Preparation and application of vanadium-phosphorus-oxygen catalyst

Abstract

The application discloses a vanadium-phosphorus-oxygen catalyst with high activity and stability, which is prepared by introducing S, Se and B-containing compounds in the process of synthesizing the vanadium-phosphorus-oxygen catalyst. The catalyst prepared by the application has very good low-temperature reaction activity and good stability in selective oxidation of hydrocarbons. In particular, in the reaction of preparing maleic anhydride by selectively oxidizing n-butane, the catalyst can reach 65% of the molar yield of maleic anhydride, greatly reduces the reaction temperature, and maintains good reaction stability. The vanadium-phosphorus-oxygen catalyst prepared by the application does not use expensive metal additives, has higher reaction stability, and has a long catalyst replacement cycle. Since the reaction can reach the ideal yield of maleic anhydride at a lower temperature, the generation and emission of carbon monoxide and carbon dioxide are reduced, the device temperature is effectively prevented from rising due to the thermal effect, and the production safety is ensured.

Description

Technical Field

[0001] This application relates to a catalyst, specifically a modified vanadium-phosphorus-oxygen catalyst, for the preparation of maleic anhydride. Background Technology

[0002] Maleic anhydride (MA), one of the world's three major acid anhydrides (acetic anhydride, phthalic anhydride, and maleic anhydride), has the molecular formula C4H2O3. It is soluble in water and most organic solvents (acetone, benzene, chloroform) and is an important chemical intermediate widely used in the petrochemical industry to prepare organic chemicals such as 1,4-butanediol, tetrahydrofuran, and fumaric acid. There are many processes for preparing MA, but currently the main processes worldwide are the n-butane oxidation method and the benzene oxidation method. The benzene oxidation method was the main method for producing MA in the mid-19th century, using a VMoO composite oxide catalyst. This method involves simultaneously introducing benzene vapor and air into a VMoO catalyst bed for the reaction, resulting in a strongly exothermic reaction. Due to its low conversion rate, poor MA selectivity, and the high price, toxicity, and environmental unfriendliness of benzene, this process has gradually been replaced by the n-butane oxidation method for MA. Currently, the most efficient catalyst for the n-butane oxidation of MA is the vanadium phosphorus oxide (VPO) catalyst, which is the only industrially successful catalyst for converting low-carbon alkanes into high-value-added chemicals. However, current VPO catalysts still require further performance improvement. According to patent literature, the molar yield of n-butane oxidation to MA has so far been between 57% and 65%, indicating that there is still significant room for improvement in VPO catalysts.

[0003] For many years, researchers have conducted extensive studies on the preparation and modification of VPO catalysts, aiming to explore an ideal catalyst that is easy to synthesize and has a low cost, and to further improve its catalytic performance for the selective oxidation of n-butane to MA.

[0004] The performance of VPO catalysts is greatly influenced by the preparation method. Different methods yield different catalytic materials, exhibiting variations in microstructure, surface valence state, pH, and redox properties. Since VPO catalysts require further activation with their precursor VOHPO4·0.5H2O (VHP), the synthesized VHP precursor also determines the performance of the VPO catalyst. Three main methods are commonly used to prepare the VHP precursor for VPO catalysts: the VPA method, the VPO method, and the VPD method.

[0005] The VPA method was the earliest method used to prepare VPO catalysts. This method uses water as a solvent, heating V₂O₅ and hydrochloric acid solution together under reflux. 5+ Restored to V 4+The solution is then reacted with added H3PO4, and after further heating under reflux for a certain period of time, the resulting solution is evaporated to obtain the green precursor VHP. This method is corrosive, more complex than other methods, and uses a catalyst with a small specific surface area. It also contains a certain amount of VO(H2PO4)2, which is detrimental to the reaction. After heat treatment, VO(PO3)2 and amorphous vanadium oxyphosphate are generated. The catalyst activity is low, resulting in low MA yield. Therefore, this method has been gradually phased out.

[0006] The VPD method involves heating V₂O₅ with a large amount of H₃PO₄ and water under reflux. The reaction in water forms VOPO₄·2H₂O. The solid is then filtered, washed, and dried. VOPO₄·2H₂O is then mixed with an alcohol solvent and heated under reflux again, gradually reducing it to the precursor VHP. The morphology and surface properties of the catalyst can be controlled by changing the type and amount of alcohol solvent. This method can synthesize VPO catalysts with a large specific surface area. However, the synthesis process uses a significant excess of phosphoric acid and involves two major steps, increasing the preparation cost. Furthermore, the synthesized catalyst contains other impurity phases, resulting in a relatively low content of the reactive phase and ultimately a low yield of the product MA.

[0007] The VPO method is considered the standard approach for synthesizing VPO catalysts due to its few steps and simple preparation process. This method involves heating V₂O₅ and H₃PO₄ together with a reducing agent (alcohol or aldehyde) under reflux for a certain time, followed by filtration, washing, and drying to obtain the catalyst precursor VHP. However, currently, VPO catalysts synthesized via the VPO method exhibit low reactivity, with both the selectivity and yield of the target product MA being very low. Therefore, the performance of VPO catalysts synthesized via the VPO method needs further improvement.

