Patent Grant
10151040
The present description relates to an hydrogen gas diffusion anode arrangement for use in electrolytic production of metals such as magnesium and aluminum producing hydrogen chloride (HCl) as a by-product.
Aluminum and magnesium are common structural metal with high commercial interest.
Pure aluminum (Al) is a silver-white, malleable, ductile metal with one-third the density of steel. It is the most abundant metal in the earth's crust. Aluminum is an excellent conductor of electricity and has twice the electrical conductance of copper. It is also an efficient conductor of heat and a good reflector of light and radiant heat.
Unlike most of the other major metals, aluminum does not occur in its native state, but occurs ubiquitously in the environment as silicates, oxides and hydroxides, in combination with other elements such as sodium and fluoride, and as complexes with organic matter. When combined with water and other trace elements, it produces the main ore of aluminum known as bauxite.
Magnesium compounds, primarily magnesium oxide (MgO), are used as a refractory material in furnace linings for producing iron, steel, nonferrous metals, glass and cement. Magnesium oxide and other magnesium compounds are also used in the agricultural, chemical, automobile, aerospace and construction industries.
Presently, aluminum is produced by separating pure alumina from bauxite in a refinery, then treating the alumina by electrolysis using the Hall-Heroult and Bayer processes. An electric current flowing through a molten electrolyte, in which alumina has been dissolved, separates the aluminum oxide into oxygen, which collects on carbon anodes immersed in the electrolyte, and aluminum metal, which collects on the bottom of the carbon-lined cell (cathode). On average, it takes about 4 t of bauxite to obtain 2 t of aluminum oxide, which in turn yields 1 t of metal. For over 120 years, the Bayer process and the Hall-Heroult process together have been the standard commercial method of the production of aluminum metal. These processes require large amounts of electricity and generate undesired by products, such as fluorides in the case of the Hall-Heroult process and red mud in the case of the Bayer process.
The production of aluminum by electrolysis of aluminum chloride has been a long-desired and theoretically feasible objective; the economic attainment thereof has never become an economic reality. Among the many reasons therefor are numerous unsolved problems occasioned, for example, the highly corrosive chlorine vapors or gases emanating from the electrolysis, as well as the complex salts or eutectics of the bath components and the products of electrolysis, all of which will be herein broadly encompassed by the term electrolyte, are of corrosive character and apparently compound the problem. Among such problems are the short life of cell components and the detrimental contamination of the bath through reaction thereof with the confining environmental elements in the electrolytic cells.
Taking out the magnesium metal from unrefined materials is a force exhaustive procedure requiring nicely tuned technologies. Presently, to extract magnesium, an electrolysis process is generally used. The tailings are leached in hydrochloric acid, creating a brine from which the magnesium is extracted using electrolysis. Thermal lessening of magnesium oxide is also used for extracting magnesium from ores.
Conventionally, during the course of electrolytic production of magnesium, chlorine gas is formed at the anode (metallic magnesium being formed at the cathode). Conventional anodes used in such process are made of graphite. At the high temperatures involved, the chlorine gas tends to attack the graphite anode and various chlorinated carbon compounds may be formed. The chlorine gas itself and the chlorinated carbon compounds are environmentally hazardous and are difficult to remove and are expensive to deal with. In addition, because the graphite anode is slowly consumed by this reaction, the anode itself must be periodically replaced, at not an insignificant expense.
There is thus still a need to be provided with improved processes for extracting metals such as aluminum and magnesium.
In accordance with the present description, there is now provided an anode arrangement for use in an electrolysis production of metals comprising an anode having a hollow body comprising a cavity extending longitudinally from a first end portion to a second end portion of the anode, said body having at least one gas outlet connected in fluid flow communication with the cavity; a gas inlet connected in fluid flow communication with the cavity of said anode, said gas inlet being connectable to a source of hydrogen gas for feeding hydrogen gas into the cavity of said anode; an electrical connector for generating a current at the anode during electrolysis; and a hydrogen chloride (HCl) recuperator surrounding at least a portion of the anode for recovering HCl gas released through the at least one gas outlet at an outer surface of the anode during electrolysis, the HCl recuperator having an outlet connectable to a HCl redistributor.
