(235d) Catalytic Hydropyrolysis of Milled Lignins Derived from Hardwood, Softwood and Herbaceous Biomass Using Bifunctional Catalysts

Yuan Xue^a, Ashokkumar Sharma^b, Xianglan Bai^a_, Feng Cheng^c, Catherine E. Brewer^c

^a Department of Mechanical Engineering, Iowa State University

^b Bioeconomy Institute, Iowa State University

^cDepartment of Chemical & Material Engineering, New Mexico State University

Lignin is the second most abundant natural polymer after cellulose and accounts for 15-30% of biomass. Lignin is also abundantly produced by paper, pulping industries and biorefineries as a low value by-product. In fact, the phenyl-propane-based lignin polymer can be a potential source of aromatic hydrocarbons. Nevertheless, lignin is also known for its recalcitrant for thermal decomposition and catalytic deoxygenation due to its structural complexity and high char and coke yields. In this work, catalytic hydropyrolysis of lignin and its model compounds was studied using several different types of bifunctional zeolite catalysts at atmospheric pressure. Three milled lignins were derived from red oak (hardwood), loblolly pine (softwood) and corn stover (herbaceous) to represent the natural lignins in different biomass species. Phenol and guaiacol were used to represent lignin-derived monomers. Catalysts tested are HZSM-5, Ni/ZSM-5, MoO₃/ZSM-5, Fe-HBeta, Ru/Fe-HBeta and Pd/Fe-HBeta, respectively. It was found that the hydrogen environment effectively increased the hydrocarbon yields from the lignins compared to the helium environment for all the catalysts. The catalytic coke with dramatically reduced yields and the aromatic hydrocarbons with an increased selectivity for benzene, toluene and xylene, were observed with the modified HZSM-5 catalysts. The model compound study shows that MoO₃/ZSM-5 and Pd/Fe-HBeta effectively hydrodeoxygenate phenolic monomers, whereas Ru/Fe-HBeta and Ni/ZSM-5 exhibit hydrocracking ability.