A Process for the Manufacture of Fluoro-Compounds.
Year: 1898

page_text: Date of Application, 24th June, 1898-Accepted, 10th Sept., 1898
COMPLETE SPECIFICATION.
A Process for the Manufacture of Fluoro-Compounds.
I, WALTER SCHMEISSER, Ph.D., of Chemische Fabrik Fluor, near Siptenfelde, in
the Harz, German Empire, Manufacturer, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
This invention relates to a process for the manufacture of fluoro-compounds and
offers the great advantage that no vapours of fluoride of silicon and hydro-
fluoric acid are developed either at the commencement or at the end of the reaction
so that the health of the workmen is not endangered as at present.
According to this invention the apparatus is fed with an absolutely non-
dangerous neutral saft mixture, and the residue in the vessels consists also of a
solid neutral mass, which does not yield the slightest amount of acid vapours after
cooling.
It is also of great importance that the reaction yields a valuable bye-product,
which with the main product can be easily formed into a product or material
which is finding steadily increasing application in the arts and manufactures.
As is well known hydro-fluoric acid has hitherto been manufactured by heating
fluor-spar (CaF2) with a high percentage of sulphuric acid (60-66° Bé).
Experiments made by me on a small scale, as well as on a large scale, have shown
that bydro-fluoric acid may also be obtained by gradually heating to a dull red
heat a mixture of fluor spar and an acid alkaline hydrogen sulphate in certain
proportions.
The operation may be expressed by the following formula, "A" representing
It will be seen that hydro-fluoric acid is the resulting main product, and sulphate
of lime (gypsum) and alkaline sulphate are the resulting bye-products.
If disintegrated silicic acid or silicic anhydride be added to the mixture of
fluor spar and acid hydrogen alkaline sulphate, fluo-silicic acid will be produced in
a similar manner according to the following formula :-
It will be seen that a double reaction takes place, fluoride of silicon is
produced first, and fluo-silicic acid is formed afterwards by combination with
water and separation of silicic acid hydrate.
Therefore during the above mentioned reactions sulphate of lime and an
alkaline sulphate are produced besides the two main products. An alkaline

page_text: sulphate is very valuable for the manufacture of hydro-fluoric acid salts of alkali
and fluo-silicic acid salts of alkali. For this purpose the cake produced is
treated with water and the alkaline sulphate accumulates in the lye leaving
sulphate of lime (gypsum) as residue.
If the main products (hydro-fluoric acid or fluo-silicic acid respectively) be
added to this lye, alkaline fluorides or silicic alkaline fluorides respectively are
precipitated.
The reaction takes place according to the following formula.
The only condition for the complete success of the operation or process is the
careful and intimate mixture of the pulverized salts.
The great advantages of this new process compared with the known-process are
as follows:
The known process for the manufacture of hydro-fluoric acid from fluor-spar with
concentrated sulphuric acid requires great attention and care. Even during feeding
the vessels, vapours of fluoride of silicon and hydro-fluoric acid are given off, which
are extremely detrimental to the health of the operator.
According to this new process, however, the apparatus is fed with an absolutely
non-dangerous neutral mixture of salt without any detrimental effect on or danger
to the workmen. The substances of the mixture re-act on one another only when
heated.
Further, after the completion of the operation according to the old process, the
cooled residue in the vessel still gave off vigorously vapour of fluor acid and thus was
very detrimental and dangerous for everything living, but according to this new
process the residue in the vessels consists of a solid neutral mass, which does not give
off any trace of acid vapours after cooling.
Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, I declare that what
I claim is—
1st. A process for the manufacture of hydro-fluoric acid and fluo-silicic acid
respectively as main products and of an alkaline sulphate as a bye product,
consisting of the heating of a mixture of fluo-spar and an acid hydrogen alkaline
sulphate to dull red heat.
2nd. The production of alkaline fluorides and silicic alkaline fluorides respectively
by the action of the main products, obtained according to the process claimed in
Claim 1 on the alkaline sulphate obtained as a bye product.
D
1000
FELL & JAMES,
Agents for the Applicant.