Improvements in Porous Diaphragms for Electrolytic Cells and Methods of Producing the same.
Year: 1899

page_text: Date of Application, 28th Mar., 1899-Accepted, 9th Dec., 1899
Improvements in Porous Diaphragms for Electrolytic Cells and
Methods of Producing the same.
I, HERBERT HENRY Dow, of the City of Midland, County of Midland, State
of Michigan, United States of America, Manufacturer, 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:-
This invention relates to improvements in porous diaphragms for electrolytic
cells and methods of producing the same.
The accompanying drawing and description set forth in detail, one mode of
carrying out the principle of my invention; such disclosed mode constituting
one of various ways in which the principle of the invention may be used.
In the said accompanying drawing, the figure represents a vertical cross-
sectional view of the electrolytic cell used in my improved process, showing
the electrodes in elevation therein.
While the invention is applicable for use in electrolytic cells employing
different electrolytes, it is principally intended for use in the electrolysis of
natural brine or common salt solution into chlorine and sodium hydrate or of
calcium chloride solution into chlorine and calcium hydrate.
The apparatus consists of an electrolytic cell of suitable shape and dimensions,
having an anode B made preferably of carbon, and a cathode C also of carbon.
The carbons are suitably insulated by means of rubber packing a', the gases
being led off from the cell through the pipe a.
My method of obtaining the halogen chlorine consists in forming a diaphragm
in the electrolytic cell by chemical and electrolytic action in the electrolyte, said
diaphragm consisting of two layers composed of different chemical agents each
capable of retarding or preventing diffusion of the product of the electrode
adjacent to it and in each of which the product of the electrode of the opposite
compartment will be chemically destroyed, while electrolizing the solution.
My method of obtaining chlorine and sodium hydrate from common brine
consisting of sodium chloride calcium chloride and magnesium chloride in solu-
tion. and constituting the electrolyte, is as follows:-
A quantity of metallic iron F, is introduced into the electrolyte in the neigh-
bourhood of the anode.
On the electric current being passed through the solution, the first actions
that take place are the decomposition of the electrolytic solution near the anode
and cathode, free chlorine being formed at or near the anode and free sodium,
calcium and magnesium being formed at the cathode; these latter in turn
react with the water of the electrolyte to form sodium, magnesium and calcium
hydrates, this formation also taking place near the cathode,
Na H₂O NaOH + H.
=
3C1 + Fe
-
Fe Cl₂.
[Price 8d.]

page_text: The sodium, calcium and magnesium hydrates and the iron chloride diffuse
toward the middle of the cell and meet between the electrodes; on such meeting
the iron is precipitated as iron hydrate which forms part of the diaphragm,
calcium and magnesium chloride;
2NaOH + CaCl2 Ca(OH)2 + 2NaCl,
2NaOH+MgCl₂
=
Mg(OH), +2NaCl.
The diaphragm begins to form and build up from these precipitates, consisting
of iron, calcium and magnesium hydrates. The chlorine diffusing toward the
cathode passing into the diaphragm is absorbed by the calcium and magnesium
hydrates forming calcium and magnesium hypochlorites, thus preventing the
contamination of the cathode solution by the chlorine. These hypochlorites,
whose formule are not positively known, decompose very rapidly, probably into
chloride and oxygen. In actual working these hypochlorites are not found
present.
The iron hydrate, being inert so far as the chlorine is concerned, is not
disturbed, so that eventually the side of the diaphragm near the anode is almost
completely depleted of calcium and magnesium hydrates by the action of the
chlorine and only iron hydrate is left, while the cathode side consists mainly
of calcium and magnesium hydrates.
The ion hydrate is precipitated throughout the pores of the diaphragm by
the action of the sodium, calcium and magnesium hydrates upon the ferric
chloride, and the hydrates of calcium and magnesium, are also precipitated
throughout said pores by the action of the sodium hydrate upon the calcium
and magnesium chlorides formed by the action of the ferric chloride upon the
calcium and magnesium hydrates which diffused from the cathode. The said
calcium and magnesium-hydrates are hence precipitated on both sides of the
diaphragm but more rapidly at the cathode side on account of the larger amount
of sodium hydrate there present, the sodium hydrate passing through the cathode
side and not used to precipitate the magnesium and calcium hydrates, performing
a double function on the anode side and namely;-precipitating iron hydrate
by its action with the ferric chloride and also precipitating calcium and magne-
sium hydrates from the calcium and magnesium chlorides, these latter, however,
being continually reconverted into a solution by the action of the ferric chloride
so that they never remain permanently in place as does a large part of the calcium
and magnesium hydrates on the cathode side where the ferric chloride never
reaches them or reaches them to only a very limited extent. The iron hydrate
prevents to a great extent the chlorine of the anode compartment from being
consumed by the parts of the diaphragm with which it will combine.
The pores of the diaphragm containing iron, calcium and magnesium chloride,
the sodium hydrate of the cathode side, upon entering the diaphragm, is absorbed
by these chlorides before it can diffuse to the anode side, so that the sodium
hydrate cannot contaminate the anode solution,

