(602u) Comparison of Catalysts for Applications in Biomass Fast Pyrolysis

Thermochemical methods such as pyrolysis combined with catalysis may be used to produce a hydrocarbon-rich liquid fuel from renewable biomass. The objective of this work was to explore the use of microporous, mesoporous and bi-functional catalysts for catalytic fast pyrolysis of biomass.

ZSM-5, SO₄^2- ZrO₂, Al-MSU-S from zeolite beta seeds and sulfated zirconia on mesoporous support 20% SO₄^2- ZrO₂ - MCM-41, were synthesized in MSU laboratories. In the first part of this study, microporous catalysts, ZSM-5 and sulfated zirconia, were compared with mesoporous catalysts Al-MSU-S and meso sulfated zirconia for their potential to upgrade oxygenated pyrolysis products. Catalyst properties such as BET surface area, BJH pore volume and acidity using NH3-TPD were measured. Catalyst preparations for upgrading poplar (DN-34) were examined using analytical pyrolysis connected to a GC/MS. Separate experiments were conducted to analyze C1-C9 volatiles using a GC/FID. The product yield, carbon selectivity and yield of hydrocarbon products was evaluated. Although the mesoporous catalysts in this study had many desirable properties such as high pore volume and high acidity, they showed low selectivity for hydrocarbons when compared with conventional ZSM-5 catalyst. The mesoporous catalysts produced a greater amount of non-condensable gases when compared with the microporous catalysts. The char and coke yields of these catalysts were estimated using a TGA. Significant coke production was observed on all catalysts except ZSM-5.

ZSM-5 catalysts may be synthesized with various silica:alumina ratios (SAR) and the change in aluminum content affects the acidity and the hydrophilicity of the catalyst. ZSM-5 catalysts with five different SAR (23, 30, 50, 80, 280) were obtained and tested for the catalytic pyrolysis reaction with the poplar biomass. The catalyst with the lowest SAR was observed to have the highest acidity and production of hydrocarbon molecules. However, the lowest coke yields were observed with SAR=30. The selectivity for various hydrocarbon molecules varied significantly with change in SAR. Metals provide the Lewis acid functionality on zeolite catalysts and may moderate coke production as well as promote olefin production, thus increasing the activity and on-stream lifetime of the catalyst. Bi-functional ZSM-5 (SAR=23) were prepared by loading various dehydrogenating metals.  The addition of metals to ZSM-5 enabled a significant increase in hydrocarbon production and decrease in coke production.