Screening acidic zeolites for catalytic fast pyrolysis of biomass and its components

Authors: Mihalcik, David; Mullen, Charles; Boateng, Akwasi

Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2011
Publication Date: 6/14/2011
Citation: Mihalcik, D.J., Mullen, C.A., Boateng, A.A. 2011. Screening acidic zeolites for catalytic fast pyrolysis of biomass and its components. Journal of Analytical & Applied Pyrolysis. 92:224-232.

Interpretive Summary: Upon rapid heating of a substance in the absence of oxygen, a reaction termed fast pyrolysis occurs. We are interested in studying the effects of fast pyrolysis when applied to lignocellulosic biomass samples from a variety of feedstocks. The rapid heating of biomass in the absence of oxygen allows for decomposition into its constituent parts. Typically, the products of fast pyrolysis of biomass are composed of non-condensable gases (CO, CO2, etc.), charcoal, and condensable gases. The condensable gas fraction is recovered by condensation and the resulting liquid, or bio-oil, contains a wide variety of compounds, the majority of which are oxygenated. With the goal of using this liquid fraction as a fuel, the high oxygen content must be lowered so as to increase its effectiveness. One method of transforming the highly oxygenated bio-oil is to subject the pyrolytic vapors to substances that alter the composition of the products. For instance, zeolites are naturally occurring materials often used in industry as adsorbents and in more specialized cases, as catalysts. Catalysts work by providing an alternative reaction pathway to the reaction product. Zeolite catalysts may be applied to the fast pyrolysis of lignocellulosic biomass to alter the product composition, in this case, to decrease the oxygen content of the condensable gas fraction. We used a small pyrolytic reactor to screen several types of zeolite and biomass feedstock combinations to determine what effect, if any, the catalyst has on the composition of the pyrolytic products. Our results show that without a catalyst, large quantities of oxygenated compounds were observed in the pyrolytic products. Upon implementation of zeolite catalysts, a highly deoxygenated condensable gas fraction was observed which would lead to a highly deoxygenated bio-oil. Furthermore, specific zeolite catalysts were capable not only of deoxygenation, but also production of energy-rich compounds typically found in fuels such as gasoline. These results show that depending on the characteristics of the zeolite used, deoxygenation of pyrolytic vapors and even production of energy-rich compounds from biomass, is possible. This information will be useful to those producing and refining bio-oil into fuels and chemicals on a larger scale.

Technical Abstract: Zeolites have been shown to effectively promote cracking reactions during pyrolysis resulting in highly deoxygenated and hydrocarbon-rich compounds and stable pyrolysis oil product. Py/GC-MS was employed to study the catalytic fast pyrolysis of lignocellulosic biomass samples comprising oak, corn cob, corn stover, and switchgrass, as well as the fractional components of biomass, i.e., cellulose, hemicellulose, and lignin. Quantitative values of condensable vapors and relative compositions of the pyrolytic products including non-condensable gases (NCG’s) and residual solids are presented to show how reaction products are affected by catalyst choice. While all catalysts decreased the oxygen-containing products in the condensable vapors, H-ZSM-5 was most effective at producing aromatic hydrocarbons from the pyrolytic vapors. We demonstrated how the Si/Al ratio of the catalysts plays a role in the deoxygenation of the vapors towards the pathway to aromatic hydrocarbons.