Title of Invention

ELECTROLYTIC CELL WITH ENLARGED ACTIVE MEMBRANE SURFACE

Abstract The invention relates to an electrolytic cell for the production of chlorine from an aqueous alkali halide solution, which mainly consists of two semi-shells, an anode, a cathode and an ion exchange membrane arranged between the electrodes. Spacer elements are arranged between the ion-exchange membrane and the electrodes for fixing the membrane in position and distributing the compressive forces, made of electrically conductive and corrosion-resistant material on at least one side of the membrane.
Full Text 1
ELECTROLYTIC CELL WITH ENLARGED ACTIVE MEMBRANE SURFACE
[0001] The invention relates to an electrolytic cell for the production of chlorine from an
aqueous alkali halide solution, said cell mainly consisting of two semi-shells, an anode,
an cathode and an ion-exchange membrane (hereinafter referred to as "membrane").
5 The internal side of each semi-shell is equipped with strips made of conductive
material, which support the respective electrode and which transfer the clamping forces
acting from the external side and spacer elements arranged between the ion-exchange
membrane and the electrodes for fixing the membrane in position and distributing the
mechanical forces. The spacers are placed on at least one side of the ion exchange
10 membrane and are made of electrically conductive and corrosion-resistant material.
[0002] Electrolytic devices of the single-cell type for the production of halogen gases
are known in the art. In the single-cell type construction up to 40 individual cells are
suspended in parallel on a rack and the respective walls of adjacent pairs of cells are
electrically connected to each other, for example by means of suitable contact strips. In
15 this way the ion-exchange membrane is subjected to high mechanical loads originated
by the externally applied clamping force, which must be transferred through this
element.
[0003] It is known in the present state of technology to weld the electrodes to the
respective semi-shells on strips placed perpendicularly to the electrode and the semi-
20 shell rear wall, and hence aligned in the direction of the clamping force. A multiplicity of
spacers are positioned in the space between the membrane and the electrodes so that
the membrane subject to the external mechanical forces is clamped by said spacers
and thus fixed in position. The spacers are arranged in opposite pairs defining a
contact area, and the strips are positioned on the opposite side of the electrode in
25 correspondence of said contact area.
[0004] Electrolytic cells of this type are disclosed in DE 196 41 125 and EP 0 189 535.
As described in DE 25 38 414, the spacer elements are made of electrically insulating
material. EP 1 073 780 and EP 0 189 535 also teach that the spacers do not consist of
metallic and electrically conductive components. This derives from the fact that the
30 opposite spacer pairs bring about a reduction of the membrane thickness in the
relevant contact area. If the spacer elements were made of electrically conductive
material, short-circuits could be originated in the membrane under the effect of the
mechanical load and of the reduced membrane thickness.

2
[0005] The membrane areas shielded by the spacer elements become inactive under
the point of view of current transmission. During the cell assembly it is virtually
impossible to ensure that a perfect matching of the spacer pairs is effectively achieved.
The resulting membrane surface is therefore somewhat larger than the theoretical
5 surface specified in compliance with the constructive design.
[0006] It is one of the objects of the present invention to provide an electrolytic cell
design overcoming the above illustrated deficiency, in particular allowing for a better
use of the membrane active surface area.
[0007] The object set forth above as well as further and other objects and advantages
10 of the present invention are achieved by providing an electrolytic cell for the production
of chlorine from an aqueous alkali halide solution, which comprises two semi-shells,
and two electrodes, an anode and a cathode, with an ion-exchange membrane
arranged therebetween. The internal side of each semi-shell is equipped with
elongated electrically conductive devices which support the respective electrode and
15 transfer the clamping forces acting from the external side. Moreover, spacer elements
are arranged between the ion-exchange membrane and the electrodes in order to fix
the membrane in position and distribute the mechanical forces, wherein on just one
side of the ion-exchange membrane said spacer elements are made of electrically
conductive and corrosion-resistant material.
20 [0008] In a preferred embodiment of the invention the spacer elements on the side of
the electric current admission, corresponding to the anode side of the membrane, are
made of electrically conductive and corrosion-resistant material whereas the spacer
elements made from electrically insulating material are installed on the cathode side.
[0009] In a particularly preferred embodiment the diameter of the spacer element
25 surfaces in contact with the membrane and consisting of electrically insulating material
is lower than 6 mm, more preferably lower than 5 mm. The inventors have surprisingly
observed that the use of spacer elements with a diameter below 6 mm or less does not
affect at all the current transmission properties of the membrane.
[0010] As mentioned above, with the cells of the prior art it was very difficult to ensure
30 a perfect matching of the opposed spacer element pairs during the cell assembly; the
present invention offers a substantial facilitation in this regard since it is possible to
couple a first narrow spacer opposite a second slightly wider spacer, the latter being
the one made of conductive material and therefore not liable to inactivate the