[0008] For the modification of VPO catalysts, the structural properties of the catalyst are often improved by adding different promoters, pore-forming agents, surfactants and supports. These promoters, pore-forming agents, surfactants and supports can act as structure directing agents or electron directing agents or increase the specific surface area of ​​the catalyst, expose more active sites, and thus improve the appearance and physicochemical properties of the catalyst.

[0009] There are some reports in literature and patents regarding the addition of one or more auxiliaries, pore-forming agents, surfactants, and supports. For example, Chinese Patent Application Publication No. CN1090224 reports a matrix powder obtained by reducing V2O5, H3PO4, and ZnSO4 with a fourth component in alcohols. Modified starch and other excipients are then added to this matrix powder, and the mixture is extruded and pelletized in an extruder to obtain the desired catalyst for the selective oxidation of n-butane to prepare MA. The fourth component is selected from rare earth metals such as Er, Ho, Gd, and Tb, and transition metals such as Mo, Fe, Co, and Ni. The molar yield of maleic anhydride on this catalyst is 59.8%–70.4%. Chinese Patent Application Publication No. CN104971750A reports a method for preparing an alkali metal-modified VPO catalyst. The alkali metal accounts for 10–400 ppm of the VPO catalyst by weight. This alkali metal-modified VPO catalyst significantly improves the conversion rate and selectivity of the target product in the oxidation of hydrocarbons. However, lower alkali metal contents have no effect on improving these properties. When the alkali metal content is too high, the catalyst may be poisoned, which in turn greatly reduces the performance of the catalyst.

[0010] Existing technologies for synthesizing and modifying VPO catalysts have drawbacks such as complex preparation processes, expensive or toxic additives, low catalyst activity, low yield, or poor stability. Summary of the Invention

[0011] One object of this application is to provide a vanadium phosphorus oxide (VPO) catalyst that, when modified with S, Se, or B elements, can improve the conversion rate of butane to maleic anhydride.

[0012] The second objective of this application is to provide a vanadium-phosphorus-oxygen catalyst that improves the conversion rate and selectivity of maleic anhydride in the preparation of maleic anhydride from butane.

[0013] The third objective of this application is to improve the stability of vanadium phosphorus oxygen catalysts.

[0014] The fourth objective of this application is to provide a method for preparing a modified vanadium phosphorus oxide (VPO) catalyst, wherein the modified vanadium phosphorus oxide catalyst obtained by this method has better catalytic activity.

[0015] The fifth objective of this application is the application of modified vanadium-phosphorus-oxygen catalysts in the reaction system for preparing maleic anhydride from alkanes.

[0016] On one hand, a modified vanadium-phosphorus-oxygen (VPO) catalyst is composed of vanadium oxide, phosphorus oxide, and a modifying component, wherein the modifying component is a non-metallic element S, Se, or / and B.

[0017] Vanadium-phosphorus-oxygen catalysts modified with nonmetallic elements S, Se, and / or B exhibit excellent catalytic activity in the preparation of maleic anhydride from butane.

[0018] This catalyst is used to prepare maleic anhydride from butane, which can improve the conversion rate of butane.

[0019] On the other hand, a method for preparing a modified vanadium-phosphorus oxide (VPO) catalyst includes heating and mixing a vanadium-containing compound and a phosphorus-containing compound in a solvent to obtain a first suspension, filtering the suspension to obtain a filter residue, drying the filter residue to obtain a first solid, mixing a solution containing S, Se, and / or B elements with the first solid, and drying the mixture to obtain a modified vanadium-phosphorus oxide catalyst precursor.

[0020] An alternative method for preparing a modified vanadium-phosphorus oxide (VPO) catalyst includes heating and mixing a vanadium-containing compound, a phosphorus-containing compound, and a solution containing S, Se, and / or B elements in a solvent to obtain a second suspension, filtering the suspension to obtain a filter residue, and drying the filter residue to obtain a modified vanadium-phosphorus oxide catalyst precursor.

[0021] It should be noted that the high-temperature treatment of the above-mentioned modified vanadium phosphorus oxygen catalyst precursor yields an active catalyst. The high-temperature treatment step can also be carried out in the atmosphere used for preparing maleic anhydride from butane, or it can be activated in an oxidizing atmosphere.

[0022] The method for preparing the modified vanadium-phosphorus-oxygen catalyst is simple, and the catalyst can improve the conversion rate of butane in the butane-to-maleic anhydride production system. Attached Figure Description

[0023] Figure 1 To characterize the stability of the catalyst in Example 13

[0024] Figure 2 To characterize the stability of the catalyst in Example 14

[0025] Figure 3 To characterize the stability of the catalyst in Example 15

[0026] Figure 4 To characterize the stability of the catalyst in Comparative Example 3

[0027] Figure 5 XRD patterns of the catalyst of this application and the catalyst of the comparative example.

[0028] Figure 6 NH3-TPD diagrams of the catalyst of this application and the catalyst of the comparative example.

[0029] Figure 7 This is a scanning electron microscope image of the catalyst of this application. Detailed Implementation

[0030] The following is a more detailed description of a modified vanadium-phosphorus-oxygen catalyst according to this application. This description does not limit the scope of protection of this application; rather, the scope of protection is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.

[0031] Unless the context otherwise requires, the terms “comprising” and “including” in the specification and claims shall be understood as open-ended and inclusive, meaning “including, but not limited to”.

