New catalyst system and process for the production of maleic anhydride by catalytic oxidation of n-butane

Abstract

Catalyst system for the production of maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube, with two catalyst layers consisting of different catalyst particles, characterized in that in the first catalyst layer in the direction of gas flow the geometric surface area per catalyst particle is larger than in the second catalyst layer and that the filling density of the catalyst particles in the first catalyst layer in the direction of gas flow is less than 0.8 g / cm3.

Description

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

[0002] The invention further relates to a process for the production of 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 the at least one reactor tube is located at an elevated temperature.

[0003] Maleic anhydride is a chemical intermediate of great economic importance. It is used, for example, in the production of alkyd and polyester resins, either alone or in combination with other acids. Furthermore, it is a versatile intermediate for chemical synthesis, for instance, in the synthesis of γ-butyrolactone, tetrahydrofuran, and 1,4-butanediol, which in turn can be used as solvents or further processed into polymers such as polytetrahydrofuran or polyvinylpyrrolidone.

[0004] The industrial production of maleic anhydride (MA) from n-butane is achieved through selective gas-phase oxidation in cooled tube bundle reactors. Catalyst particles, known as VPO catalysts, are inserted into the reactor tubes to form a catalyst bed. Since a significant amount of heat is released during the reaction (n-butane to MA: -1260 kJ / mol, n-butane to CO₂: 2877 kJ / mol), the reaction is typically carried out in tube bundle reactors with tube inner diameters of usually 21 mm. This allows the heat to be dissipated through the tube walls into the cooling medium, which consists of a molten salt.

[0005] EP 2643086 A1 discloses catalyst bodies for the catalytic conversion of n-butane to maleic anhydride in fixed-bed reactors, wherein the catalyst body is designed as a cylinder with a base, a cylinder surface, a cylinder axis and at least one continuous opening parallel to the cylinder axis, and the base of the cylinder has at least four lobes, wherein a geometric base body enclosing the catalyst body is a prism having a prism base with a length and a width, wherein the length is greater than the width.

[0006] US 6,005,121 discloses an improved process for the production of maleic anhydride by catalytic oxidation of a non-aromatic hydrocarbon with at least four carbon atoms in a straight chain, in which a gas containing oxygen and hydrocarbons is passed through a fixed catalyst bed in a tubular reactor. The activity of the catalyst bed is such that the reactor can be operated at an initial (feed gas) hydrocarbon concentration of over 1.5 vol%, an integrated mean temperature difference between the gas and the coolant of at least about 15°C across the portion of the bed where the gas temperature exceeds the coolant temperature, and a productivity of at least about 5.0 lbs. of maleic anhydride per hour, without the temperature difference between the gas and the coolant exceeding 80°C at any point in the catalyst bed during the reaction.Preferably, the catalyst activity and the gas permeability of the bed vary in the direction of the gas flow, so that both the catalyst activity and the pressure drop per unit distance are lower in a critical region where the combination of temperature and hydrocarbon concentration could otherwise cause the reaction to proceed at an excessive rate than it does in a region of low temperature and low hydrocarbon concentration.

[0007] The task therefore arises to provide a catalyst system, particularly for a tube bundle reactor, for the catalytic oxidation of n-butane to maleic anhydride, which enables thermally stable operation and a high MA yield.

[0008] The problem is solved by a catalyst system in which two types of differently shaped catalyst particles are filled in series into the reactor tube. This catalyst system comprises a reactor tube with two catalyst layers, each consisting of different catalyst particles, characterized in that the geometric surface area per catalyst particle is larger in the first catalyst layer in the direction of gas flow than in the second catalyst layer.

[0009] The problem is also solved by a process for the production of maleic anhydride by catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is passed through the catalyst system according to the invention and one reactor tube is present at elevated temperature.

