Accumulation of Inorganic Impurities on HZSM-5 Zeolites during Catalytic Fast Pyrolysis of Switchgrass

Abstract

The fate of inorganic species present in switchgrass during fluidized bed catalytic pyrolysis over HZSM-5 catalysts was studied with emphasis on their accumulation on the catalyst. Five catalytic pyrolysis experiments were performed in two series, reusing the catalyst after each sample. Catalysts were regenerated from deactivation due to carbon deposits via their removal by combustion at regular intervals. The fates of seven inorganic elements were tracked: Ca, Cu, Fe, K, Mg, Na, and P. Potassium accumulated with the HZSM-5 catalyst the fastest while iron was the metal that accumulated most preferentially on the catalysts, with about 42% of the Fe content of the biomass remaining with the HZSM-5. The total amount of these seven elements accumulated on HZSM-5 in a linear fashion during continued use of the same catalyst sample. As the catalyst was exposed to more switchgrass and accumulated more inorganic containments, its effectiveness at deoxygenating the pyrolysis liquids decreased. Selectivity for arom...