Improvements in the Manufacture of Caustic Soda and Potash, and of Nitrio and Sulphuric Acids.
Year: 1894

page_text: Date of Application, 14th Apr., 1894-Accepted, 19th May, 1894
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Caustic Soda and Potash, and
of Nitrio and Sulphuric Acids.
I, WILLIAM GARROWAY, of Netherfield Chemical Works, in the County of
Lanark, North Britain, Chemical 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 :-
This invention relates to Improvements in the Manufacture of Caustic Soda and
Potash, and of Nitric and Sulphuric Acids and has for its object to manufacture
caustic soda and potash in a cheap and efficient manner without the use of any
expensive reagent, and at the same time to obtain nitric and nitrous acids for the
manufacture of vitriol, etc. For this purpose I take nitrate of soda or of potash
and burnt lime or magnesia, and heat them in a suitable furnace or retort to redness,
and pass superheated steam over or through the heated mixture. Nitric acid is
evolved and may be condensed by known means, or sent direct from the retort or
vessel, in which it is evolved, to the chambers for the manufacture of the vitriol.
This retort or vessel, when the process is employed in connection with the
production of vitriol, may be advantageously placed on the pyrite burners or
sulphur burners in order to utilize their heat. The mixture of caustic soda or
potash and burut lime that remains in the retorts is withdrawn when the action
has ceased, and treated with water and steam. The lime remains for the most
part insoluble, while the caustic soda or potash dissolves and forms a solution
which is then filtered or settled to separate as completely as possible any traces of
suspended lime and may be either disposed of directly or boiled down or concentrated
and heated to produce caustic soda or potash, or treated in any other well-
known way.
In carrying out my invention I proceed as follows:-I mix together two hundred
and fifty parts by weight or thereby of burnt lime in the state of powder with one
hundred parts by weight or thereby of nitrate of soda, and place this mixture in a
retort or vessel, preferably of cast iron, which in the case of the manufacture of
vitriol is placed or built in the kiln and heated by the flame of the burning pyrites
or sulphur passing over and around it. I then pass superheated steam through
the hot charge, (and a little hot air when required), which effects the decomposition,
nitric acid being evolved, which is conducted directly into the vitriol chamber or
Glover tower, or it is condensed for sale or treated in any other known way. The
mixture of caustic soda and lime remaining in the retort is now withdrawn, treated
with water, and steam if necessary, by which a strong solution of caustic soda is
obtained, while the lime for the most part remains insoluble. The vessels used for
this purpose may be of iron or of any description commonly used in the treatment
or manufacture of caustic soda. The insoluble lime thus obtained, being in the
caustic state, I dry it and heat it up to redness, by which it is rendered available
for the next and succeeding operations.
When I desire to make caustic potash by my process, I employ nitrate of potash
in place of nitrate of soda, and although it is not necessary to alter the proportions
of the ingredients used 1 find that I can accomplish the desired object with
somewhat less lime than when nitrate of soda is employed.
A little moisture in the nitrate does little or no harm, but as commercial nitrate
of potash and of soda both contain variable proportions of water I prefer to dry
them before they are used in the process.
In thus producing caustic soda, caustic potash and nitric acid by improved

page_text: process, although I prefer to use lime to mix with the nitrate, I have found that
magnesia, baryta, and strontia serve the purpose very well, they being alkaline
earths like lime, and belonging to the same chemical group of bodies. They are
more expensive at first than lime but this is not of much consequence seeing that
the process leaves them in a condition available for use in successive operations.
In carrying out my invention I do not confine myself to the exact proportions
of the ingredients above stated. I find that while the reactions take place within
wide limits, the above proportions are very suitable for the process.
It will thus be seen that my process for the production of caustic soda, caustic
potash and nitric acid has great advantages over the processes hitherto in use.
For example in making caustic soda or potash by the ordinary process known as
the "Leblanc" process at least three stages or steps are necessary (1) The
preparation of alkaline sulphate by the action of sulphuric acid on the chloride,
(2) The production of alkaline carbonate by furnacing the sulphate with coal and
limestone and 3. The causticising of the carbonate by means of lime. There is
also a large amount of alkali waste produced, which is a disadvantage. My
improved process, however is accomplished in one operation and without producing
any waste material. Again in the manufacture of caustic soda from the carbonate
of soda produced in the well-known "Ammonia-soda" process three steps are also
necessary, (1) The formation of bi-carbonate of soda by acting on common salt
with ammonia and carbonic acid. (2) The production of carbonate of soda from
the bicarbonate by heating, and (3) The causticising of the carbonate so obtained;
whereas my improved process consists of only one operation. Again, in the
manufacture of nitric acid the method hitherto employed in practice has been to
act upon nitrate of soda with sulphuric acid and heat, by which nitric acid and
"nitre cake are produced, the latter being a product of comparatively little
value, but in my improved process all the products are valuable.
"
The apparatus and plant I employ, when my process is connected with the vitriol
manufacture will be readily understood from the accompanying drawings and the
following description.
Figure 1 is an elevation shown partly in section.
Figure 2 is a cross section.
A is the retort of which there may be any number, B the charging door by which
the mixed materials are introduced into the retort, C a steam pipe, D, and D¹ pipes
leading to chambers or tower, E E drawing off or discharging doors. F is the
superheated steam supply pipe. G G pyrites or sulphur burners, H Glover tower.
Two retorts may be used for a set of six chambers, but that of course will
depend on the capacity of both the retorts and the chambers. Thus one retort
may be opened and charged without in the least interfering with the process going
on in the other.
When the process is not intended to be applied in connection with the manufacture
of vitriol, the retorts or vessels may be heated by the combustion of ordinary fuel
in any suitable furnace or in any well-known manner.
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. The preparation of caustic soda or potash by passing superheated steam
through a heated mixture of burnt lime, magnesia baryta or strontia and nitrate of
soda or nitrate of potash in a manner substantially as hereinbefore described.
Second. The preparation of nitric acid by passing superheated steam through a
heated mixture of burnt lime, magnesia baryta or strontia and nitrate of soda, or
nitrate of potash in a manner substantially as herein before described.
Third. The simultaneous preparation of caustic soda or caustic potash and nitric
acid by passing superheated steam through a heated mixture of burnt lime,
magnesia, baryta or strontia and nitrate of soda or nitrate of potash, in a manner
substantially as hereinbefore described.

page_text: Fourth. The use, in the vitriol chamber or in the Glover tower, of the nitric
acid produced by my improved process, in a manner substantially as hereinbefore
described.
Dated this 13th dox of Anril 1894
JOHNSONS,
115, St. Vincent Street, Glasgow, Applicant's Agents.