Aqueous phase hydrogenation of levulinic acid using a porous catalytic membrane reactor

• PTFE membrane reactor was used for aqueous phase hydrogenation of levulinic acid.
• Porous PTFE acted as gas/liquid phase contacting membrane.
• Hydrogen is delivered directly from gas phase to liquid phase catalytic sites.
• Membrane reactor displayed high catalytic activity at low H2 pressures (0.17–5.6 bar).
• Avoiding liquid dissolved H2 allows greater catalytic benefit at higher temperatures

Membrane reactors offer an alternative approach for conducting three-phase heterogeneous chemical reactions. The membrane acts as a liquid/gas phase contactor, while also serving as the support for a solid catalyst. A significant benefit from this approach is circumvention of gas phase dissolution and diffusion in the liquid phase to reach catalytic sites. This method of gas phase mass transfer allows a significant reduction in operating pressure compared to traditional three-phase reactors that often require higher gas pressures due to low gas solubility and diffusivity in the liquid phase. The membrane reactor in this work consists of a porous expanded polytetrafluoroethylene (ePTFE) membrane with deposited Ru catalyst particles. The reaction studied is the aqueous phase hydrogenation of levulinic acid to produce γ-valerolactone. The highly hydrophobic PTFE material provides an almost impermeable barrier to the liquid phase while allowing hydrogen gas to freely transport through the pores to reach catalytic sites located at the liquid/membrane interface. The reaction kinetics displayed by the membrane reactor favorably compare to those of a packed bed reactor (PBR). In terms of hydrogen pressure the maximum catalytic benefit in comparison to the PBR is obtained at pressures greater than 0.7 bar, and a more pronounced and continuously increasing catalytic benefit is obtained with increasing temperature.

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