Stable Shaped Alumina and Method for Producing Same

Abstract

The present invention relates to a calcined shaped alumina and to a method of preparing a calcined shaped alumina. The method comprises that the alumina in the alumina suspension is hydrothermally aged to have a specific crystallite size. This in turn produces a highly stable alumina in the form of a calcined shaped alumina particularly at temperatures of 1200° C. and above.

Claims

1. A calcined shaped alumina comprising the following features a) and b): a) a crush strength between 30 and 70 N; and b) a monodispersed pore radius distribution with a median pore radius between 5 and 12 nm, wherein the calcined shaped alumina is in the form of spheroids having a sphericity of above 0.9, extrudates, tablets or mixtures thereof.

2. The calcined shaped alumina of claim 1 further comprising one or more of the features c) to f): c) a total pore volume between 0.4 and 1.2 cm.sup.3/g; d) a BET surface area between 10 and 100 m.sup.2/g after calcination at 1200° C. for 3 hours; e) a content of Na, Fe and Si impurities of the calcined shaped alumina is each below 100 ppm; and f) an alpha transition temperature above 1200° C.

3. The calcined shaped alumina of claim 2 comprising feature c).

4. The calcined shaped alumina of claim 1, wherein the calcined shaped alumina is in the form of spheroids having a sphericity of above 0.9.

5. The calcined shaped alumina of claim 1, wherein the calcined shaped alumina is in the form of a spheroid and the spheroid comprises a diameter of between 0.5 mm and 3.0 mm.

6. The calcined shaped alumina of claim 1 comprising one or more dopants.

7. A method to prepare a calcined shaped alumina, the method comprising the following steps: i) preparing an alumina suspension, the alumina suspension comprising alumina and at least water; ii) hydrothermally ageing the alumina suspension until the alumina in the alumina suspension has a crystallite size along the (120) axis and the (020) axis each of 70 to 110 Å to form a hydrothermally aged alumina suspension, iii) optionally drying the hydrothermally aged alumina suspension to obtain an alumina powder; iv) optionally preparing either an alumina paste from the alumina powder or an alumina dispersion from either the alumina powder or the hydrothermally aged alumina suspension; v) shaping the alumina powder, or the alumina paste or the alumina dispersion or the hydrothermally aged alumina suspension or mixtures thereof to form a shaped alumina; vi) drying the shaped alumina to form a dried shaped alumina; and vii) calcining the dried shaped alumina to form a calcined shaped alumina, wherein the calcined shaped alumina is in the form of spheroids having a sphericity of above 0.9, extrudates, tablets or mixtures thereof.

8. The method of claim 7, wherein the calcined shaped alumina is in the form of spheroids having a sphericity of above 0.9.

9. The method of claim 7, wherein the alumina content of the alumina suspension calculated as Al.sub.2O.sub.3 is between 2 and 20 wt.-% of the alumina suspension.

10. The method of claim 7, wherein the alumina content of the alumina dispersion calculated as Al.sub.2O.sub.3 is between 10 and 40 wt. %.

11. The method of claim 7, wherein the alumina dispersion comprises an acid.

12. The method of claim 7, wherein the alumina dispersion comprises kerosene.

13. The method of claim 7, wherein one or more dopants are added to the alumina paste, or the alumina dispersion, or the hydrothermally aged alumina suspension, or mixtures thereof prior to shaping to form the shaped alumina.

14. The method of claim 7, wherein the alumina in the alumina suspension is boehmite, gibbsite, bayerite and at least one transition alumina.

15. The method of claim 7, wherein the alumina in the alumina suspension after hydrothermal aging comprises boehmite or consists of boehmite.

16. The method of claim 7, wherein the boehmite after hydrothermal ageing has a ratio of the crystallite size along the (120) axis to the crystallite size along the (020) axis of 0.5:1 to 2.0:1.

17. The method of claim 7, wherein the hydrothermal ageing reaction is carried out at a temperature of between 60° C. and 300° C.

