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US 4,470,959 AGranted
Continuous production of silicon tetrafluoride gas in a vertical column
AssigneeAllied Corporation
InventorsJaidev S. Talwar, James Hendrickson, Jr.
Life of this patent
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Abstract
Silicon tetrafluoride gas is produced by reacting aqueous fluosilicic acid and concentrated sulfuric acid in a vertical column. The fluosilicic acid is fed to an intermediate point of the column and the sulfuric acid to the top of the column. Silicon dioxide, both dissolved and suspended, is fed with fluosilicic acid in some forms so as to produce a by-product acid substantially free of silicon and fluoride values.
Claims10
A process for the continuous production of silicon tetrafluoride gas which comprises the steps:
- (a) feeding to a vertical column at an intermediate feed point a first feed stream comprising aqueous fluosilicic acid of concentration at least about 130 g H.sub.2 SiF.sub.6 /L;
- (b) feeding to an upper feed point of the vertical column adjacent the top of the column a second feed stream comprising sulfuric acid of concentration between about 80% and about 100%;
- (c) operating said vertical column with sufficient effective plates between said intermediate feed point and said upper feed point and with sufficient feed rate of sulfuric acid to remove water vapor and HF from the gaseous SiF.sub.4 generated in said column to a combined level below 0.1 volume percent;
- and with sufficient effective plates below said intermediate feed point and sufficiently high temperature in said column and sufficient amounts of sulfuric acid fed relative to total water fed in said first and second feed streams to remove silicon values as Si from the liquid phase to levels below 0.1% by weight;
- (d) recovering, as overhead, gaseous SiF.sub.4 with combined water vapor and HF below 0.1 volume %;
- and
- (e) recovering as bottoms aqueous sulfuric acid with silicon values as Si below 0.1% by weight.
4 more elements
Dependencies are inferred from the claim text.