Title of Invention	DIAPHRAGM ELECTROLYTIC CELL
Abstract	A diaphragm electrolytic cell comprising a lower module (200) of anodes (3) and cathodes (5) and at least one upper module (100) of anodes (16) and cathodes (20) overlaid thereto, said at least one upper module (100) having an anodic compartment which is in direct fluid communication with an anodic compartment of said lower module (200), said at least one upper module (100) being equipped with generally U-shaped anodes comprising two vertical major surfaces (13) fixed to a first horizontal current collector (150), additional titanium-lined copper current collectors being externally secured to at least one of said vertical major surfaces (13), wherein diaphragm-coated cathodes are housed in the hollow space inside said vertical major surfaces (13) of said anodes (16).

Title of Invention

DIAPHRAGM ELECTROLYTIC CELL

Abstract

A diaphragm electrolytic cell comprising a lower module (200) of anodes (3) and cathodes (5) and at least one upper module (100) of anodes (16) and cathodes (20) overlaid thereto, said at least one upper module (100) having an anodic compartment which is in direct fluid communication with an anodic compartment of said lower module (200), said at least one upper module (100) being equipped with generally U-shaped anodes comprising two vertical major surfaces (13) fixed to a first horizontal current collector (150), additional titanium-lined copper current collectors being externally secured to at least one of said vertical major surfaces (13), wherein diaphragm-coated cathodes are housed in the hollow space inside said vertical major surfaces (13) of said anodes (16).

