U.S. patent application number 12/087196 was filed with the patent office on 2009-02-26 for elastic current distributor for percolating cells.
This patent application is currently assigned to UHDENORA S.p.A.. Invention is credited to Leonello Carrettin, Fulvio Federico, Dario Oldani, Peter Woltering.
Application Number | 20090050472 12/087196 |
Document ID | / |
Family ID | 38141182 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090050472 |
Kind Code |
A1 |
Federico; Fulvio ; et
al. |
February 26, 2009 |
Elastic Current Distributor for Percolating Cells
Abstract
An electrolysis cell comprising an anodic compartment and a
cathodic compartment separated by an ion-exchange membrane, at
least one of said compartments equipped with a gas-diffusion
electrode having two major surfaces, the first major surface of
said gas-diffusion electrode facing the membrane and being in
contact with a planar porous element to be traversed by an
electrode flow, the second major surface of said gas-diffusion
electrode being in contact with a current distributor comprising a
multiplicity of elastic conductive protrusions for compressing said
gas-diffusion electrode against said planar porous element.
Inventors: |
Federico; Fulvio; (Piacenza,
IT) ; Woltering; Peter; (Neuenkirchen, DE) ;
Carrettin; Leonello; (Milan, IT) ; Oldani; Dario;
(Milan, IT) |
Correspondence
Address: |
HEDMAN & COSTIGAN P.C.
1185 AVENUE OF THE AMERICAS
NEW YORK
NY
10036
US
|
Assignee: |
UHDENORA S.p.A.
Milan
IT
|
Family ID: |
38141182 |
Appl. No.: |
12/087196 |
Filed: |
January 15, 2007 |
PCT Filed: |
January 15, 2007 |
PCT NO: |
PCT/EP2007/050362 |
371 Date: |
June 25, 2008 |
Current U.S.
Class: |
204/252 |
Current CPC
Class: |
H01M 4/8605 20130101;
H01M 8/0232 20130101; Y02E 60/50 20130101; C25B 9/65 20210101; C25B
9/19 20210101; H01M 8/1004 20130101 |
Class at
Publication: |
204/252 |
International
Class: |
C25B 9/04 20060101
C25B009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 2006 |
IT |
MI2006 A 000054 |
Claims
1. An electrolysis cell comprising an anodic compartment and a
cathodic compartment separated by an ion-exchange membrane, at
least one of said compartments equipped with a gas-diffusion
electrode having two major surfaces, the first major surface of
said gas-diffusion electrode facing the membrane and being in
contact with a planar porous element to be traversed by an
electrode flow, the second major surface of said gas-diffusion
electrode being in contact with a current distributor comprising a
multiplicity of elastic conductive protrusions for compressing said
gas-diffusion electrode against said planar porous element.
2. The cell of claim 1 wherein said multiplicity of conductive
protrusions exerts a pressure of 0.1 to 0.5 kg/cm.sup.2 on the
gas-diffusion electrode.
3. The cell of claim 1 wherein said current distributor comprising
said multiplicity of conductive protrusions is obtained by cutting
and shaping of a metal sheet.
4. The cell of claim 3 wherein said conductive protrusions are
spring tags arranged according to a comb-like geometry.
5. The cell of claim 4 wherein said spring tags are arranged in
adjacent pairs and the spring tags of each of said pairs protrude
in opposite directions from the major place of said metal
sheet.
6. The cell of claim 3 wherein said conductive protrusions are
optionally quadrangular individual tiles comprising a multiplicity
of spring tags and at least one opening for gas circulation.
7. The cell of claim 6 wherein said tiles are welded to a rigid
current collector in optionally off-set parallel rows.
8. The cell of claim 3 wherein said metal sheet has a thickness of
0.5 to 1.5 millimeters.
9. The cell of claim 3 wherein said metal sheet is a punched
sheet.
10. The cell of claim 3 wherein said metal sheet is made of
nickel.
11. The cell of claim 10 wherein said nickel sheet is provided with
a coating for reducing the electric contact resistance in
correspondence of said protrusions.
12. The cell of claim 1 comprising an additional element for
distributing the mechanical compression force selected from the
group of meshes, punched sheets and expanded sheets inserted
between said current distributor and said gas-diffusion electrode.
Description
[0001] The invention relates to a cell for industrial electrolytic
processes, and in particular to a cell comprising an anodic
compartment and a cathodic compartment separated by an ion-exchange
membrane, wherein one or both compartments are equipped with
gas-diffusion electrodes and the process electrolyte flows across a
percolator or equivalent porous element.
