The response to climate change must include decisive and collaborative solutions that minimize global CO₂ emissions and enable a shift to low-carbon energy (renewable electricity) and CO₂-derived chemicals and fuels. A major challenge of minimizing fossil fuel use is producing critical chemicals and fuels for heavy industry and transportation in novel ways. These traditionally fossil-derived products can be derived from CO₂ that is captured from point sources or the atmosphere. Reactive CO₂ capture is an emerging area of research that focuses on developing materials and processes for CO₂ capture and in situ conversion to valuable chemicals or fuels. By combining these two steps, costly and energy-intensive steps of conventional integrated capture and conversion schemes are eliminated, including sorbent regeneration, CO₂ purification, pressurization, and transportation. These operations typically drive up the cost of capture and conversion processes, making them less economically attractive.
The dual function material (DFM) is an Al₂O₃-supported, nano-dispersed catalyst and sorbent combination that demonstrates both capture and catalytic conversion properties, making reactive capture possible. Feasibility of the 1% Ru, 10% “Na₂O”/Al₂O₃ DFM for CO₂ direct air capture (DAC) and in situ catalytic methanation (DACM) has been demonstrated in previous work. Recent work has prioritized advanced laboratory testing and laboratory aging of this DFM under a variety of simulated ambient capture climates to assess the advantages and limitations of the material. A monolith was used as a structured support for the DFM to minimize reactor pressure drop, a particularly relevant challenge for DAC applications where large volumes of air must be processed to separate the small volume of CO₂ (~ 400 ppm). Findings from DFM monolith studies (1% Ru, 10% “Na₂O”/Al₂O₃//monolith) were shared with an engineering partner to support scale up efforts.
Laboratory-simulated DACM cycles consisted of DAC performed at various real-world simulated ambient conditions followed by catalytic methanation, where the DFM was heated to 300°C in 15% H₂/N₂. Simulated DAC included O2 and humidity, and a surprising finding showed significant enhancement of CO₂ adsorption due to humidity in the capture feed. The maximum CO₂ capture capacity of the DFM monolith was measured to be 4.4 wt% (based on the weight of DFM material) at 25°C with 2 mol% H₂O in the DAC feed. Aging studies revealed consistent CO₂ capture and CH₄ production after over 450 hours of cyclic DACM testing that included simulated ambient conditions. No signs of deactivation of either the “Na₂O” sorbent or Ru catalyst were observed. The light-off temperature (indicative of kinetic control) observed for catalytic methanation was constant between fresh and aged cycles. These findings verified the qualifications of the 1% Ru, 10% “Na₂O”/Al₂O₃//monolith for the DACM application and supported further advanced bench and pilot plant testing by our engineering collaborator.
Additional parametric studies were conducted to evaluate the effects of varying humidity during DAC and revealed that a higher H₂O concentration in the DAC feed correlates with greater CO₂ captured and converted with no evidence of competitive adsorption between CO₂ and H₂O. Additionally, it was found that temperature changes within ambient range (0 – 40°C) played little role in varying CO₂ captured under dry conditions, whereas moisture was found to be a major driver of capture capacity. Furthermore, stable performance at a reference condition was always achieved after excursions to varying ambient conditions.
DACM tests revealed 30 – 40% of captured CO₂ desorbs during the temperature swing step, which was attributed mainly to the slow heating rate and low H₂ content (15%) required for safe laboratory operation. Unreacted CO₂ was eliminated by shortening the DAC step and engaging partial capture capacity of the DFM. This mode of cycling is more representative of that which would be carried out at scale, as shorter adsorption durations capitalize on the fastest adsorption kinetics exhibited by a capture material. Consistent with reported literature, findings suggest that CO₂ is preferentially adsorbed to stronger capture sites at the onset of DAC that are better able to retain CO₂ during heat up. Though the DFM is not fully utilized, these partial capacity cycles demonstrated higher conversions to CH₄ and a more efficient use of the material that will require less downstream purification at scale.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/s677-ed38 |
| Date | January 2024 |
| Creators | Abdallah, Monica |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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