Abstract
The present invention relates to the reduction of materials at low temperatures (<600° C.) by means of microwave radiation without needing to use chemical reducing agents or electrical contacts. It relates more specifically to a method for reducing a material, which comprises the following steps: applying microwave radiation to a material disposed in a microwave application cavity; and separating simultaneously the fluid oxidation products generated from the reduced material,
such that the method is carried out without chemical reducing agents or electrical contacts.
Claims
1. A process for the reduction of a material, comprising the following steps: applying microwave radiation to a material placed in a microwave applicator cavity, heating to at least exceeding a shot temperature in the material, and separating fluid oxidation products generated from the reduced material, such that the process is carried out without using reducing chemical agents, wherein the material is an inorganic material, and wherein the shot temperature is a temperature at which electrical conductivity of the material is increased at least 4% within a 4° C. temperature increase with respect to the electrical conductivity of the material without reduction.
2. The process according to claim 1, wherein the process is carried out without use of electrical contacts.
3. The process according to claim 1 wherein the steps are carried out in a container that has the ability to evacuate fluids.
4. The process according to claim 1 wherein the step of applying microwave radiation produces a temperature increase between 50-200° C.
5. The process according to claim 1, wherein the material that is reduced is in one of a solid state, a melted state, a suspension in a liquid, or a solution in a liquid.
6. The process according to claim 5, wherein the liquid is water or a hydrocarbon able to be in a liquid state at the conditions at which the process takes place.
7. The process according to claim 1, wherein the separation of the fluid oxidation products generated from the reduced material is carried out by means of one of: the application of vacuum, the use of an entrainment fluid, use of a reactive fluid that consumes the reduced material, use of a selective separator of the generated oxidation product, or a combination thereof.
8. The process according to claim 1, further comprising a step of in-situ measurement of the conductivity of the material to be reduced by applying microwave radiation from a second source and an associated receiver without mutual inference.
9. The process according to claim 1, wherein the material is a solid material, the composition of which comprises at least a cation of an element selected from among Ti, Fe, Co, Zr, Cr, Nb, Ta, W, Mo, rare earths and U.
10. The process according to claim 1, that further comprises the following steps: placing the material in a container capable of evacuating fluids and inert to MW radiation, inserting the container through an orifice located in a wall of the applicator cavity in an area of uniform and an electric field as intense as possible for uniform and efficient heating, identifying the “shot temperature” for that material, carrying out, while the microwave radiation is applied, a continuous adjustment of the power applied for the radiation, and separating the fluid oxidation products generated from the reduced material, wherein the process is carried out without the use of reducing chemical agents.
11. The process of claim 1 further comprising the steps of: contacting the reduced material with a gaseous stream, and selectively absorbing one or more components of the gaseous stream.
12. The process of claim 1 further comprising the steps of: contacting the reduced material with a gaseous stream, and selectively removing at least one of O.sub.2, F.sub.2, Cl.sub.2, Br.sub.2, HCl, HBr, HF, H.sub.2S or mixtures thereof from the gaseous stream.
13. The process of claim 1 further comprising the step of carrying out a reaction of the material in the reduced state, wherein an oxidized molecule, after its reduction, generates said chemical product.
14. The process of claim 13, wherein: the oxidized molecule is CO.sub.2 and the desired product is CO or the desired product is selected between H.sub.2O and H.sub.2S and the desired product is H.sub.2, or the oxidized molecule is a mixture of gases containing H.sub.2O y CO.sub.2 and the desired product are hydrocarbons.
15. The process of claim 1 further comprising the step of: carrying out a reaction of the material in a reduced state and a second organic molecule which can be reduced, to form products with new functional groups.
16. The process of claim 1 further comprising: generating a chemical product through the reaction of the material in a reduced state and a molecule selected from alkanes, alkenes, naphthenes and aromatic hydrocarbons, to form products with new functionalities.
17. The process of claim 1 further comprising the step of storing energy in the reduced material.
18. The process of claim 1 further comprising the step of simultaneously evacuating the oxidation product and selectively reducing the material comprised in the negative electrode.
19. A reduced material obtained through the process defined in claim 1.
20. An apparatus for reduction of a material, wherein the reduction of material includes applying microwave radiation to a material placed in a microwave applicator cavity, heating to at least exceeding a shot temperature in the material, and separating fluid oxidation products generated from the reduced material, and wherein the process is carried out without using reducing chemical agents, the material is an inorganic material, and the shot temperature is a temperature at which electrical conductivity of the material is increased at least 4% within a 4° C. temperature increase, with respect to the electrical conductivity of the material without reduction; the apparatus comprising: at least one microwave radiation source, a microwave applicator cavity, a container in which the material to be reduced is deposited, and a second source of microwave radiation for in-situ conductivity measurements and without interference with the first radiation source.
21. The apparatus of claim 20 further comprising: at least one temperature sensor to measure the temperature of the material during microwave application, and at least one means for evacuation of fluids originated during the reduction process.
22. The apparatus of claim 20, wherein the microwave radiation source for irradiation is selected from a magnetron-based microwave generator and a microwave generator based on a solid state amplifier.
