GB888772A - Method of producing alumina - Google Patents

Abstract

Hydrated alumina is precipitated from an aqueous solution of an aluminium compound at pH 7-10,5 and the resultant slurry subjected to comminution to reduce the particle size and render it more uniform ("homogenization"), whereby the apparent bulk density after spray drying is increased, e.g. to 0,3-1.5 gms./c.c. When the precipitation pH remains below 10, aging of the slurry at pH 10-11 is essential The alumina precipitate may be obtained by acidifying sodium aluminate solution with a mineral acid, e.g. nitric acid, or with aluminium sulphate solution. The precipitation may be conducted at 70 DEG -130 DEG F. and the amount of solids in the mixture is generally from 4-9%. Preferably the alumina is aged after formation at pH 10-11 for at least 15 minutes at 90 DEG -130 DEG F.: aging at lower pH values is also described. The alumina may, if desired, be filtered and washed prior to the homogenization, and in the flow sheet (not shown) two filters are employed with an intermediate reslurry tank to which a flocculant such as glue or polyacrylamide may be added. The homogenization may be performed with a homogenizing valve operating at 500-3,000 p.s.i.g., or by grinding or milling. After homogenization, the slurry may be dried in a tray dryes or rotating kiln, but is prefreably spray-dried, e.g. at 500 DEG -1,000 DEG F., to a moisture content of 15-40%, whereby microspheres are produced which, after pelleting, may be fully dehydrated by calcination at 1,100 DEG -1,350 DEG F. Catalytic materialr may be added to the slurry before homogenization or may be incorporated after drying. Platinic chloride may be employed, with or without subsequent treatment with hydrogen sulphide or ammonium sulphide and, as activator therewith, hydrogen fluoride, hydrogen chloride or aluminium chloride, to provide 0,1-0,8% of platinum and up to 3% of halogen in the catalyst; the alumina may be impregnated or coated with 8-20% of molybdena; catalysts may comprise 10-25% of molybdena and 1-5% of cobalt oxide (supplied as ammonium molybdate and cobalt nitrate) or 10-30% of chromic oxide or tungstic or palladium oxide. In one example, a hydrodesulphurization catalyst is prepared by adding ammonium molybdate and cobalt nitrate during the formation of the alumina and, after spray-drying, mixed with 1% of graphite, formed into pellets and calcined at 1,260 DEG F. It is then used (a) in the desulphurization of a gas oil with a boiling range of 480 DEG -630 DEG F.; (b) in desulphurization, nitrogen removal and olefin saturation of a thermal naphtha with a boiling range of 196 DEG -430 DEG F. and (c) in desulphurizing a heavy vacuum gas oil with a boiling range of 480 DEG -860 DEG F. Specification 737,429 is referred to.