[0032] The terms "implementation," "an implementation," "another implementation," or "certain implementations" used in this specification refer to specific features, structures, or characteristics described in relation to the implementation, which are included in at least one implementation. Therefore, "implementation," "an implementation," "another implementation," or "certain implementations" do not necessarily all refer to the same implementation. Furthermore, specific features, structures, or characteristics can be combined in any way within one or more implementations. Each feature disclosed in this specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0033] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0034] Maleic anhydride (MA) is short for maleic anhydride, also known as maleic anhydride.

[0035] "Mass hourly space velocity" is the ratio of the mass of feed to the mass of catalyst per unit time.

[0036] To address the shortcomings of existing VPO catalysts, such as complex preparation processes, expensive or toxic additives, low catalyst activity, low yield, and poor stability, this application introduces non-metallic S, Se, or B compounds into the synthesis process of an improved vanadium-phosphorus-oxygen catalyst. This allows for the control of the final catalyst's surface morphology, surface acidity, V valence state, and the reactivity of different crystal phases and lattice oxygens, thereby significantly altering the catalyst's reaction behavior. This modified vanadium-phosphorus-oxygen catalyst exhibits superior performance in the selective oxidation of hydrocarbons, particularly suitable for the selective oxidation of n-butane to MA.

[0037] A modified vanadium-phosphorus-oxygen (VPO) catalyst is composed of vanadium oxide, phosphorus oxide, and a modifying component, wherein the modifying component is a non-metallic element S, Se, or / and B.

[0038] In one embodiment, the molar ratio of phosphorus to vanadium in the catalyst is (0.9 to 1.4):1.

[0039] Preferably, in the catalyst, the molar ratio of phosphorus to vanadium is (1-1.2):1.

[0040] The molar ratio of the added modifying component S, Se, or B to vanadium is (0.1–20):100. Preferably, the molar ratio of the modifying component to vanadium is (0.5–5):100.

[0041] By introducing S, Se, or B elements as modifying components, the surface morphology, V valence state, crystal phase, and lattice oxygen of the catalyst are regulated, thereby modifying the catalytic performance of the catalyst.

[0042] In some embodiments, the modifying component is Se or B. These two non-metallic elements can further improve the catalytic performance of vanadium-phosphorus oxide in the preparation of maleic anhydride.

[0043] The catalyst in this application is mainly composed of tetravalent vanadium, with a small amount of pentavalent vanadium.

[0044] On the other hand, a method for preparing a modified vanadium-phosphorus-oxygen catalyst includes heating and mixing a vanadium-containing compound and a phosphorus-containing compound in a solvent to obtain a first suspension, filtering the suspension to obtain a filter residue, drying the filter residue to obtain a first solid, mixing a solution containing S, Se, and / or B elements with the first solid, and drying the mixture to obtain a modified vanadium-phosphorus-oxygen catalyst precursor.

[0045] An alternative method for preparing a modified vanadium-phosphorus oxide (VPO) catalyst includes heating and mixing a vanadium-containing compound, a phosphorus-containing compound, and a solution containing S, Se, and / or B elements in a solvent to obtain a second suspension, filtering the suspension to obtain a filter residue, and drying the filter residue to obtain a modified vanadium-phosphorus oxide catalyst precursor.

[0046] In some embodiments, the solvent is selected from one or a mixture of several of the following: ethanol, n-propanol, isopropanol, propanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, and benzyl alcohol.

[0047] In the preparation method of this application, the solvent is preferably one or a mixture of several of n-butanol, isobutanol and benzyl alcohol; more preferably a mixture of n-butanol and isobutanol.

[0048] The solvent here also acts as a reducing agent, reducing the vanadium element in vanadium-containing compounds.

[0049] In one embodiment, the solvent is a mixture of isobutanol and benzyl alcohol, wherein the mass ratio of isobutanol to benzyl alcohol is 1:9 to 9:1. Preferably, the mass ratio of isobutanol to benzyl alcohol is 1:5 to 5:1.

[0050] In another embodiment, the solvent is a mixture of isobutanol and n-butanol, wherein the mass ratio of isobutanol to n-butanol is 1:9 to 9:1. Preferably, the mass ratio of isobutanol to n-butanol is 1:5 to 5:1.

[0051] A modified vanadium-phosphorus oxygen catalyst prepared by using a mixture of isobutanol and n-butanol as a solvent or reducing agent exhibits better catalytic performance in the reaction system for preparing maleic anhydride.

[0052] In some embodiments, the vanadium in the vanadium-containing compound is in the pentavalent state. For example, vanadium pentoxide.

[0053] When vanadium-containing material is selected as vanadium pentoxide, the mass ratio of solvent to vanadium pentoxide is (2-50):1. Preferably, the mass ratio of solvent to vanadium pentoxide is (5-20):1. More preferably, the mass ratio of solvent to vanadium pentoxide is (8-15):1.

[0054] The phosphorus-containing compound is preferably phosphoric acid or pyrophosphate, and more preferably phosphoric acid.

[0055] The amount of phosphorus-containing compound used should meet the requirement that the molar ratio of phosphorus to vanadium is (0.9–1.4):1.

[0056] In some embodiments, the formation of the first or second suspension is carried out under conditions of heating and reflux at a temperature of 80–160°C.

