CATALYST FOR PRODUCING ETHYLENE OXIDE BY GAS-PHASE OXIDATION

Abstract

A shaped catalyst body for producing ethylene oxide by gas-phase oxidation of ethylene, comprising silver deposited on a porous refractory support, the shaped catalyst body having a first face side surface, a second face side surface and a circumferential surface, characterized by a content of at least 20 wt.-% of silver, relative to the total weight of the shaped catalyst body; a multilobe structure; a plurality of passageways extending from the first face side surface to the second face side surface, outer passageways being arranged around a central passageway with one outer passageway being assigned to each lobe, wherein neighboring outer passageways are arranged essentially equidistantly to each other and the outer passageways are arranged essentially equidistantly to the central passageway; a minimum wall thickness A between two neighboring passageways in the range of 0.6 to 1.3 mm; a minimum wall thickness B between each outer passageway and the circumferential surface in the range of 1.1 to 1.8 mm; and a BET surface area in the range of 1.6 to 3.0 m.sup.2/g. The shaped catalyst bodies allow for a favorable balance between mechanical stability, pressure drop and selectivity. The invention also relates to a process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of a shaped catalyst body as defined above. The invention further relates to a process for preparing a shaped catalyst body as above, comprising i) impregnating a refractory support having a BET surface area in the range of 1.4 to 2.5 m.sup.2/g with a silver impregnation solution; and ii) subjecting the impregnated refractory support to a calcination process; wherein steps i) and ii) are optionally repeated.

Claims

1. A shaped catalyst body for producing ethylene oxide by gas-phase oxidation of ethylene, comprising silver deposited on a porous refractory support, the shaped catalyst body having a first face side surface, a second face side surface and a circumferential surface, characterized by a content of at least 20 wt.-% of silver, relative to the total weight of the shaped catalyst body; a multilobe structure; a plurality of passageways extending from the first face side surface to the second face side surface, outer passageways being arranged around a central passageway with one outer passageway being assigned to each lobe, wherein neighboring outer passageways are arranged essentially equidistantly to each other and the outer passageways are arranged essentially equidistantly to the central passageway; a minimum wall thickness A between two neighboring passageways in the range of 0.6 to 1.3 mm; a minimum wall thickness B between each outer passageway and the circumferential surface in the range of 1.1 to 1.8 mm; and a BET surface area in the range of 1.6 to 3.0 m.sup.2/g.

2. The shaped catalyst body according to claim 1, wherein the cross-section of the multilobe structure has the shape of a substantially equilateral, equiangular polygon with elliptical segments attached to each side.

3. The shaped catalyst body according to claim 2, wherein each elliptical segment is mirror-symmetric with regard to a line running from the center of the polygon through the middle of the polygon side to which the elliptical segment is attached, which line bisects one outer passageway.

4. The shaped catalyst body according to claim 1, wherein a quotient of the geometric surface of the shaped catalyst body SA.sub.geo over the geometric volume of the shaped catalyst body V.sub.geo is at least 1.1 mm.sup.−1 and at most 10 mm.sup.−1, wherein the geometric surface area SA.sub.geo and the geometric volume V.sub.geo are defined by the external, macroscopic dimensions of the shaped catalyst body.

5. The shaped catalyst body according to claim 1, wherein the cross-section of the multilobe structure has a quotient of the diameter of the inscribed circle d.sub.ic over the diameter of the circumscribed circle d.sub.cc is in the range of 0.65 to 0.85, wherein “inscribed circle” means the largest possible circle that can be drawn inside the multilobe cross-section and “circumscribed circle” means the smallest circle that completely contains the multilobe cross-section within it.

6. The shaped catalyst body according to claim 1, wherein the outer passageways have an elliptical cross-section and the central passageway has a polygonal, pincushion-shaped or elliptical cross-section.

7. The shaped catalyst body according to claim 1, wherein the shaped catalyst body has a tetralobe structure with four outer passageways arranged around a central passageway.

8. The shaped catalyst body according to claim 0, wherein the shaped catalyst body has a 4-fold rotational symmetry.

9. The shaped catalyst body according to claim 1, wherein the cross-sectional area of each of the passageways is independently in the range of 0.5 to 13.0 mm.sup.2.

10. The shaped catalyst body according to claim 1, wherein the central passageway has a cross-sectional area a.sub.1 and the outer passageways each have a cross-sectional area a.sub.2, and the ratio of a.sub.1 to a.sub.2 is in the range of 0.15 to 1.0.

11. The shaped catalyst body to claim 1, having a height h in the range of 6 to 12 mm.

12. The shaped catalyst body to claim 1, wherein the quotient of the diameter of the circumscribed circle d.sub.cc over the height h is in the range of 0.25 to 2.0.

13. The shaped catalyst body to claim 1, wherein the shaped catalyst body has a side crush strength of at least 50 N.

14. The shaped catalyst body according to claim 1, wherein the shaped catalyst body comprises 400 to 2000 ppm by weight of rhenium, relative to the total weight of the shaped catalyst body.

15. The shaped catalyst body according to claim 1, wherein the shaped catalyst body comprises 260 to 1750 ppm by weight of cesium, relative to the total weight of the shaped catalyst body.

16. The shaped catalyst body according to claim 1, wherein the refractory support is an aluminum oxide support.

17. The shaped catalyst body to claim 1, wherein the shaped catalyst body has a total Hg pore volume of 0.2 mL/g to 0.6 mL/g, as determined by Hg intrusion measurements.

