Improvements in the Manufacture of Caustic Soda with the Recovery of Reagents Employed for Repeated Use.
Year: 1890

page_text: Date of Application, 21st N.v., 1890
Complete Specification Left, 15th May, 1891-Accepted, 20th June, 1891
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Caustic Soda with the Recovery
of Reagents Employed for Repeated Use.
1 JAMES SIMPSON of 8 Rumford Place Liverpool in the County of Lancaster,
Alkali Manufacturer do hereby declare the nature of this invention to be as
follows:-
The object of my invention is in a cheap and efficient manner to manufacture
caustic soda without the use of any expensive reagent and at the same time to
obtain hydrochloric acid in a suitable condition for repeated use.
For this purpose I dissolve phosphate of lime with hydrochloric acid-whereby a
solution is obtained consisting of chloride of calcium and phosphoric acid.
To this solution 1 add sulphate of soda whereby sulphate of lime is precipitated
and chloride of sodium and phosphoric acid remain in solution.
1 then boil down or evaporate this mixture of common salt and phosphoric acid
to dryness and calcine it in a suitable pot or furnace connected with condensing
towers for catching the hydrochloric acid which is given off by the decomposition of
the chloride of sodium by means of the phosphoric acid-the result being phosphate
of soda.
This phosphate of soda I dissolve in water and agitate with lime-whereby
phosphate of lime is precipitated and caustic soda remains in solution.
The phosphate of lime is again treated with hydrochloric acid obtained as above
set forth and used repeatedly while the caustic soda is concentrated and fused for
use as required.
Dated the 20th day of November 1890
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Caustic Soda with the Recovery
of Reagents Employed for Repeated Use.
1 JAMES SIMPSON of 8 Rumford Place Liverpool in the County of Lancaster,
Alkali 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 :—
The object of my invention is, in a cheap and efficient manner to manufacture
caustic soda without the use of any expensive reagent, and at the same time to
recover hydrochloric acid in a condition suitable for repeated use or sale-or for the
manufacture of any desired chlorine product.
I find as a result of an exhaustive series of experiments which I have caused to
be made since filing my Provisional Specification in November 1890 that there are
three methods by which the object of my invention can be attained, each being
strictly in accordance with the basis set forth in the aforesaid Provisional
Specification.
The first method is as follows:
A. Tricalcic phosphate is treated with just sufficient hydrochloric acid (preferably
diluted to about 10° Twaddle) to completely dissolve it. This solution may be
assumed to be a mixture of chloride of calcium and phosphoric acid.

page_text: B. To the solution thus produced in the cold-neutral sulphate of soda is added
preferably in solution in proportions equivalent to the chloride of calcium-
whereby sulphate of lime is precipitated and a solution-which is probably a
mixture of chloride of sodium and phosphoric acid-is formed.
C. The supernatant liquor is drawn off from the precipitated sulphate of lime
and concentrated by boiling in vessels of suitable material, such as wood lined with
some acid resisting material, the charge being preferably heated by a steam coil.
During this concentration the greater part of the sulphate of lime remaining in the
solution is precipitated and can be removed and also during this concentration
hydrochloric acid is evolved at first weak--but gradually increasing in strength
and may be caught in condensing towers of any well known and suitable design.
D. When the solution has been concentrated so far as to become thick or pasty,
it is run into a silica lined muffle furnace with a low crown and subjected to a red
heat--say 800 to 1000 degrees Fahrenheit or thereabouts-when strong hydrochloric
acid will be evolved and may be caught in condensing towers as required.
E. The fused mass resulting from this operation is tapped off while in the molten
state and is run into water when it disintegrates into a finely divided condition
specially suitable for dissolving and is then dissolved. The above mentioned
mass (consisting principally of phosphate of soda) will also contain a proportion of
chloride of sodium.
F. The solution of phosphate of soda and chloride of sodium is brought to a
density of about 60° to 70° Twaddle and left to settle when the two salts are
separated by the ordinary process of "salting out "the less soluble salt crystalizing
ont while the other remains in solution.
G. The phosphate of soda resulting from the preceding operation is made into a
solution of about 26° Twaddle and is agitated with caustic lime at about boiling
point when phosphate of lime is precipitated and caustic soda remains in solution.
H. The phosphate of lime can be again dissolved in hydrochloric acid for the
first operation (A) or it can be sold for the manufacture of manure, phosphate of
lime from some other source (preferably dicalcic) being employed to replace it.
The caustic soda solution can be used for soap making, paper making, or for any
other desired purpose, or can be boiled down, fused and packed in iron drums for
sale as customary.
The second method is as follows:-
In all respects the process is identical with the first except that bisulphate of
soda is used in operation B instead of neutral sulphate. By this means the chloride
of sodium found mixed with the fused phosphate of soda in operation (E) is reduced
to a minimum but a somewhat larger proportion of sulphate of lime will be carried
forward from operation (B) to the solution of phosphate of soda in operation (G).
The said sulphate of lime however is almost entirely eliminated in the causticizing
operation by being carried down with the precipitated phosphate of lime; and any
small amount of the said sulphate that may still remain in the causticized liquor
will come out as "bottoms" when the caustic is fused.
The third method is as follows:-
Instead of using tricalcic phosphate in operation (A) of the first method, I use
dicalcic phosphate whereby the use of bi-sulphate of soda as in the second method
is obviated and the chloride of sodium remaining in the solution to be causticized
-is reduced to a minimum. The dicalcic phosphate may be obtained for repeated
use by conducting the causticizing operation in the following manner-add the lime
(preferably as milk of lime) carefully in order to avoid having any excess of lime-
so as to leave a little phosphoric acid in the solution. Draw off the latter, when
the precipitate will be found to be in the dicalcic condition. The solution of caustic
soda containing a small percentage of phosphoric acid is then treated with an
excess of lime when caustic soda-practically free from phosphoric acid will be
obtained and can be drawn off. The insoluble phosphate of lime will contain some
free lime but this will be available for the succeeding causticizing operation.
Dicalcic phosphate can also be obtained by dissolving tricalcic phosphate in hydro-

