A method of preparing amorphous alumina ball. An acidic alumina

Рубрика: Articles. Автор: admin. Вторник 25 Окт 2011 в 1:38 дп

A method of preparing amorphous alumina ball. An acidic alumina hydrosol is commingled with a neutralizing or gelling agent and dispersed as droplets in a hot oil suspending media to form firm, spherical, hydrogel particles. The particles are transferred after forming to an aqueous salt solution with a pH of at least about 5.5, and with a salt concentration substantially equivalent to that of the aqueous phase of the hydrogel particles. The salt concentration of the aqueous solution is reduced gradually until the solution is salt-free. Amorphous alumina balls are recovered upon drying. It is an object of this invention to present a novel oil-drop method for the manufacture of spheroidal amorphous alumina particles. Thus, in one of its broad aspects, the present invention embodies a method of preparing amorphous alumina ball which comprises commingling an ammonia precursor and an acidic alumina hydrosol at below gelation temperature, said ammonia precursor being decomposable to ammonia with increasing temperature; dispersing the mixture as droplets in a hot oil bath effecting decomposition of said ammonia precursor and formation of hydrogel spheres therein; separating and immersing the hydrogel particles in an aqueous salt solution having a pH of at least about 5.5, and a salt concentration substantially equivalent to the salt concentration of the internal aqueous phase of said hydrogel particles; maintaining said particles in contact with said solution while reducing the salt concentration gradually at conditions to minimize the concentration gradient between said solution and the internal aqueous phase of said particles until said solution is substantially salt-free; separating, and drying and calcining the resulting salt-free hydrogel particles to form amorphous, high surface area alumina spheres. It has been the practice to retain and age the hydrogel spheres in the oil suspending media for an extended period, and thereafter in an aqueous alkaline media for a further extended period. The oil aging process has heretofore been considered as essential to obviate excessive cracking and sphere disintegration during the subsequent aqueous phase treatments. However, the practice also promotes the formation of crystalline boehmite alumina ball which, upon calcination at 370°-650° C., is converted substantially to gamma- alumina. A method of preparing amorphous alumina ball. An acidic alumina hydrosol is commingled with a neutralizing or gelling agent and dispersed as droplets in a hot oil suspending media to form firm, spherical, hydrogel particles. The particles are transferred after forming to an aqueous salt solution with a pH of at least about 5.5, and with a salt concentration substantially equivalent to that of the aqueous phase of the hydrogel particles. The salt concentration of the aqueous solution is reduced gradually until the solution is salt-free. Amorphous alumina balls are recovered upon drying. It is an object of this invention to present a novel oil-drop method for the manufacture of spheroidal amorphous alumina particles. Thus, in one of its broad aspects, the present invention embodies a method of preparing amorphous alumina ball which comprises commingling an ammonia precursor and an acidic alumina hydrosol at below gelation temperature, said ammonia precursor being decomposable to ammonia with increasing temperature; dispersing the mixture as droplets in a hot oil bath effecting decomposition of said ammonia precursor and formation of hydrogel spheres therein; separating and immersing the hydrogel particles in an aqueous salt solution having a pH of at least about 5.5, and a salt concentration substantially equivalent to the salt concentration of the internal aqueous phase of said hydrogel particles; maintaining said particles in contact with said solution while reducing the salt concentration gradually at conditions to minimize the concentration gradient between said solution and the internal aqueous phase of said particles until said solution is substantially salt-free; separating, and drying and calcining the resulting salt-free hydrogel particles to form amorphous, high surface area alumina spheres. It has been the practice to retain and age the hydrogel spheres in the oil suspending media for an extended period, and thereafter in an aqueous alkaline media for a further extended period. The oil aging process has heretofore been considered as essential to obviate excessive cracking and sphere disintegration during the subsequent aqueous phase treatments. However, the practice also promotes the formation of crystalline boehmite alumina ball which, upon calcination at 370°-650° C., is converted substantially to gamma- alumina.


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