Patent GB-778696-A (GB)
Title: Process and apparatus for producing silica sol
IPC: C01B33/141
Filed: 1953-12-09
Abstract: Apparatus for the production of silica sol by the interaction of an aqueous solution of sodium silicate and an aqueous solution of chlorine comprises, in combination, a metering device for delivering a <PICT:0778696/III/1> <PICT:0778696/III/2> flow of chlorine gas at a predetermined, controlled rate, a metering device for delivering water at a predetermined, controlled rate, a solution chamber arranged to receive said chlorine gas and water, and to dissolve the chlorine gas in the water, a reaction chamber arranged to receive chlorine solution from the solution chamber, a metering device for feeding sodium silicate solution to said reaction chamber at a predetermined, controlled rate, and an outlet from the reaction chamber for continuous delivery of the sol produced.  As shown a chlorine metering device comprises an inverted bell jar 21 having a constant level water seal.  Chlorine is admitted via inlet 27 and a constant pressure, e.g. a redecreased pressure of 2 in. of water, is maintained by means of valve 28.  Chlorine is withdrawn under suction through outlet 34 at a rate measured by means of metering orifice 32 and scale 37.  The chlorine passes to a jet-action chlorine dissolver via pipe 35 where it is sprayed with water from a jet opening 48 and movable valve member 49.  Water under pressure passes through a strainer 59, pressure reducing valve 60 and pipe 17 to jet opening 48 at a rate measured by means of a metering orifice 57 and mercury manometer 58.  The resulting chlorine water overflows in turbulent manner an inner vessel 46, and passes down a vertical column 65 to a reaction chamber comprising a vessel 12.  Sodium silicate solution passes to the chamber through a pipe 16 from a reservoir 14 via a pump 15 having a controlling device 70.  The resulting sol is withdrawn from vessel 12 through pipe 20 under the action of an ejector device 72 fed with water from pipe 79 provided with strainer 80, the ejector device being separated from inlets 16 and 65 by a baffle 106.  The ejector device also provides the necessary suction for withdrawal of chlorine from the bell jar 21.  The decreased pressure produced by the ejector device is controlled and offset to some extent by means of a valve comprising a regulating knob 100, diaphragm 96 and movable valve member 97 which allows passage of air into pipe 65 via pipe 102.  The air admitted through pipe 102 bubbles up through the liquid in vessel 12, thereby effecting mixing. Condensate from pipes 35 and 102 collects in trap tank 40.  In a modification (Fig. 5, not shown), pipe 102 passes directly into the liquid in vessel 12.  According to Fig. 6 (not shown) pipe 65 terminates above the level of liquid in vessel 12 and pipe 102, which passes directly into the liquid, may have no valve but be simply open to the atmosphere.  A chlorine control valve is also included in pipe 35.  According to Fig. 7 (shown partially), the chlorine and water are supplied to the jet-action chlorine dissolver under pressure, using controlling devices as shown.  The fluid passes into a chamber 130 via a pipe 137, the flow being controlled by a valve member 140 attached to a diaphragm 135 which separates the chamber into two spaces 133 and 134.  The fluid passes from space 133 to space 134 via a control valve 132.  Rate of flow is measured by means of manometer 142 and restrictive orifice 143.  Mixing in the reaction chamber may be effected by means of air or a blade-type stirrer.  The silicate solution may contain 28.7 per cent SiO2 and 8.9 per cent. Na2O and may be fed at the rate of 50 gallons per day.  6000 p.p.m. of chlorine in solution may be produced and may be fed at a rate of 0.64 gallons/min.  A sol containing about 2 per cent. SiO2 and having a gel induction period of about 20 min. is thereby produced.  The sol may be aged for about 8 1/2 per cent. of its gel induction period before it reaches the ejector 72.