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

Abstract

Reactor system for the production of maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube with an inner diameter greater than 23 mm, which is filled with catalyst particles, characterized in that in the at least one filled reactor tube the filling density of the catalyst particles in the reactor tube is less than 0.7 g / cm3 and the ratio of the geometric surface area of ​​the catalyst particles per unit volume to the cross-sectional area of ​​the reactor tube is equal to or less than 1.5 cm-3.

Description

[0001] The invention relates to a reactor system for the production of maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube with an inner diameter greater than 23 mm, which is filled with catalyst particles, characterized in that in the at least one filled reactor tube the ratio of the surface area of ​​the catalyst particles per unit volume to the cross-sectional area of ​​the reactor tube is less than 1.5 cm². -3 is.

[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 a reactor system according to the invention and the at least one reactor tube is located at an elevated temperature.

[0003] The invention also relates to the use of a reactor tube with an inner diameter greater than 23 mm for the production of maleic anhydride by the selective catalytic oxidation of n-butane with catalyst particles having a geometric surface area of ​​more than 2 cm². 2 exhibit.

[0004] 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.

[0005] 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 loaded 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 inner tube diameters of 21 mm. This allows the heat to be dissipated through the tube walls into the cooling medium, which consists of a molten salt. While larger inner tube diameters (D) would be economically advantageous due to the lower initial costs of the tube bundle reactor, this geometry hinders heat dissipation from the catalyst bed, resulting in lower MA yields. Furthermore, the reduced heat dissipation leads to thermally unstable operation, potentially resulting in thermal runaways."Thermal runaway" refers to the rapid and uncontrolled increase in reaction temperature, which leads to the total oxidation of n-butane. Furthermore, the larger A / D ratio (number of catalyst particles in the pipe to pipe diameter) results in a denser packing, leading to higher back pressures during operation and thus to higher investment and operating costs for a more powerful compressor.

[0006] 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.

[0007] The task therefore arises to provide a reactor system, in particular a tube bundle reactor, for the catalytic oxidation of n-butane to maleic anhydride, which has reactor tubes with an inner tube diameter greater than 23 mm, enabling thermally stable operation and a high MA yield.

[0008] The problem is solved by a reactor system for the production of maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube with an inner diameter greater than 23 mm, which is filled with catalyst particles, characterized in that in the filled reactor tube the ratio of the geometric surface area of ​​the catalyst particles per unit volume to the cross-sectional area of ​​the reactor tube is less than 1.5 cm² -3 Furthermore, the problem is solved by a process for the production of maleic anhydride by the catalytic oxidation of n-butane, wherein a mixture comprising n-butane and oxygen is passed through the reactor concept according to the invention.

[0009] The problem can also be solved by using catalyst particles that have a geometric surface area of ​​more than 2 cm². 2exhibit in a reactor tube with an inner diameter greater than 23 mm for the production of maleic anhydride by the selective catalytic oxidation of n-butane.

[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. In this catalyst-filled section of the reactor tube, 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, with the appropriate amount of n-butane and optionally water added.Preferably, small amounts of organophosphates such as trimethyl phosphate or triethyl phosphate, 0.5 to 5 ppm or 1 to 3 ppm by volume, may be present in the reactant gas to compensate for the phosphate loss of the catalyst. The reactant gas is introduced 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 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, and at the same time, it must be ensured 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. With the reactor system according to the invention, the reaction can be carried out at a lower salt bath temperature between 400 °C and 420 °C, which leads to increased thermal stability and increased selectivity.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, in the filled reactor tube, the ratio of the geometric surface area of ​​the catalyst particles per unit volume to the cross-sectional area of ​​the reactor tube must be less than 1.5 cm². -3This condition will be met with a reactor tube inner diameter of more than 23 mm and otherwise typical reaction conditions and catalyst geometries, if the catalyst particles have a geometric surface area of ​​more than 2 cm². 2 The reactor tube should ideally have an inner diameter of 24 mm or greater than or equal to 25 mm. The reactor tube typically has a wall thickness of [missing information]. 1 one to 2 mm, so that the outer diameter of the reactor tube is correspondingly larger.

[0014] It is further preferred for the embodiment according to the invention that the catalyst particles in the reactor tube have a bulk density of less than 0.8 g / cm³. 3 especially less than 0.7 g / cm² 3 exhibit

[0015] Preferred catalyst particles for use in the reactor concept 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.

[0016] According to the invention, below the geometric surface of the catalyst particles O PThis does not refer to the specific BET surface area of ​​the catalyst material, but rather to the geometric external 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 geometric external 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 of catalyst material.

