Patent Application
20230338920
Exemplary embodiments relate to perovskite oxygen carriers and methods for making same. More specifically, exemplary embodiments relate to B-site doped perovskite oxygen carriers and methods for using same. Still other exemplary embodiments relate to mesoporous perovskite oxygen carriers, methods for using same, and methods for making same.
Pure oxygen is an important commodity in the present day. Uses include, but are not limited to, medical needs, wastewater treatment, fuel cell technology, as well as coal-fired combustion plants in order to ease carbon dioxide capture, and reduce emissions. Currently there are a few methods to separate oxygen from an air stream, including cryogenics, but most are too expensive to perform on a large scale.
One economically viable alternative is chemical looping air separation systems that rely on a difference in the partial pressure of oxygen gas to activate an oxygen carrier that will selectively uptake oxygen from a higher partial pressure and release adsorbed oxygen at a lower partial pressures. As an example, an air stream is 21% oxygen whereas an inert gas stream, like nitrogen or argon, is 0% oxygen.
Most oxygen carriers can complete both halves of this process at high temperatures (673° K.-1273° K.) but factors of increased cost of materials, the need for high temperatures, and rate of oxygen release are pertinent. Each of these factors can directly limit the economic viability and profitability of the process.
There is a need in the art for oxygen carriers that overcome the disadvantages of the prior art that provide superior value, improved kinetics, higher activity at lower temperatures, and reduced or no use of high-demand and/or expensive elements such as platinum or cobalt.
Perovskite oxides of the ABO3 form are among the most commonly studied oxygen storage materials given their robust stability through the uptake/release process. The presence of oxygen vacancies in a typical perovskite carrier allows for easy oxygen transport and its reduction only requires a slight rearrangement of atoms. As such, perovskites are efficient oxygen carriers due to rapid oxygen uptake/release at reasonably low operating temperatures while other oxygen carriers require higher temperatures and more elaborate structural changes.
An embodiment of the invention provides perovskite oxygen carriers featuring a B-site doped with Ni and methods of using said perovskite oxygen carriers B-site doped with Ni to carry oxygen.
Further embodiments of the invention provide mesoporous perovskite oxygen carriers, methods of making said mesoporous perovskite oxygen carriers, and methods of using said mesoporous perovskite oxygen carriers to carry oxygen.
Briefly the invention provides a perovskite oxygen carrier comprising the formula SrFeO3, wherein the oxygen carrier comprises an A-site and a B-Site, and wherein the B-site is doped with Ni.
The invention also provides a perovskite oxygen carrier comprising the formula Sr1-xCaxFe1-yNiyO3, where 0.05<x<0.30 and 0.001<y<0.125.
The invention still further provides a method for carrying oxygen using a perovskite oxygen carrier, the method comprising: providing a reduced oxygen carrier to a reaction environment; contacting the reduced oxygen carrier with an oxygen containing gaseous stream for a predetermined time at a first temperature and a first oxygen partial pressure, wherein the reduced oxygen carrier adsorbs oxygen from the gaseous stream during this step, giving an oxygen carrier; and heating the oxygen carrier to a second temperature at a second oxygen partial pressure, causing oxygen adsorbed onto the oxygen carrier in the contacting step to be released from the oxygen carrier, reforming the reduced oxygen carrier, wherein the oxygen carrier comprises the formula Sr1-xCaxFe1-yNiyO3, where 0.05<x<0.30 and 0.001<y<0.125.
The invention also provides a perovskite oxygen carrier comprising the formula SrCaFeO3, wherein the is mesoporous.
The invention still further provides a method for carrying oxygen using a perovskite oxygen carrier, the method comprising: providing a reduced oxygen carrier to a reaction environment; contacting the reduced oxygen carrier with an oxygen containing gaseous stream for a predetermined time at a first temperature and a first oxygen partial pressure, wherein the reduced oxygen carrier adsorbs oxygen from the gaseous stream during this step, giving an oxygen carrier; and heating the oxygen carrier to a second temperature at a second oxygen partial pressure, causing oxygen adsorbed onto the oxygen carrier in the contacting step to be released from the oxygen carrier, reforming the reduced oxygen carrier, wherein the oxygen carrier comprises the formula Sr1-xCaxFeO3, where 0.01<x<0.40, and wherein said oxygen carrier is mesoporous.
The invention still further provides a method for making mesoporous perovskite oxygen carriers comprising: producing polymerized metal-carboxylate chelates; calcining the polymerized metal-carboxylate chelates at a synthesis temperature to produce the mesoporous perovskite oxygen carriers, wherein the synthesis temperature is below 1000° C.
Embodiments of the present invention are illustrated in the accompanying figures where:
The following detailed description provides illustrations for embodiments of the present invention. Each example is provided by way of explanation of the present invention, not in limitation of the present invention. Those skilled in the art will recognize that other embodiments for carrying out or practicing the present invention are also possible. Therefore, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
As used herein, “mesoporous” means a material that is porous, wherein those pores have a diameter between approximately 2 and approximately 50 nm.
As used herein, “bulk materials” are materials wherein all dimensions of said materials are above 100 nm.
As used herein, nanomaterials comprise materials having at least one dimension in the range of 1 to 100 nm.
An embodiment of the invention provides a novel perovskite oxygen carrier composition, wherein perovskite comprises a composition of the general formula ABO3. More specifically, the invention provides a perovskite composition comprising a SrFeO3 perovskite oxygen carrier wherein the A-site (Sr) of the oxygen carrier is doped with Ca and the B-site (Fe) of the oxygen carrier is doped with Ni. In an embodiment, the invented B-site doped perovskite oxygen carrier 10 as shown in
A salient feature of embodiments of the invention are that the invented B-site doped perovskite oxygen carrier does not include any of lanthanide elements, cobalt, or platinum.
In an alternative embodiment, the general formula of the invented B-site doped perovskite oxygen carrier is (Sr1-xCax)0.80-1.20Fe1-yMyO3, where 0.05<x<0.40, 0.001<y<0.25, and M is selected from the group consisting of scandium, titanium, manganese, nickel, copper, zinc, and a combination thereof.
