Comparison of the pyrolysis behavior of pyrolytic lignin and milled wood lignin by using TG–FTIR analysis

Pyrolytic lignin (PL), the main water-insoluble fraction in bio-oil, has an obvious negative effect on the application of biomass pyrolysis technology. The structures of PL and milled wood lignin (MWL) have been characterized and compared using FTIR, 1H NMR, 13C NMR and GPC. The PL was extracted from bio-oil produced by pyrolysis of a hardwood, lauan, while the MWL was isolated directly from the same lauan. The results show that PL is composed mainly of trimers and tetramers, and its average molecular weight is about one tenth of that of MWL. The proportion of methoxy groups and ether linkages in PL were lower than that in MWL. However, PL had a larger amount of unconjugated CO functional groups and saturated aliphatic structures than MWL. Furthermore, a thermogravimetric (TG) study reveals that PL has poor thermal stability and decomposes over a lower temperature range. The double-Gaussian distributed activation energy model (DG-DAEM) is introduced to analyze the thermal reaction kinetics of PL and MWL. The apparent activation energies of PL and MWL are distributed mainly in the first Gaussian region. The evolution characteristics of typical products from the pyrolysis of PL and MWL are also discussed and compared in detail.