18. The shaped catalyst body to according to claim 0, wherein the catalyst has a multimodal pore size distribution with a first pore size distribution maximum in the range of 0.1 to 3.0 μm and a second pore size distribution maximum in the range of 8.0 to 100 μm, wherein at least 40% of the total Hg pore volume of the shaped catalyst body stems from pores with a diameter in the range of 0.1 to 3.0 μm.

19. A process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of the shaped catalyst body as defined in claim 1.

20. A process for preparing a shaped catalyst body as defined in claim 1, comprising i) impregnating a refractory support having a BET surface area in the range of 1.4 to 2.5 m.sup.2/g with a silver impregnation solution; and ii) subjecting the impregnated refractory support to a calcination process; wherein steps i) and ii) are optionally repeated.

Description

[0120] The invention will be described in more detail by the accompanying drawings and the subsequent examples.

[0121] FIGS. 1a and 1b show schematic exemplary cross-sections of shaped catalyst bodies of the invention.

[0122] FIGS. 2a and 2b show a schematic cross-section of a shaped catalyst body according to FIG. 1a.

[0123] FIG. 3 shows a schematic side-view of a shaped catalyst body according to FIG. 1a.

[0124] FIG. 4 shows the pore size distribution of a preferred refractory support.

[0125] FIG. 5 and FIG. 6 show the pore size distribution of preferred shaped catalyst bodies according to the invention.

[0126] FIG. 7 shows the cross-section of a support useful for providing a shaped catalyst body of the invention.

[0127] With regard to FIGS. 1a and 1b, the shaped catalyst bodies have four outer passageways arranged equidistantly around a central passageway and have a 4-fold rotational symmetry. According to FIG. 1a, the four outer passageways and the central passageway have a circular cross-section. According to FIG. 1b, the four outer passageways have a circular cross-section and the central passageway has a cross-section in the shape of a square.

[0128] For illustrative purposes, FIG. 1a shows the shortest distance A-1 between a central passageway and a neighboring outer passageway, and the shortest distance A-2 between two neighboring outer passageways. Since A-1 is shorter than A-2, A-1 corresponds to “the minimum wall thickness A between two neighboring passageways”. Further, FIG. 1a shows the minimum wall thickness B between a passageway and the circumferential surface.

[0129] FIGS. 2a and 2b show a schematic cross-section of a shaped catalyst body according to FIG. 1a. The cross-section is derived from a circular-cylinder structure with a plurality of void spaces. The cross-section has the shape of a substantially equilateral, equiangular polygon with elliptical segments attached to each side.

[0130] In FIG. 2a, the sides of the substantially equilateral, equiangular polygon P are indicated by dashed lines. The elliptical segments E traverse the side they are attached to and meet at the corners of the polygon P.

[0131] In FIG. 2b, the circumscribed circle and the inscribed circle are indicated by dashed lines.

[0132] FIG. 3 shows a schematic side-view of a shaped catalyst body according to FIG. 1a, wherein cross-sections are shown as dashed lines. The height h of the shaped catalyst body is indicated.

[0133] FIG. 4 shows the pore size distribution of the refractory support D, as determined by mercury porosimetry. On the x-axis, the pore size diameter [μm] is plotted. On the y-axis, the log differential intrusion [mL/g] is plotted.

[0134] FIG. 5 shows the pore size distribution of the catalyst 2.4, as determined by mercury porosimetry. On the x-axis, the pore size diameter [μm] is plotted. On the y-axis, the log differential intrusion [mL/g] is plotted in.

[0135] FIG. 6 shows the pore size distribution of the catalyst 2.5, as determined by mercury porosimetry. On the x-axis, the pore size diameter [μm] is plotted. On the y-axis, the log differential intrusion [mL/g] is plotted in.

[0136] FIG. 7 shows a scan of the cross-section of support Q obtained by Computed Tomography.

EXAMPLES

[0137] Methods and Materials

[0138] Methods

[0139] Method 1 —Experimental Measurement of the Pressure Drop

[0140] The pressure drop coefficient ξ is proportional to the pressure drop and is defined as

[00001]$\xi =\frac{\Delta p}{H}.Math.d_k.Math.\frac{2}{\rho .Math.w^2}$

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

[0141] The pressure drop coefficient ξ can be described using the following equalization function:

[00002]$\xi =a+\frac{b}{R{e}_{\mathrm{dk}10}}$

where the Reynolds number Re.sub.dk10 is defined as

[00003]$R{e}_{\mathrm{dk}10}=\frac{w.Math.d_k.Math.\rho }{\eta }$

with the dynamic viscosity of the gas η in Pascal.Math.seconds. The parameters a and b can be obtained by linear regression from experimental values. A suitable Reynolds number in an ethylene oxide process is between 5,000 and 6,000, for example 5,500.

[0142] Method 2 —Simulation of the Pressure Drop

[0143] The correlation between pressure drop and catalyst shape was calculated via numerical flow simulation, which completely resolves the flow in the spaces between the catalyst bed. The procedure consists of three consecutive steps. First, the geometry of the bed is created. For this purpose, a CAD (Computer Aided Design) model of a single shaped catalyst body is created with any CAD program. This determines the shape of the catalyst (e.g. cylinder, ring, multilobe, etc.). A tube with an internal diameter typical of a technical reactor (39.5 mm) is used as the outer container for the bulk material. Both the digital container geometry and the digital catalyst geometry are fed into a simulation program which makes it possible to calculate the arrangement of the shaped catalyst bodies as they are filled into the container, using Newton's equations of motion. Pressure drop calculations were performed with air at ambient temperature and different gas space velocities (GHSV, gas hourly space velocity). Values from the scientific literature for air at a constant operating pressure of 1 bar and temperature of 20° C. were used for the thermodynamic and transport properties of the gas. The reference length used to calculate the Reynolds number is defined as 0.01 meters.

