Catalyst system for preparing maleic anhydride by catalytic oxidation of n-butane

Abstract

The present invention relates to a catalyst system for preparing maleic anhydride by catalytic oxidation of n-butane, comprising at least one reaction tube having two catalyst layers composed of different catalyst particles, characterized in that, in the direction of gas flow, the geometric surface area of ​​each catalyst particle is greater in the first catalyst layer than in the second catalyst layer. The present invention further relates to a process for preparing maleic anhydride by catalytic oxidation of n-butane, wherein a reactant gas comprising oxygen and n-butane is passed through the catalyst system according to the invention and the at least one reaction tube is subjected to an elevated temperature.

Description

Technical Field

[0001] The present invention relates to a catalyst system for preparing maleic anhydride by catalytic oxidation of n-butane, comprising at least one reaction tube having two catalyst layers composed of different catalyst particles, characterized in that, in the gas flow direction, the geometric surface area of ​​each catalyst particle in the first catalyst layer is larger than the geometric surface area of ​​each catalyst particle in the second catalyst layer.

[0002] The invention further relates to a process for preparing maleic anhydride by catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is passed through the two-layer catalyst system according to the invention and at least one reaction tube is subjected to elevated temperature. Background Art

[0003] Maleic anhydride is an economically important chemical intermediate. It is used, for example, alone or in combination with other acids, in the preparation of alkyd and polyester resins. Furthermore, it is a versatile intermediate in chemical synthesis, for example in the synthesis of gamma-butyrolactone, tetrahydrofuran, and 1,4-butanediol, which in turn can be used as a solvent or processed into polymers such as polytetrahydrofuran or polyvinylpyrrolidone.

[0004] The industrial production of maleic anhydride (MA) from n-butane is carried out via selective gas-phase oxidation in a cooled tube bundle reactor. Catalyst particles are packed into the reaction tubes as a VPO catalyst, forming a catalyst bed there. Because the reaction releases significant amounts of heat (n-butane to MA: -1260 kJ / mol, n-butane to CO₂: 2877 kJ / mol), the reaction is typically carried out in a tube bundle reactor with a typical tube inner diameter of 21 mm. This allows the heat to be dissipated through the tube walls into a cooling medium consisting of molten salt.

[0005] EP 2643086 A1 discloses a catalyst shaped body for the catalytic conversion of n-butane to maleic anhydride in a fixed-bed reactor, wherein the catalyst shaped body is shaped as a cylinder having a base, a cylindrical surface, a cylinder axis and at least one through-opening extending parallel to the cylinder axis, and the cylinder bottom surface has at least four convex corners, wherein the geometric matrix surrounding the catalyst shaped body is a prism, wherein the prism has a prism bottom surface, and the prism bottom surface has a length and a width, wherein the length is greater than the width.

[0006] US Pat. No. 6,005,121 discloses an improved process for the preparation of maleic anhydride by catalytic oxidation of non-aromatic hydrocarbons having at least four carbon atoms in a linear chain, wherein a gas containing oxygen and hydrocarbons is passed through a fixed bed of catalyst in a tubular reactor. The activity of the catalyst bed is graded so that the reactor can be operated in the portion of the bed where the gas temperature exceeds the temperature of the cooling fluid, with an initial (reactant gas) hydrocarbon concentration exceeding 1.5% by volume, an overall average temperature difference between the gas and the cooling fluid of at least about 15° C., and a production rate of at least about 5.0 pounds of maleic anhydride per hour, while the temperature difference between the gas and the cooling fluid at any point in the catalyst bed during the reaction does not exceed 80° C. Preferably, the catalyst activity and the gas permeability of the bed vary in the direction of gas flow so that the catalyst activity and the pressure drop per unit distance are lower in a critical region where the combination of temperature and hydrocarbon concentration might otherwise cause the reaction to proceed at an excessively rapid rate compared to regions of lower temperature and lower hydrocarbon concentration. Summary of the Invention

[0007] The object is therefore to provide a reactor system, in particular a tube bundle reactor, for the catalytic oxidation of n-butane to maleic anhydride, with which thermally stable operation and high MA yields are possible.

[0008] This task is achieved by a catalyst system in which two types of catalyst particles of different shapes are filled in series into a reaction tube, the catalyst system comprising a reaction tube having two catalyst layers, each consisting of different catalyst particles, characterized in that, in the direction of gas flow, the geometric surface area of ​​each catalyst particle in the first catalyst layer is larger than the geometric surface area of ​​each catalyst particle in the second catalyst layer.

