An Improved Process for the Purification of Tannin, Dye, and other Vegetable Extracts.
Year: 1893

page_text: COMPLETE SPECIFICATION.
An Improved Process for the Purification of Tannin, Dye, and
other Vegetable Extracts.
I, JEAN BAPTISTE FRANÇOIS EDOUARD ROY, of 55, Rue Louis Blanc, Paris,
France, Engineer, 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 :-
My invention relates to an improved process for the purification of tanning and
dye extracts. The methods heretofore employed are based upon the well-known
practical experience that, as regards both tanning and dye extracts, the tints
obtained are the brighter, purer, and clearer the longer the tanning liquor or the
dye bath has been in use which is equivalent to saying that the impure portions of
these extracts are carried off at the beginning of the operation of fixing the tanning
or dyeing pigment upon the fibre. It is in fact by carrying off a considerable
part of the tannin or pigment in a precipitate of metallic oxide or an organic
combination of starch, albumen, or gelatine, that the purification of the solutions
is effected but this method is costly on account of the very great loss of tannin or
pigment which is incurred, and it is also initially imperfect because whatever may
be the quantity of tannin or of pigment which is sacrificed, the result obtained is
but relative at best and the purification merely an attenuation. This method is
also objectionable inasmuch as there is nothing to justify the necessity for the loss
of tannin which is considered indispensable to purification.
The difference of
affinity attributed to these prejudicial impurities in their fixation concurrently with
that of the pigments, is a proof that their presence in the solutions is not intimately
allied with any particular state of the pigment itself, these matters not being
constituted by the pigment when oxidized by air and transformed into products
verging towards ulmic acid, for if so (as is generally believed) the sharpness of
affinity which is observed for brownish or greyish impurities would be reversed.
Vegetable pigments of all kinds oxidized by the air, lose all affinity for the fibres
when a certain degree of oxidation is exceeded, or if on the other hand they profit
by such action, it is to the benefit of the vigor of the tints they produce. Having
eliminated by observation, the error generally prevalent, as regards the nature of
these prejudicial impurities, I have been led to discover the actual truth and so
to attain perfection in the purification of all kinds of vegetable extracts or solutions.
I have found that these impurities are constituted solely by oxides of iron,
manganese, and sometimes copper, engaged in a combination which is singularly
stable for the medium in which they are found, hence my researches have been
directed towards the elimination of these matters. It might be supposed that the
majority of the reagents which precipitate ferrous oxide from its salts would be
suitable for the purpose, but some of them, however, exert no action even among
those forming with iron combinations insoluble in acetic and hydrochloric acids,
except the operation be performed in a neutral or alkaline medium, which in

page_text: practice would be an onerous condition, but which I however claim as being
applicable for my purpose.
In operating on the extracts as produced by coction, the decolorant which it is
preferred to employ is the ferro-cyanide of potassium. As regards the mode of
use the extract resulting from one ton of spent wood requires for its purification
from 200 to 600 grammes of ferro-cyanide. The extract may be of any strength
preferably between 4° and 5° B. either cold or hot, but preferably the latter, the
decolorizing re-agent being previously in solution or in powder. The manipulation
is the same in all cases, viz.: active stirring by any suitable mechanical means,
settling, decanting, filtering, and evaporating if necessary.
:
The precipitation of the metals is complete and the purification of the solutions
is absolute in the direction desired for the purpose of dyeing.
Ferro-cyanide of sodium may likewise be employed as the purifying agent and
also the ferro-cyanides of both bases, the soluble salts of the same acids, and a
large number of insoluble ferro and ferri cyanides, which act in this case by way
of displacement.
.
The invention extends to the employment of the salts of ferro and ferri hydro-
cyanic acids and also of all bodies containing cyanogen in any degree, constituting
a class of bodies not hitherto employed, for the purification of tanning or dyeing
solutions.
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―
:
1. The purification of tanning and dyeing extracts by the elimination therefrom
of the metallic compounds specified.
2. The employment, for the purpose of purifying tanning and dyeing extracts
by the elimination of certain metallic compounds therefrom, of the reagents
specified, both in the manufacture of solutions for concentration and sale and also
in the preparation of solutions for immediate use.
3. The purification by the process herein described of solutions obtained from
all kinds of vegetable matters of any degree of concentration and for all uses.
Dated this 28th day of April 1893.
Dated this 28th day of April 1893.
J. B. F. E. ROY,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.