23. The apparatus of claim 20 wherein the microwave radiation source has means to operate at frequencies between 300 MHz and 300 GHz.
24. The apparatus of claim 20, wherein the applicator cavity is a microwave resonator.
25. The apparatus of claim 20, wherein the microwave radiation is introduced into the applicator cavity through a waveguide, or through a coupling or opening based on an electrical probe or a magnetic probe.
26. The apparatus of claim 20, wherein the applicator cavity has at least one non-radiating orifice located on the upper wall and a second non-radiating orifice located on the bottom wall, which allow the passage of substances.
27. The apparatus of claim 20, wherein the non-radiating orifices located on the upper wall and bottom wall allow the introduction and evacuation of gases.
28. The apparatus of claim 20, further comprising means of evacuating fluids originated during the reduction process.
Description
[0149] FIG. 1: Scheme of the configuration of the equipment to reduce a material by treatment with microwave radiation.
[0150] FIG. 2: Scheme of the applicator cavity and additional components to reduce a material with microwaves.
[0151] FIG. 3: Scheme of an embodiment in which the material (4) to be reduced is continuously fed: A) Scheme of the applicator cavity (2) plus components followed by a separator (7) of the gas produced in the reduction, with respect to the reduced material and B) scheme of the applicator cavity (2) plus components included within the cavity itself (2) a selective separator of the gas produced in the reduction.
[0152] FIG. 4. Scheme of an embodiment in which the material (4) to be reduced is continuously fed, and a process takes place in which it performs the complete cycle of reduction induced by microwave radiation (6) and pure chemical oxidation of the material (4) that takes place in different units, such that it is the material (4) the one that circulates throughout the redox chemical cycle.
[0153] FIG. 5: Particular implementation of the reduction process in a microwave applicator (2) configured as a cylindrical cavity
[0154] FIG. 6: Arrhenius diagram of electrical conductivity for the CGO material with, and without, microwave application.
[0155] FIG. 7: Temporal evolution of the electrical conductivity, temperature and ion current (m=32) during the application of microwaves to the CGO material.
[0156] FIG. 8: Temporal evolution of the electrical conductivity and ion current (m=32) during the application of microwaves to the CGO material under a nitrogen gas current.
[0157] FIG. 9: Arrhenius diagram of electrical conductivity for porcelain material with, and without, microwave application.
[0158] FIG. 10: Temporal evolution of the electrical conductivity and temperature during the application of microwaves to the porcelain material.
[0159] FIG. 11: Arrhenius diagram of electrical conductivity for the 8YSZ material, with and without, microwave application.
[0160] FIG. 12: Temporal evolution of the electrical conductivity and ion current (m=32) during the application of a microwave radiation step to the 8YSZ material.
[0161] FIG. 13: A) Temporal evolution of the temperature and ion current (m=31.91 and M=16.03) associated with O.sub.2, and B) temporal evolution of the electrical conductivity and ion current (m=31.91) associated with O.sub.2. In both cases, during the same microwave application on the CaTi.sub.0.8Fe.sub.0.2O.sub.3-δ; material with a perovskite-type crystalline structure under constant flow of dry N.sub.2.
[0162] FIG. 14: A) X-ray diffraction diagrams for the CGO material before and after its reduction by the application of microwaves; B) XPS spectrum for the CGO material before and after its reduction by the application of microwaves
[0163] FIG. 15: A) Temporal evolution of the temperature and ion current (m=32) associated with O.sub.2, and B) temporal evolution of the temperature and ion current (m=2.09) associated with H.sub.2. In both cases during the same microwave application in three steps in a row to the CGO material under a wet Ar flow.
[0164] FIG. 16: A) Temporal evolution of the temperature and ion current (m=32) associated with O.sub.2, and B) temporal evolution of the temperature and ion current (m=28) associated with CO. In both cases during the same microwave application in three consecutive steps to the CGO material under a flow of CO.sub.2 diluted in dry Ar and free of N.sub.2.
[0165] FIG. 17: Temporal evolution of temperature and ion current during the same microwave application, with a temporal profile in the form of a step, to the CGO material under a flow of undiluted, dry and N.sub.2-free CH.sub.4 gas.
[0166] FIG. 17A: Temporal evolution of the temperature and ion current (m=32) associated with O.sub.2.
[0167] FIG. 17B: Temporal evolution of the temperature and ion current (m=16) associated with CH.sub.4.
[0168] FIG. 17C: Temporal evolution of the temperature and ion current (m=15) associated with CH.sub.4.
[0169] FIG. 17D: Temporal evolution of the temperature and ion current (m=28) associated with CO.sub.2.
[0170] FIG. 17E: Temporal evolution of the temperature and ion current (m=2) associated with H.sub.2.
[0171] FIG. 17F: Temporal evolution of the temperature and ion current (m=44) associated with CO.sub.2.
[0172] FIG. 18: Scheme of the configuration of a system for the production of energy through the use of hydrogen generated in the microwave cavity and of a fuel cell. The diagram includes the equipment for the measurement and control of the O.sub.2 and H.sub.2 generated (mass spectrometer), as well as the voltage generated in the fuel cell (potentiostat).
