Electrochemical cell

An electrode assembly for effecting electrochemical reaction between two fluid phases, the first of which is liquid, which apparatus is characterized by PA0 an electrode permeable to the fluids, PA0 means for containing the first fluid phase in contact with the electrode, PA0 means for charging the second fluid phase to the electrode PA0 means for removing a reaction product of the two phases from the electrode, and PA0 means for rotating the electrode about an axis, such that when the second fluid phase is charged to the electrically charged, rotating electrode permeated with the first fluid phase, the second fluid phase permeates the electrode from the point of charging and the reaction product is removed from the electrode; a series cell cascade comprising at least two such electrode assemblies in series; and a process for effecting electrochemical reaction between two fluid phases, one of which is a liquid, using such an electrode assembly.

This invention relates to an electrode assembly for electrochemical 
reactions, to a cell cascade comprising a plurality of such assemblies, 
and to processes for electrochemical reactions using such an assembly or 
cascade. 
Inter-phase electrochemical reactions at electrodes, for example between a 
gas and a liquid, are known. Examples of such gas-liquid reactions include 
those which reduce hydrogen overpotential, and electrosynthesis. Ensuring 
adequate inter-phase and phase-electrode contact for adequate reaction 
poses a problem. We have now found a means for, unexpectedly, enhancing 
the necessary contact and hence the inter-phase reaction. 
Accordingly the present invention provides an electrode assembly for 
effecting electrochemical reaction between two fluid phases, the first of 
which is liquid, which apparatus is characterised by 
an electrode permeable to the fluids, 
means for containing the first fluid phase in contact with the electrode, 
means for charging the second fluid phase to the electrode 
means for removing a reaction product of the two phases from the electrode, 
and 
means for rotating the electrode about an axis, such that when the second 
fluid phase is charged to the electrically charged, rotating electrode 
permeated with the first fluid phase, the second fluid phase permeates the 
electrode from the point of charging and the reaction product is removed 
from the electrode. 
The invention also provides a process for effecting electrochemical 
reaction between two fluid phases, the first of which is a liquid, 
characterised by charging the second fluid phase to an electrically 
charged rotating permeable electrode permeated with the first fluid phase, 
so as to permeate the electrode and first fluid phase from the point of 
charging with the second fluid phase. 
By "fluid" we mean a substance or a mixture of substances, which is a gas 
or a liquid at the conditions of temperature and pressure at which the 
apparatus of the invention is operated. For example, where the second 
fluid is a gas it may be one gas or a mixture of gases; the first fluid 
and/or the second fluid (where it is a liquid) may be a neat liquid or may 
be a solution of one or more solutes in the liquid, which solute may be a 
gas, liquid or solid, subject always to the proviso that the two phases 
are capable of electrochemical reaction. 
For example the second fluid may be oxygen or air, the first fluid may be a 
solution of solid sodium hydroxide in water, and the electrode may be a 
cathode. In this case the electrochemical reaction will be oxidation of 
hydrogen or hydrogen ion to water to reduce the hydrogen ion over 
potential. The water may be removed. 
Alternatively, the second fluid may be an alkene, the first fluid may be a 
solution of solid sodium chloride in water, and the electrode may be an 
anode. In this case the reaction (an electrosynthesis) will be the 
reduction of chlorine or chloride ion to halogenated alkanes which may be 
removed. 
In a further possibility, one or two electrodes in accordance with the 
invention may be used (as a cathode, or as a cathode and anode 
respectively) in a fuel cell. The cells often have a cathode where the 
second fluid is air or oxygen, the first fluid is an aqueous electrolyte 
and the reaction is the oxidation of hydrogen ion to water. 
Where the elctrolyte contains methanol, this is oxidised at an anode not 
perfused with any gas to carbon dioxide. 
Alternatively, an anode in accordance with the present invention may be 
charged with hydrogen which is anodically oxidised to water, or charged 
with a hydrocarbon gas such as a C.sub.1-4 alkane or a mixture thereof 
which is anodically oxidised to carbon dioxide. 
As discussed further hereinafter, the radial movement of the second fluid 
depends directly on relative densities of the two fluids, and depends on 
their relative flow rate, although it may also be assisted by applying a 
pressure drop to one or both fluids. It is generally preferred for 
economic reasons to minimise the need for an applied pressure drop, for 
example by maximising the difference in density of the two fluids. Since 
the first fluid is a liquid, this means that the second fluid is generally 
a gas. 
