Method for producing maleic anhydride by using vanadium phosphorus oxide catalyst grading

Abstract

The invention relates to a method for producing maleic anhydride by using vanadium-phosphorus-oxide catalyst grading, which comprises the following steps: mixing butane and oxygen-containing gas, sequentially filling a vanadium-phosphorus-oxide catalyst I, a vanadium-phosphorus-oxide catalyst II and a vanadium-phosphorus-oxide catalyst III in a fixed bed reactor filled with vanadium-phosphorus-oxide catalysts along a material flow direction through the fixed bed reactor filled with the vanadium-phosphorus-oxide catalysts, and sequentially filling the vanadium-phosphorus-oxide catalyst I, the vanadium-phosphorus-oxide catalyst II and the vanadium-phosphorus-oxide catalyst III along the material flow direction, the porosity of the three vanadium phosphorus oxide catalysts is sequentially reduced, and the bulk ratio is sequentially increased; wherein the porosity of the vanadium phosphorus oxide catalyst I is 0.63-0.66, the bulk ratio of the vanadium phosphorus oxide catalyst I is 0.45-0.55 g / cm < 3 >, the porosity of the vanadium phosphorus oxide catalyst II is 0.57-0.62, the bulk ratio of the vanadium phosphorus oxide catalyst II is 0.55-0.65 g / cm < 3 >, the porosity of the vanadium phosphorus oxide catalyst III is 0.50-0.56, and the bulk ratio of the vanadium phosphorus oxide catalyst III is 0.65-0.75 g / cm < 3 >. While the reaction efficiency is ensured, the bed pressure drop and energy consumption of the reaction device are effectively reduced, and the operation period of the device is prolonged.

Description

Technical Field

[0001] The present invention relates to a reaction process for the production of maleic anhydride by the oxidation of n-butane, and more particularly to a method for producing maleic anhydride by using a graded vanadium phosphorus oxygen catalyst. Background Art

[0002] Maleic anhydride, also known as cis-butenedioic anhydride, is the third largest organic acid anhydride after phthalic anhydride and acetic anhydride. Due to many characteristics in its structure, maleic anhydride has strong reactivity and is an important raw material for synthesizing unsaturated polyester resins, alkyd resins, etc. It is also a raw material for preparing a series of important organic chemicals and fine chemicals such as 1,4-butanediol (BOD), tetrahydrofuran (HF), and fumaric acid, and is one of the important organic chemical products. It is expected that the total consumption of maleic anhydride in the world will reach 2.009 million tons in 2020.

[0003] At present, the industrial production process routes of maleic anhydride can be divided into four types according to raw materials: benzene oxidation method, n-butane oxidation method, C4 olefin method, and phthalic anhydride by-product method. The n-butane oxidation method uses n-butane as the raw material and undergoes a gas-phase oxidation reaction to produce maleic anhydride under the action of a V 2 O 5 -P 2 O 5 -based catalyst. Due to its characteristics such as low-cost raw materials and little environmental pollution, the technology for producing maleic anhydride by the n-butane oxidation method has been dominant in the production of maleic anhydride in recent years.

[0004] The vanadium phosphorus oxygen catalyst is the core of the technology for the production of maleic anhydride by the oxidation of n-butane. Therefore, extensive reports have been made in domestic and foreign patents and literature on the preparation and application methods of the vanadium phosphorus oxygen catalyst. Existing devices for the production of maleic anhydride by the oxidation of butane often use a single catalyst system. In the actual production process, as the reaction proceeds, the gas flow distribution in the bed layer is uneven, which easily causes problems such as the dispersion of hot spots in the reactor and a relatively high bed layer pressure drop, resulting in large power consumption, thus affecting the long-term continuous production of the maleic anhydride device, and also reducing the catalytic performance of the catalyst to a certain extent.

[0005] In addition to the single loading method of vanadium phosphorus oxygen catalyst, in order to achieve better catalytic reaction effects, those skilled in the art also choose a method of grading and loading a variety of vanadium phosphorus oxygen catalysts or catalysts with other fillers. CN106732702A discloses a catalyst grading method for the oxidation of n-butane to maleic anhydride. In this method, the mixed reaction gas of n-butane and air flows through more than three series-connected vanadium phosphorus oxygen catalyst beds in parallel. The average valence state of vanadium in the more than three series-connected catalyst beds shows a trend of first high, then low, and then rising. This method can reduce the reaction hot spot of the bed, make the temperature distribution of the bed average, effectively inhibit the occurrence of side reactions, improve the selectivity of the product, and increase the maleic anhydride yield. However, the catalyst grading method requires the catalyst to pass through more than three series-connected catalyst beds, and the catalyst in each bed contains three valence states. This method has a long catalyst loading process, a complex process, and low loading efficiency. S4855459A discloses a preparation method for the oxidation of n-butane to maleic anhydride, which is carried out by diluting and loading an inert silicon-aluminum ball and a catalyst in a reaction tube to achieve the purpose of reducing the reaction hot spot temperature, improving the selectivity and yield of maleic anhydride, and at the same time extending the stable operation period of the catalyst; but the addition of inert substances in this method will inevitably reduce the effective volume of the catalyst in the reactor, thereby reducing the production efficiency. Summary of the Invention

