Hoechst Aktiengesellschaft

Michael Kotzian

Gunther R Schimmel

Alexander Tapper

Herbert Panter

Reinhard Gradl

Gerd Wingefeld

Knut Bauer

To prepare crystalline sodium disilicates having a laminar structure, a molar ratio of SiO.sub.2 to Na.sub.2 O of (1.9 to 2.1) 1 and a water content of less than 0.3% by weight, a water glass solution is first obtained by reacting sand with sodium hydroxide solution in a molar ratio of SiO.sub.2 to Na.sub.2 O of (2.0 to 2.3) : 1 at temperatures of 180.degree. to 240.degree. C. and pressures of 10 to 30 bar. This water glass solution having at least 20% by weight of solids is treated in a spray drier with hot air at 200.degree. to 300.degree. C. with the formation of a pulverulent amorphous sodium disilicate having a water content (determined as loss on heating at 700.degree. C.) of 15 to 23% by weight and a bulk density of at least 300 g/l. The spray-dried pulverulent, amorphous sodium disilicate is ground. The ground sodium disilicate is introduced into a rotary kiln equipped with devices for moving solids, externally heated via the wall and having in its interior a plurality of different temperature zones, and is treated therein at temperatures of 400.degree. to 800.degree. C. for 1 to 60 minutes with formation of crystalline sodium disilicate.

Process for the production of crystalline sodium disilicate in an

To prepare crystalline sodium silicates having a laminated structure, a molar ratio of SiO.sub.2 to Na.sub.2 O of (1.9 to 2.1) 1 and a water content of less than 0.3% by weight from a water glass solution which has a solids content of at least 20% by weight and is obtained by reaction of sand with sodium hydroxide solution in a molar ratio of SiO.sub.2 : Na.sub.2 O of (2.0 to 2.3) : 1, the water glass solution is treated with hot air of 200.degree. to 300.degree. C. in a spray drying zone to form a pulverulent, amorphous sodium silicate having a water content (determined as the loss on ignition at 700.degree. C.) of 15 to 23% by weight. The pulverulent, amorphous, water-containing sodium silicate is first ground, preferably to particle sizes of 1 to 50 .mu.m, before it is introduced into an inclined rotary tubular oven and treated in this in countercurrent with flue gas at temperatures of more than 500.degree. to 850.degree. C. to form crystalline sodium silicate. The sodium silicate issuing from the rotary tubular oven is first comminuted to particle sizes of 0.1 to 12 mm and finally ground to particle sizes of 2 to 400 .mu.m.

Process for the preparation of sodium silicates

For producing crystalline sodium silicates having a layer structure, an SiO.sub.2 /Na.sub.2 O molar ratio of (1.9 to 2.1):1 and a water content of less than 0.3% by weight from a waterglass solution containing at least 20% by weight of solids, the waterglass solution is obtained by reacting quartz sand with sodium hydroxide solution at an SiO.sub.2 /Na.sub.2 O molar ratio of (2.0 to 2.3):1 at temperatures of 180.degree. to 240.degree. C. and pressures of 10 to 30 bar. This waterglass solution is treated in a spray-drying zone with hot air at 200.degree. to 300.degree. C. for a residence time of 10 to 25 seconds and at a temperature of the exit gas leaving the spray-drying zone of 90.degree. to 130.degree. C., to form a pulverulent amorphous sodium silicate having a water content (determined as the loss on ignition at 700.degree. C.) of 15 to 23% by weight and a bulk density of more than 300 g/l. The pulverulent, amorphous, water-containing sodium silicate is introduced into an obliquely arranged rotary kiln fitted with devices for moving solids and treated therein with flue gas in countercurrent at temperatures from more than 500.degree. up to 850.degree. C. for 1 to 60 minutes to form crystalline soidium silicate. The rotary kiln is here insulated in such a way that its outside wall temperature is less than 60.degree. C. Finally, the crystalline sodium silicate emerging from the rotary kiln is comminuted by means of a mechanical crusher to grain sizes of 0.1 to 12 mm.

Process for producing crystalline sodium silicates having a layered

A process for producing amorphous sodium silicates having a water content of 0.3 to 6% by weight and an SiO.sub.2 /Na.sub.2 O molar ratio of (1.9 to 2.8) : 1 from a waterglass solution containing at least 20% by weight of solids, the water-glass solution is obtained by reacting quartz sand with sodium hydroxide solution at an SiO.sub.2 /Na.sub.2 O molar ratio of (2.0 to 2.8) : 1 at temperatures of 180 to 240.degree. C. and pressures of 10 to 30 bar. This waterglass solution is treated in a spray-drying zone with hot air at 200 to 300.degree. C. for a residence time of 10 to 20 seconds and at a temperature of the exit gas leaving the spray-drying zone of 90.degree. to 130.degree. C., to form a pulverulent amorphous sodium silicate having a water content (determined as the loss on ignition at 700.degree. C.) of 15 to 23% by weight and a bulk density of more than 300 g/l. The pulverulent sodium silicate is introduced into an obliquely arranged rotary kiln fitted with devices for moving solids and treated therein with flue gas in countercurrent at temperatures from 250.degree. up to 500.degree. C. for 1 to 60 minutes. The rotary kiln is here insulated in such a way that its outside wall temperature is less than 60.degree. C. Finally, the amorphous sodium silicate emerging from the rotary kiln is comminuted by means of a mechanical crusher to grain sizes of 0.1 to 12 mm.

Process for producing amorphous sodium silicate

To prepare crystalline sodium silicates having a layer structure and the formula Na.sub.2 Si.sub.x O.sub.2x+1, in which x is between 2 and 3, sand and soda are first fused in a molar ratio of SiO.sub.2 /Na.sub.2 O of 2 to 3.5 at temperature of 1200.degree. to 1400.degree. C. The water-glass obtained in pieces after the melt has cooled is ground to particle sizes of less than 2 mm before it is treated at temperatures of 600.degree. to 800.degree. C. for 10 to 120 minutes in an elongated reaction zone with mechanical circulation. Finally, the material leaving the reaction zone is ground to a particle fineness of less than 1 mm.

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Michael Kotzian