Effect of formation behavior of hydrocarbons and solid component from cellulose on catalytic transfer hydrogenation in straight-chain aliphatic hydrocarbon solvent

Hydrogen transfer using a hydrogen donor solvent is promising for converting cellulose to liquid fuel. Alcohol and cyclic compounds are used as a hydrogen donor solvent, but the solvent affects the properties of liquid fuel. Therefore, the cellulose-derived liquid fuel and the solvent need to be separated. We focus on a straight-chain aliphatic hydrocarbon as a hydrogen source and solvent. Hydrogen transfer is expected by using palladium on activated catalyst (Pd/C) in combination with a solvent because palladium can dehydrogenate alkanes and is used as a hydrogenation metal. After the reaction, straight-chain aliphatic hydrocarbons remain in the cellulose-derived liquid fuel because they are similar to transportation fuel. Our previous study has reported that cellulose is converted into hydrocarbons by liquefaction using hexadecane containing Pd/C. However, the factors for deriving the optimum reaction conditions are unclear, such as the conversion route of cellulose to hydrocarbon and the formation mechanism of a solid component. In this study, we investigate the mechanism of the conversion of cellulose. The results indicate that the cellulose-derived oxygenates absorb on cellulose surface and form a solid component. In contrast, when Pd/C was added to tetradecane solvent, the oxygenates are hydrogenated to solvent-soluble compounds, resulting in suppressing the formation of solid components. The solvent-soluble compounds are deoxygenated to ketones, and then, the compounds changed to cyclopentanones and cyclohexanones which are the number of carbons > 6 at 330 °C because aldol condensation with the ketones occurs. Subsequently, the ketones are deoxygenated to hydrocarbons containing C10–C20 at 350 °C.