PRODUCTION OF POROUS ALPHA-ALUMINA SUPPORTS FROM BOEHMITIC DERIVED ALUMINAS

Abstract

A porous alpha-alumina catalyst support is prepared by (i) preparing a precursor material comprising a boehmitic-derived alumina having a pore volume of at least 0.6 mL/g, wherein the boehmitic-derived alumina is obtained by thermal decomposition of a boehmitic starting material and the boehmitic starting material consists predominantly of block-shaped crystals, and optionally an inorganic bond material; (ii) forming the precursor material into shaped bodies; (iii) calcining the shaped bodies to obtain the porous alpha-alumina catalyst support. The support structure has a high overall pore volume, while keeping its surface area sufficiently large so as to provide optimal dispersion of catalytically active species, in particular metal species. The support is useful for a catalyst for producing ethylene oxide by gas-phase oxidation of ethylene.

Claims

1.-16. (canceled)

17. A process for producing a porous alpha-alumina catalyst support, comprising i) preparing a precursor material comprising a boehmitic-derived alumina having a pore volume of at least 0.6 mL/g, wherein the boehmitic-derived alumina is obtained by thermal decomposition of a boehmitic starting material and the boehmitic starting material predominantly comprises block-shaped crystals, and optionally an inorganic bond material; ii) forming the precursor material into shaped bodies; iii) calcining the shaped bodies to obtain the porous alpha-alumina catalyst support.

18. The process according to claim 17, wherein the block-shaped crystals have an aspect ratio of at most 3.0, wherein the aspect ratio is defined as the ratio of the largest crystal dimension to the smallest crystal dimension.

19. The process according to claim 17, wherein the boehmitic starting material comprises at least 60 wt.-% of block-shaped crystals, relative to the total weight of crystals constituting the boehmitic starting material.

20. The process according to claim 17, wherein the boehmitic starting material comprises boehmite and/or pseudoboehmite.

21. The process according to claim 17, wherein the precursor material comprises, based on inorganic solids content, at least 50 wt.-% of the boehmitic-derived alumina.

22. The process according to claim 17, wherein the boehmitic-derived alumina comprises alpha-alumina, a transition alumina, or mixtures thereof.

23. The process according to claim 22, wherein the transition alumina comprises at least 50 wt.-% of a transition alumina having an average particle size of 10 to 100 μm based on the total weight of transition alumina.

24. The process according to claim 17, wherein the boehmitic-derived alumina has a loose bulk density in the range of 50 to 600 g/L, a pore volume of 0.6 to 2.0 mL/g, as determined by nitrogen sorption, and a median pore diameter of at least 15 nm, as determined by nitrogen sorption.

25. The process according to claim 17, wherein the boehmitic-derived alumina has a total content of alkali metals of at most 1500 ppm.

26. The process according to claim 17, wherein the precursor material comprises, based on inorganic solids content, 1 to 30 wt.-% of the inorganic bond material.

27. The process according to claim 17, wherein the precursor material is formed into shaped bodies via extrusion, tableting, granulation casting, molding, or micro-extrusion.

28. The process according to claim 17, wherein calcining is performed at a temperature of at least 1300° C.

29. A shaped catalyst body for producing ethylene oxide by gas-phase oxidation of ethylene, comprising at least 15 wt.-% of silver, relative to the total weight of the catalyst, deposited on a porous alpha-alumina catalyst support obtained in the process according to claim 17.

30. The shaped catalyst body according to claim 29, comprising 15 to 70 wt.-% of silver, relative to the total weight of the shaped catalyst body.

31. A process for preparing a shaped catalyst body as defined in claim 29, comprising a) impregnating the porous alpha-alumina catalyst support with a silver impregnation solution; and optionally subjecting the impregnated porous alumina support to drying; and b) subjecting the impregnated porous alpha-alumina support to a heat treatment; wherein steps a) and b) are optionally repeated.

32. 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 according to claim 29.

Description

[0172] The invention is described in more detail by the accompanying drawings and the subsequent examples.

[0173] FIG. 1 shows the log differential intrusion [mL/g] and cumulative intrusion [mL/g] relative to the pore size diameter [mL/g] of inventive porous alpha-alumina catalyst support A, obtained by a process according to the invention.

