Improvements in and connected with the Manufacture of Alkaline Phosphates and Caustic Alkali.
Year: 1895

page_text: Date of Application, 9th Dec., 1895
Complete Specification Left, 3rd Sept., 1896-Accepted, 17th Oct., 1896
PROVISIONAL SPECIFICATION.
Improvements in and connected with the Manufacture of Alkaline
Phosphates and Caustic Alkali.
A communication by THE CHEMISCHE WERKE, vormals H. & E. ALBERT, of
Biebrich-on-Rhine, in the Empire of Germany, Chemical Manufacturers.
I, WILLIAM PHILLIPS THOMPSON F.C.S., M.I.M.E., of The Agency for
Foreign Patent Solicitors, 6 Lord Street, Liverpool, and 6, Bank Street,
Manchester both in the County of Lancaster, 118 New Street, Birmingham
in the County of Warwick and 31 High Holborn in the County of Middlesex,
Civil Engineer, do hereby declare the nature of this invention to be as follows:-
The process hitherto employed for making alkaline phosphates and caustic alkali
was never a rational one as the phosphoric acid obtained from raw phosphates and
sulphuric acid was neutralised with alkaline carbonates, the carbonic acid being
lost. Even the newer process of obtaining the salts in question direct from
raw phosphates is less lucrative as the return leaves much to be desired.
By the process which forms the object of this invention, the result has been
successfully obtained of producing by a cheap method the alkaline phosphates in
question in a pure condition by electrolysis from phosphoric acid and alkaline
salts, such as sulphates, nitrates and chlorides, the process, for instance where
nitrate of soda is used, being represented by the following formulæ.

page_text: directly decomposed in this way, such for instance as Chili salt petre, chloride of
sodium or the like, there are obtained in the presence of phosphoric acid, directly
products capable of saponifying oil, whilst the phosphoric acid is again utilised or is
used for other purposes. In this process it must not be overlooked that the costs
of obtaining saponifying agents are fully covered by the recovery of the phosphoric
acid, and that the yield of caustic alkali in proportion to the quantity of salt
employed which is not capable of double decomposition in this way, for instance
sulphate of soda is a considerable one.
This process has the following advantages:
(1.) The working is continuous;
(2.) In place of the expensive alkaline carbonates hitherto employed, such as
soda or the like, cheaper sources of the alkali like nitrate of soda are employed;
(3.) Valuable products such as nitric acid, sulphuric acid and the like are
obtained as bi-products;
(4.) The evaporation of the solutions can be entirely dispensed with ;
(5.) The alkaline phosphates produced in this cheap method and manner may be
converted into caustic alkali by double decomposition for instance with caustic lime,
whilst the phosphoric acid is always again utilised in the process as phosphate of
lime, or can have some other application.
Dated this 7th day of December 1895.
improvements in and connected with the Manufacture of Alkaline
Phosphates and Caustic Alkali.
A communication by THE CHEMISCHE WERKE, vormals H. & E. ALBERT, of
Biebrich-on-Rhine, in the Empire of Germany, Chemical Manufacturers.
1, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of The Agency for
Foreign Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street,
Manchester, both in the County of Lancaster, 118 New Street, Birmingham,
in the County of Warwick, and 322, formerly 31, High Holborn, in the County
of Middlesex, Civil Engineer, 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 phosphates of alkalies
and consists in the process of producing caustic alkalies by electrolysis of phosphoric
acid and such soluble salts of the alkalies as by ordinary chemical reactions do not
undergo double decomposition in presence of phosphoric acid. The phosphates of
alkalies hereby formed by electrolysis are decomposed forming caustic alkalies,
while phosphoric acid recombined as salt of lime, etcetera, is recovered.
The process hitherto used for the manufacture of phosphates of the alkalies was
never a satisfactory one for the reason that the phosphoric acid obtained from
crude phosphate and sulphuric acid was neutralised with alkaline carbonates,
whereby the carbonic acid was lost. Even the later methods for producing the
corresponding salts directly from the crude phosphate did not yield a profit on
account of the unsatisfactory results. By this invention the phosphates of the
alkalies are successfully produced in a pure state and in an economical manner by
the action of the electric current on phosphoric acid and the corresponding salts
of the alkalies such as the nitrates, sulphates, chlorides and the like of the alkalies.