In yet another alternative embodiment, the general formula of the invented B-site doped perovskite oxygen carrier is (Sr1-xCax)0.80-1.20Fe1-y-zCoyMzO3, where 0.05<x<0.40, 0.001<y<0.50, 0.001<z<0.25, and M is selected from the group consisting of scandium, titanium, manganese, nickel, copper, zinc, and a combination thereof.
The invented B-site doped perovskite oxygen carriers 10 can be formulated into any physical form desired by a user. Exemplary forms include monoliths, macroparticles, microparticles, nanoparticles, pellets, rods, and combinations thereof. Additionally, the invented B-site doped perovskite oxygen carriers 10 are suitable for use in various catalytic setups such as chemical loops, packed beds, fluidized beds, etc. and combinations thereof.
In an embodiment, the invented B-site doped perovskite oxygen carrier is suitable for use in temperature and or pressure swing reactions to selectively adsorb and release oxygen. EQUATION 1 below provides the reactions for such a process where the forward reaction of EQUATION 1 shows the reduction of the invented B-site doped perovskite oxygen carrier, i.e., the oxygen carrier releasing oxygen to form a reduced oxygen carrier. The reverse reaction of EQUATION 1 shows the oxidation of the reduced invented B-site doped perovskite oxygen carrier, i.e. the reduced oxygen carrier adsorbing oxygen to form the invented perovskite oxygen carrier 10.
As shown in
Once the reduced oxygen carrier is positioned within the reaction environment, the method continues by contacting the reduced oxygen carrier with an oxygen containing gaseous stream for a predetermined time at a first temperature and a first oxygen partial pressure 104, wherein the reduced oxygen carrier adsorbs oxygen from the gaseous stream during the contacting step 104, forming an oxygen carrier. After the contacting step 104, the method continues by heating the oxygen carrier to a second temperature at a second oxygen partial pressure, causing oxygen adsorbed onto the oxygen carrier in the contacting step to be released, reforming the reduced oxygen carrier 106.
In the first step of the method 100 described above and shown in
As described above and shown in
As described above and shown in
A salient feature of the invention is the performance of the invented B-site doped perovskite oxygen carrier when used in a process such as that shown in
Also during the contacting step 104, the invention provides maximum adsorption temperatures, the temperature where the reduced oxygen carrier adsorbs oxygen at the fastest rate, that are superior to the prior art. In an embodiment, the maximum adsorption temperature during the contacting step is between approximately 573° K. and approximately 673° K. using a reduced B-site doped perovskite oxygen carrier.
Still further, during the contacting step, the invention provides improved oxidation rates compared to the prior art. In embodiment, the oxidation rate during the contacting step is between approximately 2 wt %/min and approximately 10 wt %/min when using the invented B-site doped perovskite oxygen carrier.
As described above and shown in
As described above and shown in
A salient feature of the invention is the performance of the invented oxygen carrier when used in a process such as that shown in
Also during the heating step 106, the invention provides maximum desorption temperatures, the temperature where the oxygen carrier releases oxygen at the fastest rate, that are superior to the prior art. In an embodiment, the maximum desorption temperature during the contacting step using the invented B-site doped perovskite oxygen carrier is between approximately 673° K. and approximately 773° K.
Still further, during the heating step, the invention provides improved reduction rates compared to the prior art. In embodiment, the reduction rate during the contacting step using the invented B-site doped perovskite oxygen carrier is between approximately 0.033 wt %/min and approximately 1.5 wt %/min.
The invented Sr1-xCaxFe1-yNiyO3 oxygen carriers 10 were synthesized using methods described in E. J. Popczun, D. N. Tafen, S. Natesakhawat, C. M. Marin, T.-D. Nguyen-Phan, Y. Zhou, D. Alfonso, J. W. Lekse, Journal of Materials Chemistry A 2020, 8, 2602-2612 and E. J. Popczun, T. Jia, S. Natesakhawat, C. M. Marin, T. D. Nguyen-Phan, Y. Duan, J. W. Lekse, ChemSusChem 2021, the entirety of which are both incorporated by reference herein. Briefly, stoichiometric amounts of strontium (II) carbonate [SrCO3, 99.9%, Sigma-Aldrich], calcium (II) carbonate [CaCO3, 99.5%, Alfa-Aesar], iron (III) oxide [Fe2O3, 99.9%, Alfa-Aesar], and nickel (II) oxide [NiO, 99%, Sigma-Aldrich] powders were added to an agate mortar. The powder mixture was manually ground for roughly 15 min to ensure homogeneity. The powder mixture was then pelletized using a 13-mm die assembly in a Carver manual pellet press at a pressure of 4 metric tons. These pellets were loaded into an alumina combustion boat and calcined at 850° C. for 40 hours as pretreatment. Upon cooling, each pellet was ground and subsequently pelletized to remove any inhomogeneities from initial grinding. These pellets were calcined at 1100° C. for 64 hours to yield the final product. Samples were stored in scintillation vials as powders until used.
For experiments involving the invented B-site doped perovskite oxygen carriers, XRD patterns were collected on a PANalytical X'Pert Pro X-Ray diffractometer with a typical diffraction range of 5-80° 2-theta in a Bragg-Brentano configuration. Cu Kα (λ=1.541 Å) was used as the X-ray source.
For experiments involving the invented B-site doped perovskite oxygen carriers, ex situ synchrotron-based XRD patterns were collected on Beamline 17-BM at Advanced Photon Source (APS), Argonne National Laboratory. The X-ray wavelength was 0.24136 Å. A Perkin-Elmer amorphous silicon area detector at a diffraction distance of 0.7 m was used to collect transmission diffraction images from fine powdered samples loaded into capillary tubes. This image data was integrated in GSAS-II to a 2-theta versus intensity format.
