A catalyst for n-butane oxidation, its preparation method and use

Abstract

The present application relates to a kind of n-butane oxidation catalyst and its preparation method and application.The catalyst includes the composite oxide of vanadium and phosphorus;The bulk P / V molar ratio of the catalyst is 0.98-1.10:1;Surface P / V molar ratio 1.05-1.30:1;The surface P / V molar ratio of the catalyst is greater than the bulk P / V molar ratio.This catalyst is suitable for n-butane oxidation preparation succinic anhydride reaction, with higher catalytic activity and stability.

Description

Technical Field

[0001] The invention relates to a catalyst for preparing maleic anhydride by oxidation of n-butane, and a preparation method and application thereof. Background Art

[0002] Maleic anhydride, also known as maleic anhydride, is a key organic chemical raw material and the third most consumed anhydride worldwide, after phthalic anhydride and acetic anhydride. Maleic anhydride is widely used in industries such as petrochemicals, food chemicals, pharmaceuticals, and building materials. It can be used to synthesize a range of organic and fine chemicals, including unsaturated polyester resins, lubricant additives, food additives, and tetrahydrofuran (THF), and enjoys a broad market.

[0003] Maleic anhydride is primarily produced through selective oxidation, including benzene oxidation and n-butane oxidation. Early production was primarily through the benzene oxidation route, but this route has seen a decreasing share of maleic anhydride production due to the toxicity of the raw materials and high costs. The n-butane oxidation route is gradually becoming the primary method for maleic anhydride production due to its advantages such as low raw material costs, minimal pollution, and high carbon atom utilization.

[0004] Based on research and practical application experience, the vanadium-phosphorus-oxygen (VPO) catalyst system is by far the most effective catalyst system for the vapor-phase oxidation of n-butane to maleic anhydride. VPO catalysts are usually prepared as precursors in aqueous or organic solvents, and the resulting precursors are activated and shaped by calcination to obtain the final catalyst. Since the catalysts obtained by the organic solvent method have a larger specific surface area and a purer crystalline phase than those obtained by the aqueous phase method, their advantages are more obvious. Currently, the organic method mainly uses a single or mixed system of isobutanol and benzyl alcohol as solvents. After adding a vanadium source to disperse the reaction and dissolve it under stirring and reflux, a phosphorus source is added, and reflux is continued to obtain a precursor, and finally heat treatment is performed to activate the catalyst.

[0005] Currently, lubricants and pore-forming agents need to be added during the molding process of vanadium-phosphorus-oxygen catalysts to further improve the catalyst's molding performance, mechanical properties, pore volume and other indicators. The catalysts are then prepared into cylindrical, hollow cylindrical, clover-shaped, sheet-shaped and other structures, and heat-treated and activated under heating and atmosphere conditions.

[0006] Based on research and industrial application practice, the active ingredients in existing vanadium-phosphorus-oxygen catalysts typically adhere to the catalyst surface only through adsorption. However, these active ingredients are easily lost during heating, activation, and the reaction process, resulting in unstable surface properties and reduced catalytic performance. Therefore, addressing these issues, improving catalyst activity, and preparing more active catalysts for the oxidation of n-butane to maleic anhydride have great potential for industrial application. Summary of the Invention

[0007] To address the low pore volume and easy loss of active components in existing n-butane oxidation VPO catalysts during activation, the present invention provides an n-butane oxidation catalyst, its preparation method, and its application. This catalyst is suitable for the n-butane oxidation reaction to produce maleic anhydride and exhibits high catalytic activity and stability.

[0008] A first aspect of the present invention provides an n-butane oxidation catalyst, which includes a composite oxide of vanadium and phosphorus; the bulk P / V molar ratio of the catalyst is 0.98 to 1.10:1, preferably 1.00 to 1.10:1; the surface P / V molar ratio is 1.05 to 1.30:1, preferably 1.05 to 1.15:1; and the surface P / V molar ratio of the catalyst is greater than the bulk P / V molar ratio.

[0009] According to the present invention, further, the surface P / V molar ratio of the catalyst differs from the bulk P / V molar ratio by at least 0.01, preferably by 0.01 to 0.05.

[0010] According to the present invention, further, the specific surface area of ​​the n-butane oxidation catalyst is 10 to 100 m 2 ·g -1 , preferably 20 to 50 m 2 ·g -1 .

