Gradient solid-state membrane for selective carbon capture
The gradient membrane design with LZO and LZO-Cu sections addresses the inefficiencies of traditional LZO membranes by optimizing kinetic rates for CO2 capture, ensuring consistent performance across varying CO2 concentrations.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- VALERO SERVICES INC
- Filing Date
- 2025-11-25
- Publication Date
- 2026-07-23
Smart Images
Figure US2025057079_23072026_PF_FP_ABST
Abstract
Description
Attorney Docket No.: 122142-0045 PCT APPLICATION (SwRI 4272)GRADIENT SOLID-STATE MEMBRANE FOR SELECTIVE CARBON CAPTURECROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 745,215, filed January 14, 2025, the content of which is incorporated herein by reference in its entirety.FIELD
[0002] The present disclosure relates generally to gas separation membranes, and more particularly to compositions and physical processes for synthesizing high-selectivity solid-state membranes based on lithium zirconate with robust physical properties for the separation of carbon dioxide from gas mixtures in high-temperature effluent streams.BACKGROUND
[0003] Carbon dioxide (CO2) capture and separation from industrial gas streams represents a critical challenge in addressing climate change and reducing greenhouse gas emissions. Lithium zirconate (TUZrOs), commonly referred to as LZO, has emerged as a promising ceramic material for high-temperature CO2 separation applications. LZO demonstrates significant potential as a solid-state membrane for CO2 separation through capture and regeneration processes, primarily due to its high selectivity for CO2 (“selective carbon capture”).
[0004] The selectivity of LZO arises from a chemisorption equilibrium reaction between CO2 and LZO, which produces lithium carbonate (Li2COs) and zirconia (ZrO2) through a complex mechanism whereby CO2 is incorporated into the crystal lattice of LZO.
[0005] Despite its promising characteristics, practical implementation of LZO-only membranes faces several challenges. The membrane operates as a chemical concentration-driven system, exhibiting higher absorption rates in the presence of higher CO2 concentrations. As the exhaust stream traverses the length of the membrane, the CO2 concentration gradually decreases, leading to a corresponding reduction in the removal rate. This diminishing performance poses a significant limitation to the efficiency of traditional LZO membranes.
[0006] Therefore, there exists a need for improved compositions and methods for synthesizing solid-state membranes for selective carbon capture.BRIEF SUMMARY
[0007] The present disclosure addresses this need by introducing a gradient approach to membrane design. The disclosure provides a solid-state membrane comprising at least two sections: a first section comprising lithium zirconate (LZO) and a second section comprising LZO modified with an additional metallic element (LZO-M). These sections can be arranged either longitudinally or transversely to the gas flow and may be discrete or feature a gradual transition between compositions.
[0008] The modified LZO section exhibits enhanced kinetic rates for CO2 absorption and / or desorption compared to pure LZO, particularly within specific temperature ranges. For example, when copper is used as the modifying element, the resulting LZO-Cu composition shows superior absorption rates at temperatures below 650°C, while pure LZO demonstrates better desorption characteristics above this temperature.
[0009] This gradient approach enables optimization of CO2 capture performance across the entire membrane structure, addressing the challenge of diminishing performance along the gas flow path. The disclosure includes various embodiments featuring different arrangements and configurations of the LZO and modified-LZO sections, as well as methods for their manufacture.
[0010] Accordingly, in one aspect, the disclosure provides a solid-state membrane for capturing CO2 from a flow of gas mixture, the membrane comprising: a first section comprising LZO; and a second section comprising LZO and a metallic element other than lithium, wherein the second section exhibits modified kinetic rates for CO2 absorption and / or desorption.
[0011] In some embodiments, the first section and the second section are arranged longitudinally to the flow of gas mixture.
[0012] In some embodiments, the first section and the second section are arranged transversely to the flow of gas mixture.
[0013] In some embodiments, the first section is configured to be exposed to a higher concentration of CO2 than the second section.
[0014] In some embodiments, the first section and the second section are discrete sections.
[0015] In some embodiments, the first section transitions gradually to the second section.
[0016] In some embodiments, the second section exhibits optimized CO2 absorption kinetic rate (Ka) and CO2 desorption kinetic rate (Kd) at a given temperature.
