SHAPED CATALYST BODY WITH IMPROVED PROPERTIES, ITS PREPARATION AND USE

Abstract

A shaped catalyst body for heterogeneously catalyzed reactions of organic compounds in the gas-phase in fixed-bed reactors, containing an element from group 3 to 12 of the Periodic Table of the Elements, and having a three-lobed structure with a lateral surface around the lobes, a top cover and a bottom cover, as well as three continuous holes running from one cover side to the other cover side, wherein each hole is assigned to one lobe and wherein the cover sides have outwardly shaped arches, its production and a process for its use in the heterogeneously catalyzed reaction of an organic compound in the gas phase.

Claims

1.-15. (canceled)

16. A shaped catalyst body for heterogeneously catalyzed reactions of organic compounds in the gas-phase in fixed-bed reactors, wherein the shaped catalyst body is characterized by (a) containing at least one element from group 3 to 12 of the Periodic Table of the Elements, whereby the total amount of the elements from group 3 to 12 of the Periodic Table of the Elements is 0.01 to 85 wt.-%; (b) a cylindrical structure with a top cover, a bottom cover and a lateral surface with three notches running in the cylinder periphery along the cylinder height forming a three-lobed structure; (c) three continuous essentially circular holes as void spaces with a diameter d.sub.1 and a tolerance of d.sub.1 for each hole of 15% based on the shortest diameter of the respective hole, running from one cover side to the other cover side, wherein each hole is assigned to one lobe and wherein the midpoints of the three holes are arranged essentially equidistantly over the horizontal cross section of the cylindrical structure with a tolerance of 15% based on the shortest distance between two midpoints of two holes; wherein (d) the wall thickness d.sub.2 between two continuous holes over the horizontal cross section of the cylindrical structure at the imaginary connection line between the midpoints of the two continuous holes is essentially the same for all three walls between two continuous holes with a tolerance of d.sub.2 of 15% based on the shortest wall thickness; (e) for each of the three lobes, the wall thickness d.sub.3 between a continuous hole and the lateral surface is, within a 1800 segment, which is defined as the segment over a horizontal cross section of the cylindrical structure, whose chord is parallel to the imaginary connection line between the two midpoints of the adjacent two continuous holes, essentially constant within the respective segment and essentially the same for all three segments of the three lobes with a tolerance of d.sub.3 of 15% based on the shortest wall thickness; (f) the ratio of each of the three wall thicknesses d.sub.2 to each of the three wall thicknesses d.sub.3x, whereby d.sub.3x are the wall thicknesses located over a horizontal cross section of the cylindrical structure at the extension of the imaginary connection lines between the central midpoint of the cylinder and the midpoint of the continuous hole of the respective lobe, is 0.9 to 1.1; (g) the top cover and the bottom cover have outwardly curved arches with the highest height h.sub.2 for the top cover and the highest height h.sub.3 for the bottom cover, wherein h.sub.2 is the distance between the imaginary plane top cover area of an imaginary circular cylinder comprising a circular lateral surface which just encircles the three lobes of the shaped catalyst body, whereby the imaginary plane top cover area contacts the circular lateral surface at a right angle at the highest horizontal level at which the circular lateral surface of the imaginary circular cylinder just contacts at least one lobe; and the highest height of the top cover above the imaginary plane top cover area, measured perpendicular to the imaginary plane top cover area; h.sub.3 is the distance between the imaginary plane bottom cover area of the imaginary circular cylinder comprising a circular lateral surface which just encircles the three lobes of the shaped catalyst body, whereby the imaginary plane bottom cover area contacts the circular lateral surface at a right angle at the lowest horizontal level at which the circular lateral surface of the imaginary circular cylinder just contacts at least one lobe; and the highest height of the bottom cover above the imaginary plane bottom cover area, measured perpendicular to the imaginary plane bottom cover area; and the imaginary circular cylinder has the height h.sub.1 measured as the distance between the imaginary plane top cover area and the imaginary plane bottom cover area; and (h) the diameters d.sub.1 are independently of one another from 1 to 5 mm, the wall thicknesses d.sub.2 and d.sub.3 are independently of one another 0.5 to 3 mm, the heights h.sub.2 and h.sub.3 are independently of one another 0.2 to 3 mm, and the height h.sub.1 is 2 to 10 mm.