[0174] FIG. 2 shows the log differential intrusion [mL/g] and cumulative intrusion [mL/g] relative to the pore size diameter [mL/g] of inventive porous alpha-alumina catalyst support B, obtained by a process according to the invention.

[0175] FIG. 3 shows the log differential intrusion [mL/g] and cumulative intrusion [mL/g] relative to the pore size diameter [mL/g] of comparative porous alpha-alumina catalyst support C.

Method 1: Nitrogen Sorption

[0176] Nitrogen sorption measurements were performed using a Micrometrics ASAP 2420.

[0177] Nitrogen porosity was determined in accordance with DIN 66134.

Method 2: Mercury Porosimetry

[0178] Mercury porosimetry was performed using a Micrometrics AutoPore IV 9500 mercury porosimeter (140 degrees contact angle, 485 dynes/cm Hg surface tension, 60,000 psia max head pressure). Mercury porosity was determined in accordance with DIN 66133.

Method 3: Loose Bulk Density

[0179] The loose bulk density was determined by pouring the boehmitic-derived alumina into a graduated cylinder via a funnel, taking care not to move or vibrate the graduated cylinder. The volume and weight of the boehmitic-derived alumina were determined. The loose bulk density was determined by dividing the volume in milliliters by the weight in grams.

Method 4: BET Surface Area

[0180] The BET surface area was determined in accordance with DIN ISO 9277.

Method 5: Crystal Analysis

[0181] X-ray diffraction data of boehmitic starting materials was obtained via Cu radiation and a conventional laboratory diffractometer. The data was analyzed using a software called DIANNA (diffraction analysis of nanopowders) as described in Yatsenko and Tsybulya, Zeitschrift für Kristallographie, 233 (2018), pp. 61-66. DIANNA software implements the Debye equation, which models a diffraction pattern based on scattering contributions from all atom pairs in a crystal. ICDD (International Centre for Diffraction Data) card 59608 was used as a rigid group in this modeling. That is, unit cell parameters and fractional coordinates for boehmite were used as reported in card 59608 without any refinement in this survey. Several model diffraction pattern for boehmite crystallites were calculated and compared with one of the experimental diffraction patterns.

[0182] Model crystallites were all rectangular prisms. The smallest prism was 20 unit cells long in the crystallographic x direction (5.6 nm), 1.5 unit cells thick in the crystallographic y direction (1.8 nm) and 20 unit cells wide in the crystallographic z direction (7.2 nm). This cell is 64 nm.sup.3 in volume. Crystallites as large as 13,000 nm.sup.3 were modeled. Ensembles of crystallite size models, refined within DIANNA to assess their number fraction and weight fraction of the overall population of boehmite crystallites, were employed.

[0183] The following tables show crystal size distributions for Pural TH 200, Pural TM 100 and Pural SB1, i.e. boehmitic starting materials, which are further described below. Aspect ratios are determined by dividing the largest crystal dimension, i.e. the largest a, b and c value by the smallest crystal dimension, i.e. the smallest a, b and c value.

TABLE-US-00001 Crystal Size Distribution of Pural SB 1 Cumulative Length Thickness Width Crystal Crystal (a-axis) (b-axis) (c-axis) Aspect Amount Amount [nm] [nm] [nm] Ratio [wt. %] [wt. %] 5.6 4.7 7.2 1.53 2.5 2.5 8.5 4.7 7.2 1.81 3.8 6.3 5.6 3.5 7.2 2.06 2.4 8.7 8.5 4.7 10.9 2.32 3.9 12.5 8.5 3.5 7.2 2.43 2.5 15.1 8.5 3.5 10.9 3.11 3.5 18.6 5.6 2.3 7.2 3.13 4.1 22.7 11.3 3.5 7.2 3.23 3.8 26.4 11.3 3.5 10.9 3.23 5.5 32.0 8.5 2.3 7.2 3.70 4.4 36.3 5.6 1.6 7.2 4.50 4.5 40.8 8.5 2.3 10.9 4.74 4.5 45.3 17.1 3.5 7.2 4.89 6.7 52.1 17.1 3.5 10.9 4.89 9.4 61.4 11.3 2.3 7.2 4.91 4.8 66.2 8.5 1.6 7.2 5.31 4.9 71.1 11.3 1.6 7.2 7.06 5.3 76.4 11.3 1.6 10.9 7.06 5.2 81.6 14.2 1.6 7.2 8.88 5.6 87.2 14.2 1.6 10.9 8.88 0.0 87.2 17.1 1.6 7.2 10.69 6.1 93.2 17.1 1.6 10.9 10.69 6.8 100.0

[0184] Thus, 15.1 wt.-% of the crystals of Pural SB 1 exhibit an aspect ratio of 3.0 or lower. 15.1 wt.-% exhibit an aspect ratio of 2.5 or lower.