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corresponding membrane area. Alternatively, it is also possible to use wide spacer
elements with a suitably open structure, provided that the diameter of the opposed
surfaces effectively in contact remains well below 6 mm. In this way the assembly of
the cells is substantially simplified.
5 [0011] A further enhancement can be obtained by suitably shaping the electrode in the
strip contact area so as to form an integral spacer element on the membrane side,
allowing to avoid the use of a separate spacer element.
[0012] According to a preferred embodiment of the invention, the electrically
conductive and corrosion-resistant material used for the spacer components of the
10 electrolytic cells of the invention is selected from the group of titanium and alloys
thereof, nickel and alloys thereof, titanium-coated and nickel-coated materials.
[0013] In another preferred embodiment of the invention, the membrane thickness is
increased by at least 10% in correspondence of the contact area with the electrically
conductive spacer elements, said increase in thickness being obtained by applying an
15 additional coating on one side of the membrane, preferably the cathode side. This
membrane reinforcement permits a local compensation of the mechanical load
imparted by the small cross-sectional area of the spacer element without having to
increase the resistance of the whole membrane.
[0014] In an alternative embodiment of the invention, both the opposed spacer
20 elements are metallic and electrically conductive and the membrane thickness is
increased by at least 10% in correspondence of the contact area therewith. The
increase in thickness of the ion-exchange membrane preferably does not exceed the
double of the original membrane thickness.
[0015] According to another embodiment of the invention, the membrane thickness is
25 uniform throughout the whole surface, metallic and electrically conductive spacer
elements are installed on both sides, said spacers being coated with a material having
substantially the same or equivalent properties with respect to the ion-exchange
membrane in correspondence of the contact area.
[0016] The invention is described hereinafter with the aid of the attached drawings
30 which are provided by way of example and shall not be intended as a limitation of the
scope thereof, wherein fig. 1 is a perspective view of the electrolytic cell of the
invention, fig. 2a shows the distribution of the clamping force in a cell of the prior art,

4
fig. 2b shows the distribution of the current lines in a preferred embodiment of the cell
of the invention, fig. 3 shows the spacer elements according to one embodiment of the
invention.
[0017] Fig. 1 shows the internal components in a perspective view of the electrolytic
5 cell of the invention. Membrane 1 is clamped between spacers 2 and 3 which are in
direct contact therewith. Anode 4 is pressed against spacer element 2, whose rear side
is welded to strip 6. This strip is welded in its turn to the semi-shell wall 8. On the semi-
shell wall 8, contact strip 10 is positioned along the height of strip 6 which in this case
is shaped as a groove and accommodates the contact strips of the adjacent cell (not
10 shown in the figure).
[0018] The construction of the cathode side is analogous so that cathode 5 is in direct
contact with spacer element 3 which is welded to strip 7 on the rear side. Spacer
element 3 is provided with openings as represented in detail in Fig. 3. The strip 7 is
welded in its turn to the semi-shell wall 8.
15 [0019] Fig. 2a illustrates a section of a cell of the prior art, wherein the membrane
thickness is exaggerated to facilitate the illustration thereof. The two arrows 9 indicate
the direction of the external compressive force transmitted through the adjacent cells.
[0020] Membrane 1 has a high-resistance zone 1a on the cathode side and a low-
resistance zone 1b on the anode side, in correspondence of the electric current
20 admission. This membrane stratification helps for the uniform current distribution within
the membrane. On account of the membrane being shielded by insulating spacer
elements 2 and 3, as shown in Fig. 2a, the current flow lines are substantially diverted
in the vicinity thereof, and sections of the membrane not crossed by the electric current
flow are formed in the surrounding area. This section is identified by a dotted region.
25 Due to these inactive sections, the voltage drop within the membrane and the current
density in the active sections are increased.
[0021] Fig. 2b shows the pattern of the current lines in the membrane relative to an
embodiment of the electrolytic cell of the invention. Spacer element 2 on the anode
side is made of metal forms an integral piece with the anode, so that the current lines
30 can enter the low-resistance zone 1b of membrane 1 in parallel without being
deflected. This parallelism is maintained right through the high-resistance zone 1a
within the area of spacer element 3 on the cathode side, so that no formation of blind
areas not crossed by current lines takes place.

