Process for the Production of Phosphates of Potassium or Aluminium Soluble in Water.
Year: 1892

page_text: Date of Application, 27th Apr., 1892
Complete Specification Left, 2nd Jan., 1893-Accepted, 25th Feb., 1893
PROVISIONAL SPECIFICATION.
A. Process for the Production of Phosphates of Potassium or
Aluminium Soluble in Water.
I, Dr. HEINRICH PRECHT of New Stassfurt, in the Empire of Germany,
Doctor of Philosophy, do hereby declare the nature of this invention to be as
follows:-
The ordinary metaphosphate of potassium which may be obtained by known
methods, such for instance as by melting together phosphoric acid and carbonate of
potassium or potash or chloride of potassium, or by heating orthophosphate of
patassium, one third saturated, to a red heat is almost insoluble in water.
By my invention however I obtain this salt in a combination which is easily
soluble in water and which contains the whole of the phosphoric acid of the salt
in a form which is easily soluble in water.
In carrying out my invention I convert insoluble metaphosphate of potassium
into the soluble condition by melting the metaphosphate of potassium which is
insoluble in water, and cooling the fused mass rapidly, by which means the fused
material is prevented from passing into the crystalline condition, and soluble
metaphosphate of potash is produced.
Or by fusing metaphosphate of potassium insoluble in water with chloride of
potassium at a red heat in the presence of the vapour of water, whereby, as the
result of the action of the water vapour upon the fused mixture, pyrophosphate of
potassium soluble in water is produced.
I employ the soluble metaphosphate or pyrophosphate of potassium obtained as
described for rendering insoluble phosphate of aluminium soluble in water by fusing
the latter with metaphosphate or pyrophosphate of potassium or a mixture of the
two, and I employ the soluble phosphates of potassium obtained as described for
the production of orthophosphate of potassium either by heating a watery solution
of these salts under pressure, or by heating pyrophosphate of potassium obtained
as described (with which the soluble metaphosphate of potassium obtained as
described can be mixed) in a watery solution with so much phosphoric acid that
one molecule of the latter is present to each molecule of potash, whereupon the
formation of monopotassic orthophospate occurs.
Dated the 27th day of April 1892.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
A Process for the Production of Phosphates of Potassium or
Aluminium Soluble in Water.
I, Dr. HEINRICH PRECHT, of New Stassfurt, in the Empire of Germany,
Doctor of Philosophy 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 ordinary metaphosphate of potassium which may be obtained by known
methods, such for instance as by melting together phosphoric acid and carbonate
of potassium or potash or chloride of potassium, or by heating orthophosphate of
potassium, one third saturated to a red heat is almost insoluble in water.

page_text: By my invention however I obtain this salt in a combination which is easily
soluble in water and which contains the whole of the phosphoric acid of the salt
in a form which is easily soluble in water.
This object may be attained by subjecting metaphosphate of potassium to a
smelting process as hereinafter described. If the process be so conducted as to
cool the melted metaphosphate very rapidly, there results au easily soluble
amorphous potassium salt of the condensed metaphosphoric acid. If however the
process be carried out by melting together metaphosphate of potassium and chloride
of potassium, and allowing the vapour of water to act upon the melted materials,
a phosphate of potassium which is soluble in water is obtained chiefly pyrophos-
phate of potassium.
My process is carried out as follows :-
11
In
The insoluble metaphosphate of potassium is fused at a red heat, and is caused
to set rapidly by allowing it to run out into shallow iron boxes or moulds, so that
it remains in an amorphous condition, and does not become crystalline. By this
process is formed the potassium salt of the condensed metaphosphoric acid, and
this if allowed to cool slowly would pass into a crystalline and insoluble condition.
The fusing of the insoluble metaphosphate of potassium. is most conveniently
carried out in a reverberatory furnace, in which the metaphosphate of potassium
is heated to such a point that it can be drawn off in a liquid condition through a
vent hole. If the insoluble metaphosphate be melted in a furnace with an inclined
hearth, the process may be carried on continuously by inserting the phosphate
which is to be treated at the coolest part of the furnace, on the hearth inclined
toward the flame, passing it forward by means of rakes, so that the salt
gradually attains the fluid condition by the heat of the furnace, and the fused
phosphate is allowed to flow continuously out at the hottest part of the furnace.
It is advisable to allow an oxidizing flame to act upon the phosphate for the
purpose of fusing it, since the reducing flame might give rise to a reduction of
the phosphoric acid and thus cause loss. Experiments have shewn that a phosphate
of potassium which is perfectly soluble in water is formed if one molecule of phos-
phoric acid and one molecule of potash or if at least 66.2 parts by weight of the
latter to 100 of anhydrous phosphoric acid are present in the fused mass.
practice it is advantageous to work with a larger proportion of potash, so that the
phosphoric acid in the fused mass is present partly in the condition of pyrophos-
phate of potassium. If the proportions of potash and phosphoric acid were such
that 1 part of pyrophosphate of potassium must of necessity be formed to 4 parts of
metaphosphate of potassium, the process above described results in the production
of perfectly soluble phosphate of potassium. If it be desired to obtain such a
proportion in the fused mass the required quantity of a basic substance such as
potash or soda may be added during the process of melting. If for the manu-
facture of soluble phosphate of potassium from insoluble metaphosphate of potassium
the latter is to be fused with chloride of potassium, the presence of the vapour of
water during the process is indispensable, since the product then consists chiefly of
soluble pyrophosphate of potassium. In the above case, 1 molecule or 236 parts
by weight, of metaphosphate of potassium is melted with 2 molecules or 149 parte
by weight of chloride of potassium and the vapour of water is allowed to act upon
the fused mass; by the aid of the water soluble pyrophosphate of potassium
is formed, as shewn by the following equation:-KOP,O, + 2.KCl + H₂O=
2 (KO) P₂O, +2 HCI. The vapour of water required for this reaction may be.
passed either into or over the fused mass; in the latter case, it may be brought.
into contact with the fused mass in the gases of combustion which play over ther
mixture of salts by employing moist fuel.
The soluble phosphate of potassium obtained by the foregoing process.may now
be employed in accordance with my invention for the manufacture of a phosphate
of aluminium which is soluble in water, and also of orthophosphate, of potassium..
by the means now to be described. For the manufacture of aluminium phosphate

