Lignin is the largest renewable source of aromatic chemical building blocks on the planet and has great potential for the production of value-added chemicals.Herein, we describe lignin hydrogenolysis/depolymerization of organosolv poplar lignin (OPL) in ethanol/iso-propanol solvent in the absence of added catalysts. Different EtOH/i-PrOH ratios as well as various reaction conditions were evaluated. OPL depolymerization was more effective in the mixed media than in ethanol or iso-propanol alone. Heating OPL at 270 °C for 4 h in 50:50 (v:v) EtOH/i-PrOH in a closed pressure vessel gave an overall oil yield of 70 wt% of which about 48% consisted of the monomers (E)-4-propenyl syringol and iso-eugenol. Notably, these catalyst-free reactions in ethanol/iso-propanol media show monomer yields comparable to those reported for lignin depolymerization using precious metal catalysts and dihydrogen, which suggests unexpectedly favorable H-donor ability of this mixed alcohol medium.
A physical mixture of Ru/C and Nb2O5 is an effective catalyst for upgrading lignin monomers under low H2 pressure at 250 °C to a clean cut of hydrocarbon liquid fuels.
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