18. The method of claim 7, wherein the shaped alumina is dried at a temperature of between 90° C. and 150° C.

19. The method of claim 7, wherein calcination occurs at temperatures of between 450° C. and 1100° C.

Description

[0051] The invention will now be described with reference to the non-limiting examples and figures in which:

[0052] FIG. 1 shows the pore radius distribution of Comparative Examples 1 and 2 (sample 1 and 2) and Examples 1 and 6 (samples 3a and 7);

[0053] FIG. 2 shows the pore radius Distribution of Examples 1 and 2 calcined at different temperatures;

[0054] FIG. 3 shows the pore radius distribution for Examples 4 and 5 (samples 5 and 6) comprising different dopants;

[0055] FIG. 4 shows a DSC (Differential Scanning calorimetry)-TG (Thermal Gravimetric) Analysis of Comparative Example 1 and Example 1; and

[0056] FIG. 5 is an X-Ray Diffraction of Comparative Example 2 and Example 1 after both were calcined at 1200° C. for 3 hours;

[0057] FIG. 6 shows the pore radius distribution of Comparative Example 3.

EXAMPLES

[0058] Analytical Methods and Definitions

[0059] The crystallite sizes of the boehmite according to this invention are determined along the (120) and the (020) axis using the general Scherrer formula:

[0060] Crystallite size=(K×λ×57.3)/(β× cos θ)

[0061] Whereas: [0062] K (form factor): 0.992 [0063] λ (X-ray wave length): 0.154 nm [0064] β (corrected line broadening of apparatus): reflex dependent [0065] θ: reflex dependent

[0066] The measurements are carried out using a Bruker CubiX.sup.3 apparatus. The measurement parameters for the boehmite are 8=14° for the reflex along the (120) axis and 8=7° for the reflex along the (020) axis and 13=0.919 for both reflexes.

[0067] The specific surface area as provided herein is measured by BET using nitrogen according to DIN-ISO 9277.

[0068] The pore volume (for the pore radius range up to 1000 Å) and the pore radius distribution is measured using mercury intrusion according to DIN 66133. Median pore radius is the radius that corresponds to the 50th percentile of pore volume, i.e. the radius for which one half of the pore volume is found to be in larger pores and one half is found to be in smaller pores.

[0069] The diameter of the spheroidal aluminas is determined according to ASTM D1155.

[0070] The Crush Strength is determined according to ASTM D6175 for extrudates and according to ASTM D4179 for other shapes.

[0071] DSC is determined according to DIN 51007.

[0072] As described in ISO 13322-2 (2006) the sphericity is determined by dynamic image analysis with a Camsizer P4 from Retsch. The sphericity (SPHT3) is calculated from the measured perimeter P and area A of the particle projection using following equation

[00001]$\mathrm{SPHT}3=\frac{4\pi A}{P^2}$

[0073] The determined value is dimensionless and would be 1 for an ideal sphere and is typically below 1 for spheroidal particles which are non-ideal spheres. In the present case the sphericity is above 0.9.

[0074] These procedures were followed exactly as outlined in the prescribed method.

[0075] Particle sizes are determined by Laser Diffraction (Malvern Mastersizer 2000) using the Mie theory.

[0076] Preparation of the hydrothermally aged samples:

[0077] Sample A

[0078] The hydrolysis of Al-hexanolate was performed at 98° C. in an aqueous solution of 2% ammonium bicarbonate. The obtained alumina suspension (=boehmite suspension) having 7.5 wt.-% Al.sub.2O.sub.3 was stirred at 105° C. for 18 hours at a stirring speed of 3.2 m/s.

[0079] The aged alumina suspension was dried in a spray dryer (inlet temperature: 120° C.). A boehmite powder with a crystallite size of 101 Å along the (120) axis and 104 Å along the (020) axis was obtained.

