Improvements in the Process of Nitrating Cellulose.
Year: 1894

page_text: COMPLETE SPECIFICATION.
Improvements in the Process of Nitrating Cellulose.
I, ROBERT CHARLES SCHÖPPHAUS, of 118 Pennsylvania Avenue, in the City
of Brooklyn, County of Kings, and State of New York, United States of
America, Chemist, 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 generally to the manufacture of gun cotton and more
particularly to the nitration step of the process in such manufacture.
It is well recognized in the process of nitrating celluloso that success is based
somewhat on the uniformity of composition, which when practiced in the usual way
is hard to attain. As the acids bath is weakened after each successive treatment
of the cellulose, different methods have been proposed by which to restore the
acids bath to the proper strength. It is also well recognized that it is absolutely
essential in order to obtain a uniform product that the proportions of the com-
position of the acids shall be at all times uniform.
It is obvious that no uniform product can be obtained of the highest grade of
nitration by using the acids bath over again upon simply replenishing such bath
with a fresh concentrated mixture, for the reason that in the conversion of cellulose
into nitro-cellulose a certain quantity of water is formed, hence the acids mixture
grows richer in sulphuric acid and water and poorer in nitric acid; these relative
changes being the smaller the larger the proportion of acids mixture employed.
If we suppose that one hundred pounds of acids to each pound of cellulose are used,
and that the mixture consists of three parts of the strongest sulphuric acid and one
part of the strongest nitric acid, say of 98 per cent. strength; then, after the
nitration, on the assumption that no water has been introduced into the acids
mixture other than that formed in the reaction, that no nitric acid has evaporated,
and that all the cellulose has been converted into true gun cotton, the percentage
of composition of the remaining acids bath would be: 75-63 sulphuric acid of
98 per cent. strength, 24:00 nitric acid of 98 per cent. strength, and 37 water.
If the nitro-cellulose is withdrawn from the bath and the bath be replenished
with a quantity of the original mixture, three parts sulphuric acid and one part
nitric acid, the acids solution must necessarily grow less and less fit to produce gun
cotton, until at last a point is reached when it is essential to start with an entirely
fresh acids bath; the weakened bath in some instances being used in the preparation
of collodion cotton and in others is subjected to distillation.
The present invention is designed to overcome these difficulties and to provide a
simple and economical method of replenishing or bringing the weakened acids bath
to its proper strength and proportions; and it consists essentially in adding nitric
acid and sulphuric anhydride to the weakened acids bath.
In practicing the improved method, after withdrawing the nitro-cellulose from
the acids bath, the adhering acids are removed either by means of a centrifugal
machine, a press, or by a suction filter, and the acids thus recovered are returned
to the remainder of the bath. The bath is then analyzed and the percentage of
sulphuric and nitric acids of ninety-eight per cent. strength is ascertained. The
surplus of water in this bath is then combined with sufficient sulphuric anhydride,
., four times its weight to form ninety-eight per cent, strength sulphuric acid, and
enough ninety-eight per cent, strength nitric acid is also added to re-establish the
pre-existing proportions of three parts sulphuric acid to one part nitric acid. By
this means the original bath in its wasted state is restored to its proper strength and
proportions by the simple addition of sulphuric anhydride and nitric acid.

page_text: In the case above cited it would take to restore the weakened acids bath
1-42 pounds sulphuric anhydride, and 1.38 pounds nitric acid of ninety-
eight per cent. strength changing the one hundred pounds of waste acids into one
hundred and three and thirty-one one hundredths pounds of acids of the original
strength and proportions.
It may be stated that if this gain in weight of 3.31 pounds should not be sufficient
to restore the unavoidable loss of acids through the washing process, a solution of
sulphuric anhydride in oil of vitriol may be employed to build up the strength of
the waste acids; and a correspondingly large amount of nitric acid should also be
added in such case.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is :
1. In the art of nitrating cellulose the herein described method of restoring the
weakened acids bath, which consists in adding thereto sulphuric anhydride and
nitric acid.
2. In the art of nitrating cellulose, the herein described method of restoring the
weakened acids bath, which consists in adding thereto a solution of sulphuric
anhydride and oil of vitriol and nitric acid.
Dated this Biust day of
R. C. SCHÜPPHAUS,
Per W. H. Beck,
115, Cannon Street, London, Agent.
R. C. SCHÜPPhaus,
Per W. H. Beck,
115, Cannon Street, London, Agent.