For experiments involving the invented B-site doped perovskite oxygen carriers, scanning electron microscopy (SEM) images were collected using a FEI Quanta 600F SEM equipped with an Oxford Inca X-Act EDX detector. Images and spectra were collected at 20 keV.
For experiments involving the invented B-site doped perovskite oxygen carriers, O2-TPD experiments were carried out on a Micromeritics 2950HP system equipped with a Pfeiffer Vacuum Thermostar Mass Spectrometer. A quartz sample tube packed with quartz wool acted as the reaction vessel. The tube containing a known quantity of sample (roughly 200 mg) was heated at a ramp rate of 10° C. min−1 to 800° C. and held for one hour under zero-grade air flow at 50 sccm. The system was rapidly cooled to room temperature under air flow, before switching to ultrahigh purity He (50 sccm) for 30 minutes to ensure removal of residual oxygen. The material was then heated to 1050° C. at 10° C. min−1 while the mass spectrometer analyzed the outlet gas. Upon completion, the system was cooled rapidly to room temperature.
For experiments involving the invented B-site doped perovskite oxygen carriers, TGA data was collected on a Mettler-Toledo TGA/DSC 3+ with a standard gas flow of 75 sccm. Approximately 50 mg of sample was placed in a platinum pan to start. Prior to air/N2 cycling experiments, a priming step was necessary to enable faster kinetic response. This priming step requires heating the sample to 800° C. under zero-grade air flow at a ramp rate of 10° C. min−1 followed by switching to ultrahigh-purity N2 and holding at 800° C. for 30 minutes prior to cooling. Priming was completed a second time to analyze oxidation thermodynamics. Air/N2 cycling experiments were performed by heating the sample in air using a variable ramp rate described in the literature to reach the desired cycling temperature. See T. Jia, E. J. Popczun, J. W. Lekse, Y. Duan, Applied Energy 2021, 281, 116040; E. J. Popczun, D. N. Tafen, S. Natesakhawat, C. M. Marin, T.-D. Nguyen-Phan, Y. Zhou, D. Alfonso, J. W. Lekse, Journal of Materials Chemistry A 2020, 8, 2602-2612; E. J. Popczun, T. Jia, S. Natesakhawat, C. M. Marin, T. D. Nguyen-Phan, Y. Duan, J. W. Lekse, ChemSusChem 2021, the entirety of all three hereby incorporated by reference herein. The gas flow was then changed between N2 and air at set intervals (400° C.—1 hour, 450/500° C.—30 minutes), while weight loss was recorded. Data analysis was performed using the STARe Evaluation Software provided by Mettler Toledo.
For experiments involving the invented B-site doped perovskite oxygen carriers, density functional theory (DFT) calculations were performed with the Vienna ab initio simulation package (VASP), using the projector-augmented wave (PAW) method described in P. E. Blöchl, Physical Review B 1994, 50, 17953-17979 which is hereby incorporated by reference in its entirety herein. Electron exchange and correlation was treated using the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA). All calculations used a plane-wave expansion with an energy cutoff of 450 eV and included spin polarization. The computational models of doping materials Sr1-xCaxFe1-yNiyO3 were generated using a 2√{square root over (2)}×2√{square root over (2)}×2 supercell (80 atoms) of the cubic perovskite SrFeO3. The optimized cubic lattice constant of SrFeO3 (SFO) is 3.841 Å, which agrees well with the experimental value of 3.857 Å as reported in P. Manimuthu, C. Venkateswaran, Journal of Physics D: Applied Physics 2011, 45, 015303, the entirety of which is incorporated by reference herein. A 3×3×5 Monkhorst-Pack k-point sampling was used for this 2√{square root over (2)}×2√{square root over (2)}×2 supercell. The 80-atom Sr16Fe16O48 cell allows one to reach the Ca A-site doping value of x=0.1875, 0.25, 0.3125 and Ni B-site doping value of y=0.0625. The doping configurations of Sr1-xCaxFe1-yNiyO3 (x=0.1875, 0.25, 0.3125, y=0, 0.0625) used in these calculations are shown in
Oxygen vacancy (VO) in Sr1-xCaxFe1-yNiyO3 was modeled by removing a neutral O atom from these 2√{square root over (2)}×2√{square root over (2)}×2 supercells, producing a nonstoichiometry Sr1-xCaxFe1-yNiyO3-δ material with δ=0.0625. Considering that the change of lattice constants is negligible at such low VO concentration, only the atomic positions are fully relaxed in calculating the total energy of the nonstoichiometry materials. Then, the VO formation energy Ef could be obtained from EQUATION 2 shown below.
In EQUATION 2, Edef is the total energy of the nonstoichiometry material with one VO, Eperf is the total energy for a perfect lattice, E(O2) is the total energy of an isolated O2 molecule, and Δh is the energy correction term, which is from the oxide formation energy disagreement between experiments and DFT calculations (1.36 eV/O2 for PBE method).
Laboratory-based X-ray diffraction (XRD) was used to determine the major crystal structure and any crystalline impurities of the invented B-site doped perovskite materials.
Synchrotron-based X-ray diffraction clearly showed the presence of crystalline NiO in the Sr0.75Ca0.25Fe1-yNiyO3 (y=0.12) oxygen carrier 10 as shown in
The thermodynamics and kinetics changes of oxygen desorption or adsorption associated with nickel-doping in the invented B-site doped perovskite oxygen carrier 10 were probed using O2 temperature programmed desorption (TPD) and thermogravimetric analysis (TGA). In
TABLE 1 provides approximate onset and maximum desorption temperatures during O2 temperature programmed desorption in Sr1-xCaxFe1-yNiyO3 oxygen carriers. Generally, the onset desorption temperature decreases as Ni content is increased. The maximum desorption temperature decreases with increasing Ca content.
Oxygen adsorption experiments in the TGA reveal similar behavior for the invented oxygen carriers 10 as shown in
TABLE 2 provides the approximate maximum adsorption temperatures collected by thermogravimetric analysis of Sr1-xCaxFe1-yNiyO3 oxygen carriers. Generally, the maximum adsorption temperature decreases as Ni content increases.
