Process for production of attrition stable granulated material

Abstract

The present invention relates to granulated particles with improved attrition and a method for producing granulated particles by fluidized bed granulation of inorganic particles wherein particles of reduced particle size are fed into a fluldized-bed granulation reactor thereby producing granulated particles with improved attrition.

Claims

1. A method of producing granulated particles in a fluidized-bed granulation reactor, the method comprising feeding inorganic particles dispersed in a dispersion medium into the fluidized-bed granulation reactor, the inorganic particles in the dispersion medium having a D.sub.90 value of between 1 μm and 15 μm, wherein the dispersion medium includes between 5 and 60 wt. % inorganic particles relative to the total amount of the dispersion medium.

2. The method of claim 1 wherein the dispersion medium comprising inorganic particles dispersed therein is sprayed into a process chamber of the fluidized-bed granulation reactor while heated process gas flows through the process chamber from the bottom to the top.

3. The method of claim 2, wherein the heated gas has an inlet temperature when entering the process chamber of 50° C. to 550° C.

4. The method of claim 3, wherein the heated gas has an inlet temperature when entering the process chamber of 100° C. to 400° C.

5. The method of claim 1, wherein the D.sub.90 value of the inorganic particles in the dispersion medium fed into the fluidized-bed granulation reactor is between 1 μm and 10 μm.

6. The method of claim 1, wherein the inorganic particles include compounds of alkaline earth metals, rare earth elements, platinum group elements, iron group elements, Cu, Ag, Au, Zn, Al, In, Sn, Si, P, V, Nb, Mo, W, Mn, Re, Ti, Zr or mixtures thereof.

7. The method of claim 1, wherein the inorganic particles are particles of alumina, silica, or a mixture thereof.

8. The method of claim 1, wherein the dispersion medium comprises water or consists of water.

9. The method of claim 1, wherein a stabilizer is added to the dispersion medium.

10. The method of claim 1, including the initial step of milling the inorganic particles in the dispersion medium to a D.sub.90 value between 1 μm and 15 μm before entering into the fluidized-bed granulation reactor.

11. The method of claim 10, wherein a stabilizer is added to the dispersion medium only after the milling step.

12. The method of claim 1, wherein the dispersion medium has a pH of between 2 and 12.

13. The method of claim 1, including a calcination step, wherein the calcination is conducted at a temperature of between 350° C. and 1600° C. for a period of 30 minutes to 5 hours.

14. The method of claim 1, wherein seed material comprising primary particles having a D.sub.50 value from 5 μm to 200 μm is either further included in the dispersion fed into the fluidized-bed granulation reactor and/or is already present in the fluidized-bed granulation reactor when the dispersion is fed into the fluidized-bed granulation reactor.

15. Spherical calcinated granulated particles produced according to the method of claim 1 having a D.sub.50 value of between 100 and 5000 μm.

16. Spherical, calcined granulated particles having a D.sub.50 value of the granulated particles between 150 and 5000 μm, a volume based sphericity of the particles of the granulated material between 0.900 and 1.00 and attrition value of less than 5%, further characterized by the following characteristics: a specific surface area ranging from 150 to 300 m.sup.2/g; and a monomodal or multimodal pore size distribution with pore radii maxima between 25 and 100000 Å.

17. The spherical calcined granulated particles of claim 16, further characterized by at least one of the following characteristics: a loose bulk density between 0.3 and 2.5 g/cm.sup.3; a pore volume of 0.01 to 2.0 cm.sup.3/g.

18. The spherical calcined granulated particles of claim 16 wherein the monomodal or multimodal pore size distribution with pore radii maxima is between 25 and 500 Å.

Description

(1) The invention will now be described by way of non-limiting examples and Figures where:

(2) FIGS. 1.1 and 1.2 are scanning microscopic images of the granulated particles of Example 1;

(3) FIG. 1.3 is a scanning microscopic image of sliced granulated particles of Example 1;

(4) FIG. 2 represents a monomodal pore size distribution of granulated particles of Example 1;

(5) FIGS. 3.1 and 3.2 are scanning microscopic images of the granulated particles of Example 2;

(6) FIG. 3.3 is a scanning microscopic image of sliced granulated particles of Example 2;

(7) FIG. 4 represents a monomodal pore distribution of granulated particles of Example 2;

(8) FIGS. 5.1 and 5.2 are scanning microscopic images of the granulated particles of Comparative Example 1;

(9) FIG. 5.3 is a scanning microscopic image of sliced granulated particles of Comparative Example 1;

(10) FIG. 6 represents a monomodal pore distribution of the granulated particles of Comparative Example 1;

(11) FIGS. 7.1 and 7.2 are a scanning microscopic images of the granulated particles of Comparative Example 2;

(12) FIG. 7.3 is a scanning microscopic image of a sliced granulated particles of Comparative Example 2 and

(13) FIG. 8 represents a monomodal pore distribution of the granulated particles of Comparative Example 2.