[0006] To solve the problems of the prior art, the present invention provides a method for producing maleic anhydride by grading vanadium phosphorus oxygen catalysts. Catalysts with different porosity and bulk ratio are graded and combined with catalysts of specific configurations, so that the front catalyst bed has a larger porosity and a smaller bulk ratio, in order to achieve the purpose of overall reducing the pressure drop of the bed during the reaction process, reducing power consumption, reducing production costs, improving the stability of the catalyst system and extending the operation period of the device.

[0007] To achieve the above technical objectives, the present invention provides a method for producing maleic anhydride by grading vanadium phosphorus oxygen catalysts. After butane is mixed with an oxygen-containing gas, it passes through a fixed-bed reactor filled with vanadium phosphorus oxygen catalyst. Along the logistics direction, vanadium phosphorus oxygen catalyst I, vanadium phosphorus oxygen catalyst II, and vanadium phosphorus oxygen catalyst III are successively filled in the fixed-bed reactor. Along the logistics direction, the porosity of the three vanadium phosphorus oxygen catalysts decreases successively, and the bulk ratio increases successively; among them, the porosity of vanadium phosphorus oxygen catalyst I is 0.63 - 0.66, and the bulk ratio is 0.45 - 0.55 g / cm 3 , the porosity of vanadium phosphorus oxygen catalyst II is 0.57 - 0.62, and the bulk ratio is 0.55 - 0.65 g / cm 3 , the porosity of vanadium phosphorus oxygen catalyst III is 0.50 - 0.56, and the bulk ratio is 0.65 - 0.75 g / cm 3 .

[0008] Further, preferably, the porosity of the vanadium phosphorus oxygen catalyst I is 0.64 - 0.66, and the bulk density is 0.49 - 0.53 g / cm 3 ; the porosity of the vanadium phosphorus oxygen catalyst II is 0.58 - 0.62, and the bulk density is 0.58 - 0.62 g / cm 3 . The bulk density of the vanadium phosphorus oxygen catalyst III is 0.68 - 0.72 g / cm with a porosity of 0.52 - 0.56 3 .

[0009] Further, in the technical solution of the present invention, preferably, a catalyst with the required porosity and bulk density requirements is obtained by controlling the shape and particle size of the catalyst.

[0010] Further, the vanadium phosphorus oxygen catalyst used in the present invention has the general shape of such catalysts in the prior art. Specifically, preferably, the cross-section of the catalyst is at least one or a mixture of several of Raschig ring type, tooth ball type, honeycomb type, polyhedral star type, etc.

[0011] Further, preferably, the vanadium phosphorus oxygen catalyst I is of polyhedral star type, specifically having the catalyst configurations described in CN219424411U and CN219879943U. The vanadium phosphorus oxygen catalyst with a polyhedral star type as the basic configuration can more easily obtain the catalyst with the porosity and bulk density ratio requirements in the technical solution of the present invention. More simply, the porosity and bulk density of the catalyst can be controlled by the diameter of the central through-hole. For catalysts with other configurations such as the most commonly used Raschig ring type, it is difficult to achieve a bulk density lower than 0.62, and it is relatively difficult to obtain a vanadium phosphorus oxygen catalyst with a lower bulk density by adjusting the configuration or the catalyst raw materials.

[0012] Further, as a more specific embodiment, the multi-star catalyst is a catalyst formed body having the following structure: it includes a column extending in the longitudinal direction, and the column has a cross-section perpendicular to the longitudinal direction; the cross-section has a central through-hole, at least four first corners, and the same number of first recesses as the number of first corners; the at least four first corners are arranged at the same angular intervals in the circumferential direction to define a first circumscribed circle of the outer contour of the catalyst formed body, each first corner is tangent to the first circumscribed circle, and the at least four first corners are rotationally symmetric with respect to the center of the first circumscribed circle; the first corners and the first recesses are arranged alternately in the circumferential direction, the first corners and the first recesses have different geometric shapes, the first corner is the convex part of a first ellipse with a ratio of the major axis to the minor axis greater than 1.2, and the first recess is an inner concave arc tangent to two adjacent first corners, so as to avoid the occlusion between the first corners and / or first recesses of the catalyst formed body and the first recesses and / or first corners of adjacent catalyst formed bodies. The multi-star catalyst has a central through-hole, and by designing the parameters of the central through-hole, the external surface area and the strength of the catalyst particles are effectively increased, further significantly improving the porosity of the catalyst bed layer and alleviating the increase in the pressure drop of the industrial device bed layer.

