SHAPED CATALYST BODY FOR THE CATALYTIC OXIDATION OF SO2 INTO SO3

Abstract

The invention relates to shaped catalyst bodies for the oxidation of SO.sub.2 to SO.sub.3, which comprise vanadium, at least one alkali metal and sulfate on a silicon dioxide support material, wherein the shaped body has the shape of a cylinder having 3 or 4 hollow-cylindrical convexities, obtainable by extrusion of a catalyst precursor composition comprising vanadium, at least one alkali metal and sulfate on a silicon dioxide support material through the opening of an extrusion tool, wherein the opening of the extrusion tool has a cross section formed by 3 or 4 partly overlapping rings whose midpoints lie essentially on a circular line having a diameter of y, wherein the rings are bounded by an outer line lying on a circle having an external diameter x1 and an inner line lying on a circle having an internal diameter x2.

Claims

1-11. (canceled)

12. A shaped catalyst body for the oxidation of SO.sub.2 to SO.sub.3, which comprises vanadium, at least one alkali metal and sulfate on a silicon dioxide support material, wherein the shaped body has the shape of a cylinder having 4 hollow-cylindrical convexities, obtainable by extrusion of a catalyst precursor composition comprising vanadium, at least one alkali metal and sulfate on a silicon dioxide support material through the opening of an extrusion tool, wherein the opening of the extrusion tool has a cross section formed by 4 partly overlapping rings whose midpoints lie essentially on a circular line having a diameter of y, wherein the rings are bounded by an outer circle having an external diameter x1 and an inner circle having an internal diameter x2.

13. The shaped catalyst body according to claim 12, wherein the cross section is formed by 4 annular rings and the midpoints of the rings forming the cross section form a square.

14. The shaped catalyst body according to claim 12, wherein the ratio of the external diameter of the rings to the diameter of the circular line x1:y is from 0.8:1 to 2:1.

15. The shaped catalyst body according to claim 12, wherein the ratio of the external diameter to the internal diameter of the rings x1:x2 is from 1.5:1 to 5:1.

16. The shaped catalyst body according to claim 12, wherein the ratio of the average length z of the shaped bodies to the external diameter of the rings z:x1 is from 1:1 to 6:1.

17. The shaped catalyst body according to claim 12, wherein outer circles and inner circles of the rings are concentric.

18. The shaped catalyst body according to claim 12, wherein all rings have the same external diameter x1 and the same internal diameters x2.

19. The shaped catalyst body according to claim 12 having one or more of the features (i) to (iv): (i) diameter y of the circular line in the range from 4 to 9 mm; (ii) external diameter x1 in the range from 5.5 to 11 mm; (iii) internal diameter x2 in the range from 2.2 to 7 mm; (iv) average length z of the shaped bodies in the range from 10 to 35 mm.

20. A process for producing shaped catalyst bodies comprising vanadium, at least one alkali metal and sulfate on a silicate support material from a catalyst precursor composition comprising vanadium, at least one alkali metal and sulfate on a silicate support material by extrusion of a catalyst precursor composition comprising vanadium, at least one alkali metal and sulfate on a silicon dioxide support material through the opening of an extrusion tool, wherein the opening of the extrusion tool has a cross section formed by 4 partly overlapping annular rings which are bounded by an outer circle having an external diameter x1 and an inner circle having an internal diameter x2 and whose midpoints lie on a circular line having the diameter y.

21. A process for the oxidation of SO.sub.2 to SO.sub.3, wherein a gas mixture comprising oxygen and sulfur dioxide is brought into contact at a temperature in the range from 340 to 680 C. with a bed of shaped catalyst bodies according to claim 12.

