NEW CATALYST SYSTEM FOR PRODUCING MALEIC ANHYDRIDE BY MEANS OF THE CATALYTIC OXIDATION OF N-BUTANE

Abstract

The invention relates to a catalyst system for producing maleic anhydride by means of the catalytic oxidation of n-butane, comprising at least one reactor tube, which has two catalyst layers consisting of different catalyst particles, characterized in that the geometric surface area per catalyst particle is greater in the catalyst layer that is first in the gas flow direction than in the second catalyst layer. The invention further relates to a process for producing maleic anhydride by means of the catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is fed through the catalyst system according to the invention and the at least one reactor tube is at elevated temperature.

Claims

1. Catalyst system for producing maleic anhydride by catalytic oxidation of n-butane, comprising at least one reactor tube comprising two catalyst layers having different catalyst particles, wherein the first catalyst layer in the gas flow direction the geometric surface area per catalyst particle is greater than in the second catalyst layer.

2. Catalyst system according to claim 1, wherein the geometric surface area per catalyst particle in the first catalyst layer is at least 0.5 cm2, preferably 1 cm2, greater than in the second catalyst layer.

3. Catalyst system according to claim 1, wherein the geometric surface area per catalyst particle is more than 1.9 cm2, preferably more than 2.2 cm2, in the first catalyst layer and less than 1.8 cm2, preferably less than 1.5 cm2, in the second catalyst layer.

4. Catalyst system according to claim 1, wherein the poured density of the catalyst particles in the first catalyst layer in the gas flow direction is less than 0.8 g/cm3, preferably less than 0.7 g/cm3.

5. Catalyst system according to claim 1, wherein the catalyst particles in the first catalyst layer in the gas flow direction are in the form of a cylinder having an outer base surface [1], a cylinder surface [2], a cylinder axis and at least one uninterrupted opening [3] running parallel to the cylinder axis, and the outer base surface [1] of the cylinder contains at least four lobes [4a, 4b, 4c, 4dd], wherein a geometric base body enclosing the catalyst particles is a prism having a prism base surface having a length and a width, wherein the length is greater than the width, wherein the lobes [4a, 4b, 4c, 4dd] are enclosed by prism corners of the prism base surface.

6. Catalyst system according to claim 1, wherein the at least one reactor tube may be thermostatted in a salt bath.

7. Catalyst system according to claim 1, wherein a tube bundle reactor having a multiplicity of reactor tubes that may be thermostatted via a salt bath is concerned.

8. Catalyst system according to claim 1, wherein the filled portion of the reactor tube is 4 m to 5 m long.

9. Process for producing maleic anhydride by catalytic oxidation of n-butane, wherein a mixture of oxygen and n-butane is passed through the catalyst system according to claim 1 and the at least one reactor tube is at elevated temperature.

10. Process according to claim 9, wherein the at least one reactor tube is at a temperature between 300° C. and 420° C.

11. Process according to claim 9, wherein the reactant gas contains between 0.2% to 10% by volume of n-butane and between 5% and 50% by volume of oxygen and is passed through the reactor tube at a space velocity of 1500 h−1 to 2700 h−1, preferably 1700 h−1 to 2500 h−1.

12. Use of a catalyst system according to claim 1 for producing maleic anhydride by selective catalytic oxidation of n-butane.

13. Use according to claim 12, wherein the catalyst particles of the first catalyst layer are in the form of a cylinder having an outer base surface [1], a cylinder surface [2], a cylinder axis and at least one uninterrupted opening [3] running parallel to the cylinder axis, and the outer base surface [1] of the cylinder contains at least four lobes [4a, 4b, 4c, 4dd], wherein a geometric base body enclosing the catalyst particles is a prism having a prism base surface having a length and a width, wherein the length is greater than the width, wherein the lobes [4a, 4b, 4c, 4dd] are enclosed by prism corners of the prism base surface.

Description

[0023] FIG. 1: Catalytic test results for a catalyst system according to the invention compared to a customary catalyst system (double-alpha shape/hollow cylinder 1 and hollow cylinder 2, GHSV=1900 h.sup.−1, 1.8% by volume n-butane).

[0024] FIG. 2: Maximum bed temperature when using the catalyst system according to the invention compared to a customary catalyst system (double-alpha shape/hollow cylinder 1 and hollow cylinder 2, GHSV=1900 h.sup.−1, 1.8% by volume n-butane).

[0025] FIG. 3: Catalytic test results for a catalyst system according to the invention compared to a customary catalyst system (double-alpha shape/hollow cylinder 1, hollow cylinder 2, GHSV=2100 h.sup.−1, 1.9% by volume n-butane).

[0026] FIG. 4: Maximum bed temperature when using the catalyst system according to the invention compared to a customary catalyst system (double-alpha shape/hollow cylinder 1, hollow cylinder 2, GHSV=2100 h.sup.−1, 1.9% by volume n-butane).

[0027] FIG. 5: Preferred catalyst particle for the first catalyst layer in the gas flow direction from four angles, the “double-alpha shape”.

[0028] FIG. 6: Schematic representation of the catalyst system according to the invention compared to conventional catalyst system.