[0011] A second aspect of the present invention provides a method for preparing an n-butane oxidation catalyst, the method comprising the following steps:

[0012] The VPO precursor is mixed with P-modified graphene and a pore-forming agent, and the mixture is optionally subjected to constant temperature and humidity treatment, molded, and activated to obtain the n-butane oxidation catalyst.

[0013] According to the present invention, further, the preparation method of the P-modified graphene comprises the following steps: dispersing graphene and a phosphorus source in an organic solvent, and carbonizing the obtained mixture.

[0014] According to the present invention, further, in the method for preparing P-modified graphene, the graphene is preferably graphene oxide; the graphene oxide can be prepared using a commercial product or conventional methods of the prior art.

[0015] According to the present invention, further, in the method for preparing P-modified graphene, the organic solvent is acetone and the phosphorus source is triphenylphosphine.

[0016] According to the present invention, further, in the preparation method of P-modified graphene, the stoichiometric ratio in the raw materials is: the mass ratio of graphene to organic solvent is 1:200-1000; the mass ratio of phosphorus source to graphene is 1:0.5-2.

[0017] According to the present invention, further, in the method for preparing P-modified graphene, the carbonization treatment conditions are as follows: a carbonization temperature of 600-1000°C, a carbonization time of 1-8 hours, and an oxygen-free atmosphere. The oxygen-free atmosphere is at least one of an inert gas and nitrogen. The carbonization apparatus is preferably a tubular furnace.

[0018] According to the present invention, further, in the preparation method of P-modified graphene, the dispersion method can be conventionally selected as needed, preferably ultrasonic dispersion. The ultrasonic dispersion comprises first dispersing the graphene in an organic solvent, performing a first ultrasonic treatment for 15 to 60 minutes, then adding a phosphorus source, and performing a second ultrasonic treatment for 15 to 60 minutes.

[0019] According to the present invention, further, in the method for preparing P-modified graphene, the obtained mixture is dried before carbonization. The drying method can be conventionally selected as needed, preferably vacuum drying. Drying conditions are preferably a temperature of 60-80°C for 1-16 hours, a gauge pressure of -10 kPa to -100 kPa, and a vacuum oven.

[0020] According to the present invention, further, a method for preparing a VPO precursor comprises the following steps: dispersing a vanadium source and a phosphorus source in an organic solvent, and refluxing the obtained mixture to react, and the obtained solid product is the VPO precursor.

[0021] According to the present invention, further, in the method for preparing a VPO precursor, the phosphorus source is at least one of H3PO4 and NH4H2PO4; the vanadium source is V2O5; and the particle size of the vanadium source is 1.5 to 3 μm. The organic solvent is an alcoholic solvent with reducing ability, preferably at least one of isobutyl alcohol, benzyl alcohol, isopropyl alcohol, and ethanol. The stoichiometric ratio in the raw materials is: the molar ratio of the phosphorus source (calculated as elemental phosphorus) to the vanadium source (calculated as elemental vanadium) is 0.5 to 2.0, and the molar ratio of the organic solvent added to the vanadium source (calculated as elemental vanadium) is 5 to 50, preferably 5 to 30. The reflux reaction conditions are: a heating temperature of 60 to 160°C and a reflux time of 6 to 18 hours. The reflux is carried out under stirring. Preferably, the vanadium source is first dispersed in the organic solvent and mixed thoroughly before the phosphorus source is added.

[0022] According to the present invention, further, in the preparation method of the VPO precursor, the obtained solid product is dried at a temperature of 50 to 120° C. for 1 to 16 hours.

[0023] According to the present invention, further, in the method for preparing an n-butane oxidation catalyst, the pore-forming agent includes at least one selected from stearic acid, soluble starch, sesbania powder, polyethylene glycol, ammonium carbonate, and polystyrene microspheres. The pore-forming agent is added in an amount of 1 wt% to 10 wt% of the VPO precursor. The P-modified graphene is added in an amount of 2 wt% to 6 wt% of the VPO precursor.

[0024] According to the present invention, further, in the method for preparing the n-butane oxidation catalyst, the mixing preferably involves first uniformly mixing the precursor and the modified graphene, and then adding the pore-forming agent. The constant temperature and humidity treatment conditions are: 20-60° C., 3-24 hours, and a relative humidity of 40-95%.