[0057] Preferably, the heating reflux temperature is 100–150°C.

[0058] More preferably, the heating reflux temperature is 120–140°C.

[0059] At reflux temperatures of 80–160 °C, vanadium in the pentavalent state is easily reduced in the reaction system of this application, which is beneficial for forming the catalyst morphology of this application.

[0060] In some embodiments, the vanadium-containing compound or a mixture of the vanadium-containing compound and the modified component is first heated and refluxed in a solvent for a period of time, and then the phosphorus-containing compound is added, and the heating and reflux is continued.

[0061] Adding a phosphorus-containing compound to the vanadium-containing compound after reflux for a period of time can change the acidity or alkalinity of the reaction solution, thus allowing for better control of the crystal growth rate and morphology in the reaction system.

[0062] Preferably, the vanadium-containing compound or a mixture of a vanadium-containing compound and a substance containing a modifying component is refluxed in a solvent at a temperature ranging from 80 to 160°C for 1 / 24 to 3 / 4 of the total reflux time. More preferably, it is 1 / 8 to 1 / 2 of the total reflux time.

[0063] The total reflux time is 6h to 72h, preferably 12h to 48h, and more preferably 16h to 24h.

[0064] The total reflux time mentioned above refers to the sum of the reflux time of the vanadium-containing compound or the mixture of the vanadium-containing compound and the modified component in the solvent, as well as the reflux time after the addition of the phosphorus-containing compound.

[0065] The filter residue after filtering the first or second suspension is washed with a washing solution, which can be repeated several times to remove as much solvent as possible from the mixture. Preferably, the washing solution can be water, ethanol, or acetone, and the preferred washing method is to wash with water first, followed by washing with ethanol.

[0066] In some embodiments, the filter residue or the first solid loaded with the modified component is dried at a temperature of 60–180°C. Preferably, the drying temperature is 80–160°C.

[0067] Generally, the drying time is not limited; the solvent content can be dried to a certain extent. The drying time for this application is 8 hours to 48 hours, preferably 12 hours to 24 hours.

[0068] In some embodiments, the high-temperature treatment is carried out in an oxygen-containing atmosphere at a temperature controlled between 350 and 450°C.

[0069] Preferably, the high-temperature treatment is carried out in an oxygen-containing atmosphere at a temperature controlled between 370 and 420°C.

[0070] The desired catalyst can be obtained by reacting under or near-reaction conditions in the atmosphere used for preparing maleic anhydride for a period of time. Alternatively, the catalyst can be obtained by treating the catalyst sequentially or simultaneously with air, or a mixture of air, nitrogen, and water vapor for a period of time.

[0071] The modifying component is a compound containing S, Se, or B, including its organic compounds, oxides, oxyacids, or oxyacid salts. Preferably, it contains oxides or oxyacids containing S, Se, or B. The amount used should satisfy the molar ratio of the added modifying component S, Se, or B to vanadium as (0.1–20):100.

[0072] The modified vanadium-phosphorus-oxygen catalyst prepared in this application has a small particle size and a large specific surface area (~31.3 m²). 2 The catalyst has many active sites and high reactivity ( / g).

[0073] The modified vanadium-phosphorus-oxygen catalyst prepared by the above method exhibits good stability and maintains high activity in the reaction system for preparing maleic anhydride.

[0074] Furthermore, the modified vanadium-phosphorus-oxygen catalyst described above is applied to hydrocarbon selective oxidation systems. Preferably, it is applied in the selective oxidation of n-butane to prepare maleic anhydride.

[0075] This catalyst can be applied to different reaction processes, such as fixed-bed processes, fluidized-bed processes, and moving-bed processes.

[0076] In some embodiments, the modified vanadium-phosphorus-oxygen catalyst described above is applied to a reaction system for the selective oxidation of n-butane to prepare maleic anhydride, at a reaction temperature of 350–450 °C.

[0077] Preferably, the above-mentioned modified vanadium-phosphorus-oxygen catalyst is applied to the reaction system for the selective oxidation of n-butane to prepare maleic anhydride, and the reaction temperature is 370-420℃.

[0078] Whether an oxidant should be added to the reaction system, for example: the oxidant can be a gas containing oxygen, including air or pure oxygen.

[0079] In some embodiments, the oxidant is air, and under the same conditions, n-butane accounts for 1-2% of the volume fraction of the feed mixture.

[0080] The aforementioned feed mixture includes n-butane and air.

[0081] Same conditions refer to the same temperature and pressure.

[0082] Mass hourly space velocity 1500–2500 h -1 .

[0083] In the reaction system for the selective oxidation of n-butane to prepare maleic anhydride, the selectivity of maleic anhydride is over 60%, and the conversion rate of n-butane is over 80%, even as high as 99%.

[0084] The highly active and stable vanadium-phosphorus-oxygen catalyst provided by this invention has the following technical advantages compared with vanadium-phosphorus-oxygen catalysts synthesized and modified by traditional methods:

[0085] Compared with traditional methods that introduce noble metal or transition metal compounds as promoters of vanadium-phosphorus-oxygen catalysts, this invention introduces non-metallic compounds of S, Se, or B as promoters of vanadium-phosphorus-oxygen catalysts for the first time, reducing the increased costs caused by introducing expensive metal promoters and also reducing environmental pollution caused by introducing toxic transition metals.

