ELECTROLYSIS SYSTEM AND METHOD FOR A HIGH ELECTRICAL ENERGY TRANSFORMATION RATE
20220154352 · 2022-05-19
Inventors
Cpc classification
C25B9/17
CHEMISTRY; METALLURGY
International classification
C25B11/00
CHEMISTRY; METALLURGY
Abstract
An electrolytic cell built in the form of a capacitor of cylindrical plates. The cylindrical plates include electrodes of the electrolytic cell formed using tubes arranged in a substantially concentric way within each other defining a central electrode, an outer electrode and a space between electrodes. The central electrode corresponds to an anode of the capacitor. The outer electrode corresponds to the cathode of the capacitor. The cell includes an electrolyte corresponding to a dielectric of the capacitor.
Claims
1-37. (canceled)
38. An electrolytic cell, comprising: at least a pair of electrodes; and an electrolyte provided between the at least a pair of electrodes; the electrolytic cell being built in a form of a capacitor having cylindrical plates; the cylindrical plates are defined using one or more electrodes in the at least a pair of electrodes and formed using tubes arranged in a substantially concentric way within each other to thereby define a central electrode of the at least a pair of electrodes, an outer electrode of the at least a pair of electrodes, and a first space between the central electrode and the outer electrode, the central electrode corresponding to an anode of the capacitor, the outer electrode corresponding to a cathode of the capacitor, and the electrolyte corresponding to a dielectric of the capacitor; wherein the central electrode is a hollow cylindrical electrode having an inner space and includes one or more openings for providing a communication between the first space and the inner space, the one or more openings allowing a free circulation of the electrolyte between the first space and the inner space.
39. The electrolytic cell according to claim 38, wherein a reduction reaction is configured to occur over an inner side of the outer electrode to thereby generate a reduction reaction product; and an oxidation reaction is configured to occur over an outer side of the central electrode to thereby generate an oxidation reaction product; wherein the oxidation reaction is further configured to optionally occur over an inner side of the central electrode; wherein the one or more openings of the central electrode are configured so that the oxidation reaction product circulates from the outer side of the central electrode to the inner space of the central electrode.
40. The electrolytic cell according to claim 39, wherein the one or more openings are located in different extraction zones of the central electrode, the extraction zones being distributed along at least one portion of the central electrode; wherein each extraction zone includes at least one stopping device arranged over the outer side of the central electrode, wherein the at least one stopping device is configured to prevent a circulation of the oxidation reaction product over the outer side of the central electrode, and convey the oxidation reaction product into the inner space of the central electrode through the one or more openings.
41. The electrolytic cell according to claim 40, wherein the at least one stopping device is configured to extend into the space between electrodes to create a circulation space for the electrolyte near the inner side of the outer electrode, wherein the circulation space is provided for a free circulation of the reduction reaction product.
42. The electrolytic cell according to claim 38, wherein the central electrode is surrounded by a separation mesh.
43. The electrolytic cell according to claim 41, further comprising a separation means configured to separate the separation mesh from an outer side of the central electrode.
44. The electrolytic cell according to claim 39, further comprising one or more first extraction ducts for extraction of the oxidation reaction product, wherein each of the first extraction ducts is configured to be in communication with the inner space of the central electrode.
45. The electrolytic cell according to claim 44, further comprising one or more second extraction ducts for extraction of the reduction reaction product, wherein each of the second extraction ducts is configured to be in communication with the first space.
46. The electrolytic cell according to claim 38, wherein the electrolytic cell is configured to be vertically arranged and to operate at an atmospheric pressure.
