STAR-SHAPED CERAMIC BODY FOR USE AS CATALYST

Abstract

Star-shaped ceramic body, wherein the cross-section of the body has six lobes, the ratio of the maximum radius r2 in the star to radius r1 of a circle connecting the intersections of the lobes being in the range from 1.0 to 3.61, preferably from 2.17 to 3.61, the ratio of the area F1 inside this circle to the summed area F2 of the lobes outside this circle being in the range of from 0.54 to 0.90, the ratio of the distance x2 between the two intersections I of one lobe with neighboring lobes and the radius r1 of the circle being in the range of from 0.67 to 1.11. The ceramic body is used as catalyst-support.

Claims

1.-18. (canceled)

19. Star-shaped ceramic body, wherein the cross-section of the body has six lobes, the ratio of the maximum radius r2 in the star to radius r1 of a circle connecting the intersections of the lobes being in the range from 2.17 to 3.61, the ratio of the area F1 inside this circle to the summed area F2 of the lobes outside this circle being in the range of from 0.54 to 0.90, the ratio of the distance x2 between the two intersections I of one lobe with neighboring lobes and the radius r1 of the circle being in the range of from 0.67 to 1.11.

20. The body according to claim 19, wherein each lobe has straight outer walls with a rounded top, wherein the ratio of the length x1 from the intersection I of one lobe and neighboring lobes to the end of the straight outer wall to the distance x2 between two intersections I of one lobe and neighboring lobes is from 0.87 to 1.45.

21. The body according to claim 19, wherein each lobe has straight outer walls with a rounded top, wherein the angle α between the straight outer wall and the straight line x2 between two intersections I of one lobe and neighboring lobes is from 70 to 140 degrees.

22. The body according to claim 19, wherein each lobe has straight outer walls with a rounded top, wherein the ratio of the length x2 between two intersections I of one lobe and neighboring lobes to the length x3 between the ends of the straight outer walls is from 0.9 to 1.8.

23. The body according to claim 19, wherein each lobe has straight outer walls with a rounded top and the ratio of the lobe area of the trapeze F3 confined by the straight outer walls of a lobe and the outer lobe area F4 outside this trapeze is from 2.5 to 14.35.

24. The body according to claim 19, wherein the cross-section area is from 0.19 to 13.9 mm.sup.2.

25. The body according to claim 19, wherein the maximum radius r2 is from 0.4 to 6 mm.

26. The body according to claim 19, wherein the circle radius r1 is from 0.25 to 3.4 mm.

27. The body according to claim 19, wherein the ceramic body is an alumina body.

28. The body according to claim 27, having a pore volume in pores of diameter of over 1000 nm, as determined by mercury porosimetry, of at least 0.05 ml/g.

29. The body according to claim 27, wherein the total pore volume, as determined by mercury porosimetry, is between 0.05 and 2.0 ml/g, and/or wherein the BET surface area is at least 10 m.sup.2/g, and/or wherein the attrition in accordance with ASTM D4058-87 is less than 5 wt %.

30. The body according to claim 19, wherein the ceramic body is a silica body.

31. The body according to claim 19, wherein the cross-section of the body has six axes of mirror symmetry.

32. The body according to claim 19, having a length L of from 2 to 10 mm and/or having a length L to maximum diameter 2 r2 ratio of from 1 to 3.

33. A process for preparing a body according to claim 19 by forming a ceramic or ceramic precursor paste, optionally cutting the extrudate, drying and optionally calcining the formed paste.

34. A catalyst, comprising at least one catalytically active material supported on a body according to claim 19.

35. The catalyst according to claim 34, wherein the catalytically active material is selected from the group consisting of metals, metal oxides, metal sulfides and combinations thereof.

36. The use of a body according to claim 19 in a chemical reaction, preferably in oxidation reactions.

Description

EXAMPLE 1

[0138] 1.5 kg of aluminium trihydrate is mixed with 0.336 kg of alumina binder and 0.0237 kg of nitric acid (67%) and 0.383 kg of water.

