Note: Descriptions are shown in the official language in which they were submitted.
11485~
C-7638
MEMBRANE-ELECTRODE PACK ALXALI CHLORINE CELL
This invention relates to membrane-type electrolytic
cells and particularly to monopolar cells.
Commercial cellq for the production of chlorine
and al~ali metal hyd.roxides have been continually
developed and improved over a period of time dating
back to at least 18g2. In general, chloralkali cells
are of the depo3ited asbestos diaphragm type or the
~lowing mercury cathode type. During the past few
years, developments have been made in cells employing
ion exchange membranes (hereafter "membrane cells")
which promise advantages over either diaphragm or
mercury cells. It is desirable to take advantage of
existing technology, particularly in diaphragm cells,
but it is also necessary to provide cell designs which
meet the requirements of the membranes. Since
suitable membrane materials such as that marketed by
E. I. duPont de Nemours and Company under the trade-
mark Nafion~ and by Asahi Gla~s Company Ltd. under the
trademark Flemiontm are available principly in sheet
form, the most generally used of the membrane cells
are of the n filter press" type. In the filter press
type of cell, membranes are clamped between the flanges
of filter press frames. Filter press cells are
usually of the bipolar type. Bipolar filter press
cells have been found to have several disadvantages.
Bipolar filter press cells generally present the
problem of making corrosion-free connections from
~1485C~1
anodes to cathodes through the separating plate.
Bipolar filter press cells also have problems with
preventing electrical leakage from one cell to another
through inlet and outlet streams. Furthermore, polar
cell circuits designed for permissible safe voltages
of about 400 volts are small in production capacity
and are not ecomonical or large commercial plants.
The failure of one cell in a bank of bipolar filter
press cells in usual practice requires shutting down
the entire filter press bank.
Filter press cells of monopolar design are not
well known, probably because of the substantial
practical problem of making electrical connections
between the unit frames in the filter press and between
one cell and the next. Tieing all of the anodes
together with a single electrical bus and tieing all
of the cathodes together with a single electrical
bus interferes with drawing the frames together to
form the seal between frames and membranes. On the
other hand, use of flexible cables from cell to cell
provide~ no way of removing one cell at a time from
the circuit withoutinterrupting the current on the
entire circuit.
To il}ustrate the awkwardness of previous attempts
to design monopolar membrane cells, reference is made to
U.S. Patent No. 4,056,458, by Pohto et al, issued
November 1, 1977, to Diamond Shamrock Corporation. The
Pohto et al patent discloses a cell which, like bipolar
filter press cells, has the electrodes and end plates
oriented perpendicular (see FIG. 8 of Pohto, et al)
to the o~erall path of current flow through the cell.
Specifically, Pohto et al discloses a central electrode
assembly sandwiched between two end electrode
assemblies, with membranes in between, to form a closed
cell. A plurality of central electrode assemblies appar-
ently may also be sandwiched in a similar manner. The
end compartment and each of the center compartments of
--2--
~ ~48501
Pohto et al are flanged and maintained paired by
gaskets and fasteners holding flanges in pairs. This
type of cell may be practical for small units producing
~everal hundred pounds of chlorine per day, but it is
not economically practical for plants which produce
~everal hundred tons per day. For example, Pohto et al
diwloses connecting the cellfi to bus bars in a system
which would only be suitable economically on a small
scale. Specifically, electrode rods extend fromthe cell
tops. This includes rods of both polarities. If one
tries to design such a bus system for a cell having a
total current capacity of approximately 150,000 amperes
which is a typical commercial cell current, the bus
system will be found to be very large, cumbersome, and
expensive.