[0017] 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 (VR ) V R = π / 4 * D 2 * L, cross-sectional area of ​​the inside of the reactor tube (Q R ) Q R = D 2 * π / 4.

[0018] The geometric surface area of ​​the catalyst particles per unit volume O K In any axial section of the filled reactor tube with length L, the following results from O K = (A K * O P ) / V R , where A K The number of catalyst particles in the section is A K can be determined by the geometric catalyst particle density KD (A K = KD * π / 4 * D 2 * L), which in turn are determined by bulk density SD and mass m P expressible of a single particle (KD = SD / m P ). Thus, O K = (SD / m P ) * O P .

[0019] According to the invention, the following must apply to any axial section of the reactor tube: O K / Q R ≤ 1,5 cm − 3 preferably is (O K / Q R ) ≤ 1.45 cm -3 , more strongly preferred ≤ 1.40 cm -3 and most preferred ≤ 1.35 cm -3 . Table 1: Economic advantages of the reactor concept according to the invention parameter 21 mm pipe 25 mm pipe GHSV [h -1 ] 2.000 2.200 1.552 1.693 nC4 [Vol.-%] 2,1 1,9 2,1 1,9 Bed length [m] 5,5 5,5 5,5 5,5 Productivity [g MA / (h * pipe)] 201 200 230 229 Productivity increase [%] 0 -0.5 +15 +14,5 Reduction in the number of tubes [%] 7,2 6,8 19,0 18,7 n-Butane efficiency -5,2 -5.2 -1,0 0,0

[0020] Table 1 summarizes the economic advantages of the reactor concept according to the invention compared to the prior art. The prior art here refers to a reactor tube with an inner diameter of 21 mm and a spacetime velocity of 2,000 h⁻¹. -1(with a bed length of 5.5 m) and a butane concentration of 1.9 vol% n-butane in the reactant gas stream. The experimentally determined MA yield, in combination with the spacetime velocity, yields a productivity of MA per tube and per unit time. This productivity can be influenced by varying the spacetime velocity and the n-butane concentration, which affects the resulting MA yield. Based on this productivity for a single tube, and given a fixed total capacity of a commercial production plant (in the example in Table 1, an annual production of 50 kt with an operating time of 8,000 h / a is assumed), the corresponding number of tubes required for the reactor can be determined. Since the MA yield is influenced by the spacetime velocity and the butane concentration in the reactant gas stream, the n-butane efficiency for MA formation also changes.As Table 1 shows, increasing the spacetime velocity or the n-butane concentration in the reactant gas stream can increase productivity for both a reactor tube with a 21 mm inner diameter and the reactor concept according to the invention. However, this productivity increase in the reactor concept according to the invention is approximately twice as high as in a reactor concept according to the prior art. The resulting savings in reactor tubes are therefore also significantly higher in the case of the invention. However, when considering butane efficiency, it becomes apparent that this is only maintained in the reactor concept according to the invention. Thus, only the reactor concept according to the invention offers a combination of increased productivity and a corresponding reduction in the number of reactor tubes while simultaneously maintaining butane efficiency. Fig.1: Catalytic test results of a reactor system according to the invention compared to a conventional reactor system (GHSV = 2,000 h -1 or 1,411 h -1 , 1.9 vol.-% n-Butane). Fig. 2: Catalytic test results of a reactor system according to the invention compared to a conventional reactor system (GHSV = 2,200 h -1 or 1,552 h -1 , 1.9 vol.-% n-Butane). Fig. 3: Relationship between maximum bed temperature and turnover (GHSV = 2,000 h) -1 or 1,411 h -1 , 1.9 vol.-% n-Butane). Fig. 4: Illustrations of the preferred catalyst particle, the “double alpha form”, from four different perspectives. Examples of catalyst particle production

[0021] 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.

[0022] 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.

[0023] 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 x 0.5 H2O).

[0024] 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.

[0025] 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 a hole inner 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 to 0.62 g / cm³. 3 In a 25 mm reactor, this results in a filling density of 0.65 to 0.67 g / cm³. 3 .

[0026] For comparison, catalyst particles were pressed into the usual cylindrical shape with 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 particles have a geometric surface area of ​​1.77 cm². 2 , a volume of 1.11 cm 3and 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 .