[0010] The portion of the reactor 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 invention is particularly suitable for short reactor tubes with a filled portion between 4 and 5 m long, or for example, 4.5 m. In this section of the reactor tube filled with catalyst particles, the catalytic oxidation of n-butane to maleic anhydride takes place, so the temperature in this area must be controlled, i.e., tempered. The reactant gas, which must contain n-butane and oxygen, contains, for example, a mixture of between 0.2 and 10 vol% n-butane and 5 to 50 vol% oxygen. Typically, the reactant gas consists of a mixture of 0.5 to 3 vol% n-butane, 10 to 30 vol% oxygen, and the remainder an inert gas such as nitrogen and 1 to 4 vol% water.It is particularly preferred that the reactant gas contains air and that the appropriate amount of n-butane and optionally water are added. Preferably, small amounts of organophosphates such as trimethyl phosphate or triethyl phosphate, 0.5 to 5 ppm or 1 to 3 ppm, based on the gas volume, may be present in the reactant gas to compensate for the phosphate loss of the catalyst. The reactant gas is fed into the reactor tube (typically from below) and comes into contact with the catalyst particles in the portion of the reactor tube filled with them at an elevated temperature, whereby n-butane is oxidized to maleic anhydride.

[0011] Preferably, a plurality of reactor tubes are provided, which can be individually or collectively temperature-controlled. Since the selective oxidation of n-butane to maleic anhydride is an exothermic reaction, excess heat must be dissipated, while simultaneously ensuring that the reactor tubes maintain the necessary reaction temperature. Preferably, temperature control is achieved by means of a salt bath (for example, a eutectic of potassium nitrate and sodium nitrite, approximately in a 1:1 ratio) in which a plurality of reactor tubes are immersed. During the reaction, the salt bath typically has a temperature between 380°C and 430°C. During the reaction, a temperature profile develops within the reactor tube in the axial direction, with a region of maximum temperature ("hotspot") forming in the first third of the reactor tube.Typically, the maximum temperature in the reactor tube is between 430°C and 460°C; according to the invention, a maximum temperature between 440°C and 450°C is preferred.

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

[0013] According to the invention, the reactor tube comprises or consists of two catalyst layers containing catalyst particles that differ in geometry. The reactant gas flows through these two catalyst particle beds within the reactor tube, with one opening of the tube serving as the gas inlet and the opposite opening as the gas outlet. According to the invention, the catalyst layer closer to the gas inlet is the first catalyst layer in the direction of gas flow, while the next catalyst layer in the direction of gas flow is the second catalyst layer. Preferably, the two catalyst layers are directly adjacent to one another, i.e., in contact with each other. The length of a catalyst layer is the axial section of the reactor tube occupied by the respective catalyst particles. The length of the first catalyst layer in the direction of gas flow is equal to or greater than the length of the second catalyst layer in the direction of gas flow.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 from 2:1 to 4:1.

[0014] According to the invention, the geometric surface area per catalyst particle in the first catalyst layer (in the direction of gas flow) is larger than in the second catalyst layer. Preferably, the catalyst particles of the first catalyst layer have a surface area of ​​more than 1.9 cm². 2 , preferably more than 2.2 cm 2 The catalyst particles of the second catalyst layer have a surface area of ​​less than 1.8 cm². 2 , preferably less than 1.5 cm 2 Preferably, the inner diameter of the reactor tube is greater than or equal to 20 mm to 23 mm, preferably greater than or equal to 21 mm. The reactor tubes typically have a wall thickness of 1 to 2 mm, so that the outer diameter of the reactor tubes is correspondingly larger than the inner diameter.

[0015] It is preferred for the embodiment according to the invention that the bulk density of the catalyst particles of the first catalyst layer in the reactor tube is less than 0.8 g / cm³. 3 especially less than 0.7 g / cm² 3 The bulk density of the catalyst particles in the second catalyst layer in the reactor tube is preferably greater than 0.7 g / cm³. 3 , especially greater than 0.8 g / cm³ 3 .