Description

EXAMPLES

Example 1

Production of the Catalyst Composition

[0052] 0.8991 kg (30% by weight based on the mixture of the diatomaceous earths) of a diatomaceous earth of the type MN from EP Minerals, 1.4985 kg (50% by weight based on the mixture of the diatomaceous earths) of a diatomaceous earth of the type Masis from Diatomite SP CJSC and 0.5994 kg (20% by weight based on the mixture of diatomaceous earths) of a diatomaceous earth of the type Diatomite 1 from Mineral Resources Ltd are mixed for 30 minutes at 45 revolutions per minute in a drum hoop mixer (from Engelsmann, container volume 32 liters). The mixture of the diatomaceous earths is placed in a Mix-Muller (from Simpson, year of construction 2007, container volume 30 liters) and processed for 2 minutes at 33 revolutions per minute. A first solution consisting of 1.3706 kg of aqueous KOH solution (47.7% by weight) and 0.532 kg of ammonium polyvanadate (from Treibacher) is then added over a period of 2 minutes and the mixture is processed further for 1 minute. 2.1025 kg of 48 percent strength sulfuric acid is added over a period of 2 minutes and the mixture is processed for a further minute at 33 revolutions per minute. As next step, 0.3 kg of K.sub.2SO.sub.4 (from K+S Kali GmbH) is introduced into 1.587 kg of a 50 percent strength aqueous Cs.sub.2SO.sub.4 solution, introduced over a period of 2 minutes into the Mix-Muller and processed for 1 further minute at 33 revolutions per minute and 180 g of a starch solution (7.39% by weight of potato starch in DI water) are then added while continuing to process. The composition obtained is processed further at 33 revolutions per minute until the total processing time from introduction of the diatomaceous earth is 15 minutes altogether.

Comparative Example

[0053] The geometry of the horizontal projection of the shaped body according to the invention is determined by a die through which the composition to be extruded is conveyed under high pressure. The pressure drop of the industrial shaped bodies is influenced by many reality effects, for example the curvature of the shaped bodies, the precise length distribution, the fracture properties and the resulting nature of the shaped body, in particular of the end faces. These properties can depend on the geometry of the shaped body cross section or the geometry of the die used.

[0054] For comparison of the pressure drops of different actual shaped bodies, the pressure drops have to be determined experimentally. In industrial production, star extrudates having 7 points, an external diameter to the peaks of the points of 11 mm and a central hole having a diameter of 4 mm are extruded.

[0055] A screw extruder with a screw was used here. The introduction of solids into the screw is effected from above. The extruder is cooled by means of water. The rotation speed of the transport screw in the extruder is 10 revolutions per minute. The temperature of the solid on introduction and of the shaped bodies on leaving the extruder is about 50 C. The throughput through one extruder is 6000 kg per day. Since, inter alia, the speed of transport of the extrudates is not constant, a uniform length is not obtained but instead a length distribution is obtained. Furthermore, the average length is dependent on the geometry of the die. The shaped bodies were subsequently dried at 120 C. for 2 hours and calcined at 475 C. for 3 hours. Oversize and undersize shaped bodies are removed by means of screening devices.

[0056] For each die shape, a total of at least 100 shaped bodies were selected randomly, the longest length dimension of each shaped body was determined and the average was taken as the average length of the given shaped body. The average surface area of a given body having the average length was then calculated assuming an idealized geometry without curvature along the z axis and a smooth xy plane at right angles to the z axis.

[0057] Furthermore, the total weight of these shaped bodies and the average weight (arithmetic mean) of a shaped body were determined.

[0058] The bulk density of the shaped catalyst bodies was determined in a 500 mm long glass tube having an internal diameter of 200 mm.

[0059] The surface area density (in m.sup.1) was then calculated as (bulk densityaverage surface area)/average weight.

[0060] The pressure drop coefficient of the shaped catalyst bodies was determined in a 500 mm long glass tube having an internal diameter of 200 mm. The tube was charged for this purpose with the appropriate catalyst samples and the pressure drop was measured relative to ambient pressure at various volume flows of air at room temperature.

