Valorizing Biorefinery Lignins Using Fast Pyrolysis and Electrocatalytic Upgrading

Pretreatments such as extractive ammonia processing (EAP) create a lignin co-product in addition to cellulose and hemicellulose, which are fermented to ethanol in biorefineries.  As lignin comprises up to 30 wt.% of biomass and 40% of biomass’ energy, an opportunity exists for creating valuable products.  As a means to partially depolymerize lignin, biomass fast pyrolysis (BFP), uses heat (400-600°C) without oxygen to create bio-oil, biochar and combustible gas, where the major product, bio-oil, comprises 70 wt.% of the total product mass.  However, bio-oil is highly oxygenated, corrosive, low in energy content, chemically complex, and chemically reactive, making it unstable during storage and incompatible with carbon steel construction materials.  As a means of improving bio-oil properties, electrocatalytic hydrogenation (ECH) is employed to chemically reduce and deoxygenate reactive compounds.  In this study, lignin model compounds representative of bio-oil components were subjected to ECH under mild conditions (80°C and 1 atm) using ruthenium on activated carbon (Ru/ACC) as a catalytic cathode.  To date, model monomers (guaiacol, syringol, syringaldehyde, vanillin, p-cresol, creosol, eugenol, etc.) have been reduced to simpler compounds such as cyclohexanol and phenol, which have increased heating values when compared to the starting substrates. Additionally, model dimers such as 4-phenoxyphenol have been cleaved and chemically reduced to cyclohexanol and phenol.  Such an approach valorizes lignin into molecules with increased fuel value and material precursors.