(639d) Low Temperature Hydrogenation of Pyrolytic Lignin over Ru/TiO2 : 2D HSQC and 13 C NMR Study of Reactants and Products

Pyrolysis is a low cost method for converting lignocellulosic biomass into a liquid feedstock, in this case bio-oil. Due to high oxygen content and unsaturated compounds, hydrotreating of bio-oil is essential to produce a usable fuel, though it suffers from high amounts of coke formation causing catalyst deactivation and reactor plugging. Pyrolytic lignin is thought to be a culprit in the coke formation while little is known about the compounds responsible or how to prevent it. Low temperature hydrogenation (25-150 °C) of a mixed maple wood pyrolytic lignin over Ru/TiO₂ catalyst was studied to determine the amount of coke formation on the catalyst surface. HSQC and quantitative ¹³C NMR was used to elucidate changes in carbon functionalities of the products. Coke formed on the catalyst surface (1% carbon yield to coke) even for hydrogenation at 25 °C. The carbon yield to coke increased from 1% to 5% as the hydrogenation temperature increased from 25 to 150 °C. A single-step hydrogenation at 150 °C decreased the aromatic carbon from 65% to 39% while a three-step hydrogenation scheme at 150 °C decreased the aromatic carbon from 65% to 17%. The decrease in the aromatic carbon corresponded with an increase in the aliphatic carbon. Coke formation reduced from a 4.9% carbon yield in the first hydrogenation step to a 1% carbon yield in each of the second and third hydrogenation steps. The pyrolytic lignin was phase separated into a low and high molecular weight fraction and separately hydrogenated at 150 °C. The low and high molecular weight fractions had a 3.9% and 7.7% carbon yields to coke, respectively.