Gas-solid conversion of lignin to carboxylic acids

Conference Dates

May 22-27, 2016


Lignin is the only source of aromatics from lignocellulosic biomass and is a potential alternative to petroleum as a sustainable source of chemicals . Lignin constitutes 15% to 40% of the dry weight of lignocellulose, but because its a complex heterogeneous molecule. Thermo-chemical processes break lignin down to light gases (CO, H2, CH4) and pyrolysis oils characterized by a wide range of compounds, which requires further processing. The challenge is to activate lignin at lower temperatures to reduce the yield of light gases and to target a narrow class of compounds. Catalysts can improve selectivity towards the target molecules at lower temperature but carbonaceous species coke the active sites within seconds and minutes. Here we describe a two stage reactor in which we oxidize and steam crack lignin in the first stage (at heating rate of 5°Cmin−1 up to 550°C) of lignin and catalytically oxidize the effluent in the second stage. We targeted carboxylic acids that have a higher market than biofuel. With a gas feed composition of 10% oxygen and 50% steam all the lignin reacted. In the second stage, vanadium catalyst cleaved the remaining lignin bonds and opened up aromatic rings to make carboxylic acids — mostly C4 acids. In the presence of vanadium pyrophosphate 24% of the lignin formed a condensable product of which 48% was maleic acid 31% C5-C8 aromatics and fumaric ,malonic and gallic acid. Only ∼ 5% of the lignin formed coke.

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