[0013] And, preferably, the ratio of the major axis to the minor axis of the second ellipse is equal to the ratio of the major axis to the minor axis of the first ellipse. The ratio of the area of the second circumscribed circle of the central through-hole to the area of the first circumscribed circle of the outer contour of the catalyst formed body is 0.17 to 0.34.

[0014] Preferably, each first recess is tangent to a first inscribed circle, and the first ellipse corresponding to each first corner is tangent to a second inscribed circle. The first inscribed circle and the second inscribed circle are both concentric with the first circumscribed circle, and the radius of the first inscribed circle is greater than the radius of the second inscribed circle.

[0015] Preferably, the height of the catalyst formed body in the longitudinal direction is greater than or equal to the radius of the first circumscribed circle of the outer contour of the catalyst formed body.

[0016] Preferably, the radius of the first circumscribed circle of the outer contour of the catalyst formed body is 2 mm to 5 mm, more preferably 3 mm to 4 mm.

[0017] Preferably, the line connecting the center of the first ellipse and the center of the first circumscribed circle is perpendicular to the major axis of the first ellipse, and the ratio of the length of the major axis of the first ellipse to the radius of the first circumscribed circle is 0.2 to 1.

[0018] Preferably, the central through-hole has second corners with the same number as the first corners and second recesses with the same number as the first recesses. The second corners define a second circumscribed circle of the central through-hole. The first corners and the second corners are aligned in the circumferential direction. Each second corner is tangent to the second circumscribed circle, and the second corners are rotationally symmetric with respect to the center of the second circumscribed circle. The first recesses and the second recesses are aligned in the circumferential direction. Each second corner is an outward convex part of a second ellipse, and the second recess is an inward concave arc tangent to two adjacent second corners.

[0019] Preferably, the central through-hole of the multi-star-shaped catalyst has a profile similar to the external contour of the catalyst, which can reduce the wall thickness of the catalyst, thereby saving costs.

[0020] The bulk density of the above multi-star-shaped catalyst is reduced, the catalyst performance is improved, the product yield per unit mass of the catalyst is increased, and the production capacity of the catalyst is improved. The geometric body of the above multi-star-shaped catalyst is a cylinder. The catalyst formed body has good mechanical properties, is easy to manufacture, can be formed under low pressure, has high mechanical strength and strong compressive capacity; it has no irregular edges and corners, is easy to produce, has good abrasion resistance, is not easy to break, has good mechanical stability, reduces the loss of the catalyst formed body during transportation and use, and can ensure the structural integrity during transportation, loading and high airspeed operation, effectively reducing the increase in the pressure drop of the catalyst bed layer caused by catalyst fragmentation and abrasion.

[0021] Further, in combination with the requirements of the butane oxidation to maleic anhydride reaction process in the prior art and the requirements of the technical solution of the present invention, the length of the vanadium phosphorus oxygen catalyst I is 6.0 - 7.0 mm, and the diameter is 6.0 - 7.0 mm; the length of the vanadium phosphorus oxygen catalyst II is 5.0 - 6.0 mm, and the diameter is 5.0 - 6.5 mm; the length of the vanadium phosphorus oxygen catalyst III is 3.0 - 5.0 mm, and the diameter is 4.5 - 6.0 mm. The diameter of the catalyst herein refers to the diameter of the largest circumscribed circle of the cross-section of the catalyst based on the cross-section.

[0022] Further, from any one of the reaction tubes of the tubular reactor for the production of maleic anhydride by butane oxidation, the volume ratio of the vanadium phosphorus oxygen catalyst I is 10% - 25%, the volume ratio of the vanadium phosphorus oxygen catalyst II is 40% - 55%, and the volume ratio of the vanadium phosphorus oxygen catalyst III is 20% - 45%.

[0023] Further, the vanadium phosphorus oxygen catalyst used in the present invention is prepared by a conventional method in the prior art. First, a vanadium phosphorus oxygen catalyst precursor is prepared by a liquid phase method, and then the vanadium phosphorus oxygen catalyst is obtained through steps of forming, tabletting and activation.