[0086] The modified vanadium-phosphorus-oxygen catalyst prepared by this invention exhibits good low-temperature reaction activity and stability. Compared with vanadium-phosphorus-oxygen catalysts prepared by traditional methods, the yield of MA is increased by more than 10%, significantly improving production efficiency. Furthermore, the reaction temperature can be reduced to around 385℃, greatly reducing the generation and emission of carbon monoxide and carbon dioxide, while avoiding overheating of the equipment due to thermal effects, thus ensuring production safety.

[0087] The good low-temperature reactivity and stability extend the service life of the catalyst, which not only greatly reduces the cost of using the catalyst, but also reduces the operating and investment costs of tail gas treatment and production equipment.

[0088] The present invention will be further described in detail below with reference to specific embodiments. The implementation of the present invention is not limited thereto, and the embodiments do not limit the scope of protection of the present invention.

[0089] The substances used in the following examples are all chemically pure standards and are all commercially available products.

[0090] Example 1

[0091] 10 g V₂O₅, 80 g isobutanol, and 20 g benzyl alcohol were added to a three-necked flask. The mixture was heated and refluxed in an oil bath at 130 °C for 6 h with stirring. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system. The mixture was heated and refluxed for another 18 h with stirring to obtain a pale blue suspension. This suspension was filtered while hot, washed with copious amounts of deionized water, and finally washed with ethanol. The resulting pale blue filter cake was placed in an oven at 140 °C and dried for 12 h. An equal volume of the dried catalyst powder was impregnated with a certain amount of sulfuric acid solution, resulting in an atomic molar ratio of S to V of S / V = 2:100. The impregnated catalyst was then dried overnight in an oven at 140 °C to obtain the catalyst precursor VHP.

[0092] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 80.56%, the MA molar selectivity was 60.21%, and the MA molar yield was 48.51%.

[0093] The molar yield is the product of the conversion of n-butane and the selectivity of MA.

[0094] Example 2

[0095] 10 g V₂O₅, 50 g isobutanol, and 50 g n-butanol were added to a three-necked flask. The mixture was heated and refluxed in an oil bath at 130 °C for 6 h with stirring. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system. The mixture was heated and refluxed for another 18 h with stirring to obtain a pale blue suspension. This suspension was filtered while hot, washed with copious amounts of deionized water, and finally washed with ethanol. The resulting pale blue filter cake was placed in an oven at 140 °C and dried for 12 h. An equal volume of the dried catalyst was impregnated with a selenic acid solution, resulting in an atomic molar ratio of Se to V of Se / V = 2:100. The impregnated catalyst was then dried overnight in an oven at 140 °C to obtain the catalyst precursor VHP.

[0096] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 99.21%, the MA molar selectivity was 61.56%, and the MA molar yield was 61.07%.

[0097] Example 3

[0098] 10 g V₂O₅, 20 g isobutanol, and 80 g n-butanol were added to a three-necked flask. The mixture was heated and refluxed in an oil bath at 130 °C for 6 h with stirring. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system. The mixture was heated and refluxed for another 18 h with stirring to obtain a pale blue suspension. This suspension was filtered while hot, washed with copious amounts of deionized water, and finally washed with ethanol. The resulting pale blue filter cake was placed in an oven at 140 °C and dried for 12 h. An equal volume of the dried catalyst was impregnated with boric acid solution, resulting in an atomic molar ratio of B to V of B / V = 2:100. The impregnated catalyst was then dried overnight in an oven at 140 °C to obtain the catalyst precursor VHP.

[0099] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction stabilized for a period of time. The measured n-butane conversion was 98.08%, the MA molar selectivity was 59.60%, and the MA molar yield was 58.46%.

[0100] Example 4

[0101] 10 g V₂O₅, 20 g isobutanol, and 80 g n-butanol were added to a three-necked flask and heated under reflux in an oil bath at 130 °C for 6 h. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system, and the mixture was heated under reflux for another 18 h to obtain a pale blue suspension. This suspension was filtered while hot, washed with copious amounts of deionized water, and finally washed with ethanol. The resulting pale blue filter cake was placed in an oven at 140 °C and dried for 12 h. An equal volume of the dried catalyst was impregnated with a selenic acid solution, resulting in an atomic molar ratio of Se to V of 3:100. The impregnated catalyst was then dried overnight in an oven at 140 °C to obtain the catalyst precursor VHP.

[0102] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 99.3%, the MA molar selectivity was 60.10%, and the MA molar yield was 59.68%.

[0103] Example 5

[0104] 10 g V₂O₅, 20 g isobutanol, 80 g n-butanol, and 1.596 g of 40% selenic acid solution were added to a three-necked flask. The mixture was heated under reflux in an oil bath at 130 °C for 6 h. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system. The mixture was heated under reflux for another 18 h to obtain a light blue suspension. The suspension was filtered while hot, washed with a large amount of deionized water, and then washed with ethanol. The resulting light blue filter cake was placed in an oven at 140 °C and dried for 12 h to obtain the catalyst precursor VHP.

[0105] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹.-1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 96.5%, the MA molar selectivity was 63.15%, and the MA molar yield was 60.94%.

