Improved Frocess of Extracting Tannin from Leather and Preparing the Latter for Glue Making.
Year: 1899

page_text: Date of Application, 17th May, 1899--Accepted, 18th Nov., 1899
COMPLETE SPECIFICATION.
Improved Frocess of Extracting Tannin from Leather and Preparing
the Latter for Glue Making.
RICHARD BRAUER, in the City of Lüneburg, in the Province of Hanover, in
the German Empire, Manufacturer, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement: -
The present invention has for its object a process of extracting tannin from
leather and preparing the latter for glue making. The tannin may be extracted
from all kinds of leather cuttings and waste, by means of ammonia in liquid or
gaseous state, under a pressure of about 150 lbs. per sq. in. in the presence of as
much water as is necessary to form a concentrated solution of tannin.
It is already well known that tannin can be extracted from leather by the use
of alkalis. According to the present process, however, only ammonia is used,
no other alkali being suitable for the purpose, by reason of the great difficulty
of completely removing the solution of tannin. Furthermore, it is impossible
with other alkalis, to prevent the solution being rendered impure by the gelatine
from the hide; and this gelatine again is extremely difficult to remove from
the tannin, as it unites with the latter, forming glutin-tannin.
For the present process, therefore, ammonia is employed, and to it water is
added, but only in sufficient quantity to form a concentrated 40 or 50 per cent.
solution of tannin. If more water is used, the gelatine becomes more or less
dissolved again, thus rendering the tannin extracted impure and of less value.
This would also be objectionable in view of the preparation of the hide for
obtaining glue from it.
There are many practical reasons rendering the employment of too concen-
trated solutions of ammonia unsuitable. For instance, the tannin is but imper-
fectly extracted, the ammonia penetrating too slowly and not sufficiently deeply
into the leather so that profitable working and complete utilisation of the tannin
contained in the leather is impossible.
On the other hand, the ammonia solution cannot be warmed, as gaseous
ammonia would be given off and a pressure produced. The use of a reflex-
O cooler, such, for instance, as is employed in the extraction of fat from bones by
means of benzine, is not practicable, since ammonia, as is well known, can only
be rendered liquid under high pressure.
The method of proceeding according to the present invention is as follows:
Two apparatuses of ordinary construction are employed, evenly lined with
5 lead, and tested up to 150 lbs. pressure per sq. in. The interior of the vessels is
divided into two parts, or storeys, by means of a sieve or reticulate partition.
On the bottom of the lower part is arranged a system of heating coils. Both
apparatuses, which work alternately, are connected to an air-pump and a vacuum
boiler, and may also stand in connection with a compresser.
10
The apparatuses are filled to the sieve partition with leather waste; and in
ander to facilitate the penetration of the ammonia into the pores of the leather,

page_text: the air is exhausted. The required quantity of ammonia, either as a 25 per cent.
solution, or in gaseous state, is now let in; and by means of the compressor, a
pressure of 120 to 150 lbs. per sq. in. is produced in the apparatus for some hours.
If gaseous ammonia is used, care should be taken that the leather is sufficiently
moistened beforehand.
The ammonia solution may, if desired, be let into the apparatus before the
air is exhausted, and the ammonia vaporized by means of the heating coils, till
the desired pressure is obtained. In either case, usually in a few hours, if a
sample is taken, it will be found that a concentrated solution of tannin has
formed, free from gelatine, and therefore soluble in cold water. In this manner
the material may be nearly completely utilized.
The ammonia is now expelled from the tannin solution by use of the heating
coils, and by means of the second apparatus--in which a vacuum has been
created withdrawn, or otherwise used.
The little tannin that remains in the leather may be washed out with warm
water and after treatment with alkalis, the skin thus obtained used for glue
making.
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. The process of treating leather for the purpose of extracting tannin from it
and preparing it for glue making, which consists in allowing ammonia either in
a gaseous or liquid state, to act upon the leather in the presence of sufficient
water to obtain a 40 to 50 per cent. solution of tannin, in a vessel from which
the air has been exhausted, and then creating a pressure of about 120 to 150 lbs.
per sq. in. whereupon after some time the ammonia may be driven off by heat-
ing, and the remaining tannin in the leather washed out and treated with alkalis,
all substantially in the manner hereinbefore set forth.
2. A modification of the process of treating leather for the purpose of extract-
ing tannin from it and preparing it for glue making, as claimed in Claim 1.
whereby instead of the air being exhausted before the liquid ammonia is admitted
to the vessel, prior to the said pressure being created, the liquid ammonia is
admitted to the leather in the vessel without a vacuum being produced, and then
the desired pressure produced by vaporizing the ammonia by means of heating
coils or the like, substantially as set forth.
Dotod th 101 1
1000
WALTER FOLKMAR,
Agent for Applicant.