[0024] Further, the preparation of the vanadium phosphorus oxygen catalyst precursor by the liquid phase method is a technique well-known to those skilled in the art, which generally refers to the method of reacting phosphoric acid and vanadium oxides as raw materials in an organic solvent to prepare a vanadium phosphorus oxygen catalyst precursor solution in the prior art. Specifically, it generally refers to using an organic solvent as the solvent and preparing from vanadium pentoxide and phosphoric acid. Among them, the organic solvent is selected from at least one of isopentyl alcohol, isobutyl alcohol, isopropyl alcohol, benzyl alcohol and n-octanol.

[0025] Further, the preparation process of the vanadium phosphorus oxygen catalyst further includes a step of introducing a promoter, and the promoter includes but is not limited to at least one salt containing an element such as Li, Na, K, Ca, Mg, Zn, Fe, Bi, Ni, Si, Mo, Co, Zr, Cu, Ti, La, Nb, B, Cr or Ce; the promoter can be introduced into the catalyst in one of the following ways: (1) introducing into the reaction solution during the preparation of the vanadium phosphorus oxygen precursor; (2) introducing before or during the catalyst shaping; (3) introducing in the form of solution impregnation after the activation of the vanadium phosphorus oxygen catalyst is completed.

[0026] As one of the more specific embodiments, the vanadium phosphorus oxygen catalyst of the present invention is prepared by the following method:

[0027] (1) Mix the organic solvent, vanadium pentoxide and phosphoric acid evenly and add them to a reactor, carry out a coprecipitation reaction at a reaction temperature of 85-95 °C, and obtain a suspension, which is filtered, dried and calcined to obtain a vanadium phosphorus oxygen catalyst precursor;

[0028] (2) The vanadium phosphorus oxygen catalyst precursor is shaped first and then activated, or activated first and then shaped to obtain a vanadium phosphorus oxygen catalyst.

[0029] Further, the coprecipitation reaction is carried out under the condition of total reflux.

[0030] In step (1), vanadium pentoxide and phosphoric acid are fed according to a molar ratio of P:V of 0.85-1.30, preferably 0.90-1.20.

[0031] In step (1), the drying conditions are as follows: drying at a temperature of 60-120 °C, preferably 80-100 °C for 4-12 h; the calcination conditions are as follows: calcining at a temperature of 160-280 °C, preferably 180-260 °C for 2-12 h.

[0032] Further, the activation is carried out in an atmosphere of a mixture of air / inert gas, air / butane, air / water vapor, a mixture of butane / inert gas or a combination of several of them. The activation temperature is generally 220-420 °C, preferably 350-400 °C; the activation time is generally 2-12 h, preferably 4-10 h.

[0033] Further, the forming method may be carried out by using conventional catalyst forming methods such as tabletting, extrusion or spheronization.

[0034] Further, the reaction conditions for the oxidation of n-butane to maleic anhydride are generally as follows: reaction temperature 370 - 450 °C, pressure 0.1 - 0.6 MPa, space velocity of the n-butane mixed gas is 600 - 2500 h -1 , and the concentration of n-butane is 1.2 - 1.9% (volume percentage).

[0035] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0036] (1) By adjusting the porosity and bulk ratio of the catalysts in different reaction zones of the n-butane oxidation to maleic anhydride device, the present invention effectively reduces the bed pressure drop and energy consumption of the reaction device while ensuring the reaction efficiency of the reaction device, prolongs the operation cycle of the device, and improves the economic benefits of the enterprise.

[0037] (2) In the present invention, the vanadium phosphorus oxygen catalyst in the upstream reaction zone has a large porosity and a low bulk density, while the downstream has a small porosity and a high bulk density, and the reaction activity gradually increases along the direction of the material flow, realizing a smooth transition of the n-butane oxidation reaction, effectively reducing the hot spot temperature, and improving the selectivity of the maleic anhydride product.

[0038] (3) The catalyst grading of the present invention uses a multi-star-shaped vanadium phosphorus oxygen catalyst with a low bulk density, which can significantly reduce the bulk ratio of the whole bed catalyst and effectively reduce the overall cost of the catalyst.

[0039] (4) The present invention is mainly realized by adjusting the configuration and specifications of the catalyst forming process, and the production process and control method are relatively easy.

