GB627043A - Improvements in or relating to the production of round or lachrymiform solid particles of substantially uniform size - Google Patents

Abstract

Substantially round or lachrymiform solid particles are obtained by mixing a true or colloidal solution of the solid with a substantially immiscible liquid, passing the mixture through apparatus designed to produce eddy flow as distinct from general turbulence whereby the solution or sol is dispersed in the immiscible liquid in the form of droplets <PICT:0627043/III/1> <PICT:0627043/III/2> <PICT:0627043/III/3> <PICT:0627043/III/4> of a desired size, and causing or allowing the droplets whilst under the influence of the eddy flow to set into the desired solid particles. The process is applicable to the production of microspheroidal particles of silica, alumina, zirconia, iron oxide, chromium oxide, tin oxide, composites of silica-alumina, silica-zirconia, alumina-zirconia, glue, casein, waxes and natural and artificial resins. Solidification of the droplets may be effected by partially removing or replacing the solvent as by solution in the continuous liquid phase. Thus in a dispersion of droplets of a resin-benzene solution in aqueous alcohol, the aqueous alcohol tends to dissolve selectively some of the benzene. Alternatively, a solidifying agent may be introduced into the dispersion. Thus nitrocellulose lacquer droplets dispersed in water are solidified by introducing methyl alcohol. In the case of droplets of a sol, setting may be effected by the addition of a gelling or depeptizing agent. Alternatively solidification may be effected by chemical reaction as by the addition of a reactant and/or a catalyst to the dispersion medium. Thus, in the preparation of silica-alumina catalysts, droplets of an aqueous solution or sol of alkali aluminium silicate dispersed in kerosene or toluene are solidified by the addition of acetic acid, formic acid, hydrogen chloride, silicon tetrachloride or aluminium trichloride. Alternatively, solidification may be effected by cooling. Thus droplets of hot aqueous glue dispersed in, for example, a hydrocarbon oil, are solidified by cooling. Suitable apparatus (Fig. 1) comprises an outer cylindrical shell 1 and an inner cylindrical rotor 2. The liquids to be mixed enter the shell 1 at 9, 10 and pass downwardly through the annular forming zone between the shell 1 and rotor 2, the horizontal cross-section of the annular zone being sufficient to produce the desired throughput without turbulent flow. A solidifying agent may be introduced at 12, 13 and the suspension of solid particles withdrawn at 11. If desired the liquids may be introduced at the bottom and the dispersion withdrawn from the top. In an alternative construction (Fig. II) the shell 1 is provided with a temperature control jacket 20 and the setting agent is introduced through the perforate portion 21 of rotor 2. In apparatus (Fig. III) adapted to cause a drop in temperature in the forming zone, the rotor 2 is divided into two sections, one being cooled and the other heated. In a further modification (Fig. IV) the upper section only of rotor 2 is adapted to be heated or cooled, the lower portion of cylinder 1 being provided with a temperature control jacket 42. Instead of employing cylinders, conical or other figures of revolution may be used. A microspheroidal silica-alumina cracking catalyst is prepared by mixing a silica sol with mineral oil in the forming zone, the top of which is maintained at 90 DEG C. Butyl alcohol and a small amount of acetic acid is added and the silica gel spheres are withdrawn into a tank of aqueous butyl alcohol, separated, impregnated with alumina, washed, dried and calcined. A microspheroidal iron catalyst for Fischer-Tropsch type syntheses is obtained by mixing a sol prepared from ferric sulphate, ferrous sulphate and aluminium sulphate with kerosene, the mixture being passed through the forming zone into which a soluble amine is introduced. The solid particles are withdrawn into aqueous potassium carbonate or hydroxide, the suspension then being heated and diluted with alcohol and the particles separated, dried and reduced with hydrogen. Specifications 15365/15, [Class 82 (ii)], 313,652, 314,639, [both in Class 1 (iii)], and 576,058 are referred to.ALSO:Substantially round or lachrymiform particles of a resin or nitrocellulose lacquer are obtained by mixing a true or colloidal solution of the material with a substantially immiscible liquid, passing the mixture through apparatus (see Group III) designed to produce eddy flow as distinct from general turbulence, whereby the solution or sol is dispersed in the immiscible liquid in the form of droplets of a desired size and causing the droplets whilst under the influence of the eddy flow to set into the desired particles. In the case of particles of a benzene-soluble, alcohol insoluble resin, a benzene solution of the resin is dispersed in aqueous alcohol which is substantially immiscible but which tends to dissolve selectively some of the benzene, thereby causing setting of the droplets into the resin. In the case of particles of a lacquer containing nitrocellulose, a resin, a pigment and a plasticiser, a solution of the lacquer in an ester solvent is dispersed in water, methyl alcohol being added to the dispersion to cause solidification of the lacquer particles. Specifications 15365/15, [Class 82 (ii)], 313,652, 314,639, [both in Class 1 (iii)], and 576,058, [Group III], are referred to.ALSO:Substantially round or lachrymiform casein particles are obtained by mixing a true or colloidal solution of casein with a substantially immiscible liquid, passing the mixture through apparatus (see Group III) designed to produce eddy flow as distinct from general turbulence whereby the solution or sol is dispersed in the immiscible liquid in the form of droplets of a desired size and causing the droplets whilst under the influence of the eddy flow to set into casein particles, for example, by selective solvent extraction, by the addition of a gelling or depeptizing agent or by the addition of a chemical reactant. Specifications 15365/15, [Class 82 (ii)], 313,652, 314,639, [both in Class 1 (iii)], and 576,058, [Group III], are referred to.