GB739396A - Manufacture of spheroidal alumina - Google Patents

Abstract

Spheroidal alumina particles are manufactured from alumina sol containing aluminium and chloride ions by forming hydrogel spheres from said sol and ageing said hydrogel spheres in a basic medium comprising ammonia or an alkylamine as base and containing at least 1.0 equivalent of said base for each equivalent of chloride ion in the sol. The preferred basic agent is anhydrous ammonia; methylamine, dimethylamine and ethylamine are also specified. Initial ageing of the spheres may be effected first in a hydrocarbon oil such as a refined heavy paraffin oil or a solvnet refined neutral oil (which may also be the suspending medium used in forming the spheres) at 50-105 DEG C. for at least 4, preferably 10 hours, and then the oil may be drained off and the ageing completed by introducing to the spheres the basic agent in gaseous or liquid form, or in aqueous or hydrocarbon oil solution, preferably at 50-105 DEG C., preferably 88 DEG to 99 DEG C., for a suitable period, e.g. 10 hours. Alternatively the basic agent may be introduced, preferably gradually into a non-aqueous medium containing the spheres. It is desirable to use as much as 1.5 equivalents of base per equivalent of chloride ion in the sol, and more can be used. The base may be passed either in con- or counter-current to the spheres by passing the spheres through an inclined rotating tube through which ammonia gas passes. Batch or continuous operation may be used, and unabsorbed base may be recycled, if desired with fresh base. The base may be introduced as a liquid which evaporates at the temperature of the ageing zone. Subsequently to basic ageing the spheres may be further washed or aged in an aqueous medium containing at least 0.01 per cent, preferably 0.02 per cent, of a base, e.g. ammonia at 50-105 DEG C. for at least 10 hours, e.g. by upward or downward percolation through the spheres, or if subsequently washed with said liquid at 50 DEG to 105 DEG C., for as little as 2 hours. In one embodiment, the spheres are obtained by commingling a sol produced, e.g. by reaction of aluminium with aqueous aluminium chloride, with water to form the mixture containing substantially from 15 to 35 per cent by weight of alumina, separately commingling water with hexamethylenetetramine to form a solution containing substantially from 15 to 40 per cent by weight of hexamethylenetetramine, commingling said mixture the said hexamethylenetetramine solution at below gellation temperature and in a volume ratio of hexamethylene tetramine solution to said mixture of from 3 : 1 to 1 : 1.5, thereafter passing the resultant mixture in the form of droplets and while at below gellation temperature into an oil bath maintained at a temperature of from 50 DEG to 105 DEG C., retaining the droplets in said oil bath until the droplets set to gel spheres, and the gel spheres thus obtained are aged in the basic medium containing at least 1.0 equivalent of base for each equivalent of chloride ion in the sol. After washing, the spheres may be dried at from 93 DEG to 315 DEG C. for 2-24 hours or more and then if desired calcined at 425 DEG to 760 DEG C. for 2-12 hours or more. Detailed examples are given, several of which use a spheroidal gel-forming method similar to that described with respect to the Figure in Specification 596,591, but in which the forming chamber is heated by means of electrical elements. The spheres may be used as catalytic components, e.g. in "Platforming" catalysts comprising about 0.01 to 1 per cent by weight of platinum and 0.1 to 8 per cent of combined halogen, and with 5 to 40 per cent of a compound or oxide of one or more elements in the left-hand column of groups IV, V and VI of the Periodic Table; alumina-chromia, molybdeum, vanadia, are specified. Specification 693,648 also is referred to.