A high-density vanadium-phosphorus-oxygen catalyst precursor and catalyst

Abstract

This invention provides a high bulk density vanadium-phosphorus-oxygen catalyst precursor and catalyst. The precursor solution, prepared by a liquid-phase method, is filtered, and the resulting solid is rolled and dried under conditions of a certain moisture content to obtain the high bulk density vanadium-phosphorus-oxygen catalyst precursor. The precursor is not re-compacted; it is directly tableted and reactivated, or activated and then tableted to obtain the catalyst. This invention addresses the problem in existing technologies where the vanadium-phosphorus-oxygen catalyst powder has low density and a low bulk density after forming, leading to easy phosphorus loss and short catalyst lifetime. By rolling and drying the precursor powder with a certain moisture content, the bulk density of the dried precursor powder and the bulk density of the formed catalyst are increased. This simple method not only simplifies the preparation process but also improves the catalyst's resistance to phosphorus loss.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and more particularly to a high bulk density vanadium-phosphorus-oxygen catalyst precursor and catalyst. Background Technology

[0002] Vanadium-phosphorus-oxygen (VPO) catalysts are composed of vanadium, phosphorus, and oxygen. They possess excellent electron and oxygen transport properties and are commonly used in the oxidation of C4 hydrocarbons to maleic anhydride. They are currently the most effective catalysts used in the oxidation of n-butane to maleic anhydride. The main active phase is vanadium pyrophosphate, and its catalytic performance is closely related to the preparation method. Since the first commercial application of VPO catalysts by Monsanto in the United States in 1974, their preparation methods have been extensively studied. See CATAL.REV.-SCI.ENG.27(1985):373.

[0003] Current research focuses on the preparation of vanadium-phosphorus-oxygen catalysts. Their catalytic performance depends on the preparation method. The typical preparation process involves adding raw materials such as phosphoric acid, vanadium pentoxide, and isobutanol as reaction solvents. The pentavalent vanadium is reduced to tetravalent vanadium under the action of organic alcohols, and finally the precursor crystals are generated. The generated crystals are then subjected to different steps such as filtration, drying, calcination, shaping, and activation. The vanadium-phosphorus-oxygen catalyst obtained at the end has an active component of (VO)2P2O7.

[0004] Vanadium-phosphorus-oxygen catalysts are bulk catalysts, and their performance and lifespan are closely related to their bulk density and packing ratio. For the same packing volume, a higher packing ratio and increased catalyst loading amount are beneficial for improving reaction performance and overall operational lifespan.

[0005] Patent CN109939709A points out that in the industrial production of maleic anhydride, the cause of catalyst deactivation during operation is the loss of phosphorus from the catalyst surface. Increasing the catalyst bulk ratio can help enhance the catalyst's phosphorus loss capacity, prevent rapid catalyst deactivation, and improve the catalyst's service life.

[0006] Patents CN104971750A and CN107866245A propose that after the catalyst undergoes drying and calcination, the dried catalyst powder needs to be compacted before tableting. These patents suggest using a compaction pressure of 190 bar to increase the catalyst's bulk density and improve the bulk density of the tableted catalyst. However, this process requires an additional compaction step and introduces issues such as catalyst powder breakage during compaction, which can easily cause dust pollution and affect the health of operators. Summary of the Invention

[0007] To address the problems of low powder density and low catalyst bulk ratio in the synthesis of vanadium-phosphorus-oxygen catalysts in existing technologies, which leads to easy phosphorus loss and short catalyst life during reaction, this invention provides a method for preparing a high bulk ratio vanadium-phosphorus-oxygen catalyst. This method reduces the number of catalyst production steps and drying time, increases the catalyst bulk ratio, and gives the catalyst better resistance to phosphorus loss, while avoiding dust pollution problems caused by the compaction process of catalyst powder.

