(416c) Fast Hydropyrolysis and Hydrodeoxygenation of Biomass Model Compounds

Fast hydropyrolysis followed by in-line vapor-phase hydrodeoxygenation has been shown to have the potential to maximize carbon retention in bio-oil with modest hydrogen consumption [1]. In this work, both hydropyrolysis and vapor-phase hydrodeoxygenation have been studied in separate reactor systems with model compounds. Taking a cue from the existing hydrotreating process in petroleum refineries, both the reactor systems were designed to handle high pressure hydrogen.

The concept of the fast hydropyrolysis reactor was based on a modified hydrogen-oxygen torch igniter. This continuous feed reactor was designed to carry out hydropyrolysis on ca. twenty gram quantities of cellulose at ~30 bar hydrogen pressure with a residence time of ca.70 milliseconds. The key design goal of this novel reactor was to minimize secondary reactions by drastically reducing the residence time and diluting the feed in excess of hydrogen. At 500°C, the major product was levoglucosan (monomer) comprising about 50% of the product bio-oil, followed by glycolaldehyde and cellobiosan. Nearly 90% of the bio-oil was accounted for by products identified and quantified using a liquid chromatography – mass spectrometry technique. As the pyrolysis temperature was increased from 500 to 700°C, the yield of levoglucosan decreased by nearly 40%, compensated by an increase in proportion of C2 compounds like glycolaldehyde and formic acid, giving insights into the ring opening mechanism of levoglucosan.

A fixed-bed catalytic reactor was also built to study the kinetics of furfural hydrodeoxygenation over Pt-based catalysts supported on multi-walled carbon nanotubes. At 1 bar hydrogen pressure, the major pathway over the Pt catalyst was the decarbonylation to furan, which is consistent with literature reports on Pd catalyst [2]. However, at 20 bar hydrogen pressure, the major product was furfuryl alcohol from reduction of furfural, demonstrating the importance of hydrogen in retaining carbon in the liquid product.

References

[1] R. Agrawal, N. Singh, Synergistic Routes to Liquid Fuel for a Petroleum-Deprived Future, AIChE Journal, 55 (2009) 1898-1905.

[2] S. Sitthisa, T. Pham, T. Prasomsri, T. Sooknoi, R. Mallinson, D. Resasco, Conversion of furfural and 2-methylpentanal on Pd/SiO2 and Pd-Cu/SiO2 catalysts, Journal of Catalysis, 280 (2011) 17-27.