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

Abstract

The invention relates to the field of catalyst preparation, and discloses a vanadium-phosphorus-oxide catalyst and a preparation method and application thereof.The vanadium-phosphorus-oxide catalyst comprises, by weight, 20-35% of vanadium, 15-25% of phosphorus, 15-25% of oxygen, 15-25% of iron and 5-10% of lithium, and the vanadium-phosphorus-oxide catalyst comprises, by weight, 20-35% of vanadium, 15-25% of phosphorus, 5-10% of oxygen, 5-10% of iron and 5-10% of lithium. The content of the oxygen element is 40-65% by weight, the content of the iron element is 0.2-0.5% by weight, and the content of the lithium element is 0.02-0.1% by weight. The stability of the phosphorus element in the vanadium phosphorus oxide catalyst is high, and the vanadium phosphorus oxide catalyst has high catalytic activity and stability in the reaction of preparing maleic anhydride through hydrocarbon selective oxidation.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a vanadium-phosphorus-oxygen catalyst, its preparation method, and its application. Background Technology

[0002] Gas-phase selective oxidation of hydrocarbons is an important class of catalytic reactions that can be used to catalyze the preparation of various oxidation products, such as organic acid anhydrides. One typical product is maleic anhydride.

[0003] Maleic anhydride (MA) is an important organic chemical raw material and fine chemical product. It is currently the third largest acid anhydride globally, after phthalic anhydride and acetic anhydride, and has a wide range of applications. With increasing global environmental awareness, maleic anhydride, as an upstream raw material for biodegradable plastics such as polybutylene terephthalate (PBAT) and polybutylene succinate (PBS), will see its application scope continue to expand under the current plastic ban, and its development and utilization prospects are very broad.

[0004] There are three main routes for producing maleic anhydride: benzene oxidation, n-butane oxidation, and butene (C4 fraction) oxidation. Among these, n-butane oxidation is currently the mainstream method for maleic anhydride production, as it is a typical selective oxidation reaction. Compared to benzene oxidation, n-butane oxidation has higher carbon atom utilization and is a greener and more economical process. The core of this reaction is a vanadium-phosphorus-oxygen catalyst (VPO) composed of vanadium, oxygen, and phosphorus. For industrial applications, this catalyst needs to possess high activity, high selectivity, and high stability.

[0005] In VPO catalysts, V, P, and O elements each play their respective roles and work synergistically. P, in particular, modulates the valence state of V; its coordination effectively balances the V valence state, thus improving catalyst stability. However, P is easily lost during high-temperature reactions, resulting in a gradual decrease in P content within the VPO catalyst as the reaction progresses. According to patent application CN114682278A, phosphorus loss leads to increased n-butane conversion but decreased selectivity and yield of maleic anhydride. Therefore, industrially, trace amounts of P-containing organic compounds are typically added to the feed gas to mitigate the impact of P loss and extend the catalyst's lifespan. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low selectivity and yield of maleic anhydride and poor catalyst stability in the prior art, and to provide a vanadium-phosphorus-oxygen catalyst, its preparation method and application. The vanadium-phosphorus-oxygen catalyst contains phosphorus, which has good stability, as well as lithium and iron, and has high stability and the ability to selectively oxidize hydrocarbons to maleic anhydride.

[0007] During their research, the inventors of this invention discovered that existing methods of adding trace amounts of phosphorus-containing organic compounds to the feed gas to mitigate phosphorus loss from the catalyst and thus extend its lifespan have drawbacks. The phosphorus replenishment process incurs additional operating costs and increases the instability of the production process. Further research revealed that introducing an appropriate and stable phosphorus component into the catalyst can effectively mitigate phosphorus loss during the reaction process, reducing or even eliminating the need for phosphorus replenishment. Lithium iron phosphate (LFP) is a compound containing Li, Fe, P, and O elements. The addition of Li and Fe may also promote the selective oxidation of hydrocarbons. Currently, its most widespread application is in lithium-ion battery electrode materials. After high-temperature decomposition, the phosphorus element remains stable in the form of phosphate compounds. Therefore, introducing lithium iron phosphate into the vanadium phosphorus oxide (VPO) catalyst precursor holds promise for preparing high-performance and highly stable VPO hydrocarbon selective oxidation catalysts.

