Activation method for vanadium phosphorus oxygen catalyst for use in oxidation of butane to prepare maleic anhydride

Abstract

The present application discloses an activation method for a vanadium phosphorus oxygen catalyst for use in oxidation of butane to prepare maleic anhydride, and a use. The method comprises using different plasma-coupled thermal treatment methods to perform high-temperature calcination activation on existing vanadium phosphorus oxygen catalyst precursors, so as to obtain a vanadium phosphorus oxygen catalyst having rich defect sites, thereby achieving high adsorption and activation of butane, also exposing more active sites, and greatly improving catalytic efficiency. Compared with the prior art, by adjusting the type of plasma, the present application can regulate the microstructure of a catalyst surface, thereby avoiding the preparation process of a complex mixed gas. The method provided by the present application is simple and green, can be popularized in a large scale, and has a wide application prospect.

Description

An activation method for a vanadium phosphorus oxide catalyst used in the oxidation of butane to maleic anhydride Technical Field

[0001] This application relates to the field of vanadium phosphorus oxide (VPO) catalysts and the preparation of maleic anhydride, specifically to an activation method and application of a vanadium phosphorus oxide catalyst. Background Technology

[0002] Maleic anhydride is the world's third-largest organic acid anhydride. As an important chemical intermediate, it has wide applications and a broad market in biodegradable plastics, high-end pesticides, food, and pharmaceuticals. The selective oxidation of n-butane to produce maleic anhydride is currently the mainstream process due to its economic efficiency, environmental friendliness, and high atom utilization. Vanadium phosphorus oxide (VPO) catalyst is currently the only catalyst used to industrialize this reaction.

[0003] VPO catalysts typically use vanadium pentoxide as the vanadium source, phosphoric acid as the phosphorus source, and a mixed organic alcohol as the solvent and reducing agent. Under prolonged thermal reflux conditions, a precursor for the vanadium-phosphorus-oxygen catalyst is obtained, the main component of which is hemihydrated vanadium pyrophosphate. This precursor is then activated by high-temperature calcination under specific atmosphere and temperature to obtain the final active phase with catalytic properties. Different activation conditions often yield vanadium-phosphorus-oxygen catalysts with different crystal forms, valence states, and microstructures. Since the selective oxidation of butane is a structure-sensitive reaction, its performance is significantly affected by the catalyst's microstructure. Therefore, increasing research focuses on controlling activation conditions to modulate the structure of vanadium-phosphorus-oxygen catalysts and thus obtain optimal catalytic performance.

[0004] CN118477666A discloses a method for external activation of vanadium-phosphorus-oxygen catalysts. The method uses a mixed gas atmosphere of water vapor and nitrogen and calcines the catalyst in a self-made cylindrical external activation furnace at a temperature of 400℃~450℃ for 3~8 h. This method is suitable for large-scale catalyst activation processes, and the obtained catalyst has relatively stable butane conversion and maleic anhydride selectivity.

[0005] CN1068053A discloses a multi-step vanadium-phosphorus-oxygen catalyst activation method, which involves gradually performing high-temperature activation in a mixed gas atmosphere of air, water vapor, and inert atmosphere to obtain active components with excellent performance.

[0006] The aforementioned and existing methods all activate the precursor by controlling the calcination atmosphere and calcination process, thereby regulating the valence state and crystal phase of the active catalyst and influencing its catalytic performance. However, existing activation methods cannot effectively control the active sites of the catalyst, such as defect sites and adsorption sites, and involve complex atmosphere adjustments, making the operation quite complicated. Therefore, finding an activation method that can effectively control catalyst sites and ensure catalyst selectivity and conversion rate has become an important goal pursued by current activation methods. Summary of the Invention

[0007] This application provides a method for activating a vanadium phosphorus oxygen catalyst and its application.

[0008] The applicant's previous research found that plasma, as a novel external field enhancement strategy, can controllably construct specific defects on the catalyst surface by adjusting parameters such as plasma type, power, temperature, and time, thereby achieving the goal of controlling active sites, crystal structure, and valence ratio, and improving the catalytic performance of the catalyst.

[0009] This application provides a plasma activation method for vanadium phosphorus oxygen catalysts, which specifically includes the following steps:

[0010] (1) Spread a certain mass of vanadium-phosphorus-oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0011] (2) Ensure the system is in a vacuum state, introduce a specific gas at a certain flow rate to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the power of plasma excitation.

[0012] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, a programmable heating program is set so that the precursor powder is calcined and activated under plasma irradiation at a certain temperature and time, and finally vanadium phosphorus oxygen active catalyst is obtained.

[0013] According to the embodiments of this application, the precursor of the vanadium phosphorus oxygen catalyst can be the precursor obtained by conventional methods in the art when preparing the vanadium phosphorus oxygen catalyst. Specifically, the crystal phase structure of the precursor of the vanadium phosphorus oxygen catalyst is hemihydrated pyrophosphate oxyacid, VOHPO4·0.5H2O.

[0014] This application also provides the application of the plasma-activated vanadium phosphorus oxygen catalyst obtained by the above method in the selective oxidation of n-butane to maleic anhydride.

[0015] Compared with the prior art, this application has the following significant technical effects and advantages:

[0016] (1) The plasma activation method used in this application can construct different types of defect sites on the vanadium-phosphorus-oxygen catalyst body by controlling the type of plasma, thereby achieving efficient adsorption and activation of the reaction gas.

[0017] (2) Compared with the traditional multi-atmosphere gradient activation method, the plasma activation method provided in this application does not require a complicated atmosphere conditioning process and the process is simple;

[0018] (3) Using this method, in the later activation process, plasma can break the hydrogen bond structure between the vanadium phosphorus oxygen catalyst layers, expose more active sites, and improve the catalyst performance. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] This application provides a plasma activation method for vanadium phosphorus oxygen catalysts, which specifically includes the following steps:

[0021] (1) Spread a certain mass of vanadium-phosphorus-oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0022] (2) Ensure the system is in a vacuum state, introduce a specific gas at a certain flow rate to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the power of plasma excitation.

[0023] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, a programmable heating program is set so that the precursor powder is calcined and activated under plasma irradiation to finally obtain vanadium phosphorus oxygen active catalyst.

[0024] The following are preferred technical solutions of this application, but are not intended to limit the technical solutions provided in this application. Through the following preferred solutions, the technical objectives and beneficial effects of this application can be better achieved.

[0025] Preferably, the mass of the vanadium-phosphorus-oxygen precursor powder in step (1) is 0.5 g to 5 g, for example, 0.5 g, 1.0 g, 1.5 g, 2.0 g, 2.5 g, 3.0 g, or 5.0 g. More preferably, the mass of the vanadium-phosphorus-oxygen precursor powder is 3.0 g. When the mass is less than 0.5 g, the final catalyst mass is too small, making subsequent performance testing difficult. When the mass is greater than 5.0 g, the plasma cannot cover all the precursor powder, resulting in poor uniformity of the final catalyst.

[0026] Preferably, the gas introduced in step (2) is a combination of at least one or more of the following mixed gases: nitrogen, oxygen, argon, helium, water vapor, and butane; for example, nitrogen, oxygen, helium, nitrogen-oxygen, or nitrogen-butane. More preferably, the gas is a combination of nitrogen and butane.

[0027] Preferably, the flow rate of the gas in step (2) is 10 to 200 mL / min, for example: 10 mL / min, 30 mL / min, 50 mL / min, 100 mL / min, 130 mL / min, 170 mL / min, 200 mL / min. More preferably, the flow rate of the gas is 150 mL / min.

[0028] Preferably, the plasma excitation power in step (2) is 50 W to 200 W, for example: 50 W, 70 W, 90 W, 100 W, 150 W, 200 W. More preferably, the plasma excitation power is 150 W.

[0029] Preferably, the heating rate in step (2) is 2 to 15. o C / min, for example: 2 o C / min, 5 o C / min, 7 o C / min, 10 o C / min, 12 o C / min, 15 o C / min. More preferably, the heating rate is 5. o C / min.

[0030] Preferably, the calcination temperature in step (2) is 400~480℃. o C, for example: 400 o C, 420 o C, 460 o C, 470 o C, 480 o C. More preferably, the calcination temperature is 420°C. o C.

[0031] Preferably, the roasting time in step (2) is 10-16 h, such as 10 h, 12 h, 14 h, 14.5 h, 15 h, 15.5 h, 16 h, etc. More preferably, the roasting time is 12 h.

[0032] As a further preferred technical solution of the method described in this application, the method includes the following steps:

[0033] (1) Spread 0.5 g to 5 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0034] (2) Ensure the system is in a vacuum state, and introduce at least one or more mixed gases of nitrogen, oxygen, argon, helium, water vapor and butane at a flow rate of 10 to 200 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 50 W to 200 W.

[0035] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 2 ~ 15 o Heating rate increased to 400 ~ 480 °C / min o C, the precursor powder is calcined and activated under plasma irradiation for 10-16 h to finally obtain the vanadium-phosphorus-oxygen active catalyst.

[0036] This application also includes the application of the above-mentioned vanadium phosphorus oxygen catalyst in the selective oxidation of n-butane to maleic anhydride.

[0037] Preferably, the reaction conditions for the selective oxidation of n-butane to prepare maleic anhydride are: a hot spot temperature of 420°C and a space velocity of 2000 h⁻¹ for the n-butane-air mixture. -1 The concentration of n-butane is 1.8 v.

[0038] The following specific examples illustrate the preparation method of low-pressure-drop vanadium-phosphorus-oxygen catalysts. The compounds in the following examples can be prepared directly using existing methods.

[0039] Example 1

[0040] (1) Spread 0.5 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0041] (2) Ensure the system is in a vacuum state, introduce nitrogen gas at a flow rate of 10 mL / min to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 50 W.

[0042] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 2 o Heating rate increased to 400 °C / min oC, the precursor powder is calcined and activated under plasma irradiation for 10 h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0043] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 92.2%, the maleic anhydride selectivity was 54.3%, and the maleic anhydride yield was 84.6%.