page_text: soluble in water the phosphate of aluminium to be acted upon is mixed with the
phosphate of potassium soluble in water obtained in the preceding process (that is
to say, with pyro- or meta-phosphate of potassium soluble in water) in any propor-
tion desired, provided always that the mixture does not contain more than 40% of
phosphate of aluminium. The meta- or pyrophosphate of potash, soluble in water,
obtained by the process previously described, forms with phosphate of aluminium
compounds which are..soluble in water, and of which a watery solution does not
decompose. The phosphate of aluminium to be employed in this. process is either
added as such in its usual insoluble state during the fusion, or added to the phos-
phates of potassium in the phosphoric acid solution which serves as the liberating
agent, by employing for the preparation of insoluble phosphate of potassium a
phosphoric acid which contains phosphate of aluminium as an impurity. If the
phosphate of aluminium contains phosphate of iron in small quantity as an impurity,
the latter also assumes the soluble form. In employing meta- or pyrophosphate
of potassium soluble in water, prepared according to my invention, for the manu-
facture of orthophosphate of potassium these salts are dissolved in water to make
a solution of a degree of concentration corresponding with a specific gravity of
about 1-25 and heated under pressure, by means of high pressure steam in a
closed vessel, it may be, to a temperature beyond their boiling point. The higher
the temperature, the more rapidly does the conversion proceed, at 120° C. it is
complete in about two hours. The reaction may be accelerated by the addition
of phosphoric acid. By adding phosphoric acid when pyrophosphate of potassium
is being employed prepared as herein before described which pyrophosphate may
also be mixed with metaphosphate of potassium made soluble according to the
foregoing invention, the employment of pressure may be dispensed with, in which
case monopotassic orthophosphate is obtained.
In this case there is added to the watery solution of the pyrophosphate of
potassium, in which as above mentioned soluble metaphosphate of potassium may
also be contained, so much phosphoric acid that 1 molecule of phosphoric acid to
each molecule of potash is present in the fluid, which is afterwards boiled for
several hours.
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 :-
1. The herein described process for converting insoluble metaphosphate of
potassium into the soluble condition by
(a) Melting the inetaphosphate of potassium which is insoluble in water, and
cooling the fused mass rapidly, by which means the fused material is
prevented from passing into the crystalline condition, and soluble meta-
phosphate of potash is produced.
(b) By fusing metaphosphate of potassium insoluble in water with chloride
of potassium at a red heat in the presence of the vapour of water, whereby,
as the result of the action of the water vapour upon the fused. mixture,
pyrophosphate of potassium soluble in water is produced.
2. The employment of the soluble metaphosphate or pyrophosphate of potassium
obtained as described under (a) or (b) in Claim 1, for rendering insoluble phosphate
of aluminium soluble in water by fusing the latter with metaphosphate or pyro-
phosphate of potassium or a mixture of the two.
3. The employment of the soluble phosphates of potassium obtained as described
under (a) or (b) in Claim 1 for the production of orthophosphate of potassium.
By heating a watery solution of these salts under pressure.
By heating pyrophosphate of potassium obtained as described under (6)
in Claim 1 (with which the soluble metaphosphate of potassium obtained as
described under (a) in Claim 1 can be mixed) in a watery solution with
so much phosphoric acid that 1 molecule of the latter is present to each

page_text: molecule of potash, whereupon the formation of monopotassic orthophosphate
occurs.
Dated the 2nd day of January 1893.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.