| 摘要 |
A dichromium trioxide catalyst is made by precipitating hydrous chromic oxide from a solution of a trivalent chromium salt, e.g. by adding sodium or potassium hydroxide, or, preferably, ammonia gas or aqueous ammonium hydroxide, and subsequently heating it to 300-400 DEG C. for not less than one hour. For example, aqueous ammonia is added to a heated aqueous solution of Cr(NO3)3.9H2O to pH7, the solution is boiled and filtered hot, the precipitate hot water-washed and, dried by heating under vacuum or in an inert gas stream or in equipment with facilities for steam escape, at 100-200 DEG C. The partially dehydrated oxide is granulated to 4-20 mesh or pressed to pellets 3 mm. x 10 mm. and subjected to heat treatment at 300-400 DEG C. for a substantial period. The heat treatment may take place in an atmosphere consisting of water vapour and optionally an inert gas for at least two hours. The catalysts are substantially amorphous and have a surface area at least 5m2/g and usually above 50m2/g. Specification 794,075 is referred to.ALSO:Hexafluoroacetone, perfluorochloroacetone or a mixture thereof is made by contacting in the vapour phase at least one perhalogenated acetone containing two to five fluorine atoms and no halogen other than chlorine and fluorine at an elevated temperature up to 500 DEG C. with a dichromium trioxide catalyst obtained by precipitating hydrous chromic oxide from a solution of a trivalent chromium salt and subsequently heating it to 300 DEG -400 DEG C. for not less than one hour. The catalyst may be used in unsupported granular or pelleted form or supported on inert refractory material. The preferred starting materials are perhalogenated acetones containing two to four fluorine atoms. The process may be operated continuously and the products separated by fractional distillation. In examples using sym-tetrafluorodichloroacetone, 1,1,2 - trifluoro - 1,2,2 - tricloroacetone or pentafluorochloroacetone, the main products were CF3COCF3, CF3COCF2Cl, CF3 COCFCL2 and CF3COCL3 with CF2ClCoCCL3 in addition in the first two examples. Specification 794,075 is referred to.
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