Lignin depolymerization to aromatic monomers and oligomers in isopropanol assisted by microwave heating

Degradation of lignin to aromatic compounds in isopropanol was investigated under the mild microwave-assisted heating. The highest yield of liquid product was 45.35% achieved at 120 °C with the reaction time of 30 min, together with the yield of char as 38.65% and 14.73% residual lignin. The aromatic compounds in liquid product (both monomers and oligomers) were identified by Gas Chromatography-Mass Spectrometry and Matrix-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry. Ethanone, 1-(4-hydroxy-3-methoxyphenyl) (G2) and ethanone, 1-(4-hydroxy-3, 5-dimethoxy phenyl) (S2) were evidenced as the prominent aromatic monomers in the liquid product. Fragments from the aromatic oligomers detected by MALDI-TOF MS were mainly located from 248 m/z to 496 m/z. The chemical structure of the specific oligomers with the molecular weight of 274 m/z, 290 m/z, 316 m/z, 332 m/z, 362 m/z, 406 m/z, 454 m/z was proposed to understand the possible relationship with the formation of prominent monomers.