[0106] Example 6

[0107] 10 g V₂O₅, 20 g isobutanol, 80 g n-butanol and 0.272 g boric acid were added to a three-necked flask and heated under reflux in an oil bath at 130 °C for 6 h. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system and the mixture was heated under reflux for another 18 h to obtain a light blue suspension. The suspension was filtered while hot, washed with a large amount of deionized water, and then washed with ethanol. The resulting light blue filter cake was placed in an oven at 140 °C and dried for 12 h to obtain the catalyst precursor VHP.

[0108] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 98.2%, the MA molar selectivity was 60.1%, and the MA molar yield was 59.02%.

[0109] Example 7

[0110] 10 g V₂O₅, 20 g isobutanol, 80 g n-butanol and 0.153 g boron oxide were added to a three-necked flask and heated under reflux in an oil bath at 130 °C for 6 h. Then, 13.95 g of 85% phosphoric acid solution was gradually added to the reaction system and the mixture was heated under reflux for another 18 h to obtain a light blue suspension. The suspension was filtered while hot, washed with a large amount of deionized water, and then washed with ethanol. The resulting light blue filter cake was placed in an oven at 140 °C and dried for 12 h to obtain the catalyst precursor VHP.

[0111] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 97.3%, the MA molar selectivity was 60.8%, and the MA molar yield was 59.16%.

[0112] Example 8

[0113] 10g V₂O₅, 20g isobutanol, and 80g n-butanol were added to a three-necked flask and heated under reflux in an oil bath at 130°C for 6 hours. Then, 13.95g of 85% phosphoric acid solution was gradually added to the reaction system, and the mixture was heated under reflux for another 18 hours to obtain a light blue suspension. The suspension was filtered while hot, washed with a large amount of deionized water, and then washed with ethanol. The resulting light blue filter cake was placed in an oven at 140°C and dried for 12 hours. The dried catalyst was then impregnated with an equal volume of sodium sulfate solution, such that the atomic molar ratio of S to V was S / V = 1:100. The impregnated catalyst was then dried in an oven at 140°C overnight.

[0114] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 82.31%, the MA molar selectivity was 59.15%, and the MA molar yield was 48.69%.

[0115] Example 9

[0116] 10g V₂O₅, 20g isobutanol, and 80g n-butanol were added to a three-necked flask and heated under reflux in an oil bath at 130°C for 6 hours. Then, 13.95g of 85% phosphoric acid solution was gradually added to the reaction system, and the mixture was heated under reflux for another 18 hours to obtain a light blue suspension. The suspension was filtered while hot, washed with a large amount of deionized water, and then washed with ethanol. The resulting light blue filter cake was placed in an oven at 140°C and dried for 12 hours. The dried catalyst was then impregnated with an equal volume of sodium selenate solution, such that the atomic molar ratio of Se to V was Se / V = 4:100. The impregnated catalyst was then dried in an oven at 140°C overnight.

[0117] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 98.03%, the MA molar selectivity was 61.21%, and the MA molar yield was 60.00%.

[0118] Example 10

[0119] 10g V₂O₅, 20g isobutanol, and 80g n-butanol were added to a three-necked flask and heated under reflux in an oil bath at 130°C for 6 hours. Then, 13.95g of 85% phosphoric acid solution was gradually added to the reaction system, and the mixture was heated under reflux for another 18 hours to obtain a light blue suspension. The suspension was filtered while hot, washed with a large amount of deionized water, and then washed with ethanol. The resulting light blue filter cake was placed in an oven at 140°C and dried for 12 hours. The dried catalyst was then impregnated with an equal volume of sodium borate solution, such that the atomic molar ratio of B to V was B / V = 3:100. The impregnated catalyst was then dried in an oven at 140°C overnight.

[0120] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 97.88%, the MA molar selectivity was 60.72%, and the MA molar yield was 59.43%.

[0121] The following examples or comparative examples test the activity of the catalyst in the reaction system for the preparation of maleic anhydride from n-butane. The reaction conditions (such as space velocity, n-butane and air mixture content, etc.) are as described in Example 3.

[0122] Example 11

[0123] The catalyst preparation and activation were the same as in Example 4, except that the reaction temperature was lowered to 385°C, and the reaction stabilized for a period of time. The measured n-butane conversion was 93.26%, the MA molar selectivity was 69.68%, and the MA molar yield was 64.98%.

[0124] Example 12

[0125] The catalyst preparation and activation were the same as in Example 3, except that the reaction temperature was lowered to 385°C, and the reaction stabilized for a period of time. The measured n-butane conversion was 92.75%, the MA molar selectivity was 66.88%, and the MA molar yield was 62.03%.

[0126] Example 13

[0127] The catalyst was prepared and activated as in Example 3, activated at 410℃ for 8 h, reacted at 400℃ for 40 h, and then reacted at 385℃ for 160 h. The changes in n-butane conversion, MA selectivity, and MA yield over time are shown in [Figure Number]. Figure 1 .

[0128] Example 14

[0129] The catalyst was prepared and activated as in Example 4, activated at 410℃ for 8 h, reacted at 400℃ for 40 h, and then reacted at 385℃ for 160 h. The changes in n-butane conversion, MA selectivity, and MA yield over time are shown in [Figure Number]. Figure 2 .

