Nb-co-ti composite oxide catalyst for producing aromatic carboxylic acid and preparation and application thereof

Abstract

The application discloses a preparation method of a niobium-cobalt-titanium composite oxide catalyst for producing aromatic carboxylic acid and application thereof. The niobium-cobalt-titanium composite oxide catalyst is used for the reaction of alkyl aromatic hydrocarbon oxidation for producing aromatic carboxylic acid. The specific method is as follows: in a reaction kettle, alkyl aromatic hydrocarbon, the niobium-cobalt-titanium composite oxide catalyst, an initiator and a solvent are sequentially added, air is introduced at room temperature to 0.1-2.0 MPa, heating is carried out to 50-150 DEG C under sealing, stirring reaction is carried out for 1-10 h, and post-treatment is carried out to obtain aromatic carboxylic acid. Compared with the previous process, the catalyst has the advantages of good acid and alkali resistance, suitability for various solvent systems, good cycle stability, easy separation, no product residue of catalyst metal components and the like; the reaction condition is mild (temperature 50-150 DEG C, reaction pressure <2.0 MPa), the substrate range is wide, the conversion rate and selectivity are high, and industrialization is easy to realize.

Description

Technical Field

[0001] This invention relates to the field of aromatic carboxylic acid preparation technology, and specifically to a method for preparing a niobium-cobalt-titanium composite oxide catalyst for producing aromatic carboxylic acids and its application. Background Technology

[0002] Aromatic carboxylic acids, due to their unique chemical structures and diverse physicochemical properties, are widely used in the pharmaceutical, cosmetic, food, materials science, and catalysis industries. The preparation of aromatic carboxylic acids from the alkyl oxidation of methyl aromatic hydrocarbons is of great significance: 1) it enriches the variety of organic compounds; 2) it serves as a fundamental raw material for high-performance polymer materials and metal-organic frameworks (MOFs); and 3) it is a key step in the synthesis of pharmaceutical intermediates and pesticides.

[0003] Currently, there are four main industrial processes for producing aromatic carboxylic acids: oxidation of aromatic aldehydes, carboxylation, hydrolysis, and homogeneous liquid-phase oxidation. Among these, homogeneous liquid-phase oxidation is the primary method used industrially.

[0004] Aromatic aldehyde oxidation method: Aromatic aldehydes are mixed with a solvent, and an appropriate amount of oxidant, such as oxygen or hydrogen peroxide, is added. The oxidation reaction is carried out under suitable temperature and pressure conditions. After the reaction is complete, the target product, aromatic carboxylic acid, is separated and purified by conventional methods such as cooling, filtration, and crystallization. However, the raw material cost is relatively high. Carboxylation reaction method: Using halogenated aromatic hydrocarbons or arylboronic acids as raw materials, an aromatic carboxylic acid is generated by carboxylation with carbon dioxide in the presence of a catalyst. This method has advantages such as high atom economy and environmental friendliness, but the reaction conditions are currently quite harsh, and the catalyst cost is high. Hydrolysis reaction method: Aromatic carboxylic acids are prepared through the hydrolysis of aromatic nitriles, aromatic esters, and other compounds. The hydrolysis reaction can be carried out under acidic or alkaline conditions, and the reaction conditions are relatively mild, but the preparation process of the raw materials may be relatively complex.

[0005] Homogeneous liquid-phase oxidation involves the oxidation of alkylbenzenes in a solvent containing lower fatty acids using molecular oxygen to produce aromatic carboxylic acids. Soluble catalysts containing cobalt, manganese, and bromine are typically used. This method is suitable for large-scale production of aromatic carboxylic acids such as terephthalic acid, exhibiting high catalytic activity and relatively high feed conversion and product selectivity. However, it suffers from drawbacks including harsh reaction conditions, bromide ion corrosion of equipment, severe environmental pollution, easy contamination of the product by catalyst active components, and solvent decomposition.

[0006] In addition, the air-phase catalytic oxidation method can use vanadium-titanium catalysts and air as an oxygen source to selectively catalytically oxidize aromatic carboxylic acids in one step. This method produces no polluting raw materials or byproducts, yields high-purity target products, and has low production costs, making it an environmentally friendly and relatively economical synthetic route. However, this method involves complex equipment, high reaction temperatures, high energy consumption, and relatively low production capacity.

[0007] Based on the above, patent CN201310349535.5 discloses a method for gas-phase selective catalytic oxidation of alkyl aromatic hydrocarbons to synthesize aromatic carboxylic acids using a composite oxide of V2O5 / TiO2, MnO2, CeO2, CuO or two or more elements from manganese, cerium, and copper as a solid catalyst. However, this method has problems such as high reaction temperature (200-250℃), high energy consumption, the use of water as a solvent, the generation of a large amount of wastewater, and the poor water solubility of structurally complex alkyl aromatic compounds, resulting in a narrow range of applicable substrates.

