Vanadium phosphorus oxide catalyst as well as preparation method and application thereof

Abstract

The invention provides a vanadium phosphorus oxide catalyst. The vanadium phosphorus oxide catalyst comprises the following components in percentage by weight: 66-94% of vanadyl pyrophosphate, 0.5-6% of vanadyl phosphate, 0.8-25% of attapulgite and 1-6% of graphite. The preparation method comprises the following steps: mixing an organic solvent, vanadium pentoxide and phosphoric acid for reaction to obtain a blue pasty reaction solution containing a vanadium phosphorus oxide catalyst precursor, adding an attapulgite carrier into the blue pasty reaction solution, filtering, drying, forming, roasting, activating and the like to obtain the catalyst. The catalyst disclosed by the invention is applied to a reaction for preparing maleic anhydride by oxidizing n-butane, the reaction is carried out in a reaction temperature interval of 380-420 DEG C, and the conversion rate of the n-butane and the yield of the maleic anhydride are higher than those of the catalyst without the attapulgite.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, in particular to a vanadium phosphorus oxygen catalyst and a preparation method thereof. Background Art

[0002] Maleic anhydride, also known as maleic anhydride, is a key organic chemical raw material and the third largest organic anhydride in the world, after phthalic anhydride and acetic anhydride. Its structure contains conjugated maleoyl groups, where one vinyl group is connected to two carboxyl groups. Maleic anhydride is highly reactive chemically and can be derived into numerous downstream products through addition reactions, esterification, and sulfonation. It is widely used in the petrochemical, food processing, pharmaceutical, and building materials industries. Specific applications include the manufacture of unsaturated polyester resins, alkyd resins, maleic acid (maleic acid), and fumaric acid (fumaric acid), as well as pesticides, coatings, fiberglass reinforced plastics, lubricant additives, papermaking chemical additives, and surfactants.

[0003] Benzene oxidation and n-butane oxidation are the two main methods for producing maleic anhydride. Benzene oxidation was the earliest process used, and its reactor and catalyst technologies are mature. However, due to the relatively high price of the raw benzene and the relatively severe environmental pollution it produces, its shortcomings have become increasingly apparent. Since Monsanto's n-butane oxidation process for producing maleic anhydride was first industrialized in 1974, it has become the main route for global maleic anhydride production due to its advantages of low raw material costs, minimal environmental pollution, and low production costs. The selective oxidation of n-butane to produce maleic anhydride can be categorized into fixed-bed, fluidized-bed, and moving-bed processes. However, all of these processes require the use of a vanadium phosphorus oxide (VPO) catalyst. Since the successful commercialization of VPO catalysts, their preparation methods have been extensively studied, resulting in numerous publications and patent applications (see CATAL. REV.-SCI. ENG. 27 (1985): 373).

[0004] The selective oxidation of n-butane over vanadium-phosphorus-oxygen (VPO) catalysts is a typical example of a large class of hydrocarbon selective oxidation reactions that proceed via a redox mechanism. The chemical reaction involves the transfer of 14 electrons, including the removal of electrons from eight hydrogen atoms and the insertion of electrons from three oxygen atoms. The exploration of this reaction mechanism has long been a hot topic in VPO research. VPO catalysts are a complex catalyst system whose physical properties and structure are closely related to their preparation methods, and their preparation process has a significant impact on their catalytic performance.