[0025] According to the present invention, further, in the preparation method of the n-butane oxidation catalyst, the forming step is tableting. The tableting step is divided into two steps. The first step is tableting at a pressure of 10 to 40 MPa. After the first step, the tableting is crushed and screened, and then 20 to 160 mesh particles are selected as pre-granulated particles. The second step is tableting using a rotary tablet press. The pre-granulated particles are placed on the rotary tablet press for the second step of tableting. The resulting tableting product after the second step is a hollow cylindrical product with a height of 4 to 6 mm.

[0026] According to the present invention, further, in the method for preparing an n-butane oxidation catalyst, the activation step comprises heat-treating the formed product under an activation atmosphere. The activation atmosphere comprises an oxygen-containing atmosphere and one or more selected from light hydrocarbons, an inert gas, nitrogen, water vapor, and carbon dioxide. The light hydrocarbon is at least one of methane, ethane, propane, n-butane, ethylene, and propylene. The heat treatment temperature is 300-500°C, and the heat treatment time is 2-16 hours.

[0027] The third aspect of the present invention provides an n-butane oxidation catalyst prepared by the above preparation method.

[0028] According to the present invention, further, the n-butane oxidation catalyst includes a composite oxide of vanadium and phosphorus; the bulk P / V molar ratio of the catalyst is 0.98 to 1.10:1, preferably 1.00 to 1.10:1; the surface P / V molar ratio is 1.05 to 1.30:1, preferably 1.05 to 1.15:1; the surface P / V molar ratio of the catalyst is greater than the bulk P / V molar ratio.

[0029] According to the present invention, further, the surface P / V molar ratio of the catalyst differs from the bulk P / V molar ratio by at least 0.01, preferably by 0.01 to 0.05.

[0030] According to the present invention, further, the specific surface area of ​​the n-butane oxidation catalyst is 10 to 100 m 2 ·g -1 , preferably 20 to 50 m 2 ·g -1 .

[0031] A fourth aspect of the present invention provides the use of the above catalyst in the reaction of producing maleic anhydride by oxidation of n-butane. The conditions for the application are: the feed gas is a mixture of n-butane and air, wherein the molar fraction of n-butane is 1% to 2.2%; the volume space velocity of the feed gas is 1000 to 3000 hr -1 ; The reaction temperature is 300-500°C; the reaction pressure is 0kPa-50kPa, and the reaction pressure is gauge pressure; the reaction apparatus is a fixed bed reactor.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) In the present invention, the catalyst comprises a composite oxide of vanadium and phosphorus; the bulk P / V molar ratio of the catalyst is 0.98 to 1.10:1, preferably 1.00 to 1.10:1; the surface P / V molar ratio of the catalyst is 1.05 to 1.30:1, preferably 1.05 to 1.15:1; and the surface P / V molar ratio of the catalyst is greater than the bulk P / V molar ratio. The catalyst of the present invention has a more reasonable surface P / V molar ratio, stable surface properties, and exhibits high catalytic activity and good stability in the reaction of n-butane oxidation to maleic anhydride.

[0034] (2) In the present invention, the preparation method comprises the following steps: mixing a VPO precursor with P-modified graphene and a pore-forming agent, optionally subjecting the catalyst to constant temperature and humidity treatment, forming, and activating the catalyst to obtain the catalyst. The catalyst preparation method of the present invention includes the addition of P-modified graphene. On the one hand, the modified graphene can serve as a lubricant to facilitate better forming. On the other hand, the modified graphene doped with P elements can prevent the P on the catalyst surface from being easily lost during subsequent heat treatment and activation, thereby maintaining a suitable surface P / V molar ratio of 1.05 to 1.15:1, and making the surface P / V molar ratio greater than the bulk P / V molar ratio. The catalyst prepared by the preparation method of the present invention has high catalytic activity and stability in the reaction of n-butane oxidation to maleic anhydride.

[0035] (3) The catalyst of the present invention exhibits high catalytic activity and stability when used in the n-butane oxidation reaction to produce maleic anhydride. In this application, the n-butane conversion rate can reach 86.5% and the maleic anhydride yield can reach 60.3% after 24 hours of reaction, indicating good catalyst activity. Even after a long-term reaction operation of 120 hours, the catalyst exhibits good stability and no significant change in catalytic activity. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto, and the examples do not limit the scope of protection of the present invention.

[0037] In the embodiments of the present invention, low-temperature nitrogen adsorption analysis of the catalyst pore structure was performed using a Micromeritics TriStar 3000 multi-channel physical adsorption instrument operating at -196°C. The catalyst was vacuum degassed at 180°C for 4 hours prior to measurement. The specific surface area of ​​the molecular sieve was calculated using the Brunauer-Emmett-Teller (BET) model.