[0009] The object is also achieved by a process for the catalytic oxidation of n-butane to prepare maleic anhydride, wherein a mixture of oxygen and n-butane is passed through the catalyst system according to the invention and the reaction tubes are subjected to elevated temperature.

[0010] The portion of the reaction tube filled with catalyst particles typically has a length of 3 to 8 m, preferably 4 to 6 m. However, the catalyst system according to the present invention is particularly suitable for short reaction tubes, which have a filled portion with a length of between 4 and 5 m, or for example 4.5 m. In the section of the reaction tube filled with catalyst particles, the catalytic oxidation of n-butane to maleic anhydride occurs, so the temperature in this area must be controlled, i.e., thermoregulation is required. The reactant gas, which must contain n-butane and oxygen, comprises, for example, a mixture of 0.2 to 10% by volume of n-butane and 5 to 50% by volume of oxygen. Typically, the reactant gas consists of a mixture of 0.5 to 3% by volume of n-butane, 10 to 30% by volume of oxygen, and the remainder is an inert gas such as nitrogen and 1 to 4% by volume of water. It is particularly preferred that the reactant gas contains air and an appropriate amount of n-butane and optionally water is added. Preferably, a small amount of 0.5 to 5 ppm or 1 to 3 ppm, based on the gas volume, of an organic phosphate such as trimethyl phosphate or triethyl phosphate may be present in the reactant gas to balance the phosphate loss of the catalyst. The reactant gas is introduced into the reaction tube (typically from below) and contacts the catalyst particles at an elevated temperature in the portion of the reaction tube filled with the catalyst particles, where n-butane is oxidized to maleic anhydride.

[0011] Preferably, there are a plurality of reaction tubes that can be temperature-controlled individually or together. Since the selective oxidation of n-butane to maleic anhydride is an exothermic reaction, excess heat must be dissipated and it must be ensured that the reaction tubes have the necessary reaction temperature. Preferably, the temperature is controlled by a salt bath (e.g., a eutectic of potassium nitrate and sodium nitrite in a ratio of about 1:1), in which a large number of reaction tubes are embedded. During the reaction, the salt bath typically has a temperature between 380°C and 430°C. During the reaction, a temperature distribution is formed axially in the reaction tube, wherein a region with the highest temperature ("hot spot") is generated in the first third of the reaction tube. Typically, the maximum temperature in the reaction tube is 430°C to 460°C, and according to the present invention, a maximum temperature between 440°C and 450°C is preferred.

[0012] The catalyst particles preferably contain a vanadium pyrophosphate phase (VPO phase) and can be supported or consist entirely of the VPO phase. The VPO phase can have conventional dopants, in particular molybdenum and / or alkali metals, as described, for example, in DE 10 2014 004786 A1.

[0013] According to the present invention, the reaction tube includes or is composed of two catalyst layers, and the catalyst layers have catalyst particles of different geometric shapes. The two catalyst particle beds are passed through by the reactant gas in the reaction tube, wherein one opening of the tube is used as a gas inlet, and the opposite opening is used as a gas outlet. According to the present invention, the catalyst layer close to the gas inlet is the first catalyst layer in the direction in which the gas flows, and the subsequent catalyst layer in the direction in which the gas flows is the second catalyst layer. Preferably, when the two catalyst layers are directly successive, i.e. in contact with each other. The length of the catalyst layer is the axial cross-section of the reaction tube occupied by the respective catalyst particles. The length of the first catalyst layer in the direction in which the gas flows is equal to or greater than the length of the second catalyst layer in the direction in which the gas flows. Preferably, the ratio of the length of the first catalyst layer to the second catalyst layer is in the range of 1:1 to 5:1, particularly preferably in the range of 2:1 to 4:1.

[0014] According to the present invention, in the direction of gas flow, the geometric surface area of ​​each catalyst particle in the first catalyst layer is greater than the geometric surface area of ​​each catalyst particle in the second catalyst layer. Preferably, the catalyst particles in the first catalyst layer have a surface area greater than 1.9 cm 2 , preferably greater than 2.2cm 2 The catalyst particles in the second catalyst layer have a surface area of ​​less than 1.8 cm 2 , preferably less than 1.5cm 2 The surface area of ​​the reactor tube is preferably greater than or equal to 20 mm to 23 mm, preferably greater than or equal to 21 mm. The reactor tube typically has a wall thickness of 1 to 2 mm, so the outer diameter of the reactor tube is correspondingly greater than the inner diameter.