[0173] FIG. 19: Figure in detail of the ceramic materials used in the fuel cell and microwave cavity for the production of energy through the reduction of COG by microwave radiation (FIG. 18), as well as the composition of the current of the used gases.
[0174] FIG. 20: Temporal evolution of the temperature of the reduction material, of the ion current at the exit of the cavity (m=2, associated with H.sub.2 and m=32, associated with O.sub.2) and the potential of the fuel cell during the different H.sub.2 and energy production cycles. In all cycles, the CGO material is under a gas flow of 30 ml/min of saturated N.sub.2 in water at room temperature. The fuel cell is connected to a potentiostat and the open circuit potential is measured.
[0175] FIG. 21: Temporal evolution of the temperature of the reduction material, of the ion current at the exit of the cavity (m=2, associated with H.sub.2 and m=32, associated with O.sub.2) and of the potential of the fuel cell for the production of H.sub.2 and energy. At all times the CGO material is under a gas flow of 30 ml/min of saturated N.sub.2 in water at room temperature. The fuel cell is connected to a potential measurement equipment in galvanostat mode with a current density demand of 7.85 mA/cm.sup.2.
[0176] FIGS. 22a-22b: Scheme of an embodiment in which energy is produced by a battery in which microwave radiation is applied, O.sub.2 is released, and when the reduced material re-oxidizes, the battery is recharged by the H.sub.2 generated in the process.
[0177] FIG. 22a: Graphical representation of the battery charging from microwave radiation.
[0178] FIG. 22b: Graphical representation of the battery discharging by consumption of H.sub.2 generated during charging.
[0179] The present invention is illustrated by the following examples which are not intended to be limiting thereof.
EXAMPLES
Example 1
[0180] In a process of irradiating a sample by microwave, the resonant cylindrical cavity of FIG. 5 is used. The sample consists of 3 g of cerium oxide doped with gadolinium CGO (Ce.sub.0.8Gd.sub.0.2O.sub.1.9), that is placed in the form of granules on a support (12) inside the applicator cavity (2). A gaseous stream of nitrogen is applied (with a flow of 100 mL/min under normal conditions) (0° C. and 1 atm) which flows through the material and microwave radiation is applied (power around 100 W), such that the temperature increases progressively until reaching a shot temperature at which the reduction of the material is produced, accompanied by the release of gaseous O.sub.2.
[0181] This process has been monitored through the measurement of electrical conductivity shown in FIG. 6, where a sharp jump in conductivity is observed at a shot temperature of 136° C. with an increase in conductivity of −18% in 4° C. This abrupt increase is related to an increase in the concentration of electric charge carriers (polarons) generated thanks to the partial reduction of the material by the action of microwave radiation.
[0182] Also, the figure includes the conductivity measurement when heating occurs by conventional means, electrical resistance and/or infrared radiation. This measurement shows the absence of a reduction process, that is, no sudden changes in conductivity are observed.
[0183] The exit gas from (7) is analyzed by means of a mass spectrometer (8) of the Pfeiffer Vacuum OmniStar type. FIG. 7 shows the measurement of the mass corresponding to oxygen (m=32) as a function of the experiment time. This figure also represents the temporal evolution of electrical conductivity and temperature as a function of time. It is observed that a release of oxygen takes place that starts when a sudden change in electrical conductivity is detected. This release of molecular oxygen (02) constitutes unequivocal evidence of the reduction of the material through the application of microwave radiation.
[0184] FIG. 8 shows the results of another type of operation. In this case, microwave radiation is applied and the reduction of the CGO material occurs and the irradiation is maintained in such a way that the reduced material is kept at a constant temperature.
[0185] FIG. 8 shows the temporal evolution of electrical conductivity and the measurement of the mass corresponding to oxygen (m=32) as a function of time. It is observed that, after the reduction and stabilization of the conductivity—at the level corresponding to “reduced”—it is possible to maintain this conductivity level constantly until the microwave radiation ceases.
TABLE-US-00001 TABLE 1 Effect of the partial pressure of oxygen and the power of the radiation applied during the reduction in the increase in the electrical conductivity of the CGO material, shot temperature and the amount of O.sub.2 released after its reduction through the application of microwaves. Shot Conduc- Temper- Oxygen tivity Power ature released Δ in Material Gas (W) (° C.) (mL) 4° C. (%) Ce.sub.0.8Gd.sub.0.2O.sub.2 N2 98.90 136 0.739 18.49 108.84 146 1.012 29.92 Ar 89.14 119 0.622 45.18 0.1% O.sub.2-Ar 85.73 110 0.701 41.74 Ambient air 72.60 115 0.500 73.96 0.01% O.sub.2-Ar 74.56 124 0.160 49.25 1% O.sub.2-Ar 90.95 121 0.220 4.64
[0186] Table 1 shows a summary of the key parameters (shot temperature, quantity of O.sub.2 gas released and sudden increase in electrical conductivity) in the reduction of the CGO material by means of microwaves when the partial pressure of gaseous O.sub.2 has varied in the gasenous current that passes through the material. It is observed that when the partial pressure decreases, the reduction takes place at lower shot temperatures and more O.sub.2 is released. The increase in electrical conductivity does not seem to change noticeably with the partial pressure of O.sub.2.