[0016] Preferred catalyst particles for use in 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 designed as a cylinder with an outer base [1], a cylindrical surface [2], a cylindrical axis and at least one continuous opening [3] extending parallel to the cylindrical axis, and the outer base [1] of the cylinder has at least four lobes [4a, 4b, 4c, 4d], wherein a geometric base body enclosing the catalyst particles is a prism having a prism base with a length and a width, the length being greater than the width, and wherein the lobes [4a, 4b, 4c, 4d] are enclosed by prism vertices of the prism base.

[0017] According to the invention, O is located under the surface of each catalyst particle. PThis does not refer to the specific BET surface area of ​​the catalyst material, but rather to the external geometric surface area of ​​a catalyst particle—that is, the surface area that would result if the catalyst particle were a solid, non-porous body. The external geometric surface area of ​​the catalyst particle is determined solely by its geometric dimensions. In contrast, the specific BET surface area is the internal surface area of ​​the porous powder per gram.

[0018] The axial section of the reactor tube is defined as a section delimited by two imaginary lines perpendicular to the longitudinal direction of the reactor tube, such that the imaginary cross-sectional surfaces are circular. The axial section has a length L, resulting in the following dimensions for an inner diameter D of the reactor: surface area of ​​the reactor inner wall (O R ) O R = π * D * L, volume of this reactor section (V R ) VR = π / 4 * D 2 * L, cross-sectional area of ​​the inside of the reactor tube (Q R ) Q R = D 2 * π / 4.

[0019] According to the invention, the following must apply: O P1 > O P2

[0020] Preferred is OP1 - OP2 > 1 cm 2 especially preferred > 0.8 cm 2 , most preferred > 0.5 cm 2 .

[0021] O is preferred P1 greater than 1.9 cm 2 , especially preferred larger than 2.0 cm 2 Most preferred: larger than 2.2 cm 2 and O P2 less than 1.8 cm 2 , especially preferred to be smaller than 1.7 cm 2 Most preferred: smaller than 1.5 cm 2 .

[0022] In one embodiment, O P1 between 2.1 cm 2 and 2.8 cm 2 preferably between 2.3 cm 2 and 2.5 cm 2 and O P2 is between 0.9 cm 2 and 1.8 cm 2, preferably between 1.1 cm 2 and 1.3 cm 2 . Fig. 1: Catalytic test results of a catalyst system according to the invention compared to a conventional catalyst system (double alpha shape / hollow cylinder 1 and hollow cylinder 2, GHSV = 1,900 h -1 , 1.8 vol.-% n-Butane). Fig. 2: Maximum bed temperature when using the catalyst system according to the invention compared to a conventional catalyst system (double alpha shape / hollow cylinder 1 and hollow cylinder 2, GHSV = 1,900 h -1 , 1.8 vol.-% n-Butane). Fig. 3: Catalytic test results of a catalyst system according to the invention compared to a conventional catalyst system (double alpha shape / hollow cylinder 1, hollow cylinder 2, GHSV = 2,100 h -1 , 1.9 vol.-% n-Butane). Fig. 4: Maximum bed temperature when using the catalyst system according to the invention compared to a conventional catalyst system (double alpha shape / hollow cylinder 1, hollow cylinder 2, GHSV = 2,100 h -1 , 1.9 vol.-% n-Butane). Fig. 5: Preferred catalyst particle for the first catalyst layer in the direction of gas flow in four perspectives, the “double alpha shape”. Fig. 6: Schematic representation of the catalyst system according to the invention in comparison to conventional catalyst systems. Examples

[0023] Preparation of the reaction mixture and reduction: First, 1069.5 g of isobutanol and 156.0 g of benzyl alcohol are added. While stirring, 150 g of V₂O₅ are added. After the V₂O₅ addition, 2.52 g of ammonium dimolybdate are added. Then, 232.50 g of phosphoric acid (100%, or anhydrous) are added to the suspension and heated under nitrogen in reflux for 10 h.

[0024] Filtration: After cooling the intermediate product suspension, it is transferred from the four-necked flask to a filter funnel and the liquid is extracted. The moist filter cake is then pressed dry overnight at 14 to 18 bar.