[0008] Given the various problems with traditional industrial methods for the synthesis of aromatic carboxylic acids from the oxidation of alkyl aromatic hydrocarbons, which cannot meet the requirements of sustainable development, it is desirable to develop an efficient and green synthesis process that can rapidly and selectively achieve the branched oxidation of a wide range of alkyl aromatic hydrocarbons to obtain aromatic carboxylic acid products, thereby reducing the environmental impact. Summary of the Invention

[0009] In view of the prior art, the object of this invention is to provide a method for preparing a niobium-cobalt-titanium composite oxide catalyst for the production of aromatic carboxylic acids and its application.

[0010] This invention is achieved through the following technical solution:

[0011] A method for preparing a niobium-cobalt-titanium composite oxide catalyst for the production of aromatic carboxylic acids, characterized in that,

[0012] 1) Add niobium ammonium oxalate and cobalt precursors to water and stir to dissolve at 20-60°C to obtain solution A; wherein the mass concentration of niobium is 0.1-20%, preferably 0.1-16%, more preferably 0.5-10%;

[0013] 2) Add titanium oxysulfate to water, add 5%-10% dilute sulfuric acid to adjust the pH to 1-4, stir and dissolve at 20-60℃ to obtain solution B; wherein the mass concentration of titanium is 0.1-15%, preferably 0.1-10%, more preferably 0.2-8%;

[0014] 3) Mix solutions A and B at 20-60℃, stirring continuously during the mixing process to ensure that A and B are mixed evenly, to obtain a mixed solution;

[0015] 4) Under stirring conditions, a precipitant is added dropwise to the mixed solution at 20-60℃. After the pH of the mixed solution reaches 8-10, stirring is continued for 1-4 hours. The solution is then filtered, washed, and dried to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in a muffle furnace at 500-1000℃ for 2-12 hours to obtain the niobium-cobalt-titanium composite oxide catalyst.

[0016] The molar ratio of each component in the niobium-cobalt-titanium composite oxide catalyst is Nb:Co:Ti = 1.1-2.0:0.1-0.9:1, preferably 1.2-1.8:0.2-0.8:1, and more preferably 1.2-1.6:0.3-0.6:1.

[0017] The precursors of cobalt are one or more of the nitrates, acetates, and sulfates of the corresponding metals.

[0018] The precipitant matrix is ​​selected from one or more of ammonia water, sodium hydroxide, and potassium hydroxide aqueous solution, and the precipitant mass concentration is 2%-15wt%.

[0019] In a method for preparing a niobium-cobalt-titanium composite oxide catalyst for the production of aromatic carboxylic acids,

[0020] During the preparation of solutions A and B in steps 1) and 2), the temperature is maintained at 20-60℃ and the stirring speed is 100-500 r / min; preferably 30-50℃ and 200-300 r / min.

[0021] During the preparation of solution B, the pH value of the solution needs to be maintained between 1 and 4, preferably between 1 and 2.

[0022] In step 3), during the mixing process of solutions A and B, the temperature is maintained at 20-60℃ and the stirring speed is 200-800 r / min; preferably 30-50℃ and 300-500 r / min; the mixing time of solutions A and B is 5 min-4 h, preferably 10 min-3 h, and more preferably 0.25 h-2 h.

[0023] The stirring speed mentioned in step 4) is 200-800 r / min.

[0024] The catalyst precursor calcination temperature in step 4) is 500-1000℃, preferably 550-900℃, more preferably 600-800℃, and the calcination time is 2-12h, preferably 3-10h, more preferably 3-6h.

[0025] The method for producing aromatic carboxylic acids using the niobium-cobalt-titanium composite oxide catalyst is specifically as follows:

[0026] In a reaction vessel, alkyl aromatic hydrocarbons, niobium cobalt titanium composite oxide catalysts, initiators, and solvents are added sequentially. Air is introduced at room temperature to 0.1-4.0 MPa (preferably 0.1-3.0 MPa, more preferably 0.5-2.0 MPa). The mixture is heated to 50-180°C (preferably 60-160°C, more preferably 80-150°C) under a sealed environment. The oxygen supply is turned on to ensure that the oxygen pressure is consistent with the pressure inside the heated vessel. Oxygen is continuously introduced and the reaction is stirred for 1-20 hours (preferably 2-15 hours, more preferably 3-10 hours) to obtain aromatic carboxylic acids.

[0027] The reaction solvent is one or a mixture of several of acetonitrile, propionitrile, butyronitrile, acetic acid, and propionic acid;

[0028] The reaction initiator is one or a mixture of several of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl hydroperoxide, N-hydroxyphthalimide, N-hydroxysuccinimide, and N-hydroxysaccharin.

[0029] The catalyst is added at a mass of 0.1-15% of the alkyl aromatic hydrocarbon, preferably 0.5-10%, more preferably 1.0-8%.

