Process for Obtaining Pure Starch from Raw or Crude Starch.
Year: 1895

page_text: Date of Application, 20th Dec., 1895-Accepted, 21st Mar., 1896
.COMPLETE SPECIFICATION.
Process for Obtaining Pure Starch from Raw or Crude Starch.
We, WILHELM VON SIEMENS, of 94 Markgrafenstrasse, Berlin, Engineer, and
Dr. OTTO NICHOLAS WITT, of 33 Lindenallee, Westend, Berlin, Germany,
Professor, do hereby declare the nature of this invention aud in what manner
the same is to be performed to be particularly described and ascertained in and
by the following statement :-
We term "raw or crude starch" the starchy product obtained from a great
variety of vegetable matters by levigation in the known manner, and which retains
extractive and colouring matters from the cell juices, that are very detrimental to
the farther treatment and employment of the starch, as they become converted
partly into coloured partly into malodorous decomposition products which remain in
the derivatives obtained from the starch, and reduce the value thereof.
The removal of these impurities as also the application of the starch in various
ways, is also militated against by the fact that in the starch cells the starch proper
is enclosed in pellicles of cellulose, which impede the direct contact of the reagents
with the starch itself.
As example of the action of these cellulose pellicles may be cited the process of
paste making in which the starch material, which is perfectly soluble in hot water,
does not become actually dissolved, but is retained in the distended cell pellicles,
instead of forming perfect paste by its solution.
We have discovered that it is possible to obtain from the raw or crude starch a
substance which we will term "pure starch" and which may be characterised
as follows.
In the pure starch not only are the above mentioned colouring matters and
extractive matters removed, so that the starch granules have the pure white colour
which they naturally possess, but the cellulose membranes are acted upon in such
manner that they only just suffice to maintain the starch in its organised form, but
at once yield to any chemical treatment, are dissolved, and free the pure starch
substance, which is thus easily accessible to any farther chemical treatment. Such
a starch is for instance very readily and smoothly converted into sugar by means of
mineral acids, without a vestige of bad odour; it is easily converted into the
various kinds of dextrine without receiving any perceptible brown colouration;
in short, it is much more valuable than the crude starch from which it was
prepared.
We obtain this important result by converting the cellulose membranes of the
etarch granules into oxycellulose which, as is well known, offers much less resistance
to chemical influences than cellulose itself.
The pure starch can be readily and rapidly characterised chemically by the fact
that in dilute potash solution it is at once convertible into a clear filterable solution,
while all known raw or crude starches when treated with this reagent only swell up
to a stiff gelatinous mass.
The oxycellulose contained in our pure starch is mainly soluble in alkalies, while
the cellulose of the crude starches is only mercerised and consequently encloses and
retains the starch substance dissolved in the lye in a similar manner to that above
referred to for the formation of paste by heat.
• P
From the pure starch obtained according to our process there may be obtained
by solution in alkali, filtration and neutralisation, the chemically pure starch
substance, which was not hitherto obtainable by any known process.

page_text: The above described pure starch is obtained by subjecting raw or crude starch to
the action both of oxidising agents and of nascent chlorine, under the observance of
such conditions that the starch substance, which has tolerable powers of resistance,
is not itself attacked. By the oxidising agents the colouring and extractive
matters are destroyed, while by the nascent chlorine the highly important result of
the conversion of the cellulose into oxycellulose is effected.
This effect cannot be obtained by means of molecular chlorine, that is, by chlorine
gas or chlorinated water in such dilution that the starch substance remains
unaffected thereby, but it is readily and smoothly attained by means of chlorine in
the nascent condition.
This method of operating invented by us can be carried out practically in
a variety of ways. It may for example be assumed that to a certain extent it can
be carried out by the process described in the Specification to Patent No. 2597
of 1893 although this only has for its object the bleaching of the starch, and not the
conversion of the starch cellulose which is the main feature of the present
process.
We employ for the purposes of our invention a process which combines the
advantage of great cheapness with the capability of perfect regulation of the
process.
We stir up the crude starch with water into a milk and to this we add, slowly
and by degrees, a saturated aqueous solution of potassic permanganate until the
pink colour of the latter persists in the liquid. The quantity of permanganate thus
required depends solely upon the quantity of the impurities present, a's only these
are acted upon by the said reagent, whereas the substance of the starch itself is not
attacked by it. The manganese peroxide formed by the decomposition of the
permanganate is deposited in a state of extreme subdivision in the starch itself,
which thereby assumes a brown colour of greater or lesser intensity.
After the treatment with permanganate the starch is subjected to a thorough
washing with clean water in order to remove the soluble oxydation products of the
impurities.
After the washing the insoluble manganese peroxide deposited in the starch has
to be removed by chemical means. If it be only required to bleach the starch, it is
sufficient to treat it with a saturated aqueous solution of sulphurous acid, which
rapidly removes the peroxide and leaves the starch in a snow-white condition.
But in order to attack the cellulose membranes enclosing the starch we prefer to
make use of the peroxide for the development of nascent chlorine. To effect this
the starch is introduced into very dilute hydrochloric acid, the concentration
of which may vary, according to the nature of the starch from 0.5 per cent. and the
chocolate coloured milk thus obtained is maintained continuously in motion.
The conversion of the cellulose is now slowly effected by the nascent chlorine,
and the process is often completed before all the manganese peroxide has been
used up.
The progress of the process can be ascertained by taking samples, washing the
same with sulphurous acid and testing their solubility in alkali. As soon as perfect
solubility in alkali has been obtained, the starch is filtered off and is freed from the
excess of manganese peroxide and absorbed molecular chlorine by treatment with
aqueous sulphurous acid or dilute bisulphite solution. The product will then
possess the above described properties of our pure starch.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. Process for freeing raw or crude starch from impurities, by oxidising the
latter and simultaneously acting upon the cellulose contained in the starch by
converting the same into oxycellulose, the raw starch being for this purpose treated
with oxidising agents and nascent chlorine, substantially as described.
2. For carrying out the process referred to in the first claim, treating the raw or

page_text: crude starch consecutively with potassium permanganate and dilute hydrochloric.
acid, substantially as described.
Dated this 20th day of December 1895.
ABEL & IMRAY,
Agents for the Applicants..