The permeable electrode may be a plurality of discrete components which 
contact to conduct electric current, or an integral whole. Where the 
permeable element comprises a plurality of discrete components, preferably 
they are mutually contacting fibres, e.g. as carbon or metal gauzes or 
felts, in which case the interstices of the permeable electrode are 
between the components. Less favourably, the individual components may be 
permeable, e.g. open-ended metal tubules in which case a proportion of the 
interstices are through the components and a proportion of the interstices 
are between the components. The permeable element is not usually an 
integral whole, but if so, it may be formed with pores, e.g. cast as a 
block with pores; or have pores formed therein, e.g. cast as a solid block 
and pores drilled therein; or be arranged to form pores between the parts 
thereof, e.g. a coil of wire. 
While the permeable electrode may have straight pores, e.g. it may comprise 
aligned glass tubules or a metal or carbon block with channels drilled 
therein. Preferably the permeable electrode has tortuous pores through 
which the fluids flow, e.g. the abovementioned random gauzes or felts or 
mass of fibres, or it may be a coil of woven tape, a sintered mass, 
knitted or woven wire cloth, a crumpled mesh, skeleton foam, or particles. 
Where fibres are employed they may all have the same size and shape, or 
the sizes and/or shapes may be random, or the size and/or shape may be 
ordered. 
Gauzes and felts are preferred since they have a relatively large specific 
surface area and voidage, which tend to maximise the conductivity of any 
cell containing the electrode and the scale of the desired electrochemical 
reaction, and give a good shear mixing of the two phases, when the second 
or both move(s) through them, to reduce diffusion control of the 
inter-phase reaction rate. 
Electrodes with relatively large specific surface areas and voidages are 
generally favoured. By `relatively large specific surface area` we mean 
the surface area of the permeable electrode per unit volume of permeable 
electrode is at least 200 m.sup.-1, preferably more than 1500 m.sup.-1 and 
more preferably more than 3000 m.sup.-1. Typical voidages are at least 
85%, and preferably more than 90%. Complementary fibre diameters (mean) 
are in the range of 2 to 25 u, typically 2 to 10 u for carbon fibres and 7 
to 25 u for metal fibres. 
The permeable electrode may be formed from any material which has the 
mechanical strength to withstand the stress generated in the material 
during rotation of the permeable electrode at the rotational speeds 
employed (discussed hereinafter). Preferably the material is resistant to 
attack by or reaction with the fluids with which it is in physical 
contact. Typically, the material from which the permeable element is 
formed is carbon, optionally coated with conventional electrode coatings 
therefor, such as chemically resistant metals such as silver, platinum or 
platinum black or metal oxides, for example platinum oxide; a conductive 
or conductively coated plastic or ceramic; or a chemically resistant 
metal, e.g. stainless steel, nickel, titanium or tantalum. The electrode 
may thus be a composite of two or more materials in an appropriate 
disposition or a single material. It may in addition have a conventional 
electro-catalytic coating. 
Where, as may often be the case, the electrode is not mechanically 
self-supporting, e.g. it comprises an integral whole arranged to form 
pores between the parts thereof, or a plurality of discrete components, 
such as a felt, means to retain the permeable element in a desired shape 
and/or position in the rotating assembly and to maintain its permeability 
are often necessary. The said means is preferably in the form of at least 
one member, the or each member being rotatable about the same axis as the 
permeable electrode (hereinafter "rotatable member") and the permeable 
electrode being retained by one member or two or more members in 
cooperation. 
The member or members may also or alternatively serve to form means for 
containing the first fluid phase in contact with the electrode, for 
example an electrode chamber to contain and/or channel the first and/or 
second fluids. 
The permeable electrode may have a plane of symmetry in which the axis of 
rotation lies, e.g. it may be in the form of a permeable slat which is 
rotated about an axis perpendicular to the axis of the slat and distant 
from the mid-point thereof. Preferably the permeable element has a 
plurality of planes of symmetry which intersect at a line co-incident with 
the axis of rotation, e.g. it may be in the form of a permeable slat which 
is rotated about an axis perpendicular to the axis of the slat and 
co-incident with the mid-point thereof. More preferably the permeable 
electrode has an axis of symmetry which co-incides with the axis of 
rotation, e.g. the permeable electrode may be in the form of an annulus 
which is rotated about its axis of symmetry so that the electrode is fully 
dynamically balanced in rotation. Where the permeable element is in the 
form of an annulus the outer diameter of the annulus is typically in the 
range 250 mm to 1.25 meters, and the inner diameter is typically in the 
range 50 mm to 60 mm. 