47. An electrolyzer for conducting an oxidation reaction and/or a reduction reaction, the electrolyzer comprising: a plurality of electrolytic cells, each electrolytic cell in the plurality of electrolytic cells having at least a pair of electrodes; and an electrolyte provided between the at least a pair of electrodes; the electrolytic cell being built in a form of a capacitor having cylindrical plates; the cylindrical plates are defined using one or more electrodes in the at least a pair of electrodes and formed using tubes arranged in a substantially concentric way within each other to thereby define a central electrode of the at least a pair of electrodes, an outer electrode of the at least a pair of electrodes, and a first space between the central electrode and the outer electrode, the central electrode corresponding to an anode of the capacitor, the outer electrode corresponding to a cathode of the capacitor, and the electrolyte corresponding to a dielectric of the capacitor; wherein the central electrode is a hollow cylindrical electrode having an inner space and includes one or more openings for providing a communication between the first space and the inner space, the one or more openings allowing a free circulation of the electrolyte between the first space and the inner space; wherein the plurality of electrolytic cells are configured to be grouped in a plurality of groups of electrolytic cells, each group of electrolytic cells in the plurality of electrolytic cells having electrolytic cells connected in series, wherein the two or more groups of electrolytic cells in the plurality of groups of electrolytic cells are configured to be connected in parallel.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0080] As part of the present application the following figures are shown, which are representative of the invention and teach a preferred embodiment thereof; therefore, they should not be construed as limiting the definition of the matter claimed by the present application.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
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[0091] Additionally,
[0092] As an example, if the electrolyzer 12′ comprises a first set of electrolytic cells 14.1 formed by 50 cells connected in series, with each cell requiring a peak voltage of 2.5 v, a direct current source of 125 v will be required to supply these 50 cells, distributing said 125 v in an equivalent form over each one of the 50 cells. This configuration can be supplemented with additional groups of electrolytic cells 14.2 connected in parallel to the first group, with each group having a switch in communication with the control unit for the pulsed distribution of direct current provided by the energy source. The number of groups of cells connected in parallel will be defined preferably according to the duration factor of the current pulse.
[0093]
[0094] According to an embodiment, the central electrode 21 comprises openings in its surface allowing electrolytes entering the inner space 23 of the central electrode and the circulation of ions, and also allowing the oxidation reaction to occur both in the outer side 21′ of the central electrode 21 and in the inner side 21″ thereof. Additionally, and alternatively, the central electrode 21 can be surrounded by a separation mesh 24 with a physical barrier of separation provided that separate the oxidation zone (central electrode 21) from the reduction zone (outer electrode 22), thus facilitating the separation of gases generated in the electrolytic cell. Under this arrangement, the central electrode 21 comprises separation means (not shown) that keep distance between the separation mesh 24 and the outer side 21′ of the central electrode 21, allowing the generation of the oxidation product over the surface of said outer side 21′. Additionally, this distance allows the gas generated on the outer side 21′ of the central electrode 21 to circulate to its extraction point, whether by going into the inner space 23 of the central electrode 21 through the openings or circulating over the outer side 21′ of the electrode into the extraction point without being transferred to the generation zone of the reduction product.
[0095] In regard as openings, according to alternative embodiments, they may be formed by circular holes 25′ and/or continuous grooves 25″. The openings distribute along at least one part of the central electrode 21, preferably an upper part thereof, distributed in the extraction zones 27 provided to communicate the space between electrodes with the inner space of the central electrode 21.
[0096] The constructive aspects of the electrodes according to the preferred embodiment allow taking advantage of the capacitive and resonant characteristics of the electrolytic cell, preventing the saturation of the walls of the electrodes with the gases generated by maximizing the cell's resonant aspects, including the effect of overdamping and taking advantage of the diffusion and transfer of ions from one electrode to other in the standby cycle given by the intervals in the current supply of pulsing wave making use of the cell's capacitive aspects.
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[0101] Finally,
Working Example
[0102] In order to exemplify the implementation of the solution proposed by the present invention, the production of hydrogen and oxygen through water electrolysis is considered, using the system and methods of the present invention.