[0008] The technical objective of the first aspect of this invention is to provide a method for preparing a high bulk density vanadium-phosphorus-oxygen catalyst precursor, which involves filtering a vanadium-phosphorus-oxygen catalyst precursor solution prepared by a liquid-phase method, crushing the obtained solid under conditions with a certain moisture content, and drying it to obtain a high bulk density vanadium-phosphorus-oxygen catalyst precursor.

[0009] Furthermore, during the compaction operation, the moisture content of the solids is 10%–95%, preferably 30%–80%, and most preferably 40%–70%. The moisture content is the weight ratio of water to the moisture content in the moist solids, which can be calculated after sampling and roasting. The calculation formula is as follows:

[0010] Moisture content = (Weight of moist solids - Constant weight of solids after drying) / Weight of moist solids.

[0011] Furthermore, the rolling operation is performed before the catalyst precursor is dried or during the catalyst drying process.

[0012] Furthermore, the drying process involves drying at 40~160℃ for 1-24 hours.

[0013] Furthermore, to ensure the safety of the drying process, the drying is carried out in stages: the first stage drying temperature is 40℃~100℃, preferably 50℃~80℃, and the drying time is 1h~12h, preferably 2h~10h, and most preferably 3h~8h; the second stage drying temperature is 80℃~160℃, preferably 100℃~120℃, and the drying time is 1h~6h, preferably 2h~4h; the third stage drying temperature is 80℃~180℃, preferably 120℃~160℃, and the drying time is 1h~8h, preferably 2h~6h, and most preferably 2h~3h.

[0014] The method of this invention utilizes the characteristic of the vanadium-phosphorus-oxygen catalyst precursor having poor fluidity due to moisture. By performing a rolling operation under lower pressure and load, the catalyst particle density can be increased more uniformly, and a catalyst with a higher powder bulk density can be obtained after drying. This increases the bulk density of the catalyst after molding, thereby improving the catalyst's resistance to phosphorus loss and deactivation.

[0015] Furthermore, the pressure of the compaction operation is 0.1 MPa to 10 MPa, preferably 0.5 MPa to 8 MPa, and most preferably 1 MPa to 5 MPa. The compaction operation time is 1 min to 24 h, preferably 10 min to 60 min, and most preferably 20 min to 40 min.

[0016] Furthermore, the rolling operation is achieved using ordinary rolling equipment or rake drying equipment. More preferably, the rolling operation is achieved using rake drying equipment, which performs rolling while drying the catalyst precursor when it has a certain level of moisture. On the one hand, rolling can increase the catalyst bulk density; on the other hand, the rolling process makes the catalyst precursor powder more evenly distributed within the rake drying equipment, allowing for faster drying and reducing the likelihood of agglomeration.

[0017] Furthermore, during the compaction operation, the rotation frequency of the compaction rake in the rake-type drying equipment is 1Hz~120Hz, preferably 1Hz~60Hz, and most preferably 10Hz~20Hz. The distance between the compaction rake and the inner wall of the dryer is 0.2cm~30cm, preferably 2cm~20cm, and most preferably 3cm~10cm.

[0018] Furthermore, as the most preferred technical solution, the catalyst precursor with the required moisture content is placed in a rake-type drying device and subjected to gradient drying while being rolled: the first stage drying temperature is 40℃~100℃, preferably 50℃~80℃, and the drying time is 1h~12h, preferably 2h~10h, and most preferably 3h~8h; after the first stage drying is completed, the second stage drying is carried out, with a drying temperature of 80℃~160℃, preferably 100℃~120℃, and a drying time of 1h~6h, preferably 2h~4h; after the second stage drying is completed, the third stage drying is carried out, with a drying temperature of 80℃~180℃, preferably 120℃~160℃, and a drying time of 1h~8h, preferably 2h~6h, and most preferably 2h~3h.

