Claims
- 1. 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, which comprises
- a) obtaining the waterglass solution by reacting quartz sand with sodium hydroxide solution in an SiO.sub.2 /Na.sub.2 O molar ratio of (2.0 to 2.8) : 1 at temperatures from 180.degree. to 240.degree. C. and pressures from 10 to 30 bar,
- b) treating the waterglass solution 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,
- c) introducing the pulverulent sodium silicate according to b) into an obliquely arranged rotary kiln being fitted with devices for moving solids, said rotary kiln showing a low heat transfer through its wall because of its good insulation causing an outside wall temperature of the rotary kiln of less than 60.degree. C. with the resultant counteraction to the sticking tendency of the sodium silicate, and treating said pulverulent sodium silicate in said rotary kiln with flue gas in counter-current at temperatures from 250.degree. to 500.degree. C. for 1 to 60 minutes,
- d) exhausting the exit gas from the rotary kiln in the central region thereof and in the region of the end where the pulverulent amorphous sodium silicate having a water content of 15 to 23% by weight is introduced, purifying said exit gas by means of a dry dust filter, and admixing the sodium silicate taken from the dry dust filter, and admixing the sodium silicate taken from the dry dust filter to the pulverulent amorphous sodium silicate destined to be introduced into the rotary kiln with the resultant increase of the throughput of sodium silicate. through the rotary kiln per unit of time,
- e) communiting the amorphous sodium silicate emerging from the rotary kiln by means of a mechanical crusher to grain sizes of 0.1 to 12 mm, and
- f) grinding the comminuted sodium silicate by means of a mill to grain sizes of 2 to 400 .mu.m.
- 2. The process as claimed in claim 1, wherein a mechanical mill running at a circumferential speed of 0.5 to 60 m/s is used.
- 3. The process as claimed in claim 1, wherein an air jet mill is used.
- 4. The process as claimed in claim 1, wherein a ceramically lined ball mill is used.
- 5. The process as claimed in claim 1, wherein a ceramically lined vibratory mill is used.
- 6. The process as claimed in claim 1, wherein the ground sodium silicate is fed to a roll compactor, by means of which it is compressed at a roll-pressing force of 20 to 40 kN/cm of roll width to give compact pieces.
- 7. The process as claimed in claim 6, wherein the compact pieces are, after pre-comminution by forcing them through screens, processed to give granules having a bulk density of 700 to 1000 g/l.
- 8. The process as claimed in claim 1, wherein amorphous sodium silicates having a water content of 0.5 to 2% by weight are produced.
Priority Claims (2)
Number |
Date |
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Kind |
3935464 |
Oct 1989 |
DEX |
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4004625 |
Feb 1990 |
DEX |
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Parent Case Info
This application is a continuation, of application Ser. No. 07/595,434 filed Oct. 11, 1990, now abandoned.
US Referenced Citations (5)
Foreign Referenced Citations (3)
Number |
Date |
Country |
0293640 |
Sep 1988 |
EPX |
3718350 |
Dec 1988 |
DEX |
2157943 |
Aug 1973 |
FRX |
Non-Patent Literature Citations (1)
Entry |
Chemical Abstracts, 236101V, 1989. |
Continuations (1)
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Number |
Date |
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Parent |
595434 |
Oct 1990 |
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