Full Text	BACKGROUND OF THE INVENTION Diaphragm electrolyte cells are predominantly used in the world-wide production1 of chlorine, about 45 million tons per year. Production of chlorine is carried out in electrolytic cells of different types; among these, the diaphragm electrolytic cell, by means of which about 22 million tons of chlorine per year are produced, has a great relevance. A diaphragm electrolytic cell is generally composed of four main parts, as known to the experts in the art: a copper anodic base, lined with a protective titanium sheet, an anodic package, consisting of a multiplicity of anodes disposed in parallel rows and secured to said base, a carbon steel cathodic body, comprising a plurality of cathodes upon which a porous diaphragm is deposited, secured to a current distributor and disposed in parallel rows so that they can be intercalated to the above anodes according to a so-called "finger-type" geometry, and a cover, usually of chlorine-resistant plastic material provided with the nozzles for feeding the brine and discharging the product chlorine. In consideration of the high number of installed cells (about 25000 world-side), of the high amount of energy involved in their operation (about 60 millions of MWh/year) and of the continuous increase in the cost of electricity, the cell diaphragm technology has been, in the course of the years, remarkably improved. Among the many technological innovations which offered the major contributions for decreasing the energy consumption, the following must be noticed: the replacement of the traditional graphite anodes with box-shaped perforated metallic anodes (the so-called "box" type anodes) made of titanium, coated with electrocatalytic material based on noble metals and/or oxides thereof. The replacement of fixed sized "box" anodes with the so-called "expandable anodes", as disclosed in US 3,674,676, allowing for the reduction of the interelectrodic gap. - the suppression of the above interelectrodic gap through the introduction, within the expandable anodes, of means for exerting a pressure between the anodes and the diaphragm, as disclosed in US 5,534,122 - the evolution of the expandable anode through the introduction of the double expander, as disclosed in US 5,993,620, whereto a lower ohmic drop is associated. It may be observed that the cited innovations are all directed to improve the performances in terms of energetic consumption, by means of either an increase of the electrocatalytic activity, or an optimisation of the electrode structure, or again through the reduction of the interpolar gap and the increase in the mass transfer (lower bubble effect and higher electrolyte circulation) obtained through small modifications which do not imply a substantial redesign of the cell structure and thus of easy implementation and reduced costs. Other solutions proposed in the past provide a modification of the cell, and in particular of the cathodic package, directed to increase the electrodic surface thereby decreasing the current density at a given applied total current, and as a consequence the cell voltage and the overall energetic consumption. A further issue of present great relevance is given by the need of increasing the electric load and thus the production; such need is often in contradiction with the lack of a suitable area allowing the installation of additional electrolytic cells. In the co-pending unpublished International Application PCT/EP 02/10848, a solution allowing the increase of the cell active surface with the same projected area is disclosed, by means of the construction of a cell made of a plurality of vertically overlaid modules provided with the conventional interdigitated anodes. This solution is in itself promising, although entailing quite substantial investment costs. It is an object of the present invention to provide a new diaphragm electrolytic cell overcoming the drawbacks of the prior art. In particular, it is an object of the present invention to provide a diaphragm electrolytic cell comprising a multiplicity of overlaid modules of anodes and cathodes, the anodes of at least part of the modules allowing for a substantial reduction of the construction cost. SUMMARY OF THE INVENTION The invention consists of a diaphragm electrolytic cell made of a lower module and of an upper module or a multiplicity of upper modules vertically overlaid thereto, wherein the upper modules are provided with generally U- shaped anodes, comprising two vertical major surfaces fixed to a horizontal current collector, housing the corresponding cathodes within. The two vertical major surfaces of the anodes may be part of a single folded surface; they are preferably foraminous, to allow the circulation of the electrolyte, and are preferably provided with an electrocatalytic coating for chlorine evolution. In order to facilitate the understanding of the invention, reference will be made to the attached figures, which are not to be intended as limiting the invention itself, whose domain is solely limited by the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a side view of a diaphragm electrolytic cell of the prior art. Figure 2 shows an anode of the cell of the invention according to a first preferred embodiment. Figure 3 shows an anode of the cell of the invention according to a second preferred embodiment. Figure 4 shows an arrangement of anodes and cathodes in a module of the diaphragm electrolytic cell of the invention. DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 shows a diaphragm electrolytic cell of the prior art, according to the teaching of the co-pending non published International Application PCT/EP 02/10848. The illustrated cell consists of two vertically overlaid modules, an upper module (100) and a lower module (200), according to the most common embodiment; it is intended that the upper module (100) may be replaced by a plurality of vertically stacked upper modules, as disclosed in the cited co- pending application. The lower module (200) comprises a copper anode base (1), lined with a titanium protective sheet (not evidenced) whereto a plurality of anodes (3) is secured in parallel rows, by means of current collecting stems (4) intercalated to the cathodes (5). The surface of the anodes is preferably made of a grid of perforated sheet or rhomboidal-shaped expanded sheet coated with an electrocatalytic material. The cathodic package consists of a box (6) with open top and bottom, known as cathodic body, with a current distributor (30), provided with a plurality of cathodes (5) fixed inside, secured in correspondence of the external surface thereof. The cathodes (5), known as fingers, are shaped as tubular boxes with a flat elongated cross-section and are arranged in parallel rows intercalated