Improved Processes for the Nitration and the Denitration of Cellulose and for Regaining the Acids Employed, and Apparatus employed in connection therewith.
Year: 1890

page_text: Date of Application, 8th Apr., 1890
Complete Specification Left, 6th Jan., 1891-Accepted, 4th Apr., 1891
TROVISIONAL SPECIFICATION.
Improved Processes for the Nitration and the Denitration of
Cellulose and for Regaining the Acids Employed, and Apparatus
employed in connection therewith.
I, HILAIRE DE CHARDONNET, of 23, Boulevard de Strasbourg, Paris, France,
do hereby declare the nature of this invention to be as follows :-
I. NITRATION.
Notwithstanding the great number of processes proposed heretofore for the
industrial preparation of pyroxyline, no known method of manufacture gives uniform
results and pure pyroxyline. The processes which form the subject of my present
invention permit of the reduction to a minimum the expenditure of acids and the
obtaining of pure pyroxyline in which the nitration of the separate fibres only differs
to the extent of a very small percentage.
The nitration is effected, as ordinarily, by steeping cellulose in a suitable mixture
of sulphuric and nitric acids (for example 12 litres of nitric acid of the density
of 1.37, and 20 litres of sulphuric acid of the density of 1-83). My process includes
however special modes of operation which I will now explain.
Recuperation of the acids-This method, whereby almost the whole of the acids
can be recuperated, consists in causing about ths of the mixture flowing off, from
the centrifugal apparatus to be used over again in its existing condition, the other
fourth part of the dipping bath consists of a mixture in the same proportions of
fresh acids, but with the concentration of the nitric acid increased to 1.50 instead of
from 1.36 to 1.38.
The old acids could also be strengthened, with about one third of fresh mixture in
which the nitric acid is of the strength of from 1.40 to 1.42. The excess of old
acid is revivified by distillation; by heating the mixture of acids, the nitric acid
passes off, gradually decreasing in strength as the temperature is raised to about
200° C., without sudden action. It will then be sufficient to heat the sulphuric acid
as is ordinarily done, for concentrating it. This distillation may be rendered
continuous by the following means.
Two chambers or alembics provided with hoods and conducting tubes of cast iron
and having a thickness of from 20 to 30 mm., are heated by two fires. These fires
might be combined into one by a suitable arrangement; the second alembic would
then be heated directly and the first alembic by the return flame. The tube which
connects the two alembics is made to pass down to near the bottom of the first one
and opens a little below the liquid in the second one. A discharge tube is so
arranged as to cause the liquid to flow off from the second alembic as soon as it
attains a certain level, the tube being of siphon form, which charges itself; the
inner limb of this siphon passes down to near the bottom so as to discharge the
liquid from that point. The joints are all made to withstand pressure, are lined
with asbestos, and are secured either by screw bolts, or by means of clamps.
Thermometers are made to pass into the alembics through stuffing boxes cast on the
hoods of the same. The discharge tubes in the hoods conduct the vapours into
receivers, worms or cases, where they are condensed.
The mixture of sulphuric and nitric acids which has already been used is led into
the first alembic through a pipe from a reservoir with constant level or from a
Mariottés vessel, the supply being regulated by an earthenware cock. The first
alembic is heated to a constant temperature of from 130° to 170° C. according to
the degree of concentration of the nitric acid which it is desired to obtain. This
017

page_text: concentrated acid separates from the mixture as it is introduced into the alembic;
it distils off and is collected at the bottom of the first worm.
The purified sulphuric acid descends to the bottom of the vessel. But above
206° C. this acid still retains some nitric acid which must be removed. This is
effected in the second alembic, which is maintained at a temperature of from 200°
to 210° C., and in which the sulphuric acid is freed from the remainder of the nitric
acid and the excess of water; weak nitric acid distills over and can be collected
while the sulphuric acid concentrated to about 62° Bé. descends to the bottom of
the vessel from which it is removed by the above described siphon arrangement.
If it be desired to recuperate not only the concentrated nitric acid, but also the
monohydrated sulphuric acid, the siphon must discharge into a platinum or glass
vessel similar to those employed in sulphuric acid works, in which the concentration
will be completed in the usual manner.
Washing-After having drained the pyroxyline coming from the acid bath, so as
to extract as much acid as possible, it is washed in a copious supply of water while
avoiding all rise of temperature. The nitric acid left in the mass by the centrifugal
apparatus may be regained in the following manner. The water in which the first
rinsing is effected, can be neutralised either by adding each time an alkaline
carbonate, or by placing at the bottom of the tank some fragments of calcium.