The pre~ent invention, which will be referred to
hereinafter as the "side-stack cell" for simplicity,
eliminates many of the problems mentioned above by
providing a monopolar membrane electrolytic cell
~0 which comprises:
a plurality of vertical, hollow, foraminous, planar
anode frames extending in a direction parallel to an
overall path of current flow through said cell;
a plurality of vertical, hollow, foraminous, planar
cathode frames extending in said direction and
alternatingly interleaved with said anodes;
3 plurality of sheets of cation exchange membrane
material oriented in ~aid direction, one of s~id sheets
being pre~sed between each opposite pair of said anodes
and cathodes;
sealing means between each of said framea and
said sheets;
pressing means for pressing, transversely to said
direction, said frames together in a pack against said
membranes and sealing means so as to form a substantially
fluid-tight cell:
11485-~1
raw material supply conduits and product withdrawal
conduits communicating with the interior of each of
said hollow anode and cathode frames;
a plurality of substantially horizontal anode
S conductor rods extending into said anode frames in
said direction from a first side of said pressed pack;
a plurality of substantially horizontal cathode
conductor rods extending into said cathode frames in
said direction from a second side, opposite to said
first side, of said pressed pack;
an anode terminal outwardly extending in said
direction from said first side of said pack and a
cathode terminal outwardly extending in said direction
from said opposite second side of said pack;
an anode current collector, adjacent said first
side of said pack and oriented transversely to said
direction for electrically connecting said anode
conductor rods to said anode terminal;
a cathode current collector adjacent said opposite
second side of said pack and oriented transversely to
said direction for electrically connecting said
cath~de conductor rods to said cathode terminal;
the total number of .said anode and cathode frames
in said pressed pack being within the range of from
about 5 to about 50; and
the ratio of thickness of said pressed pack to the
height of said cathode and anode frames being no more than
approximately ~
The side-stack cell provides several major advantages
over existing membrane cells. Among the advantages
of the invention is that the electxode elements and
membranes are formed into a stack or "pack~ bGlted
between end frame~ which support the pack to form
a convenient unit with respect to capacity, floor
space, and portability. Since the number of units in
11485~1
the pack are limited to less than about 50, problems
with leakage or problems with deformation of connecting
bus due to temperature changes which are serious with
conventional filter press cells are virtually eliminated.
Another advantage is that, in case of failure of a mem-
brane, only a single cell including about 20 membranes
can readily be removed for dismantling, repair and
reassembly. This is more economical than either
taking out an entire filter press assembly on the one
hand or providing an expensive arrangement for replacing
individual membranes on the other hand. Still another
advantage is that since the anode and cathode structures
of the present invention with substantially horizontal
conductor rods permit àn extraordinarily high cell,
lS the intercell electrical connections provide, in
combination with the substantially horizontal electrode
conductor rods, a short direct current path through the
circuit, thereby minimizing the amount of conductor
material required for the cell and thereby minimizing
voltage losses through the conductors of the cell.
Yet another advantage of the present invention is that
because of the simple electrical connection taking the
cell of the invention out of service is relatively
fast and simple.
Other advantages of the invention will become
apparent upon reading the description below and the
invention will be better understood by references to
the attached drawings in which:
FIGURE 1 is a schematic view of a conventional
prior art bipolar or monopolar filter press cell circuit;
FIGURE 2 is a schematic view of the monopolar
electrical cell circuit of the invention showing, by way
of example, eight preferred cells of the invention;
FIGURE 3 is a front elevational view of two of
the eight cells of FIGURE 2, taken along line 3-3 of
FIGURE 2;
11485~1
FIGURE 4 is a side elevational view of one of the
cells of FIGURE 3 taken along line 4-4 of FIGURE 3 and
showing the anode side of that cell;
FIGURE 5 is a vertical, cross-sectional rear view
through the cell of FIGURE 4 taken along line 5-5 of
FIGURE 4 showing an electrode frame thereof;
FIGURE 6 which is identical to FIGURE 5 except that
the disengagers are omitted and the anode and cathode
terminals are vertical rather than horizontal;
FIGURE 7 is an elevational view of the electrochemical
cell 16a from the anode end illustrating the dimension h
representing the height of both the anode and the cathode
frames and the dimension t representing the thickness of
the pack 22 with some structural elements partially broken
away to emphasize the structure forming the dimensions
h and t; and
FIGURE 8 is an enlarged elevational view of the
circled portion of FIG. 7 with the tie bolt 30 of FIGURE 7
removed showing the top of an anode frame 25, a cathode
frame 27 and one of the end plates 26 to illustrate more
clearly the limits of the dimensions h and t.