[0040] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic three-dimensional structure diagram of Catalyst I in Example 1;

[0042] Figure 2 is a schematic cross-sectional view of Catalyst I in Example 1;

[0043] Figure 3 is a schematic cross-sectional view of Catalyst II in Example 1;

[0044] Figure 4 is a schematic cross-sectional view of Catalyst III in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0045] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0046] The vanadium phosphorus oxygen catalyst precursor used in the following examples and comparative examples of the present invention was prepared by the following method:

[0047] Using a four-necked flask equipped with a stirrer and a reflux condenser, 420 g of isobutanol, 20.0 g of vanadium pentoxide, and 0.15 g of calcium hydrogen phosphate as an additive were added to the four-necked flask. Subsequently, 38.0 g of concentrated phosphoric acid with a concentration of 95% was added, and stirring was started at a rotation speed of 600 r / min. Subsequently, the reaction temperature was gradually increased to 98 °C at a heating rate of 10 °C / h, and the reaction was continued for 8 hours to obtain a blue slurry suspension of the vanadium phosphorus oxygen catalyst precursor. After the reaction product was cooled to room temperature, it was vacuum filtered and dried. The filter cake during the filtration was washed three times with isobutanol, and after the filter cake was naturally air-dried at room temperature, it was placed in an oven and dried at 120 °C for 6 h. Finally, the solid product was calcined at 260 °C for 4 h to obtain a vanadium phosphorus oxide precursor. The vanadium phosphorus oxide precursor was mixed with 5% graphite, formed, and activated to obtain a vanadium phosphorus oxygen catalyst.

[0048] Through the forming step, catalysts with different configurations in the following examples were prepared to obtain vanadium phosphorus oxygen catalysts with different porosities and bulk ratios.

[0049] Example 1

[0050] Catalyst I: Catalyst I is Figure 1 and Figure 2The catalyst formed body 100 of the structure shown has a column extending in the longitudinal direction. The column has a cross-section perpendicular to the longitudinal direction, and the cross-section is a four-pointed star shape. The column is formed by sweeping the cross-section perpendicular to the height direction / longitudinal direction along the height direction. Among them, the cross-section has a central through-hole 1, four first corner portions 2, and four first concave portions 3; the four first corner portions 2 are arranged at the same angular interval in the circumferential direction to define the first circumscribed circle 101 of the outer contour of the catalyst formed body. Each first corner portion 2 is tangent to the first circumscribed circle 101, and the at least four first corner portions 2 are rotationally symmetric with respect to the center of the first circumscribed circle 101. The first corner portions 2 and the first concave portions 3 are alternately arranged in the circumferential direction. The first corner portions 2 and the first concave portions 3 have different geometric shapes. The first corner portion 2 is the convex portion of a first ellipse with a ratio of the major axis to the minor axis greater than 1.2, and the first concave portion 3 is an inward concave arc tangent to two adjacent first corner portions 2 to avoid the occlusion between the first corner portions 2 and / or the first concave portions 3 of the catalyst formed body and the first concave portions 3 and / or the first corner portions 2 of the adjacent catalyst formed body. A first concave portion 3 is connected between any two adjacent first corner portions 2, and the first concave portion 3 is an inward concave arc tangent to the two adjacent first corner portions 2; the central through-hole 1 is concentric with the first circumscribed circle 101 of the cross-section. Each first concave portion 3 is tangent to a first inscribed circle 102, and the first ellipse corresponding to each first corner portion 2 is tangent to a second inscribed circle 103. The first inscribed circle 102 and the second inscribed circle 103 are both concentric with the first circumscribed circle 101, and the radius of the first inscribed circle 102 is greater than the radius of the second inscribed circle 103.

[0051] The geometric body enclosed by the four first corner portions 2 is a cylinder, and the radius of the cylinder is 3.5 mm, that is, the radius of the first circumscribed circle 101 of the cross-section is 3.5 mm; the height of the cylinder (i.e., the length of the catalyst) is 6 mm. The four first corner portions 2 are all the convex portions of the first ellipse tangent to the first circumscribed circle 101, and the four convex elliptical portions have the same major axis length and minor axis length, where the major axis length is 2 mm and the minor axis length is 1.2 mm. The angular interval between every two adjacent first corner portions 2 is 90°.

[0052] Catalyst I has a central through-hole 1 with a continuous opening extending parallel to the axis of the cylinder. The central through-hole 1 has the same number of second corners 202 as the first corners 2 and the same number of second recesses 203 as the first recesses 3. The second corners define a second circumscribed circle 201 of the central through-hole 1. The first corners 2 and the second corners 202 are aligned in the circumferential direction. The first recesses 3 and the second recesses 203 are aligned in the circumferential direction. Each second corner 202 is a part of a second convex ellipse. Each second corner 202 is tangent to the second circumscribed circle 201, and the second corner 202 is rotationally symmetric with respect to the center of the second circumscribed circle 201. The second recess 203 is an inner concave arc tangent to two adjacent second corners 202.

[0053] That is, the central through-hole 1 is similar in cross-sectional shape. The ratio of the major axis to the minor axis of the second ellipse is equal to the ratio of the major axis to the minor axis of the first ellipse. The aperture of the central through-hole 1 makes the wall thickness of the catalyst particles 1.5 mm.