[0008] To achieve the above objectives, the first aspect of the present invention provides a vanadium-phosphorus-oxygen catalyst, wherein the catalyst comprises vanadium, phosphorus, oxygen, iron, and lithium, and based on the total amount of the catalyst, the content of vanadium is 20-35% by weight, the content of phosphorus is 15-25% by weight, the content of oxygen is 40-65% by weight, the content of iron is 0.2-0.5% by weight, and the content of lithium is 0.02-0.1% by weight.

[0009] Preferably, in the catalyst, at least a portion of the phosphorus and iron elements are present in the form of iron phosphate.

[0010] Preferably, the catalyst, as characterized by XRD, exhibits diffraction peaks at 2θ values ​​of 12.5°±0.2°, 18.5°±0.2°, 20.3°±0.2°, 22.8°±0.2°, 25.8°±0.2°, 26.5°±0.2°, 28.4°±0.2°, 29.3°±0.2°, 29.9°±0.2°, 38.0°±0.2°, 43.2°±0.2°, 48.5°±0.2°, and 49.8°±0.2°.

[0011] A second aspect of this invention provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0012] (1) In the presence of a solvent, vanadium source, phosphorus source and lithium iron phosphate compound are subjected to a solvothermal reaction;

[0013] (2) Heat-treat the solid product obtained in step (1);

[0014] (3) Activate the heat-treated precursor obtained in step (2);

[0015] The method also includes a molding process performed after step (2) or after step (3).

[0016] Preferably, in step (1), the molar ratio of the vanadium source (calculated as vanadium) to the phosphorus source (calculated as phosphorus) is 0.6-1.1:1, more preferably 0.7-1.1:1.

[0017] Preferably, in step (1), the mass of the lithium iron phosphate is 0.5-5% of the mass of the vanadium source, calculated as vanadium pentoxide, and more preferably 0.5-2%.

[0018] The third aspect of the present invention provides a vanadium-phosphorus-oxygen catalyst prepared by the preparation method described in the second aspect above.

[0019] The fourth aspect of this invention provides the application of the vanadium-phosphorus-oxygen catalyst described in the first or third aspect above in the selective oxidation of hydrocarbons to maleic anhydride.

[0020] Through the above technical solutions, the vanadium-phosphorus-oxygen catalyst provided by the present invention significantly improves the catalyst's resistance to phosphorus loss and stability by adding lithium iron phosphate compounds during the synthesis process and introducing phosphorus elements with better stability. At the same time, by introducing iron and lithium elements as promoters, the selectivity and yield of maleic anhydride in the catalytic oxidation of alkane to maleic anhydride reaction are effectively improved. Attached Figure Description

[0021] Figure 1 This is the XRD pattern of the vanadium-phosphorus-oxygen catalyst prepared in Example 1 of this invention.

[0022] Figure 2 This is the XRD pattern of the vanadium phosphorus oxygen catalyst prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of this invention provides a vanadium-phosphorus-oxygen catalyst, wherein the catalyst comprises vanadium, phosphorus, oxygen, iron, and lithium, and based on the total amount of the catalyst, the content of vanadium is 20-35% by weight, the content of phosphorus is 15-25% by weight, the content of oxygen is 40-65% by weight, the content of iron is 0.2-0.5% by weight, and the content of lithium is 0.02-0.1% by weight.

[0025] According to a preferred embodiment of the present invention, the catalyst contains, based on the total amount of catalyst, 25-30% by weight of vanadium, 17-22% by weight of phosphorus, 48-58% by weight of oxygen, 0.2-0.4% by weight of iron, and 0.03-0.05% by weight of lithium.

[0026] This implementation method is beneficial for increasing the phosphorus content and stability of the vanadium phosphorus oxygen catalyst, thereby improving the activity and structural stability of the vanadium phosphorus oxygen catalyst. At the same time, the presence of iron and lithium can further enhance the catalytic performance of the catalyst in the catalytic oxidation of alkanes to maleic anhydride.

[0027] In this invention, the content of each metal element in the vanadium-phosphorus-oxygen catalyst can be determined by inductively coupled plasma optical emission spectrometry (ICP-OES), the phosphorus content is determined by the quinomolybdate-limonene precipitation method, and the oxygen content can be calculated by the total mass of the catalyst and the content of other elements.

[0028] According to a preferred embodiment of the present invention, the iron, lithium and a portion of the phosphorus in the catalyst, calculated as lithium iron phosphate, account for 0.5-5% of the vanadium element calculated as vanadium pentoxide.

[0029] Furthermore, the iron, lithium, and a portion of the phosphorus elements in the catalyst, calculated as lithium iron phosphate, account for 0.5-2% of the vanadium element (calculated as vanadium pentoxide).

