Microporous Coordination Polymers As Selective Adsorbents For Complex Matrices.

Abstract

Crystalline microporous coordination polymers (MCPs) are ordered, porous materials that have recently seen increasing attention in the literature. Whereas gas phase separations using MCPs have been extensively studied and reviewed, studies on applications in the liquid phase, particularly from complex matrices, have lagged behind. In this thesis, MCPs have been applied to adsorption from diesel and water.

The utility of MCPs for the adsorption of large organosulfur compounds (benzothiophene, dibenzothiophene, 4,6-dimethyldibenzothiophene) found as pollutant precursors in fuels was demonstrated. Large capacities were obtained, particularly for 4,6-dimethyldibenzothiophene, the compound most difficult to remove using current industrial techniques. It was determined that the size/shape of the pores in the MCP, rather than surface area or pore volume, is the most important factor controlling adsorption capacity. This was confirmed by studying the supramolecular isomers University of Michigan Crystalline Material (UMCM)-152 and UMCM-153 which exhibited different adsorption behaviors. Electron-deficient MCPs were also tested and higher adsorption capacities were observed for the most electron-deficient structure.

MCPs were demonstrated to be efficient adsorbents for the removal of the organosulfur compounds dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) from model fuel and diesel fuel in packed bed breakthrough experiments. Unlike activated carbons, where selectivity has been a problem, MCPs selectively adsorb the organosulfur compounds over similar components of diesel. Complete regeneration using toluene at modest temperatures was achieved. The attainment of high selectivities and capacities, particularly for the adsorption of the difficult to remove refractory compounds, in a reversible sorbent indicates that fuel desulfurization may be an important application for MCPs.

Finally, the water stability of a variety of MCPs was studied using powder X-ray diffraction. It was determined that the stability of the MCP is related to the metal cluster present in the structure with trinuclear chromium clusters more stable than copper paddlewheel clusters which are more stable than basic zinc acetate clusters. Matériaux de l’Institut Lavoisier (MIL)-100 was found to be completely water stable and was used to adsorb the pharmaceuticals furosemide and sulfasalazine from water with large uptakes at low concentrations, indicating that the adsorption of wastewater contaminants may be a feasible application for these materials.