17. The shaped catalyst body according to claim 16, wherein it contains at least one element of V, Nb, Mo, Fe, Co, Ni, Pd, Pt, Cu, Ag and Zn.

18. The shaped catalyst body according to claim 16, wherein it contains an oxidic material comprising vanadium and phosphorus.

19. The shaped catalyst body according to claim 16, wherein at least one of the two outwardly curved arches has a convex shape over the respective cover.

20. The shaped catalyst body according to claim 16, wherein at least one of the two outwardly curved arches has the shape of a compressed semicircle over the respective cover.

21. The shaped catalyst body according to claim 16, wherein the inner angles ? at the edges at which the lateral surface of the imaginary circular cylinder contacts the outwardly curved arching of the top cover and the outwardly curved arching of the bottom cover are independently of one another 120 to 160?.

22. The shaped catalyst body according to claim 16, wherein the outer diameter d.sub.0, which is the diameter of the smallest circle, which just encircles the shaped catalyst body over the horizontal cross section, is from 5 to 15 mm, and the total height h.sub.0, which is the sum of h.sub.1, h.sub.2 and h.sub.3, is from 4 to 12 mm.

23. The shaped catalyst body according to claim 16, wherein the inner area of the notches at the lateral surface between two adjacent lobes, which is defined as the area between the imaginary vertical lines, at which the chords of the imaginary 180? segments as specified in feature (e) cross the lateral surface of the lobes, is at least partly filled with the oxidic material as specified in feature (a).

24. The shaped catalyst body according to claim 23, wherein the filling of the notches at the lateral surface has a concave shape.

25. A process for preparing a shaped catalyst body as claimed in claim 16, comprising (a) the preparation of a powdery or granular precursor material containing at least one element from group 3 to 12 of the Periodic Table of the Elements, and (b) its compaction to the shaped catalyst body.

26. The process according to claim 25, wherein a vanadium and phosphorus oxide containing shaped catalyst body is prepared by (a) reacting a pentavalent vanadium compound and a pentavalent or trivalent phosphorus compound with an organic reducing agent, isolating the obtained vanadium and phosphorus containing precursor, drying it, converting the dried mass into a powdery or granular precursor material, and (b) compacting it to the shaped catalyst body.

27. A reactor tube filled with ?100 particles of the shaped catalyst body as claimed in claim 16.

28. A process for the production of an oxidized organic compound by an heterogeneously catalyzed gas-phase oxidation of an organic compound in the presence of an oxygen containing gas and a shaped catalyst body as claimed in claim 16.

29. A process according to claim 28, wherein the oxidized organic compound is maleic anhydride, the organic compound is n-butane, and the shaped catalyst body containing an oxidic material comprising vanadium and phosphorus.

30. A process according to claim 28, wherein the oxidized organic compound is acrolein, acrylic acid, acrylonitrile, methacrolein or methacrylonitrile, the organic compound is propene or isobutene, and the shaped catalyst body contains an oxidic material comprising Mo, Fe and Bi.

Description

EXAMPLES

[0285] Since the advantageous features of the inventive shape of the shaped catalyst bodies regarding their physical properties such as their surface area to body volume ratio, their mechanical stability, their packing density in a typical reactor tube, their total surface area per packing volume in a typical reactor tube and their pressure drop in a typical reactor tube can better and easier be compared with the respective features of typical shaped catalyst bodies of the state of the art by numerical simulations than by laborious experiments, numerical simulations have been made. The general procedure of the numerical simulations is explained in the following.

