Base-catalyzed depolymerization of residual lignin-enriched biomass from biochemical conversion processes

Lignin is a heterogeneous, alkyl-aromatic polymer found in plant cell walls which, given effective depolymerization and upgrading strategies, could eventually serve as a feedstock for the production of hydrocarbon fuels and chemicals. However, lignin depolymerization to upgradable intermediates remains challenging in a process context. Base catalyzed depolymerization (BCD) of lignin using sodium hydroxide as well as other basic media has been shown to be a reasonably effective depolymerization strategy when using isolated lignins. To gain more insight into using BCD in lignin-rich, process relevant feedstocks, here residual biomass from typical biochemical conversion processes, namely the remaining substrates after either dilute-acid or disk refining pretreatment of corn stover, both followed by enzymatic hydrolysis were depolymerized in a batch reactor with 10 wt% solid loading in 2-4 wt% NaOH at 270-330°C for 40 min. Accurate mass balances of obtained products (aqueous soluble fraction, insoluble solid residue and gas) were measured, and characterization of each fraction was performed using gel-permeation chromatography, NMR, and GC-MS, which when taken together suggest that a significant fraction (45-78%) of the starting lignin-rich material was depolymerized to small molecular weight, soluble species. Overall, this study demonstrates that BCD of residual, lignin-rich biomass after a conventional biochemical conversion process can be depolymerized in sodium hydroxide to produce significant yields of small molecular weight aromatics that potentially can be upgraded to fuels or chemicals.