Improved Manufacture of Tannin-extract from Sulphite Cellulose Lyes.
Year: 1896

page_text: Date of Application, 18th Aug., 1896-Accepted, 3rd Oct., 1896
COMPLETE SPECIFICATION.
Improved Manufacture of Tannin-extract from Sulphite Cellulose
Lyes.
I, MAX HONIG, of Brtinn, Imperial and Royal Professor, 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 :-
The universally known methods of utilizing sulphite cellulose lyes for tanning
purposes or for producing tannin-extracts are attended by drawbacks that relate
parily to the quality of the tanning fluids obtained by means of these methods
and partly to the methods themselves.
Thus, when the lyes produced by treating wood with calcium bisulphite for the
purpose of obtaining tannin extracts direct-that is to say, without previous
neutralisation are treated with sulphuric acid, and the liquid thereby doprived
of lime is then used directly, or after being concentrated, for tanning skins, the
tanning process is effected under the influence (in many respects injurious) of the
sulphuric, acetic, and other free acids that are still present in the tanning liquor
with the tannin.
On the other hand, the method according to which the tannin is precipitated
from the sulphite cellulose lyes firat in the form of a limo salt, and the latter is
then decomposed by means of acids, can be exclusively employed only for those
lyes which result from the treatment of oak-wood with calcium bisulphite;
because of all the kinds of wood which enter into considoration for the produc-
tiou of cellulose the oak is the only one whose tannic acid is capable of being
precipitated by means of lime, whilst for the lyes produced from those kinds of
wood (such as beech, fir, and pine) that are mainly and generally employed for the
production of cellulose, this method cannot be employed at all.
Now, the present invention relates to a process for producing tannin-extract
from sulphite cellulose lyes which obviates the above mentioned drawbacks of the
processes hitherto known. According thereto the sulphite lyes are first neutralized
with the greatest possible accuracy by means of carbonate of lime or caustic lime,
then concentrated to a medium degree of concentration, then mixed with a
quantity (corresponding to that of their contained lime) of sulphuric acid or
other acid that will produce au insoluble or difficultly soluble lime salt, and,
finally, after being filtered from the precipitated sulphate of lime or other salt,
brought by a second concentration to the desired final density.
The process specified above may be carried out as follows:-
The sulphite lyes that constitute the raw material for the manufacture of tannin-
extract are first carefully neutralized with carbonate of lime or caustic lime,
because according to the above described procedure the next following con-
centration of the liquor to a medium density (between 16° and 18° Be.) can
only be properly effected after the free acids present therein have been neutralized
as accurately as possible. The lyes thus neutralized and clarified by deposition,
are then concentrated in the usual manner to between 15° and 18° Be., and are
then mixed in lead-lined boilers with a quantity of dilute sulphuric acid or other
acid that will form an insoluble or difficultly soluble lime ealt, the quantity of acid
added being suited to the amount of lime contained in the lye. The whole is
then heated by admission of steam until all the volatile acids are expelled. The
precipitated sulphate of lime is filtered off, and the filtrate is brought in a vacuum-
apparatus to the desired final density (between 28° and 30° Be.). After complete

page_text: clarification effected by deposition, this filtrate can now be used as a tannin-extract
of between 28° and 30° Be.
The process herein described is thus distinguished by the following special
features:-
(1) The careful and most accurate neutralization of the sulphite lyes with
carbonate of lime or caustic lime;
(2) The evaporation or concentration of the neutral lyes in two separate
stages;
(3) The treatment of the neutral lyes at their first degree of concentration
(between 15° and 18° Be.) with sulphurio acid or other acid which produces
insoluble lime compounds, for the purpose of separating or precipitating the lime
and liberating the volatile acids;
(4) The steaming of the lyes after treatment with acids, whereby the liberated
volatile acids are expelled; and
(5) The concentration of the lyes when freed from lime and volatile acids, to
the second degree of concentration (between 28° and 30° Be.).
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The hereinbefore described process for manufacturing tannin-extract from
sulphite cellulose lyes, consisting in carefully neutralizing the lyes with carbonate
of lime or caustic lime; then clarifying them then evaporating them to a medium
degree of concentration (between 15° and 18° Be.); then mixing them with a
quantity (corresponding to the amount of contained lime) of an acid, such as
sulphuric acid, which yields an insoluble or difficultly soluble salt; then heating
the lyes by admission of steam, so as to drive off the volatile acids; then filtering
the lyes thus freed from volatile acids, so as to separate the precipitated lime salt;
and, finally, concentrating the freed and separated lyca by evaporation in a
vacuum apparatus to a degree of concentration of between 280 and 30° Be. as set
forth.
Dated this 18th day of August 1898
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.