FIGURE 1 depicts a conventional filter press cell
circuit which includes four filter press banks 120 con-
nected in series with four electrical shut-off switches 121
and in parallel with a rectifier 122. Rectifier 122 is
connected in conventional manner with a source 123 of alter-
nating current of sufficient capacity to provide the desired
current density through the cells of filter press banks 120.
It will be noted that in the prior art filter press cell
banks 120, the electrode frames are oriented perpendicular
to the overall path of current flow through the cell banks.
If one of the electrode frames or one of the membranes be-
tween the electrode frames is damaged and must be replaced,
one switch 121 is opened to remove the particular bank 120
in which the damaged membrane or frame is located from the
electrical circuit. This obviously shuts down one entire
bank of frames so that no production is obtained from the
disconnected cell bank 120 during the time the switch 121
associated with that cell bank 120 is open.
~148501
In contrast, the electrical circuit 10 shown in
FIGURE 2 comprises a DC power source 11 and electrical
paths 12, 13 and 14. Electrical paths 12 and 14 each
include four electrical cells 16a, 16b, 16c and 16d,
16e, 16f, 16g and 16h, respectively. There is no
specific magic in the number four; rather, four cells are
-6a-
li485C~1
arbitrarily chosen by way o~ example. In a normal
commercial chloralkali plant, there might reasonably
be 100 or more cells per circuit rather than merely
eight. In cell circuit 10, DC power source 11 would
typically include a source 18 of alternating current and a
rectifier 20. Each of the cells 16a-h is comprised of
a pack 22 of electrode frames 24. ~rames 24 are hollow,
foraminous, planar and are oriented parallel to the over-
all direction of current flow through circuit 10. In
particular, cells 16a-d are oriented with their respective
frames parallel to path 12 while cells 16e-h are oriented
with their respective frames parallel to path 14. As will
be seen below in greater detail, this unconventional
orientation of frames 24 provides a major technical
advantage to circuit 10 in that the amount of conductor
material required for circuit 10 is greatly reduced by
such orientation.
FIGURE 3 is a front elevational view of cells
16a and 16b of circuit 10 of FIGURE 2 taken along
line 3-3. This view shows the anode terminals 40,42
of cell 16a on the right and cathode terminals 32,34
of cell 16b on the left. FIGURE 4 is also a view of
cell 16a, but instead taken along line 4-4 of FIGURE 3
50 as to show the anode side or end of cell 16a.
Therefore, FIGURES 3 and 4 should be viewed together
and the reference numbers in both FIGURE 3 and FIGURE 4
as well as FIGURES 2,5, and 6 all refer to the came
parts in all FIGURES. Cells 16a and 16b each comprise
a front end plate 26, a rear end plate 28, a plurality
of interleaved anode frames 25, and cathode frames 27,
a plurality of tie bolts 30, anupper anode terminal 40,
a lower anode terminal 42, anupper anode collector 41,
a lower anode collector 43, anupper cathode terminal 32,
a lower cathode terminal 34, anupper cathode collector
36, lower cathode collector 38r and a material supply
and withdrawal system 44. System 44, in turn, comprises
a fresh brine supply conduit 46, spent brine withdrawal
11485~
conduit 48, a chlorine outlet pipe 50, anolyte disengager
52, a water supply line 54, a caustic withdrawal line
56, a hydrogen outlet line 58, and a catholyte disengager
60. Chlorine outlet line 50 and hydrogen outlet line 58
are connected, respectively, to chlorine line 62 and
hydrogen line 64 which, in turn, lead to chlorine and
hydrogen collection systems (not shown). Cells 16a and
16b are supported on support legs 68 and are connected to
one another by an intercell connector 66. Cells 16a
and 16b each are pro~ided with a catholyte drain/inlet
line 72 and an anolyte drain/inlet line 70. Lines 70
and 72 can be valved drain lines connected to each
frame 24 in order to allow catholyte and anolyte to
be drained from anodes, and cathodes, respectiveIy.
