Elucidating the Role of Physiochemical Properties on Gas Transport in Ionic Liquids and Porous Liquids for Carbon Dioxide Separations

The rising concentration of atmospheric carbon dioxide to unprecedented levels has prompted global initiatives to reduce carbon emissions from anthropogenic sources. However, technologies to support these initiatives are somewhat limited and are not the most economically advantageous for cost to capture ratios. Current strategies using liquid amines are corrosive and have a significant thermal penalty for regeneration. There is a need for a passive, efficient approach for carbon dioxide sequestration. Rather than harnessing a chemical reaction, which requires added energy to release carbon dioxide and reuse the sorbent, other materials that operate by a mechanism of physical interactions will be explored.Membranes are a low energy alternative for gas separations but require thoughtful design to circumvent the inherent permeability-selectivity tradeoff. To mitigate this effect, ionic liquids (ILs) were functionalized to enhance carbon dioxide selectivity between gases of interest. Cations were designed to reduce cation-anion interactions and increase free volume in efforts to enhance permeability, but gains were minimized due to increased viscosity of the new ILs. New relationships between fractional free volume and gas solubility were examined.Mixed matrix mediums have recently gained prominence for their ability to bridge the gap between permeability and selectivity. Ionic liquid absorbents are adept at selectively separating light gases, while porous adsorbents with large surface areas have high capacities at low partial pressures. Porous liquids are a new class of fluid sorbents that combine the positive attributes of both components. Through judicious selection of the liquid and dispersed colloidal solid, permanent cavities can be achieved in the liquid phase. A porous liquid was created using zeolitic imidazolate framework nanocrystals incorporated into a bulky ionic liquid. The composite exhibited distinct enhancements in both gas solubility and selectivity.In situ Fourier transform infrared spectroscopy measurements were conducted to investigate the mode of carbon dioxide absorption in the porous liquids. While the liquid phase remains relatively unchanged, incorporation of carbon dioxide leads to slight structural fluctuations in the porous solid and liquid. The presence of both dissolved and gaseous carbon dioxide was detected, and preliminary quantitation was completed.