[0139] If required, a small amount of organic lubricant may be applied to the mix and the mixing is continued until a relatively dry product is obtained, the intermediate product is extruded using an extruder, equipped with a die having star-shaped orifices, as shown in FIGS. 1 and 2, and a cutting device.

[0140] The die has the following properties: [0141] r1: 0,62 mm [0142] r2: 1.8 mm [0143] r3: 1.66 mm [0144] r4: 0.29 mm [0145] α: 97° [0146] x1: 0.93 mm [0147] x2: 0.79 mm [0148] x3: 0.60 mm [0149] Cross section area: 6.16 mm.sup.2 [0150] x2/x3: 1.27 [0151] x1/x2: 1.18 [0152] x2/r1: 1,27 [0153] r2/r1: 2.90

[0154] The extrudates obtained are dried at 105° C. for 16 hours and subsequently calcined at 850 to 900° C. for one hour.

[0155] After drying and calcining, r2 can be 1.7 mm due to shrinking; the other parameters may change accordingly.

[0156] The final product has been analyzed for its physical properties with the following result: [0157] N.sub.2-BET surface area: 106 m.sup.2/g [0158] Total Hg pore volume: 0.45 ml/g [0159] Pore volume in pores over 1000 nm: 0.07 ml/g [0160] Side crushing strength (SCS): 75 to 83 N [0161] Bulk crushing strength (BSC): 0.66 to 0.85 MPa

[0162] The crushing strength values will change as a function of particle diameter (which is two times r2) and as illustrated below.

[0163] SCS and BCS are strongly dependent on diameter and also on calcination procedure: [0164] Diameter of 3.6 mm: SCS=75 to 83 N, BCS=0.66 to 0.85 MPa; [0165] Diameter of 3.4 mm: SCS=80 to 87 N, BCS=0.6 to 0.85 MPa; [0166] Diameter of 3.2 mm: SCS=75 to 82 N, BCS=0.51 to 0.54 MPa; [0167] Diameter of 3.0 mm: SCS=62 to 69 N, BCS=0.48 to 0.65 MPa; [0168] Diameter of 2.8 mm: SCS=52 to 55 N, BCS=0.45 to 0.63 MPa; [0169] Diameter of 2.6 mm: SCS=49 to 56 N, BCS=0.45 to 0.50 MPa; [0170] Diameter of 2.4 mm: SCS=56 to 61 N, BCS=0.43 to 0.54 MPa.

[0171] In a broad understanding of the present invention, the above values and ratios can be varied in a range of ±25%, preferably ±20%, more preferably ±15%, most preferably ±10%, in particular ±5% for all extrudates described herein.

[0172] FIG. 1 and FIG. 2 show the cross-section of the extrudate with the above parameter.

[0173] The geometric surface area (GSA) and pressure drop for a packed bed of the extrudates of different sizes were determined. The values are obtained from a detailed numerical simulation. First, a random packing is generated with a simulation using the real geometry of a reactor tube and the catalyst. The packing is generated by virtually dropping the catalyst particles into the tube and calculating the movement and impacts between particle-particle and particle-wall contacts according to Newton's second law of motion. A discrete element soft-sphere algorithm is used as numerical method. The pressure drop is the result of a detailed simulation applying computational fluid dynamics. The fluid volume is extracted from the numerically generated random packed bed. The fluid dynamics around each pellet as well as all interstitial flow phenomena are fully resolved. The pressure drop is then calculated for a bed height of 4500 mm and an inner tube diameter of 56.2 mm. Compressed air is used as fluid. The pressure at the end of the packed bed is ambient pressure. Temperature is set to ambient temperature. The applied flow rate is 1.5 Nm.sup.3/h.

[0174] The extrudates according to the present example (239) were compared to a five-star extrudate as a reference and a modified trilobe extrudate (318) as a reference. All extrudates had a length of 4 mm.

[0175] FIG. 3 shows the cross section of the reference, the six-lobe star according to the present invention (239) and a trilobe (318).

[0176] FIG. 4 shows the scaling of the geometric surface area (GSA) as a function of the catalyst particle diameter.

[0177] FIG. 5 shows the scaling of the pressure drop (dp) for different catalyst particle diameters.

