(4e) Carbon Dioxide Capture with Microporous Metal Organic Frameworks

It is our goal to incorporate extremely high pore volume MOF (metal organic framework) materials into a commercially viable adsorption process. Our approach to carbon dioxide capture from power plant flue gas and gasification streams involves a combination of molecular modeling with synthesis of novel MOFs. MOFs are a new class of nanoporous materials synthesized in a ?building-block? approach by self-assembly of metal or metal oxide vertices interconnected by rigid organic linker molecules. We found that a set of reference MOF materials show extremely high CO2 adsorption capacities and very desirable linear isotherm shapes. For example, volumetric and gravimetric carbon dioxide capacities 3 and 7 times larger, respectively, than those for high porosity zeolites, were measured. A linear correlation between carbon dioxide adsorption capacity and surface area was determined. Detailed molecular modeling of adsorption isotherms show that theory and experiment match closely. Functional groups were added to MOF linkers in an effort to enhance the possibility for chemisorption and to help further understand the effect changes in linker chemistry have on adsorption capacity and selectivity. For example, tertiary amine functionality was incorporated into the common benzene dicarboxilic acid (BDC) linker to generate MOF-32. Raman spectroscopy was shown to be useful for the facile characterization of MOF materials, and when these data are coupled with carbon dioxide adsorption measurements, we can conclude that a more basic functionality will be required to enhance CO2 chemisorption in MOF materials. Once again, the modeling work correlated closely with experiment. In fact, the rational synthesis approach described above opened up the possibility of incorporating a wide variety of metal and metal oxide vertices, as well as various functional groups into a MOF structure. Because MOF synthesis reaction products are often predictable, we were able to use molecular modeling as a way to screen new structures before they were synthesized. In this way, modeling also enabled us to reduce or eliminate extensive and expensive laboratory experiments. Finally, the hydrothermal stability of a wide variety of MOFs was investigated utilizing high throughput tools. High carbon dioxide adsorption capacity and good hydrothermal stability are the initial screening criteria to determine which materials to further evaluate for flue gas carbon dioxide capture.