Simulation Procedure

[0286] Starting point for examples 1 to 5 was the simulation of a 6.5?5.0?3.5 ring of the state of the art with an outer diameter of 6.5 mm, an inner hole with a diameter of 3.5 mm and a height of 5.0 mm, which is a typical dimension of a vanadyl pyrophosphate (VO).sub.2P.sub.2O.sub.7 catalysts (VPO catalyst) used in the oxidation of n-butane to maleic anhydride. Such a shaped catalyst body was created by CAD (Computer Aided Design) as a comparative shaped body. Based on the mentioned ring, inventive and other comparative shaped catalyst bodies have been created by CAD and compared with each other.

[0287] For examples 6 to 10, the starting point was a simulation of another ring of the state of the art with a 5.0?5.0?2.0 dimension which relate to an outer diameter of 5.0 mm, an inner hole with a diameter of 2.0 mm and a height of 5.0 mm. Such dimension is typical for a Mo, Fe and Bi multi-metal oxide catalyst used in the oxidation of propene to acrolein and acrylic acid.

[0288] Although the dimensions d.sub.0, d.sub.1, d.sub.2, d.sub.3, h.sub.0, h.sub.1, h.sub.2, and h.sub.3 are defined for the shaped catalyst body of the invention, they are also used in an analogous manner for the comparative shaped catalyst bodies as follows: [0289] d.sub.0 Outer diameter as the diameter of the smallest circle, which just encircles the shaped catalyst body over the horizontal cross section. In case of a ring as shaped catalyst body, d.sub.0 refers to the outer diameter of the ring. [0290] d.sub.1 Inner diameter of the continuous hole or holes. [0291] d.sub.2 Wall thickness between two continuous holes. Since there is only one hole in a ring, there is no d.sub.2 in rings. [0292] d.sub.3 Wall thickness between a continuous hole and the lateral surface. In case of a ring as shaped catalyst body, d.sub.3 is the wall thickness around the single hole. [0293] h.sub.0 Total height in the vertical direction. [0294] h.sub.1 Height between the (imaginary) plane bottom cover area and the (imaginary) plane top cover. In case of a shaped catalyst body with two plane covers, h.sub.1 is equal to d.sub.0. [0295] h.sub.2, h.sub.3 Height of the outwardly curved arches. In case of plane covers, h.sub.2 and h.sub.3 are 0.

[0296] Besides the geometry, two further physical properties had to be defined for comparison reasons. One of these two physical properties is the body density of the shaped catalyst body. For simplification purpose, it was set for all examples to 1 g/cm.sup.3, which is equal to 1000 kg/m.sup.3. Although this value deviates from the typical body densities of VPO and other metal oxides, such as Mo, Fe and Bi multi-metal oxides, which are higher, it does not impair the direct comparison between the different inventive and comparative shaped catalyst bodies. The other physical property is the mechanical hardness of the bulk material. Also here, a fixed value was picked out and used for all simulations. The mechanical hardness determines, together with the shape and the absolute dimensions, the side crush strength of the respective shaped catalyst body. As for the properties which are derived from the body density, also the properties which are derived from the mechanical hardness can directly be compared since the same initial value was used in all simulations.

[0297] Based on the geometry, the body density and the mechanical hardness, a specific geometric value which is called characteristic length, the side crush strength, the packing density in a model reactor tube and the pressure drop in a model reactor tube at a certain flow rate was calculated by simulation. The mentioned values are described in the following.

Characteristic Length

[0298] The characteristic length is defined as the ratio between the body volume, which is expressed as V and measured in mm.sup.3, and the surface area, which is expressed as SA and measured in mm.sup.2. It is expressed in mm. The body volume and the surface area can easily be calculated from the geometry of the shaped catalyst body. At a given body volume, the characteristic length decreases by an increasing surface area. Since a large surface area is advantageous for the mass transfer of the educt compounds of the reaction mixture into the shaped catalyst body and of the product compounds back to the reaction mixture, a low characteristic length is desirable for an efficient catalysis.