While defining the maximum oxygen storage capacity for these materials using O2-TPD and TGA adsorption experiments, the invented B-site doped perovskite oxygen carrier 10 was using pressure-swing induced O2 storage and release.
TGA traces for the x=0.25 series at 400° C. and 450° C. are found in
Investigation of the x=0.30 series at 400° C. and 450° C. is displayed in
The inclusion of Ni in place of some of the iron in Sr1-xCaxFeO3, leads to distinctly different thermodynamic or kinetic properties for the material. Oxygen temperature programmed desorption illustrates the change in the thermodynamics of oxygen release that are afforded by this change. These results can be seen in
As shown in
The kinetics aspect of this oxygen carrier can be seen in
In fact, this Sr0.75Ca0.25Fe0.94Ni0.06O3 material would be preferred to the Sr0.7Ca0.3FeO3 with similar oxygen release kinetics as well, due to its ability to maintain faster oxygen uptake kinetics. While this process is usually much faster than the reduction, a full redox cycle of the 2.1 wt. % O2 would require 6 minutes for the Ni-doped material, whereas Sr0.7Ca0.3FeO3 would require 7-8 minutes. This amounts to a 33% increase in O2 output for a realistic air separation unit.
To determine the reason for improved performance in most of the nickel-substituted perovskite oxygen carriers 10 discussed herein, density functional theory was employed on a selection of Sr1-xCaxFe1-yNiyO3 (x=0.1875, 0.25, 0.3125; y=0, 0.0625). The y=0.12 materials were excluded from DFT calculations due to substantial NiO exsolution and/or impurities at this high Ni substitution value as confirmed by XRD (
To begin, the Ca and Ni doping effect on the crystal and electronic structures was analyzed. As shown in TABLES 3-5, the lattice constants decrease with an increase in the amount of Ca and further decrease by Ca and Ni dual-substitution, due to the smaller ionic size of Ca and Ni than Sr and Fe. In addition, the single Ca substitution causes a small deviation of Fe—O bond length from 1.920 Å in SrFeO3, while dual-substitution with Ni induces a relatively larger deviation of Fe—O bond length in Fe—O—Fe chains and yields longer Ni—O and shorter O—Fe bond lengths in Ni—O—Fe chains. For example (TABLE 5), the largest difference (0.1 Å) between Ni—O and O—Fe bond lengths in Ni—O—Fe chains and a remarkable deviation of Fe—O bond length in Fe—O—Fe chains were reached at the highest Ca A-site (x=0.3125) and Ni B-site (y=0.0625) dual-substitution. Generally, Ni B-site substitution has a larger effect on the bond length than Ca A-site substitution, and Ca/Ni dual-substitution can promote the bond length deviation.
TABLE 3 provides the lattice constants a (Å), the distances of Fe—O (Ni—O) and O—Fe in Fe—O—Fe (Ni—O—Fe) chains to create VO, and the formation energies Ef (eV), related electrostatic Ebond (eV) and structural relaxation Erelax (eV) terms for Sr0.8125Ca0.1875Fe1-yNiyO3-δ (y=0, 0.0625).
TABLE 4 provides the lattice constants a (Å), the distances of Fe—O (Ni—O) and O—Fe in Fe—O—Fe (Ni—O—Fe) chains to create VO, and the formation energies Ef (eV), related electrostatic Ebond (eV) and structural relaxation Erelax (eV) terms for Sr0.75Ca0.25Fe1-yNiyO3-δ (y=0, 0.0625).
TABLE 5 provides The lattice constants a (Å), the distances of Fe—O (Ni—O) and O—Fe in Fe—O—Fe (Ni—O—Fe) chains to create VO, and the formation energies Ef (eV), related electrostatic Ebond (eV) and structural relaxation Erelax (eV) terms for Sr0.6875Ca0.3125Fe1-yNiyO3-δ (y=0, 0.0625).
The density of states (DOS) plots for Sr1-xCaxFe1-yNiyO3 (x=0.1875, 0.25, 0.3125, y=0.0625) are shown in
The effect on oxygen vacancy (VO) formation caused by Ca and Ni substitution was also investigated. As mentioned above, the O sites are not equivalent due to the lattice distortion induced by these substitutions. As shown in TABLES 1-5, a series of VO was introduced by removing the O atom from nonequivalent Fe—O—Fe or Ni—O—Fe chains. The vacancy formation energy was averaged, Ef, for all Ca/Ni substitution values and portrayed the avg. Ef versus Ca content (x) in
To explore the origin of this enhanced effect on Ef due to Ni, Ef was divided into two terms: Ef=Ebond+Erelax, where the bonding energy (Ebond) is the energy required to remove an O atom from the lattice, and the relaxation term (Erelax) is the energy gain from further relaxing the structure with an oxygen vacancy present. The corresponding avg. Ebond/Erelax versus Ca content (x) are shown in
The invention also provides a method for making mesoporous perovskite oxygen carriers and novel perovskite oxygen carriers created thereby.
In an embodiment, the mesoporous perovskite oxygen carrier 200 is a perovskite-type oxygen carrier (ABO3-δ) that has the general formula Sr1-xCaxFeO3, where 0.01<x<0.40. In alternative embodiments the invented mesoporous perovskite oxygen carrier 200 comprises a perovskite-type oxygen carrier with the general formula (Sr1-xCax)0.80-1.20Fe1-yMyO3, where 0.05<x<0.40, and where M is a metal selected from the group consisting of scandium, titanium, manganese, nickel, copper, cobalt, zinc, and combinations thereof. In still further alternative embodiments, the mesoporous oxygen carrier 200 comprises Ba1-xSrxFeO3, SrFeO3, BaFeO3, La1-xSrxFeO3, non-perovskite oxides (Ruddlesden-Popper, 314-oxides), and combinations thereof.