[0015] According to an embodiment of the present invention, it is preferred that the bulk density of the catalyst particles in the first catalyst layer in the reaction tube is less than 0.8 g / cm 3 , especially less than 0.7 g / cm 3 In contrast, the bulk density of the catalyst particles in the second catalyst layer in the reaction tube is preferably greater than 0.7 g / cm 3 , especially greater than 0.8g / cm 3 .

[0016] Preferred catalyst particles for the catalyst system according to the invention are those described in EP 2643086 A1. These preferred catalyst particles are characterized in particular in that each individual catalyst particle is shaped as a cylinder having an outer base [1], a cylindrical surface [2], a cylinder axis and at least one through-opening extending parallel to the cylinder axis [3], and the outer base [1] of the cylinder has at least four convex corners [4a, 4b, 4c, 4d], wherein the geometrical matrix surrounding the catalyst particle is a prism having a prism base, the prism base having a length and a width, wherein the length is greater than the width, and wherein the prism corners of the prism base surround the convex corners [4a, 4b, 4c, 4d].

[0017] According to the present invention, the surface area of ​​the catalyst particles is P This does not refer to the BET surface area of ​​the catalyst material, but rather the geometric external surface area of ​​the catalyst particle, i.e., the surface area that would result if the catalyst particle were a solid, non-porous object. The geometric external surface area of ​​the catalyst particle is solely due to its geometric dimensions. In contrast, the BET surface area is the internal surface area per gram of porous powder.

[0018] An axial cross section of a reaction tube is understood to be a cross section defined by two imaginary lines extending perpendicularly to the longitudinal direction of the reaction tube, so that in this case the imaginary cross section is assumed to be circular. The axial cross section has a length L, which results in the following values ​​for an inner diameter D of the reactor: the surface area of ​​the inner wall of the reactor ( R )O R =π*D*L, the volume of the reactor section (V R )V R =π / 4*D 2 *L, the cross-sectional area inside the reaction tube (Q R )Q R =D 2 *π / 4.

[0019] According to the invention it must apply that:

[0020] O P1 >O P2

[0021] Preferably, OP1-OP2>1cm 2 , particularly preferably >0.8cm 2 , most preferably >0.5cm 2 .

[0022] Preferably, O P1 Greater than 1.9cm 2 , particularly preferably greater than 2.0 cm 2 , most preferably greater than 2.2 cm 2 , and O P2Less than 1.8cm 2 , particularly preferably less than 1.7 cm 2 , most preferably less than 1.5cm 2 .

[0023] In one embodiment, O P1 Between 2.1cm 2 and 2.8cm 2 between, preferably between 2.3cm 2 and 2.5cm 2 Between, and O P2 Between 0.9cm 2 and 1.8cm 2 , preferably between 1.1cm 2 and 1.3cm 2 between. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : Catalytic test results of the catalyst system according to the present invention compared with the conventional catalyst system (double α shape / hollow cylinder 1 and hollow cylinder 2, GHSV = 1,900h -1 , 1.8 vol% n-butane).

[0025] Figure 2 : Maximum bed temperature in the case of using the catalyst system of the present invention (double α shape / hollow cylinder 1 and hollow cylinder 2, GHSV = 1,900 h -1 , 1.8 vol% n-butane).

[0026] Figure 3 : Catalytic test results of the catalyst system according to the present invention compared with the conventional catalyst system (double α shape / hollow cylinder 1, hollow cylinder 2, GHSV = 2,100h -1 , 1.9 vol% n-butane).

[0027] Figure 4 : The maximum bed temperature when using the catalyst system of the present invention (double α shape / hollow cylinder 1, hollow cylinder 2, GHSV = 2,100h) is compared with the conventional catalyst system. -1 , 1.9 vol% n-butane).

[0028] Figure 5 : Preferred catalyst particles of the first catalyst layer in the direction of gas flow at four angles, "double alpha form".