[0030] The alkyl aromatic hydrocarbon is one of methylbenzene derivatives, methylbiphenyl derivatives, and methylpyridinyl derivatives, and the alkyl aromatic hydrocarbon may carry one or more substituents of nitro, halogen (F and / or Cl).

[0031] This invention provides a method for preparing a niobium-cobalt-titanium composite oxide catalyst for the production of aromatic carboxylic acids and its application. Its advantages are mainly in the following four aspects:

[0032] 1) The niobium-cobalt-titanium composite oxide catalyst has good acid resistance and leaves no residual catalyst metal components in the reaction solution;

[0033] 2) This catalyst is suitable for a variety of solvent systems;

[0034] 3) The catalyst exhibits good cycle stability and is easy to separate;

[0035] 4) No water is added during post-treatment, and no wastewater is generated;

[0036] 5) Mild reaction conditions (temperature 50-150℃, reaction pressure <2.0MPa)

[0037] 6) It has a wide substrate range, high conversion rate (>85%) and selectivity (>95%), and is easy to industrialize. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments. The scope of protection of the present invention includes, but is not limited to, the following embodiments. Any modifications to the details and form of the technical solution of the present invention without departing from the meaning and scope of this application shall fall within the scope of protection of the present invention.

[0039] Example 1

[0040] 1) Weigh 10.0g of ammonium niobate oxalate and 4.82g of cobalt nitrate hexahydrate and slowly add them to a 200mL beaker containing 100mL of deionized water. Stir at 50℃ and 300r / min to dissolve, and obtain solution A (in which the mass concentration of niobium is 2.68%).

[0041] 2) Weigh 4.41g of titanium oxysulfate and slowly add it to a 500mL beaker containing 300mL of deionized water. Add 5% dilute sulfuric acid to adjust the pH to 1. Stir the mixture at 50℃ and 300r / min to obtain solution B (in which the mass concentration of titanium is 0.43%).

[0042] 3) In a 1000mL beaker, slowly mix solutions A and B at 50℃, stirring continuously at 800r / min during the mixing process, and continue stirring for 0.5h after mixing.

[0043] 4) Slowly add 5% wt ammonia water dropwise to the mixed solution at 50℃. After the pH of the mixed solution reaches 10, continue stirring for 2 hours. Filter, wash, and dry to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-800℃ for 154 min (heating rate 5℃ / min), and held at 800℃ for 4 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst A is obtained. The above-mentioned niobium-cobalt-titanium composite oxide catalyst was characterized by XRD as an amorphous powder, and the molar ratio of its components was determined by X-ray fluorescence spectroscopy (XRF) to be Nb:Co:Ti = 1.2:0.6:1.

[0044] Example 2

[0045] 1) Weigh 10.0 g of ammonium niobate oxalate and 2.41 g of cobalt nitrate hexahydrate and slowly add them to a 200 mL beaker containing 100 mL of deionized water. Dissolve the solutions by stirring at 300 rpm at 50 °C to obtain solution A (where the mass concentration of niobium is 2.74%). 2) Weigh 4.41 g of titanium oxysulfate and slowly add it to a 500 mL beaker containing 300 mL of deionized water. Adjust the pH to 2 with 5% dilute sulfuric acid. Dissolve the mixture by stirring at 300 rpm at 50 °C to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000 mL beaker, slowly mix solutions A and B at 50 °C, continuously stirring at 600 rpm during the mixing process. Continue stirring for 0.25 h after mixing. 4) Slowly add 10% wt sodium hydroxide to the mixed solution at 50℃. After the pH of the mixed solution reaches 10, continue stirring for 2 hours. Filter, wash, and dry to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-800℃ for 154 minutes (heating rate 5℃ / min), and held at 800℃ for 4 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst B is obtained. The above-mentioned niobium-cobalt-titanium composite oxide catalyst was characterized by XRD as an amorphous powder, and the molar ratio of its components was determined by X-ray fluorescence spectroscopy (XRF) to be Nb:Co:Ti = 1.2:0.3:1.

[0046] Example 3

[0047] 1) Weigh 13.33g of ammonium niobate oxalate and 4.82g of cobalt nitrate hexahydrate and slowly add them to a 200mL beaker containing 150mL of deionized water. Dissolve by stirring at 50℃ and a stirring speed of 400r / min to obtain solution A (where the mass concentration of niobium is 2.44%). 2) Weigh 4.41g of titanium oxysulfate and slowly add it to a 500mL beaker containing 300mL of deionized water. Adjust the pH to 1 with 5% dilute sulfuric acid. Dissolve the mixture by stirring at 50℃ and a stirring speed of 300r / min to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000mL beaker, slowly mix solutions A and B at 50℃, continuously stirring at 800r / min during the mixing process. Continue stirring for 3 hours after mixing. 4) Slowly add 10% wt potassium hydroxide dropwise to the mixed solution at 50℃. After the pH of the mixed solution reaches 10, continue stirring for 3 hours. Filter, wash, and dry to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-900℃ for 174 minutes (heating rate 5℃ / min), and held at 900℃ for 6 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst C is obtained. The above-mentioned niobium-cobalt-titanium composite oxide catalyst was characterized by XRD as an amorphous powder, and the molar ratio of its components was determined by X-ray fluorescence spectroscopy (XRF) to be Nb:Co:Ti = 1.6:0.6:1.