While the axis of rotation may be horizontal or vertical or at any angle 
between, it is often convenient to have the axis horizontal. Where a 
permeable electrode in the form of an annulus is employed, typically 
rotary movement is applied to it by a shaft projecting from the plane of 
the annulus along the axis thereof. The permeable electrode may be rotated 
by, for example, a variable speed fluid drive, a pulley which may be 
driven by a belt from an electric motor, or by turbo-propulsion. 
As the specific surface area for any particular permeable electrode is 
increased, the necessary applied pressure drop across the permeable 
electrode increases and the possibility of starvation of the electrode of 
the second fluid increases. Simple experiment will readily reveal a 
suitable permeable electrode for any desired speed of rotation and fluid 
combination. 
Where at least one rotatable member is employed to retain the electrode 
and/or to form an electrode chamber, the permeable electrode may be 
disposed throughout or in part of the member or throughout between, or 
between parts of, two members. 
The size of the permeable electrode and its disposition in the rotatable 
member may be determined by the density and the interfacial area of the 
permeable element and by the flow characteristics of the fluids. 
The or each rotatable member will generally have or comprise the same, or 
similar, form as the permeable electrode, and preferred forms and the 
reasons therefor will be as described for the electrode hereinbefore. Thus 
where the electrode is an annulus, the rotatable member will often 
comprise a disc, by which the electrode is clamped axially against e.g. 
another such disc, with an annulus between the discs which surrounds the 
outer periphery of the electrode. 
Each rotatable member, for whatever reason it is used, may be constructed 
of any material or combination of materials which has (a) the mechanical 
strength and creep resistance to withstand the stress generated in the 
material during rotation of the rotatable member at the rotational speeds 
employed and (b) the corrosion resistance to tolerate the environments 
with which the rotatable member may be in contact during use. Typical 
materials from which each rotatable member may be constructed include 
inter alia plastics which are not degraded in the electrode environment, 
such as halogenated or some halogenatable polymers such as PVC, 
chlorinated PVC, chlorinated rubbers and chloroprene rubbers and PTFE 
composites, and some engineering plastics such as ABS; graphite; and 
metals such as titanium and nickel. The material of any given part of the 
rotatable member will also be determined by its other functions, e.g. 
whether it needs to be conductive or not. Choice of a suitable material 
will present no problem to those skilled in the art. 
Where, as is usual, the second fluid is the less dense of the two, the 
speed at which the permeable electrode is rotated will depend on the 
maximum practical hydrostatic pressure which must and can be overcome to 
permeate the electrode with the second fluid; this in turn depends on the 
radial distance over which the second fluid flows in the permeable 
electrode. 
The minimum speed at which the permeable electrode is rotated is often 
determined by the flow characteristics of any liquid phase. The maximum 
speed at which the permeable electrode may be rotated is governed by the 
mechanical strength of the permeable electrode, and/or of each rotatable 
member. Where the or each rotatable member is or comprises a disc in or 
between which an annular permeable electrode is disposed throughout, the 
speed of rotation will be: for a disc of 0.5 meters diameter, 1000-3000 
rpm; for a disc of 1 meter diameter, 500-2000 rpm; for a disc of 1.5 
meters diameter, 400-1000 rpm. Average centrifugal acceleration of the 
fluids in the electrode is then typically in the range 20 to 1000 g. 
The direction of flow of the second fluid in the process according to the 
present invention will depend on the relative densities of the two fluids, 
and on their relative flow rates. As noted hereinbefore, for the first 
reason the second phase is generally a gas. 
Where, as is preferred, the permeable electrode has a relatively high 
specific surface area it may require a relatively high applied pressure 
drop to permeate the electrode with the liquid first fluid. Thus, where 
there is no risk of depletion of the first fluid or a reactant or 
electrolyte component thereof by a low first fluid flow rate through the 
electrode, a zero or low total radial flow velocity is acceptable and may 
be desirable. 