TABLE-US-00002 Crystal Size Distribution of Pural TM 100 Cumulative Length Thickness Width Crystal Crystal (a-axis) (b-axis) (c-axis) Aspect Amount Amount [nm] [nm] [nm] Ratio [wt. %] [wt. %] 17.1 14.5 14.6 1.18 6.1 6.1 17.1 18.2 14.6 1.25 9.3 15.5 5.6 5.9 7.2 1.29 8.9 24.4 17.1 12 14.6 1.43 6.1 30.5 8.5 5.9 7.2 1.44 5.6 36.1 14.2 9.6 10.9 1.48 3.1 39.2 14.2 8.4 14.6 1.74 5.5 44.7 11.3 5.9 7.2 1.92 4.3 49.0 14.2 8.4 7.2 1.97 2.7 51.7 14.2 7.1 7.2 2.00 1.6 53.3 14.2 7.1 10.9 2.00 0.0 53.3 17.1 12 7.2 2.38 3.5 56.8 17.1 7.1 7.2 2.41 0.0 56.8 17.1 7.1 10.9 2.41 0.0 56.8 17.1 7.1 14.6 2.41 4.5 61.3 17.1 5.9 7.2 2.90 1.5 62.8 17.1 5.9 10.9 2.90 1.2 64.0 17.1 5.9 14.6 2.90 3.6 67.6 14.2 3.5 7.2 4.06 9.6 77.2 14.2 3.5 10.9 4.06 2.7 79.9 17.1 3.5 7.2 4.89 4.7 84.6 17.1 3.5 10.9 4.89 0.0 84.6 14.2 2.2 7.2 6.45 6.9 91.5 14.2 2.2 10.9 6.45 0.0 91.5 17.1 2.2 7.2 7.77 6.5 98.1 17.1 2.2 10.9 7.77 1.9 100.0

[0185] Thus, 67.6 wt.-% of the crystals of Pural TM 100 exhibit an aspect ratio of 3.0 or lower. 61.3 wt.-% exhibit an aspect ratio of 2.5 or lower.

TABLE-US-00003 Crystal Size Distribution of Pural TH 200 Cumulative Length Thickness Width Crystal Crystal (a-axis) (b-axis) (c-axis) Aspect Amount Amount [nm] [nm] [nm] Ratio [wt. %] [wt. %] 14.2 12 10.9 1.30 2.7 2.7 14.2 19.4 14.6 1.37 2.0 4.7 14.2 9.6 10.9 1.48 5.4 10.1 14.2 9.6 7.2 1.48 3.2 13.3 22.8 19.4 29.3 1.51 11.4 24.8 11.3 9.6 14.6 1.52 6.8 31.6 14.2 9.6 14.6 1.52 5.0 36.5 22.8 19.4 14.6 1.56 10.4 46.9 17.1 14.5 10.9 1.57 0.7 47.6 11.3 9.6 7.2 1.57 4.1 51.8 11.3 19.4 14.6 1.72 2.8 54.6 25.6 14.5 18.3 1.77 0.5 55.0 17.1 9.6 7.2 1.78 3.6 58.6 17.1 9.6 14.6 1.78 5.9 64.5 11.3 9.6 18.3 1.91 8.6 73.1 14.2 9.6 18.3 1.91 4.1 77.2 17.1 9.6 18.3 1.91 3.8 81.0 19.9 9.6 18.3 2.07 3.3 84.3 17.1 9.6 21.9 2.28 2.8 87.1 14.2 19.4 7.2 2.69 1.8 88.9 19.9 9.6 7.2 2.76 2.7 91.6 22.8 19.4 7.2 3.17 8.4 100.0

[0186] Thus, 91.6 wt.-% of the crystals of Pural TH 200 exhibit an aspect ratio of 3.0 or lower. 87.1 wt.-% exhibit an aspect ratio of 2.5 or lower.

