(749f) Tuning the Mechanisms of Cellulose Pyrolysis Via Novel Reactor Design

High temperature cellulose pyrolysis is an important part of converting lignocellulosic biomass to bio-oils and biofuels. Cellulose is known to react through a short-lived (10-100 ms) liquid intermediate during pyrolysis^[1], which determines the product distribution in cellulose pyrolysis. Predicting the composition of the bio-oil product is necessary to improve pyrolysis economics. Therefore, our work focuses on identifying the crucial mechanisms of cellulose pyrolysis.^[2-4] Using a novel reactor design, we find that levoglucosan undergoes secondary reactions within the liquid intermediate to form pyrans, anhydrosugars, and light (C₂-C₃) oxygenates. The mechanisms of these reactions are unknown; however, we have shown the relationship between levoglucosan decomposition and hydrogen transfer within the liquid intermediate by using deuterated carbohydrates.^[5] It is likely that hydrogen serves as a Brønsted catalyst for the decomposition of levoglucosan within molten cellulose.

Additionally, we utilize a novel thin-film pyrolysis reactor technique to investigate the effect of temperature on kinetically-limited, isothermal cellulose pyrolysis yields over a range of reaction temperatures (350 - 550 °C).^[6] We observed that the total yield of furanic compounds remains constant over this range of temperatures. While the five-membered furan ring remains intact, oxygen functional groups (i.e. the aldehyde in hydroxymethylfurfural) are cleaved at higher temperatures to form deoxygenated furans (such as furan and methyl furan). The presence of these aldehyde groups in bio-oil leads to polymerization, which makes bio-oil unstable at storage conditions^[7]. We promoted this chemistry by impregnating cellulose with a carbon-supported metal catalyst to reduce the aldehyde content of bio-oil while maintaining the overall bio-oil yield.

References

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.

2. Mettler, M. S.; Paulsen, A. D.; Vlachos, D. G.; Dauenhauer, P. J., The chain length effect in pyrolysis: bridging the gap between glucose and cellulose. Green Chemistry 2012, 14, 1284-1288.

3. Mettler, M. S.; Mushrif, S. H.; Paulsen, A. D.; Javadekar, A. D.; Vlachos, D. G.; Dauenhauer, P. J., Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates. Energy & Environmental Science 2012, 5, (1), 5414-5424.

4. Paulsen, A. D., Hough, B. R., Williams, C. L., Teixeira, A. R., Schwartz, D. T., Pfaendtner, J., & Dauenhauer, P. J., Fast Pyrolysis of Wood for Biofuels: Spatiotemporally Resolved Diffuse Reflectance In situ Spectroscopy of Particles. ChemSusChem 2014, 7, (3), 765-776.

5. Mettler, M. S.; Paulsen, A. D.; Vlachos, D. G.; Dauenhauer, P. J., Pyrolytic conversion of cellulose to fuels: levoglucosan deoxygenation via elimination and cyclization within molten biomass. Energy & Environmental Science 2012.

6. Paulsen, A. D., Mettler, M. S., Vlachos, D. G., & Dauenhauer, P. J., The Role of Sample Dimension and Temperature in Cellulose Pyrolysis. Energy & Fuels 2013.

7. A.D. Paulsen, D.G. Vlachos, P.J. Dauenhauer, "Tuning Cellulose Pyrolysis Chemistry: Selective Decarbonylation via Catalyst-Impregnated Pyrolysis," M.S. Mettler, Catalysis Science & Technology 2014, 4, 3822-3825.