Batch microreactor studies of lignin and lignin model compound depolymerization by bases in alcohol solvents

The depolymerization of Kraft- and organosolv-derived lignins by KOH in sup ercritical methanol or ethanol was studied in rapidly heated batch microrea ctors. High conversions were realized, with only 78 ether insoluble materia l remaining after treating organosolv lignin in KOH/ethanol at 290 degrees C. The conversion was rapid, reaching the maximum value within 10-15 min. F urther studies with KOH, NaOH, CsOH, LiOH, Ca(OH)(2), and Na2CO3 indicate t hat strong bases give superior conversion, and that combinations of bases c an give both positive and negative synergistic effects. An excess of base r elative to lignin monomer units was required for maximum conversion. Model compound studies confirm the dominant depolymerization route is the solvoly sis of ether linkages. Ethanol solvent is also partially converted to aceti c acid, higher alcohols, and other products in addition to alkylating pheno lic rings. The formation of acidic products may account for the excess base requirement. Published by Elsevier Science Ltd.