A Process for the Production of Caustic Alkali, Carbonate of Alkaline Metals, and Useful Bye Products.
Year: 1891

page_text: A Process for the Production of Caustic Alkali, Carbonate of Alkaline
Metals, and Useful Bye Products.
I, FREDRIK EICHSTÄDT, Tutor at the Chemical Institute Göteborg in Sweden
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 :---
of
This invention consists in a process by which caustic soda or potash, or carbonate
of soda or potash may be produced without loss in a commercial sense of any
the materials used in the manufacture, these substances being either obtained in a
form suitable for using again or else delivered in a form suitable for immediate
trade, that is to say without needing any further process of manipulation, no useless
products being obtained.
The invention for the production of caustic alkali depends upon the interchange
effected between sulphates of the alkalies and hydrates of the alkaline earths,
barium and strontium, to form hydrates of the alkalies and sulphates of the alkaline
earths, and it consists broadly in the following three operations. 1st. The pro-
duction of a hydrate of barium or strontium. 2nd. The conversion of the hydro-
sulphide of the alkali, which is produced by the hereinafter described method of
conducting the first operation, into a sulphate, the sulphur in the sulphide being
recovered as hereinafter shown. 3rd. The interchange of the sulphate of the
alkali with the hydrate of the alkaline earth to form sulphate of the alkaline earth.
and caustic alkali.
The same process is followed to produce carbonate of the alkali, the caustic
alkali produced as above being afterwards converted into carbonate by passing
carbonic acid gas through the former while it is still in the form of lye.
The process is carried out as follows, the alkaline earth made use of being taken
as strontium, the alkaline hydrate to be produced being presumed to be caustic
soda.
The strontium hydrate is preferably produced by the novel reaction produced by
the sulphides of strontium and of sodium in solution in water, equal molecular
quantities of these two sulphides being converted into strontium hydrate and hydro-
sulphide of sodium according to the following reaction
SrS+Na³S + 2 H2O = SгO'H' + 2 NaS.H.
The less soluble strontium hydrate separates while the more soluble hydrosulphide
of sodium remains in solution.
The production of strontium hydrate is therefore produced by the following
process; equal molecular values of strontium sulphate and sulphate of soda made
in the usual way are well mixed with about of the weight of the mixture of clean
and fine small coal, the whole is treated to a red heat in a reducing furnace so that
the sulphates are reduced to sulphides as follows ;-
Sro³, SO + Na³O³, SO' + 8 C = SrS + Na³S + 8 CO.
The charge which will be more or less melted by the heat of the furnace is
100°C When the solution cools, the strontium
SrO³, SO + Na³O', SO² + 8 C = SrS + Na'S + 8 C
The charge which will be more or less melted by the heat of the furnace is
Brown and dissolved in water at 100° C When the solution cools, the strontium
will separate as crystallized strontium hydrate and the sodium hydrosulphide will
be left in the solution. By slightly concentrating the liquor only traces of
strontium will be found in the solution when cold. The strontium hydrate should
be cleared as far as possible from mother liquor and purified if necessary by
11:--

page_text: The solution of hydrosulphide is exposed to the air until a sufficient quantity of
the hydrosulphide has been oxydised, when it is treated with sulphuric acid as
above described. As oxydation by air requires a long time, this method is not in
practice superior to that above stated.
The solution of sulphate of soda produced as described is mixed with the
strontium hydrate-producing sulphate of the oxyde of strontium which crystallizes
out as a heavy precipitate, and hydrate of soda which remains in solution. The
reaction proceeds easily of itself and needs no special description.
When the strontium hydrate was well freed from mother liquor clean lye of
hydrate of soda is produced, if however it was not thoroughly cleansed the lye will
contain a certain amount of sulphide of soda, with careful work however the
amount of sulphide present is much less than with other processes at present in
vogue even when carried out under the best conditions.
The lye is evaporated and purified with saltpetre if necessary in the usual way.
The sulphate of strontium is washed and used again with addition of sulphate of
soda and coal as before stated.
Carbonate of soda can be made by passing carbonic acid gas through the lye,
possibly derived from the gases from the furnaces a method of deriving carbonic
acid not yet employed in practice.
To produce caustic potash or carbonate of potash the process is exactly the same
using of course potassium sulphate instead of sodium sulphate.
Barium sulphate may be used instead of strontium sulphate but is not a good
since the sulphide does not so easily conform to the reaction by which it is con-
verted into hydrate and the respective alkali into hydrosulphide. In place of
forming hydrate the barium crystallizes out in hexagonal tablets as an oxysulphide,
which even with repeated crystallization can never be freed entirely from sulphur,