[0054] It is measured that the porosity of the natural packing of Catalyst I is 0.65 and the bulk ratio is 0.52.

[0055] Catalyst II:

[0056] Catalyst II is different from Catalyst I in that the central through-hole 1 is circular, and its cross-section is as Figure 3 shown. The diameter of the central through-hole 1 is 2.5 mm, and the height of the catalyst cylinder (i.e., the length of the catalyst) is 5.8 mm.

[0057] It is measured that the porosity of the natural packing of Catalyst II is 0.60 and the bulk ratio is 0.60.

[0058] Catalyst III:

[0059] Catalyst III is different from Catalyst I in that the central through-hole 1 is elliptical, and its cross-section is as Figure 4 shown. The major axis length of the central through-hole 1 is 2.5 mm, the minor axis length is 2.0 mm, and the height of the catalyst cylinder (i.e., the length of the catalyst) is 5.0 mm.

[0060] It is measured that the porosity of the natural packing of Catalyst III is 0.54 and the bulk ratio is 0.68.

[0061] Along the flow direction of the material, in the tubular fixed-bed reactor, Catalyst I, Catalyst II, and Catalyst III are filled in sequence according to a volume ratio of 25:50:25, activated, and the activity evaluation of the oxidation of butane to maleic anhydride is carried out.

[0062] Example 2

[0063] Catalyst I, Catalyst II, and Catalyst III are the same as those in Example 1. Along the flow direction, in a shell-and-tube fixed-bed reactor, Catalyst I, Catalyst II, and Catalyst III are loaded in sequence according to a volume ratio of 25:45:30, activated, and the activity evaluation of butane oxidation to maleic anhydride is carried out.

[0064] Example 3

[0065] Catalyst I is the same as Catalyst I in Example 1;

[0066] Catalyst II is the same as Catalyst II in Example 1;

[0067] Catalyst III is in the shape of Raschig rings, with an outer diameter of 5.8 mm, an inner diameter of 2.8 mm, and a catalyst length of 5.0 mm.

[0068] It is measured that the porosity of the naturally loaded Catalyst III is 0.53, and the bulk ratio is 0.71.

[0069] Along the flow direction, in a shell-and-tube fixed-bed reactor, Catalyst I, Catalyst II, and Catalyst III are loaded in sequence according to a volume ratio of 15:55:30, activated, and the activity evaluation of butane oxidation to maleic anhydride is carried out.

[0070] Example 4

[0071] Catalyst I is the same as Catalyst I in Example 1.

[0072] Catalyst II is in the shape of Raschig rings, with an outer diameter of 6.0 mm, an inner diameter of 3.2 mm, and a catalyst length of 6.0 mm. The porosity of the naturally loaded Catalyst II is 0.61, and the bulk ratio is 0.64.

[0073] Catalyst III is in the shape of five-tooth balls, and the diameter of the catalyst particles is 5.0 mm. It is measured that the porosity of the naturally loaded Catalyst III is 0.51, and the bulk ratio is 0.74.

[0074] Along the flow direction, in a shell-and-tube fixed-bed reactor, Catalyst I, Catalyst II, and Catalyst III are loaded in sequence according to a volume ratio of 15:45:40, activated, and the activity evaluation of butane oxidation to maleic anhydride is carried out.

[0075] Comparative Example 1

[0076] Along the flow direction, in the same shell-and-tube fixed-bed reactor, all of the Raschig ring-shaped Catalyst III of Example 3 is loaded, activated, and the activity evaluation of butane oxidation to maleic anhydride is carried out.

[0077] Comparative Example 2

[0078] Along the logistics direction, the catalyst I of Example 1 was completely filled in the same tubular fixed-bed reactor, activated, and the activity evaluation of butane oxidation to maleic anhydride was carried out.

[0079] The results of the activity evaluation are shown in Table 1.

[0080] Comparative Example 3

[0081] Along the logistics direction, in the same tubular fixed-bed reactor, the catalyst III, catalyst II and catalyst I in Example 1 were filled in sequence according to the volume ratio of 25:50:25, activated, and the activity evaluation of butane oxidation to maleic anhydride was carried out.

[0082] In the above examples and comparative examples, the activation and reaction activity evaluation of the graded catalyst for butane oxidation to maleic anhydride were carried out in the following manner: The catalyst was filled into a single-tube tubular fixed-bed reactor with a tube length of 6 m and an inner diameter of 21 mm. After filling and passing the airtightness test, the raw material reaction gas was introduced. The raw material was a 1.5 v% n-butane / air mixture, and the volume space velocity was 1800 h -1 , controlling the reaction temperature at 391 °C and the reaction pressure at 0.20 Mpa.

