An Improved Method of Purifying the Liquid which has been Used in the Manufacture of Cellulose, and the Production of Useful Products therefrom.
Year: 1892

page_text: Date of Application, 10th Feb., 1892-Accepted, 23rd Apr., 1892
COMPLETE SPECIFICATION.
An Improved Method of Purifying the Liquid which has been Used
in the Manufacture of Cellulose, and the Production of Useful
Products therefrom.
I, VIGGO BENTNER DREWSEN of Bohnsdalen in the Kingdom of Norway,
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 :-
If the liquid, which has been used in the manufacture of sulphite cellulose, which
liquid has a strongly marked acid reaction is treated with caustic lime (slaked
lime) Ca (OH,) or other caustic alkalies it will, with a small excess of free
sulphurous acid (H2SO₁) form calcium monosulphite at the same time separating
a small amount of organic substances, that were dissolved in the sour liquid.
The reaction is the same at the normal as at the boiling temperature. The said
reaction is entirely different when the refuse liquid is heated with caustic lime or
other caustic alkalies, for example of barium, strontium, magnesium at a higher
temperature and under pressure in a closed vessel. By this means the lime is
capable of dividing the incrusted substances dissolved in the liquid and I obtain a
precipitate consisting of calcium monosulphite (CaSO,) or barium, strontium or
magnesium monosulphite, gypsum and the lime combinations of the incrusted
organic substances. If the precipitate which is obtained by the treatment at
90 lbs. pressure is separated from the liquid by filtration, and treated with hydro-
chloric acid (HCI) sulphuric acid (H,SO) or other strong acids, a strong evolution
of sulphurous acid will be observed, leaving behind a precipitate insoluble in water
and acids and composed of organic matter mixed with some sulphate of calcium
(gypsum).
The sulphurous acid, which has been regained in this way can again be used
for the production of sulphite of lime liquid or calcium-bisulphite liquid.
The contents of the vessel is filtered through a common filter press, and the light
yellow liquid, that runs off is if necessary, treated with carbonic acid to weaken the
alkalinity. The filtered precipitate is used instead of limestone or limewater for
the production of bisulphite-liquid, whereby the organic substances are obtained as
bye products. The light yellow liquid filtered from the original lime precipitate
appears on evaporation only to contain a very small fractional part of the
substances contained in the refuse liquid as both the easier separable sulphur com-
binations and the bulk of organic, so called incrusted substances are separated. It
is therefore possible by means of a medium as cheap as caustic lime first to purify
the refuse liquid and make it entirely harmless and secondly to obtain important
industrial products.
The improved method is carried into practice as follows: When the boiling is
completed the refuse liquid is under pressure blown over into a vessel provided
with a stirrer where the necessary amount of lime as free from carbonic acid as
possible is introduced.
On account of the acid being suddenly neutralized, this vessel may be made of
iron. When the liquid is entirely blown over into the vessel, the steam is turned
on and the stirrer put in motion, and the temperature is kept up until by testing it
is ascertained that the reaction is finished. The contents of the vessel are then
filtered through a filter-press. The light yellow liquid of alkaline reaction is if
necessary treated with carbonic acid (taken from the products of combustion of a
chimney by means of a Curtings injector) to weaken the alkalinity.
The filtered precipitate consisting of calcium monosulphite, gypsum and the
lime combinations of the organic incrusted substances is used instead of limestone

page_text: or limewater for producing the bisulphite liquid. Chiefly the organic substances
which are filtered away in a filterpress remain undissolved while the filtrate
returns in the manufacture for the boiling of wood, just as common bisulphite
liquid. In this manner, from one fourth to one half of the sulphur employed is
regained.
The organic substances which are obtained by this method can be used for many
purposes.
As will be seen by the foregoing description, this invention is an important
advance, in the first place considerable masses of sulphur can be saved at a small
cost and secondly the incrusted substances are separated in a form that gives them
extensive use while the waste water which often causes great injury is made
entirely harmless.
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 herein described method of purifying the refuse liquid from the
manufacture of sulphite cellulose and producing useful products from the same,
treating said liquid (spent bisulphite solution) with caustic lime or other caustic
alkalies for example of barium, strontium, magnesium at a temperature above
100° C. and higher pressure in closed vessels by which means the organic sulphur
combinations of said liquid are thus separated, so that a valueless and harmless
liquid is obtained together with a precipitate consisting of calcium monosulphite
(or sulphite of barium strontium, magnesium) and lime combinations of the
incrusted substances derived from the organic parts of the wood, and the use of
this precipitate (calcium monosulphite and lime combinations) for the production
of calcium bisulphite liquid instead of limestone or caustic lime by treatment with
sulphurous acid, so that the organic substances are obtained in a form insoluble in
water and acid, and treating the precipitate with a stronger acid for instance
sulphuric acid (H.SO) or hydrochloric acid (HCl) whereby sulphurous acid
escapes and the organic substances which are insoluble in water and acids is left
behind substantially as set forth.
Second. The treatment by the method hereinbefore described of spent bisulphite
solution with caustic lime or other caustic alkalies for example of barium,
strontium, magnesium in closed vessels at a temperature above 100° C. and at high
pressure.
Third. The use in the method hereinbefore described of the obtained sediment
of calcium monosulphite and organic lime combinations instead of caustic lime
for the production of calcium bisulphite liquid by treatment with sulphurous
acid.
Fourth. The treatment by the method hereinbefore described of the precipitate
with a stronger acid for instance sulphuric acid (H₂SO) or hydrochloric
acid (HCl) whereby sulphurous acid escapes and the organic substances which
are insoluble in water and acids is left behind substantially as set forth.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.