[0038] In this embodiment of the present invention, the P and V contents in the bulk catalyst phase are analyzed using ICP (Inductively Coupled Plasma Emission Spectrometry). The catalyst is first crushed and ground into a powder. The fully ground powdered catalyst is then immersed in a 2 mol / L HF solution at a volume ratio of 2:1 for 4 hours. The resulting liquid is filtered and diluted 20-fold before atomic content analysis. The bulk P / V ratio and the oxygen content of the catalyst composition are then calculated.

[0039] In the embodiment of the present invention, the surface P / V ratio of the catalyst was analyzed using XPS. The instrument used was a PerkinElmer phi5000c X-ray photoelectron spectrometer (XPS) instrument with a Mg Kα X-ray source, an operating voltage of 15 kV, and a current of 20 mA. All spectra were calibrated using a C1s value of 284.8 eV.

[0040] In the embodiment of the present invention, the n-butane conversion % and the maleic anhydride yield % are defined as follows:

[0041]

[0042]

[0043] [Example 1]

[0044] (1) Graphene oxide was dispersed in acetone at a ratio of 1:400 and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of 1:1 between the phosphorus source and graphene oxide, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 750°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0045] (2) 2 mol of benzyl alcohol was mixed with 17.5 mol of isobutanol, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 140°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 h to obtain a VPO catalyst precursor powder.

[0046] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was taken and mixed evenly with 1.5 g of fully ground P-modified graphene. 2 g of stearic acid as a pore-forming agent was then added. The mixture was then treated at a constant temperature and humidity of 30°C and a relative humidity of 85% for 12 h. The sample was then tableted at a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0047] The secondary molded catalyst was treated at 450°C for 6 h in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 32.2 m 2 ·g -1 .

[0048] The properties of the catalysts before and after activation are shown in Table 1.

[0049] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction temperature was 400°C, atmospheric pressure was maintained, and the reaction apparatus was a fixed-bed reactor. The evaluation results of the test reaction for 24 hours and the long-term reaction for 120 hours are detailed in Table 2.

[0050] [Example 2]

[0051] (1) Graphene oxide was dispersed in acetone at a ratio of 1:250 and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of phosphorus source to graphene oxide of 1:0.6, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 950°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0052] (2) 2 mol of benzyl alcohol and 8.5 mol of isobutanol were weighed and mixed, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 140°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 hours to obtain a VPO catalyst precursor powder.

[0053] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was taken and mixed evenly with 1.5 g of fully ground P-modified graphene. 2 g of stearic acid as a pore-forming agent was then added. The mixture was then treated at a constant temperature and humidity of 30°C and 70% relative humidity for 12 h. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0054] The secondary molded catalyst was treated at 450°C for 6 hours in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 27.4 m 2 ·g -1 .

[0055] The properties of the catalysts before and after activation are shown in Table 1.

[0056] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure using a fixed-bed reactor. The evaluation results for the 24-hour and 120-hour tests are shown in Table 2.

[0057] [Example 3]

[0058] (1) Graphene oxide was dispersed in acetone at a ratio of 1:300 and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of 1:1.7 between the phosphorus source and graphene oxide, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 600°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0059] (2) 2 mol of benzyl alcohol and 17.5 mol of isobutanol were weighed and mixed, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 60 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 150°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 hours to obtain a VPO catalyst precursor powder.

[0060] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was taken and mixed evenly with 1.5 g of fully ground P-modified graphene. 2 g of stearic acid as a pore-forming agent was then added. The mixture was then treated at a constant temperature and humidity of 30°C and a relative humidity of 85% for 12 h. The sample was then tableted at a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0061] The secondary molded catalyst was treated at 450°C for 6 h in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 25.1 m 2 ·g -1 .

[0062] The properties of the catalysts before and after activation are shown in Table 1.

[0063] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure using a fixed-bed reactor. The evaluation results for the 24-hour and 120-hour tests are shown in Table 2.

[0064] [Example 4]

[0065] (1) Graphene oxide was dispersed in acetone at a ratio of 1:400 and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of phosphorus source to graphene oxide of 1:0.5, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 800°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0066] (2) 2 mol of benzyl alcohol and 15.5 mol of isobutanol were weighed and mixed, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 125 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 120°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 hours to obtain a VPO catalyst precursor powder.