[0187] Even in air, it is possible to detect the release of oxygen by CGO. The oxygen released increases as the pO.sub.2 of the sweep gas decreases, reaching a plateau after de pO.sub.2˜10.sup.−4 atm (0.01% O.sub.2/Ar). The release of oxygen is a function of the applied MW power.
[0188] Table 1 also shows the effect on the key parameters in the reduction of the CGO material when different powers of radiation are applied. These results demonstrate that the reduction process can be controlled by adjusting this power. The greater the power of the applied microwave radiation, the greater the conductivity gap. More oxygen can be released and thus more oxygen vacancies are produced, and the effect is measured in the transport properties of the material as a higher level in the sudden increase in conductivity.
Example 2
[0189] On the other hand, there are materials that can be irradiated by microwaves, such as porcelain-type materials, which do not exhibit the behavior of CGO and which, therefore, cannot be reduced by microwave radiation according to the present invention. FIG. 9 shows the measurement of electrical conductivity for porcelain material as a function of temperatura, when microwave radiation is being applied (solid line in FIG. 9) and it can be seen that there is no sudden change in conductivity, this means, there is no reduction of the porcelain material and, therefore, there is no shot temperature for this type of material. This figure also includes the conductivity measurement when heating occurs by conventional means, electrical resistance and/or infrared radiation. Said measurements perfectly coincide with the measurements made by applying microwave radiation, this is why it is confirmed that for this material microwaves cannot induce a reduction of the material in the operating range proposed in the present invention. This behavior is observed both when the material is measured in a tube open to the atmosphere, and when a gaseous flow is applied to it, such as currents of Ar, He, He, N.sub.2, O.sub.2, H.sub.2, Ar/O.sub.2 mixtures (0.01%, 0.1%, 1.5%) and saturated H.sub.2O streams.
[0190] FIG. 10 shows the temporal evolution of the electrical conductivity and the temperature as a function of the test time when the microwave radiation is applied on the porcelain material. It is observed that the temperature increases linearly with time while the conductivity shows a typical behavior of thermal activation, but a sudden change that can be associated with the microwave reduction is not observed, as was observed for the CGO material (FIG. 7).
Example 3
[0191] FIG. 11 shows the Arrhenius plot of the measured electrical conductivity of 3 g of microwave irradiated Y.sub.0.16Zr.sub.0.86O.sub.2-δ (8YSZ) as a function of temperature (reciprocal) when a gaseous current in Ar (with flux 100 mL/min under normal conditions) was made to pass through said material in the form of granules. As it was appreciated for the CGO (example 1), a shot temperature of approximately 200° C. could be identified, in this case, from which a strong increase in conductivity occured with the application of microwaves, followed by a slower increase. This abrupt increase in electrical conductivity is related to the reduction of the material that makes the concentration of electronic carriers to increase noticeably. This phenomenon is accompanied by the release of gaseous O.sub.2 (FIG. 12) and the formation of oxygen vacancies in the crystalline structure, since the reduction process preserves the integrity of the fluorite structure of the 8YSZ material. It is to be pointed out that the reduction of the 8YSZ material, and in particular the Zr.sup.+4 cations of its structure, is very complex and normally requires very high temperatures (>1700° C.) combined with the use of strong chemical reducing agents. Likewise, it is noted that after microwave reduction the fluorite structure is preserved, although the number of oxygen vacancies increases as a consequence of the reduction. FIG. 11 also shows the evolution of the electrical conductivity of the material when microwave radiation is not applied, observing that it presents a curve without a sudden activation jump and following the expected curve for a pure oxygen ion (O.sub.2) conductor, as is the 8YSZ material
[0192] FIG. 12 shows the results of a test wherein microwave radiation is applied and the 8YSZ material is reduced under dry Ar flow (with flow of 100 mL/min under normal conditions) and the irradiation is maintained in such a way that the reduced material is kept at a constant temperature. FIG. 12 shows the temporal evolution of electrical conductivity and the measurement of the mass corresponding to oxygen (m=32) as a function of time. It is observed that, after the reduction and stabilization of the conductivity—at the level corresponding to “reduced”—it is possible to maintain this conductivity level constantly until the microwave radiation ceases and, at that point, an inverse peak is observed (absorption) in the O.sub.2 signal, which indicates the re-oxidation of the material, despite the fact that the O.sub.2 content in the Ar used is below 2.Math.10.sup.−5 bar. This example shows that the present invention will allow oxygen impurities to be removed from gas streams to levels even below parts per million (ppm), i.e., it will allow to selectively purify gas streams
TABLE-US-00002 TABLE 2 Effect of the partial pressure of oxygen and the power of the radiation applied during the reduction, in the increase of the electrical conductivity of the 8YSZ material, shot temperature and the amount of O.sub.2 released after its reduction by means of the application of microwaves. Shot conduc- Temper- Oxygen tivity Power ature released Δ in Material Gas (W) (° C.) (mL) 4° C. (%) Zr.sub.0.92Y.sub.0.08O.sub.2-x Ar 52.61 192 0.005 64.57 0.01% O.sub.2-Ar 57.59 180 0.013 56.56 Ambient air 27.54 261 0.07 51.98
[0193] Table 2 shows a summary of the key parameters (shot temperature, amount of O.sub.2 gas released and sudden increase in electrical conductivity) in the reduction of the 8YSZ material by microwaves when the partial pressure of O.sub.2 gas in the gaseous stream (with a flow of 100 mL/min under normal conditions) that passes through the material, has been varied. It is observed that the amount of O.sub.2 released increases as the partial pressure of O.sub.2 decreases.