to the rows of anodes (3); the two ends of the cathodes (5) are connected with a manifold (7) running along the four sides of the box (6). The cathode is made for example of an iron perforated sheet or mesh, with the diaphragm deposited on the external surface thereto, facing the anode. The diaphragm has the purpose of separating the anodic compartment from the cathodic one avoiding the mixing of the two gases and of the solutions; originally it was made of polymer modified asbestos, but the technological evolution has led to the adoption of composite asbestos-free diaphragms. The diaphragm may also consist of an ion-exchange membrane or other semipermeable material. The upper module (100) also comprises anodic and cathodic packages, substantially with the same construction materials as in the lower module (200) but in most of the cases of lower height. The upper anodic package is comprised of a frame (15), acting as the upper anodic base and ensuring for the mechanical support and the current distribution for the relevant anodes (16). The frame (15) is made of a titanium sheet provided with holes or slots, suitably dimensioned for putting the two anodic compartments in direct fluid communication. The anodes (16) of the upper module are vertically fixed to the frame, in transversal rows, generally with the same pitch as in the lower module. The anodes (16) of the upper module, fixed to the frame (15) by means of dowel screws (18), often have a lower height. The upper eathodic body is made of a box (19), having the same design and construction materials as that of the lower module and a height depending on that of the upper anodic package; the upper cathodic body is welded along the internal walls of the box (19) to a plurality of cathodes (20) arranged in parallel rows. Each finger, shaped as an elongated tubular box, is in communication with a manifold (21) positioned along the sides of the box (19). The main features of the cathodes and diaphragms of the upper module are equivalent to those of the lower module. The frame (15) and the anode base (1) are reciprocally connected by means of external conductors (not shown in the figure); the box (6) and the box (19) are also connected in a similar way. The cell cover (8), which is made a of plastic chlorine-resistant material, is provided with a chlorine gas outlet (9) and a brine inlet (10). The cell is connected to a direct current supply by means of bus bars. As known to the experts in the art, the cell operates as follows: the feed brine enters the cell through the inlet nozzle (10) placed on the cell cover and is distributed through pipe (23) to the base (1) of the lower anodic compartment, subsequently rising to the top surface thereof and overflowing through the slots of the frame (15) into the anodic space of the box (19). The chlorine disengaged in the lower anodic compartment follows the same path and leaves through the outlet nozzle (9) on the cover (8). The chloride-depleted electrolyte, driven by the pressure corresponding to the hydraulic head between the anolyte and catholyte, permeates through the diaphragm entering the upper (20) and lower (5) cathodic fingers. Hydrogen leaves the upper (21) and lower (7) cathodic compartments respectively through nozzles (25) and (11), connected in parallel to the hydrogen manifold (26). The alkali produced in the upper cathodic compartment (21) leaves through nozzle (27), and enters the lower cathodic chamber (7) through pipe (28) and nozzle (29), where it is mixed with°the alkali produced therein, then leaving the cell through the hydraulic head (12). The level of the cathodic liquor is normally adjusted so that a sufficient gas chamber is always maintained in the lower cathodic compartment (7); consequently, the upper compartment (21) works exclusively as a gas chamber and electrolysis takes place only by direct contact between the solution percolating onto the diaphragm and the cathode. To establish such condition in a reliable fashion, the pipe (28) must obviously have a sufficient large diameter in order to remain substantially full of hydrogen, so that the two cathodic compartments (7) and (21) are subjected to an identical pressure. Figure 2 shows a particular embodiment of the anode of the invention, which is conceived in a completely different manner with respect to the prior art anodes, with or without expander. As it can be observed, the anode structure is given by an electrodic surface (13), folded and open on one side to allow the insertion of a cathode, preferably consisting of a foraminous sheet or a mesh or, as an alternative, of a juxtaposition of foraminous elements such as sheets or meshes. The anode has a single curvature (14), its profile thereby assuming a U-shaped geometry, other shapes of the said profile being possible without departing from the scope of invention. At the base of the anode, in correspondence of the curvature (14), a current collector (150) provided with a preferably threaded stem (160) is welded or otherwise secured. The current collector (150) is horizontal instead of vertical as it would be the case of the prior art, as this allows the internal volume of the anode to be hollow and completely available for the insertion of the corresponding cathode. In principle, both the anodes of the upper module (100) and of the lower module (200) could be realized according to the embodiment of figure 2. However, the cell construction illustrated in figure 1 derives, in most of the case, from a retrofitting of an older diaphragm cell wherein the upper module is overlaid to the lower one in a second time, as disclosed in the co-pending International Application PCT/EP 02/10848. The anodes of the lower module (200) have therefore, in most of the cases, a geometry according to the prior art. Also when a complete replacement of the electrodes of the lower module is carried out, the advantage of employing the anode of figure 2 is partially counteracted by the fact that the anodes (3) of the lower module (200) are usually quite high (for instance 800 mm); the lack of an internal current collector may entail, in this case, substantial ohmic penalties thus lowering the faradaic yield. The anodes (16) of the upper module (100) have conversely a much reduced typical height (for instance 160 mm, as specified in the cited International Application PCT/EP 02/10848), and conducting the electric current along their whole height without resorting to internal current collectors is therefore a negligible issue. For this reason, in a preferred embodiment, the cell of the invention makes use of the anodes of figure 2 only for the upper module (100). In another embodiment, the cell of the invention makes use of such anodes also for the lower module (200), counteracting the increase