(165b) 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.