5
[0022] Fig. 3 illustrates the structure of a preferred embodiment of the spacer
elements. The bar-type spacer piece 2 on the anode side has a profiled surface on the
side in contact with the membrane, which in the illustrated example has rhombic
protrusions 11 and depressions 12. Spacer piece 3 consisting of insulating material on
5 the cathode side is provided with a multiplicity of superficial recesses so that upon
installation spacer elements 2 and 3 do not cover any membrane surface area having a
diameter above 5 mm.
[0023] The current density of the spacer elements of the invention was investigated in
a test cell. In an electrolytic cell, seventeen rows of four spacers each having a 8 mm
10 width and 295 mm length are installed. These spacer elements were provided with
openings as shown in Fig. 3 so as to obtain a diameter of max. 5 mm for the contact
surface. The recesses determined an overall open ratio of the spacer element surface,
defined as the ratio of open to total surface, of about 50%.
[0024] In this way an increase in the active membrane surface of about 0.08 m2 (from
15 2.72 m2 to 2.80 m2) was obtained. Hence, the current density decreased by 2.9%.
[0025] In this way, the operating voltage of the electrolytic cell equipped with a
standard high load N982 membrane, showing a k factor of 80 mV/(kA/m2), is decreased
by 2.3 mV/(kA/m2) which leads to a voltage reduction of 14 mV at a current density of
6 kA/m2. This corresponds to an energy saving of 10 kWh per tonne of product NaOH.
20 [0026] If the spacer is designed so as to exploit the complete membrane surface area,
the voltage reduction doubles to 28 mV, corresponding to a 20 kWh saving per tonne
of product NaOH.

CLAIMS
1. Electrolytic cell delimited by two semi-shells each fixed to an electrode by means of
a multiplicity of conductive strips, the electrodes consisting of an anode and a
cathode having a major surface separated by a membrane, the membrane and the
5 anode having a first multiplicity of spacer elements arranged therebetween, the
membrane and the cathode having a second multiplicity of spacer elements
arranged therebetween arranged in opposed pairs with said first multiplicity of
spacer elements, said opposed pairs defining a contact area on the membrane
surface and fixing the membrane in position, characterised in that at least one of
10 said first and second multiplicity of spacer elements are made of an electrically
conductive and corrosion-resistant material.
2. Electrolytic cell according to claim 1 characterised in that said multiplicity of
spacer elements made of an electrically conductive and corrosion-resistant material
are said first multiplicity of spacer elements.
15 3. Electrolytic cell according to claim 1 or 2 characterised in that at least one of the
electrodes forms an integral piece with said multiplicity of spacer elements in the
area contacting the membrane.
4. Electrolytic cell according to any one of the preceding claims characterised in that
said electrically conductive and corrosion-resistant material is selected from the
20 group of titanium and alloys thereof, nickel and alloys thereof, titanium-coated and
nickel-coated materials.
5. Electrolytic cell according to any one of the preceding claims characterised in that
one of said first and second multiplicity of spacer elements consists of a multiplicity
of electrically insulating spacer elements having a diameter not higher than 5 mm.
25 6. Electrolytic cell according to any one of the preceding claims characterised in that
the membrane thickness is increased by at least 10% in correspondence of the
contact area with said multiplicity of spacer elements made of an electrically
conductive and corrosion-resistant material.
7. Electrolytic cell according to claim 6 characterised in that said increase in the
30 membrane thickness is obtained by applying an additional coating on one side of
the membrane.
8. Electrolytic cell according to claim 7 characterised in that said additional coating is
applied on the anode side of the membrane.

