U.S. patent application number 13/382664 was filed with the patent office on 2012-06-07 for bipolar electrodes with high energy efficiency, and use thereof for synthesising sodium chlorate.
This patent application is currently assigned to MEEIR TECHNOLOGIE INC.. Invention is credited to Sylvio Savoie, Robert Schulz.
Application Number | 20120138477 13/382664 |
Document ID | / |
Family ID | 43426255 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120138477 |
Kind Code |
A1 |
Schulz; Robert ; et
al. |
June 7, 2012 |
BIPOLAR ELECTRODES WITH HIGH ENERGY EFFICIENCY, AND USE THEREOF FOR
SYNTHESISING SODIUM CHLORATE
Abstract
The invention relates to novel bipolar electrodes with a
cathodic coating on one portion of the electrode and an anodic
coating on another portion of the same electrode. The anodic
coating is preferably a DSA coating and the cathodic coating is an
alloy such as Fe.sub.3-xAl-.sub.1+xM.sub.yT.sub.z. The invention
also relates to the use of said novel electrodes for synthesising
sodium chlorate.
Inventors: |
Schulz; Robert; (Ste-Julie,
CA) ; Savoie; Sylvio; (Ste-Julie (Quebec),
CA) |
Assignee: |
MEEIR TECHNOLOGIE INC.
Candiac
QC
HYDRO-QUEBEC
Montreal
QC
|
Family ID: |
43426255 |
Appl. No.: |
13/382664 |
Filed: |
April 8, 2010 |
PCT Filed: |
April 8, 2010 |
PCT NO: |
PCT/CA2010/000531 |
371 Date: |
February 17, 2012 |
Current U.S.
Class: |
205/505 ;
204/290.01; 204/290.12 |
Current CPC
Class: |
C25B 11/091 20210101;
C25B 1/265 20130101 |
Class at
Publication: |
205/505 ;
204/290.01; 204/290.12 |
International
Class: |
C25B 11/04 20060101
C25B011/04; C25B 1/14 20060101 C25B001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2009 |
CA |
2,671,211 |
Claims
1. A bipolar electrode with high energy efficiency, which electrode
has a part provided with a cathodic coating and a second part that
is distinct from the first one and is provided with an anodic
coating.
2. A bipolar electrode according to claim 1, wherein the anodic
coating is of the DSA type.
3. A bipolar electrode according to claim 1, wherein the anodic
coating is an alloy with the formula:
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z in which: M represents one or
several catalytic species selected from Ru, Ir, Pd, Pt, Rh, Os, Re,
Ag and Ni; T represents one or several elements from Mo, Co, Cr, V,
Cu, Zn, Nb, W, Zr, Y; Mn, Cb, Si, B, C, O, N, P, F, S, Cl x is a
number greater than -1 and lower than or equal to +1; y is a number
greater than 0 and lower than or equal to +1; and z is a number
between 0 and +1.
4. A bipolar electrode according to claim 1, wherein the coatings
are applied on a substrate of steel or of titanium.
5. A bipolar module of electrodes, comprising an electrode unit
containing a plurality of electrodes in accordance with claim
1.
6. (canceled)
7. (canceled)
8. The method of synthesizing sodium chlorate which comprises
electrolysis with the bipolar electrode according to claim 1.
9. The method of synthesizing sodium chlorate which comprises
electrolysis with the bipolar module of claim 5.
10. A bipolar electrode according to claim 3, wherein the coatings
are applied on a substrate of steel or of titanium.
11. A bipolar module of electrodes, comprising an electrode unit
containing a plurality of electrodes in accordance with claim
3.
12. A bipolar module of electrodes, comprising an electrode unit
containing a plurality of electrodes in accordance with claim
4.
13. A bipolar module of electrodes, comprising an electrode unit
containing a plurality of electrodes in accordance with claim 10.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to novel bipolar electrodes
with a cathodic coating on a part of it and an anodic coating on
another part of it. It also relates to the usage of these novel
electrodes for the synthesis of sodium chlorate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0002] In the attached drawings:
[0003] FIGS. 1a and 1b are schematic views of mono-polar
electrodes;
[0004] FIGS. 2a and 2b are schematic views of bipolar
electrodes;
[0005] FIG. 3 is an illustration of an adhesion test of a coating
of iron aluminide on steel 1020;
[0006] FIG. 4 is an illustration of an adhesion test of a coating
of iron aluminide on titanium;
[0007] FIG. 5 is a scheme illustrating the assembly of traction
dowels used for the adhesion tests;
[0008] FIG. 6 is an illustration of a corrosion test in a chlorate
solution of a DSA electrode and of a coating of the type
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z on a substrate of titanium;
[0009] FIG. 7 is a schematic view of a bipolar electrode in
accordance with the invention;
[0010] FIGS. 8a, 8b are schematic views of bipolar modules in
accordance with the invention; and
[0011] FIGS. 9a, 9b and 9c are photographs of bipolar electrodes
fabricated in such a manner that a part of these electrodes is
covered by a coating of the DSA type and another part by a coating
of the type Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z.
