DE1270014B - Process for the production of silicon tetrafluoride-water vapor mixtures - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

COIb

German class: 12 i-33/08

Number: 1270 014

File number: P 12 70 014.0-41

Filing date: February 4, 1965

Opening day: June 12, 1968

The invention relates to a method for producing silicon tetrafluoride by reacting hydrogen fluoride and quartz sand.

In the process for the production of extremely finely divided silicon dioxide by hydrolysis of silicon tetrafluoride according to the equation

SiF ₄ + 2H ₂ O -> SiO ₂ + 4 HF (1)

for example in U.S. Patents 2,535,036 and 2,819,151, the cost of the Siicium tetra- ίο flourids and the value of the hydrogen fluoride formed as a by-product are important factors. Accordingly described a number of processes for the preparation of silicon tetrafluoride by reaction of cheap silica and hydrogen fluoride obtained as a by-product according to the equation

SiO ₂ + 4HF - ^ SiF ₄ + 2H ₂ O

(2)

suggested. Most of these processes are uneconomical, awkward or have another major disadvantage. This is what the German interpretative document says 1 021 339 a process for the production of a mixture of silicon tetrafluoride and water vapor described by the reaction of hydrogen fluoride with silicon dioxide, in which the silicon dioxide in a hygroscopic polyhydric alcohol serving as a solvent for hydrogen fluoride is preferred Glycerin, is suspended. Such a method is multi-valued because of the relatively high price Alcohols are uneconomical as organic products.

German Auslegeschrift 1 022 569 describes a process in which hydrofluoric acid containing SiO ₂ is decomposed with sulfuric acid to form silicon tetrafluoride and water. In this process, however, the sulfuric acid serves as a dehydrating agent, whereby it is continuously diluted and becomes ineffective as a dehydrating agent as a result of the dilution. To make up for this loss, if the process is to be made continuous, concentrated sulfuric acid must be added.

The invention relates to a process for the production of silicon tetrafluoride-water vapor mixtures by reacting a dispersion of SiO ₂ , in particular quartz sand, with hydrogen fluoride at temperatures between the boiling point of water and the boiling point of the dispersant, which is characterized in that as Dispersing agent used sulfuric acid.

The reaction temperatures that can be used are not critically important, as the Reak processes for the preparation of
Silicon tetrafluoride-water vapor mixtures

Applicant:

Cabot Corporation, Boston, Mass. (V. St. A.)

Representative:

Dr.-Ing. A. v. Kreisler, Dr.-Ing. K. Schönwald,

Dr.-Ing. Th. Meyer and Dr. J. F. Fues,

Patent Attorneys, 5000 Cologne 1, Deichmannhaus

Named as inventor:

Robert N. Secord, Wenham, Mass. (V. St. A.)

Claimed priority:

V. St. v. America 5 February 1964 (342 784)

tion between hydrogen fluoride and silicon dioxide over a wide range of temperatures takes place, namely between about 105 and 315 ° C. However, it was found that the reaction between The faster the hydrogen fluoride and silicon dioxide and accordingly the silicon tetrafluoride the faster is obtained, the higher the temperature used. Accordingly, bathing temperatures are recommended between about 120 and 232 ° C. At these temperatures the to Formation of silicon tetrafluoride leading to smooth reactions, and silicon tetrafluoride and water vapor are released practically continuously from the bath, while the vapor pressure of the sulfuric acid remains relatively low.

The reaction is preferably carried out at temperatures between 179 and 232.degree.

The concentration of sulfuric acid in the bath can vary over a relatively wide range will.

It is advantageous to work with sulfuric acid concentrations between about 50 and 90 percent by weight.

The concentration of silicon dioxide in the sulfuric acid bath, the amount of introduced into this bath Hydrogen fluoride, the amount of heat required to maintain a certain temperature of the Baths and other reaction conditions are not critical under normal circumstances.

The suitable conditions can easily be determined according to the particular circumstances.

809 559/466

In a typical case the mixture is silicon tetrafluoride and water obtained from the top of the sulfuric acid bath is very stable, as long as it is kept above the dew point of the gas mixture, and can normally immediately are introduced into a reaction chamber in which silicon dioxide is formed according to equation 1. The hydrogen fluoride formed here as a by-product is released from the reaction chamber after removal of the greater part of the silicon dioxide is fed into the sulfuric acid bath. Except for on a case-by-case basis Case to compensate for the production losses made addition of hydrogen fluoride and / or Sulfuric acid to the system thus the silicon dioxide is the only raw material that is used to manufacture silicon dioxide according to equation 1 is required in continuous operation.

Needless to say, quartz sand is used as the source of silica since it is inexpensive and is readily available in the preferred granular form. Of course, other forms of silica can also be used be used.

example

The contents of a container made of coal and containing 2000 kg of 75% sulfuric acid is ^{heated to about 170 °} C., whereupon 100 kg of hydrogen fluoride are introduced into a gas distributor located at the bottom of the container every hour. At the same time, quartz sand is introduced into the reactor in an amount of about 75 kg per hour. After several hours of continuous operation, the mixture taken from the top of the vessel is analyzed. This shows that silicon tetrafluoride and water vapor are formed in amounts of about 130 and kg, respectively, per hour.

Claims (3)

Patent claims: 1. A process for the preparation of silicon tetrafluoride-water vapor mixtures by reacting a dispersion of SiO ₂ , in particular quartz sand, with hydrogen fluoride at temperatures between the boiling point of water and the boiling point of the dispersant, characterized in that sulfuric acid is used as the dispersant. 2. The method according to claim 1, characterized in that at temperatures between 179 and 232 ° C is implemented. 3. The method according to claim 1 or 2, characterized in that sulfuric acid of a concentration between 50 and 90 percent by weight is used. Considered publications:
German Auslegeschriften No. 1 021 339, 1 022 569. 809 559/466 5.68 © Bundesdruckerei Berlin