page_text: If however a carbonate of the alkali is the ultimate purpose of the process this is
no drawback since the sulphide which will be found in the lye is decomposed
by the carbonic acid to form carbonate the hydric sulphide being driven off.
The advantages of the improved process over those in use for the same
purposes consists firstly in the fact that it depends on simple reactions which
are easily and quickly realised and complete in their operation, it produces a
relatively well concentrated and pure solution of caustic alkali and consequently
of carbonate. There is no loss of substances used in the process except the coal
used for reducing the sulphate. The undissolved substances remaining after
digestion of the charge from the furnace in water may be dissolved in hydrochloric
acid and water, and the strontium is thrown down as sulphate by the sulphuric
acid. No useless products are produced. Thus summing the formulæ of the
whole process including the preparation of sulphate of soda from chloride of soda
acid and water, and the strontium is thrown down as sulphate by the sulphuric
acid. No useless products are produced. Thus summing the formulæ of the
whole process including the preparation of sulphate of soda from chloride of soda
2 NaCl + H'O'SO' + STO³SO² + 8 C + SO2 + H³O'SO' = 2 HCl + 8 CO +
3 S + SrO SO* + 2 NaOH.
Following the process step by step, the chloride of sodium is treated with
sulphuric acid, strontium sulphate, coal, sulphurous acid and again sulphuric acid.
The chlorine is obtained as hydrochloric acid, the sulphuric acid and the sulphurous
acid are represented by free sulphur; the strontium sulphate is given back in the
same form; and the sodium appears as hydrate.
The process can be carried out entirely in works fitted to work the Leblanc
process and having apparatus for sulphur regeneration from the soda residues.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is ;-
1. In a process for producing caustic alkali or hydrate of an alkali and therefrom
a carbonate thereof
a). The production of strontium or barium hydrate by means of sulphide of
sodium or of potassium and sulphide of strontium or barium by dissolving
the said sulphides in water and thus producing a solution of hydrosulphide
of the alkali and a crystallized hydrate of the alkaline earth.
b). The conversion of the hydrosulphide by addition of sulphuric acid into
sulphate.
c). The mixture of the sulphate of the alkali with the hydrate of alkaline
earth to produce hydrate of the alkali and sulphate of the alkaline earth,
the said hydrate of the alkali being thereupon converted into carbonate if
desired by addition of carbonic acid.
2. The herein described method of producing hydrate of an alkaline earth and
solution of hydrosulphide of an alkali, consisting in reducing sulphates of the
alkaline earth and of the alkali in the presence of carbon (small coal) and digesting
the residue in hot water as herein described, the hydro sulphide being subsequently
converted into sulphate and mixed with said hydrate to form hydrate of the alkali
and sulphate of the alkaline earth as herein described.
3. In the process for manufacturing hydrate of an alkali from hydrosulphide as
herein described, the method of treatment to recover the sulphur of the hydro-
sulphide and of the sulphurous acid when used for this purpose as described and
illustrated.
Dated this 7th day of September 1891.
Dated this 7th day of September 1891.
HERBERT & Co.,
18, Buckingham Street, Strand, London, W.C., Agents to Applicant.