Where the second fluid is a gas and the first fluid has a zero or low total 
radial flow velocity (e.g. a U-shaped or C-shaped radial path, as will 
often be the case and is preferred) the second fluid will tend to flow 
radially inwards (Embodiment A). This is often facilitated and enhanced by 
increasing the speed of rotation of the permeable electrode. 
In theory, the apparatus of the present invention in its broadest aspects 
could be operated using a denser second fluid, with radially outward flow 
of the second fluid and/or with the first fluid flowing radially inwards 
or outwards. In the latter case, suitable and routine choice of the 
fluids, their radial flow velocities and the speed of electrode rotation 
could be made for co- or counter-current flow of the two fluids. 
Where Embodiment A is employed as is usual it will be appreciated that 
means are necessary distant from the axis of rotation and preferably 
adjacent to the radially outer perimeter of the permeable electrode to 
charge the permeable electrode with the second fluid. Such charging means 
typically comprise at least one charging orifice in a radially outer wall 
of an electrode chamber formed by one or more rotatable members. 
Preferably the electrode chamber is rotatably supported in a housing to 
form a space between the electrode chamber radially outer surface and the 
housing inner surface from which space the second fluid may be charged via 
a plurality of charging orifices to the permeable electrode. 
It will be appreciated that even if the first phase is not depleted by the 
reaction, it may be depleted by entrainment with the reaction product 
and/or second fluid phase leaving the electrode and/or its chamber. This 
necessitates means to deliver the first fluid to the permeable element 
which also typically comprises an orifice in an electrode chamber wall 
through which the fluid may flow. 
The delivery means is conveniently an orifice in a radially inner wall of 
an electrode chamber, although we do not exclude the possibility that it 
may be located elsewhere between the axis of rotation and the outer 
perimeter of the rotatable member. Preferably the delivery orifice 
communicates with a space extending axially through the electrode 
assembly, for example the interior of a hollow shaft (which also serves to 
rotate the electrode assembly), to which the first fluid may be charged 
conventionally. Where either fluid is a mixture of components, these may 
be delivered to the permeable electrode through the same or separate 
delivery means, e.g. they may be delivered through concentric or adjacent 
tubes. 
Means for removing a reaction product of the two phases from the electrode 
will often also serve as an outlet means for the second fluid and/or first 
fluid which has or have permeated the electrode. In Embodiment A this 
product removal means is conveniently a plurality of outlet orifices in a 
radially inner wall of an electrode chamber. Where the first fluid 
delivery orifice is also in a radially inner wall of an electrode chamber 
it is convenient that there is a single annular inner wall with the 
plurality of outlet orifices disposed uniformly around part, e.g. half, of 
the periphery and with the delivery orifice in the other part. 
Preferably the outlet means communicates with an axially extending space 
similar to and adjacent to or coaxial with the first fluid delivery space 
described above, and from which a reaction product and/or first and/or 
second fluid run-off may be collected. 
The residence time of the second fluid within the permeable electrode is a 
function of the radial dimensions of the permeable electrode, the nature 
and permeability of the permeable electrode, the rotational speed, and the 
flow rate of the fluids. These parameters interact with each other and 
affect the residence time. For example, where the radius is increased and 
the other parameters kept constant the residence time is increased; where 
the flow rate is increased and the other parameters kept constant the 
residence time is reduced; where the rotational speed is increased and the 
other parameters kept constant the residence time is reduced. 
In order to put into effect the process of the invention described 
hereinbefore, the electrode assembly is used in an electrochemical cell. 
It will be appreciated that the permeable electrode of the present 
invention may be a cathode or an anode, or both electrodes may be an 
electrode of the present invention. It is greatly preferred that, whether 
the permeable electrode is a cathode or anode, it is within an electrode 
chamber, that is, it is separated from the other electrode by conventional 
means, for example an ion-specific ion-permeable membrane such as a Nafion 
membrane with different anolyte and catholyte or a (micro)perforate inert 
membrane e.g. a PTFE (Gortex) gauze with a common electrolyte. Such an 
arrangement has the advantage of separating cathode and anode reactions 
and thus of minimising undesirable side reactions. 