[0005] Jiang Haoxi et al. studied the active phase of the catalyst for butane oxidation to maleic anhydride[J]. Chemical Industry and Engineering, 2004, 21(1): 29. The study pointed out that the process of butane oxidation to maleic anhydride can only be achieved in the VOPO4 phase (V5+ ) and (VO)2P2O7 (V 4+ ) phase can properly activate butane molecules, so that the reaction control step of butane dehydrogenation can proceed smoothly. All surface adsorption and atomic migration are carried out on the (020) crystal plane. However, in the presence of only (VO)2P2O7 phase, the conversion rate and yield of butane are not high enough, which is much lower than that with an appropriate amount of β-VOPO4 phase (V 5+ ) exists, this phenomenon indicates that the β-VOPO4 phase must have some effect on the dehydrogenation process of butane, and since the dehydrogenation reaction is the rate-controlling step of the entire butane oxidation to maleic anhydride reaction process, its presence has a significant impact on the catalyst performance. The reason for the above phenomenon may be that since the butane molecule is a saturated aliphatic hydrocarbon, its chemical properties are not very active, and dehydrogenation is difficult. A strong Lewis acid site is required to activate butane, and as the V on the (020) surface 4+ The acid strength is not very ideal, so the catalyst containing only (VO)2P2O7 shows low activity. However, when there is a β-VOPO4 phase with a V oxidation state of +5 and a strong acid strength, the situation is completely different. The β-VOPO4 phase embedded in the (VO)2P2O7 crystal lattice uses its strong acid strength to react with the V on the (020) surface of the (VO)2P2O7 phase. 4+ The combined action activates the CH atoms of butane, making the (VO)2P2O7 phase (020) surface effectively catalyze the dehydrogenation of butane. However, when the content of β-VOPO4 phase exceeds a certain limit, it will react with the V atoms on the (VO)2P2O7 (020) crystal surface. 4+ Competitive adsorption occurs, resulting in a considerable amount of butane on V 5+ The deep oxidation to CO and CO2 at the bottom of the reactor results in an increase in the butane conversion rate and a significant decrease in the maleic anhydride yield.

[0006] In the early stage, the preparation of vanadium phosphorus oxide catalysts used water as solvent and hydrochloric acid (including hydrogen chloride gas) and oxalic acid as reducing agents. The specific surface area of ​​the obtained catalyst was small (<10m 2 / g). The method developed later was to prepare the catalyst in the organic phase, using alcohols, aldehydes, esters and other reducing agents. The specific surface area of ​​the catalyst prepared in the organic phase is larger (>20m 2 / g), and the catalytic performance of the catalyst prepared in the organic phase is generally better than that of the catalyst prepared using water as the solvent.

[0007] USP 4,632,915 discloses a method for preparing and activating a vanadium-phosphorus-oxygen catalyst. In a stirred reactor equipped with a reflux cooler, isobutanol, 100% phosphoric acid, vanadium pentoxide, lithium chloride, and iron powder are added under cooling. Hydrogen chloride gas is then introduced and refluxed at 102°C for more than 2.5 hours to obtain a catalyst precursor. The catalyst is then dried, calcined, and formed. The catalyst is then activated using a butane-air reaction atmosphere at a heating rate of 3°C / min in an air atmosphere containing 1.8% water. Catalyst performance evaluation results for this method showed a butane conversion of 78.1% and a maleic anhydride molar yield of 54.5%.

[0008] CN 101157048A proposes a method for preparing a nanostructured vanadium-phosphorus-oxygen catalyst. The method improves a conventional organic solvent method by introducing auxiliary agents such as bismuth salt, dimethyl sulfoxide, and polyethylene glycol into the process of preparing a vanadium-phosphorus-oxygen catalyst precursor to directly prepare the nanostructured vanadium-phosphorus-oxygen catalyst. The method also provides a method for activating the catalyst. The method comprises activating the pressed catalyst precursor in a reaction mixture of air with a volume ratio of 1.5% and 98.5% by volume at an activation temperature of 400°C for 72 hours to obtain the activated catalyst. Performance evaluation results show a conversion rate of 68-81% and a maleic anhydride selectivity of 41-71%.