page_text: chloric acid-preferably diluted to about 10° Twaddle and treating with lime in
the same manner as described for the causticizing operation.
A certain amount of phosphoric acid will be carried off by the precipitated
sulphate of lime, but most of this can be removed by washing. If sufficiently rich
in phosphoric acid, the sulphate of lime may be sold as manure; but if not rich
enough for this purpose, it may be roasted with carbonaceous matter in a revolving
black ash furnace and converted into sulphide of calcium. The sulphide of calcium
can then be made into sulphydrate of calcium by passing sulphuretted hydrogen
under pressure through an aqueous mixture of the said sulphide of calcium in a
series of vessels such as are used in the Solvay, Chance, and other processes for
treating aqueous mixtures with gases. The insoluble phosphate of lime remaining
in the sulphydrate will subside and may be recovered by decanting off the
sulphydrate solution.
It is manifest that if the phosphate of lime which is precipitated in the causticizing
operation be again dissolved in the hydrochloric acid which is given off in the
concentration and fusion operations C and D and these reactions are operated
repeatedly, there will be very little risk of impurities being introduced into the
process, as the only raw materials required to produce the caustic soda, are sulphate
of soda and lime-the result being that caustic soda of very high strength and
purity is obtained at a very low cost.
In practical working I find that the following proportions of raw materials and
re-agents give satisfactory results the calculation being based on the quantities
required to produce one ton of caustic soda.
VQEC TO ADONG TO 1. Defore use.
Tyurocnioric act=20 IW. +14
- 1 19 0
Line-
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
First. In the manufacture of caustic soda-The cycle of operations described as
the first method and designated respectively by the letters ABCDEFG and H.
Second. The modification of the foregoing cycle of operations, consisting in the
employment of bi-sulphate of soda instead of neutral sulphate of soda-described
as the second method.

page_text: Third. The modification of the said cycle of operations consisting in the
employment of dicalcic phosphate described as the third method.
Fourth. Running the fused phosphate of soda in the inolten state into water in
order to disintegrate it and render it suitable for dissolving substantially as
described.
Fifth. The employment of a silica lined muffle furnace connected with condensing
apparatus for effecting the fusion of the phosphate of soda and chloride of sodium,
and recovering the hydrochloric acid.
.
Sixth. The two methods herein described for manufacturing the dicalcic phosphate
in combination with the manufacture of caustic soda in the manner described.
Dated the 14th day of May 1891
Per pro J. T. KING,
J. Johnson,
Agent:
Per pro
J. T. KING,
J. Johnson,
Agent: