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US3645678A
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US
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Concentrating fluosilicic acid
Assignee: Wellman-Power Gas Inc
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Filing: 1970-03-09
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Granted: 1972-02-29
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Expires: 1990-03-09
Abstract
Abstract A process for the concentration of aqueous fluosilicic acid solutions is disclosed. In the process, a dilute aqueous fluosilicic acid solution is premixed with concentrated sulfuric acid under superatmospheric pressure and elevated temperatures; the mixture is introduced to a reduced pressure, high-temperature dehydration zone to release a gaseous overhead containing essentially all of the silicon tetrafluoride and a liquid sulfuric acid bottoms; the gaseous overhead is passed to a scrubbing zone to effect reaction of the silicon tetrafluoride with the water content of a dilute aqueous fluosilicic acid solution and thereby concentrate the fluosilicic acid content therein and the concentrated fluosilicic acid solution is then recovered. Advantageously, the diluted sulfuric acid bottoms can be contacted with a siliceous material to convert any contained hydrogen fluoride to another silicon tetrafluoride-containing gaseous overhead which is also passed to the scrubbing zone to effect further concentration. Hydrogen fluoride may also be recovered in pure form in a particular embodiment.
Inventors
- 👤 William R Parish
- 👤 James C Kelley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 17:52
CPC Classifications
C; C01; C01B; C01B33/00; C01B33/08; C01B33/10; C01B33/103
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
82 words
The process of claim 1 wherein the temperature of the separation zone is about 200* to 250* F., the hydrogen fluoride formed by the dehydration of fluosilicic acid remains in solution with the dilute sulfuric acid and the hydrogen-fluoride-containing, dilute sulfuric acid bottoms are treated in a dehydrofluorination zone with a siliceous material to release the hydrogen fluoride therein as a silicon-tetrafluoride-containing gaseous overhead, while maintaining the dehydrofluorination zone temperature at less than the boiling point of the sulfuric acid solution therein.
Claim 2
Dependent Claim
44 words
The process of claim 2 wherein the silicon-tetrafluoride-containing gaseous overhead from the dehydrofluorination zone is conducted to the scrubbing zone to effect reaction between the said silicon tetrafluoride and the water of the fluosilicic acid scrubbing solution to form concentrated, aqueous fluosilicic acid solution.
Claim 3
Dependent Claim
61 words
The process of claim 1 wherein the sulfuric acid is mixed with the fluosilicic acid in step (i) in an anhydrous weight ratio of sulfuric acid to fluosilicic acid of about 5 to 30:1, sufficient to provide the dilute sulfuric acid bottoms with at least about 65 percent sulfuric acid, based on the combined weight of sulfuric acid and water therein.
Claim 4
Dependent Claim
29 words
The process of claim 4 wherein in step (i), prior to the mixing, the sulfuric acid and fluosilicic acid are at a temperature of about 90* to 240* F.
Claim 5
Dependent Claim
107 words
The process of claim 1 wherein the temperature of the separation zone is about 250* to 300* F., the hydrogen fluoride formed by the dehydration of fluosilicic acid is also evolved as a gaseous overhead and the mixed gaseous overhead, containing silicon tetrafluoride and hydrogen fluoride from the separation zone, is contacted with liquid sulfuric acid having a concentration of about 93 to 99 weight percent sulfuric acid at a temperature of up to about 120* F. in a hydrogen fluoride absorption zone to selectively absorb the hydrogen fluoride in the sulfuric acid prior to conducting said silicon-tetrafluoride-containing gaseous overhead to the scrubbing zone of step (iii).
Claim 6
Dependent Claim
52 words
The process of claim 6 wherein the hydrogen fluoride in the spent sulfuric acid from the hydrogen fluoride absorption zone is liberated from the spent acid and recovered in substantially pure form by heating the spent acid in a desorption zone to a temperature below the boiling point of the spent acid.
Claim 7
Dependent Claim
28 words
The process of claim 1 wherein any precipitated silica formed in the scrubbing zone is separated from the concentrated fluosilicic acid product solution in a silica separation zone.
Claim 8
Dependent Claim
28 words
The process of claim 2 wherein any precipitated silica formed in the scrubbing zone is separated from the concentrated fluosilicic acid product solution in a silica separation zone.
Claim 9
Dependent Claim
38 words
The process of claim 9 wherein the separated silica from the silica separation zone is at least part of the siliceous material added to the hydrogen-fluoride-containing, dilute sulfuric acid bottoms to release the hydrogen fluoride as silicon tetrafluoride.
Claim 10
Dependent Claim
38 words
The process of claim 10 wherein the separated silica is washed with dilute, aqueous fluosilicic acid solution having a concentration of about 10 to 30 weight percent H2SiF6 before addition to the hudrogen-fluoride-containing, fluoride-containing, dilute sulfuric acid bottoms.
Claim 11
Dependent Claim
26 words
The process of claim 1 wherein sufficient hydrogen fluoride is present in the scrubbing zone to provide a substantially silica-free, concentrated, aqueous fluosilicic acid product solution.
Claim 12
Dependent Claim
21 words
The process of claim 1 wherein the pressure in step (i) is at least about 5 pounds per square inch gauge.
Claim 13
Dependent Claim
24 words
The process of claim 1 wherein the sulfuric acid employed in step (i) has a concentration of above about 90 weight percent sulfuric acid.
Claim 14
Dependent Claim
43 words
The process of claim 1 wherein, in step (i), the mixing under superatmospheric pressure is conducted for a time sufficient to allow the temperature of the mixture to reach at least about the temperature of the liquid in the reduced pressure separation zone.
Claim 15
Dependent Claim
54 words
The process of claim 1 wherein the sulfuric acid is mixed with the fluosilicic acid of step (i) in an anhydrous weight ratio of about 5 to 30:1, SUFFICIENT to provide the dilute sulfuric acid in step (ii) with about 70 percent sulfuric acid, based on the combined weight of sulfuric acid and water.
Claim 16
Dependent Claim
22 words
The process of claim 1 wherein the pressure maintained in step (ii) is at least about 10 pounds per square inch gauge.
Claim 17
Dependent Claim
22 words
The process of claim 1 wherein, in step (ii), the mixing under superatmospheric pressure is conducted for about 0.1 to 10 seconds.
Claim 18
Dependent Claim
35 words
The process of claim 1 wherein the mixture in the separation zone in step (ii) is sufficiently dispersed that it has at least about 1 square centimeter of liquid-gas interface per cubic centimeter of liquid.
Claim 19
Dependent Claim
25 words
The process of claim 19 wherein, in step (ii), the mixture has a residence time in the separation zone of about 0.1 to 80 minutes.
Claim 20
Dependent Claim
50 words
The process of claim 1 wherein, in step (ii), the mixture has a residence time in the separation zone of about 0.5 to 5 minutes and is sufficiently dispersed in the zone such that it has at least about 20 square centimeters of liquid-gas interface per cubic centimeter of liquid.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-02-28 | 1975-08-30 | 1976-02-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-02-28 | 1979-08-30 | 1980-02-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-02-28 | 1983-08-30 | 1984-02-29 | $7700.00 | Window Closed / Lapsed |