[0027] 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

[0028] The catalytic test reactions were carried out in a tubular reactor with an inner diameter of 21 mm and 25 mm and a bed length of 5.5 m, each under comparable conditions. The reactant stream consisted of 1.9 vol% n-butane diluted in air, 2.5 vol% water, and approximately 2 ppm trimethyl phosphate. The space-time velocity (GHSV, expressed in h⁻¹) was -1 ) was in the reactor with a 21 mm inner diameter for 2,000 h -1 and 2,200 h -1 To ensure identical gas volumes for comparison with the 21 mm pipe, the spacetime velocity in the reactor with a 25 mm inner diameter was 1.411 h⁻¹. -1 and 1,552 h -1 Spacetime velocity is defined here as the inverse of the time it takes for the gas flowing through the reactor to equal the empty volume of the reactor tube under normal conditions. The yield of maleic anhydride is given in weight percent (wt%), based on the weight of the n-butane used.

[0029] The results of the catalytic test reactions are presented in the Fig. 1 and Fig. 2 shown. Fig. Figure 1 shows the results of the catalytic test reaction using a reactor with a 25 mm inner diameter and the double-alpha catalyst particles. The following results are obtained: ((SD / m P ) * OP) / Q R = ((0.65 to 0.67 g / cm³) 3 (0.24 g) * 2.37 cm 2 ) / (2.5 2 cm 2 * π / 4) = 1.31 to 1.35 cm -3 .

[0030] Also in Fig. Figure 1 shows the results using a reactor with a 21 mm inner diameter and cylindrical catalyst particles. The following results are obtained: ((SD / m P ) * OP) / QR = ((0.72 to 0.76 g / cm 3 (0.18 g) * 1.77 cm 2 ) / (2.1 2 cm 2 * π / 4) = 2.04 to 2.16 cm -3 .

[0031] As can be seen, at comparable spacetime velocities, the use of reactors with a 25 mm inner diameter and catalyst particles according to the invention results in a significantly increased maleic acid yield, which is attributable to a significantly higher MA selectivity with the same n-butane conversion. At a spacetime velocity of 2,000 h -1 or 1,411 h -1 In the reactor system according to the invention, the MA yield increases by 2 to 4 wt.%.

[0032] A similar effect occurs when, with an identical reactor configuration, the spacetime velocity is increased to 2,200 h. -1 or 1,552 h -1 If the yield is increased, then the reactor system according to the invention results in an increase in MA yield of more than 4 wt.%. 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 [0006, 0015] DE 102014004786 A1

[0012]

Claims

[1] Reactor system for the production of maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube with an inner diameter greater than 23 mm, which is filled with catalyst particles, characterized by , that in the at least one filled reactor tube, the ratio of the geometric surface area of ​​the catalyst particles per unit volume to the cross-sectional area of ​​the reactor tube is equal to or less than 1.5 cm² -3 is. [2] Reactor system for the production of maleic anhydride according to claim 1, characterized by that the inner diameter of the reactor tube is equal to or greater than 24 mm, preferably equal to or greater than 25 mm. [3] Reactor system according to claim 1 or 2, characterized by that the ratio of the geometric surface area of ​​the catalyst particles per unit volume to the cross-sectional area of ​​the reactor tube is less than 1.40 cm² -3 , preferably smaller than 1.35 cm -3 is. [4] Reactor system according to any one of the preceding claims, characterized by that the density of the catalyst particles in the reactor tube is less than 0.7 g / cm³ 3 is. [5] Reactor system according to any one of the preceding claims, characterized by , that the catalyst particles are designed 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. [6] Reactor system according to any one of the preceding claims, characterized bythat at least one reactor tube can be tempered in a salt bath. [7] Reactor system according to any one of the preceding claims, characterized by that it is a tube bundle reactor, with a large number of reactor tubes that can be tempered by a salt bath. [8] Process for the production of maleic anhydride by catalytic oxidation of n-butane, wherein a reactant gas comprising oxygen and n-butane is passed through the reactor system according to one of claims 1 to 7 and the at least one reactor tube is located at an elevated temperature. [9] Method according to claim 8, characterized by that at least one reactor tube is located at a temperature between 300 °C and 420 °C. [10] Method according to one of claims 8 or 9, 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 1,100 h -1up to 1,800 h -1 , preferably 1,300 h -1 up to 1,600 h -1 is guided through the reactor tube. [11] Use of a reactor tube with an inner diameter greater than 23 mm for the production of maleic anhydride by the selective catalytic oxidation of n-butane with catalyst particles having a geometric surface area of ​​more than 2 cm² 2 exhibit. [12] Use according to claim 10, characterized by, that the catalyst particles are designed 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.