[0194] The temperatures at which the difference in conductivity between the conventional process and the microwave are maximum is 361° C. for 8YSZ (example 3) and 216° C. for CGO (example 1). The difference between the materials may be related to the reducibility of their cations, since the presence of the Ce.sup.3+/.sup.4+ pair is easier to achieve than the Zr.sup.3+/.sup.4+.pair for YSZ.
Example 4
[0195] Following the procedure described in Example 1, various materials based on doped cerium oxide were reduced as follows: microwave radiation was applied at a power within the range of 25-75 W within the system described in example 1 by passing Ar through the material. Various undoped and Gd-doped cerium oxide materials (10 and 20 mol. %), Pr (20 mol. %) and (Gd 10 mol. % and Nb 4%), all of them having the crystalline structure of cubic fluorite. Table 3A shows a summary of the key parameters (shot temperature, amount of O.sub.2 gas released and sudden increase in electrical conductivity) in the reduction of the different materials by means of microwaves when a gaseous current is passed through the material with a flow of 100 mL/min under normal conditions. It is observed that the parameters that characterize the result of the reduction can be varied by controlling the composition of the crystal lattice of the material to be reduced. Doping allows modifying the reducibility of the material, but also its ionic conductivity, which is important since the mobility of the oxygen ion within the crystal lattice plays a role in the reduction process.
TABLE-US-00003 TABLE 3 A Effect of doping of the material based on cerium oxide, in the increase of the electrical conductivity of said materials, shot temperature and the amount of O.sub.2 released after its reduction through the application of microwaves. Shot Conduc- Temper- Oxygen tivity Power ature released Δ in Material Gas (W) (° C.) (mL) 4° C. (%) Ce.sub.0.9Gd.sub.0.1O.sub.2 1% O2-Ar 80.63 130 0.5 18.63 Ce.sub.0.8Gd.sub.0.2O.sub.2 Ambient air 72.60 115 0.5 73.96 CeO.sub.2 nanocristaline Argon 28.61 100 7.3 91.78 Ce.sub.0.8Pr.sub.0.2O.sub.2-x Ambient air 12.93 271 0.9 69.16 Ce.sub.0.86Gd.sub.0.1Nb.sub.0.04O.sub.2 Ambient air 38.24 221 0.6 72.91
[0196] Similarly, Table 3B shows a summary of the key parameters (shot temperature, amount of O.sub.2 gas released and sudden increase in electrical conductivity) in the reduction of the different materials, based on zirconium oxide (Zr.sub.0.86Y.sub.0.12O.sub.2-x, Zr.sub.0.94Y.sub.0.06O.sub.2-x and Zr.sub.0.86Sc.sub.0.12O.sub.2-x) by microwaves when a gaseous current is passed through the material.
TABLE-US-00004 TABLE 3B Effect of doping of the material based on zlrconlo oxide, in the increase of the electrical conductivity of said materials, shot temperature and the amount of O.sub.2 released after its reduction by means of microwave application. Shot Conduc- Power Temper- Oxygen tivity ature released Δ in Material Gas (W) (° C.) (mL) 4° C. (%) Zr.sub.0.92Y.sub.0.08O.sub.2-x Ambient 27.54 261 0.09 51.98 Zr.sub.0.97Y.sub.0.03O.sub.2-x air 45.59 220 0.05 69.20 ScYSZ 34.77 271 0.11 61.74
[0197] Table 4 shows the increase in conductivity, the amount of O.sub.2 released and the shot temperature during the reduction, through the application of microwaves of different materials with different composition and crystalline structure. The sample Si.sub.0.4Al.sub.0.3Ti.sub.0.1Fe.sub.0.2O.sub.x is representative of a typical rock on the moon. The process was carried out according to example 4. It is observed that it is possible to carry out the reduction in different materials. Specifically, the reduction of the following cations is observed: Ti.sup.+4, Gd.sup.+3, Nb.sup.+5, W.sup.+6, Fe.sup.+3/Fe.sup.+4, what allows adjusting properties of the reduction process by means of microwaves and, therefore, the use of this method in different applications. FIG. 13A shows the evolution of the temperature for the material CaTi.sub.0.8Fe.sub.0.2O.sub.3-δ with a perovskite-type crystalline structure, when microwave radiation is applied under a constant flow of dry N.sub.2 (with a flow of 100 mL/min under normal conditions) and the measurement of the masses corresponding to the gaseous oxygen released (m=31.91 and m=16.03) as a function of time. FIG. 13B shows the temporal evolution of the electrical conductivity and the measurement of the mass corresponding to the gaseous oxygen released (m=31.91) as a function of time.