in the ohmic drop along the electrode height with additional vertical current collectors (not shown), secured to the external surfaces of the anodes. The optional additional titanium- lined copper current collectors, secured externally and not internally, are much easier to remove and restore, contributing in a sensible manner to reduce the costs of reactivation. Fixing the current collectors to the anodes externally instead of internally also offers an additional benefit: when the catalytic coating is periodically deactivated, the anode must be in fact subjected to a reactivation, preceded by an etching treatment in hot concentrated hydrochloric or sulphuric acid. After applying the catalytic ink, the anode must be treated in oven at about 500°C. During these treatments, the bimetallic contact between the copper core of the state-of-the-art current collector and the relevant titanium lining would be seriously damaged by distortion phenomena, the previous detachment of the current collector and ?1s subsequent restoring after the treatment being therefore required. With the illustrated anode however, the horizontal current collector can be entirely made of titanium, with little prejudice in terms of ohmic drops, therefore no problems arise during the heat treatment of reactivation. Figure 3 shows a second particular embodiment of the anode of the invention, whose conception is not too far from the anode of figure 2. Once more, its structure is open allowing the cathode to be housed within; in this case, however, the electrodic surface (13) is formed by two distinct elements, disposed in the vertical position and secured to the current collector (150) in correspondence of one edge (17). The nature of the electrodic surface (13) is fundamentally equivalent to the one described for the previous embodiment; the use of foraminous elements such as sheets or meshes, or juxtapositions thereof, is preferred. Figure 4 is a sketch of a side view of a possible configuration of an upper module (100), according to the best mode of carrying out the invention; the same configuration could be used for the lower module (ZOO), without departing from the scope of the invention. The particular shape of the anode (16), with an open upper part and the interior free of obstacles, may be exploited for housing the cathode (20) within, so that the reduction of the electrode pitch is virtually limited by the sole thickness of the cathode (20). The adjacent anodes, in fact, can be very close to each other ad even in mutual contact, as they are maintained at the same electric potential. The figure shows also constraint elements (31), applied to adjacent pairs of anodes, that are used to open wide the latter under elastic regime so as to facilitate the insertion of the cathodes during the assembly (figure 4A); figure 4B shows how, upon completing the assembly and removing the constraint elements, the anodic surface moves back to the natural position, with the two vertical sides facing the diaphragm- coated major surfaces of the corresponding cathode (20). In figure 4, the anode (16) has an open upper part, but it is clearly possible to assemble the anodes upside down, with an open lower part. It is also possible to provide an assembly procedure that doesn't make use of constraint elements, or that utilises the same in a different fashion, without departing from the scope of the invention. The constructive solution illustrated in figure 4 easily allows an increase of active surface of 30-50% for the relevant module and for a given projected surface. In the description and claims of the present application, the word "comprise" and its variation such as "comprising" and "comprises" are not intended to exclude the presence of other elements or additional components. WE CLAIM: 1. A diaphragm electrolytic cell comprising a lower module (200) of anodes (3) and cathodes (5) and at least one upper module (100) of anodes (16) and cathodes (20) overlaid thereto, said at least one upper module (100) having an anodic compartment which is in direct fluid communication with an anodic compartment of said lower module (200), said at least one upper module (100) being equipped with generally U-shaped anodes comprising two vertical major surfaces (13) fixed to a first horizontal current collector (150), additional titanium-lined copper current collectors being externally secured to at least one of said vertical major surfaces (13), wherein diaphragm-coated cathodes are housed in the hollow space inside said vertical major surfaces (13) of said anodes (16). 2. The cell as claimed in claim 1 wherein said vertical major surfaces (13) of said anodes (16) are parts of a single folded surface delimited by a curvature (14), said horizontal current collector (150) being fixed to said vertical major surfaces (13) in correspondence of said curvature (14). 3. The cell as claimed in claim 1 or 2 wherein at least one of said vertical major surfaces (13) of said anodes (16) is foraminous. 5. The cell as claimed in any one of the previous claims wherein said generally U-shaped anodes (16) are entirely made of titanium or titanium alloys. 6. The cell as claimed in any one of the previous claims wherein said horizontal current collector (150) is made of titanium. 7. The cell as claimed in any one of the previous claims wherein said anodes (3) of said lower module (200) are U-shaped anodes. 8. The cell as claimed in any one of the previous claims wherein at least said vertical major surfaces (13) are provided with a catalytic coating for chlorine evolution. 9. The method for the assembly of the cell as claimed in any one of the previous claims, comprising fixing said U-shaped anodes (16) to the corresponding anodic base (15), maintaining said anodes (16) open wide under an elastic regimen by means of constraint elements (31), housing said diaphragm-coated cathodes (20) within said hollow space inside said vertical major surfaces (13) of said anodes (16) and removing said constraint elements (31). A diaphragm electrolytic cell comprising a lower module (200) of anodes (3) and cathodes (5) and at least one upper module (100) of anodes (16) and cathodes (20) overlaid thereto, said at least one upper module (100) having an anodic compartment which is in direct fluid communication with an anodic compartment of said lower module (200), said at least one upper module (100) being equipped with generally U-shaped anodes comprising two vertical major surfaces (13) fixed to a first horizontal current collector (150), additional titanium-lined copper current collectors being externally secured to at least one of said vertical major surfaces (13), wherein diaphragm-coated cathodes are housed in the hollow space inside said vertical major surfaces (13) of said anodes (16).