[0017] In some embodiments, the CO2 absorption kinetic rate (Ka) is less than the CO2 desorption kinetic rate (Kd) for the second section when the temperature of the flow of gas mixture is in between about 600 °C and about 700 °C.
[0018] In some embodiments, the metallic element in the second section is copper (Cu).
[0019] In some embodiments, the molar ratio of copper to lithium in the second section is in the range between about 0.04 to about 0.16.
[0020] In some embodiments, the membrane is in a form or shape of a tube, a flat sheet, or a monolith.
[0021] In another aspect, the disclosure provides a method for producing a solid-state membrane for capturing CO2 from a flow of gas mixture, the method comprising: providing a first section comprising LZO; and providing a second section comprising LZO and a metallic element other than lithium, wherein the first section is arranged to be exposed to a higher concentration of CO2 than the second section.
[0022] In some embodiments of the method, the first section and the second section are arranged longitudinally or transversely to the flow of gas mixture.
[0023] In some embodiments of the method, the first section and the second section are discrete sections, or the first section transitions gradually to the second section.
[0024] In some embodiments of the method, the CO2 absorption kinetic rate (Ka) and CO2 desorption kinetic rate (Kd) are optimized for the first section and the second section at a given temperature.
[0025] In some embodiments of the method, the CO2 absorption kinetic rate (Ka) is less than the CO2 desorption kinetic rate (Kd) for the second section when the temperature of the flow of gas mixture is in between about 600 °C and about 700 °C.
[0026] In some embodiments of the method, the metallic element in the second section is copper (Cu).
[0027] In some embodiments of the method, the molar ratio of copper to lithium in the second section is in the range between about 0.04 to about 0.16.
[0028] In some embodiments of the method, the membrane is in a form or shape of a tube, a flat sheet, or a monolith.
[0029] In some embodiments, the method further comprises a step of synthesizing the membrane using a solution-gel (sol-gel) process.
[0030] In some embodiments, the method further comprises a step of exposing the produced solid-state zirconate membrane to a high-temperature flow of gas mixture comprising CO2 to capture CO2.
[0031] Further provided is a solid-state zirconate membrane produced according to the method of any of the preceding embodiments.
[0032] Unless defined otherwise, the term “about,” particularly in reference to a given quantity, is meant to encompass deviations of plus or minus ten percent.BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 illustrates an exemplary embodiment of the membrane showing discrete zones of LZO and LZO-M (LZO modified with an additional metallic element) arranged longitudinally to the exhaust flow.
[0034] FIG. 2 depicts an alternative configuration featuring a gradual transition between LZO and LZO-M zones.
[0035] FIG. 3 shows yet another exemplary embodiment of the membrane with LZO and LZO-M zones arranged transversely to the exhaust flow.
[0036] FIG. 4 presents a graph showing the absorption rate constants for various LZO materials with and without copper modification across different temperatures.
[0037] FIG. 5 displays a graph of the desorption rate constants for the same materials across the temperature range.DETAILED DESCRIPTION
[0038] The following description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown but are to be accorded the scope consistent with the claims.
[0039] The present disclosure provides compositions and methods for improving the performance of solid-state membranes for CO2 capture through the strategic implementation of gradient chemistry. The disclosure describes multiple embodiments offering distinct advantages for specific applications.
[0040] In accordance with one embodiment, the membrane incorporates zones of varying chemical composition arranged parallel to the direction of exhaust flow. The membrane comprises a first section of pure lithium zirconate (I^ZrCh, LZO) positioned at the inlet region where CO2 concentrations in the exhaust stream are highest. A second section, comprising LZO modified with a metallic element (LZO-M), is positioned downstream where CO2 concentrations are lower but require enhanced kinetics to maintain efficient capture rates. The arrangement of the first and second sections can be implemented as discrete zones with clear boundaries between the different compositions, as shown in FIG.1
[0041] Alternatively, the composition may transition gradually from pure LZO to LZO-M, creating a continuous gradient of properties along the flow direction, as shown in FIG. 2.This gradual transition can be achieved through controlled variation in the concentration of the modifying metallic element.
[0042] The selection of the modifying metallic element significantly influences the membrane's performance characteristics. Copper has been identified as a particularly effective modifier, demonstrating notable improvements in absorption kinetics at temperatures below 650°C. The molar ratio of copper to zirconium in the modified sectionscan range from approximately 0.04 to 0.16, with different ratios providing optimal performance under specific operating conditions.