A fresh quantity of pyroxyline can then be rinsed in the same water without
inconvenience, and this may be done successively until the water is sufficiently
charged with nitrate to be advantageously evaporated.
The nitrate of lime is if requisite transformed into alkaline nitrate by means of
sulphate of soda (which is always present in abundance in the manufacture of nitric
acid) and the nitrate of soda, revivified, can again serve for the manufacture of
nitric acid.
After the first rinsing, the mass is placed in a centrifugal apparatus arranged so
that it can be charged successively with fresh water. The mass is thoroughly
drained and is then washed in a copious supply of water while turning the centrifugal
apparatus slowly; these successive washings and drainings by centrifugal action
form an essential feature of my improved process; they enable a perfect washing
to be attained after from 12 to 15 such alternations.
These operations should be carried on with as pure and cold a supply of water as
possible.
Purification and bleaching-If the cellulose be bleached with chlorine or with
alkalies before the nitration, it will be altered, and pyroxylines without cohesive
strength are obtained. Good results are obtained on the other hand if the
completed pyroxyline is purified while observing the following precautions.
The pyroxyline is placed in a large quantity of water with about one tenth part
of its weight of chloride of lime.
Water acidulated with nitric or other acid is added until the chloride of lime is
dissolved; the mass is then washed, submitted to centrifugal action; and dried.
II. DENITRATION.
Various substances when digested with pyroxylines have the property of reducing
it and bringing it back more or less rapilly and completely to the state of pure
cellulose.
(a) Nitric acid-Nitric acid, more or less concentrated and warm, acts in a
regular manner for this purpose. Thus-on-digesting-in-nitric acid of 36° Bé. and at
a temperature of from 30° to 35° C. there is obtained in a few hours a mass which
only contains about 6 per cent. of nitrogen, and which has lost the greater part of
the chemical properties of pyroxyline; it is no longer soluble, in particular, in any
of the solvents of nitrated cellulose.
The combustibility is also largely diminished.
(6) Sulphides, polysulphides-The pyroxylines are completely deprived of their
nitric acid on being digested in contact with a concentrated solution of sulphides, or
rather of polysulphides of an alkaline, alkaline earthy, or earthy nature.

page_text: If there is employed for example commercial sulphide of potassium, in which
pyroxyline fibres are plunged for from 12 to 24 hours, there is obtained at the
end of this time a cellulose free from nitric acid which is washed and dried.
(c) Sulpho carbonates-The alkaline, earthy alkaline, or earthy sulpho carbonates
also bring back the pyroxyline fibres to the condition of pure cellulose. If there
be taken a solution of sulpho carbonate of potash for example, of 36° Bé, there will
be obtained at the end of 12 hours at 35° C. or of 36 hours in the cold, white
brilliant fibres which have retained all their strength, and have the composition
of cotton or hemp, not being more combustible and having a somewhat greater
density.
cent.
(d) Sulphohydrates of ammonia-Sulphohydrate of ammonia may serve for the
denitration of pyroxyline fibres. A pyroxyline for example having about 12
per
of nitrogen if digested with commercial sulphohydrate of ammonia for from 12
to 15 hours, at a temperature of from 30° to 34° C. gradually loses its nitric acid,
without losing its physical properties.
This reagent does not act like any of the others, that is, it does not attack the
fibres of pure cellulose, either after a long digestion in the cold, nor when digested
for from 12 to 24 hours at 60° to 70°. It does also not attack the other textile
fibres, and can serve for denitrating pyroxylines mixed with other substances.
The processes of denitration can be considerably shortened by previously
impregnating the pyroxyline with an acid which softens it and commences the
decomposition of the reagents, nitric, acetic, phosphoric acids &c. &c. may be used
for this purpose.
Dated this 8th day of April 1890.
ABEL & IMRAY,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improved Processes for the Nitration and the Denitration of
Cellulose and for Regaining the Acids Employed, and Apparatus
employed in connection therewith.
I, HILAIRE DE CHARDONNET, of 23, Boulevard de Strasbourg, Paris, France,
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:-
I. NITRATION.
Notwithstanding the great number of processes proposed heretofore for the
industrial preparation of pyroxyline, no known method of manufacture gives uniform
results and pure pyroxyline. The processes which form the subject of my present
invention permit of the reduction to a minimum the expenditure of acids and the
obtaining of pure pyroxyline, in which the nitration of the separate fibres only
differs to the extent of a very small percentage.
The nitration is effected as ordinarily by steeping cellulose in a suitable mixture
of sulphuric and nitric acids (for example 12 litres of nitric acid of the density
of 137 and 20 litres of sulphuric acid of the density of 1.83). My process
includes however special modes of operation, which I will now explain.
