Conversion of lignin into light olefins and aromatics over Fe/ZSM-5 catalytic fast pyrolysis: Significance of Fe contents and temperature

Abstract

The conversion of lignin into light olefins and aromatic compounds via catalytic fast pyrolysis was performed in a fixed bed reactor over a range of Fe-modified ZSM-5 catalysts at different temperatures. More specifically, catalysts containing 0, 1, 3, 6, and 9 wt.% Fe were prepared by an impregnation method, and the resulting catalysts were characterized by XRD, NH3-TPD, H2-TPR and BET analysis. The catalyst structure remained intact upon increasing the Fe loading, although the surface area, pore volume, and number of acidic sites of the catalysts varied, and the total acidity increased upon increasing the Fe loading. The maximum carbon yield of light olefins plus aromatic compounds was 12.8%, and this was obtained with a 3 wt.% Fe loading at 600 °C. This yield decreased upon further increasing the Fe loading and upon increasing the temperature to 700 °C. Moreover, the selectivity of C2H4 was more than 80%, and it was decreased with the Fe loading and increased with temperature increasing. The total acidity had a direct relationship with aromatic production, while light olefins were mainly affected by medium acid sites.