[0043] In accordance with another embodiment, the membrane features a layered arrangement of LZO and LZO-M perpendicular to the gas flow direction, as shown in FIG. 3.This transverse gradient design facilitates efficient CO2 transport through the membrane thickness by matching the local composition to the transport requirements. The modified LZO section in this configuration exhibits desorption kinetics (Kd) greater than or equal to the absorption kinetics (Ka) at the operating temperature, ensuring consistent CO2 removal performance.
[0044] The temperature dependence of the membrane's performance represents a critical aspect of the present disclosure. The chemical reaction governing CO2 capture proceeds according to the following equilibrium:Li2ZrO3(s) + CO2(g) Li2CO3(s) + ZrO2(s)
[0045] This reaction demonstrates optimal kinetics within a temperature range of approximately 450°C to 700°C. Within this range, the relative performance of pure LZO and modified LZO varies significantly. Below 650°C, copper-modified LZO exhibits enhanced absorption and desorption rates compared to pure LZO. Above 650°C, pure LZO demonstrates superior desorption characteristics, particularly advantageous for regeneration processes.
[0046] The physical implementation of the membrane can take various forms depending on the specific application requirements. A tubular configuration provides high surface area per unit volume and can readily accommodate both longitudinal and transverse gradient arrangements. Flat sheet configurations offer simplified manufacturing and easy integration into existing systems. Monolithic structures provide mechanical robustness and can be particularly suitable for high-pressure applications.
[0047] The thickness of each section within the membrane can be optimized based on operating conditions and performance requirements. In embodiments featuring discrete zones, the relative lengths or thicknesses of the pure LZO and modified LZO sections can be adjusted to balance CO2 capture efficiency with regeneration capability. For gradual transition designs, the rate of composition change can be tailored to match the expected CO2 concentration profile along the flow path.
[0048] Manufacturing methods for the membrane may include a “sol-gel” processing, which refers to a chemical synthesis technique where a liquid precursor solution (sol) is transformed into a gel-like substance, which is then processed to form lithium zirconate powder. Due to its ability to store lithium ions, this method allows for precise control over particle size and morphology of the final product, making it advantageous for creating nanosized lithium zirconate particles. Thus, the sol-gel process enables intimate mixing of components at the molecular level, ensuring uniform distribution of the modifying element within the modified sections.EXAMPLES
[0049] The following examples are offered to illustrate provided embodiments and are not intended to limit the scope of the present disclosure.Example 1: Synthesis of Gradient Membranes
[0050] A series of gradient membranes were synthesized using a modified sol-gel process. For the pure LZO sections, stoichiometric amounts of lithium nitrate and zirconium oxychloride were dissolved in deionized water. A separate solution for the modified sections was prepared by adding copper nitrate to achieve Cu / Zr molar ratios of 0.04, 0.08, and 0.16. Citric acid was added as a complexing agent with a molar ratio of 2: 1 relative to the total metal content.
[0051] The solutions were heated to 80°C with constant stirring until gel formation occurred. The gels were dried at 120°C for 12 hours and then calcined at 900°C for 4 hours in air. For discrete zone membranes, separate sections were fabricated and joined using a ceramic paste of similar composition. For gradual transition membranes, the composition was varied continuously during the gel formation process using a controlled addition system. Example 2: Characterization of CO2 Capture Performance
[0052] The synthesized membranes were characterized using a custom-designed thermal gravimetric analysis system. Samples were tested under isothermal conditions at temperatures of 600°C, 625°C, 650°C, 675°C, and 700°C. The testing protocol consisted of exposure to pure CO2 for 2 hours followed by nitrogen for 2 hours to measure absorption and desorption kinetics.
[0053] FIG. 4 illustrates an overlap plot of the absorption rate constants for LZO materials with and without copper (Cu) over a series of temperatures. Segment A) indicatesthe temperature region, below -660 °C, where the rate constant for LZO-Cu was greater than that of LZO without copper. Segment B) indicates the temperature region, above -660 °C, where the rate constants exhibited mixed results, however, specific to LZO-Cu 0.16 the rate constants for absorption were greater for LZO without copper.