[0002] In the following description, reference will be made to a
cell suitable for depolarised chlor-alkali electrolysis, that is to
the process of alkali chloride brine electrolysis wherein the
hydrogen evolution cathodic reaction is inhibited in favour of the
reaction of oxygen consumption on a gas-diffusion cathode, for
instance as disclosed in EP 1033419; the invention is nevertheless
not limited to chlor-alkali cells, being applicable to any
industrial electrochemical process making use of gas-diffusion
electrodes.
[0003] There are known in the art depolarised chlor-alkali cells of
particularly advanced type wherein the process electrolyte flows
across a suitable porous planar element or percolator under the
action of gravity: a cell of such kind is for instance disclosed in
WO/0157290. In this kind of cell, there are typically present an
anodic compartment obtained from a titanium shell, fed with an
alkali chloride concentrated brine and containing a titanium anode
provided with a catalytic coating for chlorine evolution, and a
cathodic compartment delimited by a nickel cathodic shell; the two
compartments are separated by a cation-exchange membrane. The
caustic soda produced in the process flows by gravity across a
porous element inserted in the cathodic compartment contacting on
one side the ion-exchange membrane, on the other side a
gas-diffusion cathode. In other words, while the anode is a stiff
metallic element which is electrically and mechanically connected
to the anodic shell by means of a suitable metal structure selected
among those known in the art, for instance an array of ribs, the
cathode is a thin porous element obtained from a silver net, a
carbon cloth or other type of non self-standing equivalent
structure. For this reason, the current transmission from the
back-wall of the cathodic shell to the gas-diffusion electrode must
be effected by means of a structure providing a more delocalised
contact and capable of mechanically supporting the electrode. In
order to improve the electrochemical features, it is also necessary
that the cathode be pushed against the percolator with a certain
pressure, indicatively 0.1 to 0.5 kg/cm.sup.2, so as to allow the
electrical continuity while contributing to the confinement of the
circulating liquid electrolyte. To satisfy all of the above
conditions, the cells of the prior art are provided with an
electric current feed system relying on two distinct elements:
firstly, a rigid current collector integral to the cathodic shell
which may for instance consist of a rib array, as in the anodic
side; secondly, a metal mattress positioned between the rigid
current collector and the gas-diffusion electrode, which is
capable, in conditions of suitable compression, to transmit a
sufficient pressure to the gas-diffusion electrode thereby ensuring
the required electrical continuity. An equivalent solution is
applied for the retrofitting of chlor-alkali cells of the
traditional type, to adapt the same to a percolation-type
depolarised process, for instance as illustrated in FIG. 2 of WO
03/102271: in this case, the original cell cathode, which is a
metallic electrode for hydrogen evolution made of nickel or steel,
as known in the art, takes the role of the current collector, while
a nickel mattress (elastic current collector) acts as the
intermediate element for current transmission between the rigid
current collector and the gas-diffusion electrode.
[0004] The above indicated solution entails however a few
inconveniences hampering the commercialisation of this type of
cells: the two-component type current transmission system involves
in fact excessive costs and thicknesses, difficulties of
installation and of dimensional control of the mattress (especially
in the peripheral zone), difficulty of controlling the deformations
and the elastic forces, besides of course adding a contact
interface not particularly favourable in terms of ohmic drop, such
as the one between mattress and gas-diffusion electrode.
[0005] It is one object of the present invention to provide an
electrolytic cell separated by an ion-exchange membrane and
equipped with gas-diffusion electrode and percolator element for
electrolyte circulation overcoming the limitations of the prior
art.
[0006] Under another aspect, it is one object of the present
invention to provide an improved electric current feed system for
an electrolytic cell provided with gas-diffusion electrode and
percolator.