Recuperation of the acids-This method whereby almost the whole of the acids
can be recuperated, consists in causing about ths of the mixture flowing off from
the centrifugal apparatus, to be used over again in its existing condition, the other
fourth part of the dipping bath consists of a mixture in the same proportions of
fresh acids, but with the concentration of the nitric acid increased to 1.50 instead of.
from 1.36 to 1.38.
The old acids could also be strengthened with about one third of fresh mixture in

page_text: which the nitric acid is of the strength of from 1-40 to 1.42. The excess of old acid
is revivified by distillation by heating the mixture of acids the nitric acid passes off
gradually decreasing in strength as the temperature is raised to about 200° C.
without sudden action. It will then be sufficient to heat the sulphuric acid as is
ordinarily done for concentrating it. This distillation may be rendered continuous
by the following 'means:
Two chambers or alembics A. E provided with hoods and conducting tubes of
cast iron and having a thickness of from 20 to 30 mm. are heated by two fires F F'.
These fires might be combined into one by a suitable arrangement, the alembic E
would then be heated directly, and the alembic A by the return flame. The tube D
which connects the two alembics is made to pass down to near the bottom of the
first one, and opens a little below the liquid in the second one a discharge tube K is
so arranged as to cause the liquid to flow off from the second alembic as soon as it
attains a certain level, the tube being of siphon form, which charges itself; the
inner limb of this siphon passes down to near the bottom, so as to discharge the
liquid from that point. The joints are all made to withstand pressure, are lined
with asbestos and are secured either by screw bolts, or by means of clamps P P.
Thermometers T T are made to pass into the alembics through stuffing boxes cast
on the hoods of the same. The discharge tubes B I conduct the vapours into
receivers, worms or cases, where they are condensed.
The mixture of sulphuric and nitric acids which has already been used is led into
the first alembic, through a pipe C from a reservoir with constant level or from a
Mariottes vessel, the supply being regulated by an earthenware cock. The first
alembic A is heated to a constant temperature of from 130° to 170° according to
the degree of concentration of the nitric acid which it is desired to obtain. This
concentrated acid separates from the mixture as it is introduced into the alembic, it
distills off and is collected at the bottom of the first worm.
The purified sulphuric acid descends to the bottom of the vessel. But above
206° C. this acid still retains some nitric acid which must be removed. This is
effected in the second alembic, which is maintained at a temperature of from 200°
to 210° C., and in which the sulphuric acid is freed from the remainder of the nitric
acid and the excess of water, weak nitric acid distills over and can be collected
while the sulphuric acid concentrated to about 62° Bé. descends to the bottom of the
vessel from which it is removed by the above described siphon arrangement.
If it be desired to recuperate not only the concentrated nitric acid, but also the
monohydrated sulphuric acid, the siphon must discharge into a platinum or glass
vessel, similar to those employed in sulphuric acid works, in which the concentration
will be completed in the usual manner.
Washing After having drained the pyroxyline coming from the acid bath, so as
to extract as much acid as possible, it is washed in a copious supply of water while
avoiding all rise of temperature. The nitric acid left in the mass by the centrifugal
apparatus may be regained in the following manner. The water in which the first
rinsing is effected can be neutralised either by adding each time an alkaline
carbonate or by placing at the bottom of the tank some fragments of limestone.
A fresh quantity of pyroxyline can then be rinsed in the same water without
inconvenience and this may be done successively until the water is sufficiently
charged with nitrate to be advantageously evaporated.
The nitrate of lime is if requisite transformed into nitrate of soda by means of
sulphate of soda (which is always present in abundance in the manufacture of nitric
acid) and the nitrate_of_soda revivificd can again serve-for-the manufacture of
nitric acid.
After the first rinsing, the mass is placed in a centrifugal apparatus, arranged so
that it can be charged successively with fresh water. The mass is thoroughly
drained and is then washed in a copious supply of water, while turning the centrifugal
apparatus slowly; these successive washings and drainings by centrifugal action
form an essential feature of my improved process; they enable a perfect washing to
.be attained after from 12 to 15 such alternations.

page_text: as possioIC.
Purification and bleaching-If the cellulose be bleached with chlorine or with.
alkalies before the nitration, it will be altered and pyroxylines without cohesive
strength are obtained. Good results are obtained on the other hand, if the
completed pyroxyline is purified, while observing the following precautions.
The pyroxyline is placed in a large quantity of water with about one tenth part
of its weight of chloride of lime.