[0067] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was mixed with 1.5 g of fully ground P-modified graphene, and then 2 g of the pore-forming agent polyethylene glycol was added. The mixture was then kept at a constant temperature and humidity of 30°C and 90% relative humidity for 12 h. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0068] The secondary molded catalyst was treated at 450°C for 6 h in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 30.3 m 2 ·g -1 .

[0069] The properties of the catalysts before and after activation are shown in Table 1.

[0070] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure using a fixed-bed reactor. The evaluation results for the 24-hour and 120-hour tests are shown in Table 2.

[0071] [Example 5]

[0072] (1) Graphene oxide was dispersed in acetone at a ratio of 1:600 ​​and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of 1:2 between the phosphorus source and graphene oxide, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 700°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0073] (2) 2 mol of benzyl alcohol and 25 mol of isobutanol were weighed and mixed, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 150 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 160°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 hours to obtain a VPO catalyst precursor powder.

[0074] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was taken and mixed evenly with 1.5 g of fully ground P-modified graphene. 2 g of ammonium carbonate, a pore-forming agent, was then added. The mixture was then kept at a constant temperature and humidity of 30°C and 70% relative humidity for 12 h. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0075] The secondary molded catalyst was treated at 450°C for 6 hours in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 29.6 m 2 ·g -1 .

[0076] The properties of the catalysts before and after activation are shown in Table 1.

[0077] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure using a fixed-bed reactor. The evaluation results for the 24-hour and 120-hour tests are shown in Table 2.

[0078] [Example 6]

[0079] (1) Graphene oxide was dispersed in acetone at a ratio of 1:900 and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of 1:1.5 between the phosphorus source and graphene oxide, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 750°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0080] (2) 2 mol of benzyl alcohol and 17.5 mol of isobutanol were weighed and mixed, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 150°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 hours to obtain a VPO catalyst precursor powder.

[0081] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was taken and mixed evenly with 1.5 g of fully ground P-modified graphene. 2 g of polystyrene microspheres as a pore-forming agent were then added. The mixture was then treated at a constant temperature and humidity of 30°C and a relative humidity of 85% for 12 h. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0082] The secondary molded catalyst was treated at 450°C for 6 h in an activation atmosphere of 60 vol% nitrogen + 10 vol% oxygen + 30 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 35.1 m 2 ·g -1 .

[0083] The properties of the catalysts before and after activation are shown in Table 1.

[0084] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure using a fixed-bed reactor. The evaluation results for the 24-hour and 120-hour tests are shown in Table 2.

[0085] [Comparative Example 1]

[0086] (1) 2 mol of benzyl alcohol and 17.5 mol of isobutyl alcohol were weighed and mixed, and then 100.8 g of vanadium (V₂O₅) was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 140°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 h to obtain a VPO catalyst precursor powder.

[0087] (2) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was mixed with 1.5 g of fully ground graphite, and then 2 g of stearic acid as a pore-forming agent was added. The mixture was then kept at a constant temperature and humidity of 30°C and 85% relative humidity for 12 hours. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary formed catalyst. The tablet was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0088] The secondary molded catalyst was treated at 450°C for 6 hours in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 39.4 m 2·g -1 .

[0089] The properties of the catalysts are shown in Table 1.

[0090] The catalyst was tested for its effect in the n-butane oxidation reaction. The conditions for the application were: the feed gas was a mixture of n-butane and air, in which the molar fraction of n-butane was 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure in a fixed-bed reactor. The evaluation results of the 24-hour and 120-hour tests are shown in Table 2.

[0091] [Comparative Example 2]

[0092] (1) 2 mol of benzyl alcohol and 17.5 mol of isobutyl alcohol were weighed and mixed, and then 100.8 g of vanadium (V₂O₅) was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 140°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 h to obtain a VPO catalyst precursor powder.

[0093] (2) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was mixed with 1.5 g of fully ground graphite oxide, and then 2 g of stearic acid as a pore-forming agent was added. The mixture was then kept at a constant temperature and humidity of 30°C and 85% relative humidity for 12 hours. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary catalyst. The tablet was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary molding into hollow cylindrical catalysts with a height of 5 mm.

[0094] The secondary molded catalyst was treated at 450°C for 6 h in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 38.0 m 2 ·g -1

[0095] The properties of the catalysts are shown in Table 1.