[0019] Furthermore, the liquid-phase method for preparing vanadium-phosphorus oxide catalyst precursors is a technique well-known to those skilled in the art. Here, it generally refers to existing methods that use phosphoric acid and vanadium oxides as raw materials to react in an organic solvent to prepare a vanadium-phosphorus oxide catalyst precursor solution. Specifically, it generally refers to preparing the precursor using an organic solvent as the solvent and vanadium pentoxide and phosphoric acid as raw materials. As a more preferred embodiment, an auxiliary agent is added during the preparation of the vanadium-phosphorus oxide catalyst precursor. This auxiliary agent includes, but is not limited to, at least one salt containing Co, Ni, Zn, Bi, Zr, Cu, Li, K, Ca, Mg, Ti, La, Mo, Nb, B, Fe, Cr, or Ce. The organic solvent is selected from at least one of isoamyl alcohol, isobutanol, isopropanol, benzyl alcohol, and n-octanol.

[0020] As a more specific preferred embodiment, the preparation of the vanadium phosphorus oxygen catalyst precursor includes, but is not limited to, the preparation methods disclosed in patent applications CN105749941A, CN104549393A, CN104607220A and CN104549392A.

[0021] The technical objective of the second aspect of this invention is to provide a vanadium-phosphorus-oxygen catalyst precursor prepared by the above method.

[0022] The technical objective of the third aspect of this invention is to provide a vanadium-phosphorus-oxygen catalyst with a high bulk ratio, which is obtained by directly pressing and reactivating the above-mentioned vanadium-phosphorus-oxygen catalyst precursor without recompacting, or by pressing and reactivating it before pressing.

[0023] Furthermore, the activation is a technique well known to those skilled in the art. Specifically, it is carried out in an atmosphere of one or more combinations of nitrogen / air mixture, water vapor / air mixture, n-butane / air mixture, or cyclohexane / air mixture. The activation temperature is 350–450°C, preferably 375–425°C, and the activation time is 5–40 hours, preferably 12–20 hours.

[0024] The fourth aspect of this invention aims to provide an application of the aforementioned vanadium-phosphorus-oxygen catalyst, which is used in the oxidation of n-butane to maleic anhydride. Specifically, the reaction conditions are generally as follows: reaction temperature 320–450°C, pressure atmospheric pressure to 0.5 MPa, and n-butane gas hourly space velocity (GHSV) 1000–3500 h⁻¹. -1 The concentration of n-butane is 1.0% to 1.8% (volume percentage).

[0025] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0026] (1) In the prior art, the synthesized catalyst precursor is dried and calcined, and the dried or calcined catalyst precursor powder is compacted under high pressure to increase the catalyst powder bulk density. On the one hand, the traditional drying method is prone to causing excessively high local temperatures, which leads to the agglomeration of catalyst crystals. At the same time, the drying time is also long. On the other hand, in the high-pressure compaction operation, the catalyst powder is rolled under a pressure of 190 bar, which requires demanding rolling equipment and also causes dust pollution. The present invention uses the filtered but not dried catalyst precursor for rolling operation. On the one hand, the freshly prepared but not dried catalyst has smaller crystals and poorer fluidity. Rolling with moisture makes the crystal agglomeration more uniform and the density increase easier to control. On the other hand, the catalyst with a certain degree of moisture is less likely to generate dust when not dried, avoiding the dust pollution problem of rolling after drying.

[0027] (2) In this invention, the filtered catalyst precursor can be rolled and dried by rake drying. This method combines the rolling process with the drying process, further simplifies the catalyst production process, reduces the drying time, and improves the catalyst production efficiency.

[0028] (3) High packing ratio catalysts can increase the packing amount of bulk catalyst in the same volume of reaction tube with the same porosity, thus extending the service life of the catalyst.

[0029] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0030] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0031] The bulk density of the catalysts prepared in the following examples and comparative examples was measured using a tap density meter. 50g of the prepared catalyst powder was placed in a 100mL graduated cylinder, and the graduated cylinder was placed on the tap density meter and vibrated 200 times until the volume changed. The reading was then calculated.

