(264a) Catalytic Conversion of Lignin Fractions of Biomass

Thermochemical conversion of the lignin fractions of biomass produces a variety of substituted monomeric phenols like guaiacol, vanillin, catechol, anisole, benzaldehyde, etc. The refining strategies that we are investigating include deoxygenation (via decarbonylation and hydrogenation/dehydration), as well as transalkylation and alkylation, which result in alkylaromatic compounds with good fuel properties. Here, we describe the study of the conversion of anisole and benzaldehyde, typical components of bio-oil, over an HZSM-5 zeolite at varying space times, temperatures, carrier gas, and water concentration. Bimolecular and unimolecular reactions are proposed to explain the evolution of products observed from the conversion of anisole. The bimolecular reactions include several transalkylation reactions. A pseudo first-order kinetic model based on these bimolecular reactions was found to describe well the observed product distribution as a function of W/F. It is observed that shape selectivity effects prevail over electrophilic substitution and thermodynamic equilibrium effects in the formation of methylanisole isomers. The kinetic analysis indicates that the contribution of unimolecular reactions such as isomerization is much lower than that of bimolecular reactions. The carrier gas composition was found to have a moderate effect on catalyst activity. When hydrogen was used as a carrier, catalyst stability showed a moderate improvement in comparison to the runs under He. However, a remarkable increase in activity was observed upon the addition of water. In the case of benzaldehyde reaction, the catalysts investigated included HZSM-5 and gallium-modified ZSM 5. In the absence of hydrogen, Ga/HZSM-5 catalyzes benzaldehyde decarbonylation to make benzene and CO. The active sites for this reaction are the strong Brønsted acid sites. In the presence of hydrogen, the main product is toluene. It is believed that Ga cationic species generated during exposure to hydrogen promotes hydrogenation / hydrogenolysis to give toluene and water. In the absence of hydrogen, toluene is only observed in transient experiments when the Ga/HZSM-5 catalysts are reduced. The cationic species generated under hydrogen play an important role in the hydrogenation / hydrogenolysis. However, they readily decompose to Ga+ in the absence of hydrogen. The addition of water to the feed modifies the catalytic activity and selectivity of Ga/HZSM-5 catalysts. It generates additional Brønsted acid sites from the reaction of extra-framework Ga with chemisorbed water (GaO(OH)) and with defect hydroxyls of the zeolite framework (GaOHSi). These additional sites enhance the production of benzene but decrease toluene,