Catalytic Polymeric Hollow Fiber Membrane Modules For Use In Model Three Phase Reactions: Understanding the Influence of the Ratio of Membrane Area to Reaction Volume Treated

Membrane contactors have been evaluated for the selective hydrogenation of model compounds.  The membrane contactors considered are hollow fiber gas separation membranes, potted in bench-scale modules and coated with palladium catalyst in-situ.  Hydrogen was supplied from the bore side of the membrane fiber and permeated from the bore side to the shell side, where it adsorbed directly onto the metal surface.  Liquid reactant circulated through the shell side, allowing the liquid to come into direct contact with the metal coated surface of the membrane where the hydrogenation occurred.  Our membrane contact reactor approach replaces the traditional three phase batch slurry reactor.  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.  In the case of partial hydrogenation of soybean oil (the model compound considered), the undesirable side reaction is the production of trans fats.

Modules with varying numbers of membrane fibers were produced and used to evaluate the impact of the ratio (membrane area / reaction volume treated) on the overall performance of the system.  The rate of reaction increases with increasing membrane area (which results in an increase in catalyst available and an increase in the availability of hydrogen).  Additionally, the system is shown to be nearly zero order in hydrogen, indicating that the catalyst surface maintains high hydrogen coverage throughout the experiments.  Implications for system design and operation will be discussed.