A catalyst grading method for preparing n-butyric anhydride by n-butane oxidation

Abstract

The application provides a catalyst grading method for preparing maleic anhydride by n-butane oxidation, which adopts a fixed bed reactor, and at least two catalyst bed layers exist in the fixed bed reactor; according to the contact sequence of the catalyst and the reaction gas, the catalyst stack ratio in the catalyst bed layer is distributed from large to small. According to the strong heat release characteristics of the n-butane oxidation reaction, along the reaction material flow direction, the catalyst stack ratio is distributed from large to small, the catalyst with high stack ratio controls the reaction degree and inhibits the reaction hot spot, the grading method makes the hot spot position of the reaction process move down and the speed slow down, the anti-phosphorus loss capacity of the catalyst with high stack ratio is enhanced, thereby the anti-deactivation capacity of the catalyst at the reactor inlet is improved, and the service life and performance of the catalyst in the whole reactor are improved.

Description

Technical Field

[0001] This invention relates to the field of maleic anhydride production by n-butane oxidation, specifically a catalyst gradation method for maleic anhydride production by n-butane oxidation. Background Technology

[0002] Maleic anhydride, also known as maleic acid anhydride, is an important organic chemical raw material. It is the world's third largest organic acid anhydride after phthalic anhydride and acetic anhydride, and is widely used in petrochemical, food processing, pharmaceutical, and building materials industries. Specific applications include the manufacture of unsaturated polyester resins, alkyd resins, maleic acid (maleic acid), fumaric acid (fumaric acid), as well as pesticides, coatings, fiberglass, lubricant additives, papermaking chemical additives, and surfactants. Since the first commercial application of VPO catalysts by Monsanto in the United States in 1974, its preparation methods have been extensively studied; see CATAL.REV.-SCI.ENG.27(1985):373.

[0003] Currently, in the production of maleic anhydride from n-butane oxidation, the fixed-bed process has become the main method for maleic anhydride production due to its high butane feedstock utilization, stable product quality, and simple operation. However, in the fixed-bed production process, due to the strongly exothermic nature of the oxidation reaction, the heat of reaction for the main reaction to produce maleic anhydride is 1236 kJ / mol, while the heats of reaction for the side reaction to produce CO2 are 2656 kJ / mol and 1521 kJ / mol, respectively. Therefore, in industrial production, molten salt circulating in the reactor jacket is used to remove the heat of reaction. However, hot spots still exist locally on the catalyst, which are difficult to optimize and control. The presence of hot spots will adversely affect the performance of the catalyst. Therefore, suppressing hot spots during the reaction process is the key to controlling the reaction process. The height of the hot spots in the catalyst bed directly affects the conversion rate of butane, the selectivity of maleic anhydride, the yield of maleic anhydride, and the stability of the catalyst.

[0004] Patent CN109939709A points out that during the industrial production of maleic anhydride, the deactivation of the catalyst is caused by the loss of phosphorus from the catalyst surface. Specifically, excessively high temperatures at the reaction hotspots can easily lead to rapid phosphorus loss, accelerating catalyst deactivation.

[0005] Meanwhile, in the n-butane oxidation reaction, the performance of the vanadium-phosphorus-oxygen catalyst is closely related to the reaction pressure. Chen Nan of Zhejiang University, in his paper "Kinematics and Process Study of Fixed-Bed n-Butane to Maleic Anhydride Production," pointed out that with increasing reaction pressure, the n-butane conversion rate and hot spot temperature increase sharply. In fixed-bed reactors, the inlet pressure is mostly 0.18~0.25 MPa, which is relatively low. Therefore, the catalyst bed pressure drop accounts for a large proportion of the overall reaction pressure. This indicates that the catalyst region at the reactor inlet is located in the area with the highest reaction pressure, the highest butane concentration, and the fastest reaction rate; it is also the region most prone to phosphorus loss and catalyst deactivation.