[0009] USP4,855,459 proposes a method for preparing maleic anhydride by oxidation of n-butane, which uses a method of diluting and loading inert silica-alumina balls with a catalyst. By diluting and loading at the hot spot generating portion of the reaction tube, the purpose is to reduce the reaction hot spot temperature, improve maleic anhydride selectivity, and increase maleic anhydride yield. At the same time, the stability period of the catalyst is extended. However, a disadvantage is that the addition of inert materials reduces the effective volume of the reactor and also reduces production efficiency. Summary of the Invention

[0010] During the research and development process, the inventors of this case surprisingly discovered that the two-component vanadium-phosphorus-oxygen catalyst prepared by compounding attapulgite powder has improved the physicochemical properties and catalytic performance of the vanadium-phosphorus-oxygen catalyst due to the colloidal properties, adsorption properties, reinforcement properties, support properties, and high-temperature thermal stability of the attapulgite in its components, as well as the catalytic function of the acid-base synergistic effect of the Lewis acidifying and alkalizing centers of the attapulgite. This method and results are novel and unexpected. That is, those skilled in the art would not have expected that vanadium-phosphorus-oxygen catalysts could be prepared using attapulgite as a support and active component. Due to the positive carbon ionization effect of attapulgite in organic reactions and its acid-base synergistic effect, the vanadium-phosphorus-oxygen catalyst-attapulgite composite catalyst prepared by this method has improved selective oxidation ability. The catalyst is used in the catalytic reaction of n-butane oxidation to maleic anhydride, and has high n-butane conversion rate, good maleic anhydride selectivity, and high maleic anhydride yield.

[0011] The technical purpose of the first aspect of the present invention is to provide a vanadium phosphorus oxygen catalyst having the following components by weight: Vanadyl pyrophosphate 66-94% Vanadyl phosphate 0.5-6% Attapulgite 0.8-25% Graphite 1-6%.

[0012] More preferably: Vanadyl pyrophosphate 70-92% Vanadyl phosphate 0.75-5% Attapulgite 3-20% Graphite 1-5% Most preferably: Vanadyl pyrophosphate 72-92% Vanadyl phosphate 1-5% Attapulgite 5-18% Graphite 1-5% Furthermore, the catalyst also includes an auxiliary agent, which is selected from at least one of Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr and Ce elements, and the auxiliary agent is 0.001 to 0.2 times the amount of V atoms in terms of metal elements.

[0013] The second aspect of the present invention provides a method for preparing a vanadium phosphorus oxygen catalyst, comprising: reacting an organic solvent, vanadium pentoxide, and phosphoric acid to obtain a blue slurry containing a vanadium phosphorus oxygen catalyst precursor; adding attapulgite to the mixture to obtain a composite catalyst precursor; filtering, drying, shaping, and calcining the mixture to obtain the vanadium phosphorus oxygen catalyst; Based on the total weight of the prepared catalyst, the mass percentages of the components are as follows: Vanadyl pyrophosphate 66-94% Vanadyl phosphate 0.5-5% Attapulgite 0.8-25% Graphite 1-6%.

[0014] Furthermore, the particle size of the attapulgite is 80-800 mesh, preferably 100-400 mesh.

[0015] Furthermore, the attapulgite is refined attapulgite, which is obtained by treating raw attapulgite powder with hydrochloric acid for purification, specifically, mixing the raw attapulgite powder with 1-5 mol / L, preferably 2-3 mol / L, hydrochloric acid, stirring for 5-10 hours, filtering, washing until there is no chloride ion, and drying.

[0016] Furthermore, the organic solvent, vanadium pentoxide and phosphoric acid are reacted in a reactor equipped with a stirring device and a reflux condenser. The organic solvent and vanadium pentoxide are first mixed and reacted for 2-4 hours, and then phosphoric acid is added and reacted for 4-8 hours. The reaction temperature range is 95-120°C.

[0017] Furthermore, the organic solvent is a solvent suitable for preparing a vanadium-phosphorus-oxygen catalyst system, which is well known to those skilled in the art. It can be a single solvent or a mixture of two or more solvents. As a more specific embodiment, the organic solvent is selected from at least one of isobutanol, benzyl alcohol, ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol; preferably, it is a mixture of isobutanol and benzyl alcohol, with a volume ratio of 5:1 to 100:1, preferably 10:1 to 25:1.