[0080] Sample B

[0081] The hydrolysis of Al-hexanolate was performed at 98° C. in an aqueous solution of 2% ammonium bicarbonate. The obtained alumina suspension (=boehmite suspension) having 7.5 wt.-% alumina calculated as Al.sub.2O.sub.3 was stirred at 100° C. for 16 hours at a stirring speed of 3.2 m/s. The aged alumina suspension was dried in a spray dryer (inlet temperature: 120° C.). A boehmite powder with a crystallite size of 94 Å along the (120) axis and 93 Å along the (020) axis was obtained.

EXPERIMENTS

Example 1=Sample 3a

[0082] An alumina dispersion was prepared by dispersing boehmite according to sample A in acidic water. The dispersion contained 32.5 wt.-% boehmite, calculated as Al.sub.2O.sub.3, and 0.03 g nitric acid per g of boehmite. After stirring for 10 minutes the sol was fed in the form of drops into a forming column according to U.S. Pat. No. 4,542,113 at a temperature of 20° C. to 25° C. which was filled with an 8 wt.-% solution of ammonia. The green spheroids discharged from the forming column were dried at 120° C. until a constant weight was obtained. The dried spheroids were calcined at 650° C. for 3 hours.

Example 2=Sample 3b

[0083] Example 2 was performed as per Example 1 but the dried spheroids were calcined at 950° C. for 3 hours.

Example 3=Sample 4

[0084] Example 3 was performed as per Example 1 but the boehmite starting alumina is sample B.

Example 4=Sample 5

[0085] Example 4 was performed as per Example 3 but in addition to boehmite, water and acid, the dispersion contained the dopant SnCl.sub.4×2 H.sub.2O corresponding to 0.4 wt.-% Sn, calculated as SnO.sub.2 and on the basis of the calcined alumina spheres.

Example 5=Sample 6

[0086] Example 5 was performed as per Example 3 but in addition to boehmite, water and acid, the dispersion contained the dopant Bi(NO.sub.3).sub.3×5 H.sub.2O corresponding to 0.1 wt.-% Bi, calculated as Bi.sub.2O.sub.3 on the basis of the calcined alumina spheres.

Example 6=Sample 7

[0087] Example 6 was performed as per Example 3 but in addition to boehmite, water and acid the dispersion contained 0.1 g kerosene per g of boehmite.

Example 7=Sample 8 (Extrudates)

[0088] An alumina paste was prepared by mixing 1500 g of sample B with 1250 g 4 wt.-% acetic acid in a high shear mixer for 15 minutes. This paste was pressed through a hole disk obtaining extrudates with a diameter of 1.69 mm. The green bodies were dried at 120° C. until constant weight. The dried extrudates were calcined at 650° C. for 3 hours.

Example 8=Sample 9 (Tablets)

[0089] The tablets (5.1×5.2 mm) were pressed by processes known in the art using the boehmite powder of sample B and calcined at 650° C. for 3 hours.

Comparative Example 1=Sample 1 (without Kerosene)

[0090] An alumina dispersion was prepared by mixing a boehmite powder having a crystallite size of 38 Å along the (120) axis and 30 Å along the (020) axis, which has been prepared without an ageing step, in acidic water. The dispersion contained 32.5 wt.-% solid and 0.03 g nitric acid per g of boehmite. After stirring for 10 minutes the sol was fed in the form of drops into a forming column at a temperature of 20° C. to 25° C. which was filled with an 8 wt.-% solution of ammonia. The green spheroids discharged from the forming column were dried at 120° C. until constant weight. The dried spheroids were calcined at 650° C. for 3 hours.

Comparative Example 2=Sample 2 (with Kerosene)

[0091] Comparative Example 2 was performed as per Comparative Example 1 but in addition to boehmite, water and acid the dispersion contained 0.1 g kerosene per g of boehmite.

[0092] A summary of the Examples and Comparative Examples 1 and 2, including the results, are included in Table 1 hereunder.