9
9. Electrolytic cell according to any one of the preceding claims 1 to 4
characterised in that both the first and second multiplicity of spacer elements are
metallic and electrically conductive and the membrane thickness is increased by at
least 10% in correspondence of the contact area defined by said opposed pairs of
5 spacer elements.
10. Electrolytic cell according to any one of claims 6 to 9 characterised in that said
membrane thickness is increased to a final thickness not exceeding the double of
the original thickness.
11. Electrolytic cell according to any one of claims 1 to 4 characterised in that both
10 the first and second multiplicity of spacer elements are metallic and electrically
conductive, at least one of the first and second multiplicity of spacer elements
being coated with the same material of the membrane or with a material of
equivalent properties.

The invention relates to an electrolytic cell for the production of chlorine from an
aqueous alkali halide solution, which mainly consists of two semi-shells, an anode, a
cathode and an ion exchange membrane arranged between the electrodes. Spacer
elements are arranged between the ion-exchange membrane and the electrodes for
fixing the membrane in position and distributing the compressive forces, made of
electrically conductive and corrosion-resistant material on at least one side of the
membrane.

Documents:

02688-kolnp-2007-abstract.pdf

02688-kolnp-2007-claims.pdf

02688-kolnp-2007-correspondence others.pdf

02688-kolnp-2007-description complete.pdf

02688-kolnp-2007-drawings.pdf

02688-kolnp-2007-form 1.pdf

02688-kolnp-2007-form 2.pdf

02688-kolnp-2007-form 3.pdf

02688-kolnp-2007-form 5.pdf

02688-kolnp-2007-gpa.pdf

02688-kolnp-2007-international publication.pdf

02688-kolnp-2007-pct request form.pdf

02688-kolnp-2007-priority document.pdf

2688-KOLNP-2007-ABSTRACT.pdf

2688-KOLNP-2007-AMANDED CLAIMS.pdf

2688-KOLNP-2007-CORRESPONDENCE.pdf

2688-KOLNP-2007-DESCRIPTION (COMPLETE).pdf

2688-KOLNP-2007-DRAWINGS.pdf

2688-KOLNP-2007-ENGLISH TRANSLATION.pdf

2688-KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

2688-KOLNP-2007-EXAMINATION REPORT.pdf

2688-KOLNP-2007-FORM 1.pdf

2688-KOLNP-2007-FORM 18.1.pdf

2688-KOLNP-2007-FORM 2.pdf

2688-KOLNP-2007-FORM 26.pdf

2688-KOLNP-2007-FORM 3.1.pdf

2688-KOLNP-2007-FORM 3.pdf

2688-KOLNP-2007-FORM 5.pdf

2688-kolnp-2007-form-18.pdf

2688-KOLNP-2007-FORM-27.pdf

2688-KOLNP-2007-GRANTED-ABSTRACT.pdf

2688-KOLNP-2007-GRANTED-CLAIMS.pdf

2688-KOLNP-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

2688-KOLNP-2007-GRANTED-DRAWINGS.pdf

2688-KOLNP-2007-GRANTED-FORM 1.pdf

2688-KOLNP-2007-GRANTED-FORM 2.pdf

2688-KOLNP-2007-GRANTED-SPECIFICATION.pdf

2688-KOLNP-2007-OTHERS.pdf

2688-KOLNP-2007-OTHERS1.1.pdf

2688-KOLNP-2007-PETITION UNDER RULE 137.pdf

2688-KOLNP-2007-REPLY TO EXAMINATION REPORT.pdf

2688-KOLNP-2007-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

abstract-02688-kolnp-2007.jpg


Patent Number 249852
Indian Patent Application Number 2688/KOLNP/2007
PG Journal Number 46/2011
Publication Date 18-Nov-2011
Grant Date 16-Nov-2011
Date of Filing 19-Jul-2007
Name of Patentee UHDENORA S.P.A.
Applicant Address VIA BISTOLFI, 35 20134 MILAN
Inventors:
# Inventor's Name Inventor's Address
1 DULLE, KARL, HEINZ MARIE CURIE STRASSE 20-D-50399 OLFEN
2 BECKMANN, ROLAND DORFSTRASSE 125B D-44534 L√úNEN
3 KIEFER, RANDOLF LANGENDREER STRASSE 52A-D-44892 BOCHUM
4 WOLTERING, PETER SANDWEG 18-D-48485 NEUENKIRCHEN
PCT International Classification Number C25B 9/08
PCT International Application Number PCT/EP2006/000643
PCT International Filing date 2006-01-25
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10 2005 003 527.2 2005-01-25 Germany