[0006] Therefore, how to regulate the reaction rate in the inlet section and achieve uniform and complete utilization of the catalyst in the fixed bed is an important factor in improving the catalyst life and the overall performance of the reactor. Summary of the Invention

[0007] This invention addresses the problem in the fixed-bed reaction of n-butane oxidation to maleic anhydride, where high inlet reaction pressure leads to a sharp increase in n-butane conversion rate and hot spot temperature, resulting in easy phosphorus loss and / or deactivation of the catalyst. It proposes a catalyst gradation method to mitigate the damage to the catalyst caused by excessively high reaction hot spots, reduce catalyst bed hot spots, and extend catalyst lifespan.

[0008] The technical objective of this invention is to provide a catalyst gradation method for the oxidation of n-butane to maleic anhydride, which employs a fixed-bed reactor with at least two catalyst beds. The catalyst bed packing ratio is distributed from large to small according to the contact sequence between the catalyst and the reactant gas.

[0009] Furthermore, the fixed-bed reactor contains 2-6 catalyst beds, preferably 2-4.

[0010] Furthermore, according to the contact sequence between the catalyst and the reactant gas, the bulk density of the downstream catalyst bed is 1 g / cm³ lower than that of its adjacent upstream catalyst bed. 3 -10g / cm 3 3g / cm 3 -7g / cm 3 The optimal value is 4g / cm³. 3 -5g / cm 3 In the reaction process of oxidizing n-butane to maleic anhydride, a molded catalyst is used. The bulk density of the molded catalyst is measured using a tap density meter. The specific procedure is as follows: 50g of the prepared intact molded catalyst is placed in a 100mL graduated cylinder, the graduated cylinder is placed on the tap density meter, and it is shaken 200 times until the volume changes. The reading is then calculated.

[0011] Furthermore, according to the contact sequence between the catalyst and the reactant gas, the specific surface area of ​​the catalyst in the downstream catalyst bed is 1 m² higher than that of the catalyst in its adjacent upstream catalyst bed. 3 / g-10m 3 / g, preferably 2m 3 / g-8m 3 / g, optimal value 3m 3 / g-5m 3 / g. Generally, catalysts with a high bulk density have a smaller specific surface area; therefore, specific surface area can be used as an auxiliary indicator in the technical solution of this invention.

[0012] The methods for controlling the catalyst bulk density in this invention include, but are not limited to, rolling the precursor before catalyst drying, rolling the powder before catalyst forming, controlling the pressure during catalyst tablet forming, controlling the catalyst forming shape, and controlling the bulk density of different catalysts.

[0013] The methods for controlling the specific surface area of ​​the catalyst in this invention include, but are not limited to, controlling the rolling of the precursor before catalyst drying, rolling of powder before catalyst forming, pressure control during catalyst tablet forming, adding pore-forming agents during the preparation process, and controlling the particle size of the catalyst precursor.

[0014] As one specific implementation method, the catalyst is prepared using the following method to control the bulk ratio:

[0015] (1) The precursor of VPO catalyst can be prepared using conventional methods in this technical field;

[0016] (2) The catalyst precursor obtained in step (1) is formed into Raschig ring or cylindrical catalyst particles by a pelletizing method. This method can control the diameter and pore size of the Raschig ring catalyst by controlling the pressure and pin diameter in the ring pressing machine, and can also control the height and diameter length of the cylindrical catalyst, thereby controlling the packing ratio of the catalyst in the reaction tube.

[0017] The method for preparing the precursor of the VPO catalyst in step (1) is to use a liquid phase method. Specifically, the method disclosed in Chinese Patent CN103769181A or US Patent USP4,632,915 can be used to obtain a brown catalyst precursor.

[0018] Furthermore, the reaction for the oxidation of n-butane to maleic anhydride is as follows: n-butane is mixed with air, and the resulting mixed reaction gas flows in parallel through a catalyst bed connected in series to carry out the oxidation reaction. Specifically, the reaction conditions are generally: reaction temperature 320–450℃, pressure atmospheric pressure to 0.5 MPa, and n-butane mixed gas space velocity 1000–3500 h⁻¹. -1 The concentration of n-butane is 1.0% to 2.5% (volume percentage).

[0019] Those skilled in the art will understand that the catalyst is activated in a nitrogen or inert gas atmosphere before the reaction. Specifically, the activation is carried out in one or more combinations of nitrogen / air mixture, water vapor / air mixture, n-butane / air mixture, or cyclohexane / air mixture, at an activation temperature of 350–450°C, preferably 375–425°C, and for an activation time of 5–40 hours, preferably 12–20 hours.

