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, 31 P and 13 C 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.