[0030] This implementation method helps to ensure the formation of VPO, the main active component in the vanadium-phosphorus-oxygen catalyst, and avoids the destruction of the structure of VPO due to the addition of additives. At the same time, lithium iron phosphate can still form stable phosphates after high-temperature decomposition, which can effectively replenish the content of phosphorus element in the main component of the catalyst and enhance the stability of the replenished phosphorus element in the structure.

[0031] In this invention, the mass relationship between lithium iron phosphate and vanadium pentoxide in the catalyst can be calculated by the amount of lithium iron phosphate and vanadium source added during the catalyst preparation process. The mass of vanadium pentoxide can be calculated by the vanadium content in the actual added vanadium source.

[0032] According to a preferred embodiment of the present invention, at least a portion of the phosphorus and iron elements are present in the catalyst as iron phosphate. This embodiment facilitates the enhancement of phosphorus stability in the catalyst through the chemical bond between phosphorus and iron.

[0033] In this invention, the presence of iron phosphate can be determined by X-ray diffraction (XRD). Specifically, the catalyst is tested using a Rigaku D / max-1400 powder X-ray diffractometer (Japan). The specific test parameters are: Cu Kα radiation (λ = 0.15406 nm), current 200 mA, tube voltage 40 kV, scanning range 5°–80°, and scanning rate 12° / min.

[0034] According to a preferred embodiment of the present invention, XRD characterization revealed that the catalyst exhibited diffraction peaks at 2θ values ​​of 20.3°±0.2°, 25.8°±0.2°, and 48.5°±0.2°. Based on fundamental knowledge in the art, diffraction peaks satisfying these shifts are attributed to iron phosphate compounds, thus demonstrating the presence of the iron phosphate component in the catalyst.

[0035] According to a particularly preferred embodiment of the invention, the catalyst has diffraction peaks at 12.5°±0.2°, 18.5°±0.2°, 20.3°±0.2°, 22.8°±0.2°, 25.8°±0.2°, 26.5°±0.2°, 28.4°±0.2°, 29.3°±0.2°, 29.9°±0.2°, 38.0°±0.2°, 43.2°±0.2°, 48.5°±0.2°, and 49.8°±0.2°.

[0036] In this invention, when the diffraction peak shifts in the XRD pattern of the catalyst meet the above-mentioned range, the resulting catalyst simultaneously contains the main active components VPO compound and iron phosphate compound, thereby enhancing the catalytic activity and stability of the vanadium phosphorus oxygen catalyst.

[0037] This invention does not impose any particular limitation on the morphology of the catalyst, and those skilled in the art can make adaptive selections according to specific application scenarios. It can be a shaped catalyst or an unshaped catalyst. When it is a shaped catalyst, according to a preferred embodiment of the present invention, the catalyst further comprises a lubricant.

[0038] Furthermore, the lubricant is selected from at least one of graphite and carbon nanotubes.

[0039] According to a preferred embodiment of the present invention, the lubricant content is 0.5-5% based on the total mass of the catalyst. This embodiment is advantageous for improving the mechanical strength of the catalyst material.

[0040] In this invention, the content of the lubricant can be obtained by testing with an inorganic carbon-sulfur analyzer.

[0041] The present invention does not particularly limit the shape of the shaped catalyst, and it can be any shape commonly used in the art. Those skilled in the art can choose according to the actual reaction needs. Specifically, the shaped catalyst is a hollow cylinder with a height of 4-6 mm.

[0042] A second aspect of this invention provides a method for preparing a vanadium-phosphorus-oxygen catalyst, the method comprising the following steps:

[0043] (1) In the presence of a solvent, vanadium source, phosphorus source and lithium iron phosphate compound are subjected to a solvothermal reaction;

[0044] (2) Heat-treat the solid product obtained in step (1);

[0045] (3) Activate the heat-treated precursor obtained in step (2);

[0046] The method also includes a molding process performed after step (2) or after step (3).

[0047] In this invention, the range of types of vanadium sources selected in step (1) is relatively wide, and can be various vanadium-containing compounds commonly used in the art. Specifically, the vanadium source can be selected from at least one of vanadium oxide, ammonium metavanadate, and organic vanadium acid.

[0048] According to a preferred embodiment of the present invention, in step (1), the vanadium source is vanadium oxide.

[0049] Furthermore, the vanadium source is vanadium pentoxide.

[0050] According to a preferred embodiment of the present invention, in step (1), the phosphorus source may be phosphoric acid.