[0018] Furthermore, the weight ratio of the organic solvent to vanadium pentoxide is 5:1-25:1, preferably 10:1-20:1.

[0019] Furthermore, the weight percentage concentration of the concentrated phosphoric acid is 85%-100%.

[0020] Furthermore, the amount of phosphoric acid added is such that the molar ratio of phosphorus to vanadium is 0.85-1.35, preferably 0.95-1.20.

[0021] Furthermore, the drying is carried out at a temperature of 95-170° C., preferably at a temperature of 120-150° C., for 8-12 hours.

[0022] Furthermore, the forming is a conventional forming method in the art such as extrusion, sheeting or pelletization, and the catalyst is generally in the shape of a solid cylinder, a hollow cylinder, a Raschig ring or a clover leaf.

[0023] Furthermore, the calcination temperature is 250-350° C., preferably 270-300° C.; the calcination time is 3-10 hours, preferably 4-6 hours.

[0024] Furthermore, the above preparation method further includes the step of introducing an auxiliary agent. The auxiliary agent is selected from one or more of the elements Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr and Ce; the auxiliary agent is 0.001 to 0.2 times the V atom in terms of metal element. The auxiliary agent is introduced into the catalyst in one of the following ways: (1) introduced into the reaction solution during the preparation of the vanadium phosphorus oxide precursor; (2) introduced before or during the catalyst molding process.

[0025] Furthermore, the above preparation method further includes a step of activating the catalyst. The activation is carried out in an atmosphere of one or more combinations of air / inert gas, air / butane, air / water vapor, or butane / inert gas mixtures, preferably a butane / air mixture, wherein the butane content of the butane / air mixture is 0.8-1.5% by volume, preferably 1.0-1.2%. The activation temperature is generally 260-450°C, preferably 370-430°C, and most preferably 400-420°C; the activation time is 10-40 hours, preferably 15-25 hours. The heating rate during activation is 1-10°C / min, preferably 3-5°C / min.

[0026] The technical purpose of the second aspect of the present invention is to provide a method for preparing maleic anhydride by oxidation of n-butane, using a vanadium phosphorus oxide catalyst prepared by the above method.

[0027] Furthermore, the reaction of producing maleic anhydride by oxidation of n-butane adopts a fixed bed reaction mode, a fluidized bed reaction mode or a moving bed reaction mode.

[0028] Furthermore, the reaction conditions for the oxidation of n-butane to maleic anhydride are: reaction temperature 380-450°C, pressure normal pressure-0.5 MPa, n-butane mixed gas space velocity 1000-3500h -1 , the concentration of n-butane in the mixed gas is 1.0%-1.85% (volume percentage).

[0029] The vanadium phosphorus oxygen catalyst of the present invention is applied to the reaction process of producing maleic anhydride by oxidizing n-butane, and has high n-butane conversion rate, good maleic anhydride selectivity, and less acetic acid and acrylic acid by-products.

[0030] Compared with the prior art, the technical solution provided by the present invention has the following advantages: (1) The process of butane oxidation to maleic anhydride requires that the butane molecules be dehydrogenated and activated first before the reaction can proceed smoothly. In other words, butane dehydrogenation is the controlling step of this reaction. In the catalytic process of the vanadium phosphorus oxide catalyst-attapulgite composite catalyst, attapulgite as the active component has a strong Lewis acidification center, which can accelerate the controlling step of the butane dehydrogenation reaction and synergize with the oxidative active components VOPO4 and (VO)2P2O7 of the vanadium phosphorus oxide catalyst, thereby obtaining excellent catalytic performance for butane oxidation to maleic anhydride.

[0031] (2) The vanadium-phosphorus-oxygen catalyst-attapulgite composite catalyst has a high specific surface area and a large pore volume, and the catalyst has high activity; the thermal stability of attapulgite as a catalyst carrier can disperse the heat of the oxidation reaction, facilitate heat transfer to remove the reaction heat, effectively reduce the reaction hot spots, and improve the selectivity of the product maleic anhydride; the adhesion of attapulgite enables a wide range of catalyst strength control; attapulgite is cheap and easy to obtain, which can effectively reduce the cost of catalyst manufacturing.

