(540e) Three-Phase Hydrogenation Reactions Using a Ruthenium Coated Polymeric Membrane Reactor

Three-phase
Hydrogenation Reactions using a Ruthenium Coated Polymeric Membrane Reactor

John
Stanford^1,2, Peter Pfromm²,
and Mary Rezac²*

¹IGERT
Trainee in Biorefining
²Department of Chemical Engineering, Kansas State University

Manhattan, Kansas, United States

*rezac@ksu.edu

Catalytic
membrane reactors afford an alternative and potentially more efficient method
for performing three-phase heterogeneous chemical reactions.  Traditional three-phase reactors often
present mass transfer limitations, namely relatively large diffusional
distances to reach catalytic sites exacerbated by low gas solubility in the
liquid phase.   Membrane reactors can alleviate the inherent mass transfer
limitations by directly and abundantly supplying gas to the catalytic sites located
on the membrane surface, which acts as a gas/liquid phase contactor, and thus
lessening the necessity for higher gas phase pressures.  The reactions investigated in this work
include the hydrogenation of 5-hydroxymethylfurfural (HMF) in an alcohol
solvent and the hydrogenation of levulinic acid (LA) in an aqueous solvent.

Polyimide
polymers are used in this work for membrane synthesis because of their good
chemical and high temperature resistance. 
The polymer solutions are cast as asymmetric integrally-skinned flat
sheet membranes and are then coated with a ruthenium catalyst on the non-porous
surface.  The completed membrane is
positioned in a flow over configuration maintaining liquid contact on the metal
coated surface while allowing hydrogen gas to permeate from the porous support
side to the catalytic sites on the non-porous surface.  The multi-functionality of the membrane
reactor/contactor has allowed several areas to be investigated, including
catalytic activity and reaction kinetics, membrane performance and characterization,
and solvent/polymer interactions.  Quantitative
hydrogenation product formation with reaction kinetics similar to or better
than more traditional three-phase reactors has been achieved.  The membrane reactors are shown to be stable
and catalytically active for several days of continuous operation.  This work has also demonstrated that unless
the dense separating layer of the polymeric membrane exhibits and maintains a
high degree of ?defect free' quality, then the penetrating liquid reaction solvent
reintroduces the mass transfer limitations for the gas phase that the membrane
was intended to eliminate.  Continued
efforts to improve membrane reactor performance such as increasing hydrogen permeance, increasing catalytic site availability, and
decreasing liquid phase permeance should yield an
increasingly favorable comparison to traditional reactor systems.