[0061] The pressure drop coefficient is proportional to the pressure drop and is defined as

[00001]$=\frac{.Math..Math.p}{H}.Math.d_K.Math.\frac{2}{.Math.w^2}$

with the pressure drop p in pascal, the bed height H in meters, the constant reference length d.sub.K of 0.01 meters, the average gas density in kg/m.sup.3 and the average superficial gas velocity w.

[0062] The pressure drop coefficient can be described using the following equalization function:

[00002]${}_K=a+\frac{b}{\mathrm{Re}}$

where the Reynolds number is defined as

[00003]$\mathrm{Re}=\frac{w.Math.d_K.Math.}{}$

with the dynamic viscosity of the gas q in pascal seconds.

[0063] The parameters a and b can be obtained by linear regression from the experimental values. Typical Reynolds numbers in a sulfuric acid reactor are about 100.

[0064] The characteristic physical catalyst parameters cutting hardness and abrasion were determined by the methods described in EP 0019174.

Examples 2 to 4

[0065] Dies as per FIGS. 1a and 1b and also matching insert pins as per FIGS. 2a (Example 2), 2b (Example 3) and 2c (Example 4) were made.

[0066] Thus, y=5.6 mm and x1=7.4 mm (FIGS. 1a and 1b), y=5.6 and x2=3 mm (FIG. 2a), y=6.0 and x2=3.2 mm (FIG. 2b) or y=5.6 mm and x2=3.6 mm (FIG. 2c). According to FIG. 2b (Example 3), the inner circles of the annular rings are arranged eccentrically relative to the die 1a.

[0067] Shaped bodies were extruded using these dies in industrial production in a manner analogous to the comparative example.

[0068] Further processing was likewise carried out in a manner analogous to the comparative example.

[0069] Length, average surface area, bulk density, average weight, surface area density, the parameters a and b, the relative surface area density based on the star extrudate, the relative pressure drop coefficient (zeta.sub.rel at Re=100 [%]) based on the star extrudate, the cutting hardness and the abrasion are reported in the following table.

TABLE-US-00001 Comparative Example 1 Example 2 Example 3 Example 4 Star Cloverleaf4 Cloverleaf4, Cloverleaf3, 11 4 13 3 13 3.2 13 3.6 Length [mm] 16.9 16.5 18.0 20.0 Surface area [m.sup.2/body] 1.07 10.sup.3 1.454 10.sup.3 1.608 10.sup.3 1.606 10.sup.3 Bulk density [kg/m.sup.3] 420 440 439 437 Weight [g/body] 1.264 1.475 1.564 1.557 Surface area density [m.sup.2/m.sup.3] 356 433 451 451 a 14.24 15.55 17.47 16.78 b 684 962.36 668.01 1635.68 Rel. surface area density [%] 100 122 127 127 zeta.sub.rel at Re = 100 [%] 100 119 115 157 Cutting hardness 86 109N 101N 98N Abrasion 1.6% 1.4% 0.7% 0.8%

[0070] It can be seen that the surface area density of the catalysts of Examples 2 to 4 is 122% or 127% of the surface area density of the catalyst of Comparative Example 1. The increase in the surface area density is associated with an only moderate increase in the pressure drop coefficient at a Reynolds number of 100, which is proportional to the pressure drop established in an industrial reactor under typical reaction conditions of the SO.sub.2 oxidation. The pressure drop coefficient of the catalysts of Examples 2-4 at a Reynolds number of 100 is only 119%, 115% or 157%, respectively, of the pressure drop coefficient of the catalyst of Comparative Example 1. The increase in the pressure drop coefficient for the catalysts having four holes (Examples 2 and 3) is lower than that for the catalyst having three holes. The cutting hardness of the catalysts according to the invention of Examples 2 to 4 is greater than that of the catalyst of Comparative Example 1, whereas the abrasion is lower. Accordingly, the mechanical properties of the catalysts according to the invention are likewise superior to the prior art.