[0048] Example 4

[0049] 1) Weigh 13.33g of ammonium niobate oxalate and 4.02g of cobalt nitrate hexahydrate and slowly add them to a 200mL beaker containing 150mL of deionized water. Dissolve by stirring at 60℃ and a stirring speed of 500r / min to obtain solution A (where the mass concentration of niobium is 2.45%). 2) Weigh 4.41g of titanium oxysulfate and slowly add it to a 500mL beaker containing 300mL of deionized water. Adjust the pH to 2 with 10% dilute sulfuric acid. Dissolve the mixture by stirring at 60℃ and a stirring speed of 500r / min to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000mL beaker, slowly mix solutions A and B at 50℃, continuously stirring at 800r / min during the mixing process. Continue stirring for 1 hour after mixing. 4) Slowly add 10% wt sodium hydroxide to the mixed solution at 50℃. After the pH of the mixed solution reaches 9, continue stirring for 3 hours. Filter, wash, and dry to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-700℃ for 134 minutes (heating rate 5℃ / min), and held at 700℃ for 6 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst D is obtained. The above-mentioned niobium-cobalt-titanium composite oxide catalyst was characterized by XRD as an amorphous powder, and the molar ratio of its components was determined by X-ray fluorescence spectroscopy (XRF) to be Nb:Co:Ti = 1.6:0.5:1.

[0050] Example 5

[0051] 1) Weigh 14.16 g of ammonium niobate oxalate and 3.22 g of cobalt nitrate hexahydrate and slowly add them to a 200 mL beaker containing 150 mL of deionized water. Dissolve the solutions by stirring at 60 °C and 500 r / min to obtain solution A (where the mass concentration of niobium is 2.60%). 2) Weigh 4.41 g of titanium oxysulfate and slowly add it to a 500 mL beaker containing 300 mL of deionized water. Adjust the pH to 2 with 10% dilute sulfuric acid. Dissolve the mixture by stirring at 60 °C and 500 r / min to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000 mL beaker, slowly mix solutions A and B at 50 °C, continuously stirring at 800 r / min during the mixing process. Continue stirring for 0.5 h after mixing. 4) Slowly add 10% wt sodium hydroxide to the mixed solution at 50℃. After the pH of the mixed solution reaches 9, continue stirring for 3 hours. Filter, wash, and dry to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-700℃ for 134 minutes (heating rate 5℃ / min), and held at 700℃ for 6 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst E is obtained. The niobium-cobalt-titanium composite oxide catalyst described above was identified as an amorphous powder by XRD characterization. X-ray fluorescence spectroscopy (XRF) determined the molar ratio of its components to be Nb:Co:Ti = 1.7:0.4:1.

[0052] Comparative Example 1

[0053] 1) Weigh 10.0 g of ammonium niobate oxalate and 0.80 g of cobalt nitrate hexahydrate and slowly add them to a 200 mL beaker containing 100 mL of deionized water. Dissolve by stirring at 50 °C and 300 r / min to obtain solution A (where the mass concentration of niobium is 2.78%). 2) Weigh 4.41 g of titanium oxysulfate and slowly add it to a 500 mL beaker containing 300 mL of deionized water. Adjust the pH to 5 with 5% dilute sulfuric acid. Dissolve the mixture by stirring at 50 °C and 300 r / min to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000 mL beaker, slowly mix solutions A and B at 50 °C, continuously stirring at 800 r / min during the mixing process. Continue stirring for 0.5 h after mixing. 4) Slowly add 5% wt ammonia water dropwise to the mixed solution at 50℃. After the pH of the mixed solution reaches 10, continue stirring for 2 hours. Filter, wash, and dry to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-800℃ for 154 min (heating rate 5℃ / min), and held at 800℃ for 4 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst a is obtained. The niobium-cobalt-titanium composite oxide catalyst described above was identified as an amorphous powder by XRD characterization. X-ray fluorescence spectroscopy (XRF) determined the molar ratio of its components to be Nb:Co:Ti = 1.2:0.1:1.

[0054] Comparative Example 2

[0055] The catalyst Mn-Ce-O was prepared according to patent CN201310349535.5. The sol-gel method was used: manganese nitrate and cerium nitrate were used as raw materials, with a molar ratio of cerium ions to manganese ions of 0.85:0.15. After dissolving in deionized water, citric acid (twice the molar amount of the total metal cations) and polyethylene glycol (1 / 10 the mass of citric acid) were added. After stirring, the mixture was evaporated to dryness to obtain a gel. The gel was dried at 110℃ for 12 h, pre-calcined at 300℃ for 1 h, and calcined at 500℃ for 3 h to obtain catalyst b, Mn0.15Ce0.85O2, denoted as Mn-Ce-O.