Alternatively, lines 70 and 72 can also be connected to
disengager 52 and 60, respectively, in order to provide
the recirculation path for disengaged anolyte and catho-
lyteliquid. In the embodiment of FIGURES 3-5, lines
70-72 are connected in that manner to disengagers
52 and 60. In the event that line~ 70 and 72 are merely
drain lines, an internal ~downcomer" pipe would be
required from disengager 52 to each anode frame 25
and a separate "downcomer" would be required from
disengager 60 to each cathode frame 27 in order to allow
recirculation of anolyte and catholyte within cells 16a
and 16b. Referring to FIGURES 2, 3, and 5, it is seen
that the overall current flow path through cells 16a
and 16b is from right to left in FIGURE 3, from top to
bottom in FIGURE 2, and from left to right in FIGURE 5.
This current flow is best seen in FIGURES 3 and 5.
In particular, current flows from anode tenminals
40,42 to anode collectors 41,43 then to anode conductor
rods 94 (see FIGURE 5). From conductor rods 94, the
current flows to a planar anode surface 96,98 and then
through the anolyte, the membrane, and the catholyte to
the surfaces 82,84 of cathode frames 27 and then to cathode
conductor rods 86 (again see FIG. 5) and then to cathode
collectors 36,38 and then onto cathode terminals 32,34
11485~1
Cathode terminals 32 and 34 are connected by intercell
connectors 66 to the anode terminals 40,42 of the next
cell in the series of circuit 10. Thus, it is seen
that current flows in a very straight and direct path
through circuit 10 with the only transverse flow occurring
through the actual inter-electrode gap. If an electrode
frame or membrane of any of cells 16a-h is damaged, it
is a simple matter to bypass current around the cell
containing the damaged frame or membrane while allowing
the current to flow through the other seven cells. In
this manner, a minimum amount of interruption in production
results. In fact, a spare cell (not shown) is preferably
available and could be substituted for any disconnected
cell which was removed for repair.
FIGURE 5 shows the preferred structural configuration
of cathode frames 27. Each cathode frame 27 comprises
top channel 74 and anode side channel 76, a cathode side
channel 78 and a bottom channel 80 as well as a rear
mesh surface 82 and a front mesh surface 84. The height
of each frame 27 is at least half and preferably at least
twice the thickness the pack 22. In other words,
channels 76 and 78 are at least half and preferably twice
as long the distance between end plates 26 and 28.
FIGURES 7 and 8 best illustrate the height and thickness
dimensions with h indicating the height dimension and t
indicating the thickness dimension for the cell. A
plurality of vertically spaced conductor rods 86 pass
through and are supported by cathode side channel 78.
Rods 86 extend from collector plates 36,38 substantially
horizontally across the width of frame 27 and are slightly
inclined at the end furthest from collector 36,38 in order
to direct hydrogen gas evolved by frame 27 toward an
"upcomer" 90 leading to disengager 60 and to provide partial
disengagement within the confines of frame 27, if desired.
Rods 86 could also be horizonal, if desired, and could
have the configuration described in U.S. Patent Nos.
~148501
3,932,261, and 4,008,143 commonly assigned or the
inclination disclosed in U.S. Patent No. 3,963,596, also
commonly assigned. Other substantially horizontal
condustor rods configurations which encourage desirable
gas flow patterns could also be utilized. Each cathode
frame 27 alqo includes eyes 88 or some other alternative
guide in order to allow frames 27 to be properly
aligned with frames 25 and end plates 26 and 28 during
assembly of the cells 16a-h. Top channel 74 is
preferably of an inverted U-shape in order to better
collect generated gases and direct the collected gases
to upcomer 90. Upcomer 90 connects top channel 74
with disengager 60. In actual operation, the fluid
flowing into and through upcomer 90, likely to be a
~froth" or "foam" rather than a fully separated gas.