page_text: The reactions occurring, in case nitrate of soda is used,
following equations:
are
explained by the
3. 3 NaNO3 + H3PO₁ = 3 HNO3 + NaзPO
If solutions of phosphoric acid and of the salts of the alkalies like nitrates,
sulphates, chlorides and the like of whatsoever concentration are submitted, whilst
separated by a proper diaphragm, for instance of porous earthenware asbestos and
the like to the action of the electric current, either at ordinary or an elevated
temperature, separation of the respective acids takes place, and nitric acid,
sulphuric acid or chlorine are set free at the anode.
In order to obtain the volatile substances like nitric acid, chlorine, etcetera, it is
only necessary to heat the solutions. Inasmuch as hereby the volume of the
solution in contact with the anode is quickly reduced, a continual addition of fresh
salt solution is needed. At the cathode, the corresponding phosphate salt is
formed, as for instance the mono-, di- or tribasic phosphate of potash, soda and the
like, the formation of these respective salts depending on the quantity of salts used
at the anode. The process may be interrupted at the proper time for the purpose
of obtaining either the mono- or the di- or tribasic salt. If the solution of
phosphoric acid be sufficiently strong, the salts formed are deposited in a solid
state at the cathode and may be dipped out, otherwise the cathode solution has to
be concentrated.
The phosphates obtained electrolytically in this manner may also be applied
directly to the manufacture of caustic alkalies, for instance, with caustic lime.
Salts as chilisaltpetre and chloride of sodium and so on, which heretofore could not
be directly split up into their constituents are, in the presence of phosphoric acid,
converted by electrolysis into products, which can be directly split up, whereby the
phosphoric acid returns to the manufacturing process or may be otherwise employed.
It must be remembered that in this process the cost of the splitting up operation
performed on the salts is completely covered by the recovery of the phosphoric
acid and that the yield of caustic alkali is theoretically proportional to the amount
of the salt used as for instance nitrate of soda.
This process possesses the following advantages-
1. The process is a continuous one;
2. In place of the expensive carbonates of alkalies hitherto used, such for instance
as soda, such cheap salts as chilisaltpetre and the like are employed;
3. Valuable substances like nitric acid, sulphuric acid and the like are obtained
as bi-products;
4. The concentration of the solution by evaporation may be completely omitted;
5. The alkaline phosphate, thus cheaply produced, may be directly converted
into caustic alkali by treatment, for instance with quicklime, whilst the phosphoric
acid in the shape of phosphate of lime returns to the manufacture or is otherwise
employed.
An apparatus for carrying out this process is shown in the accompanying
drawing.
In this drawing a is a wrought iron vessel which is coated with cement or similar
material b. This vessel is divided by a diaphragm d covered by a coating cof
cement or similar material. The phosphorous solution (phosphoric acid) is
contained in the compartment A and a chloride of sodium solution in the compart-
ment B, the phosphorous solution (phosphoric acid) being fed through the pipe e
and the salt solution through the pipe f. Electrodes K K dip into these solutions
and receive electric current by means of the wires D D' respectively.

page_text: The anode consists preferably of carbon, the cathode of lead or other suitable'
metal which is not attacked by the phosphoric acid.
The chlorine which is liberated by the process of decomposition escapes
through the pipe g. A cock is provided for draining off the liquid when
desired.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to
me by my foreign correspondent, I declare that what I claim is :-
1. The herein described process of manufacturing phosphates of the alkalies,
which consists in forming a bath of phosphoric acid and one or more soluble salts
of the alkali metals and electrolysing the said bath by passing a current of
electricity therethrough, whereby a mono- di- or tribasic phosphate of the alkali
employed is produced at the cathode substantially as herein before set forth.
2. The herein described process of manufacturing caustic alkalies, which consists
in electrolysing phosphoric acid and a solution of alkaline salts, which are separated
in a bath by means of a diaphragm or are mixed with one another, the caustic
alkali deposited at the anode being absorbed at the moment of its production
(statu nascendi) by the phosphoric acid and alkaline phosphate being formed, which
is converted into caustic alkali by treatment with caustic lime, phosphate of lime
resulting substantially as herein before set forth.
Dated this 2nd day of September 1896.
WM. P. THOMPSON & Co.,
Agents.