[0020] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0021] The oxidation of n-butane is a strongly exothermic reaction. Due to the high reaction pressure and butane concentration at the reaction inlet, n-butane reacts more readily, leading to the formation of hot spots. Excessively high hot spot temperatures accelerate the rapid loss of phosphorus from the catalyst, and the rate of phosphorus loss directly affects the catalyst's operating cycle. Therefore, high hot spot temperatures are a key factor affecting the stability of catalyst activity, and phosphorus loss is unavoidable given the reaction characteristics. Thus, the main focus in this field is on how to reduce the rate of phosphorus loss from the catalyst, thereby extending its operating cycle. As the reaction proceeds, the upstream catalyst loses activity first, and the hot spot gradually moves downwards. In industrial plants, the movement of the hot spot can be used to determine the degree of catalyst activity loss, thus predicting the plant's operating cycle. Simultaneously, as the reaction apparatus operates, the catalyst at the reaction tube inlet loses activity, requiring an increase in reaction temperature to ensure optimal reaction performance. However, further increases in reaction temperature can lead to even faster catalyst deactivation, reducing reaction stability and hindering the smooth operation of the apparatus.

[0022] The inventors discovered that during the preparation of maleic anhydride catalyst, the catalyst powder is compacted and then tableted. By controlling the pressure during different compaction and tableting operations, the catalyst bulk ratio can be controlled. Further analysis showed that higher pressure during compaction and tableting resulted in a higher bulk ratio of the formed catalyst, while the specific surface area of ​​the catalyst decreased relatively.

[0023] This invention addresses the highly exothermic nature of the n-butane oxidation reaction by employing catalysts with varying bulk ratios distributed along the reactant flow direction. The inventors discovered that high bulk ratio catalysts control the reaction rate. Due to their relatively lower specific surface area, they can reduce the reaction rate under high pressure and high butane concentration conditions compared to low bulk ratio catalysts, suppressing reaction hotspots. Furthermore, the downward movement of reaction hotspots is slower compared to low bulk ratio catalysts. This gradation method further slows down the downward movement of hotspot positions during the reaction process. Experiments also revealed that high bulk ratio catalysts exhibit enhanced resistance to phosphorus loss, thereby improving the catalyst's resistance to deactivation at the reactor inlet and enhancing the overall catalyst lifespan and performance within the reactor.

[0024] In the subsequent bed, as the butane reacts and flows, the reaction pressure and butane concentration continuously decrease. At this point, a catalyst bed with a low bulk density is loaded. Catalysts with a low bulk density generally have a higher specific surface area and higher activity, which helps to further complete the butane reaction under relatively low pressure, improves the overall butane conversion rate, and makes the butane react more uniformly in the bed. This results in a more even distribution of the reaction temperature, effectively suppresses the occurrence of side reactions, improves product selectivity, and increases the yield of maleic anhydride.

[0025] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0026] 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.

[0027] 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, intact catalyst was placed in a 100mL graduated cylinder, which was then placed on the tap density meter and vibrated 200 times until no volume change was observed. The reading was then calculated. The specific surface area of ​​the catalyst was determined using an AUTOSORB3B fully automated specific surface area and pore size distribution meter from Quantachrome, USA.

[0028] Catalysts with different bulk ratios were prepared in Examples 1-2:

[0029] Example 1

[0030] (1) Preparation of precursor filter cake by liquid phase reaction: In the reaction vessel, add 649 mL of isobutanol solution, 29.53 g of vanadium pentoxide, 0.4 g of ferric nitrate hexahydrate, 0.3 g of zirconium nitrate, 0.3 g of molybdenum nitrate, 0.1 g of potassium nitrate, and 34.98 g of concentrated phosphoric acid. Start stirring, raise the reaction temperature and keep it at 100 °C, carry out the reflux reaction, keep the reflux time for 6 hours, and 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.

[0031] (2) Preparation of vanadium-phosphorus-oxygen catalyst precursor: The catalyst precursor filter cake was placed in a drying oven for drying. The first stage of drying was carried out at a temperature of 60℃ for 7 hours. After the first stage of drying was completed, the second stage of drying was carried out at a temperature of 120℃ for 3 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 stages were completed, the catalyst powder was calcined at 275℃ for 3 hours.

[0032] (3) Catalyst powder forming: After calcination, the catalyst powder is pressed into Raschig rings and cylindrical catalysts by a ring pressing machine. The pressing pressure of the tablet press is 30kN.

[0033] (4) Activation to obtain catalyst: The shaped catalyst is placed in a tubular reactor and activated in an inert nitrogen atmosphere with a nitrogen / air / water vapor ratio of 3:1:4 and a total space velocity of 1000 h⁻¹. -1 The heating rate was 10℃ / min, and the activation temperature was raised from room temperature to 400℃ for calcination treatment. The temperature was then maintained at 400℃ for 6 hours. The activation process was then completed, and Raschig annular vanadium phosphorus oxygen catalyst B1 and cylindrical vanadium phosphorus oxygen catalyst B2 were obtained. Their bulk ratio and specific surface area were measured, and the results are listed in Table 1.

[0034] Example 2

[0035] Steps (1) and (2) are the same as in Example 1.

[0036] (3) Catalyst powder compaction and molding: The calcined catalyst powder is compacted in a compactor under different pressures. The calcined precursor is compacted under a pressure of 10 MPa. The compacted powder is re-granulated and then pressed into Raschig rings and cylindrical catalysts by a ring press. The pressing pressure of the ring press is 80 kN.

[0037] The catalyst was activated using the same process as step (4) in Example 1 to obtain Raschig vanadium phosphorus oxygen catalyst C1 and cylindrical catalyst C2. Their bulk ratio and specific surface area were measured, and the results are listed in Table 1.

[0038] Table 1.

[0039]

[0040] Example 3

[0041] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following gradation combination method. The catalyst gradation loading amount was based on the total volume of the catalyst. The first section of the reactor inlet used B2 catalyst with a loading amount of 50%, and the second section used B1 catalyst with a loading amount of 50%. The catalyst loading was carried out using conventional operating methods in the art.

[0042] Example 4

[0043] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following gradation combination method. The catalyst gradation loading amount was based on the total volume of the catalyst. The first section of the reactor inlet used C2 catalyst with a loading amount of 50%, and the second section used C1 catalyst with a loading amount of 50%. The catalyst loading was carried out using conventional operating methods in the art.

[0044] Example 5

[0045] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following graded combination method. The catalyst graded loading amount was based on the total volume of the catalyst. The first section of the reactor inlet used C2 catalyst with a loading amount of 20%, the second section used C1 catalyst with a loading amount of 40%, and the third section used B1 catalyst with a loading amount of 40%. The catalyst loading was carried out using conventional operating methods in the art.

[0046] Comparative Example 1

[0047] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following gradation method. The catalyst gradation loading amount was based on the total volume of the catalyst. The reactor was 100% loaded with B1 catalyst. The catalyst loading was carried out using conventional operating methods in the art.

[0048] Comparative Example 2

[0049] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following gradation method. The catalyst gradation loading amount was based on the total volume of the catalyst. The reactor was 100% loaded with B2 catalyst. The catalyst loading technology was a conventional operation method in the field.

[0050] Comparative Example 3

[0051] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following gradation method. The catalyst gradation loading amount was based on the total volume of the catalyst. The reactor was 100% loaded with C1 catalyst. The catalyst loading technology was a conventional operation method in the field.

[0052] Comparative Example 4

[0053] The vanadium-phosphorus-oxygen catalyst prepared above was loaded according to the following gradation method. The catalyst gradation loading amount was based on the total volume of the catalyst. The reactor was 100% loaded with C2 catalyst. The catalyst loading was carried out using conventional operating methods in the art.

[0054] In the examples and comparative examples, the catalyst was packed in a stainless steel reaction tube with an inner diameter of 21 mm. The reaction temperature was 410 °C, the reaction pressure was 0.15 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 was evaluated under the given reaction conditions. The catalyst performance and bed hotspot temperatures are shown in Table 2.

[0055] Table 2.