[0051] According to the present invention, preferably, in step (1), the phosphoric acid is provided in the form of a phosphoric acid solution.

[0052] Furthermore, the phosphoric acid solution also contains a solvent, specifically, the solvent includes, but is not limited to, water.

[0053] According to a preferred embodiment of the present invention, the mass fraction of phosphoric acid is 85-110 wt%, based on the total mass of the phosphoric acid solution.

[0054] According to a particularly preferred embodiment of the present invention, the mass fraction of phosphoric acid is 95-105 wt%, based on the total mass of the phosphoric acid solution.

[0055] In this invention, the method of adding the phosphorus source to the reaction system is not specifically limited. Conventional methods in the art can be used to add it to ensure the safe conduct of the reaction and to ensure that the phosphorus source is in uniform and sufficient contact with other reactants. Specifically, it can be slowly added to the reaction system under stirring.

[0056] According to a preferred embodiment of the present invention, the molar ratio of the vanadium source (calculated as vanadium) to the phosphorus source (calculated as phosphorus) is 0.6-1.1:1.

[0057] Furthermore, the molar ratio of the vanadium source (calculated as vanadium) to the phosphorus source (calculated as phosphorus) is 0.7-1.1:1.

[0058] In this invention, when the amounts of the vanadium source and the phosphorus source meet the above-mentioned range, the main active phase VPO can be accurately synthesized, thereby improving the catalytic activity of the catalyst.

[0059] In this invention, the source and purity of the lithium iron phosphate compound are not particularly limited. It can be prepared by conventional methods in the art or purchased directly, as long as it can provide the active lithium iron phosphate component for the reaction.

[0060] According to a preferred embodiment of the present invention, the lithium iron phosphate is high-purity lithium iron phosphate with a purity greater than 97%.

[0061] Furthermore, the lithium iron phosphate is high-purity lithium iron phosphate with a purity greater than 98%.

[0062] In this invention, when the purity of the lithium iron phosphate meets the above-mentioned range, it is possible to avoid introducing too many impurities into the reaction, which would affect the formation of the active components of the catalyst.

[0063] According to a preferred embodiment of the present invention, in step (1), the mass of the lithium iron phosphate is 0.5-5% of the mass of the vanadium source, calculated as vanadium pentoxide.

[0064] Further, in step (1), the mass of the lithium iron phosphate is 0.5-2% of the mass of the vanadium source, calculated as vanadium pentoxide.

[0065] This implementation method allows for the appropriate addition of phosphorus to the vanadium-phosphorus-oxygen catalyst, preventing a decrease in catalytic activity due to phosphorus loss. The addition of small amounts of iron and lithium can increase the active sites of the catalyst and optimize its electronic structure, resulting in higher catalyst activity.

[0066] According to a preferred embodiment of the present invention, in step (1), the solvent is an organic solvent.

[0067] According to a particularly preferred embodiment of the present invention, in step (1), the solvent is an organic alcohol.

[0068] In this invention, the type of organic alcohol is not particularly limited. It can be any organic alcohol solvent commonly used in the art that can play a reducing role in the catalyst preparation process and provide a suitable reaction environment. Specifically, the organic alcohol is selected from at least one of isobutanol, benzyl alcohol and ethylene glycol.

[0069] According to a preferred embodiment of the present invention, in step (1), the solvent is isobutanol and benzyl alcohol.

[0070] Furthermore, the molar ratio of isobutanol to benzyl alcohol is 2:1-6:1.

[0071] According to a preferred embodiment of the present invention, the mass-to-volume ratio of the vanadium source to the solvent is 0.05-0.1 g / mL.

[0072] Furthermore, the mass-to-volume ratio of the vanadium source to the solvent is 0.07-0.1 g / mL.

[0073] In this invention, when the amount of solvent added meets the above-mentioned range, the ratio of reactants helps to accurately synthesize the main active phase of the catalyst. At the same time, the reactants are evenly and stably dispersed in the reaction system, which is conducive to the smooth and complete progress of the reaction.

[0074] In this invention, the apparatus used for the solvothermal reaction in step (1) is not specifically limited. Those skilled in the art can make adjustments according to the specific circumstances of the reaction. Preferably, the solvothermal reaction is carried out under reflux conditions. There are no particular limitations on the reflux conditions, as long as the reaction system is heated to just reach the reflux state and can maintain this reflux state.

[0075] According to a preferred embodiment of the present invention, in step (1), the time for the solvothermal reaction is 2-20 h.