[0056] Comparative Example 3

[0057] According to patent CN201310349535.5, the catalyst V2O5 / TiO2 was prepared as follows: 5g of oxalic acid was dissolved in 100ml of deionized water at 60℃ and stirred until completely dissolved. Then, 3.5g of ammonium metavanadate was added and stirred until completely dissolved. At this point, 27.0g of TiO2 was added and stirred thoroughly. The mixture was impregnated for 2 hours, and then all the support and impregnation solution were evaporated to dryness using a rotary evaporator. The resulting solid was dried at 110℃ for 10 hours, ground into powder, and calcined at 450℃ for 4 hours to obtain a 10% loaded V2O5 / TiO2 catalyst c.

[0058] Comparative Example 4: Catalyst Preparation by Ball Milling

[0059] 10.0 g of niobium ammonium oxalate, 4.82 g of cobalt nitrate hexahydrate, and 4.41 g of titanium oxysulfate were weighed and added to a ball mill reaction vessel. The mixture was ball-milled for 2 hours. The resulting niobium-cobalt-titanium catalyst precursor was calcined in air at a temperature of 30-800℃ for 154 min (heating rate 5℃ / min), and held at 800℃ for 4 hours. After cooling, the niobium-cobalt-titanium composite oxide catalyst d was obtained. XRD characterization confirmed that the niobium-cobalt-titanium composite oxide catalyst was an amorphous powder. X-ray fluorescence spectroscopy (XRF) determined the molar ratio of its components to be Nb:Co:Ti = 1.2:0.6:1.

[0060] Comparative Example 5

[0061] 1) Weigh 10.0 g of ammonium niobate oxalate and 3.62 g of nickel nitrate hexahydrate and slowly add them to a 200 mL beaker containing 100 mL of deionized water. Dissolve by stirring at 50 °C and 300 r / min to obtain solution A (where the mass concentration of niobium is 2.71%). 2) Weigh 4.41 g of titanium oxysulfate and slowly add it to a 500 mL beaker containing 300 mL of deionized water. Adjust the pH to 1 with 5% dilute sulfuric acid. Dissolve the mixture by stirring at 50 °C and 300 r / min to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000 mL beaker, slowly mix solutions A and B at 50 °C, continuously stirring at 800 r / min during the mixing process. Continue stirring for 0.5 h after mixing. 4) Slowly add 5% wt ammonia water to the mixed solution at 50℃. After the pH of the mixed solution reaches 10, continue stirring for 2 hours. Filter, wash, and dry to obtain the niobium-nickel-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-800℃ for 154 min (heating rate 5℃ / min), and held at 800℃ for 4 hours. After cooling, the niobium-nickel-titanium composite oxide catalyst e is obtained. The niobium-cobalt-titanium composite oxide catalyst described above was identified as an amorphous powder by XRD characterization. X-ray fluorescence spectroscopy (XRF) determined the molar ratio of its components to be V:Ni:Ti = 1.2:0.45:1.

[0062] Comparative Example 6

[0063] 1) Weigh 5.16g of ammonium metavanadate and 3.62g of cobalt nitrate hexahydrate and slowly add them to a 200mL beaker containing 100mL of deionized water. Dissolve by stirring at 50℃ and a stirring speed of 300r / min to obtain solution A (where the mass concentration of vanadium is 2.07%). 2) Weigh 4.41g of titanium oxysulfate and slowly add it to a 500mL beaker containing 300mL of deionized water. Adjust the pH to 1 with 5% dilute sulfuric acid. Dissolve the mixture by stirring at 50℃ and a stirring speed of 300r / min to obtain solution B (where the mass concentration of titanium is 0.43%). 3) In a 1000mL beaker, slowly mix solutions A and B at 50℃, continuously stirring at 800r / min during the mixing process. Continue stirring for 0.5h after mixing. 4) Slowly add 5% wt ammonia water to the mixed solution at 50℃. After the pH of the mixed solution reaches 10, continue stirring for 2 hours. Filter, wash, and dry to obtain the niobium-nickel-titanium catalyst precursor. The catalyst precursor is calcined in air at 30-800℃ for 154 min (heating rate 5℃ / min), and held at 800℃ for 4 hours. After cooling, the niobium-nickel-titanium composite oxide catalyst f is obtained. The niobium-cobalt-titanium composite oxide catalyst described above was identified as an amorphous powder by XRD characterization. X-ray fluorescence spectroscopy (XRF) determined the molar ratio of its components to be Nb:Co:Ti = 1.6:0.45:1.