As mentioned previously the permeable electrode, with a relatively large 
specific surface area, may effectively fill the greater part, or 
substantially all, of the electrode chamber, and may thus offer a 
relatively large surface area to electrolyte volume ratio and thus a 
relatively low cell internal resistance. The permeable electrode, any 
electrode chamber and membrane and the cell may conveniently be of the 
lamellar form found in conventional cell presses. Thus the electrode 
itself may typically be a felt lamella 0.05 to 3 mm thick. The lower end 
of this range will be inappropriate where it is necessary to continually 
feed to the electrode a first fluid phase which is depleted by the 
reaction, since the pressure drop over the electrode due to the thinness 
of the electrode will not be practically surmountable. 
It is also greatly preferred that all the components of the cell such as 
the electrodes, any electrode chambers including a membrane and any other 
rotatable member are of the same form with respect to the axis of rotation 
and of similar transverse dimensions. Thus discoidal and/or annular 
components of substantially the same overall radius are particularly 
preferred. 
A plurality of such cells, may conveniently be joined in series 
electrically to give a series cell cascade, i.e. a bipolar arrangement. 
This arrangement offers a number of advantages. Spatially it is convenient 
that the cells are arranged to have a common axis of rotation, i.e. they 
may all be rotated by a common driveshaft. As mentioned hereinbefore each 
cell may conveniently be lamelliform and provide greater compactness for a 
given current rating and/or electro-chemical cell or electrode reaction 
rate. This compactness may be enhanced by making the cells axially 
contiguous in a cell press, and further enhanced by providing each pair of 
adjacent cells with a common conductive wall (typically a rotatable 
member) to provide an anode-cathode connection between adjacent cells. 
Such an arrangement has the added advantage of eliminating the material 
and maintenance costs associated with the low-resistance bus-bars 
necessary for parallel cell banks. Typically, the cells in the cascade 
will be identical; it is particularly convenient to design the number of 
cells in the cascade so that the operational voltage drop across the 
cascade corresponds to a conventional industrial supply voltage for 
example (440) v. 
Accordingly the invention further provides a series cell cascade for 
electrochemical reaction between two fluid phases one of which is a 
liquid, characterised by comprising at least two electrode assemblies in 
accordance with the present invention, in series. 
The cascade will in general comprise a plurality of identical electrode 
assemblies in which the electrodes are of the same polarity. Favoured and 
preferred assemblies and components thereof in the cascade are as so 
described hereinbefore. 
It will be appreciated that the fluid charging and supply means and fluid 
collecting means for the anode series and the cathode series within the 
cell series will respectively be in parallel from a manifold. 
For this reason, these means must be so designed and arranged to minimise 
leakage currents across cells and to avoid shorting-out cells in the 
series. 
Thus, where the first or, less likely, the second fluid phase is 
electrically conductive, the means for delivering the first fluid, or 
charging the second fluid, to the permeable electrode, will be highly 
resistive, for example any connection between the manifold and the 
electrode chamber will be of maximised length and minimised cross-section. 
Similarly, any manifold for removing and/or collecting any of the two fluid 
phases and/or any reaction product which is conductive will generally be 
of sufficiently large cross-section and/or of material of relatively high 
surface tension with respect to the removed and/or collected material, so 
that the latter will tend to be in dispersed or particulate form in the 
manifold. 
The present invention also provides a process for effecting electrochemical 
reaction between two fluid phases, the first of which is a liquid, 
characterised by charging the second fluid phase in parallel to a 
plurality of rotating permeable electrodes of the same polarity in a 
series cell cascade. 
The processes according to the present invention may be employed in any 
electrochemical reaction between two fluid phases one of which is a 
liquid; inter alia for the reduction of the overpotential required to 
discharge species in the first fluid phase, by removing those species by 
reaction; and for continuous-mode electrosynthesis: and for fuel cells; 
where the present apparatus is particularly advantageous in ensuring 
intimate reactive contact between gaseous second fluids and liquid first 
fluids. 
In the first instance it will not in general be desired to collect the 
product of the electrochemical reaction. Example of such reactions include 
the cathodic oxidation of hydrogen ion in an aqueous first fluid phase 
with any reducible second fluid phase, to reduce the hydrogen 
overpotential. Examples of suitable reducible second fluid phases include 
gases and gas mixtures, such as oxygen and air. 
The reduction in overpotential in this way may lead to considerable energy 
savings in conventional electrolytic processes, even taking into account 
the energy expenditure in operating the present apparatus, and e.g. the 
loss of electrolytic hydrogen as a recycled energy source. 
