Catalytic Bio-Oil Upgrading With Continuous Flow Microreactors

We present a high pressure and high temperature microreactor platform for investigation of multiphase catalytic bio-oil upgrading to increase the H/C ratio. The continuous flow platform facilitates extraction of kinetic data. A multichannel packed-bed microreactor has been microfabricated from silicon and Pyrex, as shown in the figure below. To achieve rapid kinetic data, the system is integrated with two in-line characterization tools: attenuated total reflection(ATR)- FTIR for liquid phase analysis and quadrupole mass spectrometer for gas phase analysis. The system has the advantage of handling experiments with small amount of catalyst (~10mg) and reagent. However, such small quantities pose challenges in analysis. A specific system and a procedure to address these hurdles will be presented.

Using this microreactor platform, we investigated liquid phase hydrogenation and hydrodeoxygenation mechanisms of lignin fragments such as phenol, anisole, guaiacol and vanillin. Hydrogenation of phenol using water as solvent has been achieved with 99% selectivity to cyclohexanone at 100% conversion using a Pd/Carbon catalyst. Our data suggest that further hydrogenation of cyclohexanone to cyclohexanol is the slower step. High selectivity has been also obtained for hydrodeoxygenation of vanillin to creosol at 100% conversion.  To gain mechanistic insights, we studied the effects of temperature, hydrogen pressure, residence time, and feed composition on conversion and selectivity. Based on the experimental conditions explored, mechanistic propositions are also made. Finally, the influence of solvent as well as catalyst support on selectivity for the studied reactions will be discussed.