Pyrolytic Conversion of Biomass to Fuels: Deoxygenation Via Elimination and Cyclization within Molten Cellulose

Pyrolytic Conversion of Biomass to Fuels: Deoxygenation via Elimination and Cyclization within Molten Cellulose

Alex D, Paulsen, Matthew S. Mettler, Dionisios G. Vlachos, Paul J. Dauenhauer

Abstract: Converting lignocellulosic biomass to bio-oils and biofuels via thermochemical methods relies on the chemistry of high temperature cellulose pyrolysis. It is known that cellulose reacts through a short-lived (10-100 ms) liquid intermediate during pyrolysis [1], which is important in determining product distributions in cellulose pyrolysis. We investigate the effect of temperature on kinetically-limited, isothermal cellulose pyrolysis yields over a range of reaction temperatures (350 - 550 °C) using a novel thin-film pyrolysis technique. The yield of permanent gases and light oxygenates was found to increase with increasing pyrolysis temperature. Yields of anhydrosugars and pyrans decrease with increasing pyrolysis temperature, while furan yields remain unchanged. The yield of levoglucosan remains constant with reaction temperature

            The secondary reactions of levoglucosan during cellulose pyrolysis are also investigated using novel co-pyrolysis experiments. Levoglucosan is a major product of cellulose pyrolysis which does not decompose when pyrolyzed alone (pure), but it does decompose in a liquid intermediate environment.  Through the use of ¹³C-labeled sugars, we show that levoglucosan breaks down within the molten phase to form pyrans, light (C₂-C₃) oxygenates, and other anhydrosugars.  The mechanisms of these reactions is unknown; however, we have shown using deuterated carbohydrates that levoglucosan decomposition products exhibit a distinct relationship between extent of elimination reactions and hydrogen exchange during reaction.  This demonstrates that hydrogen, which likely serves as a Brønsted catalyst within molten cellulose, plays a role in the decomposition of levoglucosan during cellulose pyrolysis.

 

1.         Dauenhauer, P. J.; Colby, J. L.; Balonek, C. M.; Suszynski, W. J.; Schmidt, L. D., Reactive boiling of cellulose for integrated catalysis through an intermediate liquid. Green Chemistry 2009, 11, (10), 1555-1561.