[0007] The invention consists of an electrolysis cell with an
anodic compartment and a cathodic compartment separated by an
ion-exchange membrane, wherein at least one of the two compartments
is equipped with a gas-diffusion electrode having two major
surfaces, a first major surface facing the membrane being in
contact with a percolator traversed by an electrolyte flow, and a
second major surface, opposed to the first major surface, being in
contact with a current distributor comprising a multiplicity of
elastic conductive protrusions suitable for compressing the
gas-diffusion electrode against the percolator. As percolator it is
intended any porous planar element suitable for being traversed by
gravity by a liquid flow, as disclosed in WO/0157290. In one
preferred embodiment, the current distributor, which replaces the
rigid current collector-elastic current collector assembly of the
prior art, is obtained by cutting and shaping of a single metal
sheet, for instance a nickel sheet in the case of a cathodic
collector for chlor-alkali cells. In this case, the nickel sheet is
a sheet of thickness typically comprised between 0.5 and 1.5 mm,
preferably provided with a coating suitable for reducing the
contact resistance. The nickel material of the sheet may be
variously alloyed and for instance selected from the assortment of
commonly available products; the choice of a nickel material of
grade and mechanical characteristics suitable for the manufacturing
of springs, for instance with superior elastic features, will prove
particularly advantageous. In one particularly simple and effective
embodiment, the conductive protrusions capable of imparting a
sufficient pressure to the electrode are spring tags arranged in
couples so that two adjacent spring tags protrude in opposite
direction from the major plane of the metal sheet from which they
are obtained. In this way a more effective and homogeneous support
of the whole electrode surface is obtained. The above indicated
solution is suited to an optimum cell design in almost every
process condition; nevertheless, the use of the mattress according
to the prior art as a contact element at high current density has
the advantage of allowing an effective gas circulation (for the
case of depolarised chlor-alkali electrolysis for example, an
effective supply of oxygen to the gas-diffusion electrode) which
could fall short with a simple lamellar structure. In this case, a
particularly preferred embodiment provides the conductive
protrusions to be in form of individual tiles, in their turn
comprising one or more spring tags for providing the electrical
contact but also one or more openings to favour the gas passage.
The conductive protrusions may for instance be disposed in parallel
rows distributed along the whole electrode surface.
[0008] The current distributor in accordance with the invention is
suitable for achieving an efficient electrical contact directly on
the gas-diffusion electrode surface, at a pressure preferably
comprised between 0.1 and 0.5 kg/cm.sup.2, thereby getting rid of a
contact interface with respect to the system of the prior art in
which a rigid current collector is coupled to an elastic current
collector; on the other hand, in one embodiment of the invention an
additional element for distributing the mechanical compression
force may be inserted between current distributor and gas-diffusion
electrode, for example consisting of a thin mesh, or of an expanded
or punched sheet. In such case the number of contact interfaces is
equivalent to that of the prior art, nevertheless the corresponding
resistance is substantially lower than what would be obtained with
the scarcely elastic mattress of the prior art directly in contact
with a gas-diffusion electrode. Moreover, as it will be easily
appreciated by one skilled in the art, the overall thickness of the
cell is substantially lower.
[0009] The invention will be described more in detail with the aid
of the attached drawings, which have a merely exemplifying purpose
and are not intended to limit the invention.
[0010] FIG. 1 represents a percolation type depolarised
chlor-alkali cell according to the prior art.
[0011] FIG. 2 represents a percolation type depolarised
chlor-alkali cell according to the present invention.
[0012] FIG. 3 represents a first embodiment of the current
distributor according to the invention.
[0013] FIG. 4 represents a second embodiment of the current
distributor according to the invention.
[0014] FIG. 5 represents a third embodiment of the current
distributor according to the invention.
[0015] In FIG. 1 it is shown a percolation type depolarised
chlor-alkali cell according to the prior art, comprising one anodic
and one cathodic compartment separated by an ion-exchange membrane
(500). The cathodic compartment is delimited by a cathodic
back-wall (101), in contact with an electric current feed system
relying on two distinct elements, a rigid current collector (201)
integral thereto, and an elastic current collector (210) consisting
of a mattress, for instance made of nickel. The cathode (301)
consists of a porous gas-diffusion electrode fed with oxygen,
contacting on one side the mattress (210), on the other side a
percolator (400) consisting of a planar porous element traversed by
the electrolyte flow under the action of gravity. The ion-exchange
membrane (500) acting as the separator has a cathodic surface in
contact with the percolator (400) and an anodic surface facing an
anode (302) which may be in contact therewith or kept at a small
predetermined distance. The anode (302) is normally comprised of a
titanium substrate consisting of a mesh or of an expanded or
punched sheet, or optionally of a juxtaposition of two such
elements; the anodic substrate is provided with a catalytic coating
for chlorine evolution as known in the art. The electrical
continuity between anode (302) and anodic compartment back-wall
(102) is ensured by a rigid current collector (202). The cathodic
(201) and anodic (202) rigid current collectors may consist of rib
arrays, undulated sheets, sheets provided with suitably spaced
gophers or other types of current collectors as known by those
skilled in the art. In FIG. 2 it is shown a percolation type
depolarised chlor-alkali according to the present invention,
wherein the elements in common with the cell of FIG. 1 are
indicated by the same reference numerals.