TECHNOLOGICAL BACKGROUND
[0012] Sodium chlorate (NaClO.sub.3) is currently used as bleaching
agent in the pulp and paper industry. It is produced by
electrolysis of sodium salt (NaCl) in accordance with the chemical
reaction:
NaCl+3H.sub.2O.fwdarw.NaClO.sub.3+3H.sub.2
[0013] The process is very energy-consuming and requires between
5000 and 5500 kW of electricity per ton of sodium chlorate. The
electrolysis cells in which a high continuous current circulates
customarily comprises anodes that are dimensionally stable (DSA)
and uncoated cathodes of steel or of titanium. DSA anodes are
well-known in the art of electrolysis cells, see, for example:
WO4101852, WO4094698, U.S. Pat. No. 6,071,570, U.S. Pat. No.
4,528,084, U.S. Pat. No. 5,989,396, U.S. Pat. No. 6,572,758, U.S.
Pat. No. 4,233,340; U.S. Pat. No. 5,419,824; U.S. Pat. No.
5,593,556 and U.S. Pat. No. 5,672,394.
[0014] These DSA anodes typically comprise a substrate of titanium
on which a coating of ruthenium oxide is applied possibly with
other oxides or compounds such as iridium oxide. By virtue of this
catalytic coating the energy losses on the anodic side are low.
This is reflected by a low anodic overvoltage several tens of
millivolts. However, it is not the same on the cathodic side. The
cathodic overvoltage on the surface of a steel plate is
approximately 900 mV whereas on the surface of a plate of titanium
it is approximately 1200 mV. The energy losses on the cathodic side
thus represent the main source of energy losses in the process. It
is for this reason that in the course of recent years the inventors
of the present invention attempted to find performing cathode
coatings that allow the overpotential on these electrodes to be
lowered.
[0015] WO/2008/138148 which also originates from the inventors of
the present invention, gives an example of such cathode coatings.
It describes alloys of the type Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z
that are applied on the surface of an electrode for making a coated
cathode that is very performing in regards to energy.
[0016] Cathodes and anodes are assembled in electrolysis cells
according to different configurations. Two types of assembly are
distinguished. The mono-polar cells and the bipolar cells. FIG. 1
shows schematic views of mono-polar electrodes. In such
configurations each electrode only plays one role, that of anode or
of cathode. Consequently, there is no ambiguity about the type of
coating to be applied if one wishes to improve the energy
efficiency of such cells. For the anode, a substrate of titanium
will be selected and a coating of ruthenium oxide will be applied
in order to make a DSA and for the cathode a steel plate could be
selected and a coating of the type
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z could be applied in order to
make a cathode with high energy performance.
[0017] FIG. 2 shows schematic views of bipolar electrodes. In a
bipolar configuration an electrode or a module of electrodes
simultaneously plays the role of anode and that of cathode. In the
scheme at the top of FIG. 2a the negative face of the bipolar
electrode is cathodic while the positive face is anodic. In the
scheme at the bottom of FIG. 2b the electrodes in the left part of
the bipolar module (negative sign) are cathodic while the
electrodes on the right side (positive sign) are anodic. These
electrodes are assembled and welded together in order to make a
bipolar module of electrodes. Since a bipolar electrode such as the
one shown in FIG. 2a simultaneously plays the role of anode and
cathode, which type of electrode should be selected in order to
globally improve the efficiency of the process? Should one choose a
DSA electrode on a substrate of titanium that was developed for
optimizing the anodic reaction or a steel plate with catalytic
coating in order to favor the cathodic reaction? In addition to
this difficulty, a bipolar module of electrodes such as the one
shown at the bottom of FIG. 2 presents an additional problem. The
electrodes on the anodic side (right side of the module) are
customarily DSAs on substrates of titanium whereas the electrodes
on the cathodic side (left side of the module) are steel plates.
Now, it is very difficult to weld titanium to steel. Such a module
therefore presents a difficulty in the assembly.
[0018] Finally, when different metals such as steel and titanium
are in direct contact in a highly corrosive solution such as that
of sodium chlorate, there is an additional problem of galvanic
corrosion. When production stops and the current is cutted in a
plant, a current caused by the galvanic corrosion circulates in the
opposite direction in the modules of bipolar electrodes and this
effect causes a severe deterioration of the less noble
electrodes.
[0019] The present invention has the goal of solving these problems
associated with bipolar electrodes.