In an embodiment, the first end portion is a top portion of the anode and the second end portion is a bottom portion of the anode, the gas inlet connected to the top portion or bottom portion of the anode.
In another embodiment, the electrical connector extends into the cavity of the anode.
In a further embodiment, the electrical connector extends into the gas inlet into the cavity of the anode.
In an embodiment, the metals are magnesium or aluminum.
In an alternative embodiment, the anode is a cylindrical anode.
In a further embodiment, the anode comprises a plurality of gas outlets symmetrically spaced on the body of the anode.
In another embodiment, the size of the gas outlets increases from the top portion of the anode to the bottom portion of the anode.
In a further embodiment, the gas outlets are spaced in rows and columns on the body of the anode.
In another embodiment, each gas outlets within each row are of the same size.
In a supplemental embodiment, the gas outlets are cylindrical bores.
In another embodiment, the gas outlets are elongated taper channels from the bottom portion to the top portion of the anode.
In a further embodiment, the anode is a metal diffuser.
In another embodiment, the anode is made of sintered metal powders.
In an additional embodiment, the anode is made of graphite or Hastalloy X.
In an embodiment, the gas inlet is the HCl recuperator, extending partially and surrounding at least a portion of the anode recovering HCl gas released through the gas outlet at the outer surface of the anode during electrolysis.
In a further embodiment, the HCl recuperator is a sintered alumina tube.
In an embodiment, the at least one gas outlet as an opening of at least 5 μm.
In another embodiment, the anode described herein further comprises an electrocatalyst.
It is also provided in an embodiment an electrolytic cell for electrolyzing metals chloride comprising, the anode arrangement as described herein; a cathode being separated from the anode, the HCl gas released through the gas outlet at the outer surface of the anode is separated from the metals produced at the cathode; and an electrolytic chamber containing an electrolyte, said cathode and said anode arrangement.
In accordance with the present description, there is also provided an anode arrangement for use in an electrolysis production of aluminum comprising an anode having a hollow body comprising a cavity extending longitudinally from a first end portion to a second end portion of the anode, said body having at least one gas outlet connected in fluid flow communication with the cavity; a gas inlet connected in fluid flow communication with the cavity of said anode, said gas inlet being connectable to a source of hydrogen gas for feeding hydrogen gas into the cavity of said anode; an electrical connector for generating a current at the anode during electrolysis; and a hydrogen chloride (HCl) recuperator surrounding at least a portion of the anode for recovering HCl gas released through the at least one gas outlet at an outer surface of the anode during electrolysis, the HCl recuperator having an outlet connectable to a HCl redistributor.
In accordance with the present description, there is now provided an anode arrangement for use in an electrolysis production of magnesium comprising an anode having a hollow body comprising a cavity extending longitudinally from a first end portion to a second end portion of the anode, said body having at least one gas outlet connected in fluid flow communication with the cavity; a gas inlet connected in fluid flow communication with the cavity of said anode, said gas inlet being connectable to a source of hydrogen gas for feeding hydrogen gas into the cavity of said anode; an electrical connector for generating a current at the anode during electrolysis; and a hydrogen chloride (HCl) recuperator surrounding at least a portion of the anode for recovering HCl gas released through the at least one gas outlet at an outer surface of the anode during electrolysis, the HCl recuperator having an outlet connectable to a HCl redistributor.
Reference will now be made to the accompanying drawings, in which:
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
It is provided an hydrogen gas diffusion anode arrangement for use in electrolytic production of metals such as magnesium and aluminum producing hydrogen chloride (HCl) gas as a by-product.
The anode described herein can be used in extraction processes of magnesium and aluminum using hydrochloric acid which is recycled during the processes as described in International Application No. PCT/CA2013/050659 and in U.S. Patent Application No. 61/827,709, filed May 27, 2013, the content of which are incorporated by reference herein in their entirety.
