(4dq) Closing the Carbon Cycle for Sustainable Energy and Environment:CO2 Capture Using Nanoparticle Ionic Materials (NIMs) and Methane Recovery in Clathrate Hydrates with Integrated Carbon Storage

Sustainability has become an urgent global issue with the exhaustion of fossil fuel and the climate debate. Thus, developments in alternative energy sources and capture/storage of carbon dioxide have been the focus of recent research in the energy and environment field. My research has specifically focused on two distinct engineered and natural materials: i) the synthesis of organic-inorganic nanoparticle ionic materials (NIMs) for CO2 capture and ii) the combined methane recovery and CO2 sequestration in complex structured naturally-occurring gas hydrate.

In order to capture carbon dioxide from flue gas streams, various absorbents have been suggested, and amine-based aqueous solution such as MEA solvent exhibits tremendous CO2 capture capacity. However, the undesired effects of amine-based solvents such as corrosion, vaporization/degradation loss, and large energy penalty during solvent regeneration have been obstacles for its large scale industrial application. As an alternative option to these amine-based solvents for CO2 capture, NIMs have been designed and synthesized with negligible vapor pressure. NIMs are organic-inorganic hybrid materials which comprise oligomer or polymer counterions tethered to a surface-modified nano-sized core by strong primary ionic bonds. Because it is the molecular analogs of ionic liquids, NIMs exhibit negligible vapor pressure with enhanced thermal stability. Since there is no solvent (i.e., water) associated with this CO2 capture medium, the energy requirement for NIMs regeneration is significantly lower than that of MEA. In addition, various physical and chemical properties such as rheological, optical, and electrical properties with the range from glassy solids to solvent-free nanoparticle suspension could be expected by tuning the core and canopy (ionically tethered corona and counterion species). It is proposed that ionic bonds located in corona chains would contribute electrostatic repulsion among corona chains and as the corona chains are frustrated by electrostatic forces the free volume within the system would increase. Therefore, CO2 capture by NIMs can be maximized by controlling both enthalpic and entropic effects.

Once CO2 is captured, it is important to store this carbon with long-term stability. Clathrate hydrates, so called gas hydrates, are non-stoichiometric crystalline compounds formed when guest molecules are incorporated in host water frameworks made up of hydrogen-bonded water molecules under the appropriated pressure and temperature conditions. Because of its various and unique physical and chemical properties, clathrate hydrates have been studied for energy gas storages such as hydrogen and for other material engineering applications. The total amount of natural gas hydrates on continental margins and in permafrost regions has been estimated to be about twice as much as the energy contained in fossil fuel reserves. Thus it could be serve as an alternative option as an energy source if efficient recovering way is provided. The option of swapping enclathrated methane and CO2 molecules is proposed for the combined methane production and CO2 sequestration. It is experimentally confirmed that ~ 90% of methane molecules in naturally-occurring gas hydrate can be recovered without structural decomposition while storing CO2 in place of methane. It is also found that due to the large and small cage structure of the gas hydrate for the maximum recovery of methane, both CO2 and smaller gaseous molecule such as N2 should be used simultaneously.

As shown in these studies, my research aims to close the carbon cycle by extracting maximum energy possible from the new natural resources while efficiently storing excess waste carbon in natural systems. The findings from these studies will provide valuable fundamental knowledge for the environmental field and energy sustainability.