[0064] Example 6

[0065] In a high-pressure reactor, 20 g of o-chlorotoluene, 0.2 g of catalyst, and 0.1 g of azobisisobutyronitrile initiator were added sequentially, followed by 80 g of acetic acid. Air was introduced at room temperature to a pressure of 0.3 MPa, and the reactor was heated to 80°C under a sealed environment. At this pressure, the reaction pressure was 0.5 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 0.5 MPa with stirring for 6 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the reactor was opened. The niobium-cobalt-titanium composite oxide catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis was performed. The target yield of o-chlorobenzoic acid is shown in the table below. Niobium-cobalt-titanium residue in the reaction solution was tested: 100 mg of the reaction solution was taken and diluted to 50 mL in a volumetric flask, and the residue was determined by ICP-OES. The niobium-cobalt-titanium composite oxide catalyst can be recycled as a catalyst for the next reaction.

[0066]

[0067]

[0068] As can be seen from the comparison in the table above, when acetic acid is used as the reaction solvent, the total residual niobium, cobalt, and titanium metal in the reaction solution after ten cycles of the niobium-cobalt-titanium composite oxide catalyst of the present invention is 0 ppm, which shows that the catalyst has good tolerance to acetic acid and good cycle stability.

[0069] Example 7

[0070] In a high-pressure reactor, 20 g of o-fluorotoluene, 0.4 g of catalyst A, and 0.2 g of N-hydroxysuccinimide initiator were added sequentially, followed by 80 g of acetonitrile. Air was introduced at room temperature to a pressure of 0.3 MPa, and the reactor was heated to 80°C under a closed system. At this pressure, the reaction pressure was 0.5 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 0.5 MPa with stirring for 6 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the reactor was opened. The filtrate was filtered to obtain the niobium-cobalt-titanium composite oxide catalyst. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed that the yield of o-fluorobenzoic acid was 99%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst A was filtered off, and the filtrate was rotary evaporated. The resulting solid was washed with methanol and dried to obtain 24.0 g of o-fluorobenzoic acid, with a separation yield of 95%.

[0071] Example 8

[0072] In a high-pressure reactor, 40 g of 4,4'-dimethylbiphenyl, 0.6 g of catalyst D, and 0.5 g of N-hydroxysaccharin initiator were added sequentially, followed by 160 g of acetonitrile. Air was introduced at room temperature to a pressure of 0.3 MPa, and the reactor was heated to 100°C under a sealed environment. At this point, the reaction pressure was 0.6 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 0.6 MPa with stirring for 10 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the mixture was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed a 4,4'-biphenyl dicarboxylic acid yield of 98%. 200 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst D was filtered off, and the filtrate was rotary evaporated. The resulting solid was washed with methanol and dried to obtain 49.50 g of 4,4'-biphenyl dicarboxylic acid, with a separation yield of 95%.

[0073] Example 9

[0074] In a high-pressure reactor, 20 g of p-xylene, 0.6 g of catalyst C, and 0.5 g of N-hydroxyphthalimide initiator were added sequentially, followed by 100 g of acetonitrile. Air was introduced at room temperature to 0.5 MPa, and the mixture was heated to 120 °C under a sealed environment. At this point, the reaction pressure was 0.9 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 0.9 MPa with stirring for 6 hours. After the reaction was completed, the reactor was cooled, the gas was released, and the mixture was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed that the yield of p-benzoic acid was 95%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst C was filtered off. After rotary evaporation of the filtrate, the resulting solid was washed with methanol and dried to obtain 28.50 g of p-benzoic acid, with a separation yield of 96%.

[0075] Example 10

[0076] In a high-pressure reactor, 20 g of 4-methylbiphenyl, 0.6 g of catalyst E, and 0.7 g of N-hydroxyphthalimide initiator were added sequentially, followed by 100 g of acetonitrile. Air was introduced at room temperature to a pressure of 0.8 MPa, and the mixture was heated to 150 °C under a sealed environment. At this point, the reaction pressure was 1.4 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 1.5 MPa with stirring for 6 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the mixture was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed a biphenyl-4-carboxylic acid yield of 96%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst E was filtered off, and the filtrate was rotary evaporated. The resulting solid was washed with methanol and dried to obtain 21.68 g of biphenyl-4-carboxylic acid, with a separation yield of 92%.

[0077] Example 11

[0078] In a high-pressure reactor, 20 g of 4-methylbiphenyl, 0.6 g of catalyst E, and 0.4 g of N-hydroxysuccinimide initiator were added sequentially, followed by 100 g of acetonitrile. Air was introduced at room temperature to a pressure of 1.4 MPa, and the mixture was heated to 150 °C under a closed system. At this point, the reaction pressure was 2.0 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 2.0 MPa with stirring for 3 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the mixture was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed a biphenyl-4-carboxylic acid yield of 98%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst E was filtered off. The filtrate was rotary evaporated, and the resulting solid was washed with methanol and dried to obtain 22.15 g of biphenyl-4-carboxylic acid, with a separation yield of 94%.