In the second instance the planned product(s) of a specific electrochemical 
reaction will in general be collected. Examples of such reactions include 
the cathodic reduction of any reducible second fluid phase liquid or gas 
with hydrogen ion, such as phases comprising species which contain oxo or 
thiooxo groups bonded to carbon, nitrogen, phosphorus or sulphur atoms. 
Examples of such reactions also include the anodic oxidation of any 
oxidisable second fluid phase with for example amide, hydroxide or halide 
ion; the second fluid phase may advantageously be gaseous and may comprise 
unsaturated species such as alkenes or other oxidisable organic species. 
Further features of the apparatus of the invention will now be described in 
terms of that embodiment in which the second, inwardly flowing fluid is a 
gas and the first fluid has zero or low total radial flow velocity. The 
skilled man will however appreciate that similar considerations will apply 
mutatis mutandis to other embodiments such as those mentioned hereinbefore 
.

In FIG. 1, a series cell cascade 1 is made up of a series of identical 
repeat unit cells, which except for the two end cells of the cascade, 
consist of a conductive (e.g. titanium) disc 2 having a central joint 3A 
and a peripheral gasket 4A axially abutting one face, each being 
insulative and of equal axial thickness. (The gasket 4A is annular, the 
joint 3A is essentially annular, but described in greater detail 
hereinafter) and a permeable (metal felt) annular cathode 5 located by and 
between the joint 3A and gasket 4A, in contact with a discoidal membrane 
6, which is either ion-permeable (e.g. Nafion) or inert and 
(micro)perforate (e.g. Gortex) axially abutting on one face the joint 3A 
and gasket 4A and on the other a second central joint 3B and second 
peripheral gasket 4B, each being insulative and of equal axial thickness 
(the gasket 4B is annular; the joint 3B is essentially annular, but 
described in greater detail hereinafter). The joint 3B and gasket 4B 
axially abut the disc 2 of the adjacent repeat unit cell. 
Thus, in each cell the disc 2, joint 3A, gasket 4A and membrane 6 define a 
cathode chamber for retaining a catholyte first fluid phase in contact 
with the permeable electrode (cathode) 5 enclosed in the chamber. 
In each cell the membrane 6, joint 3B, gasket 4B and the disc 2 of the 
adjacent repeat unit cell define an anode chamber for anolyte, the disc 2 
of the adjacent cell being the anode of this cell and the anode-cathode 
bridge between this and the adjacent cell. The disc 2 may serve as an 
anode, or the chamber may be filled with an annular felt anode 42 similar 
to the cathode. 
In FIGS. 1 and 2, each gasket 4A has a plurality of radial inlet ports, 28 
which may be radial perforations through, and/or radial channels in a face 
of, the gasket 5A, and which are means for charging a gaseous second fluid 
phase to the cathode 5. In this particular embodiment they are disposed 
uniformly about the gasket periphery. 
In FIGS. 1, 2 and 3, each central joint 3A has a plurality of outlet ports 
7A which may be radial perforations through, and or radial channels in a 
face of the joint 4A and which are inter alia means for removing a 
reaction product of the two phases from the cathode 5 in its chamber. In 
this particular embodiment they are disposed uniformly about half the 
joint periphery. 
The two end cells of the cascade are provided in place of conductive discs 
2 as their outer axial faces, with conductive flanges 8A and 8B of 
slightly greater radius, and integral with hollow half-shafts 9A and 9B, 
which may be respectively positively and negatively charged as described 
hereinafter. Each flange 8A or 8B has the same number of axial holes 10 
uniformly disposed about its periphery, each fitted with an insulative 
grommet 11 and axially in register with a hole 10 in the other flange 8B 
or 8A respectively. Through each axial pair of holes 10 pass elongate 
clamping bolts 12 with nuts 13 which may be self-locking (as shown) or 
provided with other conventional locking means such as locking nuts or 
washers or flanged washers each with a lug and set-pin (not shown). These 
bolts 12 and nuts 14 clamp the half-shafts 9A and 9B into a rigid, 
rotatable cascade assembly. (Pairs of concentric annular lips 18 on the 
faces of the discs 2 and flanges 8A and 8B locate the joints 3A and 3B and 
gaskets 4A and 4B in the clamped assembly. The assembly is rotatably 
mounted in a housing 15 in insulative bearings 16A and 16B and there are 
means for rotating the assembly, and hence the cathode, such as an 
electric motor and belt or fluid clutch drive (not shown). Slip rings 17A 
and 17B about the half-shafts 9A and 9B are means for charging the flanges 
8A and 8B respectively positive and negative. 