[0144] Method 3—Mercury Porosimetry

[0145] Mercury porosimetry was performed using a Micrometrics AutoPore IV 9500 mercury porosimeter (140 degrees contact angle, 485 dynes/cm Hg surface tension, 60000 psia max head pressure). The Hg porosity is determined in accordance with DIN 66133.

[0146] Method 4—BET Surface Area

[0147] The BET surface area was determined in accordance with DIN ISO 9277.

[0148] Method 5—Water Absorption

[0149] Water absorption refers to vacuum cold water uptake. Vacuum cold water uptake is determined by placing about 100 g of support (“initial support weight”) in a rotating flask, covering the support with deionized water, and rotating the rotary evaporator for 5 min at about 30 rpm. Subsequently, a vacuum of 80 mbar is applied for 3 min, the water and the support are transferred into a glass funnel, and the support is kept in the funnel for about 5 min with occasional shaking in order to ensure that adhering water runs down the funnel.

[0150] The support is weighed (“final support weight”). The water absorption is calculated by subtracting the initial support weight from the final support weight and then dividing this difference by the initial support weight.

[0151] Method 6—Side Crush Strength

[0152] The side crush strength was determined using an apparatus of the “Z 2.5/T 919” type supplied by Zwick Roll (Ulm), stamp size: 12.7 mm×12.7 mm. Based on measurements of 25 randomly selected shaped bodies, average values were calculated. The measurements of tetralobes were performed along two directions—along the side and along the diagonal. In the measurement along the diagonal, the force is exerted along an axis running through a first outer passageway, the central passageway and a second outer passageway opposite to the first outer passageway. In the measurement along the side, the force is exerted along two axes each running through a two outer passageways.

[0153] Method 7—Packing tube density

[0154] Packing tube density was determined by filling catalyst shaped bodies in a glass tube with an inner diameter of 39 mm to a marker marking an inner tube volume of 1 L.

[0155] Method 8—Geometric measurements

[0156] Geometric dimensions were measured using a caliper with the accuracy of 0.01 mm. Reported are average values of 25 randomly selected shaped bodies.

[0157] Alternatively, geometric dimensions were measured using 3-dimensional Computed Tomography (CT) X-ray Scanning. CT data were collected using Phoenix Nanotom M (General Electric), scan time=1 h, 150 kV/80 μA, resolution=21.67 μm/Voxel size. This method is a preferable way for geometric measurements of complex shapes within the scope of claims of the current invention. Results are provided as average values of 28 randomly selected shaped bodies.

[0158] Method 9 —Simulation of Geometric Surface and Geometric Volume

[0159] A CAD (Computer Aided Design) model of a single shaped catalyst body is created with any CAD program to calculate the geometric surface and geometric volume.

[0160] Method 10—Analysis of Silver Content

[0161] Shaped catalyst bodies were crushed and pulverized so as to obtain homogenized samples. 300 to 700 mg of pulverized catalyst bodies were weighed into a titrator (888 Titrando, Metrohm). The sample was brought into contact with 10 mL of a mixture of 65% HNO.sub.3: H.sub.2O (1:1) at boiling temperature. The obtained mixture was diluted with 150 mL of H.sub.2O and titrated with a 0.1 M solution of ammonium thiocyanate, using a silver electrode.

[0162] Refractory Supports

[0163] The refractory supports were alumina supports and comprised Si, Ca, Mg, Na, K and Fe as chemical impurities. The properties of the refractory supports are indicated in Table 1 below. The supports were obtained from EXACER s.r.l. (Via Puglia 2/4, 41049 Sassuolo (MO), Italy), under the following lot numbers:

TABLE-US-00001 A COM 84/13 B COM 63/17 86/17S C Bimal 889 D Q888 E Q901 F Q902 G Q903 H Q904 I Q905 K Q908 L Q907 M Q909C N Q909L O Q910 P Q920 Q COM 48/18 Support A has Si.sub.Al2O3 = 400 ppm, Ca.sub.Al2O3 = 200 ppm, Mg.sub.Al2O3 = 100 ppm, Na.sub.Al2O3 = 80 ppm, K.sub.Al2O3 = 60 ppm, Fe.sub.Al2O3 = 200 ppm. The supports B to P have Si.sub.Al2O3 = 500 ppm, Ca.sub.Al2O3 = 400 ppm, Mg.sub.Al2O3 = 200 ppm, Na.sub.Al2O3 = 100 ppm, K.sub.Al2O3 = 185 ppm, Fe.sub.Al2O3 = 100 ppm. Support Q has Si.sub.Al2O3 = 450 ppm, Ca.sub.Al2O3 = 350 ppm, Mg.sub.Al2O3 = 130 ppm, Na.sub.Al2O3 = 100 ppm, K.sub.Al2O3 = 150 ppm, Fe.sub.Al2O3 = 150 ppm.

[0164] Support A has a bimodal pore size distribution with the first log differential pore volume distribution peak at 1.2 μm and the second log differential pore volume distribution peak at 49 μm. The supports B to Q have a bimodal pore size distribution with smaller pores with the first log differential pore volume distribution peak in the range of 0.4 to 0.6 μm and the second log differential pore volume distribution peak in the range of 17 to 30 μm.

[0165] The cross-section of all passageways of the refractory supports had a circular shape, with the exception of the central passageways of support H and support L. The cross-sections of the central passageways of support H and support L were pincushion-shaped.