Full Text

BACKGROUND OF THE INVENTION
Diaphragm electrolyte cells are predominantly used in the world-wide production1 of
chlorine, about 45 million tons per year. Production of chlorine is carried out in
electrolytic cells of different types; among these, the diaphragm electrolytic cell, by
means of which about 22 million tons of chlorine per year are produced, has a great
relevance.
A diaphragm electrolytic cell is generally composed of four main parts, as known to the
experts in the art: a copper anodic base, lined with a protective titanium sheet, an
anodic package, consisting of a multiplicity of anodes disposed in parallel rows and
secured to said base, a carbon steel cathodic body, comprising a plurality of cathodes
upon which a porous diaphragm is deposited, secured to a current distributor and
disposed in parallel rows so that they can be intercalated to the above anodes according
to a so-called "finger-type" geometry, and a cover, usually of chlorine-resistant plastic
material provided with the nozzles for feeding the brine and discharging the product
chlorine.
In consideration of the high number of installed cells (about 25000 world-side), of the
high amount of energy involved in their operation (about 60 millions of MWh/year) and
of the continuous increase in the cost of electricity, the cell diaphragm technology has
been, in the course of the years, remarkably improved. Among the many technological
innovations which offered the major contributions for decreasing the energy
consumption, the following must be noticed:
the replacement of the traditional graphite anodes with box-shaped
perforated metallic anodes (the so-called "box" type anodes) made of
titanium, coated with electrocatalytic material based on noble metals and/or
oxides thereof.
The replacement of fixed sized "box" anodes with the so-called "expandable
anodes", as disclosed in US 3,674,676, allowing for the reduction of the
interelectrodic gap.
- the suppression of the above interelectrodic gap through the introduction,
within the expandable anodes, of means for exerting a pressure between the
anodes and the diaphragm, as disclosed in US 5,534,122
- the evolution of the expandable anode through the introduction of the double
expander, as disclosed in US 5,993,620, whereto a lower ohmic drop is
associated.
It may be observed that the cited innovations are all directed to improve the
performances in terms of energetic consumption, by means of either an
increase of the electrocatalytic activity, or an optimisation of the electrode
structure, or again through the reduction of the interpolar gap and the increase
in the mass transfer (lower bubble effect and higher electrolyte circulation)
obtained through small modifications which do not imply a substantial redesign
of the cell structure and thus of easy implementation and reduced costs.
Other solutions proposed in the past provide a modification of the cell, and in
particular of the cathodic package, directed to increase the electrodic surface
thereby decreasing the current density at a given applied total current, and as a
consequence the cell voltage and the overall energetic consumption.
A further issue of present great relevance is given by the need of increasing the
electric load and thus the production; such need is often in contradiction with
the lack of a suitable area allowing the installation of additional electrolytic cells.
In the co-pending unpublished International Application PCT/EP 02/10848, a
solution allowing the increase of the cell active surface with the same projected
area is disclosed, by means of the construction of a cell made of a plurality of
vertically overlaid modules provided with the conventional interdigitated anodes.
This solution is in itself promising, although entailing quite substantial
investment costs.
It is an object of the present invention to provide a new diaphragm electrolytic
cell overcoming the drawbacks of the prior art.
In particular, it is an object of the present invention to provide a diaphragm
electrolytic cell comprising a multiplicity of overlaid modules of anodes and
cathodes, the anodes of at least part of the modules allowing for a substantial
reduction of the construction cost.
SUMMARY OF THE INVENTION
The invention consists of a diaphragm electrolytic cell made of a lower module
and of an upper module or a multiplicity of upper modules vertically overlaid
thereto, wherein the upper modules are provided with generally U-
shaped anodes, comprising two vertical major surfaces fixed to a horizontal
current collector, housing the corresponding cathodes within.
The two vertical major surfaces of the anodes may be part of a single folded
surface; they are preferably foraminous, to allow the circulation of the
electrolyte, and are preferably provided with an electrocatalytic coating for
chlorine evolution.
In order to facilitate the understanding of the invention, reference will be made
to the attached figures, which are not to be intended as limiting the invention
itself, whose domain is solely limited by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a side view of a diaphragm electrolytic cell of the prior art.
Figure 2 shows an anode of the cell of the invention according to a first
preferred embodiment.