During the course of electrolytic production of magnesium or aluminum, chlorine gas is formed at the anode and the metallic magnesium or aluminum being formed at the cathode. An electric current flowing through a molten electrolyte, separates the aluminum chloride or magnesium chloride into HCl which collects on the anode immersed in the electrolyte, and aluminum and magnesium metal, which collects at the cathode.
The anode is immersed into molten salt electrolyte and the HCl gas generated at the surface goes on the top of the cell. The cell is generally feed with an inert gas in order to prevent oxygen contact with the molten metal. The HCl is therein mixed with this inert gas. This very dry mixture is leaving the cell at 700° C. and could be used as a drying agent for the conversion for example of MgCl2-hydrate brine into MgCl2 prill. The gas is then pass throw a water scrubber (HCl redistributor) device where the HCl gas is convert to HCl liquid and the inert gas is return to the electrolytic cell after a drying step. The HCl liquid concentration is adjusted by the number of pass of the liquid in contact with the HCl charged mixing gas. When the concentration reach 32% wt, the HCl liquid solution is flush to be return to the tank and fresh water is introduce into the scrubber.
Magnesium and aluminum are presently isolated using electrolytic processes. The electrolytic reduction of molten magnesium chloride (MgCl2) is a commonly used process for the production of magnesium. Two major problems are related to this process. First, it generates a large amount of Cl2 which combines with the carbon of the anodes, inducing the formation of numerous organochlorine compounds most of which are part of the 12 persistent organic pollutants target for elimination by the United Nations Environment Program. Additionally, the production of magnesium requires a huge quantity of energy. Based on the free Gibbs energy of formation, a minimum power of 5.5 kWh is required for the production of 1 kg of Mg. However, by taking into account the different resistance components (electrolyte, bubbles, and electrodes) present in the system, the actual power consumption varies between 10 to 18 kWh kg−1 depending on the cell design.
U.S. Patent Pub. No. 2002/0014416 describes the use of a high surface area anode, the anode being porous and to which hydrogen gas is fed, to produce magnesium metal by electrolysis of magnesium chloride. The design of the anode in the 2002/0014416 publication does not take into account the variance in the hydrostatic pressure exerted by the molten magnesium chloride in the electrolytic cell (prior to electrolysis). Because the anode is a vertical cell, the hydrostatic pressure exerted by the molten magnesium chloride is greater at the bottom of the anode than at the top of the anode. The hydrostatic pressure thus starts at a particular value near the top of the anode and increases towards the bottom of the anode where it is greatest. Because of this, an anode such as that of the 2002/0014416 publication (wherein the channels or pores—as the case may—are similar and equally spaced around and up-and-down across the anode) yields a structure where more hydrogen gas will exit the anode at the top (where the hydrostatic pressure is less) than will exit at the bottom (where the hydrostatic pressure is greater). This results (depending on the pressure and volume of the hydrogen gas in the cavity of the anode) either in an insufficient amount of hydrogen gas exiting the anode near the bottom or an excess amount of hydrogen gas exiting near the top. Neither situation is ideal.
Contrary to the anode described in U.S. Patent Pub. No. 2002/0014416, the anode described herein is part of an assembly that allows recuperation of HCl produced. Further, the anode described herein contains channel/pore volume which are varied to compensate for the variance in the hydrostatic pressure presented by molten magnesium for example. Thus, in the anode disclosed herein, nearer to the top of the anode (where the hydrostatic pressure is less) the anode comprises a smaller channel/pore volume. Nearer to the bottom of the anode (where the hydrostatic pressure is greater) the anode comprises a greater channel/pore volume. Preferably, the channel/pore volume will progressively increase as one progresses down the length of the anode from top to bottom. The channel/pore volume can be calculated and will increase proportionally with the increase in hydrostatic pressure—thus attempting to ensure that substantially the same amount of hydrogen gas exits the anode across its external surface area whatever the distance be from the top/bottom of the anode. This results in a sufficient amount of hydrogen gas exiting the anode, reducing or eliminating the attack by chlorine gas on the carbon in the anode, reducing or eliminating the production of chlorinated carbon compounds, reducing or eliminating the production of chlorine gas and substituting therefor the production of hydrogen chloride gas, and reducing the voltage required with respect to the electrolysis of the magnesium chloride or aluminum chloride without requiring an excess of hydrogen gas.
