Process for producing metal oxide powders by means of flame spray pyrolysis

Abstract

Process for producing metal oxide powders by means of flame spray pyrolysis, in which an aerosol comprising a metal compound is introduced into a flame in a reactor and reacted therein, and the metal oxide powder obtained is separated from gaseous substances, wherein a) the flame is formed by the ignition of an oxygen-containing gas (1) with a fuel gas, b) the aerosol is obtained by joint atomization of a solution containing a metal compound and an atomization gas by means of one or more nozzles and c) the ratio of the spray area to the cross-sectional reactor area is at least 0.2.

Claims

1. A process for producing metal oxide powders by flame spray pyrolysis, the process comprising: introducing an aerosol comprising a metal compound into a flame in a reactor and reacted therein, and separating the metal oxide powder obtained from gaseous substances, wherein a) the flame is formed by the ignition of an oxygen-containing gas (1) with a fuel gas, b) the aerosol is obtained by joint atomization of a solution comprising a metal compound and an atomization gas via one or more nozzles and c) a ratio of the spray area to the cross-sectional reactor area is at least 0.2.

2. The process according to claim 1, wherein the atomization form of the aerosol is a circular cone having a scatter region of 70-130.

3. The process according to claim 1, wherein a mean droplet size of the atomized aerosol is 10-150 m.

4. The process according to claim 1, wherein the aerosol is produced by virtue of the solution comprising the metal compound and the atomization gas flowing into a mixing chamber within the one or more nozzles and internals provided within the mixing chamber dividing the solution into individual droplets under the action of the atomization gas and aerosol from the mixing chamber being introduced through holes into the reactor.

5. The process according to claim 1, wherein an oxygen-containing gas (2) that surrounds the flame is introduced into the reactor through one or more points in the reactor wall.

6. The process according to claim 5, wherein an amount ratio of the oxygen-containing gas (2)/oxygen-containing gas (1)=0.12.

7. The process according to claim 1, wherein a metal component of the metal compound is selected from the group consisting of Al, Co, Cr, Cu, Fe, Hf, In, Li, Mn, Mo, Nb, Ni, Si, Sn, Ta, Ti, V Y, Zn and Zr.

8. The process according to claim 1, wherein the metal compound comprises carbon and a metal component.

9. The process according to claim 1, wherein the metal compound is a silicon compound selected from the group consisting of silanes, polysiloxanes, cyclic polysiloxanes, silazanes and any desired mixtures thereof.

10. A process for producing a silica powder having a BET surface area of at least 50 m.sup.2/g and a carbon content of less than 0.1% by weight by flame spray pyrolysis, the process comprising: introducing an aerosol comprising a silicon compound into a flame in a reactor and reacted therein, and the silica powder obtained is separated from gaseous substances, wherein a) the flame is formed by the ignition of an oxygen-containing gas (1) with a fuel gas, b) the silicon compound is selected from the group consisting of silanes, polysiloxanes, cyclic polysiloxanes, silazanes and any mixtures thereof, c) the aerosol is obtained by joint atomization of a solution comprising the silicon compound and an atomization gas via one or more nozzles and a ratio of the spray area to the cross-sectional reactor area is at least 0.2 and d) an oxygen-containing gas (2) is additionally introduced into the reactor, where an amount ratio of oxygen-containing gas (2)/oxygen-containing gas (1)=0.12.

Description

EXAMPLES

Example 1

(1) 1.0 kg/h of D4 and 4.0 kg/h of atomizer air are used to produce, by means of an internally mixing two-phase nozzle, Schlick model 0/60-0/64, an aerosol which is atomized into a flame in a reactor. The result is a spray area of 0.88 dm.sup.2. The ratio of spray area/cross-sectional reactor area is 0.5. Burning within the reactor is a hydrogen/oxygen gas flame composed of hydrogen (2 m.sup.3 (STP)/h) and primary air (20 m.sup.3 (STP)/h), in which the aerosol is reacted. In addition, secondary air (5 m.sup.3 (STP)/h) is introduced into the reactor. After cooling, the silica is separated from gaseous substances at a filter. The mean residence time of the reaction mixture in the reactor is 1.67 s. The temperature 0.5 m below the flame is 642 C. The silica has a BET surface area of 202 m.sup.2/g and a carbon content of 0.04% by weight.

(2) Examples 2-8 are conducted analogously. The amounts used are shown in the table.

(3) The ratio of spray area/cross-sectional reactor area varies from 0.35-0.62. The silicas obtained have a BET surface area of 85-293 m.sup.2/g, with a consistently very low carbon content of 0.01%-0.04% by weight.

(4) Comparative examples C1-C4 are also conducted analogously to Example 1, except that an externally mixing two-phase nozzle, Schlick model 02-09, is used here. The result is distinctly smaller spray areas and correspondingly much lower ratios of spray area/cross-sectional reactor area. The silicas obtained have a BET surface area of 16-70 m.sup.2/g, with a distinctly increased carbon content of 0.13%-0.16% by weight.

(5) TABLE-US-00001 TABLE Feedstocks and reaction conditions; physical properties Example 1 2 3 4 5 6 7 8 C1 C2 C3 C4 D4 kg/h 1.0 2.0 18 15 15 15 110 120 250* 240* 10 15 Atomizer air rate m.sup.3 4.0 3.4 30 30 15 30 55 50 35.8 17.3 12.0 7.00 (STP)/h D4/atomizer air rate kg/m.sup.3 0.25 0.58 0.60 0.50 1.00 0.50 2.00 2.40 6.98 13.87 0.83 2.14 (STP) Spray area.sup.1 dm.sup.2 0.88 0.88 3.44 3.44 2.68 3.44 12.2 12.2 0.41 0.41 0.18 0.18 Spray area/ 0.50 0.50 0.45 0.45 0.35 0.45 0.62 0.62 0.05 0.05 0.02 0.02 cross-sectional reactor area Hydrogen m.sup.3 2.0 4.0 24 20 22 30 45 50 40 45 27 27 (STP)/h Primary air m.sup.3 20 20 110 80 90 100 600 800 5000 5100 152 152 (STP)/h Secondary air m.sup.3 5 25 40 45 60 50 400 250 (STP)/h Secondary/primary air 0.25 1.25 0.36 0.56 0.67 0.50 0.67 0.31 Mean temperature C. 642 664 413 681 826 750 695 752 950 1030 869 974 Mean residence time s 1.67 1.02 1.96 1.78 1.40 1.45 0.59 0.52 0.04 0.04 1.31 1.11 BET surface area m.sup.2/g 202 128 85 139 197 293 120 200 60 70 25 16 Carbon content % by wt. 0.04 0.01 0.02 0.03 0.04 0.03 0.02 0.03 0.14 0.15 0.13 0.16 *D4 content = 75% by weight diluted with petroleum spirit; .sup.130 cm below nozzle