[0083] After the reaction was stable, gas chromatography was used to analyze the composition of the product, and the conversion rate and selectivity results were obtained. The hot spot temperature was measured by a multi-point thermocouple, and the hot spot height was measured starting from the material inlet. The bed pressure drop was measured by a differential pressure gauge. The experimental results are shown in Table 1.

[0084] Table 1.

[0085]

[0086] It can be seen from the results of the single-tube tubular fixed-bed reactor in the table that in Examples 1-4, the filling method with a large porosity and low bulk density of the vanadium phosphorus oxygen catalyst in the upstream reaction zone and a small porosity and high bulk density in the downstream can, on the one hand, adjust the hot spot position to after 1 / 3 of the bed layer, avoiding the problem of strong catalyst activity and low maleic anhydride selectivity in the upstream reaction zone; at the same time, this graded filling also reduces the hot spot temperature of the single-tube reactor. For an industrial reactor for n-butane oxidation to maleic anhydride with more than 20,000 single tubes, this grading method can effectively achieve a smooth transition of the reaction and avoid the phenomenon of reactor runaway temperature.

Claims

1. A method for producing maleic anhydride by using a graded vanadium phosphorus oxygen catalyst. After butane is mixed with an oxygen-containing gas, it passes through a fixed-bed reactor filled with a vanadium phosphorus oxygen catalyst. Characterized in that, Along the logistics direction, vanadium phosphorus oxygen catalyst I, vanadium phosphorus oxygen catalyst II, and vanadium phosphorus oxygen catalyst III are successively filled in the fixed-bed reactor. Along the logistics direction, the porosity of the three vanadium phosphorus oxygen catalysts decreases successively, and the bulk ratio increases successively. Among them, the porosity of vanadium phosphorus oxygen catalyst I is 0.63 - 0.66, and the bulk ratio is 0.45 - 0.55 g / cm 3 , the porosity of vanadium phosphorus oxygen catalyst II is 0.57 - 0.62, and the bulk ratio is 0.55 - 0.65 g / cm 3 , the porosity of vanadium phosphorus oxygen catalyst III is 0.50 - 0.56, and the bulk ratio is 0.65 - 0.75 g / cm 3 .

2. The method according to claim 1, Characterized in that, The porosity of vanadium phosphorus oxygen catalyst I is 0.64 - 0.66, and the bulk density is 0.49 - 0.53 g / cm 3 ; The porosity of vanadium phosphorus oxygen catalyst II is 0.58 - 0.62, and the bulk density is 0.58 - 0.62 g / cm 3 . The bulk density of vanadium phosphorus oxygen catalyst III is 0.68 - 0.72 g / cm with a porosity of 0.52 - 0.56 3 .

3. The method according to claim 1 or 2, Characterized in that, The catalyst with the required porosity and bulk ratio requirements is obtained by controlling the shape and particle size of the catalyst.

4. The method according to claim 3, Characterized in that, The cross-section of the vanadium phosphorus oxygen catalyst used is at least one or a mixture of several of Raschig ring type, tooth ball type, honeycomb type, multi-angle star type, etc.

5. The method according to claim 4, Characterized in that, The vanadium phosphorus oxygen catalyst I is of multi-angle star type.

6. The method according to claim 1, Characterized in that, The multi-angle star type is a catalyst formed body with the following structure: it includes a column extending in the longitudinal direction, and the column has a cross-section perpendicular to the longitudinal direction; the cross-section has a central through-hole, at least four first corner parts and the same number of first concave parts as the number of first corner parts; the at least four first corner parts are arranged at the same angular interval in the circumferential direction to define a first circumscribed circle of the outer contour of the catalyst formed body, each first corner part is tangent to the first circumscribed circle, and the at least four first corner parts are rotationally symmetric with respect to the center of the first circumscribed circle; the first corner parts and the first concave parts are arranged alternately in the circumferential direction, the first corner parts and the first concave parts have different geometric shapes, the first corner part is the convex part of a first ellipse with a ratio of the major axis to the minor axis greater than 1.2, and the first concave part is an inner concave arc tangent to two adjacent first corner parts to avoid the occlusion between the first corner part and / or the first concave part of the catalyst formed body and the first concave part and / or the first corner part of the adjacent catalyst formed body.

7. The method according to claim 6, Characterized in that, The ratio of the major axis to the minor axis of the second ellipse is equal to the ratio of the major axis to the minor axis of the first ellipse; the ratio of the area of the second circumscribed circle of the central through-hole to the area of the first circumscribed circle of the outer contour of the catalyst formed body is 0.17 to 0.

34.