The cell reaction in aluminium chloride electrolysis is:
2AlCl3→2Al+6Cl2
For this reaction at 700° C., the reversible decomposition voltage works out to be about 1.8 volts.
For the extraction of aluminum, the overall reaction becomes:
2AlCl3+3H2→2Al+6HCl (eq. 1)
During conventional magnesium electrolysis, MgCl2 decomposes into liquid magnesium at the cathode and gaseous chlorine at the anode according to the Eq. 1. In this case, the theoretical voltage of the reaction is 2.50 V.
MgCl2→Mg+Cl2 (eq. 2)
For the process using hydrogen gas diffusion anode, the overall reaction becomes:
MgCl2+H2→Mg+2HCl (eq. 3)
For such a reaction, the decomposition voltage decreases to 1.46 V, allowing a theoretical voltage reduction of about 1V, the overall cell voltage could reach a reduction of 0.86 V. This represents a reduction of 25% in energy consumption.
One important benefit provided by the anode described herein is the production of HCl as by-product of the process. Since the purification process of MgCl2 and AlCl3 ores consumes gaseous HCl for the dehydration step, this is of great interest to produce on-site the HCl required for this process. This lead to economic benefits and a simplification of the process because the amount of HCl produced by electrolysis should be sufficient to feed the chemical reactor for the dehydration process. The theoretical amount of HCl which can be produced during magnesium electrolysis can be estimated from Eq. 4:
where i is the current (A), n(e−) the number of electron exchanged (in the present case n(e−)=1 per mole of HCl), F the Faraday constant and t the electrolysis time (s). Thus, the maximum amount of HCl which could be extracted from the electrolysis process and supplied to the MgCl2 or AlCl3 purification facilities may theoretically reached 37.3 10−3 mol h−1 A−1. Therefore, for one electrochemical cell running at 300 kA, about 410 kg of gaseous HCl could be produced per hour and used for the extraction of magnesium and aluminum.
Additionally, the formation of HCl instead of Cl2 at the anode could drastically reduce the formation of undesirable organochlorine compounds, leading to a more ecological process and best fitting the increasing restriction concerning the greenhouse gas emissions. As additional benefit, by reducing the reaction of chlorines with the carbon of the anode, the life time of this one will be increased, leading to a decrease of the anode replacement frequency and consequently to a lower Mg production cost.
Referring to
Anodes for the electrolysis could be made, as encompassed herein, of a self-sustaining matrix of sintered powders of at least one oxy-compound such a soxides, multipleoxides, mixed oxides, oxyhalides and oxycarbides, of at least one metal selected from the group consisting of lanthanum, terbium, erbium, ytterbium, thorium, titanium, zirconium, hafnium, niobium, chromium and tantalum and at least one electroconductive agent, the anode being provided over at least a portion of its surface with at least one electrocatalyst for the electrolysis reaction and bipolar electrodes for the cells which electrodes are resistant to corrosion in molten salt electrolysis and have a good electroconductive and good electrocatalytic activity.
The anode 10 has an elongated body 12. The body 12 can be made of graphite for example, preferably porous graphite. The body can be of any shape, such has being cylindrical. The shape of the anode ideally needs to be easy to machine, present a homogenous gas distribution at its surface and fit easily with electrochemical cell components. Alternatively, the anode body can be a metal diffuser, fabricated from sintered metal powders, leading to interconnected porosity through which the gas is able to diffuse. The bubbles generated at the surface are homogeneously distributed and their size can be easily varied with the pore diameter. Sintered metal diffusers are available in a large choice of materials and in different ranges of porosity, such as for example Hastalloy X. Pore size of as low as 5 μm can be used in such metal diffuser.