[0076] Furthermore, the solvothermal reaction takes 15-20 hours.

[0077] In this invention, when the conditions of the solvothermal reaction meet the above-mentioned range, the reaction can proceed fully and the probability of side reactions can be reduced, thus enabling the precise synthesis of vanadium-phosphorus-oxygen catalyst active phase materials.

[0078] In this invention, the method of separating the solid products in the mixture after the solvothermal reaction in step (1) is not particularly limited. Conventional solid-liquid separation methods in the art can be used. Specifically, it can be done by filtration.

[0079] According to the present invention, preferably, the solid product obtained in step (1) needs to be washed.

[0080] In this invention, the solution used for the washing process can be the solvent described in step (1), which will not be repeated here.

[0081] According to a preferred embodiment of the present invention, in step (2), the temperature of the heat treatment is 250-400℃, preferably 250-300℃.

[0082] According to a preferred embodiment of the present invention, in step (2), the heat treatment time is 10-25 hours, preferably 15-20 hours.

[0083] In this invention, the conditions and methods of the activation treatment are not particularly limited. They can be conventional methods for activating vanadium-phosphorus-oxygen catalysts in the art. Those skilled in the art can select the appropriate methods based on the characteristics of the obtained catalyst precursor, as long as the purpose of activating the vanadium-phosphorus-oxygen catalyst can be achieved.

[0084] According to a preferred embodiment of the present invention, in step (3), the activation treatment is carried out in the presence of at least one of oxygen-containing gas, inert gas, carbon dioxide and water vapor.

[0085] Furthermore, the inert gas is selected from at least one of nitrogen, helium, and argon.

[0086] According to a preferred embodiment of the present invention, in step (3), the temperature of the activation treatment is 250-480°C.

[0087] According to a preferred embodiment of the present invention, in step (3), the activation treatment time is 1-20h.

[0088] According to a preferred embodiment of the present invention, the activation process includes a three-stage activation process.

[0089] According to a particularly preferred embodiment of the present invention, the atmosphere for one stage of the activation treatment is air.

[0090] According to a preferred embodiment of the present invention, the temperature of the first-stage activation treatment is 200-350°C and the time is 2-5 hours.

[0091] According to a particularly preferred embodiment of the present invention, the atmosphere for the two-stage activation process is air, nitrogen, carbon dioxide and water vapor.

[0092] Further, the volume ratio of air, nitrogen, water vapor, and carbon dioxide is 1-5:1-5:3-11:1. According to a particularly preferred embodiment of the present invention, the temperature of the two-stage activation treatment is 300-450°C, and the time is 2-5 hours.

[0093] According to a particularly preferred embodiment of the present invention, the atmosphere for the three-stage activation process is nitrogen, carbon dioxide and water vapor.

[0094] Furthermore, the volume ratio of nitrogen, water vapor, and carbon dioxide is 2-10:3-9:1.

[0095] According to a preferred embodiment of the present invention, the temperature of the three-stage activation treatment is 400-450°C and the time is 2-5 hours.

[0096] According to a preferred embodiment of the present invention, the preparation method further includes a molding process performed after step (2) or after step (3).

[0097] According to a particularly preferred embodiment of the present invention, the preparation method further includes a molding process after step (2).

[0098] In this invention, the molding process is a process of mixing catalyst material and lubricant material and obtaining a catalyst of a fixed shape using conventional methods and equipment in the art. This invention does not particularly limit the methods and equipment used; specifically, it can be carried out by tableting and using a rotary tablet press.

[0099] According to a preferred embodiment of the present invention, the molding process is a tableting method.

[0100] Furthermore, the processing conditions of the tableting method include: tableting, crushing and sieving at 10-40 MPa to obtain pre-granulated particles, and then performing secondary tableting.

[0101] In this invention, the particle size of the pre-granulated particles obtained after sieving is not particularly limited. Those skilled in the art can select according to actual needs. Specifically, particles with a particle size of 20-160 mesh can be selected as pre-granulated particles.

[0102] In this invention, the crushing and screening operation methods are not particularly limited, and can be methods and means conventionally used in the field.

[0103] According to a preferred embodiment of the present invention, the vanadium-phosphorus-oxygen catalyst obtained by secondary pressing is a hollow cylindrical shape.

[0104] Furthermore, the height of the hollow cylinder is 4-6 mm.