Figure 3 shows an anode of the cell of the invention according to a second
preferred embodiment.
Figure 4 shows an arrangement of anodes and cathodes in a module of the
diaphragm electrolytic cell of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS
Figure 1 shows a diaphragm electrolytic cell of the prior art, according to the
teaching of the co-pending non published International Application PCT/EP
02/10848. The illustrated cell consists of two vertically overlaid modules, an
upper module (100) and a lower module (200), according to the most common
embodiment; it is intended that the upper module (100) may be replaced by a
plurality of vertically stacked upper modules, as disclosed in the cited co-
pending application. The lower module (200) comprises a copper anode base
(1), lined with a titanium protective sheet (not evidenced) whereto a plurality of
anodes (3) is secured in parallel rows, by means of current collecting stems (4)
intercalated to the cathodes (5). The surface of the anodes is preferably made
of a grid of perforated sheet or rhomboidal-shaped expanded sheet coated with
an electrocatalytic material. The cathodic package consists of a box (6) with
open top and bottom, known as cathodic body, with a current distributor (30),
provided with a plurality of cathodes (5) fixed inside, secured in correspondence
of the external surface thereof. The cathodes (5), known as fingers, are shaped
as tubular boxes with a flat elongated cross-section and are arranged in parallel
rows intercalated to the rows of anodes (3); the two ends of the cathodes (5)
are connected with a manifold (7) running along the four sides of the box (6).
The cathode is made for example of an iron perforated sheet or mesh, with the
diaphragm deposited on the external surface thereto, facing the anode. The
diaphragm has the purpose of separating the anodic compartment from the
cathodic one avoiding the mixing of the two gases and of the solutions;
originally it was made of polymer modified asbestos, but the technological
evolution has led to the adoption of composite asbestos-free diaphragms. The
diaphragm may also consist of an ion-exchange membrane or other
semipermeable material. The upper module (100) also comprises anodic and
cathodic packages, substantially with the same construction materials as in the
lower module (200) but in most of the cases of lower height. The upper anodic
package is comprised of a frame (15), acting as the upper anodic base and
ensuring for the mechanical support and the current distribution for the relevant
anodes (16). The frame (15) is made of a titanium sheet provided with holes or
slots, suitably dimensioned for putting the two anodic compartments in direct
fluid communication. The anodes (16) of the upper module are vertically fixed to
the frame, in transversal rows, generally with the same pitch as in the lower
module. The anodes (16) of the upper module, fixed to the frame (15) by means
of dowel screws (18), often have a lower height. The upper eathodic body is
made of a box (19), having the same design and construction materials as that
of the lower module and a height depending on that of the upper anodic
package; the upper cathodic body is welded along the internal walls of the box
(19) to a plurality of cathodes (20) arranged in parallel rows. Each finger,
shaped as an elongated tubular box, is in communication with a manifold (21)
positioned along the sides of the box (19). The main features of the cathodes
and diaphragms of the upper module are equivalent to those of the lower
module. The frame (15) and the anode base (1) are reciprocally connected by
means of external conductors (not shown in the figure); the box (6) and the box
(19) are also connected in a similar way. The cell cover (8), which is made a of
plastic chlorine-resistant material, is provided with a chlorine gas outlet (9) and
a brine inlet (10). The cell is connected to a direct current supply by means of
bus bars. As known to the experts in the art, the cell operates as follows: the
feed brine enters the cell through the inlet nozzle (10) placed on the cell cover
and is distributed through pipe (23) to the base (1) of the lower anodic
compartment, subsequently rising to the top surface thereof and overflowing
through the slots of the frame (15) into the anodic space of the box (19). The
chlorine disengaged in the lower anodic compartment follows the same path
and leaves through the outlet nozzle (9) on the cover (8). The chloride-depleted
electrolyte, driven by the pressure corresponding to the hydraulic head between
the anolyte and catholyte, permeates through the diaphragm entering the upper
(20) and lower (5) cathodic fingers. Hydrogen leaves the upper (21) and lower
(7) cathodic compartments respectively through nozzles (25) and (11),
connected in parallel to the hydrogen manifold (26). The alkali produced in the
upper cathodic compartment (21) leaves through nozzle (27), and enters the
lower cathodic chamber (7) through pipe (28) and nozzle (29), where it is mixed
with°the alkali produced therein, then leaving the cell through the hydraulic head
(12). The level of the cathodic liquor is normally adjusted so that a sufficient gas
chamber is always maintained in the lower cathodic compartment (7);
