Improvements in Bleaching.
Year: 1892

page_text: Date of Application, 4th Mar., 1892-Accepted, 5th Nov., 1892
Improvements in Bleaching.
We, HEINRICH THIES of Laaken near Barmen-Rittershausen, in the Kingdom
of Prussia, Empire of Germany and EMIL HERZIG, of 15, Belforterstrasse,
Mulhouse, Alsace, in the German Empire, Chemists 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 :-
Our invention relates to an improvement in the preparatory treatment of fibrous
materials, prior to scalding the same, as described in our British Patent No. 12950,
dated Dec. 8th, 1890.
The preparatory treatment, as described in the said Patent, consists in precipi-
tating alkaline earths on the fibres and in steaming the same hereafter, the object
of these operations is to protect the material from the noxious influence of the
boiling caustic alkaline lye by expelling the air from the fibres.
We have now made experiments with the mentioned preparatory treatment,
and have found that the same may be replaced with equally good results,
and sometimes with more advantageous effect, by the treatment described
hereinafter.
Instead of forming a deposit of alkaline earths on the fibres and of steaming
the same subsequently, we employ another method for the purpose of expelling
the air from the fibres, said method consisting in subjecting to a pressure the
materials placed in the scalding vessel filled with alkaline liquid which thereby
absorbs the air adhering to the fibres, and in driving hereafter the said alkaline
liquid into an accessory reservoir, where it is freed of the absorbed air by reducing
the pressure, and whence it is drawn back into the scalding vessel in order to undergo
the same operations again.
By means of this circulation of the alkaline liquid the absorption of air by
alternately applying and removing the pressure to and from the alkaline liquid is
effected in a very thorough manner, and we secure a still better result by admixing
to the alkaline liquid towards the end of the operation, such chemicals as will readily
combine with oxygen.
Immediately after this treatment, or during the last part of the same, the scalding
vessel containing the materials and the alkaline liquid is lieated, whereupon the
boiling lye is introduced into the same.
The process is therefore performed as follows: We place the materials within
the scalding vessel, and fill the latter with alkaline liquid, which we pump into the
same from a reservoir filled with alkaline liquid and hermetically closed. Besides
the pipe through which the alkaline liquid is thus forced, we provide a second
pipe, connecting the top of the scalding vessel and of the reservoir, and during
the filling of the scalding vessel a suitable cock is turned so as to cut off the
communication by means of the said second pipe. As the alkaline liquid is driven
out of the reservoir by means of the pump, a vacuum is formed in the upper
part of the same; and the scalding vessel being closed, the alkaline liquid
within the same is compressed by the action of the pump and therefore absorbs
the air adhering to the fibres. Then the cock in the mentioned pipe is turned so
as to establish communication between the scalding vessel and the reservoir, and
the water from the former rushes into the vacuum of the latter. Then the alkaline
liquid being relieved of the pressure, allows the air it has absorbed to escape; here-
after the alkaline liquid is pumped back into the scalding vessel. Thus a continuous
circulation is maintained.
In order to remove the last traces of air (that is to say, of oxygen) we add to

