Characterization of Coke Deposition in the Catalytic Fast Pyrolysis of Biomass Derivates

Abstract

Coke deposition on the zeolite catalysts in the conversion of furan (a main intermediate of biomass fast pyrolysis) is of serious concern for catalyst deactivation and product distribution. It is important to find out the nature and composition of coke on the spent ZSM-5 catalyst to study the coke-depositing behaviors. In this work, spent ZSM-5 catalysts obtained from furan catalytic conversion for chemicals at different reaction times and pyrolysis temperatures were characterized. The spent catalysts were first treated with hydrofluoric acid, and then the organics were extracted with CH2Cl2. The characterization of the origin coke and the treated insoluble coke were analyzed by the combination of some analytical techniques, including Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The extracted organics were analyzed by HPLC to determine the chemical composition of the soluble coke. The results show that coke formation mainly involves condensation and rearrangement steps at a low reaction temperature (<200 °C). Coke components are polyaromatics, which formed by hydrogen transfer in addition to condensation and rearrangement steps at high temperatures (>200 °C). In the FTIR analysis, high aromaticity of coke species was obtained with increasing temperature, which indicates that the pyrolysis temperature plays a dominant role in the coke formation. TGA reveals that high temperature favors the formation of hard coke. The results enhance the understanding of coke formation and adjusting mechanism in biomass catalytic pyrolysis process.