TABLE-US-00005 TABLE 4 Increase in the electrical conductivity of these materials, shot temperature and the amount of O.sub.2 released after its reduction through the application of microwaves of different materials. Conduc- Shot Oxygen tivity Temper- re- Δ in Power ature leased 4° C. Material Gas (W) (° C.) (mL) (%) Nb.sub.2O.sub.5 Ambient 64.8 549 0.05 78.3 air Gd.sub.1.98Ca.sub.0.02O.sub.4-δ Ambient 59.8 339 0.07 12.7 air TiO.sub.2 N.sub.2 117.6 320 0.12 90.0 La5.5WO12.sub.-δ Ambient 30.0 361 0.25 31.8 air NdBaLnO4 Ambient 115.7 226 0.3 33.3 air CaTi.sub.0.8Fe.sub.0.2O.sub.3-δ N.sub.2 22.3 207 1.9 42.5 Si.sub.0.4Al.sub.0.2Mg.sub.0.1Ca.sub.0.05- Ti.sub.0.1Fe.sub.0.15O.sub.1.7-δ N.sub.2 68.3 325 0.13 23.2
Example 6
[0198] FIG. 14 describes the physicochemical characterization of materials reduced by microwave radiation. FIG. 13A shows in the X-ray diffraction diagrams for the CGO sample (Example 1) without reduction and after reduction by microwave. A shift of the diffraction peaks to the right is observed for the microwave-treated sample, confirming that the material has been reduced. This increase in the size of the crystal lattice is characteristic of the partial reduction of the Ce.sup.+4 to Ce.sup.+3 cation.
[0199] FIG. 14B shows the XPS (X-ray photoelectron spectroscopy) diagrams that allow characterizing the oxidation state of different chemical elements in the most superficial atomic layers of the materials. In this case, as in FIG. 14A, measurements are shown for the original untreated and microwave-treated CGO sample. In general terms, the reduction of the Ce.sup.+4 to Ce.sup.+3 cation is observed, while in this case the reduction of the Gd.sup.+3 cation is not appreciated for this material, given the greater reducibility of the Ce.sup.+4 cation.
Example 7
[0200] This example describes how hydrogen can be generated by reacting reduced CGO material (by microwave radiation) with water vapor.
[0201] The process was carried out in a set-up as described in example 1 and passing a stream of Ar (with flow of 100 ml/min under normal conditions) wet (3% vol). The process consisted of three cycles and each one is described as follows: (i) microwave radiation is applied in such a way that the temperature rises until the shot temperature is reached and the CGO material is reduced, releasing O.sub.2 gaseous which is entrained by the current of wet Ar, (ii) the microwave radiation is kept on and the temperature is maintained for a few minutes, then (iii) the microwave radiation is stopped and the CGO material is oxidized by the extraction of the oxygen atom from the water (steam) of the gas stream, what gives rise to the production of H.sub.2 gas, and (iv) finally, the material is allowed to cool down to room temperature. FIG. 15A shows the temporal evolution of the temperature and the measured signal corresponding to the mass of oxygen (m=32) as a function of the experiment time. The release of O.sub.2 in each cycle is observed, when the temperature rises under microwave radiation, such that the material is reduced and, subsequently, it is maintained for a few minutes at the maximum temperature reached until the microwave radiation ceases and then it is cooled to room temperature. FIG. 15B shows the temporal evolution of the temperature and the measurement of the mass corresponding to H.sub.2 (m=2) as a function of time. In each cycle, the release of H.sub.2 is observed when the microwave radiation ceases and the temperature drops, such that the water vapor in the gas stream is reduced to form H.sub.2 and the CGO material is re-oxidized. This figure therefore demonstrates a reproducible and cyclic method for H.sub.2 production according to the present invention.
Example 8
[0202] This example describes how CO.sub.2 can be reduced to form CO by reacting the reduced CGO material (by microwave radiation) with CO.sub.2 from a gaseous stream. The process was carried out in a setup as described in example 1 and passing a dry gas stream (with a flow of 100 ml/min under normal conditions) composed of CO.sub.2 (25% vol.) diluted in Ar and totally free of N.sub.2. Analogously to the process described in Example 7, the process consisted of three cycles and each one is described as follows: (i) microwave radiation is applied in such a way that the temperature rises until the shot temperature is reached and the CGO material is reduced, releasing gaseous O.sub.2 that is carried along by the gaseous current, (ii) the microwave radiation is kept on and the temperature is maintained for a few minutes, then (iii) the microwave radiation is stopped and the material CGO is oxidized by the extraction of an oxygen atom from CO.sub.2 from the gas stream, what results in the production of CO.sub.2 gas, and (iv) finally, the material is allowed to cool down to room temperature. FIG. 16A shows the temporal evolution of the temperature and the measured signal corresponding to the mass of O.sub.2 (m=32) as a function of the time of the experiment. In each cycle, the release of O.sub.2 is observed when the temperature rises under microwave radiation, such that the material is reduced and, subsequently, it is maintained for a few minutes at the maximum temperature reached until the microwave radiation ceases, and the cooling down to room temperature is produced. FIG. 16B shows the temporal evolution of the temperature and the mass measurement (m=28) directly related to the presence of CO. In each cycle, the release of CO is observed in two steps (a) when the reduction of the CGO material has taken place (all the gaseous O.sub.2 has been evacuated) and the temperature begins to stabilize, what means that the control system of microwave reduces the power of the applied radiation and increases its ability to re-oxidize, and (b) when microwave radiation completely ceases and the temperature drops. In both stages, the CO.sub.2 in the gas stream is reduced to form CO while the CGO material is re-oxidized. This figure therefore demonstrates a reproducible and cyclable method for CO.sub.2 reduction and CO production according to the present invention.