[0032] The moisture content of the solids in the following examples and comparative examples was calculated using the following method:

[0033] Three random samples were taken from the solid powder and weighed. The samples were then calcined at 250℃ to constant weight and weighed again. The average of the three moisture contents was calculated using the following formula.

[0034] Moisture content = (Weight of moist solids - Constant weight of solids after drying) / Weight of moist solids

[0035] Example 1

[0036] (1) Liquid-phase reaction: In a reaction vessel, add 649 mL of isobutanol solution, 29.53 g of vanadium pentoxide, 0.3 g of ferric nitrate hexahydrate, 0.5 g of zirconium nitrate, and 34.98 g of concentrated phosphoric acid. Start stirring, raise the reaction temperature and maintain it at 100 °C, and carry out the reflux reaction for 6 hours. After the reaction is completed, the reaction solution is cooled to room temperature and then vacuum filtered. The filter cake is washed three times with a small amount of isobutanol. The moisture content of the catalyst precursor after filtration is measured to be 71%.

[0037] (2) Rolling: Place the catalyst precursor in the roller and roll it for 30 minutes at a pressure of 2 MPa.

[0038] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by drying and calcination: The crushed catalyst precursor powder was crushed and placed in a drying oven for drying. The first stage of drying was carried out at a temperature of 60℃ for 8 hours. After the first stage of drying was completed, the second stage of drying was carried out at a temperature of 120℃ for 4 hours. After the second stage of drying was completed, the third stage of drying was carried out at a temperature of 160℃ for 3 hours. After the drying stage was completed, the catalyst precursor powder was calcined at 275℃ for 3 hours.

[0039] (4) Catalyst preparation by molding and activation: The precursor is placed in a tubular reactor after being pressed into tablets. In an inert nitrogen atmosphere, the nitrogen / air / water vapor ratio is 3:1:4 and the total space velocity is 1000 h⁻¹. -1 The temperature was increased at a rate of 10°C / min, and the activation temperature was raised from room temperature to 400°C for calcination. This calcination was then maintained at 400°C for 6 hours, at which point the activation process was complete, yielding the green vanadium-phosphorus-oxygen catalyst C1 of this invention. The bulk density of the catalyst after molding was measured by crushing and sieving the catalyst (10-20 mesh).

[0040] The moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder, and the bulk ratio of the shaped catalyst are shown in Table 1.

[0041] Example 2

[0042] (1) Liquid phase reaction: Same as step (1) in Example 1.

[0043] (2) Rolling: Rolling is not performed separately.

[0044] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by rake-type compaction drying and calcination: The catalyst precursor prepared by the liquid-phase reaction was placed in a rake-type dryer with a frequency of 5 Hz and a distance of 5 cm between the rake and the wall. The first stage of drying was carried out at a temperature of 80 ℃ for 8 h. After the first stage of drying was completed, the second stage of rake-type drying was carried out at a temperature of 120 ℃ for 3 h. After the second stage of drying was completed, the third stage of drying was carried out at a temperature of 160 ℃ for 2 h. After the drying stages were completed, the catalyst powder was calcined at 275 ℃ for 3 h.

[0045] (4) Catalyst preparation by molding and activation: Following the same steps (4) in Example 1, the green catalyst C2 prepared in this invention can be obtained. The bulk density of the catalyst after molding is measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0046] The moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder, and the bulk ratio of the shaped catalyst are shown in Table 1.

[0047] Example 3

[0048] (1) Liquid phase reaction: Same as step (1) in Example 1. After filtration and washing, the catalyst precursor was placed in a filter press for filtration. After filtration, the moisture content of the catalyst precursor was measured to be 45%.

[0049] (2) Rolling: Rolling is not performed separately.