The anode 10 is inserted in a tube 22 consisting of a HCl recuperator closed at one extremity by a cap 26. The HCl recuperator 22 is for example a sintered alumina tube of 1 inch. The cap 26 can be a T-shape Swagelok fitting as depicted in
Within the body 12 of the anode 10, there is a longitudinal cavity 14 (as seen in
In an embodiment, as seen in
In an alternative embodiment, referring to
It is demonstrated that a significant cell voltage reduction and in-situ generation of HCl can be obtained by using the hydrogen anode as described herein. The conversion efficiency of the reaction corresponds to the ratio of the HCl produced experimentally to the theoretical HCl production. The theoretical HCl production was calculated by taking into account the theoretical amount of Cl2 produced from the Faraday's law and the amount of H2 injected through the anode. In order to obtain the experimental HCl produced, short electrolysis tests were performed at different current densities with a gas flow rate at the anode varying from 376 to 845 cm3 min−1 for the Ar-5% H2 gas mixture and 9 to 30 cm3 min−1 for pure H2.
The fact that the conversion rate is approaching 80% at 0.5 A cm−2 indicates that it is a viable solution for in-situ HCl production for the dehydration of MgCl2 or AlCl3. A significant voltage reduction of 0.2-0.4 V is obtained depending on the current density. Keeping in mind the huge power consumption of the Mg electrolysis process for example, even if minimal, the reduction of the cell voltage may represent an attractive benefits giving rise to a significant cost saving. Best results were obtained with a carbon anode with graphitic plans perpendicular to the electrode axis through which hydrogen diffuses to generate tiny and relatively well-distributed H2 bubbles on the anode surface.
The hydrogen anode can be further modified by maximizing the gas diffusion through the graphitic anode. The incorporation of an electrocatalyst in the anode to decrease the overpotential for H2 oxidation and thus the cell voltage is also encompassed.
The present disclosure will be more readily understood by referring to the following examples which are given to illustrate embodiments rather than to limit its scope.
4-Hole Graphite Anode
Four holes were drilled on the edge of the lower part of the anode. This kind of electrodes presents the main advantage of being cheap, quickly and easily machined. However, as the holes were relatively large (about 0.3 mm in diam.), the bubbles generated are large in size, heterogeneously distributed and diffuse very fast on the surface of the anode. In order to slow down the diffusion of the bubbles on the anode surface, digs were machined perpendicularly to the axe of the anode.
Sintered Metal Diffuser Anode
The second type of hydrogen gas diffusion anode evaluated was a metal diffuser. This anode was fabricated from sintered metal powders, made of Hastalloy X, leading to interconnected porosity through which the gas is able to diffuse. Such an anode is very attractive because the bubbles generated at the surface are homogeneously distributed and their size can be easily varied with the pore diameter. In order to obtain the smallest bubbles, the finest available pore size of about 5 μm were chosen. The pore distribution size could be adapted along the surface to take into account the hydrostatic pressure variation from top to bottom of the electrolytic cell.
Porous Graphite Anode
For the last type of electrodes, porous graphite anodes were evaluated. This kind of electrode consist of a graphite rod drilled along its axis in order to give wall thickness of about ⅛″. To prevent any H2 leaks at the gas inlet connector tube/graphite interface, the upper part of the graphite electrode was machined to give exactly the same diameter than the inside diameter of the gas inlet connector tube. Then, the lowermost part of the gas inlet connector tube was heated leading to its thermal expansion, allowing the graphite electrode to be inserted. During cooling, the gas inlet connector tube contracted around the graphite electrode leading to a strong and leak-free connection between the two parts. To protect the stainless tube against corrosion appearing close to the gas inlet connector tube/graphite interface, this area was protected by a sintered alumina tube while the upper part was protected by alumina cement.