However, if the design of rods 86 and frames 27 is
such that partial separation can and does occ~r within
the confines of frame 27, then top channel 74 may
provide sufficient space to complete the disengagement
of catholyte liquids from gases. Nevertheless, it is
desirable to have a disengager 60 as a safety feature
even if it is not normally needed. Disengager 60 is
also fluidly connected to a downcomer 92 as previously
noted. Downcomer ~2 is preferably in fluid communi-
cation with catholyte drain inlet 72 or bottom channel
80 so that the disengaged liquid catholyte can be
recirculated, if desired, to the bottom of each cathode
frame 27.
FIGURE 5 also shows, in cut away, the configuration
of anode frames 25 (see FIGURE 4). Anode frames 25
are generally similar in construction to cathode frames
27 and comprise top and bottom and two side channels.
As with frames 27, frames 25 have a front mesh
surface 96 and a rear mesh surface 98 which will
electrically connect to anode terminals 40, 42
by anode conductor rods 96 and anode collectors 41,
43. Anode conductor rods 96 are inclined in similar
--10--
~14BS~l
fashion to cathode conductor rods 86. However, as
with rods 86, rods 96 could be horizontal or offset,
or both, if desired. An anolyte disengager 52 is
connected to each anode frame 25 in similar fashion to
the connection of disengager 60 to cathode frames 27.
Therefore, a downcomer 112 and an upcomer 110 are
provided to conduct fluids from and to disengager 52,
respectively. Downcomer 112 is connected to anolyte
drain/inlet line 70 in order to allow recirculation
of anolyte within anode frames 25. Cathode surfaces
96,98 and anode surfaces 82 and 84 are separated by
a membrane 100, and a cathode spacer 104. In order
to seal between each anode frame 25 and cathode frame 27,
an anode gasket 106 is pressed be_ween membrane 100
and the channels of anode 25 while a cathode gasket is
pressed between membrane 100 and channels 74,76,78,
and 80 of cathode frame 27. When bolts 30 (see FIGURE 4)
are tightened so as to press in plates 26 and 28
toward each other, gaskets 106 and 108 are pressed
against the membranes and channels and the pack 22
see FIGURE 2) is thereby sealed against fluid leakage.
FIGURE 6 shows a cathode frame 27 which is identical
to cathode frame 27 as seen in FIGURE S except that in
FIGURE 6 a vertical cathode collector plate 114 and
a vertical cathode terminal 116 are substituted for
collectors 36 and 38 and terminals 32 and 34 and vertical
anode collector 118 and vertical anode terminal 119
is substituted for collectors 41,43 and terminals 40,42.
The choice between vertical and horizontal terminals
and collectors will depend upon the particular method
and apparatus disconnecting the cells 16a-h, which is
desired.
~148S~l
With the above detailed description in mind,
modifications to the particular configuration will
be seen to be within the scope of the invention as
claimed below. The preferred embodiment disclosed
above is merely provided by way of example and it
is envisioned that modifications will be made without
departing from the scope of the invention. It will
be noted that, for example, the electrode frames are
shown to be of picture-fxame type configuration with
four peripheral channels and two parallel, planar,
mesh surfaces attached to the front and back of the
frame. The channels could be replaced by
tubes or bars. Single wall construction is preferred
for the top channel in order to allow the top channel
to serve as a gas collector. Preferably, this single
wall top channel i8 reinforced at its open bottom to
prevent bending, buckling, or collapse. The remaining
channels could be of any suitablé configuration which
would allow the frames to be pressed together against
~ a gasket in order to achieve a fluid-type cell. While
a flat front and rear surface is shown for the channels,
it would be possible to have many other configurations
such as round or even ridged channels. The mesh is
shown in FIGUR~ 5 to be welded to the inside of the
peripheral channels of the frame but could be welded to
the front and back outside surfaces if the configuration
of such outside surfaces did not interfere with gasket
sealing when the mesh surfaces were on the outside
rather than inside.
The cells 16a-h could be disconnected by the ty2e
of procedure disclosed in commonly assigned, commonly
invented U.S. Patent Nb. 4,227,987, issued ~ber 14, 1980.
