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US 4,363,792 AGranted
Defluorination of fumed silica
AssigneeThe Dow Chemical Company
InventorsMarylu B. Gibbs, Robert D. Biggs, David W. Alsgaard
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Abstract
A process for defluorination of a fluoride-containing fumed silica, which comprises entraining the silica in a high velocity stream of steam at an elevated temperature for a few seconds and then separating the defluorinated silica from the steam, thereby obtaining a fumed silica product with a substantially reduced fluoride content.
Claims4
A process for defluorinating fluoride-containing fumed silica, which comprises the steps of:
- a. premixing the silica and super-heated steam in a venturi ejector thereby forming a high -velocity stream of entrained silica and super-heated steam having a linear flow velocity of at least about three hundred centimeters per second and a temperature above about 1200.degree. F.;
- b. passing the stream of entrained silica and steam through an elongated passageway while maintaining the stream at a linear velocity of at least about three hundred centimeters per second and at a temperature above about 1200.degree. F.;
- the residence time of the stream in the venturi ejector and elongated passageway being betwee about one second and about twelve seconds and the ratio of steam to silica being between about two to one and about twenty to one on a weight basis and
- c. separating the silica from the steam, said silica containing less than about 0.5 weight % fluoride.
1 more element
Dependencies are inferred from the claim text.