TABLE-US-00002 TABLE 1 A .sup.1 B .sup.1 C .sup.1 D E F G H I K L M N O P Q Shape ring tetralobe Passageways 1 1 1 5 5 5 5 5 5 5 5 5 5 5 5 5 Geometry diameter of circumscribed 8.0 9.7 8.4 8.5 8.5 8.5 8.5 8.5  8.5 9.1 9.0  8.5 8.5 7.3 8.85 8.72 circle d.sub.cc [mm] diameter of inscribed 8.0 9.7 8.4 6.5 6.5 6.5 6.5 6.5  6.5 6.5 6.5  6.5 6.5 5.7 5.9 6.46 circle d.sub.ic [mm] quotient d.sub.ic/d.sub.cc 1 1 1 0.76 0.76 0.76 0.76 0.76 0.76 0.71 0.72 0.76 0.76 0.78 0.67 0.74 height h [mm] 7.9 9.7 8.5 8.5 8.5 8.5 8.4 8.6  8.1 8.0 8.3  7.6 9.8 6.7 9.0 8.5 quotient d.sub.cc/h 1.01 1.00 0.99 1.00 1.00 1.00 1.01 0.99 1.05 1.14 1.08 1.12 0.87 1.09 0.98 1.03 diameter of four outer — — — 1.3 1.4 1.4 1.5 1.4  1.5 1.5 1.5  1.5 1.5 1.2 1.55 1.6 passageways [mm] diameter of central 2.6 2.9 2.8 0.9 1.0 1.3 0.8  1.4 .sup.2 0.9 1.1  1.3 .sup.2 0.9 0.9 0.8 1.3 1.0 passageway [mm] minimum wall — — — 1.0 0.9 0.75 0.95 0.8  0.9 1.05 0.95 0.9 0.9 0.75 0.9 0.9 thickness A [mm] minimum wall 2.7 3.4 2.8 1.5 1.45 1.45 1.4 1.45 1.4 1.45 1.5  1.4 1.4 1.3 1.3 1.4 thickness B [mm] distance between outer — — — 1.64 1.60 1.55 1.51 1.55 1.52 1.79 1.79 1.52 1.52 1.33 1.77 1.47 passageways [mm] distance between central — — — 1.0 0.9 0.75 0.95 0.8  0.9 1.05 0.95 0.9 0.9 0.75 0.9 0.9 passageway and outer passageways [mm] ratio of total cross- 0.11 0.09 0.11 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 0.19 n.d. sectional area of passageways to cross- sectional area of shaped catalyst body geometric surface 353 518 397 459 471 478 470 n.d. 459 n.d. n.d. 435 538 n.d. 543 n.d. area SA.sub.geo [mm.sup.2] geometric volume 355 652 418 358 349 345 340 n.d. 327 n.d. n.d. 307 395 n.d. 357 n.d. V.sub.geo [mm.sup.3] quotient SA.sub.geo/V.sub.geo 0.99 0.79 0.95 1.28 1.35 1.39 1.38 n.d. 1.40 n.d. n.d. 1.42 1.36 n.d. 1.52 n.d. [mm.sup.−1] Physical Properties BET surface 0.71 2.02 1.95 2.03 2.06 2.04 1.98 1.98 1.99 2.07 2.08 2.06 2.06 2.08 2.09 1.95 area [m.sup.2/g] water uptake 0.46 0.55 0.55 0.59 0.58 0.58 n.d..sup.6 n.d. n.d. n.d. n.d. 0.58 0.57 0.62 0.56 0.57 [mL/g] total Hg pore 0.45 0.59 0.52 0.56 0.53 0.52 0.55 0.54 0.53 0.53 0.58 0.51 0.51 0.54 0.54 0.53 volume [mL/g] 1st log diff. 1.5 0.6 0.4 0.5 0.4 0.4 0.4 0.4  0.4 0.4 0.4  0.4 0.4 0.4 0.4 0.4 peak [μm] .sup.4 2nd log diff. 46 17 21 26-30 22 22 27 22    24 20 24    23 23 25 25 30 peak [μm] .sup.4 Percentage of 46 64 n.d. 54 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 56 55 pores with a diameter of 0.1 to 3 μm [%] .sup.5 carrier density 700 588 621 579 564 555 568 558    571 539 520    559 561 597 540 577 [g/L] .sup.3 side crush 98 74 50 70 51 52 55 40    54 58 57    42 56 46 60 76 strength [N] along diagonal side crush n.d. n.d. n.d. 92 74 62 73 41    77 75 60    77 99 68 93 111 strength [N] along side Pressure Drop Data .sup.3 a n.d. n.d. n.d. 22.3 19.8 22.3 21.1 20.7  20.0 17.3 18.6  21.7 21.6 33.0 18.5 19.7 b n.d. n.d. n.d. 3,980 5,169 2,809 2,128 2,718    1,994 2,078 1,640    3,726 2,332 4,062 1,373 2,354 Relative pressure n.d. n.d. n.d. 100 90 99 93 92    88 77 82    97 96 146 82 87 drop coefficient at Re = 5,500 [%].sup.7 .sup.1 Reference Example .sup.2 pincushion-shaped cross-section; diameter = longest possible distance between two points on the circumference of the passageway's cross-section .sup.3 measured in a tube with a diameter of 39 mm .sup.4 log diff. peak = log differential pore volume distribution peak .sup.5 based on the total Hg pore volume .sup.6n.d. = not determined .sup.7relative to support D

