Researchers at Shanghai Jiao Tong University and the University of Toronto have developed a novel solid–liquid phase change absorbent (PCA) system that offers highly efficient CO₂ capture across a wide concentration range and low-energy consumption regeneration. The study, published in Engineering, highlights the potential of this new PCA system for both direct air capture (DAC) and industrial CO₂ emissions.

The PCA system uses isophorone diamine (IPDA) as the sole CO₂ capture carrier and ketone-based organic molecules as the phase change medium. This innovative approach allows for efficient CO₂ capture from concentrations ranging from 400 ppm in ambient air to 150 000 ppm in coal-fired industrial emissions. The study reveals that the IPDA-based PCA system achieves a CO₂ capture efficiency of over 95% for more than 13 hours at an initial concentration of 400 ppm, with a molar ratio of IPDA to CO₂ of 1.11 mol/mol. This efficiency underscores its potential for DAC applications.

One of the key findings of the study is the low-energy consumption required for regeneration. The IPDA-based PCA system begins CO₂ desorption at temperatures as low as 303 K and fully releases CO₂ under N₂ flow at 333 K. This low-temperature thermal regeneration process is made possible by the modulation of hydrogen bonding within IPDA(NHCOO⁻)₂ by noncovalent bond interaction (NCI) forces. The study's results indicate that this NCI modulation allows for a small-scale hydrogen-bonding network, which facilitates the release of CO₂ at lower temperatures compared to traditional aqueous systems.

The researchers conducted a comprehensive evaluation of the PCA system’s performance, including CO₂ absorption, desorption, and cycling stability. The IPDA-methyl isobutyl ketone (MIK) variant demonstrated the highest CO₂ removal efficiency, with complete desorption and release of absorbed CO₂ at 333 K. The system maintained high efficiency over 20 absorption–desorption cycles, showcasing its stability and potential for continuous operation.

Technoeconomic evaluation (TEA) results further highlight the cost-effectiveness of the ketone-based PCA system. The estimated cost of CO₂ capture for the IPDA-MIK system is approximately 72.05 CNY/t CO₂, significantly lower than the conventional MEA chemical absorption system, which costs around 233 CNY/t CO₂. This cost advantage, combined with the system’s high efficiency and low-energy consumption, positions it as a promising candidate for industrial-scale CO₂ capture applications.

The study also provides insights into the reaction mechanisms and molecular interactions within the PCA system. Quantum chemical calculations and molecular dynamics simulations revealed that the NCI forces between IPDA and ketone-based solvent molecules modulate the hydrogen bonding within IPDA(NHCOO⁻)₂, allowing for the low-temperature regeneration process. The researchers found that the average number of hydrogen bonds between IPDA(NHCOO⁻)₂ molecules significantly increased after CO₂ absorption, indicating the formation of large-scale hydrogen-bonding networks.

Despite these promising results, the study acknowledges several challenges that need to be addressed for the scalability and commercial viability of solid–liquid PCA systems. These include the energy requirements for solid–liquid separation, the risk of clogging, and the need for advanced solvents with optimized viscosity and stability. Future research should focus on developing more efficient solvents, enhancing the design of three-phase contactors, and integrating heat recovery systems to further reduce energy costs.

The development of the ketone-based PCA system represents a significant step forward in the field of CO₂ capture technology. Its ability to efficiently capture CO₂ across a wide concentration range, coupled with low-energy consumption regeneration, makes it a valuable addition to the toolkit for addressing climate change and achieving carbon neutrality.

The paper “Novel ketone-based IPDA phase change absorbents for highly efficient wide-concentration-range CO₂ capture and low-energy regeneration,” is authored by Qingrui Zeng, Ziang Jia, Yingyang Song, Yiwen Fan, Xu Liu, Jinping Cheng. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.05.008. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.