[0050] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by rake-type compaction drying and calcination: The catalyst precursor prepared by the liquid-phase reaction was placed in a rake-type dryer with a frequency of 5 Hz and a distance of 5 cm between the rake and the wall. The first stage of drying was carried out at a temperature of 80 ℃ for 6 h. After the first stage of drying was completed, the second stage of rake-type drying was carried out at a temperature of 120 ℃ for 2 h. After the second stage of drying was completed, the third stage of drying was carried out at a temperature of 160 ℃ for 1 h. After the drying stages were completed, the catalyst powder was calcined at 275 ℃ for 3 h.

[0051] (4) Catalyst preparation by molding and activation: Following the same steps (4) in Example 1, the green catalyst C3 prepared in this invention can be obtained. The bulk density of the catalyst after molding is measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0052] The results of the moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the shaped catalyst are shown in Table 1.

[0053] Example 4

[0054] (1) Liquid phase reaction: Same as step (1) in Example 1. After filtration and washing, the catalyst precursor was placed in a filter press for filtration. After filtration, the moisture content of the catalyst precursor was measured to be 45%.

[0055] (2) Rolling: Place the catalyst precursor in the roller and roll it for 20 minutes at a pressure of 1 MPa.

[0056] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by drying and calcination:

[0057] The crushed catalyst precursor powder was placed in a drying oven for drying. The first stage of drying was carried out at 60℃ for 6 hours. After the first stage of drying, the second stage of drying was carried out at 120℃ for 2 hours. After the second stage of drying, the third stage of drying was carried out at 160℃ for 2 hours. After the drying stages were completed, the catalyst precursor powder was calcined at 275℃ for 3 hours.

[0058] (4) Catalyst preparation by molding and activation: Following the same steps (4) in Example 1, the green catalyst C4 prepared in this invention can be obtained. The bulk density of the catalyst after molding is measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0059] The results of the moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the shaped catalyst are shown in Table 1.

[0060] Example 5

[0061] (1) Liquid phase reaction: Same as step (1) in Example 1. After filtration and washing, the catalyst precursor was placed in a filter press for filtration. After filtration, the moisture content of the catalyst precursor was measured to be 30%.

[0062] (2) Rolling: The catalyst precursor is placed in the roller and rolled for 10 minutes at a pressure of 0.3 MPa.

[0063] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by drying and calcination:

[0064] The crushed catalyst precursor powder was placed in a drying oven for drying. The first stage of drying was carried out at 60℃ for 5 hours. After the first stage of drying, the second stage of drying was carried out at 120℃ for 2 hours. After the second stage of drying, the third stage of drying was carried out at 160℃ for 2 hours. After the drying stages were completed, the catalyst precursor powder was calcined at 275℃ for 3 hours.

[0065] (4) Catalyst preparation by molding and activation: Following the same steps (4) in Example 1, the green catalyst C5 prepared in this invention can be obtained. The bulk density of the catalyst after molding is measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0066] The results of the moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the shaped catalyst are shown in Table 1.

[0067] Example 6

[0068] (1) Liquid phase reaction: Same as step (1) in Example 1. After filtration and washing, the catalyst precursor was placed in a filter press for filtration. After filtration, the moisture content of the catalyst precursor was measured to be 45%.

[0069] (2) Rolling: Place the catalyst precursor in the roller and roll it for 20 minutes at a pressure of 1 MPa.

[0070] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by drying and calcination: The precursor powder was dried in an oven at 150°C for 6 hours. After the drying stage, the catalyst precursor powder was calcined at 275°C for 3 hours.

[0071] (4) Catalyst preparation by molding and activation: Following the same steps (4) in Example 1, the green catalyst C6 prepared in this invention can be obtained. The bulk density of the catalyst after molding is measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0072] The results of the moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the shaped catalyst are shown in Table 1.

[0073] Comparative Example 1

[0074] (1) Liquid phase reaction: Same as step (1) in Example 1.

