An Improved Manufacture of Potassium Carbonate from Potassium Sulphate.
Year: 1892

page_text: Date of Application, 26th Jan., 1892
Complete Specification Left. 20th Oct., 1892-Accepted, 31st Dec., 1892
PROVISIONAL SPECIFICATION.
An Improved Manufacture of Potassium Carbonate from Potassium
Sulphate.
I, PETER RÖMER of Nienburg on the Saale, Germany, Chemist, do hereby
declare the nature of this invention to be as follows:-
My invention has for its object a more advantageous manufacture of potassium
carbonate than that obtained by the processes heretofore employed. It consists
mainly of the following operations.
1. Production of potassium chromate from potassium sulphate.
2. Decomposition of the potassium chromate by carbonic acid into potassium
bicarbonate and potassium bichromate; separation of these salts and conversion of
the bichromate into carbonate.
3. Purification of the obtained potassium carbonate containing chromium by the
use of carbonic acid or alkaline reducing agents.
These operations are effected very readily in aqueous solution, so that the losses
of potassium which occur in other processes, in particular with the Leblanc potash
process, are obviated.
I will describe by way of example a practical mode of carrying out the said
manufacture of potassium carbonate according to my invention.
Potassium sulphate and potassium bichromate are dissolved in their molecular
proportions by weight in as little water as possible, preferably at a temperature of
from 60° to 80° C. and are accurately neutralised by milk of lime, whereby
potassium chromate and calcium sulphate are produced according to the following
equation.
K₂SO, + KC₂O, + Ca(OH), = 2 K2CrO, + CaSO + H₂O.
The mass must not be heated to boiling point as otherwise combinations that are
not readily soluble are produced, containing potassium, calcium, chromic acid and
sulphuric acid, at the expense of the first formed potassium chromate.
The gypsum produced is separated from the liquid obtained, which is a solution
of potassium chromate; the latter contains calcium sulphate in solution, which is
precipitated as calcium carbonate by means of potassium carbonate or is removed
by evaporation in vacuo at 80° C.
In place of the hydrate of lime, may also be employed baryta or strontia.
The solution of the potassium chromate is then evaporated to a concentrated
saturated chromate lye, at 35° to 40° C.
This concentrated solution is then treated, under effectual cooling, with carbonic.
acid in a vessel provided with a stirring apparatus, either at atmospheric or higher
pressure.
This operation can also be effected in the so called saturating apparatuses such as
are employed in the ammonia-soda process. The process is preferably carried on
with carbonic acid as pure as possible; this may however be used in the dilute
form in which it is obtained from lime kilns, or is regenerated in the hereinafter
described decomposition of the potassium bicarbonate.
The carbonic acid effects the decomposition according to the formula:
2 K,CrO4 + 2 CO, + H,O = 2 HKCO₂ + K,Cг₂O,.
The potassium bichromate formed is precipitated while potassium bicarbonate,

page_text: intended to employ the regenerated' carbonic acid, it is evaporated in closed vessels
with suitable discharge channels, to a concentration of from 45° to 50° Bé.
now
Potassium chromate is thus separated, and, if the dissolved gypsum was removed
with potassium carbonate, also potassium sulphate. The so called "final lye
remaining, contains mainly potassium carbonate together with small quantities of
potassium chromate, and gives, on evaporation, potassium carbonate containing
chromium.
In order from this to obtain potassium carbonate free from chromium, the
solution or final lye is saturated with carbonic acid under cooling, when the
potassium bicarbonate will separate in crystalline form, while the chromium remains
as bichromate in the solution.
By repeated precipitation by means of carbonic acid, the bicarbonate is obtained
free from chromium, and it is finally separated into carbonate and carbonic acid.
Instead of precipitating twice by means of carbonic acid, the chromate can also
be removed by means of alkaline reducing agents, preferably potassium sulphide
or the like, the chromate being thereby converted into insoluble chromium oxide.
Dated this 26th day of January 1892.
ABEL & IMRAY,
Agents for the Applicant..
COMPLETE SPECIFICATION.
An Improved Manufacture of Potassium Carbonate from Potassium
Sulphate.
I, Peter Römer, of Nienburg on the Saale, Germany, Chemist, 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 :-
My invention has for its object a more advantageous manufacture of potassium
carbonate than that obtained by the processes heretofore employed. It consists
mainly of the following operations.
1. Production of potassium chromate from potassium sulphate.
2. Decomposition of the potassium chromate by carbonic acid into potassium
bicarbonate and potassium bichromate ; separation of these salts and conversion of
the bichromate into carbonate.
3. Purification of the obtained potassium carbonate containing chromium by the
use of carbonic acid or alkaline reducing agents.
These operations are effected very readily in aqueous solution so that the losses
of potassium which occur in other processes; in particular with the Leblanc potash
process, are obviated:
1 will describe by way of example a practical mode of carrying out the said
manufacture of potassium carbonate according to my invention.
Potassium sulphate and potassium bichromate are dissolved in their molecular
proportions by weight in as little water as possible, preferably at a temperature of
from 60° to 80° C. and are accurately neutralised by milk of lime, whereby
potassium chromate and calcium sulphate are produced according to the following
equation :
K₂SO, K,C,O, + Ca(OH),2 K,CrO, + CaSO, + H₂O.
The mass must not be heated to boiling point as otherwise combinations that
are not readily soluble are produced,, containing potassium, calcium, chromic acid
and sulphuric acid at the expense of the first formed potassium chromate.
The gypsum produced is separated from the liquid obtained, which is a solution
of potassium chromate; the latter contains calcium sulphate in solution which is
precipitated as calcium carbonate by means of potassium carbonate or is removed
by evaporation in vacuo at 80° C.

