GB761712A - Silica-alumina compositions and process for the preparation thereof - Google Patents

Abstract

A silica-alumina composition suitable for use in catalysis is prepared by adding an acid (e.g. sulphuric or hydrochloric) to an aqueous alkali metal silicate (sodium or potassium ortho- or meta-silicate), adding an aqueous salt containing aluminium in the cation (e.g. aluminium chloride or sulphate) to the so-formed slurry to precipitate hydrous alumina, adding an aqueous salt containing aluminium in the anion (e.g. sodium or calcium aluminate), to precipitate a further quanitity of hydrous alumina, and recovering the solid product. By filtering the final slurry and reslurrying or removing water from the final slurry, in either case to give a total solids content by weight of 8 per cent and spray-drying, microspheres of clear, glasslike structure are obtained which may be washed and dried for use in fluidized catalytic processes. The compositions may be used alone or in association with oxides of other elements e.g. magnesium, zirconium, titanium, thorium, chromium and/or boron. In comparative tests, the catalyst was steamed prior to use in a cracking process by dripping water upon it while a pressure of 40 lbs. per sq. inch gauge and a temperature of 1200 DEG F. were maintained. The following specific details are given : (a) in the initial step the concentration of acid should be sufficiently low to prevent local reaction and heat generation; 25 to 35 per cent H2SO4 is suitable, and agitation is desirable especially with concentrations greater than this: (b) whilst the acidification of silicate can be completed at as low a pH as 5, it is preferably retained above 7, e.g. 8 to 10.5 (c) the quantity of salt having aluminium in the cation should be such as to render the mixture acid and precipitate alumina, e.g. by lowering the pH to below 2: (d) in examples, the sodium aluminate solution contains also sodium hydroxide and in some, sodium carbonate; the ratio water to salt in the aqueous solution of the salt containing aluminium in the anion is preferably at least 7.5 to 1, better 15 to 1 (as Na2Al2O4): (e) the quantity of said salt to be added may be only such as to precipitate alumina in acid medium e.g. at a pH of 5 to 5.5: (f) the temperature of the reaction mixture is preferably 40 to 140 DEG F.; if precipitation is performed in the cold, it is desirable to heat to 100 to 190 DEG F. preferably 110 to 150 DEG F. before filtration: (g) the slurry is preferably dried by passing a spray in the same direction as a hot gas at 200 to 1000 DEG F. to give a particle temperature of 150 to 300 DEG F., preferably 150 - 230 DEG F.: (h) the catalysts may contain 5 to 45 per cent by weight of alumina on a dry basis, and catalysts containing 13 per cent and 20 to 40 per cent of alumina, the latter of which are particularly stable to steam, are referred to: (i) the preferred particle size is 20 to 100 microns. Examples are also given.