Structure and pyrolysis characteristics of enzymatic/mild acidolysis lignin isolated from palm kernel shell

Firstly, lignin of palm kernel shell (PKS) and wheat straw (WS) were isolated by enzymatic/mild acidolysis method (EMAL). Then the functional groups and thermal decomposition characteristics of the two EMALs were analyzed with Fourier transform infrared spectroscopy (FT-IR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and TG-FTIR. At last, the Ozawa-Flynn-Wall method was used to calculate the activation energy of pyrolysis of the two EMALs. FT-IR result show that both PKS-EMAL and WS-EMAL are Type HGS. Phenols, acids, few of alcohols, aldehydes and ketones are detected in volatile products from 500℃ pyrolysis of the two EMALs. Meanwhile, H-type, G-type and S-type phenols with proportions of 47.61%, 25.64% and 17.18% are obtained in phenolic products from PKS-EMAL pyrolysis; while they are 23.66%, 51.90% and 15.50%, respectively, in phenolic products of WS-EMAL. During 200-380℃, the main weight loss rate of PKS-EMAL pyrolysis is 50.80%/min, which is obviously lower than that (78.63%/min) of WS-EMAL. A shoulder peak of 27.40%/min at 265℃ is also observed in PKS-EMAL pyrolysis, which is closely related to release of H-derivatives during PKS-EMAL pyrolysis. The activation energy (127.92 kJ/mol) of PKS-EMAL pyrolysis at a conversion of 20% reduced by the exothermic effect corresponding torelease of H-derivatives, which was the main reason that the average activation energy (152.32 kJ/mol) of PKS-EMAL pyrolysis (20%-80%) was lower than that (161.75 kJ/mol) for WS-EMAL pyrolysis.