Side Crush Strength

[0299] The side crush strength, which is expressed as SCS, indicates the mechanical strength of a shaped catalyst body. In practice, it is measured by diametrically compressing a ring shaped, cylindrical shaped or trilobe shaped catalyst body in parallel to the axis by two even plates and determining the force at which the shaped catalyst body crushes. The side crush strength is expressed in N. For the present numerical simulation, a numerical method was used to simulate the side crush strength test under the consideration of the shape of the shaped catalyst body, its absolute dimensions and the mechanical hardness of the bulk material. A high side crush strength is generally advantageous since it is an indication for a high mechanical stability of the shaped catalyst body. Nevertheless, the side crush strength of a shaped catalyst body has to be seen in relation to its mass, or, if the body density is the same, in relation to its body volume. The higher the mass of a shaped catalyst body, the higher shall the side crush strength be in order to avoid a cracking during the filling of the reactor tubes. In other words, a big shaped catalyst body with a specific side crush strength is mechanically weaker than a small shaped catalyst body with the same side crush strength. Therefore, the more meaningful value is the side crush strength SCS per body volume V, measured in N/mm.sup.3.

Packing Density

[0300] The packing density indicates how dense the shaped catalyst bodies are located in a vertical reactor tube if they are slackly filled in from the top of the tube. For the present numerical simulations, an inner diameter ID of the reaction tube of 21 mm for examples 1 to 5 and of 26 mm for examples 6 to 10 was taken since these are typical values for shell-and-tube reactors, e.g. regarding the 21 mm for the oxidation of n-butane to maleic anhydride or the 26 mm for the oxidation of propene to acrolein. The arrangement of the shaped catalyst bodies in the reactor tube during their filling was calculated by using Newton's equations of motion and the spatial geometry of the filled tube was visualized by CAD. The packing density is expressed in kg/m.sup.3. A high packing density of the shaped catalyst bodies is generally preferred, since it relates to a high amount of catalytically active material per volume reaction zone, which inter alia enables a more compact design of the reactor for a given conversion.

Surface Area Per Packing Volume

[0301] The surface area per packing volume indicates the available surface area of the shaped catalyst body in a vertical reactor tube if they are slackly filled in from the top of the tube. For the present numerical simulations, the same inner diameter ID of the reaction tube as for the packing density was taken, i.e. 21 mm for examples 1 to 5 and 26 mm for examples 6 to 10. The arrangement of the shaped catalyst bodies in the reactor tube during their filling was calculated by using Newton's equations of motion and the spatial geometry of the filled tube was visualized by CAD. The surface area per packing volume is expressed in m.sup.2/m.sup.3. A high surface area per packing volume is generally preferred, since it relates to a large surface area of the catalyst bodies per volume of the reaction zone.

Pressure Drop

[0302] Based on the geometric shape and the filling of the reactor tube as described under packing density above, the pressure drop in the reactor tube was calculated for a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs. The flow rate was based on the empty reaction tube, so that for each example the same amount of air was passed. The numerical calculation was performed with the thermodynamic and transport properties of air specified in the recognized scientific literature. The pressure drop is expressed in Pa/m. A low pressure drop is advantageous since it enables a lower pressure of the gas at the top of the reaction tube and thus also a lower energy demand for pressing the gas through the reaction tube.

[0303] Examples 1 to 5 relate to comparative and inventive dimensions for the oxidation of n-butane to maleic anhydride, and examples 6 to 10 to comparative and inventive dimensions for the oxidation of propene to acrolein and acrylic acid.

Example 1 (Comparative)

[0304] Example 1 relates to a 6.5?5.0?3.5 ring with an outer diameter of 6.5 mm, an inner hole with a diameter of 3.5 mm and a height of 5.0 mm, which is a typical shape and dimension of a VPO catalyst. It was already mentioned above as starting point of the simulation of examples 1 to 5. The properties of such rings have been simulated as mentioned above and are summarized in FIG. 6.

