Doctor of Philosophy (PhD)
Present work demonstrates the use of vibrations to enhance performance of two multi-phase contacting systems: a bubble column for gas-liquid contacting (physical absorption) and a Piston Oscillating Monolith Reactor (POMR) for gas-liquid-solid contacting (catalytic reactions). In a bubble column reactor, enhancements of mass transfer coefficient and gas hold up were experimentally studied for the air-water system. Mass transfer coefficient enhancements up to 500% and gas hold-up improvements up to 200% were achieved under the application of low amplitude (0.5-2.5 mm) vibration at low frequencies (0-25 Hz). A fundamental theory was developed from first principles to explain these enhancements. The theory satisfactorily predicts the mass transfer coefficient and the gas hold-up as a function of operating parameters including the frequency and the amplitude of vibrations, the gas superficial velocity and the viscosity of the system. Effects of vibrations on the bubble size distribution were also investigated and population balance modeling was performed to explain the experimental observations. Performance of a novel three phase POMR was studied for two reactions: hydrogenation of alpha-methyl styrene to cumene and partial hydrogenation of soybean oil using a monolith catalyst washcoated with Pd/Al2O3. Hydrogenation of alpha-methyl styrene reaction was carried out under external mass transfer controlled conditions in the POMR and also in a stirred tank reactor. Results show activity improvement of up to 84% at 17.5 Hz over no-pulsing conditions. It was shown that the POMR provides for rapid mass transfer rates, superior to traditional reactors, and even superior to a stirred tank when compared on a power-per-volume basis. Soybean oil was partially hydrogenated in the POMR and also in a stirred tank reactor. The reaction was found to be internal diffusion controlled at these conditions. Activity enhancements up to 112% were achieved at 17.5 Hz over no-pulsing conditions. The enhancements can be attributed to either the increased intra-pore transport or the improved wetting distribution due to the application of vibrations. Improvement in serial pathway selectivity was observed with increasing frequency but stereo-selectivity remained unaffected by the vibrations.
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Waghmare, Yogesh G., "Vibrations for improving multiphase contact" (2008). LSU Doctoral Dissertations. 1420.
F. Carl Knopf