That application discloses use of a remotely operated
jumper switch, bolt rotator, and hydraulic jack
together with a slide-back type intercell connector
in order to allow the cells to be positioned very
close together and yet be safely and rapidly disconnected.
-12-
1~48501
In that procedure, a pair of conductor arms are
closed together against both the cathode terminals
32,34 of th~ cell preceding the cell to be disconnected,
and a separate pair of conductor arms are similarly
closed or clamped against anode terminals 40,42 of
the cell following the cell to be disconnected.
The remotely operated bolt rotator is then positioned
in an operative position adjacent bolts fastening
the intercell connectors 66 between the cell to be
disconnected and the preceding and following cells.
The bolt rotator is then remotely actuated to loosen
those bolts and a hydraulic jack is the-n inserted between
the intercell connector and one of the cells and is
remotely actuated to force the intercell connector out
of engagement with the cell to be disconnected. A new
cell is then substituted for the cell which has thus
been disconnected and this new cell is reconnected by
sliding the intercell connectors back into engagement
with the new cell through use of the remotely operated
jack and then tightening the engagement connector by
use of the remotely operated bolt rotator. Following
that operation, the remotely operated jumper switch
can be diRconnected. Other jumper switches and other
disconnection procedures could be utilized to disconnect
cells 16a-h within the scope of the invention. The
advantage of the preferred disconnection method
just described is that it enables the cells to be
placed very close together even though they may be
quite large and carry large current. This close
spacing of the cells helps in realizing the objective
of maximizing the amount of product that can be produced
in a plant with a limited floor space.
The cathode frames are preferably built of nickel
and the mesh surfaces on the cathode are also preferably
made of nickel. The mesh surfaces are coated with a
~1485C~
catalytic coating, such as Raney nickel, to reduce
their hydrogen overvoltage to a very low level. There
are several methods known for accomplishing such coating.
One particularly desirable method is to apply a very
thin coating through the use of a cathode sputtering
procedure. The anodes are preferably dimensionally
stable metal anodes made of titanium and the anode mesh
surfaces are preferably titanium coated with a catalytic
coating such as a mixed crystal of TiO2-Ru02. Procedures
for applying such mixed crystal coatings are also well
known. The spacers be*ween the membrane and the mesh
surfaces are preferably electrolyte-resistant netting
having a spacing which is preferably about 1/4" in
both the vertical and horizontal directions so as to
lS effectively reduce the interelectrode gap to the thickness
of the membrane plus two thicknesses of gasketing.
The netting also restricts the vertical flow of gases
evolved by the mesh surfaces and drives the evolved
gases through the mesh and into the center of the hollow
electrodes. That is, since the netting has horizontal
as well as vertical threads, the vertical flow of gases
i~ blocked by the horizontal threads and directed through
the mesh surfaces of the electrode frames into the interior
space of the electrode frames, i.e. the space within
each frame between the mesh surfaces of that frame.
~ith a 1/4" rectangular opening in the netting, the
effective cell size in the interelectrode gap is
reduced to about l/4"x 1/4". This reduced effective
cell size allows the cell to be much hlgher than it
could otherwise be because gases are not accumulated
in the interelectrode gap but rather are rorced through
the electrode surfaces to the interior of the electrode.
$he use of horizontal conductor rods further assist
in this gas flow pattern by creating limited restrictions
within the space between mesh surfaces of each electrode
so as to generate a venturi or low pressure effect
which pulls the gases from the interelectrode
gap through the mesh surfaces and into the interior
-14-
~1485~
of the electrodes. The horizontal conductor rods can
further assist gas flow by altering the gas flow
direction from vertical to substantially horizontal
along the outside of the conductor rods, if desired.
The conductor rods can thereby serve as gas directing
channels which forces the gas to flow to one side of
the frame so as to provide an efficient upward flow of
gases within the frames.
Many other similar modifications will also be
a~parent, and it is, therefore, easily recognized
that the invention claimed below should be entitled
to full range of equivalence.