page_text: where the diffusion is the greatest, and should any portion become detached or
mutilated, diffusion will be greater at the mutilated point and the consequent
greater precipitation will mend the break, it is thus seen that the diaphragm will
thicken evenly.
While one or more sheets of porous material, such as paper, cloth, asbestos
and the like, might be placed as a nucleus upon which the two essential layers
of the diaphragm would be precipitated, in the practical working of the cell
such a procedure has not been found necessary or advantageous, the diaphragm
being readily produced in the proper place without such foundation.
The physical qualities of the mixed hydrates when made into a diaphragm in
this manner are such that they form a coherent and self-supporting mass imposing
very little resistance to the passage of the electric current, but at the same time
impose a high resistance to the diffusion of the products of electrolysis, and
the electrolyte.
In place of forming the iron chloride in the cell by the action of the electro-
lytic chlorine on the metallic iron, a solution of a soluble iron salt such as feirous
sulphate, may be slowly added to the solution near the anode.
I have found that similar solutions of the alkalis or alkaline earths, including
magnesium, may be treated in the above manner with like results.
Other modes of applying the principle of my invention may be employed,
instead of the one explained; change being made as regards the mechanism
herein disclosed, provided the means covered by any one of the following claims
be employed.
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. In a diaphragm, the combination of two layers, the one on the cathode side
composed of a chemical substance which will consume free halogens by chemical
action; the layer on the anode side composed of a different chemical substance
that will not be consumed by free halogens and containing a substance with
which any soluble alkali diffusing from the cathode side will readily combine
chemically, substantially as set forth.
2. In diaphragm, the combination of two layers, the one on the anode side
composed of an amorphous chemical substance that will not be consumed by
free halogens and containing a substance with which any soluble alkali diffusing
from the cathode side will readily combine chemically; the layer on the cathode
side being capable of combining chemically with halogens, substantially as set
forth.
3. In a diaphragm, the combination with a layer on the anode side consisting
of a substance inert to halogens and containing a substance capable of readily
combining chemically with an alkaline substance, so that any alkali diffusing
from the cathode compartment, is completely destroyed; of a layer on the cathode
side, consisting of a different chemical substance inert to alkaline substances and
capable of readily combining chemically with halogens, substantially as set forth.
4. In a diaphragm, the combination with a layer on the cathode side consisting
of a substance entirely inert to an alkaline substance, of a layer on the anode
side consisting of a different chemical substance and containing a substance
capable of readily combining chemically with an alkaline substance, thus com-
pletely preventing the entrance of alkaline substances into the anode compart-
ment, substantially as set forth.
5. In a diaphragm, the combination with a layer on the anode side consisting
of a substance inert to chlorine and containing a substance capable of readily
combining chemically with sodium hydrate, the product of such combination
forming the anode side of the diaphragm, of a laver on the cathode side con-
sisting of a different chemical substance entirely inert to sodium hydrate, and
capable of readily combining chemically with halogens, substantially as set forth.