Example 1—Simulation of the Pressure Drop

[0166] The pressure drop induced by varying catalyst body geometries was additionally calculated by the above-described method 2. It should be appreciated that the calculation is based on the assumption that all catalyst bodies have exactly the same height (whereas the height of industrially produced shaped catalyst bodies is subject to a height distribution around an average height). The following geometries were examined: [0167] 1-1: geometry corresponds to an ideal cylinder with a height of 8.0 mm, a diameter of 8.0 mm and an inner diameter of 2.6 mm [0168] 1-2: geometry corresponds to a cylinder with a height of 8.0 mm, a diameter of 8.0 mm, seven passageways with a cylindrical cross-section and a diameter of 1.22 mm (one passageway being central and the others being regularly spaced on a circle with a diameter of 4.39 mm, concentric to the circumference of the cylinder); according to examples 1 to 8 of U.S. Pat. No. 4,837,194 [0169] 1-3: geometry corresponds to support I, except for the height, which was 7.5 mm [0170] 1-4: geometry corresponds to support M, except for the height, which was 8.5 mm [0171] 1-5: geometry corresponds to support N, except for the height, which was 9.5 mm [0172] 1-6: geometry corresponds to support P [0173] 1-7: geometry essentially corresponds to support Q [0174] 1-8: geometry corresponds to a tetralobe with a height of 14.05 mm, an outer diameter of 8.5 mm, one central passageway with a cylindrical cross-section and an inner diameter of 1.24 mm, and rounded edges calculated on the basis of FIGS. 2 and 3 of US 2015/0045565

TABLE-US-00003 TABLE 2 1-1 * 1-2 * 1-3 1-4 1-5 1-6 1-7 1-8 * shape hollow 7-hole cylinder cylinder tetralobe tetralobe tetralobe tetralobe tetralobe tetralobe SA.sub.geo [mm.sup.2] 355 498 431 477 524 543 528 504 V.sub.geo [mm.sup.3] 359 339 303 343 383 357 364 649 SA.sub.geo/V.sub.geo [mm.sup.−1] 0.99 1.47 1.42 1.39 1.37 1.52 1.45 0.78 % (SA.sub.geo/V.sub.geo) ** 100% 149% 144% 141% 138% 154% 147% 79% pressure drop 5,292 5,275 4,440 4,352 4,120 3,711 3,998 3,614 [Pa .Math. m.sup.−1] *** Relative pressure drop in 100% 99.7%  83.9%  82.2%  77.8%  70.1%  75.5%  68.3%   comparison to 1-1 [%] * reference example ** based on the ratio of SA.sub.geo/V.sub.geo of example 1-1 *** at 2.0 m/s, Re = 5,221

[0175] The shaped catalyst body 1-2* with a 7-hole cylinder structure and the shaped catalyst bodies 1-3, 1-4, 1-5, 1-6, 1-7 with a tetralobal structure both have favorable quotients of the geometric surface of the shaped catalyst body SA.sub.geo over the geometric volume of the shaped catalyst body V.sub.geo in comparison to 1-1* and 1-8*. The shaped catalyst bodies 1-3, 1-4, 1-5, 1-6, 1-7 and 1-8 with a tetralobal structure induce a significantly lower pressure drop in comparison to the shaped catalyst bodies 1-1* and 1-2*.

Example 2—Preparing Shaped Catalyst Bodies

[0176] Shaped catalyst bodies according to Tables 2,3 below were prepared by impregnating the refractory supports disclosed in Table 1 with a silver impregnation solution. The supports were obtained from EXACER s.r.l. (Via Puglia 2/4, 41049 Sassuolo (MO), Italy), under the lot numbers shown above.

TABLE-US-00004 TABLE 3 Catalyst composition (Ag-contents are reported in percent by weight of total catalyst, promotor values are reported in parts per million by weight of total catalyst) Ag.sub.CAT Li.sub.CAT S.sub.CAT W.sub.CAT Cs.sub.CAT Re.sub.CAT K.sub.ADD K.sub.CAT Example Support [wt-%] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] 2.2 A 15.2 */14.7 ** 190 14 200 425 450 51 102 2.3 B 29.1 */26.8 ** 486 36 556 979 1190 99 229 2.4 D 30.9 */29.3 ** 470 35 540 950 1150 105 232 2.5 Q 29.1 */28.3 ** 482 36 551 973 1178 100 205 * calculated Ag values, ** analyzed Ag values; all promoter values are calculated values; *** K.sub.ADD is understood to mean the amount of potassium added during impregnation and does not include the amount of potassium comprised in the alumina support prior to impregnation; **** K.sub.CAT is understood to mean the total amount of potassium in the catalyst

TABLE-US-00005 TABLE 4 Physical Properties of Catalysts Catalyst 2.2 2.3 2.4 2.5 comparative comparative inventive inventive Carrier A B D Q Carrier Shape hollow hollow tetra tetra cylinder cylinder lobe lobe Number of holes in the carrier 1 1 5 5 Physical Properties BET surface area [m.sup.2/g]    0.95   2.4   2.4    2.5 Total Hg pore volume [ml/g]    0.34    0.35    0.33    0.39 1.sup.st log diff peak [μm]   1.7   0.7   0.7    0.6 2.sup.nd log diff peak [μm] 40 15 17 255 Percentage of pores 0.1 to 3 μm in 45 62 58  52 relation to the total Hg pore volume [%] Catalyst density in 39 mm tube [g/L] 826  876  838  906 Ag density in 39 mm tube [g/L]  126 *  255 *  259 *   264 *   121 **   235 **   246 **   256 ** Side crush strength [N] along longest diagonal n.d. *** 97 80 108 along side 114  142 * calculated values ** analyzed values *** n.d. = not determined

[0177] 2.1 Production of the Silver Complex Solution

[0178] 783 kg of an aqueous ethylenediamine solution with an ethylenediamine content of 59 wt.-% were pumped into a stirring reactor 1. Subsequently, the ethylenediamine solution was diluted under stirring with 94 kg of deionized water. Next, 26.6 kg of 0.95 wt.-% KOH solution were added to form an aqueous KOH/ethylenediamine solution. The solution was cooled to a temperature of below 20° C. Then 300 kg of oxalic acid dihydrate (purity≥99.6%) were added into the stirring reactor 1 stepwise over a period of about 180 minutes under stirring and cooling to control the reaction temperature in the range of 20 to 25° C. Once the addition of oxalic acid dihydrate was completed and the temperature profile from the addition of the last portion of oxalic acid dihydrate passed a maximum, cooling was terminated and the reaction mixture was stirred further for the next 60 min to form an aqueous oxalic acid/ethylenediamine solution.

