Adsorption equilibrium and mass transfer in metal-organic frameworks and adsorption on carbon surfaces in the Henry's law region
The purpose of the first part of this dissertation is to study the potential use of metal-organic frameworks (MOFs) as novel adsorbents to capture carbon dioxide from flue gases mainly generated by coal-fired power plants. Over 30 MOF candidates were screened for the highest carbon dioxide capacities at 0.1 atm and 100 OF. Carbon dioxide adsorption rates and mechanisms were studied for HKUST-1 and Ni/DOBDC pellets using a concentration swing frequency response (CSFR) method. Preloaded water and acid gas conditioning effects on the carbon dioxide adsorption in MOFs were also investigated. Acid gas conditioning did not affect the carbon dioxide adsorption in HKUST-1 and Ni/DOBDC. Ni/DOBDC was found to be more stable than Mg/DOBDC although it has a smaller carbon dioxide capacity at 0.1 atm. Also, pyridine modified Ni/DOBDC was found to have a smaller water to carbon dioxide selectivity and a larger carbon dioxide capacity at 0.1 atm compared with unmodified Ni/DOBDC. In the second part of this dissertation, some key thermodynamic properties of gas adsorption, including isosteric heats of adsorption, Henry's law constants, and accessible pore radius, were studied for gas adsorbed in carbon nanopores with different geometries and numbers of wall layers. Surface mean curvature was found to be very important to the isosteric heat of adsorption for gas molecules adsorbed in carbon nanopores with sizes comparable to the gas molecule. General plots were developed to estimate pore diameters at which maximum isosteric heats of adsorption occur for non-polar or weakly polar molecules adsorbed in carbon nanopores. The isosteric heat of adsorption study was extended to carbon nanopores with multilayer walls. An accessible pore volume was adopted to replace the absolute void volume in order to avoid negative Henry's law constants at high temperatures. Finally, accessible pore volume was calculated as a function of pore radius for gas adsorbed in carbon nanopores with different geometries and numbers of wall layers.