[0305] This shaped catalyst body of the state of the art has a characteristic length V/SA of 0.57 mm, which is a fairly high value and which indicates that the volume V is fairly high compared with the surface area SA. The simulation of the side crush strength SCS shows a value of 22.3 N and a side crush strength per body volume SCS/V of 0.191 N/mm.sup.3. A SCS/V value of <0.2 N/mm.sup.3 indicates a higher crushing risk during the filling of the reaction tubes and is therefore not a preferred value. The visualized catalyst bed in a 21 mm reaction tube is shown in FIG. 7. The simulated geometrical arrangement results in a packing density of 354 kg/m.sup.3, which is a good value. The surface area SA per packing volume was 616 m.sup.2/m.sup.3 which is a viable value. With this simulated catalyst bed, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs was calculated. It amounts to 1080 Palm. Although this is a viable value, a pressure drop of <1000 Pa/m would be more advantageous.

Example 2 (Comparative)

[0306] Example 2 relates to a 5.5?3.0?3.0 ring with an outer diameter of 5.5 mm, an inner hole with a diameter of 3.0 mm and a height of 3.0 mm. It was derived from the 6.5?5.0?3.5 ring of example 1 by reducing the outer diameter from 6.5 mm to 5.5 mm while keeping the ratio of the outer diameter d.sub.0 to the inner diameter of the hole d.sub.1 constant. By this downsizing, also the total height h.sub.0 was reduced from 5.0 mm to 3.0 mm, which is a common height for 5.5 mm rings. This shaped catalyst body is also state of the art due to its classical ring shape. The properties of these rings have been simulated as mentioned above and are summarized in FIG. 6.

[0307] This shaped catalyst body has a characteristic length V/SA of 0.44 mm, which is significantly lower than that of the ring of example 1 and in absolute terms an advantageous low value. It indicates that the surface area SA is fairly high compared with the volume V. The simulation of the side crush strength SCS shows a value of 12.3 N and a side crush strength per body volume SCS/V of 0.247 N/mm.sup.3. This indicates a fairly stable shaped body with a low crushing risk during the filling of the reaction tubes. The visualized catalyst bed in a 21 mm reaction tube is shown in FIG. 7. Compared with the visualized catalyst bed of the shaped body of example 1, it is much more dense. The simulated geometrical arrangement results in a packing density of 381 kg/m.sup.3, which is a good value. The surface area SA per packing volume was 865 m.sup.2/m.sup.3 which is a high value. With this simulated catalyst bed, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs was calculated. It amounts to a very high value of 2174 Pa/m.

[0308] Although the characteristic length, the side crush strength per body volume and the packing density are advantageous, such a high pressure drop is technically and energetically very disadvantageous. Targeted pressure drops are at <1000 Pa/m.

Example 3 (Comparative)

[0309] Example 3 relates to a trilobe with three continuous holes and two flat cover sides. Due to the flat covers, this trilobe refers of the state of the art. It was designed such that the characteristic length V/SA is around 0.5 mm, which is pretty well between the characteristic lengths V/SA of the shaped catalyst bodies of examples 1 and 2. The wall thicknesses d.sub.2 and d.sub.3 have been set to 1.00 mm and the diameter of the inner holes d.sub.1 to 2.00 mm. Both values are significantly lower than those of the rings of examples 1 and 2. This reduction was required to keep the outer diameter d.sub.0 at a value which is still suitable for the filling of 21 mm tubes. With the above-mentioned values of d.sub.1, d.sub.2 and d.sub.3, the outer diameter d.sub.0 amounts to 7.5 mm. Significantly lower values of d.sub.2 and d.sub.3 would lead to a significantly lower mechanical stability compared with the rings of examples 1 and 2, and a significantly lower diameter of the inner holes d.sub.1 would have negatively influenced the mass transfer behavior compared with that of the rings of examples 1 and 2. As a consequence, significantly lower values of d.sub.1, d.sub.2 and d.sub.3 would have negatively influenced the comparability of the rings of examples 1 and 2 with the trilobe of this example 3. Based on the fixed values of d.sub.1, d.sub.2, d.sub.3 and a characteristic length V/SA of about 0.5 mm, a total height h.sub.0 of 9.2 mm results.