EXAMPLE 1

(14) For preparation of non-calcined granulated alumina particles, a dispersion medium including the alumina was prepared as follows:

(15) 12 kg Pural SB (boehmite) with a crystallite size of 5 nm (120 reflection) was added to 80 kg of water to form a dispersion medium. The dispersion medium was transferred into a vessel including a stirrer and successively wet-milled using an agitator ball mill (Drais Werke GmbH Mannheim Germany, PMC5 TEX) equipped with 1.0-1.2 mm α- (alpha) alumina grinding balls.

(16) After milling, a 10 wt.-% solution of an organic binder of polyvinyl alcohol (KURARAY Poval 4-88 -Poval 4-88 has a viscosity measured for a 4wt-% solution in water at 20° C. according to DIN 53015 of approximately 4 mPa*s and a grade of hydrolysis of 88mo1% (meaning that 88% of the vinyl acetate functional groups are saponified) was added to the dispersion medium such that the amount of polyvinyl alcohol was 5 wt.-% relative to the used boehmite. The resulting dispersion medium had an inorganic particle solid content of 12%, a pH value of 7.8 and a D.sub.90 of 9.4 μm.

(17) For granulation, seed material in the form of 3.6 kg of Pural SB (boehmite) with a D.sub.50 value of 50 μm was placed in the Vario 7 process chamber of a ProCell Labsystem fluidized bed granulator from Glatt.

(18) The granulation was conducted using bottom spray configuration with a two-component jet with an orifice of 1.8 mm. The Pural SB seed material was fluidized applying a heated air flow with a superficial velocity of 0.8 m/s, a fluidization number of 5 and an inlet temperature of 110-120° C.

(19) The dispersion medium was sprayed with a flow rate of 4-5 kg/h into the fluidized bed using a spraying pressure of 1.1-1.3 bar (gauche pressure). The evaporation rate related to the bed mass was 1.2-2.1 kg/(kg*h) and 60-96 kg/(m.sup.2*h) related to the area of the distribution plate.

(20) During the whole granulation process the temperature inside the process chamber was held between 50° C. and 60° C. while the relative humidity inside the process chamber was adjusted ranging from 35% to 45%. The material inside the process chamber was held in the fluidized state and the air flow rate and inlet temperature was adjusted to keep the temperature and humidity inside the process chamber in the desired range.

(21) The particle growth was conducted until the targeted particle size (D.sub.50) of 450 μm was reached. During the growth phase, material was discharged periodically out of the process chamber every hour to keep the bed mass on a constant level. After the targeted particle size was reached the material was discharged over a zig-zag sifter applying a sifter counter pressure of 1.4 bar (gauche pressure).

(22) Finally, the boehmite granulated particles were calcined under air atmosphere at 550° C. for 3h in a muffle oven.

(23) Scanning microscopic images of the granulated particles are shown in FIGS. 1.1 to 1.3. FIGS. 1.1 to 1.3 show the granulated particles with a high sphericity and a smooth outer surface. FIG. 2 shows the monomodal size distribution of the granulated particles of Example 1.

(24) Properties of the calcined boehmite granulated particles are included in Table 1.

(25) TABLE-US-00001 TABLE 1 Sphericity/— 0.974 Amount of attrition/% 1.2 D.sub.10/μm 350 D.sub.50/μm 449 D.sub.90/μm 553 Specific surface area/m.sup.2/g 191 Pore volume/cm.sup.3/g 0.46 Loose bulk density/g/cm.sup.3 0.78 Pore radius maximum/Å 35

EXAMPLE 2

(26) For preparation of attrition stable granulated alumina particles the granulation dispersion was prepared as follows:

(27) Suspending 12 kg Pural TM50 (boehmite) with a crystallite size of 7.2 nm (120 reflection) in 100 kg water with a stirrer and successively wet-milling the dispersion using an agitator ball mill (Drais Werke GmbH Mannheim Germany, PMC5 TEX) equipped with 1.0-1.2 mm α- (alpha) alumina grinding balls. After milling, a 10 wt.-% solution of polyvinyl alcohol (KURARAY Poval 4-88) was added to the dispersion so that the amount of an organic binder of polyvinyl alcohol was 5 wt-% related to the used boehmite. Furthermore, formic acid was added to adjust the pH of the dispersion to a value of 6. The resulting granulation dispersion had after dilution with water an inorganic particle solid content of 10% and a D.sub.90 of 12.0 μm.