[0179] Next, 1113 kg of the aqueous oxalic acid/ethylenediamine solution were transferred from the stirring reactor 1 to a stirring reactor 2. The reaction medium was cooled to a temperature below 20° C. Then, 500 kg silver oxide powder (from Ames Goldsmith, chemical composition shown below), was added over a period of 225 min under stirring and cooling to control the reaction temperature in the range of 20 to 25° C. Once the addition of silver oxide was completed, and the temperature profile from the addition of the last portion of silver oxide passed a maximum, cooling was terminated and the reaction mixture was heated under stirring in a temperature range of about 25-30° C. for the next 3 hours to form an aqueous Ag complex suspension.

[0180] The silver oxide used is commercially available from Ames Goldsmith. Its chemical composition is described below:

TABLE-US-00006 Silver Content as Ag.sub.2O ≥99.90% moisture content ≤0.20% chlorides ≤15 ppm nitrates ≤100 ppm  carbonates ≤0.25% sulfates ≤20 ppm copper ≤20 ppm iron ≤20 ppm lead ≤20 ppm nickel ≤20 ppm sodium ≤50 ppm other trace metals ≤20 ppm

[0181] Subsequently, the silver impregnation solution was obtained by passing the reaction mixture through a filtration unit SUPRAdisc® II KS 100 Depth Filter Modules available from Pall Corporation, Port Washington, USA, to remove a minor amount of undissolved solid. The resulting silver impregnation solution had a density of 1.530 g/mL and a silver content of 29.5 wt-%.

[0182] 2.2. Preparation of Catalyst Based on Comparative Support A

[0183] 174.3 g of support A listed in Table 1 was placed into a 2 L glass flask. The flask was attached to a rotary evaporator which was set under vacuum pressure of 80 mbar. The rotary evaporator system was set in rotation of 30 rpm. 105.98 g of the silver complex solution prepared according to Example 2.1 was mixed with 1.3722 g of promoter solution I, 2.0583 g of promoter solution II, and 2.5033 g of promoter solution III. Promoter solution I was made from dissolving lithium nitrate (FMC, 99.3%) and ammonium sulfate (Merck, 99.4%) in DI water to achieve Li content of 2.85 wt.-% and S content of 0.21 wt.-%. Promoter solution II was made from dissolving tungstic acid (HC Starck, 99.99%) in DI water and cesium hydroxide in water (HC Starck, 50.42%) to achieve target Cs content of 4.25 wt.-% and W content of 2.0 wt.-%. Promoter solution III was made from dissolving ammonium perrhenate (Engelhard, 99.4%) in DI water to achieve Re content of 3.7 wt.-%. The combined impregnation solution containing silver complex solution, promoter solutions I, II, and III was stirred for 5 minutes. The combined impregnation solution was added onto the support A over 15 minutes under vacuum of 80 mbar. After addition of the combined impregnation solution, the rotary evaporator system was continued to rotate under vacuum for another 15 minutes. The impregnated support was then left in the apparatus at room temperature and atmospheric pressure for 1 hour and mixed gently every 15 minutes.

[0184] The impregnated material was calcined for 10 minutes at 290° C. under 23 m3/h flowing nitrogen in a calcination oven to yield the final catalyst 2.2.

[0185] 2.3. Preparation of Catalyst Based on Comparative Support B.

[0186] Step 2.3.1. Preparation of Ag-Containing Intermediate

[0187] 585 kg of a commercially available alpha-alumina support B listed in Table 1 were placed in a vacuum tumble mixer having a volume of 1.8 m.sup.3. The support was impregnated with 468 kg of Ag complex solution prepared according to Example 2.1 under a reduced pressure of 50 mbar and at a rate of rotation of 0.5 revolutions/min. Impregnation was carried out at room temperature over a period of 4 hours. The vacuum was then broken and the impregnated support was transferred to a belt calciner. The impregnated material was further heated on a belt calciner at a temperature of 290° C. in nitrogen flow according to calcination parameters described in WO2012/140614 to form a Ag-containing intermediate product.

[0188] Step 2.3.2. Preparation of Final Catalyst

[0189] 328 kg of Ag complex solution prepared according to Example 2.1 were mixed with 13.23 kg of promoter solution I containing Li and S, 14.37 kg of promoter solution II containing Cs and W, and 24.93 kg of promoter solution III containing Re to form Ag impregnation solution.

[0190] The promoter solution I was prepared by dissolving LiNO.sub.3 and (NH.sub.4).sub.2SO.sub.4 in water to form a solution with Li-content of 2.85 wt.-% and S-content of 0.21 wt.-%. The promoter solution II was prepared by dissolving CsOH and H.sub.2WO.sub.4 in water to form a solution with Cs-content of 5.3 wt.-% and W-content of 3.0 wt.-%. The promoter solution III was prepared by dissolving NH.sub.4ReO.sub.4 in water to form a solution with Re-content of 3.7 wt.-%.

