PROCESS FOR MANUFACTURING ANHYDROUS CHROMIUM SESQUIOXIDE VY REDUCTION OF A HEXAVALENT COMPOUND OF CHROMIUM

摘要

1341607 Chromium sesquioxide CERAVER 6 May 1971 [6 May 1970] 13570/71 Heading C1A [Also in Division B1] Anhydrous chromium sesquioxide is made by subjecting a dried hexavalent chromium compound, preferably chromium trioxide which is not decomposed thermally under 300‹ C. in the absence of a reducing agent, to heating in a non- reducing atmosphere at between 197‹ C. and 280‹ C. and then to heating in a reducing atmosphere between 250‹ C. and 350‹ C. An organic amino compound as reduction catalyst, e.g. pyridine may be added to the hexavalent chromium compound. The reducing atmosphere may be hydrogen or a mixture of hydrogen and inert gas. In the examples a rod of Al 2 O 3 is impregnated with solution containing 1 kg/litre of CoO 3 , pyridine being added to the solutions in Examples 2-5, the rods dried in an oven, non- reducing atmospheres of air or nitrogen and a temperature of 240‹ C. being used for the first step and reducing atmospheres of hydrogen with or without nitrogen at 280‹ to 340‹ C. for the second step. It is also possible to impregnate Cr 2 O 3 , ZnO, MgO, or SiO 2 (e.g. for the manufacture of catalysts) with the CrO 3 solution.