8. The method according to claim 6, Characterized in that, Each first concave part is tangent to a first inscribed circle, and each first ellipse corresponding to a first corner part is tangent to a second inscribed circle. The first inscribed circle and the second inscribed circle are both concentric with the first circumscribed circle, and the radius of the first inscribed circle is greater than the radius of the second inscribed circle.

9. The method according to claim 6, Characterized in that, The height of the catalyst formed body in the longitudinal direction is greater than or equal to the radius of the first circumscribed circle of the outer contour of the catalyst formed body; the radius of the first circumscribed circle of the outer contour of the catalyst formed body is 2 mm to 5 mm; the connection line between the center of the first ellipse and the center of the first circumscribed circle is perpendicular to the major axis of the first ellipse, and the ratio of the length of the major axis of the first ellipse to the radius of the first circumscribed circle is 0.2 to 1.

10. The method according to claim 6, Characterized in that, The central through-hole has second corners with the same number as the first corners and second recesses with the same number as the first recesses. The second corners define a second circumscribed circle of the central through-hole. The first corners and the second corners are aligned in the circumferential direction. Each second corner is tangent to the second circumscribed circle, and the second corners are rotationally symmetric with respect to the center of the second circumscribed circle. The first recesses and the second recesses are aligned in the circumferential direction. Each second corner is an outward convex part of a second ellipse, and the second recess is an inward concave arc tangent to two adjacent second corners.

11. According to the method described in claim 10, wherein, the central through-hole of the multi-star-shaped catalyst has a profile similar to the external contour of the catalyst.

12. According to the method described in claim 1, wherein, the vanadium phosphorus oxygen catalyst I has a length of 6.0 - 7.0 mm and a diameter of 6.0 - 7.0 mm; the vanadium phosphorus oxygen catalyst II has a length of 5.0 - 6.0 mm and a diameter of 5.0 - 6.5 mm; the vanadium phosphorus oxygen catalyst III has a length of 3.0 - 5.0 mm and a diameter of 4.5 - 6.0 mm, where the diameter of the catalyst refers to the diameter of the largest circumscribed circle of the cross-section of the catalyst.

13. According to the method described in claim 1, wherein, Taking any one of the reaction tubes of the tubular reactor for producing maleic anhydride by butane oxidation, the volume ratio of the vanadium phosphorus oxygen catalyst I is 10% - 25%, the volume ratio of the vanadium phosphorus oxygen catalyst II is 40% - 55%, and the volume ratio of the vanadium phosphorus oxygen catalyst III is 20% - 45%.

14. According to the method described in claim 1, wherein, the vanadium phosphorus oxygen catalyst used is first prepared as a vanadium phosphorus oxygen catalyst precursor by a liquid-phase method, and then obtained through steps of shaping, tabletting, and activation; the liquid-phase method uses phosphoric acid and vanadium oxide as raw materials and reacts in an organic solvent to prepare a vanadium phosphorus oxygen catalyst precursor solution; the organic solvent is selected from at least one of isopentyl alcohol, isobutyl alcohol, isopropyl alcohol, benzyl alcohol, and n-octyl alcohol.

15. According to the method described in claim 1, wherein, the vanadium phosphorus oxygen catalyst used is prepared by the following method: (1) Mix an organic solvent, vanadium pentoxide, and phosphoric acid evenly and add them to a reactor. Carry out a coprecipitation reaction at a reaction temperature of 85 - 95 °C. The obtained suspension is filtered, dried, and calcined to obtain a vanadium phosphorus oxygen catalyst precursor; (2) The vanadium phosphorus oxygen catalyst precursor is first shaped and then activated, or first activated and then shaped to obtain the vanadium phosphorus oxygen catalyst.

16. According to the method described in claim 15, wherein, The coprecipitation reaction is carried out under total reflux conditions; in step (1), the molar ratio of vanadium pentoxide to phosphoric acid is 0.85 - 1.30 in terms of P:V; in step (1), the drying conditions are as follows: drying at a temperature of 60 - 120 °C for 4 - 12 h; the calcination conditions are as follows: calcining at a temperature of 160 - 280 °C for 2 - 12 h; the activation is carried out in an atmosphere of one or several combinations of a mixture of air / inert gas, air / butane, air / water vapor, and a mixture of butane / inert gas; the activation temperature is 220 - 420 °C, and the activation time is 2 - 12 h; the shaping method can be carried out by conventional catalyst shaping methods such as tabletting, extrusion, or spheronization.

17. According to the method described in claim 1, it is characterized in that The reaction conditions for the oxidation of n-butane to maleic anhydride are as follows: reaction temperature is 370 - 450 °C, pressure is 0.1 - 0.6 MPa, the space velocity of the n-butane mixed gas is 600 - 2500 h -1 , and the volume percentage concentration of n-butane is 1.2 - 1.9%.

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