Detailed compositional analysis and structural investigation of a bio-oil from microwave pyrolysis of kraft lignin

This work investigates composition and structure of a bio-oil produced form microwave pyrolysis of kraft lignin at different conditions. The studied variables were content of microwave-absorber (20–40 wt%) and nominal setting power (1.5–2.7 kW). The measured temperatures after applying the selected conditions for 800 s were 900, 980, 1065, 1150, and 1240 K. The obtained yields of the aqueous phase, oil phase, non-condensable gas, and solid were 17–21%, 15–20%, 21–27%, and 32–40%, respectively. To investigate the extracted chemicals quantitatively and qualitatively, GC–MS and GC–FID were performed on the liquid samples. In addition, 31P and 13C NMR spectroscopy were implemented to provide detailed structure information for the whole oil phase and the raw material. Furthermore, different degradation pathways were suggested to represent the thermal-decomposition of lignin bonds.