[0310] This shaped catalyst body has a characteristic length V/SA of 0.51 mm, which is pretty well between the characteristic lengths V/SA of the shaped catalyst bodies of examples 1 and 2. The simulation of the side crush strength SCS shows a high value of 57.1 N and a side crush strength per body volume SCS/V of 0.264 N/mm.sup.3. This indicates a stable shaped body with a low crushing risk during the filling of the reaction tubes. The visualized catalyst bed in a 21 mm reaction tube is shown in FIG. 7. It is notably less dense than the catalyst bed of the small rings of example 2 and also visibly less dense than the catalyst bed of the rings of example 1. Due to the relatively high total length of 9.2 mm, the visualized catalyst bed shows some areas of free space. Such areas of free space are disadvantageous since they represent unused volume in the reactor tubes. Furthermore, such areas of free space may facilitate the slip of unreacted educt to the reactor outlet. The simulated geometrical arrangement results in a packing density of only 304 kg/m.sup.3, which is a relatively low value and which underlines the unfavorable findings of the visualized catalyst bed. The surface area SA per packing volume was only 596 m.sup.2/m.sup.3 which is very low. With this simulated catalyst bed, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs was calculated. It amounts to 612.1 Pa/m, which is a very low value and which is fully in line with the loosely packed catalyst bed.

[0311] Although the characteristic length, the side crush strength per body volume and the very low pressure drop are advantageous, the low packing density clearly illustrates that the total amount of catalytically active material is only low and the volume of the reactor tubes not optimally used. In practice, this would require a larger reactor with a larger reaction volume.

Example 4 (Inventive)

[0312] Example 4 relates to an inventive trilobe with three continuous holes and outwardly curved arches at the two cover sides. The objective of example 4 was to take the comparative trilobe of example 3 as basis and to implement outwardly curved arches, which are essential for the inventive shaped catalyst bodies, in order to demonstrate the advantages of the invention. Following the trilobe of comparative example 3, also the inventive trilobe of example 4 was designed such that the characteristic length V/SA is around 0.5 mm. Also the wall thicknesses d.sub.2 and d.sub.3 and the diameter of the inner holes d.sub.1 are the same as in example 3, namely 1.00 mm for the two wall thicknesses d.sub.2 and d.sub.3 and 2.00 for the diameter of the inner holes. Consequently, the outer diameter d.sub.0 also amounts to 7.5 mm. For example 4, two semispheres with a diameter of 7.5 mm have been taken as the two outwardly curved arches, whose heights have been rammed from 3.75 mm of the full semisphere to 0.45 mm. Thus, h.sub.2 and h.sub.3 are 0.45 mm. h.sub.1 was then calculated such that a characteristic length V/SA of 0.50 mm resulted. The respective value of d.sub.1 amounts to 6.60 mm, which at the end relates to a total height do of only 7.5 mm.

[0313] The shaped catalyst body of inventive example 4 has a characteristic length V/SA of 0.50 mm, which is approximately the same as of the comparative trilobe of example 3. The simulation of the side crush strength SCS shows a value of 46.7 N and a high side crush strength per body volume SCS/V of 0.273 N/mm.sup.3. This indicates a stable shaped body with a low crushing risk during the filling of the reaction tubes. The visualized catalyst bed in a 21 mm reaction tube is shown in FIG. 7. Compared with the visualized catalyst bed of the comparative trilobe of example 3, it filled more regularly with less areas of open spaces. This is inter alia due to the lower total height. The simulated geometrical arrangement results in a packing density of only 322 kg/m.sup.3, which is approximately 6% higher than that of the comparative trilobe of example 3. The surface area SA per packing volume was 648 m.sup.2/m.sup.3 which is a very suitable value. With this simulated catalyst bed, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs was calculated. It amounts to 779.9 Pa/m, which is higher than that of the comparative trilobe of example 3, but significantly below 1000 Palm.

[0314] In an overall view and valuation of the characteristic length, the side crush strength per body volume, the packing density and the pressure drop of the inventive trilobe of example 4, the values are in their entirety advantageous over the values of the comparative rings of examples 1 and 2 and the comparative trilobe of examples 3. This relates to the facts that the comparative rings of examples 1 and 2 are mainly disadvantageous due to their high pressure drop of >1000 Pa/m, and the comparative trilobe of example 3 is mainly disadvantageous due to its low packing density and its unfavorable geometrical arrangement in the reaction tube, although its pressure drop is even lower than that of the inventive trilobe of example 4. In contrast to examples 1, 2 and 3, the inventive trilobe of example 4 avoids all these disadvantages and demonstrates well balanced overall features.