Water acidulated with nitric or other acid is added until the chloride of lime is
dissolved, the mass is then washed, submitted to centrifugal action and dried.
II. DENITRATION.
Various substances when digested with pyroxylines have the property of reducing
it and bringing it back more or less rapidly and completely to the state of pure
cellulose.
(a) Nitric acid-Nitric acid more or less concentrated and warm acts in a regular,
manner for this purpose. Thus on digesting in nitric acid of 36° Bé. and at a
temperature of from 30° to 35° C. there is obtained in a few hours a mass which
only contains about 6 per cent. of nitrogen and which has lost the greater part of
the chemical properties of pyroxyline; it is no longer soluble in particular in any
of the solvents of nitrated cellulose. The combustibility is also largely diminished.
(b) Sulphides polysulphides-The pyroxylines are completely deprived of their
nitric acid on being digested in contact with a concentrated solution of sulphides,.
or rather of polysulphides of an alkaline, alkaline earthy or earthy nature.
If there is employed for example commercial sulphide of potassium in which
pyroxyline fibres are plunged for, from 12 to 24 hours, there is obtained at the
end of this time a cellulose free from nitric acid which is washed and dried.
(c) Sulpho-carbonates-The alkaline, carthy alkaline or earthy sulpho-carbonates
also bring back the pyroxyline fibres to the condition of pure cellulose. If there
be taken a solution of sulpho-carbonate of potash for example of 36° Bé. there will
be obtained at the end of 12 hours at 35° C. or of 36 hours in the cold, white
brilliant fibres which have retained all their strength, and have the composition of
cotton or hemp, not being more combustible and having a somewhat greater
density.
(d) Sulpho-hydrates of ammonia-Sulpho-hydrate of ammonia may serve for
the denitration of pyroxyline fibres. A pyroxyline for example having about
12 per cent. of nitrogen if digested with commercial sulpho-hydrate of ammonia for
from 12 to 15 hours, at a temperature of from 30° to 34° C. gradually loses its
nitric acid, without losing its physical properties.
This reagent does not act like any of the others, that is, it does not attack the
fibres of pure cellulose, either after a long digestion in the cold, nor when digested
for from 12 to 24 hours at 60° to 70°. It does also not attack the other textile
fibres and can serve for denitrating pyroxylines mixed with other substances.
The processes of denitration can be considerably shortened by previously
impregnating the pyroxyline with an acid which softens it, and commences the
decomposition of the reagents; nitric, acetic, phosphoric acid &c. &c. may be used
for this purpose.
All the above described methods of denitration can be moderated by the dilution
of the liquors or by lowering the temperature.
It is preferable to stop at a certain point of nitration such as 2 to 4 per cent. of
nitrogen. The latter composition is preferable to pure cellulose on the ground
of solidity, elasticity and aptitude for dyeing.
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 :-
1. In the process of nitration of cellulose, the recuperation of the acids, extracted

page_text: by centrifugal action from the pyroxyline after removal from the bath and the
utilisation of these acids for nitration after having been strengthened by the
addition of fresh acids in which the concentration of the nitric acid is higher,
the old acid being revivified by distillation, substantially as described.
2. The herein described apparatus for continuous distillation for the separation
and revivification of sulphuric and nitric acids.
3. The herein described method of rinsing the pyroxyline and neutralising the
rinsing waters, for the purpose of recuperating the nitric acid remaining after the
centrifugal action.
4. The herein described method of effecting successive washings of the pyroxyline
alternating with centrifugal action, the washings being effected in the centrifugal
machine by means of pure cold water while this revolves at a slow speed, so as to
prevent rise of temperature.
5. The herein described method of purifying and bleaching the finished pyroxyline
by placing the same in a large body of water, containing about one tenth part of
chloride of lime, and adding water acidulated with nitric acid, the pyroxyline being
then washed and dried.
6. The method of denitrating pyroxylines by digesting the same with a solution
of sulphides or polysulphides of either an alkaline, earthy alkaline, or earthy
character, substantially as described.
. 7. The method of denitration of pyroxyline by digestion in contact with sulpho
carbonates of either an alkaline, earthy alkaline, or earthy character, substantially
as described. .
8. The method of denitration of pyroxyline by contact with commercial sulpho
hydrate of ammonia, substantially as described.
9. The method of accelerating the denitration of pyroxyline by the several
reagents above referred to by the preliminary action thereon with an acid for
impregnating the pyroxyline substantially as described.
10. The application of all the above described processes of denitration to
pyroxylines of various forms, and in particular to that known as artificial silk or
spun cellulose.
Dated this 6th day of January 1891.
ABEL & IMRAY,
Agents for the Applicant.