[0075] (2) Rolling: without rolling operation.

[0076] (3) Drying and calcining to prepare vanadium phosphorus oxygen catalyst precursor: The drying and calcining stage is the same as step (3) in Example 1.

[0077] (4) Catalyst preparation by molding and activation: Same as step (4) in Example 1, the green catalyst A prepared in this invention can be obtained. The moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the molded catalyst are shown in Table 1. The bulk ratio of the catalyst after molding was measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0078] Comparative Example 2

[0079] (1) Liquid phase reaction: Same as step (1) in Example 1.

[0080] (2) Rolling: without rolling operation.

[0081] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by drying and calcination: The precursor was dried in an oven at 150°C for 8 hours.

[0082] (4) Preparation of catalyst by molding and activation: Same as step (4) in Example 1, the green catalyst B prepared in this invention can be obtained. The moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the molded catalyst are shown in Table 1. The bulk ratio of the catalyst after molding is measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0083] Comparative Example 3

[0084] (1) Liquid phase reaction: Same as step (1) in Example 3.

[0085] (2) Rolling: without rolling operation.

[0086] (3) Preparation of vanadium-phosphorus-oxygen catalyst precursor by drying and calcination: The precursor was dried in an oven at 150°C for 8 hours.

[0087] (4) Catalyst preparation by molding and activation: Same as step (4) in Example 1, the green catalyst C prepared in this invention can be obtained. The moisture content of the catalyst precursor, the bulk ratio of the catalyst precursor powder and the bulk ratio of the molded catalyst are shown in Table 1. The bulk ratio of the catalyst after molding was measured by crushing and sieving the catalyst (10 mesh to 20 mesh).

[0088] Table 1.

[0089]

[0090] Performance determination of the catalyst in the oxidation of n-butane to maleic anhydride:

[0091] Performance determination of the catalyst in the oxidation of n-butane to maleic anhydride: The reaction of n-butane to maleic anhydride under the catalysis of a vanadium phosphorus oxyhydroxide catalyst has a suitable conversion range. As the conversion rate increases, some maleic anhydride is peroxidized to CO2 and CO, and the reaction selectivity gradually decreases. The overall yield of maleic anhydride is highest when the n-butane conversion rate is around 82%~85%. Therefore, in the examples and comparative examples, the overall yield at an initial n-butane conversion rate of 82%~85% was used as the evaluation standard. To demonstrate the catalyst's resistance to phosphorus loss, no phosphorus replenishment was performed during operation, and the catalyst activity was evaluated over 100 hours. The specific evaluation method is as follows.

[0092] The catalysts were crushed and sieved separately. 5 mL of catalyst particles (10-20 mesh) were measured and diluted 1:1 with quartz sand of the same mesh size. This mixture was then packed into a stainless steel reaction tube with an inner diameter of 10 mm. The reaction was carried out at a temperature of 410℃, a pressure of 0.1 MPa, and the reaction gas was a butane / air mixture with a butane volume concentration of 1.5% and a gas hourly space velocity of 1600 h⁻¹. -1 Catalytic performance evaluation tests were conducted under the specified reaction conditions. The results of the catalyst performance evaluation are shown in Table 2.

[0093] Table 2.

[0094]

[0095] The results show that the catalyst with a high bulk ratio produced using this patented technology has higher phosphorus loss resistance than the catalyst produced by traditional production methods. It remains stable for 100 hours without phosphorus replenishment, and the maleic anhydride yield does not decrease significantly, demonstrating high stability.

Claims

1. A method for preparing a high-bulk-ratio vanadium-phosphorus-oxygen catalyst precursor, characterized in that, The vanadium-phosphorus-oxygen catalyst precursor solution prepared by liquid phase method is filtered, and the resulting solid is rolled and dried under certain moisture content conditions to obtain a vanadium-phosphorus-oxygen catalyst precursor with high bulk ratio. During the compaction operation, the moisture content of the solids should be 30%-80%. The rolling operation is performed before the catalyst precursor is dried or during the drying process. The drying process involves drying at 40~160℃ for 1-24 hours.

