Mechanism on microwave-assisted acidic solvolysis of black-liquor lignin

•Microwave-assisted degradation of black-liquor lignin with formic acid was studied.•Bio-oil 1 and bio-oil 2 were respectively identified by GC–MS and MALDI-TOF MS, and solid residue by GPC and FTIR.•A possible mechanism was proposed for the microwave-assisted acidic solvolysis of lignin. Microwave-assisted degradation of black-liquor lignin with formic acid was studied, concerning the product yield and distribution of phenolic compounds against reaction temperature (110–180°C) and reaction time (5–90min). The liquid product consisting of bio-oil 1 and bio-oil 2, achieved the maxima yield of 64.08% at 160°C and 30min (bio-oil 1: 9.69% and bio-oil 2: 54.39%). The chemical information of bio-oil 1 and bio-oil 2 were respectively identified by means of Gas Chromatography–Mass Spectrometer (GC–MS) and Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), while the solid residue was analyzed by Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). A possible mechanism was proposed for the microwave-assisted acidic solvolysis of lignin, specifying the kinetic relationship among the primary cracking of lignin, repolymerization of the oligomers and formation of solid residue.