Hydropyrolysis of Lignin Using Pd/HZSM-5

Abstract

The aim of this work was to study the formation of cycloalkanes from hydropyrolysis of lignin with HZSM-5 and Pd/HZSM-5 catalysts. Cycloalkanes are high-octane-rating molecules and are a major component of jet fuels. We observed that palladium supported on HZSM-5 catalyzed hydrogenation and deoxygenation reactions that converted phenolic compounds into aromatic hydrocarbons and cycloalkanes. This in situ study analyzed the effect of the catalyst-to-lignin ratio, H2 partial pressure, and temperature on the yields of hydrocarbons with HZSM-5 and 1 wt % Pd/HZSM-5. Pd/HZSM-5 produced 44% more aromatic hydrocarbons than HZSM-5 at a catalyst-to-lignin ratio of 20:1, 650 °C, and a constant H2 partial pressure of 1.7 MPa. The presence of palladium led to a significant difference in yields only at 1.7 MPa H2 partial pressure. In addition, the hydropyrolysis temperature played a substantial role in the equilibrium conversion of hydrogenation reactions that led to cycloalkanes directly from lignin. In an attempt to bypass the thermal limitations of the in situ process, we performed ex situ catalytic upgrading experiments and also observed formation of cycloalkanes at a hydropyrolysis temperature of 650 °C, packed bed temperature of 300 °C, and H2 partial pressure of 1.7 MPa.