[0178] FIG. 6 shows the scaling of the pressure drop (dp) as a function of the geometric surface area (GSA).

[0179] Whereas all shapes show a comparable trend for the scaling of pressure drop (dp) versus geometric surface area (GSA), the 6-star geometry according to the present invention (239) has a lower onset value and is therefore beneficial.

EXAMPLE 2—ALCOHOL DEHYDRATION EXPERIMENTS

[0180] 1200 grams of boehmite is mixed with 972 grams of water. The mixing is continued until a relatively dry product is obtained and the intermediate product is then extruded using an extruder, equipped with a die having star-shaped orifices, as shown in FIGS. 1 and 2.

[0181] For alcohol dehydration testing (ethanol used), 25 cc of catalyst was loaded into a 1″ OD (0.834″ ID)×4 ft stainless steel fixed bed downflow reactor. The reactor was equipped with a thermowell that housed five thermocouples.

[0182] The reactor was heated by a furnace, with the catalyst loaded such that its location was in the middle furnace section.

[0183] Catalyst mass loading was determined by multiplying catalyst bulk density by 25 cc.

[0184] In all cases, ⅛″ Denstone spheres were used as bed support and in the pre-heat zone above the catalyst bed to provide surface area for the feedstock to vaporize.

[0185] Once loaded, the reactor was purged with 300 sccm N.sub.2 for approximately 30 minutes to remove air and subsequently heated to 400° C. under flowing N.sub.2 and held for at least 4 hours.

[0186] Once pretreatment of the catalyst was completed, the reactor was cooled to 375° C. and pressurized to 118 psig. Once pressure and temperature were stable, N.sub.2 flow was stopped and feed consisting of 90 wt % ethanol/10 wt % water was introduced to the reactor at a rate of LHSV.sub.EtOH=1.926 hr-1, where LHSV.sub.EtOH is defined as volumetric flow rate of ethanol per catalyst volume. The reactor was held at these conditions for approximately 24 hours.

[0187] Product analysis was performed with an online gas chromatograph equipped with a flame ionization detector (FID), a heated sample injection valve, and an HP-PLOT Q capillary column (30 m×0.320 mm×20.Math.μm). The reaction effluent was delivered to the GC through heated sample lines at 180 to 200° C. and injected approximately every 15 min.

[0188] The following quantities were calculated and used to assess and compare catalyst performance: percent ethanol conversion and percent selectivity to ethylene.

Percent conversion is defined as [(molar flow rate of ethanol in−molar flow rate of ethanol out)/(molar flow rate of ethanol in)]×100.

[0189] Percent selectivity is defined as [moles ethylene produced/moles ethanol consumed]×100.

[0190] Despite lower loaded catalyst mass in the reactor, samples of shape 239 performed notably better as compared to the reference and displayed higher conversion and selectivity levels. This is especially visible at lower reaction temperatures.

TABLE-US-00001 TABLE 1 five-star extrudate (reference) Shape 239 Shape 239 diameter 3.5 mm 3.6 mm 2.4 mm packed density 0.542 g/cm.sup.3 0.488 g/cm.sup.3 0.46 g/cm.sup.3 loaded 13.55 g 12.2 g 11.5 g Conversion (400° C.) 99.83% 99.86% 99.85% Selectivity (400° C.) 97.19% 97.26% 97.35% Conversion (375° C.) 97.03% 98.62% 99.86% Selectivity (375° C.) 96.53% 97.20% 97.26%

EXAMPLE 3−COMPUTER TOMOGRAPHY

[0191] The measurement of the geometric surface area per reactor volume of the catalyst of the individual shapes was carried out on a GE Phoenix nanotom m CT instrument with a Voxel size of 36,667 um, a voltage of 150 uV, a current of 80 uA and 1500 pictures in 360°. The geometric surface area was determined through a post processing of the data using VGSTUDIO MAX software from Volume Graphics.

TABLE-US-00002 TABLE 2 five-star extrudate (reference) Shape 239 Diameter, mm 3.5 2.4 Geometric surface area per 1.64 3.59 mass, m.sup.2/kg Geometric surface area per 1.46 2.55 reactor volume, m.sup.2/L