[0105] In this invention, the hollow cylinder refers to a column structure with a circular cross-section and a hollow interior. The cross-section of the hollow part is also circular. This invention does not impose any particular limitation on the diameter of the circular cross-section of the column and the diameter of the circular cross-section of the hollow part. Those skilled in the art can make adjustments according to actual needs.

[0106] According to a preferred embodiment of the present invention, the lubricant is selected from at least one of graphite powder and carbon nanotubes.

[0107] According to a preferred embodiment of the present invention, the content of the lubricant is 0.5-5 wt%, based on the total mass of the catalyst.

[0108] The third aspect of the present invention provides a vanadium-phosphorus-oxygen catalyst prepared by the preparation method described in the second aspect above.

[0109] A fourth aspect of this invention provides the application of the vanadium-phosphorus-oxygen catalyst described in the first or third aspect above in the selective oxidation of hydrocarbons to maleic anhydride. The catalyst provided by this invention is particularly suitable for catalyzing the selective oxidation of hydrocarbons to maleic anhydride.

[0110] According to a preferred embodiment of the present invention, the application is the selective oxidation of n-butane to maleic anhydride.

[0111] The present invention does not particularly limit the specific reaction conditions for the selective oxidation of n-butane to maleic anhydride, and can be any range conventional in the art. Preferably, the volume concentration of n-butane in the raw material is 1-1.7%.

[0112] In this invention, the raw materials also contain an oxidant, which can be any oxygen-containing gas that can play an oxidizing role in the reaction system. Those skilled in the art can select the oxidant according to the actual reaction conditions. Specifically, the oxidant can be air.

[0113] According to a preferred embodiment of the present invention, the space velocity of the n-butane is 1000-3000 hr. -1 .

[0114] Furthermore, the space velocity of the n-butane is 1200-2000 hr. -1 .

[0115] In this invention, the air velocity is the gas volume passing through a unit volume of catalyst material per unit time.

[0116] According to a preferred embodiment of the present invention, the reaction temperature is 300-500°C, preferably 350-450°C.

[0117] According to a preferred embodiment of the present invention, the pressure of the reaction is 0.08 to 0.2 MPa.

[0118] This implementation method is beneficial for increasing catalyst activity and improving the conversion rate of n-butane and the selectivity of maleic anhydride.

[0119] The present invention will be described in detail below through embodiments.

[0120] Example 1

[0121] 250g of vanadium pentoxide and 5g of lithium iron phosphate compound were added to a mixed solution of 2500mL isobutanol and 1000mL benzyl alcohol. Stirring was started, and approximately 300g of 100wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 300℃ for 16 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under 20MPa pressure to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 430°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:2:5:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:5:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0122] X-ray diffraction analysis of the catalyst yielded the following results: Figure 1 As shown, the XRD pattern of the catalyst exhibits major diffraction peaks at 2θ = 12.5°, 18.5°, 20.3°, 22.8°, 25.8°, 26.5°, 28.4°, 29.3°, 29.9°, 38.0°, 43.2°, 48.5°, and 49.8°. The peaks at 2θ = 20.3°, 25.8°, and 48.5° are attributed to the diffraction peaks of the iron phosphate compound. The peaks of the lithium-formed compound overlap with those of the main VPO compound and do not show their characteristic diffraction peaks.

[0123] The obtained catalyst was applied to the selective oxidation of n-butane to maleic anhydride, with n-butane at 1.5 vol% for 2000 hr. -1 The catalyst was introduced into a fixed-bed reactor at 420°C and atmospheric pressure, and the reaction was carried out. The conversion rate of n-butane was measured to be 85.8%, and the selectivity of maleic anhydride was 64.2%. After long-term evaluation of the catalyst (120 hours), the conversion rate of n-butane was 85.2%, and the selectivity of maleic anhydride was 63.7%.

[0124] Example 2

[0125] 300g of vanadium pentoxide and 3g of lithium iron phosphate compound were added to a mixed solution of 2500mL isobutanol and 1000mL benzyl alcohol. Stirring was started, and approximately 300g of 100wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 250℃ for 16 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under a pressure of 20MPa to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 430°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:3:5:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:4:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0126] Using the same application method as in Example 1, the n-butane conversion was measured to be 85.4%, and the maleic anhydride selectivity was 63.9%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 85.0%, and the maleic anhydride selectivity was 63.4%.