[0096] The catalyst was tested for its effect in the n-butane oxidation reaction. The conditions for the application were: the feed gas was a mixture of n-butane and air, in which the molar fraction of n-butane was 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure in a fixed-bed reactor. The evaluation results of the 24-hour and 120-hour tests are shown in Table 2.

[0097] [Comparative Example 3]

[0098] (1) 2 mol of benzyl alcohol and 17.5 mol of isobutyl alcohol were weighed and mixed, and then 100.8 g of vanadium (V₂O₅) was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of 85 wt% phosphoric acid was added, and the mixture was heated under reflux at 140°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 h to obtain a VPO catalyst precursor powder.

[0099] (2) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was mixed with 1.5 g of fully ground graphene oxide and 0.3 g of triphenylphosphine, and then 2 g of stearic acid as a pore-forming agent was added. The mixture was then kept at a constant temperature and humidity of 30°C and 85% relative humidity for 12 hours. The sample was then pressed into a tablet under a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0100] The secondary molded catalyst was treated at 450°C for 6 hours in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 18.5 m 2 ·g -1

[0101] The properties of the catalysts are shown in Table 1.

[0102] The catalyst was tested for its effect in the n-butane oxidation reaction. The conditions for the application were: the feed gas was a mixture of n-butane and air, in which the molar fraction of n-butane was 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction was carried out at 400°C and atmospheric pressure in a fixed-bed reactor. The evaluation results of the 24-hour and 120-hour tests are shown in Table 2.

[0103] [Comparative Example 4]

[0104] (1) Graphene oxide was dispersed in acetone at a ratio of 1:400 and ultrasonicated for 15 min. Triphenylphosphine was then weighed and added to the mixture at a mass ratio of 1:1 between the phosphorus source and graphene oxide, and ultrasonicated for another 30 min. The mixture was dried in a vacuum oven at 60°C under -30 kPa for 8 h. The resulting mixture was then placed in a tube furnace and carbonized at 750°C for 4 h under a nitrogen atmosphere to obtain phosphorus-modified graphene.

[0105] (2) 2 mol of benzyl alcohol and 17.5 mol of isobutanol were weighed and mixed, and then 100.8 g of V2O5 was added and stirred. The particle size of the vanadium source was 2 μm. 140 g of NH4H2PO4 was added, and the mixture was heated under reflux at 140°C for 16 h with continuous stirring. The resulting product was filtered and dried at 80°C for 6 h to obtain a VPO catalyst precursor powder.

[0106] (3) The powdered catalyst precursor was sieved, and 50 g of the precursor with a mesh size less than 200 was taken and mixed evenly with 1.5 g of fully ground P-modified graphene. 2 g of stearic acid as a pore-forming agent was then added. The mixture was then treated at a constant temperature and humidity of 30°C and a relative humidity of 85% for 12 h. The sample was then tableted at a pressure of 20 MPa to obtain a primary formed catalyst. The catalyst was then crushed and sieved, and particles with a mesh size of 80 to 140 were selected and transferred to a rotary tablet press for secondary forming into hollow cylindrical catalysts with a height of 5 mm.

[0107] The secondary molded catalyst was treated at 450°C for 6 h in an activation atmosphere of 40 vol% nitrogen + 10 vol% oxygen + 50 vol% water vapor to obtain an activated catalyst. The specific surface area of ​​the catalyst was 32.2 m 2 ·g -1 .

[0108] The properties of the catalysts before and after activation are shown in Table 1.

[0109] The activated catalyst was tested for its application in the n-butane oxidation reaction. The application conditions were as follows: the feed gas was a mixture of n-butane and air, with a molar fraction of n-butane of 1.5%; the volumetric space velocity of the feed gas was 2000 hr -1 The reaction temperature was 400°C, atmospheric pressure was maintained, and the reaction apparatus was a fixed-bed reactor. The evaluation results of the test reaction for 24 hours and the long-term reaction for 120 hours are detailed in Table 2.

[0110] Table 1 Catalyst properties of each example

[0111]

[0112] Table 2 Catalytic reaction results of each case

[0113]

[0114] The above describes in detail the specific embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present invention and fall within the scope of protection of the present invention.

Claims

1. A n-butane oxidation catalyst comprising a composite oxide of vanadium and phosphorus; the catalyst having a bulk P / V molar ratio of 0.98 to 1.10:1; a surface P / V molar ratio of 1.05 to 1.30:1; the surface P / V molar ratio of the catalyst being greater than the bulk P / V molar ratio; The difference between the surface P / V molar ratio of the catalyst and the bulk P / V molar ratio is 0.01-0.

