Doctor of Philosophy / Department of Chemical Engineering / Peter H. Pfromm / Mary E. Rezac / Multiphase reactions are often constrained by mass transfer limitations which in many cases lead to low reaction rates and undesirable product distribution. Here we fabricate integral-asymmetric polymeric membranes decorated with metal catalysts, to supply hydrogen directly at or near the surface of the catalyst, thus minimizing mass-transfer limitations. The metal decorated polymeric membranes were used for partial hydrogenation of soybean oil with the goal to minimize trans fatty acid (TFA) formation. It was discovered that polymeric membranes with “defective” metal coatings are well suited to achieve low-TFA hydrogenation of soybean oil at quite moderate process conditions. The metal decorated polymeric membranes studied produced significantly lower trans fatty acid as compared to traditional reactors (3.5 wt% at an Iodine Value of 95 as compared to 8 wt% in slurry reactor), at pressures and temperatures which are compatible with the existing systems. The process concept is simpler than some of the alternatives being studied and no catalyst recovery from the oil is needed since the catalyst is immobilized on the membrane. Metal decorated polymeric membranes having a variety of hydrogen fluxes, skin defects, and catalyst loadings were evaluated. All the metal decorated polymeric membranes evaluated produced low TFA. Membranes with high hydrogen fluxes resulted in higher hydrogenation rates but had little influence on TFA formation. Membranes with higher catalyst loadings resulted in lower TFA but increased saturate formation. Metal decorated polymeric membranes behaved differently to changes in temperature and pressures when compared to traditional slurry reactors. They showed a minor increase in TFA with temperature (50-90 °C) as compared to traditional slurry reactors. The hydrogenation rate and cis-trans isomerization also showed a modest dependence on pressure. Due to the defective nature of the metal layer on the polymeric membrane skin and the low temperatures (50-90 °C) at which the reactor is operating, the hydrogen permeability of metals has a minor influence on hydrogenation reaction. A range of metal catalysts can be used for the given system. Repeat runs using the same membrane showed a decrease in hydrogenation activity, without any change in isomerization or hydrogenation selectivity. Initial results indicate the decreased activity may not be from leaching of catalyst from membrane surface nor from sulfur poisoning.

Doctor of Philosophy / Chemical Engineering / Mary E. Rezac / Membrane contact reactors (MCRs) have been evaluated for the selective hydro-treating of model reactions; the partial hydrogenation of soybean oil (PHSO), and the conversion of lactic acid into commodity chemicals. Membranes were rendered catalytically active by depositing metal catalyst onto the polymer "skin" of an asymmetric membrane. Hydrogen was supplied to the support side of the membrane and permeated from the support side to the skin side, where it adsorbed directly onto the metal surface. Liquid reactant was circulated over the membrane, allowing the liquid to come into direct contact with the metal coated surface of the membrane, where the reaction occurred. Our membrane contact reactor approach replaces traditional three-phase batch slurry reactors. These traditional reactors possess inherent mass transfer limitations due to low hydrogen solubility in liquid and slow diffusion to the catalyst surface. This causes hydrogen starvation at the catalyst surface, resulting in undesirable side reactions and/or extreme operating pressures of 100 atmospheres or more. By using membrane reactors, we were able to rapidly supply hydrogen to the catalyst surface. When the PHSO is performed in a traditional slurry reactor, the aforementioned hydrogen starvation leads to a high amounts of trans-fats. Using a MCR, we were able to reduce trans-fats by over 50% for equal levels of hydrogenation. It was further demonstrated that an increase in temperature had minimal effects on trans-fat formation, while significantly increasing hydrogenation rates; allowing the system to capture higher reaction rates without adversely affecting product quality. Additionally, high temperatures favors the hydrogenation of polyenes over monoenes, leading to low amounts of saturated fats. MCRs were shown to operator at high temperatures and: (1) capture high reaction rates, (2) minimize saturated fats, and (3) minimize trans-fats. We also demonstrated lactic acid conversion into commodity chemicals using MCRs. Our results show that all MCR experiments had faster reaction rate than all of our controls, indicating that MCRs have high levels of hydrogen coverage at the catalyst. It was also demonstrated that changing reaction conditions (pressure and temperature) changed the product selectivities; giving the potential for MCRs to manipulate product selectivity.