heated by circulating hot oil. The reaction steps were as follows:

[0107] 1) Weigh 80 g of p-xylene, 400 g of acetic acid, 20 g of metal acetate (in the whole solution, containing 500 ppmw Co 2+ , 250 ppmw Mn 2+ ), 0.44 g of 1,1,2,2-tetrabromoethane (in the whole solution, bromine was 800 ppmw), and 0.10 g of sodium potassium tartrate. Mix them evenly and add them to the autoclave, then seal it.

[0108] 2) Add nitrogen at 2.0 MPa for a 30-minute airtight test. If the pressure drop is not more than 0.1 MPa within 30 minutes, it is qualified.

[0109] 3) Add nitrogen with an air velocity of 4 h -1 , start the stirrer with a stirring rate of 400 rpm, and heat up to 186 °C while maintaining the pressure at 1.0 MPa.

[0110] 4) Switch to air at 186 °C with an air velocity of 4 h -1 , and keep the temperature constant for 120 minutes of reaction.

[0111] 5) After the reaction, switch back to nitrogen again, cool to room temperature, relieve the pressure of the reaction kettle to atmospheric pressure. The oxidized product is vacuum filtered, and the filtered solid is washed with 1000 ml of pure water. Then the washed solid is filtered again. The obtained solid is dried in an oven at 130 °C for 8 h. After cooling to room temperature in a dryer, the solid sample is analyzed for organic impurities and metal impurities.

[0112] The tail gas is analyzed online by infrared. The tail oxygen content is controlled between 3 - 6 wt%, and the CO2 content is controlled between 1.0 - 1. (Please note that the value after 1.0 - 1.5wt% seems incomplete in the original text. Here it is translated as 1.0 - 1. according to the original).5 wt%. The catalyst formulation is shown in Table 1, and the main impurity analysis results of the product are shown in Table 2.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A catalyst for the liquid-phase oxidation production of aromatic polycarboxylic acids, said catalyst comprising Co salt, Mn salt, Group IVB salt, hydroxycarboxylate, and bromine-containing compound; wherein, by weight, Co: Mn: Group IVB element: hydroxycarboxylate: Br is 500: (200~300): (5~20): (10~50): (500~2000); The hydroxycarboxylic acid salt is at least one of tartrate, heptarate, gluconate, and alginate.

2. The catalyst according to claim 1, characterized in that... The Co salt is cobalt acetate.

3. The catalyst according to claim 1, characterized in that... The Mn salt is manganese acetate.

4. The catalyst according to claim 1, characterized in that... The group IVB salt is at least one of zirconium acetate or hafnium acetate.

5. The catalyst according to claim 1, characterized in that... The bromine-containing compound is selected from at least one of inorganic bromides and bromohydrocarbons.

6. The catalyst according to claim 5, characterized in that... The inorganic bromide is selected from hydrogen bromide or alkali metal bromide.

7. The catalyst according to claim 5, characterized in that... The bromohydrocarbon is selected from at least one of tetrabromoethane, tetrabromopropane, and tetrabromobutane.

8. A method for producing aromatic polycarboxylic acids by liquid-phase oxidation, the method comprising reacting a polyalkyl-substituted aromatic hydrocarbon with an oxidant in the presence of a catalyst as described in any one of claims 1 to 7, using acetic acid as a solvent, to obtain aromatic polycarboxylic acids.

9. The method according to claim 8, characterized in that: The aromatic hydrocarbon is benzene or naphthalene; the oxidant is a gas containing elemental oxygen.

10. The method according to claim 9, characterized in that: The reaction temperature is 160–250 °C; the reaction pressure is 0.8–2.0 MPa; the reaction time is 1–5 h; the mass ratio of polyalkyl substituted aromatic hydrocarbons, solvent, and catalyst (calculated as Co) is 1:(2–10):(1×10⁻⁶). -4 ~1×10 -3 ).

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