(729f) Effects of Feedstock on the Product Yields and Selectivity of Lignocellulosic Biomass Pyrolysis Using HZSM-5 Catalyst

Lignocellulosic Biomass Pyrolysis Using HZSM-5 Catalyst

Brendon Shea, Charles Coe, Justinus Satrio*

Department of Chemical Engineering

Villanova University, Villanova, PA 19085

One promising process of utilizing lignocellulosic biomass for the production of fuels and chemicals is fast pyrolysis. In this approach, the biomass is thermally treated at temperatures around 400-600°C in the absence of oxygen. The products formed include a solid char, a liquid bio-oil, and a mixture of non-condensable gases. The liquid bio-oil is composed of a multitude of organic compounds; many of them are oxygenated, such as ketones, phenols, and carboxylic acids. The high presence of these oxygenated compounds is not desirable since they cause bio-oil to be highly acidic, highly polar, chemically unstable, and low in heating value products. The use of solid acid catalysts, such HZSM-5, an aluminosilicate zeolite, can alter the liquid product distribution in favor of non-oxygenated compounds such as aromatics. These hydrocarbon compounds are desirable in bio-oil, especially when the bio-oil is used as intermediate feedstock for the production of liquid transportation fuels.

The product distribution is heavily affected by the feedstock of biomass that is pyrolyzed. A study on fast pyrolysis of 5 different biomass feedstocks was conducted with and without H-ZSM-5(40) as a solid acid catalyst. Feedstocks tested included pinewood, mixed hardwood, switchgrass, horse-barn bedding, and phragmites (common reeds). Fast pyrolysis experiments were conducted using a micropyrolyzer system which was connected to a GC/MS and a TCD gas analyzer for analyzing chemical composition of the pyrolytic vapors and non-condensable gases respectively. Catalytic pyrolysis experiments were performed in ex-situ mode, in which catalytic vapors were passed through a heated catalyst bed before being sent to the vapor and gas analyzers. The ex-situ catalytic pyrolysis configuration allowed multiple catalytic pyrolysis runs were done in series on the same catalyst sample to observe the effect of biomass feedstock on the catalyst activity. For completing mass balance, the amount of char formed was also measured in each run.

Experimental results indicated that biomass feedstock has a significant effect on pyrolysis product yields and selectivity as well as on the catalyst activity. Switchgrass and phragmites produced significantly more char than the other biomass feedstock. In non-catalyzed pyrolysis, these two grass-type feedstock produced less CO and more CO₂. The composition of chemical moieties of bio-oil products also was affected by the type of feedstock used for the fast pyrolysis reaction. In catalytic pyrolysis, pinewood and mixed hardwood were found to produce the most CO. while mixed hardwood and phragmites produced the most CO2. There was little correlation in the light gas formation as the catalyst deactivated. The bio-oil composition did vary as the catalyst deactivated; however the light gas formation showed very little correlation with the catalyst deactivation. For all biomass types, as the catalyst deactivated, the amounts of aromatics produced decreased while the amounts of ketones, phenols, and carboxylic acids produced increased. It appeared that pinewood had the greatest rate of change in bio-oil composition as the catalyst deactivated. While catalytic pyrolysis of pinewood showed the largest hydrocarbon yields initially, after several runs the yield difference compared to those from catalytic pyrolysis of different biomass feedstock became negligible.

*Contact: Justinus Satrio, Ph.D. Email: justinus.satrio@villanova.edu