Bubbling tests in water demonstrated that hydrogen diffuses well through the electrode, leading to the formation of very small bubbles on the anode surface. This kind of anode was tested as hydrogen gas diffusion anode for Mg electrolysis. Subsequently, in order to optimize the size and the distribution of the H2 bubbles on the surface of the electrode, several pieces of graphite were machined from a large block of graphite according to different orientations. This provides graphite rods with a preferential orientation of the graphitic plans perpendicular to the electrode axis, where hydrogen bubbles were well distributed on the anode surface and where no growth of large bubbles was observed.
The graphitisation level for synthetic graphite determine the level of orientation of graphite plan among the cross section of the anode. This graphitization level is the result of parameter such as temperature, pressure and reaction time while anode manufacturing. This property could be use to control the channeling-porosity along the anode for hydrostatic pressure control.
Graphite anode drilled with 4 holes on the edge of the lowermost part of the rod and presenting digs was evaluated as hydrogen anode for magnesium production. Electrochemical measurements were conducted at 700° C. with the apparatus for the gas capture as described previously. Electrolysis test conducted at 0.5 A·cm−2 for one hour with an Ar-5% H2 flow rate of 845 cm3·min−1 demonstrated a stable behavior as shown in
In order to evaluate the effect of hydrogen on the cell voltage, short time chronopotentiometric measurements at different current densities were performed with and without hydrogen. For this experiment, the cell voltage was first recorded without hydrogen until it reached a stable voltage and then 376 cm3·min−1 of Ar-5H2 was injected through the anode. The evolution of the cell voltage with the current density is shown in
It was observed that the use of a H2 anode induces a decrease of the cell voltage. However, the voltage diminution is much lower than predicted by the thermodynamic calculation and tends to decrease with the increasing current density. Indeed, the difference between the two curves disappears to give the same value of 4.5V at 0.6 A cm−2. However, the fact that a significant reduction of 0.15 V of the cell voltage can be observed at low current density is promising considering the use of a non-optimized H2 anode.
Electrochemical measurements were realized with an anode made of Hastalloy X generally employed to resist to high temperature corrosive environments. Compared to the previous type of electrode, sintered metal diffusers have the advantage of diffusing gas very homogeneously. Thus, hydrogen bubbles generated at the anode surface are very small and well distributed. Chronopotentiometric measurements were carried out with different flow rates of Ar-5% H2 and at various current densities. The evolution of the cell voltage with the gas flow rate for different current densities is plotted in
Porous graphite represents the most promising type of hydrogen anodes for magnesium electrolysis tested. No noticeable trace of corrosion were found on the carbon anodes. Thus, it appears that carbon represents an ideal choice of anode material for magnesium electrolysis because of its excellent corrosion resistance at high temperature in MgCl2 based molten salt. In addition, it was observed that hydrogen was capable of diffusing through the electrode wall providing a good distribution of small bubbles at the surface of the electrode. However, the first tests were conducted with a carbon rod in which the hydrogen seems to diffuse preferentially along the axis of the rod leading to a higher concentration of bubbles at the bottom part of the electrode. Knowing that the most common process for producing carbon rod is hot extrusion, it can be assumed that gas diffuses preferentially along the axis of extrusion. In a second part, measurements with anode presenting a preferential gas diffusion perpendicularly to the axis of the rod were conducted. Preliminarily examination of the gas diffusion (by immersion in water) has shown that the bubbles are homogeneously distributed on the anode surface and the growth of large bubbles at the bottom part of the electrode is not observed.
The influence of the hydrogen flow rate on the cell voltage was measured. For that purpose, short chronopotentiometry measurements (1 to 5 min) at 700° C. were carried out at different current densities and with different pure H2 flow rates. The variation of the cell voltage as a function of the current density for 0, 9, 18 and 30 cm3 min−1 H2 is plotted in
For low current densities, it can be seen that the cell voltage tends to decrease as the H2 flow rate increases. The highest potential decrease (0.35V) is obtained for a H2 flow rate of 30 cm3 min−1 at a current density of 0.03 A cm−2. This indicates that the cell reaction is not optimal and it could certainly be improved by a better distribution of the H2 bubbles at the surface of the electrode.