[0029] Figure 6 : Schematic diagram of the catalyst system according to the present invention compared with a conventional catalyst system. DETAILED DESCRIPTION

[0030] Example

[0031] Preparation and reduction of the reaction mixture: First, add 1069.5 g of isobutanol and 156.0 g of benzyl alcohol. Add 150 g of VO with stirring. After the VO addition, add 2.52 g of ammonium dimolybdate. Then, add 232.50 g of phosphoric acid (100% or anhydrous) to the suspension and heat under reflux under N for 10 h.

[0032] Filtration: After the intermediate product suspension has cooled, it is transferred from the four-necked flask to a suction filter and the liquid is sucked off. The moist filter cake is pressed dry in a press at 14 to 18 bar overnight.

[0033] Drying: The pressed filter cake was placed in the evaporating flask of a rotary evaporator. The filter cake was dried at 110°C overnight under a water jet vacuum. The thus dried powder was placed in a suitable calcining crucible in an oven and calcined at a temperature of 200 to 300°C in a N2 atmosphere for 9 hours. The dried intermediate product (VMo) was obtained. 0.0088 OHPO4 x 0.5H2O).

[0034] Tabletting: Before compacting / tabletting, 5 wt% graphite was added to the calcined powdered intermediate product and mixed with a cage mixer. The powder was compacted into tablets using a roller compactor with a pressing force of 190 bar, a gap width of 0.60 mm and a roller speed of 7 revolutions / min and granulated through a 1 mm sieve.

[0035] The granules are compressed into the desired tablet shape and side compression strength using a rotary tablet press:

[0036] The double alpha shape was pressed out with a height of 5.6 mm, a length of 6.7 mm, a width of 5.8 mm, and a pore inner diameter of 2.1 mm. These catalyst particles have a diameter of 2.37 cm 2 The geometric surface area, 0.154 cm 3 When filled into a 21 mm reactor, it produces 0.60 to 0.62 g / cm 3 The filling density.

[0037] For comparison, the catalyst particles were pressed into a conventional cylindrical shape 1 having a height of 4.7 mm, an outer diameter of 4.7 mm and a central axis opening with a diameter of 1.3 mm. The shaped body had a diameter of 1.2 cm 2 The geometric surface area is 0.075 cm 3 When filled into a 21 mm reactor, it produces 0.85 to 0.89 g / cm 3 The filling density.

[0038] The molded body has a height of 5.6 mm, an outer diameter of 5.5 mm and a central axis opening with a diameter of 2.3 mm. 2 The geometric surface area is 0.111 cm 3 When filled into a 21 mm reactor, the resulting mass is 0.72 to 0.76 g / cm 3 The filling density.

[0039] Activation to Pyrophosphate: Activation to produce vanadium pyrophosphate takes place under controlled conditions in a retort built into a programmable furnace. The calcined pellets are uniformly filled into the retort and sealed. The catalyst is then activated in a moist air-nitrogen mixture (50% absolute humidity) initially at over 300°C for 5 hours and then at over 400°C for 9 hours.

[0040] Pilot test, reaction conditions

[0041] The catalytic test reactions were carried out in a 21 mm inner diameter tubular reactor with a catalyst bed length of 4.5 m under comparable conditions. The catalyst was tested under two conditions: a low loading scenario and a high loading scenario. In the first scenario, 1,900 h -1 Space-time velocity (GHSV, in h -1 % water and about 2 ppm trimethyl phosphate. For the high load scenario, 2,100 h was used with a reactant gas composition of 1.9 vol% n-butane diluted in air, 3 vol% water and about 3 ppm trimethyl phosphate. -1 The yield of maleic anhydride is given in weight percent (wt%) based on the weight of n-butane used.

[0042] Figures 1 to 4 The results and temperature distribution of a catalytic test reaction are shown when using a catalyst system according to the invention, which uses double α-shaped catalyst particles in the first catalyst layer and catalyst particles in the shape of hollow cylinders 1 in the second catalyst layer. In contrast, in conventional catalyst systems, only catalyst particles in the shape of hollow cylinders 2 are present in the reaction tube. Figure 1 and Figure 2 shows a low load scenario, while Figure 3 and Figure 4 A high load scenario is shown.

[0043] It is clear that the use of the catalyst system according to the invention results in a yield of maleic anhydride that is approximately 2% by weight higher at the same conversion under low loading conditions. In other words, the catalyst system according to the invention exhibits a higher selectivity for the desired reaction product, maleic anhydride, at the same conversion. A similar effect was observed under high loading conditions, with the catalyst system according to the invention subsequently leading to an increase in the MA yield of more than 4% by weight.