[0054] FIG. 5 illustrates an overlap plot of the desorption rate constants for LZO materials with and without copper (Cu) over a series of temperatures. Segment A) indicates the temperature region, below -660 °C, where the rate constants exhibited mixed results, however, specific to LZO-Cu 0.16 the rate constants for absorption were greater then LZO without copper. Segment B) indicates the temperature region, above 660 °C, where the rate constant for LZO without copper was greater than all the LZO-Cu rate constants for desorption.
[0055] As shown in the figures, the measured rate constants for absorption and desorption of CO2 varied for each of the formulations. At lower temperatures (<650 °C), LZO-Cu formulations had greater rate constants for absorption then the LZO without copper, whereas the LZO without copper had a greater rate of desorption then the LZO-Cu samples at temperatures greater than 650 °C. In specific, the following can be derived when comparing the material LZO-Cu 0.16 to LZO without copper:< < < < > >> >
[0056] The examples illustrate the feasibility of synthesizing both discrete and gradual transition membranes using sol-gel processing, as well as confirm the temperature-dependent performance advantages of copper-modified LZO compositions. Taken together, these examples establish successful implementation of using the disclosed compositions and methods for producing gradient solid-state membranes with enhanced CO2 capture capabilities.
Claims
CLAIMSWhat is claimed is:
1. A solid-state membrane for capturing carbon dioxide (CO2) from a flow of gas mixture, the membrane comprising:a first section comprising lithium zirconate (LZO); anda second section comprising LZO and a metallic element other than lithium, wherein the second section exhibits modified kinetic rates for CO2 absorption and / or desorption.
2. The membrane of claim 1, wherein the first section and the second section are arranged longitudinally to the flow of gas mixture.
3. The membrane of claim 1, wherein the first section and the second section are arranged transversely to the flow of gas mixture.
4. The membrane of claim 1, wherein the first section is configured to be exposed to a higher concentration of CO2 than the second section.
5. The membrane of claim 1, wherein the first section and the second section are discrete sections.
6. The membrane of claim 1, wherein the first section transitions gradually to the second section.
7. The membrane of claim 1, wherein the second section exhibits optimized CO2 absorption kinetic rate (Ka) and CO2 desorption kinetic rate (Kd) at a given temperature.
8. The membrane of claim 1, wherein the CO2 absorption kinetic rate (Ka) is less than the CO2 desorption kinetic rate (Kd) for the second section when the temperature of the flow of gas mixture is in between about 600 °C and about 700 °C.
9. The membrane of claim 1, wherein the metallic element in the second section is copper (Cu).
10. The membrane of claim 9, wherein the molar ratio of copper to lithium in the second section is in the range between about 0.04 to about 0.16.
11. The membrane of claim 1, wherein the membrane is in a form or shape of a tube, a flat sheet, or a monolith.
12. A method for producing a solid-state membrane for capturing carbon dioxide (CO2) from a flow of gas mixture, the method comprising:providing a first section comprising lithium zirconate (LZO); and providing a second section comprising LZO and a metallic element other than lithium,wherein the first section is arranged to be exposed to a higher concentration of CO2 than the second section.
13. The method of claim 12, wherein the first section and the second section are arranged longitudinally or transversely to the flow of gas mixture.
14. The method of claim 12, wherein the first section and the second section are discrete sections, or the first section transitions gradually to the second section.
15. The method of claim 12, wherein the CO2 absorption kinetic rate (Ka) and CO2 desorption kinetic rate (Kd) are optimized for the first section and the second section at a given temperature.
16. The method of claim 12, wherein the CO2 absorption kinetic rate (Ka) is less than the CO2 desorption kinetic rate (Kd) for the second section when the temperature of the flow of gas mixture is in between about 600 °C and about 700 °C.
17. The method of claim 12, wherein the metallic element in the second section is copper (Cu).
18. The method of claim 17, wherein the molar ratio of copper to lithium in the second section is in the range between about 0.04 to about 0.16.
19. The method of claim 12, wherein the membrane is in a form or shape of a tube, a flat sheet, or a monolith.
20. The method of claim 12, further comprising synthesizing the membrane using a solgel process.
21. The method of claim 12, further comprising exposing the produced solid-state zirconate membrane to a high-temperature flow of gas mixture comprising CO2 to capture CO2.
22. A solid-state zirconate membrane produced according to the method of claim 12.