[0056]

[0057] During the reaction, the hot spot temperature of the reaction apparatus was measured. It was found that the hot spot temperature in the mixed packing scheme was significantly lower than that in the packing scheme with only one low bulk density catalyst (Comparative Example 1). At the same time, the conversion rate and yield of the mixed packing scheme were also significantly higher than those of the packing scheme with only one high bulk density catalyst (Comparative Examples 3 and 4), demonstrating better catalytic reaction performance.

Claims

1. A catalyst grading method for the oxidation of n-butane to maleic anhydride, characterized in that, The fixed bed reactor has at least two catalyst beds, the catalysts in the catalyst beds are distributed in descending order of the contact ratio of the catalysts to the reaction gas, and the catalyst bed downstream in the contact sequence of the catalysts to the reaction gas has a catalyst stack ratio that is 3 g / cm 3 -7 g / cm 3 less than the catalyst stack ratio of the catalyst bed upstream adjacent thereto. The specific surface area of the catalyst in the downstream catalyst bed is increased by 1 m2 / g to 10 m2 / g compared to the specific surface area of the catalyst in the upstream catalyst bed adjacent thereto, in the order of contact of the catalyst with the reaction gas. 3 / g to 10 m 3 / g.

2. The catalyst grading method of claim 1, wherein, The catalyst bed in the fixed bed reactor is 2-6.

3. The catalyst grading method of claim 2, wherein, The catalyst bed in the fixed bed reactor is 2-4.

4. The catalyst grading method of claim 1, wherein, The downstream catalyst bed has a stack of 4 g / cm less than the catalyst in the upstream catalyst bed adjacent thereto, in terms of the order of contact of the catalyst with the reaction gas 3 - 5 g / cm 3 .

5. The catalyst grading method of claim 1, wherein, The specific surface area of the catalyst in the downstream catalyst bed is increased by 2 m2 / g to 8 m2 / g compared to the specific surface area of the catalyst in the upstream catalyst bed adjacent thereto, in the order of contact of the catalyst with the reaction gas. 3 / g-8 m 3 / g.

6. The catalyst grading method of claim 5, wherein, The specific surface area of the catalyst in the downstream catalyst bed is increased by 3 m2 / g to 5 m2 / g compared to the specific surface area of the catalyst in the upstream catalyst bed adjacent thereto, in the order of contact of the catalyst with the reaction gas. 3 / g to 5 m 3 / g.

7. The catalyst grading method of claim 1, wherein, The regulation method of catalyst bulk density includes: grinding the precursor before catalyst drying, grinding the powder before catalyst molding, pressure control during tablet molding, shape control of the catalyst, and control of the bulk density of different catalysts.

8. The catalyst grading method of claim 1, wherein, The regulation method of catalyst specific surface area includes: grinding degree control of the precursor, grinding the powder before catalyst molding, pressure control during tablet molding, pore-forming agent addition during preparation, and particle size control of the catalyst precursor.

9. The catalyst grading method of claim 1, wherein, The catalyst is prepared by the following method to control the bulk density: (1) using the conventional method in the technical field to prepare the precursor of the VPO catalyst; (2) using the tabletting method to mold the precursor into a Raschig ring or cylindrical catalyst particle, the method controls the diameter and pore size of the Raschig ring catalyst by controlling the pressure in the pressure ring machine and the diameter of the ejector pin, or controls the height-diameter length of the cylindrical catalyst, thereby controlling the loading bulk density of the catalyst in the reaction tube.

10. The catalyst grading method of claim 1, wherein, The reaction of n-butane oxidation to prepare dinitrile is as follows: n-butane is mixed with air, and the obtained mixed reaction gas is passed through the catalyst bed in series to perform the oxidation reaction.

11. The catalyst grading method of claim 1, wherein, The reaction conditions for preparing maleic anhydride from n-butane oxidation are as follows: reaction temperature 320-450 DEG C, pressure normal pressure-0.5 MPa, n-butane mixed gas space velocity 1000-3500 h -1 , n-butane concentration 1.0%-2.5%.

12. The catalyst grading method of claim 1, wherein, The catalyst is activated in a nitrogen or inert gas atmosphere before the reaction.

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