[0191] 634 kg of Ag-containing intermediate prepared according to Step 2.3.1 were impregnated with 357 kg of the Ag impregnation solution under a reduced pressure of 50 mbar and at a rate of rotation of 0.5 revolutions/min. Impregnation was carried out at room temperature over a period of 3 hours. The vacuum was then broken and the impregnated support was transferred to a belt calciner. The impregnated material was further heated on a belt calciner at a temperature of 290° C. in nitrogen flow according to calcination parameters described in WO2012/140614 to form a final ethylene oxide catalyst 2.3.

[0192] 2.4. Preparation of Catalyst Based on Support D.

[0193] Step 2.4.1. Preparation of Ag-Containing Intermediate

[0194] 174 g of support D listed in Table 1 was placed into a 2 L glass flask. The flask was attached to a rotary evaporator which was set under vacuum pressure of 80 mbar. The rotary evaporator system was set in rotation of 30 rpm. 149.2 of silver complex solution prepared according to Example 2.1 was added onto support D over 15 minutes under vacuum of 30 mbar. After addition of the silver complex solution, the rotary evaporator system was continued to rotate under vacuum for another 15 minutes. The impregnated support was then left in the apparatus at room temperature and atmospheric pressure for 1 hour and mixed gently every 15 minutes. The impregnated support was calcined for 12 minutes at 290° C. under 23 m.sup.3/h flowing nitrogen in a calcination oven to yield Ag-containing intermediate product.

[0195] Step 2.4.2. Preparation of Final Catalyst 2.1 with Properties Listed in Tables 3 and 4.

[0196] 213 g of Ag-containing intermediate product prepared according to step 2.4.1 were placed into a 2 L glass flask. The flask was attached to a rotary evaporator which was set under vacuum pressure of 80 mbar. The rotary evaporator system was set in rotation of 30 rpm. 112.52 g of the silver complex solution prepared according to step 3.1 was mixed with 4.0728 g of promoter solution I, 4.4454 g of promoter solution II, and 7.6761 g of promoter solution III. Promoter solution I was made from dissolving lithium nitrate (FMC, 99.3%) and ammonium sulfate (Merck, 99.4%) in DI water to achieve Li content of 2.85 wt.-% and S content of 0.21 wt.-%. Promoter solution II was made from dissolving tungstic acid (HC Starck, 99.99%) in DI water and cesium hydroxide in water (HC Starck, 50.42%) to achieve target Cs content of 5.28 wt.-% and W content of 3.0 wt.-%. Promoter solution III was made from dissolving ammonium perrhenate (Engelhard, 99.4%) in DI water to achieve Re content of 3.7 wt.-%. The combined impregnation solution containing silver complex solution, promoter solutions I, II, and III was stirred for 5 minutes. The combined impregnation solution was added onto the silver-containing intermediate product 2.4.1 over 15 minutes under vacuum of 80 mbar. After addition of the combined impregnation solution, the rotary evaporator system was continued to rotate under vacuum for another 15 minutes. The impregnated support was then left in the apparatus at room temperature and atmospheric pressure for 1 hour and mixed gently every 15 minutes. The impregnated material was calcined for 10 minutes at 290° C. under 23 m.sup.3/h flowing nitrogen in a calcination oven to yield the final catalyst 2.4.

[0197] 2.5. Preparation of Catalyst Based on Support Q.

[0198] Catalyst 2.5, having the chemical composition and properties listed in Tables 3 and 4, was prepared according to steps 2.3.1 and 2.3.2, wherein Comparative Support B was replaced with inventive Support Q, and the amount of the promoter solutions was adjusted to obtain the target composition as shown in Table 3.

Example 3—Catalyst Testing

[0199] 3.1. Testing of Crushed Catalysts with Different Particle Sizes in a Mini Plant.

[0200] The epoxidation reaction was conducted in a vertically-placed test reactor constructed from stainless steel with an inner-diameter of 6 mm and a length of 2.2 m. The reactor was heated using hot oil contained in a heating mantel at a specified temperature. All temperatures below refer to the temperature of the hot oil. The reactor was filled with 29 g of inert steatite balls (1.0-1.6 mm), then packed with a desired amount of crushed catalyst screened to a desired particle size and then again packed with additional 9 g of inert steatite balls (1.0-1.6 mm). The inlet gas was introduced to the top of the reactor in a “once-through” operation mode.

[0201] Catalyst 2.2.a and catalyst 2.3.a were screened to a particle size of 0.5-0.9 mm. Catalyst 2.2.b and catalyst 2.3.b were screened to a particle size of 2-3.15 mm. The filling amount of the catalysts 2.2.a and 2.2.b was 34.9 g. The filling volume of the catalyst 2.2.a was 31.1 ml. The filling volume of the catalyst 2.2.b was 43.9 ml. The filling amount of the catalysts 2.3.a and 2.3.b was 33.5 g. The filling volume of the catalyst 2.3.a was 31.1 ml. The filling volume of the catalyst 2.3.b was 39.3 ml.

[0202] The catalysts were conditioned in the inlet gas consisted of 20 vol % ethylene, 4 vol % oxygen, 1 vol % CO.sub.2, and ethylene chloride (EC) moderation of 2.5 parts per million by volume (ppmv), with methane used as a balance at the total gas flow rate of 152.7 NI/h, a pressure of about 15 bar. The conditioning temperature during tests o catalysts 2.2.a and 2.2.b was 250° C. with duration of 61 hours. The conditioning temperature during tests of catalysts 2.3.a and 2.3.b was 245° C. with duration of 108 hours.

