| 摘要 |
Activated alumina is prepared from aluminium hydroxide produced by Bayer's process by heating to a temperature of at least 400 DEG C., preferably in the range 400 DEG -600 DEG C., neutralizing with an acid solution in a quantity at least sufficient to convert the sodium compounds contained in the aluminium hydroxide into a salt or salts, and reactivating by heating the material at a temperature within the range of from 400 DEG C. to 600 DEG C. The acid solution may be a dilute or concentrated solution of an acid or of an acid salt, e.g. of hydrochloric acid, aluminium nitrate, or ammonium chloride, and may be used at a temperature of not more than 100 DEG C. In an example, a table is given showing the activity of five different samples of catalyst in the dehydration of ethyl alcohol to ethylene. Samples 1 to 3 are prepared from aluminium hydroxide obtained by Bayer's process and activated by heating to 400 DEG C. for four hours in a current of air. Sample 1 is used without further treatment, sample 2 after washing with hydrochloric acid solution, stirring while the temperature is brought to 100 DEG C., drying, and reactivating at 500 DEG C., and sample 3 after treatment in aluminium nitrate solution, agitating, removing excess water, drying, and reactivating at 500 DEG C. (bringing the pH of the product in suspension from 10 to about 4,5). Sample 4 is obtained by reacting aluminium nitrate solution and ammonia, thoroughly washing, drying, and activating at 500 DEG C. Sample 5 is a commercial dehydration catalyst. Organic compounds deposited on the surface during use may be eliminated by periodic treatments with a current of air at 350 DEG -400 DEG C. Acetonitrile may be prepared by passing a mixture of equimolar parts of acetic acid vapour and ammonia, at a flow rate of 20 moles of the mixture per litre of catalyst per hour, over the catalyst heated to 380 DEG C. Methylamines may be formed from methanol and ammonia, and dimethylaniline from aniline and dimethyl ether or methanol. |