[0127] Example 3

[0128] 250g of vanadium pentoxide and 10g of lithium iron phosphate compound were added to a mixed solution of 2500mL isobutanol and 1000mL benzyl alcohol. Stirring was started, and approximately 300g of 100wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 250℃ for 20 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under 20MPa pressure to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 420°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:2:5:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:5:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0129] Using the same application method as in Example 1, the n-butane conversion was measured to be 85.0%, and the maleic anhydride selectivity was 63.5%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 84.8%, and the maleic anhydride selectivity was 63.1%.

[0130] Example 4

[0131] 250g of vanadium pentoxide and 12g of lithium iron phosphate compound were added to a mixed solution of 2500mL isobutanol and 1000mL benzyl alcohol. Stirring was started, and approximately 300g of 100wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 300℃ for 16 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under 20MPa pressure to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 420°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:2:4:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:5:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0132] Using the same application method as in Example 1, the n-butane conversion was measured to be 83.0%, and the maleic anhydride selectivity was 62.8%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 82.8%, and the maleic anhydride selectivity was 62.0%.

[0133] Example 5

[0134] 250g of vanadium pentoxide and 5g of lithium iron phosphate compound were added to a mixed solution of 2500mL isobutanol and 800mL benzyl alcohol. Stirring was started, and approximately 320g of 105wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 300℃ for 20 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under 20MPa pressure to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 430°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:2:5:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:5:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0135] Using the same application method as in Example 1, the n-butane conversion was measured to be 85.4%, and the maleic anhydride selectivity was 64.0%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 85.0%, and the maleic anhydride selectivity was 63.4%.

[0136] Example 6

[0137] 300g of vanadium pentoxide and 5g of lithium iron phosphate compound were added to a mixed solution of 2400mL isobutanol and 900mL benzyl alcohol. Stirring was started, and approximately 280g of 105wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 250℃ for 16 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under a pressure of 20MPa to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 430°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:2:5:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:5:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0138] Using the same application method as in Example 1, the n-butane conversion was measured to be 85.2%, and the maleic anhydride selectivity was 63.8%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 85.0%, and the maleic anhydride selectivity was 63.1%.

[0139] Example 7

[0140] 250g of vanadium pentoxide and 3g of lithium iron phosphate compound were added to a mixed solution of 2500mL isobutanol and 1000mL benzyl alcohol. Stirring was started, and approximately 300g of 100wt% phosphoric acid was slowly added. The mixed solution was heated to reflux and maintained for 16 hours. After heating was stopped, the mixed solution was filtered and washed with isobutanol. The resulting filter cake was heat-treated at 300℃ for 16 hours to obtain a powdered catalyst precursor. The precursor, smaller than 200 mesh, was obtained after sieving and thoroughly mixed with 2% graphite powder to form a homogeneous mixture. This mixture was then pressed into tablets under a pressure of 20MPa to obtain a one-time shaped catalyst product. The tablets were then crushed, sieved, and the 20-160 mesh fraction was collected. The pre-granulated particles were transferred to a rotary tablet press with a catalyst structure height of 5mm. After rotary pressing, a hollow cylindrical vanadium phosphorus oxide catalyst was obtained. The catalyst was calcined at 250°C for 3 hours in air, then calcined at 430°C for 3 hours in an atmosphere with a volume ratio of air, nitrogen, water vapor, and carbon dioxide of 2:2:5:1, and finally calcined at 450°C for 3 hours in an atmosphere with a volume ratio of nitrogen, water vapor, and carbon dioxide of 4:5:1 to obtain the active catalyst. The compositional parameters of the catalyst are shown in Table 1.

[0141] Using the same application method as in Example 1, the n-butane conversion was measured to be 85.4%, and the maleic anhydride selectivity was 63.9%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 85.0%, and the maleic anhydride selectivity was 63.4%.

[0142] Comparative Example 1

[0143] The catalyst was prepared using the same method as in Example 1, except that no lithium iron phosphate compound was added. The composition parameters of the catalyst are shown in Table 1.

[0144] The prepared catalyst was subjected to X-ray diffraction analysis, and the results are as follows: Figure 2 As shown, the XRD pattern of the catalyst shows main diffraction characteristic peaks at 2θ = 12.5°, 18.5°, 22.8°, 26.5°, 28.4°, 29.3°, 29.9°, 38.0°, 43.2° and 49.8°. These peaks are basically characteristic diffraction peaks of vanadium pyrophosphate compounds.

[0145] Using the same application method as in Example 1, the n-butane conversion was measured to be 83.8%, and the maleic anhydride selectivity was 62.9%. After a long-term evaluation of the catalyst (120 hours), the n-butane conversion was 83.0%, and the maleic anhydride selectivity was 60.5%.