(28) For granulation, 3.6 kg of Pural TM50 (boehmite) seed material with a median particle size (D.sub.50) of 75 μm was placed in the Vario 7 process chamber of a ProCell Labsystem fluidized bed granulator from Glatt.

(29) The granulation was conducted using bottom spray configuration with a two-component jet with an orifice of 1.8 mm. The Pural TM50 was fluidized applying a heated air flow with a superficial velocity of 0.8 m/s, a fluidization number of 5 and an inlet temperature of 110-120° C.

(30) The dispersion medium was sprayed with a flow rate of 4-5 kg/h into the fluidized bed using a spraying pressure of 1.1-1.3 bar (gauche pressure). The evaporation rate related to the bed mass was 1.2-2.1 kg/(kg*h) and 60-96 kg/(m.sup.2*h) related to the area of the distribution plate. During the whole granulation process the temperature inside the process chamber was held between 50° C. and 60° C. while the relative humidity inside the process chamber was adjusted ranging from 35% to 45%. The material inside the process chamber was held in the fluidized state and the air flow rate and inlet temperature was adjusted to kept the temperature and humidity inside the process chamber in the desired range.

(31) The particle growth was conducted until the targeted particle size (D.sub.50) of 500 μm was reached. During the growth phase material was discharged periodically out of the process chamber every hour to keep the bed mass on a constant level. After the targeted particle size was reached the material was discharged over a zig-zag sifter applying a sifter counter pressure of 1.2 bar (gauche pressure).

(32) Finally, the boehmite granules were calcined under air atmosphere at 650° C. for 3 h in a muffle oven.

(33) Scanning microscopic images of the granulated particles are shown in FIG. 3. FIG. 3 shows that the particles have a high sphericity and a smooth outer surface. FIG. 4 shows the monomodal pore size distribution of the granulated particles of Example 2.

(34) Properties of the calcined boehmite granulated particles are included in Table 2:

(35) TABLE-US-00002 TABLE 2 Sphericity/— 0.973 Amount of attrition/% 1.5 D.sub.10/μm 387 D.sub.50/μm 499 D.sub.90/μm 600 Specific surface area/m.sup.2/g 188 Pore volume/cm.sup.3/g 0.73 Loose bulk density/g/cm.sup.3 0.61 Pore radius maximum/Å 72 Å

COMPARATIVE EXAMPLE 1

(36) For comparison, the granulation was conducted using a dispersion medium based on EP 0790859 B1, i.e. without selecting the size of the inorganic particles in the dispersion medium or adjusting the size of the inorganic particles in the dispersion medium though a wet-milling step. A 10 wt.-% solution of polyvinyl alcohol (KURARAY Poval 4-88) was added to the dispersion medium so that the amount of polyvinyl alcohol was 5 wt-% related to the used boehmite.

(37) The dispersion medium had an inorganic particle solid content of 11%, a pH value of 8.1 and a D.sub.90 of 95 μm.

(38) All other granulation parameters were analog the procedure described in Example 1.

(39) FIG. 5 shows the particles with a rougher outer surface and a significantly higher amount of attrition than shown for the Examples of the invention.

(40) Properties of the calcined boehmite granulated particles of Comparative Example 1 are included in Table 3:

(41) TABLE-US-00003 TABLE 3 Sphericity/— 0.941 Amount of attrition/% 6.4 D.sub.10/μm 262 D.sub.50/μm 356 D.sub.90/μm 465 Specific surface area/m.sup.2/g 220 Pore volume/cm.sup.3/g 0.44 Loose bulk density/g/cm3 0.81 Pore radius maximum/Å 27

COMPARATIVE EXAMPLE 2

(42) For comparison, the granulation was conducted using a dispersion medium based on dispersing Pural SB in water acidified with nitric acid without further adjusting the particle size in dispersion through a wet-milling step. A 10 wt.-% solution of polyvinyl alcohol (KU Y Poval 4-88) was added to the dispersion so that the amount of polyvinyl alcohol was 3 wt-% related to the used boehmite. The dispersion medium had an inorganic particle solid content of 23%, a pH value of 3.8 and a D.sub.90 of 22 μm.

(43) All other granulation parameters were analog the procedure described in Example 1.

(44) TABLE-US-00004 TABLE 4 Sphericity/— 0.975 Amount of attrition/% 10.2 D.sub.10/μm 233 D.sub.50/μm 309 D.sub.90/μm 388 Specific surface area/m.sup.2/g 233 Pore volume/cm.sup.3/g 0.38 Loose bulk density/g/cm.sup.3 0.87 Pore radius maximum/Å 28