AN IMPROVED METHOD OR PROCESS FOR THE MANUFACTURE OF CARBONATE OF SODA OR SODA-ASH
Year: 1885

page_text: I, HENRY HARRIS Lake, of the firm of Haseltine, Lake & Co, Patent Agents,
Southampton Buildings, in the County of Middlesex, do hereby declare the nature
of my invention for "AN IMPROVED METHOD OR PROCESS FOR THE MANUFACTURE
OF CARBONATE OF SODA OR SODA-ASH" 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 the manufacture of carbonate of soda or soda ash
from common salt, and has for its object to produce the carbonate of soda in a
simpler, more convenient and less expensive manner than heretofore, as hereinafter
described.
The said invention is based upon the discovery that sulphate of soda, when
exposed at a low red heat to a current of carbon-monoxide in the presence of a
sufficient volume of carbon-dioxide, is decomposed and converted into carbonate of
soda, while the sulphur is driven off in the form of sulphurous acid.
In practising this invention the sulphate of soda may be produced in any known
or suitable manner, but I prefer to produce it by subjecting common salt, in a
battery of cast-iron cylinders, to the action of sulphurous acid according to the
well known "Hargreaves" method. These cylinders are connected by suitable gas
conduits, so that the sulphurous acid gas derived from roasting pyrites or burning
sulphur, is passed successively through the several cylinders. The gas enters first
the cylinder containing salt which is most nearly converted into sulphate of soda,
and passes then successively through the several cylinders, the charge, in each
following cylinder, containing a smaller proportion of sulphate of soda until the last
cylinder is reached which contains fresh unconverted salt. The cylinder containing
the finished sulphate of soda is disconnected from the battery through which the
current of sulphurous acid gas flows. All of this is old and well known.
In the ordinary method of manufacturing carbonate of soda by the "Le Blanc'
process, the sulphate of soda is removed from the cylinder when finished, and then
converted into carbonate of soda by melting the salt together with carbon and
carbonate of lime, leaching out the soda and evaporating the liquid &c.
According to the best method of practising this invention, the sulphate of soda
is not removed from the cylinder when finished, but a current of carbon dioxide
and carbon monoxide, one equivalent of each, is caused to flow through the cylinder
containing the sulphate of soda, the latter being kept at a low red heat, below the
melting point of both sulphate and carbonate of soda. The mixture of gases
required for this process is readily generated by burning coal or other carbonaceous

page_text: fuel free of bydrogen in a suitable furnace, either by a natural draught or blast, the
column of coal being kept so high that only carbon-monoxide is produced by the
combustion taking place at the base of the column. A jet of air is admitted to
the carbon-monoxide escaping from the fuel, and the quantity of air admitted is so
regulated that only a portion of the carbon-monoxide is burnt and converted into
carbon-dioxide, so that the gas escaping from the generating furnace consists of a
mixture of one equivalent of carbon-monoxide and one of carbon-dioxide.
The air blast or draft of the furnace and the air jet admitted to the gas conduit
are controlled by suitable valves or dampers, so that the composition of the gas can
be regulated by the operator..
Care should be taken that the proper proportion of carbon-dioxide is maintained,
because when the gas mixture is deficient in carbon-dioxide, sulphur is evaporated
instead of sulphuric acid and, sodium sulphide is formed which is fusible at a low
temperature and melts and fills the pores of the salt under treatment, whereby the
process of conversion is not only retarded, but the sulphide so formed and the
unconverted sulphate enclosed by the fused sulphide represent so much lost
material.
I employ at least one equivalent of carbon-dioxide and one equivalent of
monoxide of carbon to one equivalent of sulphate of soda, but a small excess of
carbon-dioxide is desirable. The reaction taking place under this treatment may
be represented by the following formula:
Na₂ SO + CO₂+ CO = N₁₂ CO₂ + So, + Co
An excess of carbon dioxide is less objectionable than an excess of carbon-
monoxide, because the excess of carbon-dioxide operates principally as an un-
necessary diluting agent, while an excess of carbon-monoxide defeats the object of
the process altogether.
This gas mixture is drawn, by a suitable exhaust fan, through the cylinder
containing the sulphate of soda and converts the sulphate of soda into carbonate of
soda, sulphurous acid gas being liberated and drawn off by the exhaust pump
together with the nitrogen. The conversion is completed when the escaping gases
show no trace of sulphurous acid.
The sulphurous acid gas which is liberated in this process is conducted to the
battery of cylinders in which the salt is converted into sulphate of soda and utilized
for this conversion together with the sulphurous acid gas which is freshly generated
as above described, whereby a great saving in the required quantity of fresh
sulphurous acid gas is effected. The sulphur contained in the sulphate of soda is
in this manner to a large extent used over, whereby the cost of the carbonate of
soda is greatly reduced.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, as communicated to
me by my foreign correspondents, I declare that what I claim is
The process herein described, of converting sulphate of soda into carbonate of
soda (without converting the sulphate of soda into sulphide of sodium), which
process consists in heating the sulphate of soda in a suitable vessel to a low red
heat below the melting point of the sulphate, and causing a current of carbon-
dioxide and carbon-monoxide; substantially in the proportion specified, to flow
through the heated sulphate, forming carbonate of soda and sulphurous acid;
substantially as set forth.
Dated thia 18th day of Tuns 100%.