[0025] Drying: The pressed filter cake is placed in the evaporator flask of a rotary evaporator. Under water jet vacuum, the filter cake is dried overnight at 110°C. The dried powder is placed in a suitable calcining pot in an oven and calcined in a nitrogen atmosphere at temperatures of 200 to 300°C for 9 hours. The dried intermediate product (VMo) is then separated. 0,0088 OHPO4×0.5 H2O).

[0026] Tableting: Before compaction / tableting, 5 wt% graphite is added to the calcined, powdered intermediate product and homogeneously mixed using a Rhönrad mixer. This powder is compacted into tablets using a roller compactor with a contact pressure of 190 bar, a gap width of 0.60 mm, and a roller speed of 7 rpm, and then granulated through a 1 mm sieve.

[0027] The granules are pressed into the desired tablet shape and side pressure strength using a rotary tablet press: A double alpha shape was pressed, with a height of 5.6 mm, a length of 6.7 mm, a width of 5.8 mm, and an inner hole diameter of 2.1 mm. These catalyst particles have a geometric surface area of ​​2.37 cm². 2 , a volume of 0.154 cm 3 and a mass of 0.24 g. When poured into a 21 mm reactor, this results in a filling density of 0.60 g / cm³. 3 up to 0.62 g / cm³ 3.

[0028] For comparison, catalyst particles were pressed into the usual cylindrical shape 1, according to hollow cylindrical form 1 with a height of 4.7 mm, an outer diameter of 4.7 mm and a mean axial opening with a diameter of 1.3 mm. These bodies have a geometric surface area of ​​1.2 cm². 2 , a volume of 0.075 cm 3 and a mass of 0.12 g. When poured into a 21 mm reactor, this results in a filling density of 0.85 to 0.89 g / cm³. 3 .

[0029] According to the hollow cylinder 2, which has a height of 5.6 mm, an outer diameter of 5.5 mm, and a mean axial opening with a diameter of 2.3 mm, these bodies have a surface area of ​​1.77 cm². 2 , a volume of 0.111 cm³ 3 and a mass of 0.18 g. When poured into a 21 mm reactor, this results in a filling density of 0.72 to 0.76 g / cm³. 3 .

[0030] Activation to pyrophosphate: The activation process, which produces vanadium pyrophosphate, is carried out under controlled conditions in a retort installed in a programmable oven. The calcined tablets are evenly loaded into the retort, which is then tightly sealed. The catalyst is then activated in a moist air-nitrogen mixture (50% absolute humidity), first at over 300°C for 5 hours and subsequently at over 400°C for 9 hours. Pilot test, reaction conditions

[0031] The catalytic test reactions were carried out in a tubular reactor with an inner diameter of 21 mm and a catalyst bed length of 4.5 m under comparable conditions. The catalysts were tested under two conditions: a low-load and a high-load scenario. In the first scenario, a spacetime velocity (GHSV expressed in h) was used. -1 ) of 1,900 h -1The reactant stream used consisted of 1.8 vol% n-butane diluted in air, 2.3 to 2.7 vol% water, and approximately 2 ppm trimethyl phosphate. A spacetime velocity of 2,100 h⁻¹ was assumed for the high-loading scenario. -1 The reaction is performed with a reactant gas composition of 1.9 vol% n-butane diluted in air, 3 vol% water, and approximately 3 ppm trimethyl phosphate. The yield of maleic anhydride is given in weight percent (wt%) based on the weight of the n-butane used.

[0032] Fig. 1 to Fig. Figure 4 shows the results of the catalytic test reaction and the temperature distributions when using the catalyst system according to the invention using catalyst particles in double alpha form in the first catalyst layer and catalyst particles according to hollow cylinder shape 1 in the second catalyst layer in comparison to the conventional catalyst system in which only catalyst particles according to hollow cylinder shape 2 are in the reactor tube. Fig. 1 and Fig. Figures 2 show the low-load scenario, while the Fig. 3 and Fig. 4. Show the heavy load scenario.