The skilled man will appreciate that, although this specific embodiment is 
described in terms of a permeable cathode for a cathodic reaction with a 
gaseous second fluid phase, the cascade may be arranged and used, mutatis 
mutandis in a self-evident manner with a permeable anode for a similar 
anodic reaction; or with a permeable cathode and anode for cathodic and 
anodic reactions with the same or different cathodic and anodic second 
fluid phases. 
The skilled man will also appreciate that if it is desired to use a liquid 
second fluid phase, different embodiments of the cascade may be necessary, 
in particular as regards the specific design of the means for charging the 
second fluid phase to the permeable electrode and of the electrode itself. 
Further details of the cascade relate to the solution of problems 
associated with the use of a cascade rather than a single cell and are 
thus inessential to the cell per se. 
Some of these details such as catholyte and anolyte feeds also relate to 
the specific use of the described embodiment for the electrolysis of brine 
anolyte to give chlorine with the cathoid oxidation of hydrogen ion in 
caustic soda (first fluid phase) catholyte by (second fluid phase) air or 
oxygen. The total cell reaction may be represented as: 
EQU 4H.sup.+ +4Cl.sup.- +O.sub.2 .fwdarw.2H.sub.2 O+2Cl.sub.2 
These specific details may thus be inessential to the cascade when used in 
other reactions. 
In the specific embodiment, it will be seen that it is necessary to feed 
fresh brine anolyte continuously to the anode chamber to compensate for 
electrolytic depletion, and to provide outlet and collection means for the 
chlorine evolved. Similarly it is necessary to feed fresh catholyte 
caustic continuously to the cathode chamber to compensate for dilution by 
the water produced and for depletion by catholyte carried out of the 
chamber in the air or oxygen stream through outlet ports 7A. 
As mentioned hereinbefore it is necessary to ensure that any inlet feed and 
outlet collection manifolds and the liquid rates therethrough are designed 
to minimise leakage currents therethrough and to avoid the shorting-out of 
any cell in the cascade. 
In FIGS. 1, 2 and 3 the cascade is provided with a caustic (catholyte) 
inlet manifold 19 and a brine (anolyte) inlet manifold 20, each of 
semicircular cross-section and disposed with their plane walls adjacent to 
each other on opposite sides of the cascade axis 21. 
Concentric with the caustic inlet manifold 19 and brine inlet manifold 20 
respectively are a caustic (catholyte) outlet manifold 21 and a brine 
anolyte and chlorine outlet manifold 22, each of semi-annular cross 
section. 
The walls of the inlet manifolds 19 and 20 are defined by the centre joints 
3A and 3B, and those of the outlet manifolds 21 and 22 by the discs 2, 
centre joints 3A, membranes 6 and centre joint 3B, as follows: 
In FIG. 4 a centre joint 3A consists of an outer annulus 23A joined by webs 
24A to an inner annulus 25A bisected by a brace 26A. The outer annulus 23A 
webs 24A and inner annulus 25A define spaces which are parts of the outlet 
manifolds 21 and 22, and the inner annulus 25A and brace 26A define spaces 
which are parts of the inlet manifolds 19 and 20. Each disc 2 and membrane 
6 has a circular aperture 27 which is so dimensioned, and the cascade 
assembly is so mounted, that it is in register with the inner periphery of 
the outer annulus 23A, which latter thus abuts a disc 2 or membrane 6 in 
the cascade assembly. 
The webs 24A, inner annulus 25A and brace 26A stand proud of the faces of 
the outer annulus 23A by approximately half the thickness of the disc 2 or 
membrane 6 respectively when compressed in the cascade press. 
Radial outlet ports 7A which pass radially through the outer annulus 23A or 
are channels in that face thereof which abuts the membrane 6 in the 
cascade assembly, communicate between the caustic outlet manifold 21 and 
the outer periphery of the outer annulus 23, that is the cathode chamber 
in the cascade assembly. 