page_text: In place of the hydrate of lime may also be employed baryta or strontia.
The solution of the potassium chromate is then evaporated to a concentrated
saturated chromate lye at 35° to 40° C.
This concentrated solution is then treated, under effectual cooling, with carbonic
acid in a vessel provided with a stirring apparatus, either at atmospheric or higher
pressure.
This operation can also be effected in the so called saturating apparatus, such
as are employed in the ammonia soda process.
The process is preferably carried on with carbonic acid as pure as possible; this
may however be used in the dilute form in which it is obtained from lime kilns
or it is regenerated in the hereinafter described decomposition of the potassium
bicarbonate.
The carbonic acid effects the decomposition according to the formula:
2 K,Cro₁ + 2 CO, + H,O=2 HKCO, + K,Cг,O,.
The potassium bichromate formed is precipitated while potassium bicarbonate
together with small quantities of potassium bichromate remain in solution.
The liquid is then separated from the precipitated bichromate and if it be
intended to employ the regenerated carbonic acid, it is evaporated in closed vessels
with suitable discharge channels to a concentration of from 45° to 50° Bé.
Potassium chromate is thus separated, and, if the dissolved gypsum was removed
with potassium carbonate, also potassium sulphate. The so called "final lye" now
remaining contains mainly potassium carbonate together with small quantities of
potassium chromate, and gives, on evaporation, potassium carbonate containing
chromium.
In order from this to obtain potassium carbonate free from chromium, the
solution or final lye is saturated with carbonic acid under cooling when the
potassium bicarbonate will separate in crystalline form (owing to the large pro-
portion of the carbonate present as compared to the potassium chromate), while
the 'chromium remains as bichromate in the solution.
By repeated precipitation by means of carbonic acid the bicarbonate is obtained
free from chromium, and it is finally separated into carbonate and carbonic acid.
Instead of precipitating twice by means of carbonic acid, the chromate can also
be removed by means of alkaline reducing agents, preferably potassium sulphide
or the like, the chromate being thereby converted into insoluble chromium oxide.
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
1. The process for the production of potassium carbonate from potassium sulphate
consisting in first converting a mixture of equal molecules of potassium sulphate
and potassium bichromate in aqueous solution under 100° C. by means of calcium
hydrate or barium or strontium hydrate, into potassium chromate, then saturating
with carbonic acid the potassium chromate in a concentrated and cooled condition
after separating therefrom the gypsum, or barium or strontium sulphate, then
separating the precipitated potassium bichromate from potassium bicarbonate
produced, then evaporating the latter, whereby the potassium bichromate remaining
in solution will be mostly separated as potassium chromate, and lastly obtaining
from the remaining final lye by further evaporation, a potassium carbonate
containing chromium.
2. A process for purifying the potassium carbonate containing chromium obtained
as set forth in the preceding claim, consisting in saturating with carbonic acid the
cold saturated aqueous solution thereof, or the final lye containing the same referred
to, whereby potassium bicarbonate is separated while the chromate remains in
solution in the form of bichromate, the potassium bicarbonate being lastly converted
into carbonate by heating.
3. The modification of the process referred to in the preceding claim consisting

page_text: in effecting the separation of the chromate from the final lye referred to in the
first claim in the form of chromium oxide by means of alkaline reducing agents, .
such as alkaline sulphides and the like.
1002
ABEL & IMRAY,
Agents for the Applicant.