[0032] (3) The catalyst of the present invention is used in the reaction of n-butane oxidation to prepare maleic anhydride, with high butane conversion rate, maleic anhydride selectivity and catalytic activity. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are not intended to limit the scope of protection of the present invention. Those skilled in the art may make appropriate extensions based on the specification and full text of the present invention, and these extensions should all fall within the scope of protection of the present invention.

[0034] In the examples, the catalyst strength was measured using a DLⅡ Intelligent Particle Strength Tester from Dalian Chemical Research and Design Institute, and the specific surface area was measured using an AUTOSORB3B Fully Automatic Surface Area and Pore Size Distribution Analyzer from Quantachrome, USA. The catalyst evaluation results were analyzed using an HP7890A gas chromatograph from Agilent.

[0035] The contents of vanadyl pyrophosphate and vanadyl phosphate in the catalyst prepared by the present invention are determined by a potassium permanganate oxidation-ammonium ferrous sulfate titration method (YB-T5328-2009), specifically as follows: tetravalent vanadium is oxidized to pentavalent vanadium using potassium permanganate in a sulfuric acid medium, excess potassium permanganate is decomposed using sodium nitrite in the presence of urea, the total vanadium content of the catalyst is determined by titration using a ferrous ammonium sulfate standard solution with N-phenylanthranilic acid as an indicator, another sample is taken in parallel, and the pentavalent vanadium in the catalyst is determined by titration using a ferrous ammonium sulfate standard solution with N-phenylanthranilic acid as an indicator in a sulfuric acid medium to determine the content of vanadyl phosphate, and the content of tetravalent vanadyl pyrophosphate is calculated based on the total vanadium content of the catalyst.

[0036] Example 1 To a reactor equipped with a stirring device and a reflux condenser, 649 mL of a mixture of isobutanol and benzyl alcohol was added, the volume ratio of isobutanol / benzyl alcohol was 10:1, 29.53 g of vanadium pentoxide, 0.3 g of nickel nitrate hexahydrate as an auxiliary, and 0.5 g of zirconium nitrate as an auxiliary. Stirring was started, the reaction temperature was increased and maintained at 100 ± 2 ° C, and the reflux reaction was maintained for 4 hours. Then, 34.98 g of 100% phosphoric acid was added, and the phosphorus / vanadium molar ratio was 1.1. The reaction was continued to reflux for 4 hours, and then 0.5 g of 100 mesh refined attapulgite was added. Stirring was continued for 5 hours. After the reaction solution was cooled to room temperature, vacuum filtration was performed, and the filter cake was rinsed three times with a small amount of isobutanol. The filter cake was placed in an enamel tray and naturally air-dried at room temperature. It was dried in an oven at 100 ° C for 8 hours to obtain a lake blue catalyst precursor.

[0037] The catalyst precursor prepared above was added with 1.8 g of graphite powder, and after thorough mixing, a rotary tablet press was used to extrude the catalyst into a Raschig ring-shaped finished product by appropriately adjusting the impact force.

[0038] The above-mentioned Raschig ring catalyst particles were calcined in a muffle furnace at a temperature of 300°C for 4 hours. The calcined catalyst was placed in a tubular reactor and heated at a gas volume space velocity of 1000 h in an atmosphere of a butane / air mixture with a butane volume content of 1.2%. -1 The activation temperature is raised to 400° C. at a heating rate of 3° C. / min and maintained at 400° C. for 20 hours. The activation process is completed to obtain the vanadium phosphorus oxygen catalyst of the present invention.

[0039] The contents of vanadyl pyrophosphate and vanadyl phosphate were determined by titration, and the contents of attapulgite, graphite and additives (in terms of metal elements) were calculated based on the feed ratio. The results are shown in Table 1.

