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Silicon tetrafluoride byproduct separation process

a technology of silicon tetrafluoride and byproduct, which is applied in the field of silicon tetrafluoride byproduct separation process, can solve the problems of low yield of conversion of raw materials into silicon tetrafluoride and undesirable by

Inactive Publication Date: 2011-02-17
REVANKAR VITHAL +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0007]Embodiments of the invention provide a process for recovering useful compounds from a byproduct composition produced in a silicon tetrafluoride production process. The process may include the steps of: calcining a byproduct composition comprising sodium sulfate and aluminum sulfate and forming a liquid phase mixture comprising suspended alumina solids, and sodium sulfate and a gaseous phase comprising sulfur trioxide; absorbing the gaseous sulfur trioxide in a mixture of sulfuric acid and water to produce oleum; cooling the liquid phase mixture to produce a cooled solid phase mixture; mixing the liquid phase mixture with water to produce a dissolved product comprising dissolved sodium sulfate and suspended alumina solids; filtering the dissolved product to obtain a cake comprising

Problems solved by technology

A characteristic common to all these processes is constituted by the low yields of conversion of raw materials into silicon tetrafluoride and undesirable by-products.

Method used

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  • Silicon tetrafluoride byproduct separation process
  • Silicon tetrafluoride byproduct separation process
  • Silicon tetrafluoride byproduct separation process

Examples

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example 1

[0015]A kiln byproduct mixture having the elemental composition show in Table 1 was calcined in oxygen-enriched air for 25 minutes at several temperatures of about 700° C. and greater. As used herein, “oxygen-enriched air” means air having at least 18% oxygen.

TABLE 1By-product elementalcompositionO52.54%S26.32%Na 8.97%Al10.52%Ca 1.64%

[0016]FIG. 1 tabulates the results of the calcination process. As can be seen in FIG. 1, the aluminum sulfate is significantly converted by calcination while the calcium sulfate and sodium sulfate concentrations are unaffected.

[0017]FIG. 2 illustrates the effect of temperature on conversion of the sulfate content in the by-product composition The graph predicts that above 800° C. temperature is necessary to achieve greater than 99% conversion of aluminium, titanium and iron compounds (as a total oxidation). The residence time is also critical and reasonable. One other factor we have to keep in mind is that of easily soluble salts of strong acid-base—in ...

example 2

[0021]A kiln byproduct mixture having the elemental composition show in Table 2 was calcined in oxygen-enriched air for 25 minutes at several temperatures of about 700° C. and greater. As used herein, “oxygen-enriched air” means air having at least 18% oxygen.

By-product elementalcompositionO52.87%S26.49%Na 9.50%Al11.15%

[0022]FIG. 5 is a table of the results of the calcination process. As can be seen in FIG. 5, the aluminum sulfate is significantly converted by calcinations while the sodium sulfate is unaffected. The calcination products may be further processed as discussed in connection with Example 1.

[0023]Embodiments of the invention may also be used to treat kiln byproduct compositions containing fluoride salts. Such fluoride salts may arise from the incomplete conversion of sodium tetrafluoroaluminate (NaAlF4), which is one of the raw materials utilized in certain silicon tetrafluoride production processes. NaAlF4 is the combination of AlF3 and NaF. AlF3 has no liquid state und...

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Abstract

Embodiments of the invention provide a system and process for recovering useful compounds from a byproduct composition produced in a silicon tetrafluoride production process.

Description

BACKGROUND OF THE INVENTION[0001]Silicon tetrafluoride is an important chemical intermediate, useful for the production of valuable products, such as pure silica, silanes, pure silicon for solar cells, silicon nitride for ceramic products and fluorinated carbon-silicon polymers for materials for architectural uses. Other uses of silicon tetrafluoride include: treating dried concrete parts in order to provide a considerable improvement of their waterproofness and resistance to corrosion and abrasion; increasing the hydrophobic character of crystalline molecular sieves for producing orthosilicic acid esters; and as an etching medium for materials containing silicon in the semiconductor industry.[0002]Known methods for producing silicon tetrafluoride, along with hydrogen fluoride, include reacting sulfuric acid with fluorspar, forming calcium sulfate as by-product. The reaction is endothermic and heat must be externally provided. Methods have been devised to improve heat transfer chara...

Claims

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Application Information

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IPC IPC(8): C01B33/107C01D5/16C01B17/48
CPCC01B17/745C01F11/04C01F7/32C01D5/00Y02P20/129
Inventor REVANKAR, VITHALLAHOTI, SANJEEV
Owner REVANKAR VITHAL