page_text: 6. A diaphragm, composed on the anode side of metallic hydrate or oxide
other than that employed in the cathode layer and which is substantially inert
to halogens and on the cathode side of alkaline earth hydrates, substantially as
set forth.
7. In a diaphragm, the combination with a cathode side consisting of a sub-
stance capable of chemically combining with halogens, of a layer on the anode
side consisting of a hydrate or oxide of a metal substantially inert to halogens,
substantially as set forth.
8. A diaphragm composed of iron hydrate or oxide on the anode side and other
hydrates on the cathode side, latter hydrates capable of chemically combining
with chlorine, substantially as set forth.
9. A diaphragm composed on the anode side of a metallic hydrate capable of
being precipitated by calcium hydrate and composed on the cathode side of
alkaline earth hydrates, substantially as set forth.
10. A diaphragm composed of iron hydrate or oxide on the anode side and of
alkaline earth hydrates on the cathode side, substantially as set forth.
11. A diaphragm composed of iron hydrate on the anode side and calcium
and magnesium hydrate on the cathode side, substantially as set forth.
12. The improved method of forming the porous diaphragm in electrolytic
cells, which consists in slowly precipitating hydrates capable of readily combining
with halogens, by the action of soluble alkali (as the fatter is formed in the cell
by electrolysis) on a soluble alkaline earth salt, and the subsequent precipitation
of another metallic hydrate substantially inert to halogens by part of the alkaline
earth hydrate first precipitated, the method being carried out with solutions of
such composition that a coherent diaphragm is formed in place, substantially
as set forth.
13. The improved method of forming a porous diaphragm in electrolytic cells
for the electrolytic production of chlorine, which consists in electrolyzing a
solution containing a chloride of an alkaline earth base, whereby the hydrate
of said base is precipitated adjacent to the cathode and introducing into the
electrolyte in the neighbourhood of the anode a soluble salt of a metal which
will be precipitated as an insoluble metallic hydrate by the action of part of the
alkaline earth hydrate on said salt, the method being carried out with solutions
of such composition that a coherent two layered diaphragm is formed in place
wholly from the products of electrolysis, substantially as set forth
14. The improved method of forming a porous diaphragm in electrolytic cells
for the electrolytic production of chlorine, which consists in electrolyzing a solu-
tion containing a chloride of an alkaline earth base, whereby the hydrate of said
base is precipitated adjacent to the cathode and introducing into the neighbour-
hood of the anode a soluble iron salt, whereby the iron of said salt is precipitated
as an insoluble hydrate by the action of part of the alkaline earth hydrate on
said salt, the method being carried out with solutions of such composition that
a coherent two layered diaphragm is formed in place wholly from the products
of electrolysis, substantially as set forth.
15. The improved method of forming a two part porous diaphragm in electro-
lytic cells for the electrolytic production of chlorine which consists in electro-
lyzing a solution containing sodium, magnesium and calcium chlorides, and
introducing into the neighbourhood of the anode a soluble iron salt, whereby
the hydrates of iron, calcium and magnesium are precipitated to form a coherent
porous diaphragm, and whereby said calcium and magnesium hydrates are dis-
solved out of the anode side of said diaphragm by the action of electrolytic
chlorine, the method being carried out with solutions of such composition that
a coherent diaphragm is formed on the anode side of the diaphragm consisting
wholly of iron hydrate, substantially as set forth.
16. An improved method of making two part diaphragms for the electrolytic
production of chlorine, consisting in forming the diaphragm wholly by the action
of electrolysis on the cell contents, consisting in electrolyzing a solution con-

page_text: taining sodium, calcium and magnesium and iron chlorides, whereby the hydrates
of calcium, magnesium and iron are precipitated near the cathode, and whereby
said calcium and magnesium hydrates nearest the anode react on the iron salt
there present, precipitating iron hydrate, the method being carried out with
solutions of such composition that a coherent diaphragm is formed wholly of
hydrates in position where it is to be used, substantially as set forth.
Dal 01 J 1900
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.