SUMMARY OF THE INVENTION
[0020] When they did their research about the cathodic coatings
with high energy performance of the type
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z that constitute the subject
matter of the invention WO/2008/138148, the inventors of the
present invention found to their great surprise that the coatings
of this type adhere as well to substrates of steel as to substrates
of titanium.
[0021] The invention therefore has, as first subject matter, a
bipolar electrode with high energy efficiency, which electrode has
a part provided with a cathodic coating and another part that is
distinct from the first one and that is provided with an anodic
coating.
[0022] In the invention as claimed:
[0023] the anodic coating is of the DSA type; and
[0024] the cathodic coating consists of an alloy with the
formula:
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z
[0025] in which:
[0026] M represents one or several catalytic species selected from
Ru, Ir, Pd, Pt, Rh, Os, Re, Ag and Ni;
[0027] T represents one or several elements from Mo, Co, Cr, V, Cu,
Zn, Nb, W, Zr, Y;
[0028] Mn, Cd, Si, B, C, O, N, P, F, S, Cl and Na;
[0029] x is a number greater than -1 and lower than or equal to
+1;
[0030] y is a number greater than 0 and lower than or equal to +1;
and
[0031] z is a number between 0 and +1.
[0032] The substrate on which the coatings are applied can be a
substrate of steel or a substrate of titanium.
[0033] The invention also has as subject matter a bipolar module of
electrodes containing several electrodes such as those described
above.
[0034] The invention also has as subject matter the use of the
bipolar electrode or of the bipolar module in accordance with the
invention for the electrosynthesis of sodium chlorate.
EXAMPLES
[0035] FIG. 3 shows an adhesion test of the coating of the type
Fe.sub.3Al on a substrate of steel 1020 according to ASTM C633. The
fracture took place at a stress of 11,922 psi, that is quite close
to the fracture limit of the glue serving for the mounting of the
dowels (see the scheme of FIG. 5). Thus, the adhesion of a coating
of iron aluminide on a steel substrate is excellent.
[0036] FIG. 4 shows a similar test for the adhesion of the coating
of the same type on a substrate of titanium. The fracture took
place at a stress of 10,604 psi, that is, a value almost as high as
the previously measured one. Consequently, the adhesion of the
coating is just as good on a substrate of titanium as on a
substrate of steel.
[0037] Since titanium customarily serves as substrate for coatings
of the DSA type, this discovery opens the possibility of applying a
DSA coating on one side of the substrate of titanium for the anodic
reaction and on the other side a coating of the
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z type for the cathodic reaction.
In other words, this discovery leads directly to the energy
optimization of electrodes of the bipolar type.
[0038] However, it is possible to also use a substrate of steel,
preferably a stainless steel of the ferritic type not containing
Ni. In this case a layer of Ti is preferably applied on one side by
a method such as "cold spray" before applying the DSA coating on
the same side and on the layer of Ti. A coating of the type
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z is applied on the other side as
previously but this time on steel.
[0039] The only potential problem remaining in such electrode
configurations is that of galvanic corrosion caused by the fact
that there is on one side of the electrode an oxide of ruthenium of
the DSA type and on the other side an alloy of the type
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z. Now, it was discovered that it
was possible to adjust the chemical composition of alloys of the
type Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z by a judicious choice of
the elements M and T and of the compositions x, y and z in such a
manner as to balance out the potentials with respect to the DSA and
to cancel the galvanic corrosion of the couple constituting the
bipolar electrode.
[0040] FIG. 6 shows the "current-voltage" curves in a chlorate
solution at 22.degree. C. measured relative to a reference
electrode Ag/AgCl by sweeping the potential 5 mV/sec for a DSA
electrode and a coating of the type
Fe.sub.3-xAl.sub.1+xM.sub.yT.sub.z on a substrate of titanium. We
observe that the cathodic coating is just as resistant to corrosion
as the DSA. The corrosion threshold is approximately 1.2 V. The
galvanic couple between these dissimilar materials is thus reduced
by an appropriate selection of the chemical composition of the
coating based on iron aluminide.
[0041] Without being restrictive, FIG. 7 shows schematic views of
bipolar electrodes in accordance with the invention. For the first
electrode, one face has an anodic coating while the other face has
a cathodic coating. In the second bipolar electrode, one end of the
electrode is covered on two sides by a cathodic coating whereas the
other end is covered by an anodic coating.
[0042] Without being restrictive, FIG. 8 shows schematic views of
bipolar modules constituted by an assembly of bipolar electrodes
represented in FIG. 7.
[0043] FIGS. 9a and 9b show photographs of bipolar electrodes such
as those represented schematically in FIG. 7, and FIG. 9c shows the
appearance of a bipolar electrode in accordance with the invention
after an immersion of 69 hours in a chlorate solution at 22.degree.
C. A beginning of pitting corrosion is observed on the cathodic
part but the structural integrity of the coating is still
excellent.
* * * * *