[0103] In the process of water alkaline electrolysis to generate H.sub.2 and O.sub.2, processes of oxidation and reduction take place as follows:
[0104] The electrolysis of a mole of water produces one mole of hydrogen gas and half mole of oxygen gas in the normal diatomic forms thereof. A detailed analysis of the process shows the use of the thermodynamic potentials and the first law of thermodynamics. It is assumed that this process is carried out at 298° K and at one atmosphere of pressure, and that the relevant values are taken from the following table of thermodynamic properties (table 1):
TABLE-US-00001 TABLE 1 Amount H.sub.2O H 0.5O.sub.2 Change Enthalpy −285.83 kJ 0 0 H = 285.83 kJ Entropy 69.91 J/K 130.68 J/K 0.5 × 205.14 J/K TS = 48.7 kJ
[0105] The process must provide energy for the dissociation plus the energy to expand the produced gases. Both are included in the enthalpy change of the above table. At a temperature of 298° K and one atmosphere of pressure the system operation is as follows:
W=PΔV=(101.3×103 Pa)(1.5 mol)(22.4×10.sup.−3 m.sup.3/mol)(298 K/273 K)=3715 J
[0106] As the enthalpy H=U+PV, the change of internal energy Y is therefore:
ΔU=ΔH−PΔV=258.83 kJ−3.72 kJ=282.1 kJ
[0107] This change in the internal energy must be accompanied by the expansion of the gases produced, so the change in enthalpy represents the energy necessary to carry out the electrolysis. Nevertheless, it is not necessary that the energy source inserts this energy in total, as electrical power, since the entropy increases in the dissociation process; the TAS amount can be provided by the environment at temperature T. Then, the amount of energy to be supplied by the energy source is in fact the change in Gibbs' free energy, which is expressed as follows:
ΔG=ΔH−TΔS=285.83 kJ−48.7 kJ=237.1 kJ
[0108] As the result of the electrolysis process there is an increase of the entropy, the environment “helps” the process by providing a TAS amount. The usefulness of Gibbs' free energy consists in indicating the amount of other energy forms that must be supplied in order to execute the process.
[0109] For practical purposes of calculating the mass obtained in an electrolysis process, and considering the unified Faraday's law and a distribution of constant current, the equation can be presented as:
[0110] Using the known values of the Chemical Equivalent of H.sub.2 and Faradays Constant, and considering the generation of 1 g of H.sub.2 in one second, the following is obtained:
I=95724.9 A
[0111] With this information it is possible to calculate the optimum voltage matching the input energy of the cell with the output energy. In this case, once the current necessary has been obtained to produce one unit of mass of the reaction product using the chemical equivalent to said product for that purposes, it is possible to determine the electrical energy required at the cell entry for the time of 1 second, for the production of one gram H.sub.2 through the following equation:
Entry energy=∫.sub.t=0.sup.t≤1[s](I*V.sub.optimal)dt
[0112] Then, and considering the output energy as the thermal product of the reaction, this case considering that the energy contained in 1 gram of H.sub.2 is 120011 J (Low Heat Value) and considering a 100% electrical efficiency, the following result is obtained:
V.sub.optimal=1.24 [v]
[0113] Here it is important to note that the electrolysis process for the generation of hydrogen is widely known; thus, it is not an object of the present invention to restate the thermodynamics balances and equations associated with said process. Without prejudice to that and as shown by the present example of application, the optimum application to favor reactions in the production of hydrogen through electrolysis is about 1.24 volts, so that to obtain the maximum efficiency of energy transformation.
[0114] The optimum voltage can be also obtained by applying the standard potentials of reduction corresponding to the potentials measured in each electrode to favor the reduction and oxidation processes under standard conditions. Using the standard potentials of reduction, it can be defined that the oxidation reactions in the anode (2H.sub.2O⇄O.sub.2+4H.sup.++4e) has a reduction potential of 1.229 V, while the reduction reaction in the cathode (4H.sup.++4e.fwdarw.2H.sub.2) has a potential of 0 V, with this valued being defined as the reduction potential in reference. Then, it is possible to calculate the potential of the cell (E°.sub.cell) as follows:
E°.sub.cell=E°.sub.cathode−E°.sub.anode
[0115] Wherein E°.sub.cathode and E°.sub.anode correspond to the potential standards of the cathode and anode for this reaction, respectively. Then, for the electrolytic cell in question the potential of the cell would be −1.229 V, this being the necessary potential to carry out the non-spontaneous reaction of hydrogen and oxygen production through water electrolysis.