A salient feature of the invention is the high and superior surface area of the invented mesoporous perovskite oxygen carrier 200 when compared with prior art oxygen carriers. In an embodiment the surface area of the invented mesoporous perovskite oxygen carriers is preferably between approximately 0.4 m2/g of oxygen carrier and approximately 10 m2/g of oxygen carrier, typically between approximately 2.3 m2/g of oxygen carrier and approximately 9 m2/g of oxygen carrier.
The invention also provides a method to generate mesoporous perovskite oxygen carriers. A schematic of that method 300 shown is shown in
As described above and shown in
In an embodiment, the alpha-hydroxycarboxylic acid provided into aqueous solution with the metal ions in step 302 is any alpha-hydroxycarboxylic acid suitable to provide ligands to chelate the metal ions added to solution in step 302. Suitable and exemplary alpha-hydroxycarboxylic acids include citric acid, glycolic acid, lactic acid, mandelic acid, and combinations thereof.
In an embodiment, the polyhydroxy alcohol added in step 308 is any polyhydroxy alcohol suitable to promote polymerization of the metal-carboxylate chelates generated from the metal ions and alpha-hydroxycarboxylic acid combined in step 302. A suitable and exemplary polyhydroxy alcohol is ethylene glycol.
A salient feature of the invented method 300 is the calcining step 304. In the invented method, the polymerized metal-carboxylate chelates are calcined at a synthesis temperature. Said synthesis temperature is below 1000° C. In an embodiment, the synthesis temperature is between approximately 650° C. and approximately 850° C.
The invented mesoporous perovskite oxygen carrier 200 is suitable for use in temperature and or pressure swing reactions to selectively adsorb and release oxygen. EQUATION 3 above provides the reactions for such a process where the forward reaction of EQUATION 3 shows the reduction of the invented mesoporous perovskite oxygen carrier, i.e., the oxygen carrier releasing oxygen to form a reduced oxygen carrier. The reverse reaction of EQUATION 3 shows the oxidation of the reduced mesoporous perovskite oxygen carrier, i.e., the reduced oxygen carrier adsorbing oxygen to form the invented mesoporous perovskite oxygen carrier 200. The invented mesoporous perovskite oxygen carrier 200 is suitable for use in the method 100 shown in
A salient feature of the invention is the performance of the invented mesoporous perovskite oxygen carrier when used in a process such as that shown in
Also during the contacting step 104, when the invented mesoporous perovskite oxygen carrier is used, the invention provides maximum adsorption temperatures, the temperature where the reduced oxygen carrier adsorbs oxygen at the fastest rate, that are superior to the prior art. In an embodiment, the maximum adsorption temperature during the contacting step is between approximately 473° K. and approximately 673° K.
Still further, during the contacting step, when the invented mesoporous perovskite oxygen carrier is used, the invention provides improved oxidation rates compared to the prior art. In embodiment, the oxidation rate during the contacting step is between approximately 0.08 wt %/min and approximately 2.24 wt %/min.
A salient feature of the invention is the performance of the invented oxygen carrier when used in a process such as that shown in
Also during the heating step 106, when the invented mesoporous perovskite oxygen carrier is used in the method 100, the invention provides maximum desorption temperatures, the temperature where the oxygen carrier releases oxygen at the fastest rate, that are superior to the prior art. In an embodiment, the maximum desorption temperature during the contacting step is between approximately 473° K. and approximately 773° K.
Still further, during the heating step, when the invented mesoporous perovskite oxygen carrier is used in method 100, the invention provides improved reduction rates compared to the prior art. In an embodiment, the reduction rate during the contacting step is between approximately 0.03 wt %/min and approximately 1.55 wt %/min.
As described above and shown in
To synthesize test samples of the mesoporous Sr1-xCaxFeO3 materials, stoichiometric amounts of strontium nitrate [Sr(NO3)2, Fisher-Scientific, Cert. ACS Grade], calcium nitrate tetrahydrate [Ca(NO3)2·4H2O, Sigma-Aldrich, 99%] and iron (III) nitrate nonahydrate [Fe(NO3)3·9H2O, Sigma-Aldrich, 98%] were added to a large beaker. In addition, citric acid [C3H5O(COOH)3, Alfa-Aesar, anhydrous 99.5%] was added to the vessel at a 2.5:1 molar ratio of citric acid to total metal ions along with roughly 10 mL DI water. This mixture was heated to roughly 60° C. and stirred to promote dissolution. At this point, ethylene glycol [(CH2OH2)2, 99%] was added to the warmed solution at a 3.75:1 molar ratio of ethylene glycol to total metal ions. Following this addition, the solution was heated to 120° C. to dehydrate the material. During this heating step, visible NOx gas was released from the reaction vessel. The sample was heated further to drive off most of the water, leaving a yellow-orange rigid, porous solid. This beaker was placed directly into an oven to dwell at 120° C. overnight for drying. The resulting powder was removed from the vessel and ground into a rough powder. This powder was then placed in an alumina combustion boat within a quartz tube furnace. The powder was heated in air by ramping with 5° C. min−1 to a desired synthesis temperature (i.e., 700, 750, 800, 850, 900, 950, 1000° C.) and holding for 8 hours. Finally, the resulting black samples were cooled and stored in scintillation vials prior to characterization.
Following synthesis, the perovskite crystal structure was confirmed for all the materials using pXRD, shown in
The bulk materials were synthesized using the traditional solid-state method developed previously for these materials. Briefly, strontium carbonate [SrCO3, Aldrich, 99.9%], calcium carbonate [CaCO3, Alfa Aesar, 99.5%], and iron (III) oxide [Fe2O3, Alfa Aesar, 99.9%] were combined using manual pulverization and pressed into compact pellets which were thermally treated at 850° C. for 40 hours, followed by a second calcination at 1100° C. for 64 hours.