page_text: the alkaline liquid a chemical compound which combines with oxygen, for instance
a sulphite. At the same time as the alkaline liquid circulates the scalding vessel is
heated, and we may also introduce soda into the same during this heating, in order
to remove part of the impurities.
This preparatory treatment being terminated, we draw off from the scalding
vessel by means of a pump or of steam a sufficient quantity of liquid, so that the
most appropriate amount of lye is present in the scalding vessel alter letting in the
concentrated caustic lye.
And in order that our invention may be more fully understood we have caused
to be appended hereto one sheet of drawings, in which
Fig. 1 is an elevation, and Fig. 2 a top view of the apparatus employed for
carrying our improved method into effect, like letters of reference denoting like
parts in both views.
A is a vessel or vat in which the vacuum is produced, and receiving the solutions
with which the goods placed in the vessel B are to be treated. Both vessels are
connected to an oscillating pump and to an intermediary tubular boiler C, which
serves for heating the circulating liquids. Four three-way cocks 2 3 4 and 9 effect
the communication between the said three vessels and the connecting pipes. The
single-way cocks 1, 5, 10, and 11 serve the purpose of shutting off or draining the
liquids. Cocks 7 and 8 are for letting steain in, cocks 6 and 9 for allowing the
escape of air or steam.
The operation of the apparatus is as follows:-
Vessel A is filled with an alkaline liquid to which reducing agents may be
admixed, such as bisulphite, or grape-sugar. In most cases the scalding lye left
from previous operations may be employed, as it contains a sufficient proportion of
non-saponified alkali, of sugar, and of pectine bodies.
The goods to be bleached are introduced into the vessel B. The liquid contained
in A is drawn off through cocks 1 and 2 by means of the pump and hereafter forced
upwards through the tubular boiler C and the cocks 3 and 4 into the vessel B.
The air escapes at the top of the latter through cock 6; as soon as the liquid gets
to this cock, the latter is closed. Thereupon the pressure in vessel B is increased
by means of the pump up to about 2 atmospheres, and then the cock 5 is opened so
as to afford a communication between the vessels A and B. Cock 5 is only opened to
such an extent, that the pressure in B remains constant, while the liquid flows back
into A through the top pipe. In consequence of the action of the pump, a vacuum
is formed in A, and the liquid, having absorbed the gases (especially the air)
adhering to the goods owing to the pressure to which said liquid was subjected, is
freed of these gases by the reduction of pressure. The liquid is then pumped back
into the vessel B, thence again drawn into A by the production of a vacuum, and
thus the intermitted circulation is continued till a manometer provided on vessel A
(said manometer is not shown on the drawing) indicates no appreciable change in
the condition of the gas (air) or liquid contained in said vessel. Hereafter the
circulation liquid is heated by means of the tubular boiler C till the contents of the
latter attain the boiling point, or a pressure of 1 atmospheres. Thereupon the liquid
is driven out of B. through cock II by means of steam or by means of the pump.-
Meanwhile the bucking or scalding lye is boiled in A; for 5000 kilogrammes of
cotton we take for instance about 6000 litres of clear caustic lye, which is prepared
by mixing with water 200 kilogrammes of soda containing 98% of carbonate of
soda, and 150 kilogrammes of caustic lime. After having subjected this lye to a
pressure of two atmospheres in vessel A, it is pumped through the cocks 1 and 2,
tubular boiler C and the cock 3 into the upper part of B. The pressure in A
is reduced thereby, and the pressure in 13 increased. When the level of the
liquid in vessel A sinks to the bottom-which may be ascertained by the aid of
the gauge-glass D-, the cock 10 is opened so as to allow the lye to flow back
from the lower part of vessel B through cock 4 into vessel A. By employing
a difference of pressure of about 1 atmospheres (in the vessels A and B), a
very rapid circulation is obtained, which is already found in our Patent No. 12950%,

page_text: but which has been greatly improved in our present invention. This difference of
pressure is kept constant by heating the boiler C and by blowing off steam through
the cock 9 at the top of vessel A.
After the circulation has been kept up for about three hours the scalding even
of very reluctant goods is completed. The bleaching liquid is collected in A, to
be used at the following operation, and the contents of the vessel B are washed
with water, which is admitted through pipe 6. As a rule the goods are sufficiently
white when taken out of the vessel B, so that it is but necessary to wash the
goods first in a weak acid bath and then in water in order to remove the remainder
of alkali and to obtain goods bleached thoroughly. When the fibrous materials
are strongly soiled, they may be treated with chloride of lime in the vessel B; but
the quantity used is greatly reduced, being only of the amount required hitherto.
The objects of this process are similar to those stated in our Patent 129500,
and consist:-
1. In protecting the fibrous materials against the noxious influence of the caustic
alkaline lye (ie. against shrinking and oxidation);
2. In bringing the fibrous material into a condition called reduction in
chemisty, whereby indigo and azo-colours may be transformed into the colourless
soluble compounds, and the natural colouring matters of the fibres permit of better
solution ;
3. In securing the possibility of utilizing the alkali still contained in the scalding
lye which has been used once;
4. In effecting a better circulation of the lye by a suitable difference of pressures,
and a better concentration of the same by the escape of steam.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what
we claim is :-
:-
:
In bleaching The preparatory treatment of the fibres, prior to the scalding
operation, by means of alkaline liquid alternately subjected to pressure and drawn
into a vacuum, and of chemicals readily combining with oxygen, which are added
to said alkaline liquid, substantially and for the purpose as hereinbefore described.
Dated this 3rd day of March 1902.
HEINRICH THIES.
EMIL HERZIG.
By F. Bosshardt & Co.,
4, Corporation Street, Manchester, Agents for the Applicants.