Example 9
[0203] This example describes how the partial oxidation of CH.sub.4 can occur through the release of oxygen species from the crystalline lattice of the CGO material as it is reduced by the effect of microwave radiation. This example shows how—as the material is reduced-, the oxidation product (oxygen in this case) is consumed in situ thanks to the use of a reactive fluid (CH.sub.4) that consumes it. The process was carried out in a set-up as described in example 1 and passing a dry gas stream (with a flow of 100 mL/min under normal conditions) composed of CH.sub.4 (10% vol.) diluted in Ar and totally free of moisture and N.sub.2.
[0204] The process consisted of applying microwave radiation in such a way that the temperature rises until the shot temperature is reached and the CGO material is reduced, releasing oxygen species that reacts on the surface of the CGO material and gives rise to partial oxidation products (mainly CO, H.sub.2, CO.sub.2), which are entrained by the gaseous stream and measured by a mass spectrometer. Subsequently, the material is allowed to cool down to room temperature.
[0205] FIG. 17A shows the temporal evolution of the temperature and the measured signal corresponding to the mass of O.sub.2 (m=32) as a function of the time of the experiment. The release of O.sub.2 is barely detectable when the temperature rises under microwave radiation, so that although the material is reduced at the shot temperature, the oxygen is consumed through the partial oxidation reactions of methane in the gas stream. FIGS. 17B-C show the evolution of the masses m=16 and m=15 corresponding to the CH.sub.4, and show that from the shot temperature a significant amount of the CH.sub.4 gas is consumed to produce other gaseous products.
[0206] FIGS. 17D-EF show the temporal evolution of temperature and the measurement of the mass (m=28) directly related to the presence of CO, the mass (m=2) directly related to the formation of H.sub.2 and the mass (m=44) directly related to the presence of CO.sub.2. It is observed that when the CGO material is reduced by the action of microwaves, part of the CH.sub.4 is converted into CO, H.sub.2 and CO.sub.2 among other partial oxidation products. This figure, therefore, demonstrates a reproducible method for the oxidation and functionalization of a refractory molecule such as CH.sub.4.
Example 10
[0207] In this example—illustrated by FIG. 18—the operation of a battery powered with the H.sub.2 produced using microwave energy is shown. In a first step, a mass of 0.963 g of COG is placed in the microwave cavity, and it is reduced by microwave radiation (power around 100 W) in the presence of water vapor, 30 ml/min of N.sub.2 with 2.5% vol. of H.sub.2O. The O.sub.2 generated, as well as the N.sub.2 and H.sub.2O present in the gas leaving the cavity, are released in this step by means of a vent. In a second step, the power of the microwave radiation is reduced (around 30 W) and the material is re-oxidized with the 2 5% volumetric water present in the N.sub.2 fed to the cavity.
[0208] This second step leads to the production of H.sub.2. At this point, the battery is charged, the discharge is carried out by consuming the generated H.sub.2. The H.sub.2 produced is fed to the anode of a fuel cell, while air is introduced into the cathode. For the electrochemical characterization of the fuel cell, a potentiostat is used. Likewise, the generation of gases in the microwave cavity is controlled by means of a mass spectrometer, which allows continuous monitoring of the signal associated with each of the gases under study (m=2, associated with H.sub.2 and m=32, associated with O.sub.2).