A radial inlet 29A, which passes radially through a web 24 or is a channel 
in that face of the web nearest the membrane 6 in the cascade assembly, 
communicates between the caustic inlet manifold 19 and the outer periphery 
of the outer annulus 23 or cathode chamber. 
In FIG. 5 a centre joint 3B is similar to a joint 3A in corresponding 
essential features via outer annulus 23A, webs 24B, inner annulus 25B and 
brace 26B, but is mounted in the cascade assembly rotated through 
180.degree. with respect to each corresponding joint 3B. 
Thus, radial outlet ports 7B, which, if channels, are again in that face of 
the outer annulus 23B which abuts the membrane 6 in the cascade assembly, 
communicate between the brine and chlorine outlet manifold 22 and the 
anode chamber in the cascade assembly. 
Similarly radial inlet 29B, which, if a channel, is again in that face of 
the outer annulus 23B nearest to the membrane 6 in the cascade assembly, 
communicates between the brine inlet manifold and the anode chamber in the 
cascade assembly. 
At one end of the cascade, the centre of cathodic flange 8A has a 
semi-annular aperture 30A in register with the caustic outlet manifold 21 
and a semi-circular opening 31A in register with the caustic inlet 
manifold 19. 
The aperture 30A communicates with the interior 32A of the hollow 
half-shaft 9A and thence via the hollow interior 33A of axial bearing 34A 
to an air-caustic separator 35A with air outlet 36A and caustic outlet 
37A. 
The interior 33A of the half-shaft 9A is provided with a caustic inlet pipe 
38A running between the opening 31A and a caustic inlet port 39A, which 
opens into the interior of a water cooled radial bearing 40A. The bearing 
40A has a caustic inlet 41A. 
Similarly, at the other end of the cascade, the centre of anodic flange 8B 
has a semi-annular 30B in register with the brine outlet manifold 22 and a 
semi-circular opening 31B in register with the brine inlet manifold 20. 
The aperture 30B communicates with the interior 32B of the hollow 
half-shaft 9B and thence via the hollow interior 33B of axial bearing 34B 
to chlorine-brine separator 35B with chlorine outlet 36B and brine outlet 
37B. 
The interior 33B of the half-shaft 9B is provided with a brine inlet pipe 
38B running between the opening 31B and a brine inlet port 39B, which 
opens into the interior of a water-cooled radial bearing 40B. The bearing 
40B has a brine inlet 41B. 
As mentioned hereinbefore the radial inlet ports 28 in the gaskets 4A are 
means for charging a gaseous second fluid phase (here air or oxygen) to 
each cathode 5. The ports 28 communicate with the interior of the housing 
15, which has an air/oxygen inlet 43 and a sump 44 with a ball-valve 45 in 
a caustic outlet 46. The latter handles any catholyte leakage from the 
inlet ports 28. 
In operation, first fluid phase caustic solution at 70.degree. C. is fed to 
permeate each cathode 5 from the caustic inlet 41A via the bearing 40A, 
inlet pipe 38A, caustic inlet manifold 19 and radial inlet 29A, and 
escapes from the cathode 5 via the radial outlet ports 7A, caustic outlet 
manifold 21, half-shaft interior 33A, and bearing interior 33A to the 
separator 35A. 
At the same time, brine also at 70.degree. C. is fed to each anode 42 from 
the brine inlet 41B via the bearing 40B, inlet pipe 38B, brine inlet 
manifold 20 and radial inlet 29B and escapes from the anode 42 via the 
radial outlet ports 7B, brine outlet manifold 22, half-shaft interior 33B 
and bearing interior 33B to the separator 35B. 
The cathodic flange 8A is charged negatively via the slip ring 17A, and the 
anodic flange 8B is charged positively via the slip-ring 17B, to a 
potential difference of (about) 15 v. 
Each cathode 5 in the cascade is rotated by driving the half-shaft 9A, via 
a pulley or pinion 46 mounted on the half-shaft 9A, with an electric motor 
(not shown). 
Second fluid phase air is charged to each cathode 5 from the air inlet 43 
at 6.5 ats via the housing 15 and inlet ports 28, and permeates each 
cathode 5 from the ports 28 and is removed from each cathode 5 via the 
same route as the caustic, described hereinbefore, together with water 
produced by the cathode reaction. 
Chlorine produced anodically escapes from each anode 42 by the same route 
as the brine, described hereinbefore.