Powder X-ray diffraction (pXRD) was collected using a PANalytical X'Pert Pro XRD using Cu Kα source (λ=1.541 Å) in a Bragg-Brentano configuration. Scans were collected from 5-80° 2-theta.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, in-situ pXRD analyses were carried out using a PANalytical PW 3040 X-Pert Pro XRD system equipped with a 60 kv PW 3373/00 Cu LFF high power ceramic tube with a Cu anode and a PW 3011/20 detector. High temperature in-situ pXRD experiments were conducted with an Anton-Parr HTK 1200N equipped with a customized gas inlet System for reactive gas injection and gas switching. In situ reduction was conducted in UHP Argon (50 ml/min) to 1000° C. at a ramp rate of 10° C./min with a 20-minute hold at 700° C. to capture the phase composition at that temperature. Scan parameters were optimized so a single scan (10-110 2θ) would occur over an 18-minute period. A scan was collected at 1000° C. before ramping down to 700° C. where another scan was collected prior to the TPO experiment. The in situ oxidation was carried out in Air (50 ml/min) from 700-1000° C. at a rate of 10° C./min and a scan captured after the sample reached 1000° C. Phase identification was done using PANalytical X-Pert Pro Plus Diffraction analysis software coupled with PDF4-2022 database.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, scanning electron microscopy was collected using a FEI Quanta 600F SEM with a 20 kV beam and a working distance of 10 mm.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, Brunauer-Emmett-Teller (BET) surface area and total pore volume were determined by volumetric N2 adsorption isotherm at −196° C. in a Quantachrome Autosorb 1-C surface area analyzer. Prior to measurements, approximately 2 g of sample was degassed to remove surface moisture under vacuum at 110° C. for 1 hour. Multi-point BET analysis was conducted to determine surface area from the amount of N2 adsorbed at the relative pressure between 0.1 and 0.3. Total pore volume was calculated from the amount of N2 adsorbed at P/P0=0.99.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, O2-TPD experiments were carried out in a Micromeritics 2950HP analyzer equipped with a Pfeiffer Vacuum Thermostar MS. All the gas flow rates and ramp rate used were 50 sccm and 10° C. min−1, respectively. In these experiments, the pretreatment temperature was chosen at 650° C., which is below the lowest synthesis temperature to avoid structural changes during pretreatment. Initially, approximately 250 mg of sample was loaded in a U-shaped quartz cell packed with quartz wool and then pretreated in flowing air at 650° C. for 1 hour. Following cooling to room temperature in air, the sample was then heated to 1050° C. in ultra-high purity Ar while evolution of O2 (m/z=32) and CO2 (m/z=44) in the outlet stream from the quartz sample cell was monitored by the MS.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, TGA was performed on a Mettler Toledo TGA/DSC 3+ with a standard gas flow of 75 sccm. Approximately 30-40 mg of sample was placed in a platinum pan to start. A pretreatment was performed to generate rapid kinetics during cycling experiments. Pretreatment requires heating the sample under air flow at a ramp rate of 10° C. min−1 to the investigated temperature, not to exceed the synthesis temperature. The sample is then cooled to room temperature under N2 flow. This pretreatment step was completed twice to yield valuable information regarding the reoxidation thermodynamics. Following pretreatment, O2 pressure cycling experiments were performed by heating the sample pan at a rate of 20° C. min−1 under air flow to 250° C. Up to 350° C., the ramp rate was reduced to 10° C. min−1 to avoid an unnecessary overage. The gas flow was then cycled between ultra-high purity N2 (6 minutes) and zero-grade air (4 minutes), while heat flow and weight loss were recorded. This 10-min cycle was repeated five times for each studied temperature: 350, 375, 400, 450, and 500° C. Data analysis was performed using the STARe Evaluation Software provided by Mettler Toledo.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, to confirm surface area changes with synthesis temperature in these materials, N2 adsorption isotherm at −196° C. was conducted to determine Brunauer-Emmett-Teller (BET) surface area and total pore volume.
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, pore volume and textural differences for these materials were visualized using SEM. Using Sr0.75Ca0.25FeO3 as a second representative perovskite oxygen carrier, the increase in particle size as synthesis temperature rises can be seen in
For studies involving the invented Sr1-xCaxFeO3 mesoporous perovskite oxygen carriers and Sr1-xCaxFeO3 bulk materials, CO2-TPD was utilized to determine the quantity of carbon in each sample, shown in
Elemental composition of the perovskite materials within the Sr1-xCaxFeO3 plays a significant role in the oxygen storage capacity of these materials. Briefly, Ca2+ for Sr2+ substitution leads to lower desorption temperatures, higher adsorption temperatures, and lower overall oxygen storage capacity (OSC), due to the increased structural instability caused by this substitution. Validation of this can be found in
Oxygen temperature-programmed desorption was utilized to offer an insight into the role synthesis temperature plays on the thermodynamics of oxygen release for all three compositions. While calcium content plays a large role in the onset temperature, maximum desorption temperature, and total oxygen desorption in the bulk materials, synthesis temperature can greatly affect these properties as well. As shown in
The position of the major desorption feature in the O2-TPD also changes. Unlike the emerging surface oxygen peak, the bulk desorption feature shifts towards higher temperatures and decreases in oxygen released (peak area) as the surface area is decreased. The shift to higher temperatures is most pronounced in the Sr0.7Ca0.3FeO3 series and weakest in the Sr0.8Ca0.2FeO3 series, but both shifts are subdued in comparison to changes in the surface oxygen feature. It is difficult to establish a trend for the area under the individual peaks due to broadening and overlap. However, a decrease was observed in the maximum mass spectrometer (MS) signal when Ts is lowered, as expected from the increase in surface oxygen. Overall, the largest total oxygen desorption over the entire temperature range occurs in the highest surface area materials. Materials with the smallest surface areas tend to have the lowest total oxygen desorption, but some variance does exist amongst these materials.