[0130] Example 15

[0131] The catalyst preparation and activation were the same as in Example 5, involving activation at 410℃ for 8 h, reaction at 400℃ for 40 h, and then reaction at 385℃ for 160 h. The changes in n-butane conversion, MA selectivity, and MA yield over time are shown in [Figure Number]. Figure 3 .

[0132] Comparative Example 1

[0133] The method for preparing the catalyst precursor in this comparative example is basically the same as the process and parameters in Example 1, except that the step of adding sulfuric acid solution and subsequent steps are omitted. The light blue filter cake was placed in an oven at 140°C and dried for 12 hours to obtain the catalyst precursor.

[0134] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 71.03%, the MA molar selectivity was 64.28%, and the MA molar yield was 45.66%.

[0135] Comparative Example 2

[0136] The method for preparing the catalyst precursor in this comparative example is basically the same as the process and parameters in Example 3, except that the step of adding boric acid solution and subsequent steps are omitted. The light blue filter cake was placed in an oven at 140°C and dried for 12 hours to obtain the catalyst precursor.

[0137] The catalyst precursor VHP was tableted, screened to obtain 40-60 mesh particles, and placed in a fixed-bed reactor. The reactor was operated at a space velocity of 2000 h⁻¹. -1 In an atmosphere of air and a mixture of n-butane with a n-butane concentration of 1.7%, the temperature was increased to 410℃ at a heating rate of 5℃ / min, and activated for 8 hours. The temperature was then lowered to 400℃, and the reaction was allowed to stabilize for a period of time. The measured n-butane conversion was 86.91%, the MA molar selectivity was 63.94%, and the MA molar yield was 55.57%.

[0138] Comparative Example 3

[0139] The catalyst prepared in Comparative Example 2 was subjected to stability tests. After activation at 410℃ for 8 h, the catalyst was reacted at 400℃ for 40 h, followed by a further reaction at 385℃ for 160 h. The changes in n-butane conversion, MA selectivity, and MA yield over time are shown in the figure. Figure 4 Experimental Example 1

[0140] X-ray powder diffraction analysis was performed on the vanadium-phosphorus-oxygen catalysts prepared in Examples 1-4 (catalysts containing modified components) and Comparative Examples 1-2 (catalysts without modified components). The X-ray diffraction (XRD) patterns of the catalysts were obtained on a diffractometer (X'Pert PRO MPD) using Cu Kα radiation at 40 kV and 40 mA. The results are as follows. Figure 5 As shown in the XRD patterns of the catalysts before and after modification, it can be seen that the intensity and full width at half maximum (FWHM) of the (200) active crystal plane diffraction peak at 2θ = 23° of the modified catalyst are significantly increased, indicating that the crystallite size of the modified catalyst is smaller and the content of the (200) active crystal plane is higher.

[0141] Experimental Example 2

[0142] The acid sites / acidity of the vanadium-phosphorus oxygen catalysts prepared in Examples 1-4 (catalysts containing modified components) and Comparative Example 1 (catalyst without modified components) were characterized. The NH3-TPD spectra of the catalysts were determined using a PCA-1200 chemisorption analyzer. Approximately 0.1 g of sample was heated at 600 °C (30 ml / min) for 1 h under He conditions, then cooled and stabilized at 100 °C, followed by NH3 (2% NH3 / N2) adsorption for 30 min. Finally, the temperature was increased from 100 °C to 900 °C at a rate of 10 °C / min under a He (30 ml / min) atmosphere. The results are attached. Figure 6 The NH3-TPD shown.

[0143] As can be seen from the NH3-TPD diagrams before and after modification, the acidity content of the modified catalyst is significantly increased, which is related to the high reactivity of the modified catalyst.

[0144] Experimental Example 3

[0145] The BET specific surface area of ​​the vanadium phosphorus oxygen catalysts prepared in Examples 1 and 3 (catalysts containing modified components) and Comparative Example 1 (catalyst without modified components) was measured, and the results are shown in Table 1.

[0146] Table 1 BET results for different catalysts

[0147]

[0148] BET data for different catalysts were obtained using a "Mesoporous Specific Surface Area and Porosity Analyzer - McTristar II 3020". Before adsorption measurement, all catalysts were degassed under vacuum at 200°C for 6 hours.

[0149] Experimental Example 3

[0150] Scanning electron microscopy (SEM) tests were performed on the catalyst precursors (dried and without high-temperature treatment) and the catalysts after high-temperature treatment during the catalyst preparation process of Examples 2-3 (catalysts containing modified components), as shown in the attached figures. Figure 7 .

[0151] From the prepared catalyst precursor ( Figure 7 First row) and catalyst after high temperature treatment ( Figure 7 As can be seen from the SEM image in the second row, the catalyst precursor consists of a plate-like structure and some spherical particles. After high-temperature treatment, the plate-like structure is broken into finer particles, which further increases the specific surface area of ​​the catalyst, leading to a significant increase in catalyst activity.