Example 5 (Inventive)

[0315] Example 5 relates to a further inventive trilobe with three continuous holes and outwardly curved arches at the two cover sides. As the inventive trilobe of example 4, it is also based on a characteristic length V/SA of 0.50 mm, wall thicknesses d.sub.2 and d.sub.3 of 1.00 mm and a diameter of the inner holes d.sub.1 of 2.00 mm. Consequently, the outer diameter d.sub.0 also amounts to 7.5 mm. The trilobe of example 5 differs from that of example 4 by the shape and the dimension of its outwardly curved arches. For example 5, two circle segments with a height of 1.00 mm have been taken as the two outwardly curved arches. Thus, h.sub.2 and h.sub.3 are 1.00 mm. h.sub.1 was then calculated such that a characteristic length V/SA of 0.50 mm resulted. The respective value of d.sub.1 amounts to 5.50 mm, which at the end relates to a total height do of only 7.5 mm.

[0316] The shaped catalyst body of inventive example 5 has a characteristic length V/SA of 0.50 mm, which is approximately the same as of the comparative trilobe of example 3 and exactly the same of the inventive trilobe of example 4. The simulation of the side crush strength SCS shows a value of 48.1 N and a high side crush strength per body volume SCS/V of 0.292 N/mm.sup.3. This indicates a stable shaped body with a low crushing risk during the filling of the reaction tubes. The visualized catalyst bed in a 21 mm reaction tube is shown in FIG. 7. The visualized catalyst bed looks similar to that of inventive example 4 and is, compared with that of comparative example 3, filled more regularly with less areas of open spaces. This is inter alia due to the lower total height. The simulated geometrical arrangement results in a packing density of only 330 kg/m.sup.3, which is approximately 9% higher than that of the comparative trilobe of example 3. The surface area SA per packing volume was 653 m.sup.2/m.sup.3 which is a very suitable value. With this simulated catalyst bed, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs was calculated. It amounts to 870.5 Pa/m, which is higher than that of the comparative trilobe of example 3 and the inventive trilobe of example 4, but still significantly below 1000 Palm.

[0317] An overall view and valuation of the characteristic length, the side crush strength per body volume, the packing density and the pressure drop of the inventive trilobe of example 5 comes to the same conclusion as in example 4. Also the respective values of the inventive trilobe of example 5 are in their entirety advantageous over the values of the comparative rings of examples 1 and 2 and the comparative trilobe of examples 3.

[0318] FIG. 8 summarizes the results of examples 1 to 5 in an illustrative overview, in which each result of the four criteria characteristic length, side crush strength per body volume, packing density and pressure drop is evaluated by ? (disadvantageous), o (neutral) and + (advantageous). It shows that the inventive trilobes of examples 4 and 5 with three continuous holes and outwardly curved arches at the two cover sides are advantageous in all four criteria, whereas the comparative shapes of examples 1, 2 and 3 have at least one disadvantageous criterion.

Example 6 (Comparative)

[0319] Example 6 relates to a 5.0?5.0?2.0 ring with an outer diameter of 5.0 mm, an inner hole with a diameter of 2.0 mm and a height of 5.0 mm, which is a typical shape and dimension of a Mo, Fe and Bi multi-metal oxide catalyst. It was already mentioned above as starting point of the simulation of examples 6 to 10. The properties of such rings have been simulated as mentioned above and are summarized in FIG. 9. As for examples 1 to 5, also for examples 6 to 10 the visualized catalyst beds and an illustrative overview is shown: the visualized catalyst beds in a 26 mm reactor tube in FIG. 10 and the illustrative overview in FIG. 11.