Similar trends are also observed for oxygen adsorption. To examine the role of synthesis temperature on the oxygen adsorption, each material was first pretreated at 700° C. in N2 and then heated from 30-700° C. at a steady ramp rate of 10° C. min−1. These oxygen adsorption plots can be found in
While the prior experiments are helpful in determining the maximum oxygen storage capacity for these materials, the reduction and oxidation kinetics of these materials are important for air separation applications. To study this, short air/N2 cycling was performed at operating temperatures of 350, 375, 400, 450, and 500° C. allowing 6 minutes for reduction and 4 minutes for oxidation. Each of these experiments was preceded with a standard pretreatment in N2 at 700° C. Each experiment can be broken down into three distinct factors averaged over three full cycles; oxygen storage capacity for the full cycle, as well as the initial reduction and oxidation rates averaged across the first minute. A collection of this data can be found in the table shown in
Analysis began with the lowest operating temperature experiments (i.e., 350, 375, and 400° C.). Upon investigation of the data shown in
Unlike the lowest three temperatures, Sr0.7Ca0.3FeO3 and Sr0.75Ca0.25FeO3 are both viable at 450° C. While SCF25-1000 has the highest oxygen storage capacity (2.34 wt. %), there are seven total materials with capacities greater than 2.00 wt. %, including SCF30-SSR and the Sr0.75Ca0.25FeO3 with the six highest synthesis temperatures. As with the lower operating temperatures, the initial oxidation rate is within 90% of the oxygen storage capacity for the Sr0.75Ca0.25FeO3 series. This is not the case with the bulk Sr0.7Ca0.3FeO3 material, as only 80% of the oxygen is recovered after 1 minute. Inversely, this Sr0.7Ca0.3FeO3 material displays the fastest initial reduction rates, releasing nearly 1 wt. % O2 in the first minute, 66% higher than the maximum rate achieved using Sr0.75Ca0.25FeO3. Aside from SCF25-SSR (0.6 wt. %/min), the initial reduction rate for the Sr0.75Ca0.25FeO3 series stays near 0.5 wt. %/min. Combining these factors, the highest synthesis temperatures are most viable at this temperature, but calcium content plays the largest role.
Similar effects were observed when studying materials at 500° C. The oxygen storage capacity reaches a maximum of 2.29 wt. % in SCF20-950 and SCF20-1000. Aside from SCF20-700 (1.82 wt. %) and SCF20-SSR (2.17 wt. %), the storage capacity of the full Sr0.8Ca0.2FeO3 series is above 2.2 wt. % along with SCF25-1000. Oxidation at this temperature is more rapid than that at lower temperatures for all materials. Reduction favors the highest calcium content materials, with SCF30-SSR having a rate of 1.55 wt. %/min and SCF25-SSR at 1.11 wt. %/min, whereas rates for the Sr0.8Ca0.2FeO3 series are roughly 0.5 wt. %/min. Changes in synthesis temperature only play a small role in oxygen storage at 500° C., confirming calcium content is a more influential variable.
Experiments were also performed to determine the optimal pretreatment conditions for Sr1-xCaxFeO3 oxygen carriers, investigating a Tp range from 700-1000° C. To start, the oxidation profile of the best performing citrate-based materials of each composition when pretreated at 700° C. can be found in
Sr0.75Ca0.25FeO3 and Sr0.7Ca0.3FeO3 materials when oxidized past 850° C. showed some peculiar behavior. At this temperature, the mass of the materials increases even after nearly reaching full reduction in the case of Sr0.7Ca0.3FeO3. This temperature range aligns with the unexpected decrease in oxygen storage capacity for the SCF30 series at higher synthesis temperatures discussed above. In situ pXRD using a heating profile shown in
The table shown in
Due to these inconsistencies in the averages, identifying the specific best performing materials for each operating temperature allows for better analysis of the trends. Starting at an operating temperature of 350° C., the maximum oxygen storage capacities achieved by SCF30-800-P800, SCF30-850-P850, SCF30-850-P800, SCF30-750-750, and SCF30-850-P750 were 1.23, 1.16, 1.13, 1.11, and 1.10 wt. %, respectively. A similar selection of materials was found to have the fastest initial reduction rate at this temperature. SCF30-750-P750, SCF30-850-P700, SCF30-800-P800, SCF30-700-P700, and SCF30-850-P750 had reduction rates of 0.45, 0.44, 0.43, 0.42, and 0.42 wt. %/min, respectively. Oxidation rates for all the listed materials were rapid, with roughly 80-95% of maximum oxygen uptake occurring within the first minute. Therefore, the three materials with the most rapid kinetics and highest oxygen storage capacities are SCF30-800-P800, SCF30-850-P750, and SCF30-750-P750. Unsurprisingly, these materials have the maximum calcium content at 30% and the highest BET surface areas (2.32-5.32 m2/g).
Increasing the operating temperature to 375° C. has similar results to the experiments at 350° C. (data shown in TABLE 7). The maximum oxygen storage capacities were 1.70, 1.69, 1.51, 1.42, and 1.40 wt. % using SCF30-800-P800, SCF30-850-P850, SCF30-850-P800, SCF30-800-P750, and SCF30-750-P750. Four of these materials are the same as the top materials at 350° C., with SCF30-850-700 as the lone exception (6th highest OSC at 350° C.). The highest reduction rates of 0.56, 0.56, 0.55, 0.54, and 0.53 wt. %/min were reached by SCF30-850-P700, SCF30-800-P800, SCF30-850-P750, SCF30-850-P800, and SCF30-850-P850. As previously observed at 350° C., agreement with three of the top storage capacities and reduction rates: SCF30-800-P800, SCF30-850-P750, and SCF30-850-P850 was observed.
At 400° C., w the same collection of materials were observed attaining the highest storage capacities and reduction kinetics. To visualize the individual roles of composition, synthesis temperature, and pretreatment temperature, storage capacity vs. reduction rate plots are provided in
When the operating temperature reaches 450° C., unlike the previous three temperatures, the materials with the highest oxygen storage capacities do not have the fastest reduction rates (
A similar outcome is found at To=500° C. as well, but with a greater disparity in reduction rates between materials. The SCF20-950 series has the five highest oxygen storage capacities tested, aligning with a sequential decrease in pretreatment temperatures from 950° C. to 750° C. (
The increased surface area of oxygen carriers synthesized using the invented method determined visually and confirmed by BET measurements, leads to distinctly different thermodynamic and kinetic properties for the material. Oxygen temperature programmed desorption illustrates the change in the thermodynamics of oxygen release that are afforded by this change. These results can be seen in
As shown in
Kinetics of oxygen carriers made using the invented method can be seen in
In the embodiment, the invention provides a perovskite oxygen carrier comprising the formula SrFeO3, wherein the oxygen carrier comprises an A-site and a B-Site, and wherein the B-site is doped with Ni.