consequently, the upper compartment (21) works exclusively as a gas chamber
and electrolysis takes place only by direct contact between the solution
percolating onto the diaphragm and the cathode. To establish such condition in
a reliable fashion, the pipe (28) must obviously have a sufficient large diameter
in order to remain substantially full of hydrogen, so that the two cathodic
compartments (7) and (21) are subjected to an identical pressure.
Figure 2 shows a particular embodiment of the anode of the invention, which is
conceived in a completely different manner with respect to the prior art anodes, with or
without expander. As it can be observed, the anode structure is given by an electrodic
surface (13), folded and open on one side to allow the insertion of a cathode,
preferably consisting of a foraminous sheet or a mesh or, as an alternative, of a
juxtaposition of foraminous elements such as sheets or meshes. The anode has a single
curvature (14), its profile thereby assuming a U-shaped geometry, other shapes of the
said profile being possible without departing from the scope of invention. At the base of
the anode, in correspondence of the curvature (14), a current collector (150) provided
with a preferably threaded stem (160) is welded or otherwise secured. The current
collector (150) is horizontal instead of vertical as it would be the case of the prior art, as
this allows the internal volume of the anode to be hollow and completely available for
the insertion of the corresponding cathode. In principle, both the anodes of the upper
module (100) and of the lower module (200) could be realized according to the
embodiment of figure 2. However, the cell construction illustrated in figure 1 derives, in
most of the case, from a retrofitting of an older diaphragm cell wherein the upper
module is overlaid to the lower one in a second time, as disclosed in the co-pending
International Application PCT/EP 02/10848. The anodes of the lower module (200) have
therefore, in most of the cases, a geometry according to the prior art. Also when a
complete replacement of the electrodes of the lower module is carried out, the
advantage of employing the anode of figure 2 is partially counteracted by the fact that
the anodes (3) of the lower module (200) are usually quite high (for instance 800 mm);
the lack of an internal current collector may entail, in this case, substantial ohmic
penalties thus lowering the faradaic yield. The anodes (16) of the upper module (100)
have conversely a much reduced typical height (for instance 160 mm, as specified in the
cited International Application PCT/EP 02/10848), and conducting the electric current
along their whole height without resorting to internal current collectors is therefore a
negligible issue. For this reason, in a preferred embodiment, the cell of the invention
makes use of the anodes of figure 2 only for the upper module (100).
In another embodiment, the cell of the invention makes use of such anodes also
for the lower module (200), counteracting the increase in the ohmic drop along
the electrode height with additional vertical current collectors (not shown),
secured to the external surfaces of the anodes. The optional additional titanium-
lined copper current collectors, secured externally and not internally, are much
easier to remove and restore, contributing in a sensible manner to reduce the
costs of reactivation.
Fixing the current collectors to the anodes externally instead of internally also
offers an additional benefit: when the catalytic coating is periodically
deactivated, the anode must be in fact subjected to a reactivation, preceded by
an etching treatment in hot concentrated hydrochloric or sulphuric acid. After
applying the catalytic ink, the anode must be treated in oven at about 500°C.
During these treatments, the bimetallic contact between the copper core of the
state-of-the-art current collector and the relevant titanium lining would be
seriously damaged by distortion phenomena, the previous detachment of the
current collector and ?1s subsequent restoring after the treatment being
therefore required. With the illustrated anode however, the horizontal current
collector can be entirely made of titanium, with little prejudice in terms of ohmic
drops, therefore no problems arise during the heat treatment of reactivation.
Figure 3 shows a second particular embodiment of the anode of the invention,
whose conception is not too far from the anode of figure 2. Once more, its
structure is open allowing the cathode to be housed within; in this case,
however, the electrodic surface (13) is formed by two distinct elements,
disposed in the vertical position and secured to the current collector (150) in
correspondence of one edge (17). The nature of the electrodic surface (13) is
fundamentally equivalent to the one described for the previous embodiment; the
use of foraminous elements such as sheets or meshes, or juxtapositions
thereof, is preferred.
Figure 4 is a sketch of a side view of a possible configuration of an upper
module (100), according to the best mode of carrying out the invention; the
same configuration could be used for the lower module (ZOO), without departing
from the scope of the invention. The particular shape of the anode (16), with an
