Corporation De I'ecole Polytechnique

La Corporation De L'ecole Polytechnique Gaz Metropolitain

Company Limited Partnership

Danilo Klvana

Kebir Ratnani

Christophe Guy

Jitka Kirchnerova

Jamai Chaouki

Hristo Sapoundjiev

The new preparation process for making fine high specific surface ceramic powders suitable as catalysts or precursors for ceramics uses lanthanum (or other rare earth lanthanide) oxide as one of the precursors. The oxide is mixed with water to form a liquid slurry, whereby it is transformed to the hydroxide by reaction with water. The resulting hydroxide slurry, which can be milled to reduce the particle size and to speed up the reaction, is then combined, while stirring vigorously to assure homogenous mixing, with a solution of required amount of remaining metal nitrate precursors, for example strontium and cobalt nitrates. The reaction between lanthanum hydroxide and transition metal nitrates produces a colored (color depending on the transition metal) slurry consisting of metal hydroxides suspended in aqueous nitrate solution with pH&gt;2. This perovskite precursor slurry is spray-frozen and freeze dried. The freeze-dried material is transformed to perovskite by slow controlled calcination at temperatures above 550.degree. C. For example calcination 12 h at 585.degree. C. and subsequently 4 h at 620.degree. C. produces nearly phase pure perovskite having specific surface area of &gt;10 m.sup.2 /g, depending on the composition. The perovskite precursor slurry can alternatively be processed first by spray-drying (instead of spray-freezing/freeze-drying) and subsequent calcination.

Process of making fine ceramic powders from aqueous suspensions

The gas phase exothermic reaction of a feed gas mixture is carried out by providing first and second chambers in fluid communication with one another and each containing a bed of solid heat exchange material and at least one bed of catalyst material, each chamber being selectively operable in cooling and heating modes. The feed gas mixture is introduced into a selected one of the chambers when the selected chamber is in the cooling mode and the other chamber is in the heating mode so that the feed gas mixture flowing through the selected chamber contacts the bed of heat exchange material before contacting the bed of catalyst material, the feed gas mixture being reacted in the catalyst bed to form a gaseous product. The gaseous product is conducted from the selected chamber to the other chamber so that the gaseous product flowing through the other chamber contacts the bed of catalyst material before contacting the bed of heat exchange material. The direction of gas flow through the chambers is periodically reversed so that the first and second chambers alternately operate in the cooling and heating modes, thereby forming between the first and second chambers a hot zone containing the gaseous products. A portion of the gaseous product is discharged from the hot zone so as to withdraw sufficient heat to maintain the reaction in the catalyst bed of the selected chamber at a temperature below a predetermined maximum temperature, while maintaining autothermicity.

Process and apparatus for gas phase exothermic reactions

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Montreal, Canada

Danilo Klvana