EXAMPLES

[0029] Production of reaction mixture and reduction: 1069.5 g of isobutanol and 156.0 g of benzyl alcohol are initially added. 150 g of V.sub.2O.sub.5 are added with stirring. The V.sub.2O.sub.5 addition is followed by addition of 2.52 g of ammonium dimolybdate. Subsequently, 232.50 g of phosphoric acid (100%, anhydrous) are added to the suspension and the mixture is heated under reflux under N.sub.2 for 10 h.

[0030] Filtration: After cooling the intermediate suspension, said suspension is transferred from the four-necked flask into a filter funnel and the liquid is removed by vacuum. The damp filtercake is pressed dry overnight at 14 to 18 bar in a press.

[0031] Drying: The pressed filtercake is transferred into the evaporator flask of a rotary evaporator. The filtercake is dried at 110° C. overnight under water jet vacuum. The powder dried in this way is placed in a furnace in a suitable calcining pot and calcined at temperatures of 200° C. to 300° C. in an N.sub.2 atmosphere for 9 hours. This affords the dried intermediate (VMo.sub.0.0088OHPO.sub.4×0.5 H.sub.2O).

[0032] Tableting: Prior to compacting/tableting the calcined pulverulent intermediate is admixed with 5% by weight of graphite and commixed to homogeneity using a drum hoop mixer. This powder is compacted into plates with a roller compactor at a compaction pressure of 190 bar, a gap width of 0.60 mm and a roller speed of 7 rpm and granulated through a 1 mm sieve.

[0033] The granulate is pressed to afford the desired tablet shape and lateral compressive strength using a rotary tablet press.

[0034] 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 internal hole diameter of 2.1 mm. These catalyst particles have a geometric surface area of 2.37 cm.sup.2, a volume of 0.154 cm.sup.3 and a mass of 0.24 g. Filling into a 21 mm reactor results in a poured density of 0.60 g/cm.sup.3 to 0.62 g/cm.sup.3.

[0035] For comparison, catalyst particles were pressed in the customary cylinder shape 1, hollow cylinder shape 1, with a height of 4.7 mm, an external diameter of 4.7 mm and a central axial opening having a diameter of 1.3 mm. These bodies have a geometric surface area of 1.2 cm.sup.2, a volume of 0.075 cm.sup.3 and a mass of 0.12 g. Filling into a 21 mm reactor results in a poured density of 0.85 to 0.89 g/cm.sup.3.

[0036] Hollow cylinder 2 has a height of 5.6 mm, an external diameter of 5.5 mm and a central axial opening having a diameter of 2.3 mm. These bodies have a surface area of 1.77 cm.sup.2, a volume of 0.111 cm.sup.3 and a mass of 0.18 g. Filling into a 21 mm reactor results in a poured density of 0.72 to 0.76 g/cm.sup.3.

[0037] Activation to afford the pyrophosphate: The activation to form vanadium pyrophosphate is performed under controlled conditions in a retort installed in a programmable furnace. The calcined tablets are uniformly filled into the retort and the latter is tightly sealed. The catalyst is subsequently activated in a moist air/nitrogen mixture (50% atmospheric humidity) initially at over 300° C. for 5 h and subsequently at over 400° C. for 9 h.

[0038] Pilot test, reaction conditions

[0039] The catalytic test reactions were performed under comparable conditions in a tube reactor having a 21 mm internal diameter at a catalyst bed length of 4.5 m. The catalysts were tested under two conditions, a low-load scenario and a high-load scenario. In the first scenario a space velocity (GHSV expressed in h.sup.−1) of 1900 h.sup.−1 was used and the reactant stream consisted of 1.8% by volume of n-butane, diluted in air, 2.3% to 2.7% by volume of water and about 2 ppm of trimethyl phosphate. The high-load scenario used a space velocity of 2100 h.sup.−1 at a reaction gas composition of 1.9% by volume of n-butane, diluted in air, 3% by volume of water and about 3 ppm of trimethyl phosphate. The yield of maleic anhydride is expressed in percent by weight (% by weight) based on the weight of the employed n-butane.

[0040] FIGS. 1 to 4 show the results of the catalytic test reaction and the temperature distributions when using the catalyst system according to the invention using double-alpha shaped catalyst particles in the first catalyst layer and catalyst particles of hollow cylinder shape 1 in the second catalyst layer compared to the conventional catalyst system where exclusively catalyst particles of hollow cylinder shape 2 are present in the reactor tube. FIGS. 1 and 2 show the low-load scenario while FIGS. 3 and 4 show the high-load scenario.

[0041] It is apparent that use of the catalyst system according to the invention results in yields of maleic anhydride that are about 2% by weight higher at identical conversions under the low-load conditions. In other words the catalyst system according to the invention shows higher selectivity for the desired reaction product maleic anhydride at identical conversion. A similar effect is established under high-load conditions, the catalyst system according to the invention then bringing about an increase in the MA yield of more than 4% by weight.

[0042] As is apparent in FIGS. 2 and 4 the reactor system according to the invention reduces the hotspot temperature on the reactor outlet side by broadening the profile and partially forming a second hotspot. This results in an elevated MA selectivity.