Development of membrane reactors for heterogeneously catalysed aerobic oxidation of alcohols

Heterogeneously catalysed aerobic oxidation of alcohols has great potential in chemical synthesis, but its wide application is still limited by safety issues with the combination of gaseous oxygen and flammable organics. The aim of this thesis is to develop Teflon AF-2400 membrane reactors for the intrinsically safe use of oxygen in oxidation of alcohols. Initially, oxidation of benzyl alcohol and cinnamyl alcohol on Au-Pd/TiO2 catalyst was studied in a trickle bed microreactor. The catalyst deactivation in cinnamyl alcohol oxidation, rather than benzyl alcohol oxidation, was attributed to Pd leaching and a complex role of oxygen. Then, a Teflon AF-2400 packed tube-in-tube membrane microreactor was investigated for benzyl alcohol oxidation, which allowed continuous oxygen supply during the reaction and presented higher conversion and selectivity as compared to a reactor with oxygen pre-saturated feed. A novel approach using the tube-in-tube membrane contactor was demonstrated for measuring gas solubility in liquids. To simplify the reactor scale-up, a Teflon AF-2400 flat membrane microreactor was developed for benzyl alcohol oxidation, and the mass transfer and reaction in the reactor were experimentally and theoretically investigated with different catalysts. The oxygen transverse mass transfer in the catalyst bed, rather than oxygen permeation through membrane or oxygen internal/external transfer in the catalyst particles, was indicated to be the controlling process. An effectiveness factor analysis akin to internal/external mass transfer and reaction in a catalytic particle was provided to guide the catalyst choice and the membrane reactor design. For direct usage of small catalyst particles in continuous flow reactors, a stirred membrane reactor with a sintered metal filter and an external membrane contactor was experimentally demonstrated and mathematically simulated for benzyl alcohol oxidation. The reactant conversion and the catalyst utilization were indicated to be affected by various operation parameters, which were correlated to guide the reactor design and operation.