(592b) Toward Sustainable Metal-Organic Frameworks for Post-Combustion Carbon Capture – Identifying Improvement Opportunities By Molecular Simulation and Life Cycle Assessment

Anthropogenic CO₂ emitted from the combustion of fossil fuels has been a significant contribution to the global warming effect, and fossil fuels will continue to be used for electricity generation in the coming years. To sustain the usage of fossil fuels and decrease CO₂ emission, carbon capture and sequestration (CCS) has been regarded as a near-term viable solution, but implementing such a process using the amine technology that uses monoethanolamine (MEA) to capture CO₂ involves a large energy penalty which decreases the efficiency of power generation. To achieve a more energy-efficient CCS process, exploring novel materials to efficiently capture CO₂ has drawn significant attention. Specifically, metal-organic frameworks (MOFs) have been identified as promising candidates for carbon capture, owing to many of their favorable properties (e.g., highly tunable nature, large adsorption capacity, and selective adsorption). Identifying promising MOF candidates has been an important research area, and most of the studies reported to date mainly attempted to evaluate MOFs based on their adsorption properties (e.g., selectivity) or their performance using a process model. Although MOFs have been demonstrated to possess potentially better performance (i.e., less energy intensity) than MEA, the overall impact by this emerging class of materials remains unknown. To this end, to facilitate the development of a new technology based on MOF adsorbents, the impacts of implementing MOF-based carbon capture, including the environmental impacts and resource depletion imposed from MOF synthesis process, should be considered. In this study, we carry out a comprehensive lifecycle assessment (LCA), coupled with molecular simulations, to investigate a selected set of 50 MOFs with diverse characteristics for their impacts when used in carbon capture and compared with that by using MEA. A variety of indicators such as global warming potential, eutrophication potential, and resource depletion are quantified from this study to shed light on different aspects of environmental impacts by using MOFs in carbon capture. In this study, extensive experimental data reported in the literature is used as a reference in the LCA to estimate the impact by the MOF synthesis from, e.g., solvent usage and synthesis energy. Molecular simulations are also conducted to calculate the adsorption properties of each studied MOF, which are subsequently used to determine the energy requirement of the MOF to separate a given amount CO₂ as well as the amount of adsorbent materials needed. Our results again show the great promise of MOFs in carbon capture, from the life cycle point of view. Moreover, our study highlights the significant environmental impact due to the usage and the type of the solvents, which suggests the importance of optimizing the synthesis conditions as well as seeking for the use of green solvents in the synthesis. The key role of MOF stability is also identified in determining the impact of MOFs in carbon capture. Overall, the insights obtained in this study can help guide the development of MOF-based CCS, and the analysis framework established herein can also be used to facilitate the development of other applications using MOFs.