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

Authors: 
McClelland, D. J., University of Wisconsin-Madison
Chen, W., University of Wisconsin-Madison
Azarpira, A., Great Lakes Bioenergy Center, University of Wisconsin
Ralph, J., University of Wisconsin-Madison
Luo, Z., Zhejiang University
Huber, G. W., University of Wisconsin-Madison
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.