[0146] Table 1

[0147]

[0148] The data above show that the vanadium-phosphorus-oxygen catalyst obtained by the preparation method provided by this invention can improve the conversion rate of n-butane and the selectivity of maleic anhydride in the selective oxidation of n-butane to maleic anhydride. After long-term evaluation, the catalyst also has high catalytic activity.

[0149] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A vanadium-phosphorus-oxygen catalyst, characterized in that, The catalyst comprises vanadium, phosphorus, oxygen, iron, and lithium. Based on the total amount of the catalyst, the content of vanadium is 20-35% by weight, the content of phosphorus is 15-25% by weight, the content of oxygen is 40-65% by weight, the content of iron is 0.2-0.5% by weight, and the content of lithium is 0.02-0.1% by weight.

2. The catalyst according to claim 1, wherein, Based on the total amount of catalyst, the content of vanadium is 25-30% by weight, the content of phosphorus is 17-22% by weight, the content of oxygen is 48-58% by weight, the content of iron is 0.2-0.4% by weight, and the content of lithium is 0.03-0.05% by weight.

3. The catalyst according to claim 1 or 2, wherein, Iron, lithium, and a portion of phosphorus, expressed as lithium iron phosphate, constitute 0.5-5% by weight of vanadium, expressed as vanadium pentoxide, preferably 0.5-2% by weight.

4. The catalyst according to any one of claims 1-3, wherein, In the catalyst, at least a portion of the phosphorus and iron elements exist in the form of iron phosphate; And / or, as characterized by XRD, the catalyst has diffraction peaks at 2θ of 20.3°±0.2°, 25.8°±0.2° and 48.5°±0.2°; Preferably, the catalyst has diffraction peaks at 2θ of 12.5°±0.2°, 18.5°±0.2°, 20.3°±0.2°, 22.8°±0.2°, 25.8°±0.2°, 26.5°±0.2°, 28.4°±0.2°, 29.3°±0.2°, 29.9°±0.2°, 38.0°±0.2°, 43.2°±0.2°, 48.5°±0.2°, and 49.8°±0.2°.

5. A method for preparing a vanadium-phosphorus-oxygen catalyst, characterized in that, The method includes the following steps: (1) In the presence of a solvent, vanadium source, phosphorus source and lithium iron phosphate compound are subjected to a solvothermal reaction; (2) Heat-treat the solid product obtained in step (1); (3) Activate the heat-treated precursor obtained in step (2); The method also includes a molding process performed after step (2) or after step (3).

6. The method according to claim 5, wherein, In step (1), the vanadium source is selected from at least one of vanadium oxide, ammonium metavanadate, and organic vanadium acid, preferably vanadium oxide; Preferably, the vanadium source is vanadium pentoxide; In step (1), the phosphorus source is phosphoric acid; Preferably, the molar ratio of the vanadium source (calculated as vanadium) to the phosphorus source (calculated as phosphorus) is 0.6-1.1:1, more preferably 0.7-1.1:

1.

7. The method according to claim 5 or 6, wherein, In step (1), the mass of the lithium iron phosphate is 0.5-5% of the mass of the vanadium source, calculated as vanadium pentoxide, preferably 0.5-2%.

8. The method according to any one of claims 5-7, wherein, In step (1), the solvent is an organic solvent; Preferably, the solvent is an organic alcohol; Preferably, the mass-to-volume ratio of the vanadium source to the solvent is 0.05-0.1 g / mL.

9. The method according to any one of claims 5-8, wherein, In step (1), the solvothermal reaction is carried out under reflux conditions, preferably for 2-20 hours; And / or, in step (2), the heat treatment temperature is 250-400℃ and the time is 10-25h; And / or, in step (3), the activation treatment conditions include: being carried out in the presence of at least one of oxygen-containing gas, inert gas, carbon dioxide and water vapor, at a temperature of 250-480°C, and for a time of 1-20h.

10. A vanadium-phosphorus-oxygen catalyst prepared by the method of any one of claims 5-9.

11. The use of a vanadium-phosphorus-oxygen catalyst according to any one of claims 1-4, 10 in the selective oxidation of hydrocarbons to maleic anhydride.

12. The application according to claim 11, wherein, The application is the selective oxidation of n-butane to maleic anhydride; Preferably, the process conditions for the application include: a n-butane concentration of 1-1.7% by volume and a space velocity of 1000-3000 hr. -1 The temperature is 300-500℃ and the pressure is 0.08-0.2MPa.

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