[0093] FIG. 1 compares the pore radius distribution of Comparative Example 1 (Sample 1), Comparative Example 2 (Sample 2) and Example 1 (Sample 3a), Example 6 (Sample 7). As per FIG. 1 it is clear that the median pore radius of the Comparative Example 1 is below that of the inventive examples. FIG. 2 shows the pore radius distribution of Example 1 and 2 having the same starting material but being calcined at different temperatures. FIG. 3 shows the pore radius distribution of Example 4 and 5 (Sample 5 and 6) having different dopants. FIG. 4 is a DSC (Differential Scanning calorimetry)-curve that shows the phase transitions of alumina as per Comparative Example 1 (Sample 1) and Example 1 (Sample 3a). As shown Com-ic) parative Example 1 (Sample 1) is characterized by a phase transition into the alpha-phase at 1188.6° C. whilst Example 1 (Sample 3a) prepared acc. to the invention, shows a phase transition into the alpha-phase at 1314° C. The phase transition into the alpha-phase is attended with a reduction of the surface area. FIG. 5 shows the comparison between Comparative Example 2 (Sample 2) and again Example 1 (Sample 3a) after both were calcined at 1200° C. for 3 hours. Comparative Example 2 shows the alpha phase whilst Example 2 shows only the theta phase.

TABLE-US-00001 TABLE 1 Comp Comp Characteristic ** (unit) Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Alumina Crystallite size <30 <30 104 104 93 93 93 93 93 93 (020) (nm) Alumina Crystallite size 38 38 101 101 94 94 94 94 94 94 (021) (nm) Ratio (020)/(021) of starting <0.79 <0.79 1.03 1.03 0.99 0, .99 0.99 0.99 0.99 0.99 alumina BET Surface Area* (m.sup.2/g) 282 282 195 195 193 193 193 193 193 193 of starting alumina Total pore volume of starting 0.47 0.47 0.86 0.86 0.82 0.82 0.82 0.82 0.82 0.82 alumina (cm.sup.3/g) Shape spheroid spheroid spheroid spheroid Spheroid spheroid spheroid spheroid extrudate Tablet Size (mm) (largest dimension) 2.57 1.88 1.82 1.79 1.83 1.76 1.87 1.67 1.69 5.1 × 5.2 Crush Strength (N) 185 76 57 50 43 36 40 32 57 63 Surface Area (m.sup.2/g) 215 188 154 111 149 108 139 171 172 162 Surface Area - 1200° C. 7 7 44 63 57 71 27 52 11 13 (m.sup.2/g) Total Pore Volume (Hg-1000 0.49 0.83 0.76 0.75 0.80 0.77 0.80 0.96 0.78 0.76 Å) (cm.sup.3/g) Median Pore Radius (nm) 2.9 3.9 7.7 9.2 8.1 9.8 8.2 8.1 7.5 8.6 Alpha transition 1188 1220 1314 1314 1314 1345 1314 1318 1272 1290 temperature (° C.) *BET Surface area and Total Pore Volume at 550° C. and Hg, 550° C. respectively ** content of Na, Si and Fe is each below 50 ppm for all

Comparative Example 3 (Example 5 of U.S. Pat. No. 4,542,113)

[0094] Comparative Example 3 was performed by reworking Example 5 of U.S. Pat. No. 4,542,113. The exact same experimental procedure was used. The raw material was a mixture of two boehmites with the following properties:

TABLE-US-00002 TABLE 2 Boehmite (020) (120) 30 wt. % 65 Å 96 Å 70 wt. % 40 Å 54 Å

[0095] Comparing the properties of the resulting material to the properties reported in example 5 of U.S. Pat. No. 4,542,113, the conclusion is that the reworking is representative (see Table 3).

TABLE-US-00003 TABLE 3 Data mentioned for Example 5 of U.S. Comparative Pat. No. 4,542,113 Example 3 Diameter (mm) 2-3 1.6 Crush strength (N/spheroid) 40 41 Pore volume (ml/g) 0.68 0.85 Specific surface area (m.sup.2/g) 242 260

[0096] FIG. 6 shows the pore radius distribution of Comparative Example 3. The measured median pore size is 4.9 nm, and the pore radius distribution is bimodal.