Microfibrous Entrapped Catalysts and Sorbents: Microstructured Heterogeneous Contacting Systems with Enhanced Efficiency
Type of DegreeDissertation
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Catalyst/adsorbent particles were entrapped in sinter-locked networks of microfibers to form composite materials for use in heterogeneous catalysis and adsorption applications. These novel microstructured materials called as microfibrous entrapped catalysts/sorbents (MFECS), which have high voidages and uniform structures showed great enhancement in reaction rates and significant reduction in pressure drops in many heterogeneous contacting applications. In this work two different case studies - Hexane adsorption on activated carbon and Ozone catalytic decomposition for aircraft cabin air purification - were used to demonstrate and understand the anomalous reactivity enhancement in MFECS. Theoretical as well as experimental comparisons of MFECS were made with the conventional reactor systems in both the cases. Further, 2D Computational Fluid Dynamics (CFD) studies were used to analyze the effect of fibers on mass transfer rates in these microstructured geometries. Hexane breakthrough experiments showed that, the negative effect of the axial dispersion and channeling were predominantly present in packed beds of small particle diameters (< 3mm). On the other hand, high voidages and uniformity of MFES decreased the axial dispersion and channeling effects and increased the radial dispersion of the adsorbate, thus improving the fluid phase mass transport rates. In the ozone decomposition study, performance comparisons of microfibrous entrapped catalysts (MFEC) were made with monoliths of various cells per square inch (cpsi) and packed beds of various particle sizes for catalytic ozone decomposition. The analysis showed that the monoliths are severely affected by external mass transfer limitations, while the MFEC systems with lower pleat factor and packed beds were restricted by high pressure drops. But MFEC systems with higher pleat factor were able to combine the dual advantages of low pressure drops with high mass transfer rates and there by exceed the performance of the monoliths and packed beds. Further, CFD analysis in 2D channel geometries showed that the presence of fibers caused significant improvement in mass transfer rates at higher Re numbers. This increase was found to be due to elimination of peaking velocities i.e. creation of plug flow conditions. The two case studies and the CFD analysis have demonstrated the potential advantages of MFECS as heterogeneous contacting systems for use in high throughput applications as well as for applications requiring multi-log-removal capability.