2. The preparation method according to claim 1, characterized in that, When performing the compaction operation, the moisture content of the solids is 40%-70%.

3. The preparation method according to claim 1, characterized in that, The drying process is carried out in stages: the first stage of drying is at a temperature of 40℃ to 100℃ and a drying time of 1h to 12h; the second stage of drying is at a temperature of 80℃ to 160℃ and a drying time of 1h to 6h; and the third stage of drying is at a temperature of 80℃ to 180℃ and a drying time of 1h to 8h.

4. The preparation method according to claim 3, characterized in that, The drying process is carried out in stages: the first stage of drying is at a temperature of 50℃ to 80℃ and a drying time of 2h to 10h; the second stage of drying is at a temperature of 100℃ to 120℃ and a drying time of 2h to 4h; and the third stage of drying is at a temperature of 120℃ to 160℃ and a drying time of 2h to 6h.

5. The preparation method according to claim 4, characterized in that, The first drying time is 3-8 hours, the second drying time is 2-4 hours, and the third drying time is 2-3 hours.

6. The preparation method according to claim 1, characterized in that, The pressure of the rolling operation is 0.1 MPa to 10 MPa.

7. The preparation method according to claim 6, characterized in that, The pressure of the rolling operation is 0.5 MPa to 8 MPa.

8. The preparation method according to claim 7, characterized in that, The pressure of the rolling operation is 1MPa~5MPa.

9. The preparation method according to claim 1, characterized in that, The compaction operation takes 1 minute to 24 hours.

10. The preparation method according to claim 1, characterized in that, The compaction operation takes 10 to 60 minutes.

11. The preparation method according to claim 10, characterized in that, The compaction operation takes 20 to 40 minutes.

12. The preparation method according to claim 1, characterized in that, The rolling operation is carried out using ordinary rolling equipment or rake-type drying equipment.

13. The preparation method according to claim 1, characterized in that, During the rolling operation, the rotation frequency of the rolling rake in the rake-type drying equipment is 1Hz~120Hz, and the distance between the rolling rake and the inner wall of the dryer is 0.2cm~30cm.

14. The preparation method according to claim 13, characterized in that, The process involves placing the catalyst precursor with the required moisture content into a rake-type drying device and performing gradient drying while rolling: the first stage of drying is carried out at a temperature of 40℃~100℃ for 1h~12h; after the first stage of drying is completed, the second stage of drying is carried out at a temperature of 80℃~160℃ for 1h~6h; after the second stage of drying is completed, the third stage of drying is carried out at a temperature of 80℃~180℃ for 1h~8h.

15. The preparation method according to claim 14, characterized in that, While compaction is being carried out, gradient drying is also being performed: the first stage of drying is at a temperature of 50℃~80℃ and a drying time of 2h~10h; after the first stage of drying is completed, the second stage of drying is carried out at a temperature of 100℃~120℃ and a drying time of 2h~4h; after the second stage of drying is completed, the third stage of drying is carried out at a temperature of 120℃~160℃ and a drying time of 2h~6h.

16. The preparation method according to claim 15, characterized in that, The first drying time is 3-8 hours, the second drying time is 2-4 hours, and the third drying time is 2-3 hours.

17. The vanadium-phosphorus-oxygen catalyst precursor prepared by the method according to any one of claims 1-16.

18. A high-density vanadium-phosphorus-oxygen catalyst, characterized in that, It is obtained by directly pressing and reactivating the vanadium-phosphorus-oxygen catalyst precursor as described in claim 17 without recompacting, or by pressing and reactivating it.

19. The application of the vanadium-phosphorus-oxygen catalyst according to claim 18 in the catalytic oxidation of n-butane to maleic anhydride.

Images