05.

2. The catalyst according to claim 1, characterized in that The bulk P / V molar ratio of the catalyst is 1.00-1.10:1; the surface P / V molar ratio is 1.05-1.15:

1.

3. The catalyst according to claim 1, characterized in that The specific surface area of ​​the n-butane oxidation catalyst is 10-100 m 2 ·g -1 .

4. The catalyst according to claim 3, characterized in that The specific surface area of ​​the n-butane oxidation catalyst is 20 to 50 m 2 ·g -1 .

5. A method for preparing the n-butane oxidation catalyst according to any one of claims 1 to 4, comprising the steps of: mixing a VPO precursor with P-modified graphene and a pore-forming agent, optionally subjecting the mixture to a constant temperature and humidity treatment, forming the mixture, and activating the mixture to obtain the n-butane oxidation catalyst; The preparation method of the P-modified graphene comprises the following steps: dispersing graphene and a phosphorus source in an organic solvent, and then subjecting the graphene to a carbonization treatment; The graphene is graphene oxide; The phosphorus source is triphenylphosphine; The activation is to heat-treat the formed product under an activation atmosphere; the activation atmosphere includes an oxygen-containing atmosphere and one or more selected from light hydrocarbons, inert gases, nitrogen, water vapor, and carbon dioxide.

6. The preparation method according to claim 5, characterized in that: In the preparation method of the P-modified graphene, The organic solvent is acetone; And / or, the mass ratio of graphene to organic solvent is 1:200-1000; the mass ratio of phosphorus source to graphene is 1:0.5-2; And / or, the carbonization treatment conditions are: carbonization temperature is 600-1000°C, carbonization time is 1-8 h; atmosphere is oxygen-free atmosphere; And / or, the dispersion is ultrasonic dispersion.

7. The preparation method according to claim 6, characterized in that: The oxygen-free atmosphere of the carbonization treatment is at least one of an inert gas and nitrogen; And / or, the ultrasonic dispersion is to first disperse the graphene in an organic solvent, perform a first ultrasonic treatment for 15 to 60 min, then add a phosphorus source, and perform a second ultrasonic treatment for 15 to 60 min.

8. The preparation method according to claim 5, characterized in that: The preparation method of the VPO precursor comprises the following steps: dispersing a vanadium source and a phosphorus source in an organic solvent, and subjecting the obtained mixture to a reflux reaction, to obtain a solid product, which is the VPO precursor.

9. The preparation method according to claim 8, characterized in that: In the preparation method of the VPO precursor, the phosphorus source is at least one of H3PO4 and NH4H2PO4; and / or, the vanadium source is V2O5; And / or, the organic solvent is at least one of isobutanol, benzyl alcohol, isopropanol, and ethanol; And / or, the molar ratio of the phosphorus source calculated as phosphorus element to the vanadium source calculated as vanadium element is 0.5-2.0; the molar ratio of the amount of the organic solvent added to the vanadium source calculated as vanadium element is 5-50; And / or, the reflux reaction conditions are: heating temperature 60-160° C., reflux time 6-18 h.

10. The preparation method according to claim 9, characterized in that: The molar ratio of the added amount of the organic solvent to the vanadium source calculated as vanadium element is 5 to 30.

11. The preparation method according to claim 5, characterized in that: The pore-forming agent comprises at least one selected from stearic acid, soluble starch, sesbania powder, polyethylene glycol, ammonium carbonate, and polystyrene microspheres; and / or, the amount of the pore-forming agent added is 1 wt% to 10 wt% of the mass of the VPO precursor; And / or, the amount of the P-modified graphene added is 2 wt% to 6 wt% of the mass of the VPO precursor; And / or, the conditions of the constant temperature and humidity treatment are: temperature 20-60° C., time 3-24 hours, relative humidity 40%-95%.

12. The preparation method according to claim 5, characterized in that: The heat treatment temperature is 300-500° C., and the heat treatment time is 2-16 h.

13. An n-butane oxidation catalyst prepared by the preparation method according to any one of claims 5 to 12.

14. Use of the catalyst according to any one of claims 1 to 4, or the catalyst prepared by the preparation method according to any one of claims 5 to 12, or the catalyst according to claim 13 in the reaction of oxidizing n-butane to prepare maleic anhydride.

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