open upper part and the interior free of obstacles, may be exploited for housing
the cathode (20) within, so that the reduction of the electrode pitch is virtually
limited by the sole thickness of the cathode (20). The adjacent anodes, in fact,
can be very close to each other ad even in mutual contact, as they are
maintained at the same electric potential. The figure shows also constraint
elements (31), applied to adjacent pairs of anodes, that are used to open wide
the latter under elastic regime so as to facilitate the insertion of the cathodes
during the assembly (figure 4A); figure 4B shows how, upon completing the
assembly and removing the constraint elements, the anodic surface moves
back to the natural position, with the two vertical sides facing the diaphragm-
coated major surfaces of the corresponding cathode (20). In figure 4, the anode
(16) has an open upper part, but it is clearly possible to assemble the anodes
upside down, with an open lower part. It is also possible to provide an assembly
procedure that doesn't make use of constraint elements, or that utilises the
same in a different fashion, without departing from the scope of the invention.
The constructive solution illustrated in figure 4 easily allows an increase of
active surface of 30-50% for the relevant module and for a given projected
surface.
In the description and claims of the present application, the word "comprise"
and its variation such as "comprising" and "comprises" are not intended to
exclude the presence of other elements or additional components.
WE CLAIM:
1. A diaphragm electrolytic cell comprising a lower module (200) of anodes (3)
and cathodes (5) and at least one upper module (100) of anodes (16) and
cathodes (20) overlaid thereto, said at least one upper module (100) having
an anodic compartment which is in direct fluid communication with an
anodic compartment of said lower module (200), said at least one upper
module (100) being equipped with generally U-shaped anodes comprising
two vertical major surfaces (13) fixed to a first horizontal current collector
(150), additional titanium-lined copper current collectors being externally
secured to at least one of said vertical major surfaces (13), wherein
diaphragm-coated cathodes are housed in the hollow space inside said
vertical major surfaces (13) of said anodes (16).
2. The cell as claimed in claim 1 wherein said vertical major surfaces (13) of
said anodes (16) are parts of a single folded surface delimited by a curvature
(14), said horizontal current collector (150) being fixed to said vertical major
surfaces (13) in correspondence of said curvature (14).
3. The cell as claimed in claim 1 or 2 wherein at least one of said vertical major
surfaces (13) of said anodes (16) is foraminous.
5. The cell as claimed in any one of the previous claims wherein said
generally U-shaped anodes (16) are entirely made of titanium or
titanium alloys.
6. The cell as claimed in any one of the previous claims wherein said
horizontal current collector (150) is made of titanium.
7. The cell as claimed in any one of the previous claims wherein said
anodes (3) of said lower module (200) are U-shaped anodes.
8. The cell as claimed in any one of the previous claims wherein at least
said vertical major surfaces (13) are provided with a catalytic coating
for chlorine evolution.
9. The method for the assembly of the cell as claimed in any one of the
previous claims, comprising fixing said U-shaped anodes (16) to the
corresponding anodic base (15), maintaining said anodes (16) open
wide under an elastic regimen by means of constraint elements (31),
housing said diaphragm-coated cathodes (20) within said hollow space
inside said vertical major surfaces (13) of said anodes (16) and
removing said constraint elements (31).
A diaphragm electrolytic cell comprising a lower module (200) of anodes (3) and
cathodes (5) and at least one upper module (100) of anodes (16) and cathodes (20)
overlaid thereto, said at least one upper module (100) having an anodic
compartment which is in direct fluid communication with an anodic compartment of
said lower module (200), said at least one upper module (100) being equipped with
generally U-shaped anodes comprising two vertical major surfaces (13) fixed to a
first horizontal current collector (150), additional titanium-lined copper current
collectors being externally secured to at least one of said vertical major surfaces
(13), wherein diaphragm-coated cathodes are housed in the hollow space inside said
vertical major surfaces (13) of said anodes (16).

Documents:

« Previous Patent

Next Patent »

Patent Number

225419

Indian Patent Application Number

01089/KOLNP/2004

PG Journal Number

46/2008

Publication Date

14-Nov-2008

Grant Date

12-Nov-2008

Date of Filing

29-Jul-2004

Name of Patentee

DE NORA ELETRODI S. P. .A.

Applicant Address

VIA DEI CANZI, 1, I-20134 MILAN

Inventors:

#	Inventor's Name	Inventor's Address
1	MENEGHINI, GIOVANNI	VIA PISTOIA, 11, I-20153 MILAN

PCT International Classification Number

C25B 11/02

PCT International Application Number

PCT/EP03/01977

PCT International Filing date

2003-02-26

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	MI2002A000416	2002-03-01	Italy