[0079] Example 12

[0080] In a high-pressure reactor, 20 g of o-fluorotoluene, 0.6 g of catalyst B, and 0.6 g of N-hydroxysuccinimide initiator were added sequentially, followed by 80 g of acetonitrile. Air was introduced at room temperature to a pressure of 1.4 MPa, and the reactor was heated to 120 °C under a closed system. At this point, the reaction pressure was 1.8 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 1.8 MPa with stirring for 6 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the reactor was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed that the yield of o-fluorobenzoic acid was 98%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst B was filtered off. The filtrate was rotary evaporated, and the resulting solid was washed with methanol and dried to obtain 23.7 g of o-fluorobenzoic acid, with a separation yield of 94%.

[0081] Example 13

[0082] In a high-pressure reactor, 20 g of o-fluorotoluene, 1.6 g of catalyst B, and 0.4 g of N-hydroxysuccinimide initiator were added sequentially, followed by 80 g of acetonitrile. Air was introduced at room temperature to a pressure of 1.2 MPa, and the mixture was heated to 140 °C under a closed system. At this point, the reaction pressure was 2.0 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 2.0 MPa with stirring for 3 hours. After the reaction was completed, the reactor was cooled, the gas was released, and the mixture was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed that the yield of o-fluorobenzoic acid was 99%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst B was filtered off. After rotary evaporation of the filtrate, the resulting solid was washed with methanol and dried to obtain 24.1 g of o-fluorobenzoic acid, with a separation yield of 95.5%.

[0083] Comparative Example 7

[0084] In a high-pressure reactor, 20 g of o-fluorotoluene, 4.0 g of catalyst C, and 0.4 g of N-hydroxysuccinimide initiator were added sequentially, followed by 80 g of acetonitrile. Air was introduced at room temperature to a pressure of 1.8 MPa, and the reactor was heated to 150 °C under a closed system. At this point, the reaction pressure was 2.4 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 2.4 MPa while stirring for 3 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the mixture was opened. The catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis showed that the yield of o-fluorobenzoic acid was 75%. 100 mL of LDM was added to the reaction solution and stirred to dissolve the product. Catalyst B was filtered off. The filtrate was rotary evaporated, and the resulting solid was washed with methanol and dried to obtain 17.7 g of o-fluorobenzoic acid, with a separation yield of 95.5%.

[0085] As shown in Comparative Example 7, the catalyst addition amount was 20% of the substrate mass. The increased number of active sites on the catalyst led to a peroxidation side reaction, resulting in a decrease in the selectivity of o-fluorobenzoic acid and a reduction in yield.

[0086] Example 14 Effect of Solvent

[0087] In a high-pressure reactor, 20 g of o-chlorotoluene, 0.6 g of catalyst, and 0.6 g of azobisisobutyronitrile initiator were added sequentially, followed by 80 g of solvent. Air was introduced at room temperature to a pressure of 0.3 MPa, and the reactor was heated to 90°C under a closed system. At this point, the reaction pressure was 0.5 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 0.5 MPa while stirring for 4 hours. After the reaction was complete, the reactor was cooled, the gas was released, and the reactor was opened. The niobium-cobalt-titanium composite oxide catalyst was obtained by filtration. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis was performed. The target yield of the product, o-chlorobenzoic acid, is shown in the table below.

[0088] solvent Yield (%) Acetonitrile 85.9 Propylon 85.5 Nitrile 83.3 Acetic acid 90.5 propionic acid 88.5

[0089] As can be seen from Example 14, the yield of o-fluorobenzoic acid can reach more than 80% under the reaction conditions of Example 14 and the niobium-cobalt-titanium composite metal oxide catalyst, using nitrile and organic acid solvents protected by the present invention.

[0090] Effect of other organic solvents in Comparative Example 8

[0091] In a high-pressure reactor, 20 g of 4-methylbiphenyl, 1 g of catalyst E, and 0.4 g of N-hydroxysuccinimide initiator were added sequentially, followed by 100 g of solvent. Air was introduced at room temperature to a pressure of 1.4 MPa, and the reactor was heated to 150 °C under a closed system. At this point, the reaction pressure was 2.0 MPa. The online continuous oxygen supply valve was opened, and oxygen was continuously introduced at 2.0 MPa while stirring for 3 hours. After the reaction was completed, the reactor was cooled, the gas was released, and the reactor was opened. The filtrate was filtered to obtain the niobium-cobalt-titanium composite oxide catalyst. Nitrobenzene internal standard was added to the filtrate, and after dilution, LC analysis was performed. The yield of biphenyl-4-carboxylic acid was as follows.