On the other hand, even if the highest cell voltage reduction was obtained for the highest H2 flow rate of 30 cm3·min−1, it can be noted that reduction of the cell voltage becomes less significant with increasing H2 flow rate. Indeed, the cell voltage decrease while the H2 flow rate increases from 0 to 9 cm3 min−1 is far greater (0.25V) than between 9 and 30 cm3 min−1 (0.1 V).
In order to reach a cell voltage reduction at high current, the anodic oxidation of H2 must be favored for instance by increase the effective surface area of the anode (resulting in a decrease of the current density) or/and by adding an electrocatalyst for H2 oxidation (resulting in a decrease of the anodic overpotential).
The conversion efficiency was calculated by comparing the amount of HCl produced during electrolysis with the amount of HCl theoretically produced.
The amount of hydrogen gas injected through the anode is controlled by a flow meter. Depending on the pressure inside the gas transportation pipe, the flow rate can be easily corrected by using a conversion table. The accuracy of a ball flow meter is limited to ±1-2 cm3 min−1 which therefore has a slight influence on the calculation of the theoretical produced HCl. Assuming that the amount of HCl which can be produced only depends on the H2 flow rate, the theoretical molar flow rate of produced HCl follow a linear law as represented by the black solid line in
The second factor which may limit the formation of HCl is the Cl2 produced at the anode during the electrolysis tests considering that HCl may also be produced by the reaction: H2+Cl2=HCl. The theoretical production of Cl2 can be calculated from the faraday law which depends on the anodic current. After calculation, it can be found that for a current density of 0.5 A cm−2, the amount of produced Cl2 is in excess for H2 flow rates of 9 and 18 cm3 min−1 and is equimolar for 30 cm3 min−1. At 0.5 A cm−2 and for all studied flow rates, the reaction is only limited by the H2 flow rate. On the other hand, at a current density of 0.25 A cm−2, the conversion reaction occurs with an excess of Cl2 at 9 cm3 min−1, is equimolar at 15 cm3 min−1 and therefore, occurs with an excess of H2 for higher flow rates (i.e. 18 and 30 cm3·min−1) as illustrated by the break in the linearity of the solid line in
The dotted lines plotted in
For a current density of 0.25 A·cm−2 (
Thus, it can be considered that the conversion efficiency of the process is very high, between 80 and almost 100%. On the other hand, the relatively poor faradic yield of the Mg electrolysis observed during the tests should not be seen as an end since industrial electrolysis cells usually run with faradic yield by far higher thanks to their optimized design and operation conditions. In this way, if assumed that a faradic yield of 90% and a conversion efficiency of 90% can be obtained in an industrial cell, it can be estimated that about 365 kg h−1 of HCl could be produced by an electrochemical cell running at 300 kA.
The use of porous carbon anodes with a preferential gas diffusion perpendicular to the anode axis was investigated.
Chronopotentiometric measurements were conducted in order to evaluate the influence of the distribution and the size of hydrogen bubbles generated at the surface of the electrode. The evolution of the cell voltage as a function of the current density with a H2 flow rate varying from 0 to 30 cm3 min−1 is depicted in
For a better understanding, the variation of the maximum drop of cell voltage is plotted in
While the invention has been described with particular reference to the illustrated embodiment, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as illustrative of the invention and not in a limiting sense.
While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.
This application is a National entry of PCT/CA2014/050102 filed Feb. 14, 2014, in which the United States of America was designated and elected, and which remains pending in the International phase until Aug. 14, 2015, which application in turn claims priority under 35 USC 119(e) from U.S. Provisional Application Ser. No. 61/764,711, filed Feb. 14, 2013.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2014/050102 | 2/14/2014 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2014/124539 | 8/21/2014 | WO | A |
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| Number | Date | Country | |
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| 20150345038 A1 | Dec 2015 | US |
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| 61764711 | Feb 2013 | US |