Example 11
[0209] In this example—illustrated by FIG. 19—the components of the electrochemical cell used in the proof of concept, as well as in the microwave cavity, are sown in detail. The fuel cell consists of a 15 mm diameter cell, supported on the anode. The anode is composed of a composite of nickel metal (after reduction with H.sub.2) and yttrium stabilized with zirconium. The zirconium stabilized yttrium electrolyte has a thickness of ≈7 μm. The cathode is composed of a 50% by volume mixture of La.sub.0.85Sr.sub.0.15MnO.sub.3 and Ce.sub.0.8Gd.sub.0.2O.sub.2, and infiltrated with a 2M solution (ethanol-water) of Pr(NO.sub.3).sub.3.6H.sub.2O. The cathode is calcined in air at 750 C for 2 hours, for the elimination of nitrates and the formation of nanoparticles (<40 nm) of praseodymium oxide (PrO.sub.1.833). For the microwave cavity, a bed of 0.963 g of Ce.sub.0.8Gd.sub.0.2O.sub.2 is used, and it is fed with a stream of 30 ml/min of N.sub.2 saturated with water at room temperature (2.5%. Vol.). When the microwave radiation is turned on and the shot temperature is reached (around 100 W), O.sub.2 is released, and this is sent to a vent. Ce.sub.0.8Gd.sub.0.2O.sub.2 is heated up to temperatures close to 450° C. Subsequently, the power applied (around 30 W) to the Ce.sub.0.8Gd.sub.0.2O.sub.2 is reduced, allowing a constant temperature (close to 400° C.) and a controlled production of hydrogen. This H.sub.2 is fed into the fuel cell, on the anode side. A constant flow of synthetic air with a flow rate of 50 ml/min is introduced on the cathode side. The electrochemical cell works at a constant temperature of 700° C. The O.sub.2 present in the cathode is reduced to oxygen ions (O.sup.2−), and these ions pass through the electrolytic material, due to its ionic conduction. Once the ions reach the anode, they react with the H.sub.2 present, generating H.sub.2O and a flow of electrons. This flow of electrons circulates through an external circuit and is controlled with a potentiostat. The mass spectrometer was used to qualitatively control the production of H.sub.2 and O.sub.2.
Example 12
[0210] In this example—illustrated by FIG. 20, the experimental results obtained in the operation of a fuel cell fed with hydrogen produced by means of microwave radiation are shown, and described in FIGS. 18 and 19. For this test, different cycles were carried out continuously. Each cycle can be divided into two steps. In a first step, the CGO is fed with 30 ml/min of N.sub.2 saturated with H.sub.2O at room temperature, and microwave radiated. After exceeding the shot temperature (around 100 W), O.sub.2 is generated. This cavity outlet stream is vented. In a second step, the applied microwave power is reduced (around 30 W) and the COG temperature is kept close to 400° C. The CGO is re-oxidized with H.sub.2O, generating a continuous flow of H.sub.2 that is fed to the anode of the fuel cell. In the meantime 50 ml/min of synthetic air is introduced into the cathode of the fuel cell.
[0211] Due to the incorporation of H.sub.2 (generated in step two) in the electrochemical cell, there is an increase in the open circuit potential, as can be seen in FIG. 20. After consumption of H.sub.2, the anode of the electrochemical cell is fed with a current of He of 50 ml/min, again reducing the open circuit potential of the cell. The open circuit potential is measured with the help of a potentiostat. The production of H.sub.2 (m=2) and O.sub.2 (m=32) is continuously monitored by means of a mass spectrometer. In the first step, microwave radiation, a substantial increase in the O.sub.2-related signal is observed (m=32). Once the power is reduced, it is verified by means of the mass spectrometer, how the signal of mass 2 (H.sub.2) increases, and this current is fed into the anode of the fuel cell. Once H.sub.2 is no longer produced, the cell is re-fed with He. Likewise, this example shows the temperature of the microwave-radiated material (COG) and the open circuit potential of the electrochemical cell as a function of time.
Example 13
[0212] In this example—illustrated by FIG. 21—the results of the same cell of the previous example (FIGS. 18, 19 and 20) are shown, working in galvanostatic mode. The fuel cell operates continuously with a current demand of 7.85 mA/cm.sup.2. In a first step, the fuel cell is fed with a flow of 50 l/min of H.sub.2, and a reduction in power is observed. Once the O.sub.2 has been released after the reduction of 0.963 g of CGO with a stream of 30 ml/min of N.sub.2 saturated in H.sub.2O at room temperature, the electrochemical cell is fed with the H.sub.2 generated in the re-oxidation. The potential of the cell increases, generating an average power of 5.6 mW/cm.sup.2 during the 35 minutes of operation with the H.sub.2 generated in the microwave cavity. After disconnecting the outlet current from the microwave cavity, and reintroducing 50 ml/min of H.sub.2, the potential of the cell decreases again. In this example the temperature in the microwave cavity, as well as the signal measured by a mass spectrometer, for the H.sub.2 (m=2) and O.sub.2 (m=32) of the gas stream leaving it, are shown.
[0213] This signal allows the continuous production of all the gases generated in the microwave cavity to be followed.
Example 14
[0214] In this example—illustrated by FIG. 22a/22b—the operation of a battery is described, wherein the two parts described above (fuel cell and microwave cavity) are integrated. The same material acts as an anode and as a material for the production of H.sub.2 by microwave radiation. The device is radiated with microwaves and there is an instantaneous release of O.sub.2 (FIG. 22a), after this moment, the microwaves are turned off, and H.sub.2 is generated in the same chamber. The battery is discharged through the energy demand from the battery and the consumption of the generated H.sub.2 (FIG. 22b). Once the H.sub.2 has been consumed, the battery is recharged by means of a new microwave radiation. In a second case, two twin devices are used, while one of them produces the reduction of the material and its subsequent oxidation with the generation of H.sub.2, the other ones supplies the energy demanded by the system to which it is connected. In a third case, the material radiated with microwaves and the one that works as an electrode, are separated, but integrated in the same device. After eliminating the O.sub.2 produced by microwave radiation, steam is introduced into the chamber, and after re-oxidation of the material, the electrode is fed with the produced H.sub.2.