[0203] The temperature during evaluation of catalysts 2.2.a and 2.2.b. was decreased after the conditioning phase to 235° C., while maintaining the EC concentration at 2.5 ppmv. The temperature during evaluation of catalysts 2.3.a and 2.3.b. was decreased after the conditioning phase to 225° C., the EC concentration was decreased to 1.5 ppmv.

[0204] Then, for all tested catalysts, the inlet gas composition was gradually changed to 35 vol % ethylene, 7 vol % oxygen, 1 vol % CO.sub.2 with methane used as a balance and the total gas flow rate of 147.9 NI/h. The temperature during tests was adjusted to achieve comparable ethylene oxide (EO) concentrations in the outlet gas for selected couple of catalysts (2.2.a/2.2.b or 2.3.a/2.3.b). At every selected condition, the EC concentration was adjusted to optimize the selectivity.

[0205] Results of the catalyst tests are shown in Table 5.

TABLE-US-00007 TABLE 5 Test Reaction Results catalyst EO outlet EO time on stream particle size volume concentration selectivity temperature incl. condition work rate catalyst [mm] [mL] [vol-%] [%] [° C.] phase [d] [kg.sub.EO/(m.sup.3.sub.cath)] 2.2.a 0.5-0.9  31.1 2.73 91.3 245 13 250 2.2.b 2.0-3.15 43.9 2.73 91.0 243 13 178 2.2.a 0.5-0.9  31.1 2.0 91.6 238 21 180 2.2.b 2.0-3.15 43.9 2.0 91.4 237 21 128 2.2.a 0.5-0.9  31.1 3.07 90.9 250 27 280 2.2.b 2.0-3.15 43.9 3.07 90.9 247 27 198 2.3.a 0.5-0.9  31.1 3.04 89.9 232 41 280 2.3.b 2.0-3.15 39.3 3.04 89.3 235 41 222

[0206] The test results show that for the catalysts 2.2.a/2.2.b with a Ag-content of 15 wt.-% and a BET surface area of 0.95 m.sup.2/g within the tested range of comparable EO outlet concentrations of 2.0-3.07 vol-%, the difference in selectivity is ≤3%. On the other hand, for the catalysts 2.3.a/2.3.b with a Ag-content of 29 wt.-% and a BET surface area of 2.4 m.sup.2/g the difference in selectivity is 0.6%. Therefore, the increase of particle size has a more pronounced negative effect on the catalysts with a Ag-content of 29 wt.-% and a BET surface area of 2.4 m.sup.2/g.

[0207] 3.2. Testing of Catalyst Bodies in a Pilot Plant.

[0208] The epoxidation reaction was conducted in a vertically-placed test reactor constructed from stainless steel with an inner-diameter of 44 mm and a length of 12.80 m. The reactor was equipped with a thermocouple of an outer diameter of 8 mm positioned in the center of the reactor. Reactor temperature was regulated using pressurized water contained in the reactor mantel. Catalyst temperatures were measured using the thermocouple at five different positions equally distributed along the reactor length. All temperatures below refer to an average catalyst temperature of the five measurements. Catalyst bodies (14.5 kg of Comparative Catalyst 2.3 in a first test, and 16.3 kg of Inventive Catalyst 2.5 in a second test) were charged into the reactor so as to provide a catalyst bed with a height of 11.9 m. 0.65 m of inert ceramic balls were packed on top of the catalyst bed.

[0209] The catalysts were conditioned in a mixture of 55 to 60 Nm.sup.3/h of reaction gas and 25 to 30 Nm.sup.3/h of nitrogen at an average catalyst temperature of 255 to 260° C. and a reactor outlet pressure of about 15 bar for about 36 hours. The reaction gas contained 35 to 40 vol.-% of ethylene, 6.5 to 7.5 vol.-% of oxygen, 0.4 to 0.8 vol.-% of carbon dioxide, 0.5 to 4 vol.-% of nitrogen, 0.1 to 0.3 vol.-% of ethane, 0.15 to 0.25 vol.-% of water, about 1 ppm of vinyl chloride, and methane as a balance gas. Additionally, 1.7 to 2.0 ppm of ethyl chloride were dosed into the feed during conditioning.

[0210] Subsequently, the catalyst temperature was decreased to about 235 to 240° C., the nitrogen flow was gradually decreased to 0 Nm.sup.3/h, and the reaction gas flow was gradually increased to adjust the GHSV to 4800 h.sup.−1. Then, the temperature was adjusted to control a work rate at 280 kg(EO)/m.sup.3(cat)h or an EO outlet concentration of 2.97 vol %. The concentration of chlorine-containing components (ethyl chloride, vinyl chloride and methyl chloride) was optimized to achieve the highest possible selectivity.

[0211] Results of the catalyst tests are shown in Table 6.

TABLE-US-00008 TABLE 6 Test Reaction Results Example 2.3 2.5 Comparative Inventive Shape Ring Tetralobe Passageways cumulative EO 1 5 production Performance 100 t(EO)/m.sup.3(cat) Catalyst temperature [° C.] 243 232 Selectivity [%] 86.0 87.5 300 t(EO)/m.sup.3(cat) Catalyst temperature [° C.] 245 235 Selectivity [%] 87.6 89.1 500 t(EO)/m.sup.3(cat) Catalyst temperature [° C.] 245 237 Selectivity [%] 87.4 89.1 700 t(EO)/m.sup.3(cat) Catalyst temperature [° C.] 245 239 Selectivity [%] 87.5 89.7 900 t(EO)/m.sup.3(cat) Catalyst temperature [° C.] 247 240 Selectivity [%] 87.5 90.0

[0212] The test results show that the catalyst temperature is lower and the selectivity is higher for catalyst 2.5 than for catalyst 2.3 at all production rates.