[0016] The electric current feed system consists of a multiplicity
of conductive protrusions (220), for instance an assembly of
springs or elastic spring tags suitable for compressing the
gas-diffusion electrode (301) against the percolator (400); between
the assembly of conductive protrusions (220) and the gas-diffusion
electrode (301) an optional element for distributing the mechanical
compression force (230) is inserted, for instance a thin mesh, or
an expanded or punched sheet.
[0017] FIG. 3 shows one embodiment of the multiplicity of
conductive protrusions obtained from a single metal sheet and
consisting in this case of an assembly of elastic spring tags (221)
disposed in parallel according to a comb-like geometry: the spring
tags are arranged in couples, so that each two spring tags protrude
in opposite directions from the major plane of the original metal
sheet. Depending on the cell size, a single row of spring tags
(221) may cover the whole active surface, or more rows may be
arranged side by side, as will be evident to one skilled in the
art.
[0018] FIG. 4 shows a preferred embodiment of the multiplicity of
conductive protrusions obtained from a single metal sheet: in this
case the protrusions are preferably quadrangular individual tiles
(222) obtained by cutting and shaping of a sheet, optionally welded
directly to the rigid current collector (201), each of them
comprising elements performing different functions: for example, by
means of a suitable folding step, each tile is provided with edges
with a curvature angle of about 90.degree. (223) in order to impart
the required stiffness. A multiplicity of suitably spaced apart
spring tags (224) acts as the contact element with the
gas-diffusion electrode (301), and a multiplicity of holes (225)
favours the gas supply and circulation, in this case with
particular reference to the oxygen required for the cathodic
reaction. The various tiles welded to the rigid current collector
(201) are preferably arranged on optionally off-set parallel
rows.
[0019] FIG. 5 shows a variation of the preferred embodiment shown
in FIG. 4 of the multiplicity of conductive protrusions obtained
from a single metal sheet: in this case the original metal sheet is
a punched sheet, and the multiplicity of holes (225') extends on
the whole body of the tile (222), including the spring tags (224).
In this way an enhanced gas supply is obtained, also effective when
the spring tags (224) are compressed until the end of stroke,
coming in contact with the sheet from whence they are projected. An
albeit marginal saving in the manufacturing phase is also obtained,
consisting of the independent execution of holes (225) indicated on
tile (222) of FIG. 4. The tile configuration also presents a
further mechanical advantage: in case of a sudden high cathode
counterpressure (for instance due to errors in the control of
process conditions, or to element handling and assembling
mistakes), the spring tags do not undergo a permanent deformation
in view of the abutment of the GDE on the whole tile surface. In
this case, the fact that the tiles are obtained from a punched
sheet is even more important to guarantee the correct gas supply in
any case, as is it evident to one skilled in the art.
EXAMPLE 1
[0020] A lab experimental electrolysis cell of 0.16 m.sup.2 active
area was equipped according to the scheme of FIG. 2 with a titanium
DSA.RTM. anode (302) provided with a ruthenium and titanium
oxide-based catalytic coating, a Nafion.RTM. N982 ion-exchange
membrane (500) commercialised by Dupont/USA, a nickel foam
percolator, a gas-diffusion electrode consisting of a silver net
activated with a silver-based catalyst.
[0021] The electric current feed system was comprised of a
multiplicity of elastic conductive protrusions each consisting of a
tile (222) as illustrated in FIG. 5, obtained from a 1 mm thick
nickel punched sheet.
[0022] The cell anodic compartment was fed with a circulating
sodium chloride brine having a concentration of 210 g/l, at a
current density of 4 kA/m.sup.2 and at a temperature of 90.degree.
C. The cathodic product consisted of 32% by weight caustic soda
flowing downwards across the percolator. In these conditions, after
stabilising the process conditions on the plant for ten days, a
cell voltage comprised between 2.00 and 2.05 V was detected.
EXAMPLE 2
[0023] The test of example 1 was repeated in analogous conditions,
making use of a cell of the prior art. The only substantial
difference consisted therefore in the cathodic current feed system,
comprising a rigid current collector structure consisting of a
nickel rib array welded to the cathodic back-wall coupled to a
commercial nickel mattress.
[0024] In the same process conditions of example 1, after ten days
of stabilisation a cell voltage comprised between 2.10 and 2.15 V
was detected.
[0025] The foregoing description is not intended to limit the
invention, which may be used according to different embodiments
without departing from the scopes thereof, and whose extent is
univocally defined by the appended claims.
[0026] Throughout the description and claims of the present
application, the term "comprise" and variations thereof such as
"comprising" and "comprises" are not intended to exclude the
presence of other elements or additives.
* * * * *