| 摘要 |
Alumina particles of high attrition resistance and hardness are made by impregnating powdered aluminium trihydrate with an aqueous solution of a water-soluble salt of aluminium and a small amount of a workability agent (e.g. sodium bentonite, agar, potato or corn starch, or methyl cellulose), and working mechanically the resulting readily flowable powder until it forms a plastic dough which contains 8 to 11 per cent of water; then forming the dough into particles and drying at 220 DEG to 300 DEG F. to remove the free water in 10 to 60 mins.; slowly heating up to about 600 DEG F. to form gamma alumina, and finally heating for more than 1 hour at 800 DEG to 1700 DEG F. In the presence of the workability agent, the water added can be reduced to very small quantities, while preserving the property of forming a plastic dough when the impregnated alumina is subjected to mechanical milling. For example, aluminium trihydrate powder is sprayed in a tumbling drum with a small amount of hot concentrated solution of aluminium nitrate or sodium aluminate, whereby about 1.8 parts of potential alumina is added per 100 parts of trihydrate. At the same time 0.3 to 0.7 parts per cent by weight of methyl cellulose are added. The mixture consisting of a flowable powder is then subjected to heavy mechanical pressure for up to 5 hours in a muller, when it assumes a plastic form, which is extruded to form rods and pellets, e.g. 4.75 mm. diameter. These are first dried at about 270 DEG F. in heated air, and then submitted to slow drying raising the temperature at the rate of 35 DEG F. per hour up to 600 DEG F. A final more rapid heating up to 1700 DEG F. is then employed. The product may be impregnated with chromium oxide or a platinum group metal. Platinum, rhodium, palladium, rhodium, and osmium are specified. If desired after the heating stage at 600 DEG F. the pellets may be leached with nitric or acetic acid to remove alkali before the final heating stage. The impregnated catalysts may be used for dehydrogenating or hydroforming reactions. Specification 675,349 is referred to. |
