Improvements in the Manufacture of Pigments.
Year: 1899

page_text: COMPLETE SPECIFICATION (AMENDED).
Improvements in the Manufacture of Pigments.
I, HERMAN CHARLES WOLTERECK, of 15/25, Whitehall Street, New York, United
States of America, Consulting 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 :-
My invention relates to the manufacture of pigments, such as white lead, zine
white, cinnabar and the like, also of the different lakes used in the arts, by
electrolysis, and it consists in certain novel methods of operation and in the
application of certain electro-chemical reactions, which permit the successful operation
of a continuous and practical process.
A large number of experiments had to be executed on a manufacturing scale
to arrive at a modus operandi which, while producing a quality of pigments
equal if not superior to the best in the market, will do so quickly and economically.
The results of these experiments demonstrated clearly which conditions would
be most favorable for a successful operation of the process.
These conditions may be
briefly stated as follows:
1) The electrolyte must be kept at a constant temperature.
2) The electrolyte must be continuously circulated.
3) The chemicals required for the regeneration of the electrolyte must be
introduced outside of the sphere of influence of the electric current. .
4) The product must be continuously removed from the electrolyte as quickly as
formed.
The conditions were met by using hollow kathodes through which cold or hot
water or steam may be circulated as the particular pigment may require, by removing
the electrolyte together with the pigment suspended therein continuously from the
bottom of the electrolyzing tank, passing the same through filter presses where
the pigment is retained, passing the filtered electrolyte through a regenerator where
the chemicals, gases or solutions necessary for the regeneration of the spent
electrolyte are introduced, and by returning the regenerated electrolyte to the
electrolyzing tank and distributing the flow of the same as evenly as possible between
the anodes and kathodes.
The means by which this process is executed on a manufacturing scale are illustrated
in the accompanying drawings in which
Fig. 1 shows a plan of a set of five electrolyzing tanks, complete with pumps and
filter presses.
Fig. 2 shows a cross section of the same,
Fig. 3 shows a cross section through a tank and kathode to show the manner of
the water or steam circulation, not shown in the plan. Like letters mark like parts
in the different figures.

page_text: 1, 2, 3, 4, 5 are the dynamoes for producing the electric current; 6, 7, 8, 9, 10
are the electrolyzing tanks. 11 is a circulating pump for the circulation of the
electrolyte and a separate pump is provided for each tank. 12 are the anodes and
13 the kathodes. The circulation of the electrolyte with the different electrolyzing
tanks is secured by means of a pipe 14 which leads into a storage tank 15, whence
the liquid is pressed into the filter presses 17, 18, 19 by means of a pressure pump 16.
A regenerator 20 serves for regenerating the spent electrolyte.
In Fig. 1 tank 6 shows the subdivision of the bottom in three funnels as well
as the small circulating pump 11 which is provided for each tank separately
though not shown. Tank 7 shows the alternate position of the anodes 12 and the
kathodes 13, and their connection with the switchboard and the dynamo 2. A switch-
board is provided for each tank separately. Tank 8 shows the arrangement of the
branch of the return pipe on the top of the tank which distributes the regenerated
electrolyte between the anodes and kathodes by means of the small slits or
openings 22.
Fig. 3 shows the water or steam circulation through the kathodes, the water or
steam entering the kathodes from the main by the connecting pipe 23 and its
escape by the connecting pipe 24 into the discharge main.
+
The operation of the system is started as follows: After making all necessary
connections the tanks are filled with the electrolyte and the circulation pumps are
started. After the storage tank 15 is about half filled the pressure pump 16 is
started and electrolyte in sufficient quantity is added to the tanks to maintain the
desired level of the surface until the return pipes begin to run and to return the
electrolyte to the tanks, the dynamoes and the supply of chemicals, gases or solu-
tions for the regeneration of the electrolyte are now turned on and the water circula-
tion through the kathodes is regulated in such a manner as to maintain the electrolyte
constantly at the temperature required by the process. The production proceeds in
a regular and smooth manner and requires very little attention. The pigments
formed by the action of the current and by the reaction of the different compounds
used are of exceeding fineness and are suspended in the electrolyte which is regularly
withdrawn from the bottom of the tanks by means of the small circulating pumps
and delivered to the storage tank; from here the pressure pump 16 forces it through
one of the filter presses 17. As soon as a filter press is nearly filled, the electrolyte
is turned into the next filter press.
If it is desired to obtain the pigments in solid cakes the press may be filled by
means of a small supplementary pump of high pressure. A washing of the product
will not be necessary in most cases but the last rest of electrolyte contained in the
cakes may be removed by forcing a current of air through the same. The filtered
electrolyte after leaving the press enters the regenerator 20 at the bottom and meets
here a supply of the chemicals necessary for its regeneration, be it in form of gases,
solutions or in pieces which are only soluble in the free caustic alkali. The
regenerated electrolyte next returns to the electrolyzing tanks and starts through
the same circuit again. This process may be advantageously applied to a great number
of pigments, such as white lead, zinc white, cinnabar, as well as the different lead,
zinc or tin lakes.
I will illustrate the process as applied to the manufacture of white lead. The
electrolyte consists of a solution of ammonium nitrate and ammonium bicarbonate.
In the electrolyte are present :

page_text: NH,H.CO..
On the anodes the HNO, combines with the lead of the same in forming Pb(NO3)2,
this reacts with the free ammonia and the bicarbonate according to the following
equation :
SE
2 NH¸OH + 2 CO₂ = 2 NH¸.H.CO
when it returns to the electrolyzing tanks.
For the production of other pigments the corresponding metals are used as anodes
and the bath is prepared from the usual salts used for the purpose.
In the manu-
facture of lakes the hydroxides of the metals are precipitated by the action of the
current and the solution of the required color is introduced in the regenerator in
calculated quantity and concentration. The advantages of the process as described
by me consists in the production of absolutely uniform products proceeding
automatically and requiring a minimum of labor and attention in this
execution.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
In a process of producing pigments by electrolysis the process of cooling or heating
the electrolyte as required, of continuously circulating the electrolyte and of
regenerating the same, after removing the product and before returning the
electrolyte to the electrolyzer, by the introduction of gases, chemicals or solutions of
the same as required, substantially as and by the apparatus hereinbefore described.
Dated this 1st day of February 1899
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.