Preparation of Porous Alpha-Alumina Catalyst Supports

[0187] The properties of the boehmitic-derived aluminas used to obtain porous alpha-alumina catalyst supports are shown in Table 1. The boehmitic-derived aluminas were obtained from Sasol.

TABLE-US-00004 TABLE 1 Amount of Block-Shaped Crystals of Boehmitic Bulk Pore Median Pore Starting Density Volume Diameter Crystalline Material [g/L] [mL/g] * [nm] * Phase [wt.-%] ** Puralox TH 200/70 300 1.23 37.4 delta 91.6 .sup.(1) Puralox TM 100/150 420 0.87 21.0 gamma 67.6.sup.(2)  Puralox SBa 200 650 0.5 10.0 gamma 15.1 .sup.(3) * determined by nitrogen sorption ** calculated by PXRD pattern analysis using DIANNA software; aspect ratio of at most 3.0 .sup.(1) the boehmitic starting material of Puralox TH 200/70 is believed to be a material available as Pural TH 200 .sup.(2)the boehmitic starting material of Puralox TM 100/150 is believed to be a material available as Pural TM 100 .sup.(3) the boehmitic starting material of Puralox SBa 200 is believed to be a material available as Pural SB1

EXAMPLE1—PREPARATION OF SUPPORTS A, B AND C

[0188] Boehmitic-derived aluminas and inorganic bond materials, as specified in Table 2, were mixed to obtain a powder mixture. Kollidon® VA64 (a vinylpyrrolidone-vinyl acetate copolymer from BASF) was added to the powder mixture. Water was then added to obtain a malleable precursor material. The amounts of all components are shown in Table 2.

[0189] The malleable precursor material was mixed to homogeneity via a mix-muller and subsequently extruded using a ram extruder to form shaped bodies. The shaped bodies were in the form of hollow cylinders having an outer diameter of about 10 mm and an inner diameter of about 5 mm. The extrudates were dried at 110° C. for approximately 16 h, followed by heat treatment in a muffle furnace at 600° C. for 2 h and subsequently at 1,500° C. for 2 h. Heat treatment was performed in an atmosphere of air.

TABLE-US-00005 TABLE 2 Boehmitic- Inorganic Derived Bond Burnout Support Alumina Material Material Liquid A Puralox TH Pural Kollidon Water 200/70 SB1 VA64 454 g 340 g 146 g 15 g B Puralox TM Pural Kollidon Water 100/150 SB1 VA64 439 g 340 g 146 g 15 g C * Puralox Pural Kollidon Water SBa 200 SB1 VA64 404 g 340 g 146 g 15 g * comparative example

[0190] Table 3 shows the physical properties of supports A, B, and C. FIGS. 1 to 3 show the log differential intrusion and cumulative intrusion relative to the pore size diameter of supports A, B, and C.

TABLE-US-00006 TABLE 3 BET Surface Pore Pore Volume Contained in Pores [mL/g] ** Area Volume (Proportion of the Total Pore Volume) Support [m.sup.2/g] [mL/g] <0.1 μm 0.1-1 μm 1-10 μm 10-100 μm >100 μm r.sub.pv *** A 1.57 0.27 0 0.21 0.05 0.01 0 0.23 (0%) (77.9%) (16.9%) (5.2%) (0%) B 1.65 0.26 0 0.18 0.07 0.01% 0 0.39 (0%) (71.0%) (25.9%) (3.1%) (0%) C * 1.03 0.27 0 0.11 0.15 0.01 0 1.44 (0%) (40.7%) (55.6%) (3.7%) (0%) * comparative example ** determined by mercury porosimetry *** r.sub.pv = ratio of the pore volume contained in pores with a diameter in the range of more than 1 to 10 μm to the pore volume contained in pores with a diameter in the range of 0.1 to 1 μm

[0191] It is evident that supports A, and B exhibit advantageously high proportions of pores with a diameter in the range of 0.1 to 1 μm in comparison to supports C. Supports A, and B also exhibit lower r.sub.pv values than supports C.

[0192] The surface area of supports A and B is significantly larger than that of support C.