[0092] solvent Yield (%) methanol 8.5 Tetrahydrofuran 15.5 Butyl acetate 5.8 1,4-Dioxane 10.5

[0093] In the solvents shown in Comparative Example 8, the yields of biphenyl-4-carboxylic acid were all less than 20%, which is due to the solvents' involvement in the oxidation reaction and their poor solubility in the substrate.

Claims

1. A method for preparing a niobium-cobalt-titanium composite oxide catalyst for the production of aromatic carboxylic acids, characterized in that, 1) Add niobium ammonium oxalate and cobalt precursors to water and stir to dissolve at 20-60°C to obtain solution A; wherein the mass concentration of niobium is 0.1-20%, preferably 0.1-16%, more preferably 0.5-10%; 2) Add titanium oxysulfate to water, add 5%-10% dilute sulfuric acid to adjust the pH to 1-4, stir and dissolve at 20-60℃ to obtain solution B; wherein the mass concentration of titanium is 0.1-15%, preferably 0.1-10%, more preferably 0.2-8%; 3) Mix solutions A and B at 20-60℃, stirring continuously during the mixing process to ensure that A and B are mixed evenly, to obtain a mixed solution; 4) Under stirring conditions, a precipitant is added dropwise to the mixed solution at 20-60℃. After the pH of the mixed solution reaches 8-10, stirring is continued for 1-4 hours. The solution is then filtered, washed, and dried to obtain the niobium-cobalt-titanium catalyst precursor. The catalyst precursor is calcined in a muffle furnace at 500-1000℃ for 2-12 hours to obtain the niobium-cobalt-titanium composite oxide catalyst.

2. The preparation method according to claim 1, characterized in that, The molar ratio of each component in the niobium-cobalt-titanium composite oxide catalyst described above is Nb:Co:Ti = 1.1-2.0:0.1-0.9:1, preferably 1.2-1.8: 0.2-0.8:1, more preferably 1.2-1.6:0.3-0.6:

1.

3. The preparation method according to claim 1, characterized in that, The precursors of cobalt are one or more of the nitrates, acetates, and sulfates of the corresponding metals. The precipitant matrix is ​​selected from one or more of ammonia water, sodium hydroxide, and potassium hydroxide aqueous solution, and the precipitant mass concentration is 2%-15wt%.

4. The preparation method according to claim 1, characterized in that, During the preparation of solutions A and B in steps 1) and 2), the temperature is maintained at 20-60℃ and the stirring speed is 100-500 r / min; preferably 30-50℃ and 200-300 r / min. During the preparation of solution B, the pH value of the solution needs to be maintained between 1 and 4, preferably between 1 and 2. In step 3), during the mixing process of solutions A and B, the temperature is maintained at 20-60℃ and the stirring speed is 200-800 r / min; preferably 30-50℃ and 300-500 r / min; the mixing time of solutions A and B is 5 min-4 h, preferably 10 min-3 h, and more preferably 0.25 h-2 h. The stirring speed mentioned in step 4) is 200-800 r / min.

5. The preparation method according to claim 1, characterized in that, The catalyst precursor calcination temperature in step 4) is 500-1000℃, preferably 550-900℃, more preferably 600-800℃, and the calcination time is 2-12h, preferably 3-10h, more preferably 3-6h.

6. A niobium-cobalt-titanium composite oxide catalyst prepared by any one of the preparation methods described in claims 1-5.

7. A method for producing aromatic carboxylic acids using the niobium cobalt titanium composite oxide catalyst of claim 6, comprising: sequentially adding alkyl aromatic hydrocarbons, niobium cobalt titanium composite oxide catalyst, initiator and solvent to a reaction vessel; introducing air at room temperature to 0.1-4.0 MPa (preferably 0.1-3.0 MPa, more preferably 0.5-2.0 MPa); heating to 50-180°C (preferably 60-160°C, more preferably 80-150°C) under sealed conditions; turning on the oxygen supply to maintain the oxygen pressure consistent with the pressure inside the heated vessel; continuously introducing oxygen and stirring the reaction for 1-20 h (preferably 2-15 h, more preferably 3-10 h) to obtain aromatic carboxylic acids.

8. The method according to claim 7, characterized in that: The reaction solvent is one or a mixture of several of acetonitrile, propionitrile, butyronitrile, acetic acid, and propionic acid; The reaction initiator is one or a mixture of several of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl hydroperoxide, N-hydroxyphthalimide, N-hydroxysuccinimide, and N-hydroxysaccharin.

9. The method according to claim 7, characterized in that: The catalyst is added at a mass of 0.1-15% of the alkyl aromatic hydrocarbon, preferably 0.5-10%, more preferably 1.0-8%.

10. The method according to any one of claims 7-9, wherein the alkyl aromatic hydrocarbon is one of a methylbenzene derivative, a methylbiphenyl derivative, or a methylpyridinyl derivative, and the alkyl aromatic hydrocarbon may carry one or more substituents selected from nitro, halogen (F and / or Cl).

Images