[0152] The above specific embodiments and comparative examples describe in detail the specific preparation method of the catalyst of the present invention, its application in the selective oxidation of n-butane to maleic anhydride, and its specific catalyst reaction performance. Within the scope of the technical concept of the present invention, simple variations can be made to the technical solution of the present invention, including combinations of various catalyst preparation techniques and other suitable methods. These simple variations 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. The application of a modified vanadium-phosphorus-oxygen catalyst in an alkane oxidation system, the alkane oxidation system comprising a reaction system for preparing maleic anhydride from n-butane, characterized in that, The modified vanadium-phosphorus-oxygen catalyst is composed of vanadium oxide, phosphorus oxide and a modifying component, wherein the modifying component is Se element; The molar ratio of phosphorus to vanadium is (0.9~1.4):1, and the molar ratio of the modified component to vanadium is (0.1~20):

100.

2. The application according to claim 1, characterized in that, In the modified vanadium-phosphorus-oxygen catalyst, the molar ratio of phosphorus to vanadium is (1~1.2):

1.

3. The application according to claim 1, characterized in that, In the modified vanadium-phosphorus-oxygen catalyst, the molar ratio of the modified component to vanadium is (0.5~5):

100.

4. The application according to claim 1, characterized in that, A method for preparing a modified vanadium-phosphorus-oxygen catalyst includes: heating and mixing a vanadium-containing compound and a phosphorus-containing compound in a solvent to obtain a first suspension; filtering the suspension to obtain a filter residue; drying the filter residue to obtain a first solid; mixing a solution containing Se with the first solid; and drying the mixture to obtain a modified vanadium-phosphorus-oxygen catalyst precursor. Alternatively, the preparation method includes heating and mixing a vanadium-containing compound, a phosphorus-containing compound, and a solution containing Se in a solvent to obtain a second suspension, filtering the suspension to obtain a filter residue, and drying the filter residue to obtain a modified vanadium-phosphorus-oxygen catalyst precursor. The solvent may be one or a mixture of several of the following: ethanol, n-propanol, isopropanol, propanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, and benzyl alcohol.

5. The application according to claim 4, characterized in that, The solvent is one or a mixture of several of n-butanol, isobutanol, and benzyl alcohol.

6. The application according to claim 4, characterized in that, The modified vanadium-phosphorus-oxygen catalyst precursor was obtained by treating the oxygen-containing component at medium and high temperatures.

7. The application according to claim 4, characterized in that, The solvent is a mixture of isobutanol and benzyl alcohol, wherein the mass ratio of isobutanol to benzyl alcohol is 1:9 to 9:

1.

8. The application according to claim 7, characterized in that, The mass ratio of isobutanol to benzyl alcohol is 1:5 to 5:

1.

9. The application according to claim 4, characterized in that, The solvent is a mixture of isobutanol and n-butanol, wherein the mass ratio of isobutanol to n-butanol is 1:9 to 9:

1.

10. The application according to claim 9, characterized in that, The mass ratio of isobutanol to n-butanol is 1:5 to 5:

1.

11. The application according to any one of claims 4-10, characterized in that, In vanadium-containing compounds, vanadium is in the pentavalent state; The vanadium-containing compound is vanadium pentoxide; the mass ratio of solvent to vanadium pentoxide is (2~50):

1.

12. The application according to claim 11, characterized in that, The mass ratio of solvent to vanadium pentoxide is (5~20):

1.

13. The application according to claim 11, characterized in that, The mass ratio of solvent to vanadium pentoxide is (8~15):

1.

14. The application according to any one of claims 4-10, characterized in that, The formation of the first or second suspension is carried out under conditions of heating and reflux at a temperature of 80~160°C.

15. The application according to claim 14, characterized in that, The heating reflux temperature is 100~150℃.

16. The application according to claim 14, characterized in that, First, heat the vanadium-containing compound or a mixture of the vanadium-containing compound and the modified component in a solvent under reflux for a period of time. Then, add the phosphorus-containing compound and continue heating under reflux.

17. The application according to claim 16, characterized in that, The vanadium-containing compound or a mixture of the vanadium-containing compound and the modified component is refluxed in a solvent at a temperature of 80-160°C for 1 / 24 to 3 / 4 of the total reflux time.

18. The application according to claim 17, characterized in that, The vanadium-containing compound or a mixture of the vanadium-containing compound and the modified component is refluxed in a solvent at a temperature of 80-160°C for 1 / 8 to 1 / 2 of the total reflux time.

19. The application according to any one of claims 4-10, characterized in that, The filter residue or the first solid loaded with modified components is dried at a temperature of 60~180℃.

20. The application according to claim 19, characterized in that, The drying temperature is 80~160℃.

21. The application according to any one of claims 4-10, characterized in that, The conditions for high-temperature treatment are as follows: treatment is carried out in an oxygen-containing atmosphere at a temperature controlled between 350 and 450°C. Alternatively, the desired catalyst can be obtained by reacting at a high temperature under the reaction atmosphere or near the reaction atmosphere for the preparation of maleic anhydride for a period of time.

22. The application according to claim 21, characterized in that, The treatment is carried out under conditions where the temperature is controlled at 370~420℃.

23. The application according to any one of claims 1-3, characterized in that, The modified vanadium-phosphorus-oxygen catalyst was applied to the reaction system for the selective oxidation of n-butane to prepare maleic anhydride at a reaction temperature of 350~450℃.

24. The application according to claim 23, characterized in that, The modified vanadium-phosphorus-oxygen catalyst was applied to the reaction system for the selective oxidation of n-butane to prepare maleic anhydride at a reaction temperature of 370~420℃.

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