[0040] The lateral pressure strength, specific surface area and pore volume of the obtained catalyst were measured. The results are shown in Table 2.

[0041] Example 2 Except that 2.6 g of 200 mesh refined attapulgite was used instead of 0.5 g of attapulgite, the other steps were the same as those in Example 1. The catalyst composition is shown in Table 1.

[0042] Example 3 Except that 5.2 g of 300-mesh refined attapulgite was used instead of 0.5 g of attapulgite, the other steps were the same as those in Example 1. The catalyst composition is shown in Table 1.

[0043] Example 4 Except that 7.8 g of 200 mesh refined attapulgite was used instead of 0.5 g of attapulgite, the other steps were the same as those in Example 1. The catalyst composition is shown in Table 1.

[0044] Example 5 Except that 13.0 g of 100 mesh refined attapulgite was used instead of 0.5 g of attapulgite, the other steps were the same as those in Example 1. The catalyst composition is shown in Table 1.

[0045] Comparative Example 1 To a reactor equipped with a stirrer and reflux condenser, add 649 mL of a mixture of isobutanol and benzyl alcohol (with a volume ratio of 10:1), 29.53 g of vanadium pentoxide, 0.3 g of ferric nitrate hexahydrate (a catalyst), and 0.5 g of zirconium nitrate (a catalyst). Stirring was initiated, and the reaction temperature was raised and maintained at 100 ± 2°C for reflux reaction. The reaction was then refluxed for 4 hours. 34.98 g of 100% phosphoric acid (with a phosphorus / vanadium molar ratio of 1.1) was then added. Reflux was continued for another 4 hours to complete the reaction. After cooling the reaction mixture to room temperature, vacuum filtration was performed. The filter cake was rinsed three times with a small amount of isobutanol and then placed in an enamel dish to air-dry at room temperature. The filter cake was then dried in an oven at 100°C for 8 hours to yield a blue catalyst precursor.

[0046] The catalyst precursor prepared above was added with 1.8 g of graphite powder by mass, and after thorough mixing, a rotary tablet press was used to extrude the catalyst into a Raschig ring-shaped catalyst product by appropriately adjusting the impact force.

[0047] 50 g of the above-mentioned Raschig ring catalyst particles were calcined in a muffle furnace at a temperature of 300 ° C for 4 hours. The calcined catalyst was placed in a tubular reactor and heated at a gas volume space velocity of 1000 h in an atmosphere of a butane / air mixture with a butane volume content of 1.2%. -1 The activation temperature is raised to 400° C. at a heating rate of 3° C. / min and maintained at 400° C. for 20 hours. The activation process is completed to obtain the vanadium phosphorus oxygen catalyst of the present invention.

[0048] The catalyst composition is shown in Table 1. The results of lateral pressure strength, specific surface area and pore volume are shown in Table 2.

[0049] Table 1

[0050] Table 2

[0051] The catalysts obtained in the above examples and comparative examples were crushed and sieved. 5 mL of catalyst particles (10-20 mesh) were diluted with quartz sand of the same mesh size at a ratio of 1:1 and loaded into a stainless steel reaction tube with an inner diameter of 10 mm. The reactor was heated at a controlled temperature of 400°C, an inlet pressure of 0.25 MPa, and a mixture of n-butane and air with a butane volume concentration of 1.5% was used as the raw material. The gas space velocity was 1600 h / min. -1 The catalytic performance evaluation test was carried out under the reaction conditions of . The product composition was analyzed by gas chromatography, and the performance evaluation results are shown in Table 3.

[0052] Table 3

Claims

1. A vanadium phosphorus oxygen catalyst, characterized in that It has the following components by weight: Vanadyl pyrophosphate 66-94% Vanadyl phosphate 0.5-6% Attapulgite 0.8-25% Graphite 1-6%.

