Future of Carbon Capture: Materials and Strategies.

Abstract

Emissions of greenhouse gases into the atmosphere represent a long-term social and environmental challenge. Fossil fuels, which are the main source of these emissions, will likely continue to be used in energy production and transportation for the foreseeable future. In order to mitigate these emissions and prevent the worst potential effects of climate change, carbon capture technologies will need to achieve widespread use across various industries. To inform further development of next-generation carbon capture systems, two potential technologies were explored. The first technology, flexible metal-organic frameworks, represent alternative materials for carbon capture. A group of flexible frameworks known as elastic layer-structured metal organic frameworks (ELMs) were chosen as a representative class. These crystalline materials have exotic “gated” isotherms which show abrupt reversible transitions from nonporous structures to porous structures through cooperative adsorption of guest molecules between layer planes. These unique materials show potential for selective CO2 capture combined with energy efficient adsorbent regeneration. Two aspects of CO2 capture using ELMs were investigated in detail. First, the ability of ELMs to maintain their structure and capture performance in the presence of unwanted trace species present in flue gas streams, such as NOx, SOx, and water vapor, was analyzed using both experimental and computational techniques. It was found that ELMs can be tailored for robust performance through careful choice of framework components, such as metal ion or counter ion substitution. Second, the breakthrough performance of ELMs was explored using a combination of experimental breakthrough curves and theoretical treatment. ELMs show a “stepped” breakthrough curve not seen in rigid adsorbents. These “stepped” curves are representative of the breakthrough curves of flexible frameworks and pose a potential hurdle to their use in carbon capture applications. The second technology, mobile carbon capture, represents an alternative strategy for mitigating emissions from the transportation sector. Using a combination of techniques, the potential costs and design trade-offs associated with implementing a mobile carbon capture scheme were explored. It was found that mobile carbon capture could greatly reduce transportation emissions while being cheaper to implement than competing direct air capture schemes, which suffer from significant thermodynamic penalties.