GB1070216A - Improvements in or relating to silica and silica-alumina gels - Google Patents

Abstract

An improved hydrogel is prepared by mixing a washed, partially dried to 25 to 40% moisture content, finely-divided silica or silica-alumina hydrogel with sufficient aqueous medium to permit subsequent working without exceeding the "incipient wetness" of the gel until the mixture becomes plastic, and drying the mixture, say, to not less than 5% moisture content at 200 DEG C., or first at a lower temperature followed by activation at, say, 590 DEG C. The partially dried gel may be obtained in finely-divided form in a pulverizer which breaks up the gel by means of rapidly rotating blades. The aqueous medium may be water or water containing acid, e.g. any mineral acid such as sulphuric, phosphoric, hydrochloric, nitric acid or water-soluble organic acid, such as acetic, formic acid. The mixture may be passed and re-passed through, e.g. a screw mixer until in plastic condition, and the plasticized gel may be shaped, e.g., by extrusion, injection moulding, compression moulding or casting. The gels may be dried continuously in a forced draft oven. Silica gels containing an acid binder are dried at 93 DEG C. prior to activation at 200 DEG C. The shaped gels can be used as desiccants, desiccant fillers, catalyst bases.ALSO:Hydrogels of silica-alumina which do not decrepitate when contacted with water and which, when shaped, can be used as desiccants or desiccant filters are produced by mixing a washed, partially dried to 25 to 40% moisture content, finely divided silica-alumina hydrogel with sufficient aqueous medium to permit subsequent working until the mixture becomes plastic without exceeding the incipient wetness of the gel after the mixture has been rendered plastic, and drying the mixture say to not less than 5% moisture content at 200 DEG C or firstly at a lower temperature followed by activiation at say 590 DEG C. The partially dried gel may be broken up to the finely divided condition in a pulverizer. The aqueous medium may be water or mineral acid such as sulphuric, phosphoric, hydrochloric, nitric acid or water soluble organic acid such as acetic, formic acid. The mixture may be passed and repassed through a screw mixer until in plastic condition, and then shaped by extrusion, injection moulding, compression moulding or casting. The gels may be dried continuously in a forced draft oven.