[0116] With this optimum voltage of the electrolysis process and with the cell design consideration, operating parameters of the current power supply can be obtained such as pulse duration time, frequency and amplitude thereof, thus optimizing the application of current by minimizing the voltage required to operate the electrolytic cell in a resonant and capacitive fashion. In fact, by using this value and the above-defined equations the duration factor of the current pulse is:
Then, and considering the design parameters, wherein the cell charge voltage in t=DT is V.sub.cell(DT)=2 [v] and the cell voltage in t=T is V.sub.cell(T)=1.8 [v], with those parameters being defined according to the constructive aspects of the cell, the frequency parameter (period) of the pulse wave is:
Therefore, the duration of the pulse wave is:
[0117] Then, the current flowing through the cell under these design parameters is configured as:
[0118] Obtaining the current values for several values of V.sub.max.
[0119] Considering a power supply with V.sub.max=2,52 v is it possible to determine that the pulse duration factor is D≈0.24 for the optimum voltage desired. Then, considering the equation for the period and frequency and a high-capacitance electrolytic cell according to design parameters, as for example with a capacitance of 1.1 F and with a resistance resulting in a duty cycle of 0.18 ohm, it is possible to obtain that the pulse wave frequency supplying power to the system is about 50 Hz (a period of 0.02 seconds).
[0120] With this information it is possible to calculate the current circulating through the cell, which in this case is about 7.19 A. Then, using the ohm law it is possible to evidence that applying an optimum voltage to an electrolytic cell under the constructive parameters of a high-capacitance capacitor and under the operating parameters of the present invention in transient regimes, results in an apparent resistance of the system of 0.17 ohm, which is an advantageous situation compared with the standard electrolytic cells. In fact, below comparative values are presented between a standard cell operated in a standard way with direct current (table 2) and a cell according to the present invention and operated according to the solution stated (table 3), both of them under the same parameters of amplitude and current flow.
TABLE-US-00002 TABLE 2 Energy Effective Effective Consumption Effective Production H.sub.2 energy Efficiency consumed resistance voltage per kilo of H.sub.2 current [A] H.sub.2 [gr/hr] [Wh] [%] [Wh] [ohm] [V] [kWh/kg] 7.19 0.27 9.02 60.0% 15.0 0.2906 2.09 55.6
TABLE-US-00003 TABLE 3 Effective Effective H.sub.2 Energy Consumption Effective voltage resistance production H.sub.2 energy consumed per kilo of H.sub.2 current [A] [V] [ohm] [gr/hr] [Wh] [Wh] [kWh/kg] 7.19 1.27 0.177 0.27 9.02 9.1 33.3
[0121] In view of the above, it is possible to prove that for the same level of H.sub.2 production—considering the electrolysis system of the invention compared with a conventional system-reducing the energy consumption of the cell about 40% is possible, which translates into a substantial reduction of the disadvantages of implementing the alkaline electrolysis process at industrial scale. The big differences resulting between the implementation of a conventional solution and the solution of the present invention are given by the constructive considerations of the cell as capacitor, considering the capacitive and inductive aspects, along with the resistive ones in order to operate the cell under charge and discharge transient regimes. This approach results in current peaks over the electrolytic cell at the beginning of each charge period, which reflects in an apparent or reduce effective resistance, in this case about 0.17 ohm. Taking advantage of said current peak through supplying pulse wave and operation under transient regimes translates into increased efficiency, which exceeds the operation of a conventional cell and making the industrial solutions for the production of hydrogen and oxygen in an alkaline way competitive.
[0122] At this point it should be highlighted that the preceding example of application can be extrapolated to other electrolysis processes, being relevant to calculate the optimal voltage of this process and consider the transient regimes of the electrolytic cell both in charge as in discharge, where the capacitive, inductive and resonant aspects of said cell should be stressed.