[0044] Example 2

[0045] (1) Spread 2 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0046] (2) Ensure the system is in a vacuum state, introduce nitrogen gas at a flow rate of 50 mL / min to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 100 W.

[0047] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 5 o Heating rate increased to 420 °C / min. o C, the precursor powder is calcined and activated under plasma irradiation for 12 h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0048] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 93.6%, the maleic anhydride selectivity was 55.7%, and the maleic anhydride yield was 88.1%.

[0049] Example 3

[0050] (1) Spread 3 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0051] (2) Ensure the system is in a vacuum state, and introduce a combination of nitrogen and butane gas at a flow rate of 150 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 150 W.

[0052] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 5 o Heating rate increased to 420 °C / min. oC, the precursor powder is calcined and activated under plasma irradiation for 12 h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0053] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 95.7%, the maleic anhydride selectivity was 65.3%, and the maleic anhydride yield was 105.6%.

[0054] Example 4

[0055] (1) Spread 5 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0056] (2) Ensure the system is in a vacuum state, introduce oxygen at a flow rate of 200 mL / min to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 200 W.

[0057] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 10 o Heating rate increased to 450 °C / min o C, the precursor powder is calcined and activated under plasma irradiation for 16 h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0058] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 96.3%, the maleic anhydride selectivity was 59.2%, and the maleic anhydride yield was 96.3%.

[0059] Example 5

[0060] (1) Spread 5 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0061] (2) Ensure the system is in a vacuum state, and introduce argon gas at a flow rate of 200 mL / min to excite the plasma. After the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 200 W.

[0062] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 15 o Heating rate increased to 480 °C / min oC, the precursor powder is calcined and activated under plasma irradiation for 16 h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0063] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 90.8%, the maleic anhydride selectivity was 62.7%, and the maleic anhydride yield was 96.2%.

[0064] Example 6

[0065] (1) Spread 3 g of vanadium phosphorus oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0066] (2) Ensure the system is in a vacuum state, introduce nitrogen gas at a flow rate of 150 mL / min to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the plasma excitation power to 200 W.

[0067] (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, according to 10 o Heating rate increased to 420 °C / min. o C, the precursor powder is calcined and activated under plasma irradiation for 16 h to finally obtain the vanadium phosphorus oxygen active catalyst.

[0068] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 95.7%, the maleic anhydride selectivity was 60.2%, and the maleic anhydride yield was 97.3%.

[0069] Comparative Example

[0070] (1) Spread 3 g of vanadium phosphorus oxygen precursor powder evenly in a quartz ceramic boat, place it in a tube furnace, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state.

[0071] (2) Ensure the system is in a vacuum state, and introduce a combination of nitrogen and butane gas at a flow rate of 150 mL / min without turning on the plasma excitation device.

[0072] (3) According to 5 o Heating rate increased to 420 °C / min. o C, calcined and activated for 12 h, finally obtaining vanadium phosphorus oxygen active catalyst.

[0073] Detection: At the reaction hotspot temperature of 420℃, the space velocity of the n-butane-air mixture was 2000 h⁻¹. -1 Under reaction conditions with a n-butane concentration of 1.8 v%, the n-butane conversion rate was 85.3%, the maleic anhydride selectivity was 59.7%, and the maleic anhydride yield was 86.1%.

[0074] Comparing Example 3 with the Comparative Example, it can be found that with the same catalytic material and activation calcination procedure, under the condition of plasma application, due to the formation of defective active sites on the catalyst surface, the mass yield of maleic anhydride in Example 3 was 105.6%, while in the Comparative Example it was only 86.1%.

[0075] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A plasma activation method for vanadium phosphorus oxygen catalysts, comprising the following steps: (1) Spread a certain mass of vanadium-phosphorus-oxygen precursor powder in a quartz ceramic boat, place it in a tube furnace connected with a plasma excitation device, and evacuate the entire system for 10 minutes to ensure that the system is in a vacuum state. (2) Ensure the system is in a vacuum state, introduce a specific gas at a certain flow rate to excite the plasma, and after the flow rate stabilizes, turn on the plasma excitation device and set the power of plasma excitation. (3) Under the condition that plasma is continuously generated and introduced into the tube furnace, a programmable heating program is set so that the precursor powder is calcined and activated under plasma irradiation to finally obtain vanadium phosphorus oxygen active catalyst.

2. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The mass of the vanadium phosphorus oxygen precursor powder is 0.5 g to 5 g.

3. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The introduced gas is a combination of at least one or more of the following: nitrogen, oxygen, argon, helium, water vapor, and butane.

4. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The flow rate of the gas is 10 ~ 200 mL / min.

5. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The plasma excitation power is 50 W ~ 200 W.

6. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The heating rate is 2 to 15. o C / min.

7. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The calcination temperature is 400~480℃. o C.

8. The plasma activation method for vanadium-phosphorus-oxygen catalyst according to claim 1, wherein, The roasting time is 10-16 h.