[0044] As in Figure 2 and 4 As is evident from the figure, the reactor system according to the invention reduces the hotspot temperature on the reactor outlet side by widening the curve and partially forming a second hotspot. This leads to an increased MA selectivity.

Claims

1. A catalyst system for preparing maleic anhydride by catalytic oxidation of n-butane, comprising at least one reaction tube having two catalyst layers composed of different catalyst particles, characterized in that: In the gas flow direction, the geometric surface area of ​​each catalyst particle in the first catalyst layer is larger than the geometric surface area of ​​each catalyst particle in the second catalyst layer, wherein the catalyst particles contain a vanadium pyrophosphate phase; wherein, in the direction of gas flow, the catalyst particles in the first catalyst layer are shaped into a cylinder having an outer bottom surface [1], a cylindrical surface [2], a cylinder axis, and at least one opening [3] extending parallel to the cylinder axis, and the outer bottom surface [1] of the cylinder has at least four convex corners [4a, 4b, 4c, 4d], wherein the geometric matrix surrounding the catalyst particles is a prism, the prism having a prism bottom surface, the prism bottom surface having a length and a width, wherein the length is greater than the width, and wherein the prism corners of the prism bottom surface surround the convex corners [4a, 4b, 4c, 4d]; and The catalyst particles in the second catalyst layer are in the shape of hollow cylinders.

2. The catalyst system according to claim 1, characterized in that The geometric surface area of ​​each catalyst particle in the first catalyst layer is at least 0.5 cm greater than the geometric surface area of ​​each catalyst particle in the second catalyst layer. 2 .

3. The catalyst system according to claim 1, characterized in that The geometric surface area of ​​each catalyst particle in the first catalyst layer is 1 cm larger than the geometric surface area of ​​each catalyst particle in the second catalyst layer. 2 .

4. The catalyst system according to any one of claims 1 to 3, characterized in that The geometric surface area of ​​each catalyst particle in the first catalyst layer is greater than 1.9 cm 2 , while the geometric surface area of ​​each catalyst particle in the second catalyst layer is less than 1.8 cm 2 .

5. The catalyst system according to any one of claims 1 to 3, characterized in that The geometric surface area of ​​each catalyst particle in the first catalyst layer is greater than 2.2 cm 2 , while the geometric surface area of ​​each catalyst particle in the second catalyst layer is less than 1.5 cm 2 .

6. The catalyst system according to any one of claims 1 to 3, characterized in that In the gas flow direction, the bulk density of the catalyst particles in the first catalyst layer is less than 0.8 g / cm 3 .

7. The catalyst system according to any one of claims 1 to 3, characterized in that In the gas flow direction, the bulk density of the catalyst particles in the first catalyst layer is less than 0.7 g / cm 3 .

8. The catalyst system according to any one of claims 1 to 3, characterized in that The at least one reaction tube can be temperature-controlled in a salt bath.

9. The catalyst system according to any one of claims 1 to 3, characterized in that This is a tube bundle reactor having a plurality of reaction tubes which can be temperature-controlled by means of a salt bath.

10. The catalyst system according to any one of claims 1 to 3, characterized in that The filled part of the reaction tube was 4 to 5 m long.

11. Process for preparing maleic anhydride by catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is passed through the catalyst system according to any one of claims 1 to 10 and at least one reaction tube is subjected to elevated temperature.

12. The method according to claim 11, characterized in that The at least one reaction tube is at a temperature between 300°C and 420°C.

13. The method according to claim 11 or 12, characterized in that The reactant gas contains between 0.2 and 10% by volume of n-butane and between 5 and 50% by volume of oxygen, and is heated at 1,500 h -1 Up to 2,700 hours -1 The space-time velocity between them is guided through the reaction tube.

14. The method according to claim 11 or 12, characterized in that The reactant gas contains between 0.2 and 10% by volume of n-butane and between 5 and 50% by volume of oxygen, and is heated at 1,700 h -1 Up to 2,500 hours -1 The space-time velocity between them is guided through the reaction tube.

15. Use of the catalyst system according to any one of claims 1 to 10 for preparing maleic anhydride by selective catalytic oxidation of n-butane.

Images