[0320] Although the characteristic length V/SA, the packing density and the surface area SA per packing volume show good values, the side crush strength per tablet volume SCS/V is not outstanding but at least acceptable. However, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs is very high. In an overall view, the comparative ring is very disadvantageous due to its very high pressure drop.

Example 7 (Comparative)

[0321] 35 Example 7 relates to a 8.0?7.5?1.5 trilobe with three continuous holes, d.sub.2 and d.sub.3 values of 1.5 mm and two flat cover sides. It was designed on the basis of typical state of the art catalyst dimensions used in 26 mm reactor tubes for the oxidation of propene to acrolein or acrylic acid.

[0322] Compared with the ring of example 6, the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs amounts only to roughly a third of the value of the ring and is very low. The characteristic length V/SA also shows a good value, and the side crush strength per tablet volume SCS/V as well as the surface area SA per packing volume are acceptable. However, the packing density is very low. In an overall view, the comparative trilobe is very disadvantageous due to its very low packing density.

Example 8 (Inventive)

[0323] Example 8 shows the very advantageous effect of outwardly curved arches at the two cover sides of a trilobe with three continuous holes. Its outer dimensions d.sub.0 and h.sub.0 are the same as of the comparative trilobe of example 7, namely 8.0 mm for do and 7.5 mm for h.sub.0. Also the diameters d.sub.1 of the three inner holes as well as the wall thicknesses d.sub.2 and d.sub.3 are the same, namely 1.5 mm for d.sub.1, d.sub.2 and do. The inventive trilobe of example 8 only differs from the comparative trilobe of example 7 by having two outwardly curved arches at the two cover sides with a height h.sub.2 and h.sub.3 of 0.6 mm.

[0324] The simulation clearly shows that the characteristic length V/SA, the packing density, the surface area SA per packing volume and the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs are very beneficial, and even the side crush strength per tablet volume SCS/V remains acceptable. In an overall view, the inventive trilobe is very advantageous since all the five significant values are predominantly very beneficial but at least acceptable and none of the five values is disadvantageous.

Example 9 (Comparative)

[0325] Example 9 is a variation of comparative example 7, in which the outer diameter d.sub.0 was increased from 8.0 mm to 8.3 mm, the total height h.sub.0 from 7.5 mm to 7.8 mm and the d.sub.2 and d.sub.3 values from 1.50 mm to 1.83 mm.

[0326] The increased wall thicknesses d.sub.2 and d.sub.3 lead to an increased side crush strength per tablet volume SCS/V. The pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs remained at a very low value and was actually a bit lower than in example 7, and the characteristic length V/SA increased from 0.71 mm to 0.86 mm, which is still an acceptable value for this trilobe size. However, the packing density is still very low and the surface area SA per packing volume significantly decreased from 580 m.sup.2/m.sup.3 to only 505 m.sup.2/m.sup.3, which is very low. In an overall view, the comparative trilobe is very disadvantageous due to its very low packing density and its very low surface area SA per packing volume.

Example 10 (Inventive)

[0327] Example 10 shows the very advantageous effect of outwardly curved arches at the two cover sides of a trilobe with three continuous holes. Its outer dimensions d.sub.0 and h.sub.0 are the same as of the comparative trilobe of example 9, namely 8.3 mm for do and 7.8 mm for h.sub.0, as well as its wall thicknesses d.sub.2 and d.sub.3, namely 1.83. The inventive trilobe of example 10 differs from the comparative trilobe of example 9 by smaller inner holes having a diameter of only 1.2 mm instead of 1.5 mm, and by having two outwardly curved arches at the two cover sides with a height h.sub.2 and h.sub.3 of 0.35 mm.

[0328] The simulation clearly shows that the side crush strength per tablet volume SCS/V, the packing density and the pressure drop at a flow of 1.0 m/s of air at 20? C. and a pressure at the end of the reactor tube of 0.1 MPa abs are very beneficial, and even the characteristic length V/SA and the surface area SA per packing volume remains acceptable. In an overall view, the inventive trilobe is very advantageous since all the five significant values are predominantly very beneficial but at least acceptable and none of the five values is disadvantageous.