In an embodiment, the invention provides a perovskite oxygen carrier comprising the formula Sr1-xCaxFe1-yNiyO3, where 0.05<x<0.30 and 0.001<y<0.125.
In an embodiment, the invention provides a method for carrying oxygen using a perovskite oxygen carrier, the method comprising: providing a reduced oxygen carrier to a reaction environment; contacting the reduced oxygen carrier with an oxygen containing gaseous stream for a predetermined time at a first temperature and a first oxygen partial pressure, wherein the reduced oxygen carrier adsorbs oxygen from the gaseous stream during this step, giving an oxygen carrier; and heating the oxygen carrier to a second temperature at a second oxygen partial pressure, causing oxygen adsorbed onto the oxygen carrier in the contacting step to be released from the oxygen carrier, reforming the reduced oxygen carrier, wherein the oxygen carrier comprises the formula Sr1-xCaxFe1-yNiyO3, where 0.05<x<0.30 and 0.001<y<0.125. In an embodiment, during the contacting step, the reduced oxygen carrier adsorbs between approximately 1.50 wt % and approximately 3 wt % of oxygen. In an embodiment, during the contacting step, the reduced oxygen carrier adsorbs at least 2.00 wt % oxygen. In an embodiment, the reduced oxygen carrier has a maximum adsorption temperature between approximately 573° K. and approximately 673° K. In an embodiment, the reduced oxygen carrier is oxidized at a rate between approximately 2.00 wt %/min and approximately 10.00 wt %/min during the contacting step. In an embodiment, the oxygen carrier is reduced at a rate between approximately 0.033 wt %/min and approximately 1.5 wt %/min during the heating step. In an embodiment, the oxygen carrier has a desorption onset temperature between approximately 473° K. and approximately 523° K. In an embodiment, the oxygen carrier has a maximum desorption temperature between approximately 673° K. and approximately 773° K.
In an embodiment, the invention provides a perovskite oxygen carrier comprising the formula SrCaFeO3, wherein the oxygen carrier is mesoporous. In an embodiment, the oxygen carrier comprises the formula Sr1-xCaxFeO3, where 0.01<x<0.40. In an embodiment, the oxygen carrier comprises a network of nanoparticles sintered together. In an embodiment, the perovskite oxygen carrier has a surface area between approximately 2.3 m2/g and approximately 9 m2/g.
In an embodiment, the invention provides a method for carrying oxygen using a perovskite oxygen carrier, the method comprising: providing a reduced oxygen carrier to a reaction environment; contacting the reduced oxygen carrier with an oxygen containing gaseous stream for a predetermined time at a first temperature and a first oxygen partial pressure, wherein the reduced oxygen carrier adsorbs oxygen from the gaseous stream during this step, giving an oxygen carrier; and heating the oxygen carrier to a second temperature at a second oxygen partial pressure, causing oxygen adsorbed onto the oxygen carrier in the contacting step to be released from the oxygen carrier, reforming the reduced oxygen carrier, wherein the oxygen carrier comprises the formula Sr1-xCaxFeO3, where 0.01<x<0.40, and wherein said oxygen carrier is mesoporous. In an embodiment, the oxygen carrier has a surface area between approximately 2.3 m2/g and approximately 9 m2/g. In an embodiment, the reduced oxygen carrier adsorbs between approximately 2.00 wt % and approximately 3.00 wt % of oxygen. In an embodiment, the reduced oxygen carrier adsorbs at least 2.00 wt % oxygen. In an embodiment the reduced oxygen carrier has a maximum adsorption temperature between approximately 473° K. and approximately 673° K. In an embodiment, the reduced oxygen carrier is oxidized at a rate between approximately 0.08 wt %/min and approximately 2.24 wt %/min during the contacting step. In an embodiment, the oxygen carrier is reduced at a rate between approximately 0.03 wt %/min and approximately 1.55 wt %/min during the heating step. In an embodiment, the oxygen carrier has a desorption onset temperature between approximately 313° K. and approximately 573° K. In an embodiment, the oxygen carrier has a maximum desorption temperature between approximately 473° K. and approximately 773° K.
In an embodiment, the invention provides a method for making mesoporous perovskite oxygen carriers comprising: producing polymerized metal-carboxylate chelates; calcining the polymerized metal-carboxylate chelates at a synthesis temperature to produce the mesoporous perovskite oxygen carriers, wherein the synthesis temperature is below 1000° C. In an embodiment, the mesoporous oxygen carriers comprise the general formula Sr1-xCaxFeO3, where 0.01<x<0.40. In an embodiment, the synthesis temperature is between approximately 650° C. and approximately 850° C. In an embodiment, the mesoporous oxygen carriers comprise a surface area between approximately 2.3 m2/g and approximately 9 m2/g.
A person having ordinary skill in the art will readily understand that temperatures given in ° C. and ° K. are readily convertible from one to the other according to standard convention where a measurement given in ° C. can be converted to ° K. by adding 273.15, and a measurement given in ° K. can be converted to ° C. by subtracting 273.15.
It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements.
The recitation of numerical ranges by endpoints includes all numbers and subranges within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, and 2 to 4).
Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. § 112, ¶ 6. In particular, the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. § 112, ¶ 6.
This Utility Patent Application claims priority benefit as a U.S. Non-Provisional of U.S. Provisional Patent Application Ser. No. 63/333,889, filed on Apr. 22, 2022, currently pending, the entirety of which is incorporated by reference herein.
This invention was made with United States Government support under the Department of Energy Number DE-FE0004000. The United States Government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 63333889 | Apr 2022 | US |
