Session: 04-01-01: Advanced Materials for Energy

Paper Number: 150613

150613 - Advanced Co2 Sorbent Materials for Solar Thermaldriven Direct Air Captre: Overcoming Limitations in Direct Air Capture Technologies 

Climate change presents significant challenges, necessitating both reducing greenhouse gas emissions and actively removing CO₂ from the atmosphere. Direct Air Capture (DAC) technologies offer a promising solution for CO₂ removal, but current methods are hindered by high costs, low capture capacities, and significant energy requirements. Additionally, DAC technologies often operate at harsh conditions for the sorbent material, typically between 120-800°C, resulting in a short sorbent life cycle. Conventional DAC systems use highly nonequilibrium process parameters such as hot steam around 100°C to accelerate adsorbent regeneration rates and maximize carbon capture throughput. However, this also accelerates degradation, limiting adsorbent lifetime and significantly increasing levelized costs. Current technologies operate at $500-800 per ton of CO₂ captured, with the biggest cost driver being the sorbent material's short life cycle.

To address these challenges, we are developing a novel Metal-Organic Framework (MOF)-based sorbent material for use in solar thermal-driven DAC systems. The amine-appended MOF was selected as an adsorbent capable of capturing CO₂ at high capacity from air and, due to its unique cooperative adsorption characteristic, releasing CO₂ with only a small temperature increase. This MOF-based sorbent material is specifically engineered to operate within a temperature window of 70-100°C, which aligns with the solar thermal heat generated during the day. This temperature range significantly reduces energy consumption and avoids the high temperatures that typically accelerate sorbent degradation in conventional DAC systems.

The methodology involved comprehensive testing of the MOF-based sorbent materials under real outdoor conditions and simulating these conditions in a controlled laboratory setting. We employed Thermogravimetric Analysis (TGA) to measure the isotherm of the materials and to run fast adsorption and desorption cycles at different temperatures during the regeneration phase. With the TGA, we used different gas compositions for the adsorption phase to evaluate the material's performance under varied conditions. Other characterization techniques such as Breakthrough Analysis and accelerated aging tests were employed to assess the stability, structural integrity, and performance of the materials.

Our results indicate that the enhanced sorbent regeneration method, fully solar-powered and operating under mild conditions, effectively eliminates external energy infrastructure requirements and maintains sorbent stability. Detailed analysis revealed three primary factors contributing to sorbent decomposition: humidity, high temperature, and oxygen exposure. Under oxidative and humid conditions, the adsorbents maintained >90% of original capacity after 8000 and 10000 cycles, respectively. The adsorbent maintains >90% of the original capacity after 10000 cycles under dry conditions, implying higher stability in a dry environment. Despite a small reduction in material performance observed during a 30-day continuous outdoor experiment, we identified and developed solutions to mitigate these effects: preventing the sorbent's exposure to high temperatures and separating the evaporation of water and CO₂ by applying a vacuum before the sorbent heats up under sunlight.

In conclusion, the advanced MOF-based sorbent material developed for solar thermal-driven DAC demonstrates significant potential for practical application. This concept offers a cost-effective and scalable solution for CO₂ removal, with the added benefit of being entirely self-sufficient in terms of energy. The findings from this study provide a robust foundation for future research and development in DAC technologies. The sorbent material in this research promises to last over 25 years due to operation at lower temperatures, potentially bringing down the net CO₂ capture cost to as low as $90 per ton.

Future work will involve further long-term outdoor experiments to validate our hypotheses and continue degradation studies to isolate and mitigate the effects of water, high temperature, and oxygen. Additionally, we plan to explore integrating this system into larger-scale operations, potentially contributing to global efforts to combat climate change. Understanding sorbent material degradation and solving this problem with new technologies is crucial for the advancement and longevity of sorbent materials. This research will deepen our understanding of sorbent material degradation of MOF-based materials in a DAC system and advance knowledge in carbon capture and thermal management in porous materials.

Presenting Author: Hannes Albers Boston University

Presenting Author Biography: I completed my Master's degree at ETH Zurich in Mechanical Engineering with a specialization in Energy and a minor in Data Science. In parallel to my Master's, I worked as a Data Scientist in the Industry. I conducted my master's thesis through a collaboration between Boston University and the Electrochemical Energy Systems laboratory at ETH Zurich, working on the system modeling and optimization of solar-thermal carbon capture processes. After my Master's, I joined Lawrence Berkeley Lab as a research engineer 2023, and transitioned in a PhD program in Fall 2024 focusing on my research in material studies and application of MOF materials.

Authors:

Hannes Albers Boston University
Sean Lubner Boston University