[0033] As can be seen, the use of the catalyst system according to the invention results in maleic anhydride yields that are approximately 2 wt% higher under low-loading conditions at the same conversions. In other words, the catalyst system according to the invention exhibits higher selectivity with respect to the desired reaction product maleic anhydride at the same conversion. A similar effect occurs under high-loading conditions, where the catalyst system according to the invention increases the MA yield by more than 4 wt%.

[0034] As in the Fig. 2 and Fig. As can be seen in Figure 4, the reactor system according to the invention lowers the hotspot temperature by broadening the profile and partially forming a second hotspot on the reactor outlet side. This leads to increased MA selectivity. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 2643086 A1 [0005, 0016] US 6005121

[0006] DE 102014004786 A1

[0012]

Claims

[1] Catalyst system for the production of maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube, with two catalyst layers consisting of different catalyst particles, characterized by , that in the first catalyst layer in the direction of gas flow the geometric surface area per catalyst particle is larger than in the second catalyst layer. [2] Catalyst system according to claim 1, characterized by that the geometric surface area per catalyst particle in the first catalyst layer is increased by at least 0.5 cm² 2 , preferably by 1 cm 2 is larger than in the second catalyst layer. [3] Catalyst system according to claim 1 or 2, characterized by , that the geometric surface area per catalyst particle in the first catalyst layer exceeds 1.9 cm² 2 , preferably over 2.2 cm 2 lies, while in the second catalyst layer it is below 1.8 cm 2, preferably less than 1.5 cm 2 lies. [4] Catalyst system according to any one of the preceding claims, characterized by , that the filling density of the catalyst particles in the first catalyst layer in the direction of gas flow is less than 0.8 g / cm³ 3 , preferably less than 0.7 g / cm³ 3 amounts. [5] Catalyst system according to any one of the preceding claims, characterized by, that the catalyst particles in the first catalyst layer in the direction of gas flow are formed as cylinders with an outer base [1], a cylinder surface [2], a cylinder axis and at least one continuous opening [3] running parallel to the cylinder axis and the outer base [1] of the cylinder has at least four lobes [4a, 4b, 4c, 4d], wherein a basic geometric body enclosing the catalyst particles is a prism having a prism base with a length and a width, wherein the length is greater than the width, and wherein the lobes [4a, 4b, 4c, 4d] are enclosed by prism vertices of the prism base. [6] Catalyst system according to any one of the preceding claims, characterized by that at least one reactor tube can be tempered in a salt bath. [7] Catalyst system according to any one of the preceding claims, characterized bythat it is a tube bundle reactor, with a large number of reactor tubes that can be tempered by a salt bath. [8] Catalyst system according to any one of the preceding claims, characterized by that the filled part of the reactor tube is 4 m to 5 m long. [9] Process for the production of maleic anhydride by catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is passed through the catalyst system according to one of claims 1 to 8 and the at least one reactor tube is located at an elevated temperature. [10] Method according to claim 9, characterized by , that at least one reactor tube is located at a temperature between 300°C and 420°C. [11] Method according to one of claims 9 or 10, characterized by that the reactant gas contains between 0.2 and 10 vol% n-butane and between 5 and 50 vol% oxygen and travels at a spacetime velocity of 1,500 h -1 up to 2,700 h-1 , preferably 1,700 h -1 up to 2,500 h -1 is guided through the reactor tube. [12] Use of a catalyst system according to any one of claims 1 to 8 for the production of maleic anhydride by the selective catalytic oxidation of n-butane. [13] Use according to claim 12, characterized by , that the catalyst particles of the first catalyst layer are formed as cylinders with an outer base [1], a cylindrical surface [2], a cylindrical axis and at least one continuous opening [3] running parallel to the cylindrical axis and the outer base [1] of the cylinder has at least four lobes [4a, 4b, 4c, 4d], wherein a basic geometric body enclosing the catalyst particles is a prism having a prism base with a length and a width, wherein the length is greater than the width, and wherein the lobes [4a, 4b, 4c, 4d] are enclosed by prism vertices of the prism base.

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