Pyrolysis of boron-crosslinked lignin: Influence on lignin softening and product properties

In this study, ammonium borate was used as an additive to inhibit lignin softening during the pyrolysis process, and the influence on the pyrolysis process and product characteristics were investigated with potential mechanism being explored in depth. Results showed that with boron addition, glassy transition temperature and thermal stability of lignin increased, and the yield of gas and liquid decreased, while the content of CO, CO₂ and H₂ increased. Simultaneously, liquid oil showed higher content of simple phenols, especially the diphenols which the maximum reached 80% with 3%BN at 650 ℃, while the yield of heavy components (300 ∼ 400 Da) decreased. With regard to B-doped char, oxygenic groups and specific surface area (509 m²/g of 5%BN at 650 ℃) increased greatly. Increasing temperature promoted the transformation of B doping form from BC₂O to BCO₂.