2. The vanadium phosphorus oxygen catalyst according to claim 1, characterized in that It has the following components by weight: Vanadyl pyrophosphate 70-92% Vanadyl phosphate 0.75-5% Attapulgite 3-20% Graphite 1-5%.

3. The vanadium phosphorus oxygen catalyst according to claim 1, characterized in that The catalyst also includes an additive, which is selected from at least one of the elements Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr and Ce. The mass percentage of the additive element is 0.5-4% based on the total weight of the vanadium phosphorus oxygen catalyst.

4. A method for preparing a vanadium phosphorus oxygen catalyst, comprising: An organic solvent, vanadium pentoxide and phosphoric acid are mixed and reacted to obtain a blue slurry reaction liquid containing a vanadium phosphorus oxygen catalyst precursor, attapulgite is added thereto to obtain a composite catalyst precursor, and the vanadium phosphorus oxygen catalyst is obtained after filtering, drying, molding and calcining; Based on the total weight of the prepared catalyst, the mass percentage of each component is as follows: Vanadyl pyrophosphate 66-94% Vanadyl phosphate 0.5-5% Attapulgite 0.8-25% Graphite 1-6%.

5. The preparation method according to claim 4, characterized in that: The particle size of the attapulgite is 40-800 meshes.

6. The preparation method according to claim 4, characterized in that: The attapulgite is refined attapulgite, which is obtained by treating raw attapulgite powder with hydrochloric acid to refine it.

7. The preparation method according to claim 4, characterized in that: The organic solvent, vanadium pentoxide and phosphoric acid react in a reactor equipped with a stirring device and a reflux condensing device. The organic solvent and vanadium pentoxide are first mixed and reacted for 2-4 hours, and then phosphoric acid is added and reacted for 4-8 hours. The reaction temperature ranges from 95 to 120°C.

8. The preparation method according to claim 4, characterized in that: The organic solvent is selected from at least one of isobutyl alcohol, benzyl alcohol, ethylene glycol, 1,3-propylene glycol and 1,4-butanediol.

9. The preparation method according to claim 1, characterized in that: The weight ratio of the organic solvent to vanadium pentoxide is 5:1-25:

1.

10. The preparation method according to claim 4, characterized in that: The weight percentage concentration of the concentrated phosphoric acid is 85%-100%, and the amount of phosphoric acid added is such that the molar ratio of phosphorus to vanadium is 0.85-1.

35.

11. The preparation method according to claim 4, characterized in that: The method also includes the step of introducing an auxiliary agent, wherein the auxiliary agent is selected from one or more of the elements Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Al, Si, Cr and Ce; wherein the auxiliary agent is added in an amount of 0.5-4% of the total weight of the catalyst by weight of the above elements.

12. The preparation method according to claim 11, characterized in that: The auxiliary agent is introduced into the catalyst in one of the following ways: (1) introduced into the reaction solution during the preparation of the vanadium phosphorus oxide precursor; (2) introduced before or during the catalyst molding process.

13. The preparation method according to claim 4, characterized in that: The method also includes the step of activating the catalyst, wherein the activation is carried out in an atmosphere of one or more combinations of air / inert gas, air / butane, air / water vapor, butane / inert gas mixture; the activation temperature is 260-450° C., the activation time is 10-40 hours, and the heating rate during activation is 1-10° C. / min.

14. A method for preparing maleic anhydride by oxidation of n-butane, using the vanadium phosphorus oxygen catalyst according to claim 1 or the vanadium phosphorus oxygen catalyst prepared by the preparation method according to claim 4 for catalytic reaction.

15. The method according to claim 14, characterized in that The reaction is carried out in a fixed bed, fluidized bed or moving bed manner.

16. The method according to claim 14, characterized in that The reaction conditions for the oxidation of n-butane to maleic anhydride are: reaction temperature 380-450°C, pressure normal pressure-0.5MPa, n-butane mixed gas space velocity 1000-3500h -1 , the volume concentration of n-butane in the mixed gas is 1.0%-1.8%.

Images