Title
Thermal behavior of enzymatic hydrolysis lignin based on TG-FTIR analysis
Authors
XIAOJUN ZHU YUGUO DONG XINYU LU HAN QUE YIMENG ZHANG and XIAOLI GU

Received April 16, 2018
Published Volume 53 Issue 1-2 January-February
Keywords enzymatic hydrolysis lignin, pyrolysis, kinetics, TG-FTIR

Abstract
The thermal decomposition of enzymatic hydrolysis lignin (EHL) was investigated by the thermogravimetric technique (TG/DTG) within the temperature range from room temperature to 920 °C at different heating rates (10, 20, 30, 40 and 50 °C/min). Little differences in the mass losses as a function of the heating rates were observed from TG analysis. It was established that EHL pyrolysis consisted of three main stages: water evaporation (<200 °C), devolatilization of organic volatiles (200-500 °C) and char formation (>500 °C). The evolved gases or volatiles were investigated by Fourier transform infrared spectrometry (FTIR), coupled to a thermo-balance, at the heating rate of 20 °C/min, for identifying the gaseous or volatile species and their evolution during EHL thermal degradation. The temperatures corresponding to the maximum evolution rate of H2O, CO2, CO, CH4 and C2H4, as well as the volatile fragments originating from the breaking of covalent chemical bonds, such as C-C, C=O and C-O-C groups, were in agreement with the temperature corresponding to the maximum mass loss rate – of about 385~400 °C. The maximum release rates of H2O, CO2, CO, CH4 and C2H4 took place at 387, 385, 392, 392 and 389 °C, respectively. While the maximum rates of evolution of both alkyl groups and oxygen-containing compounds occurred at about 400 °C. The kinetic processing of non-isothermal TG/DTG data was performed by the model-free methods proposed by Flynn, Wall, Ozawa (known as FWO method) and Kissing, Akahira and Sunose (KAS method). The average activation energies calculated by the FWO and KAS methods were 191.2 kJ mol-1 and 191.0 kJ mol-1, respectively. Experimental results showed that the values of kinetic parameters obtained by both methods were analogous and thus these methods could be successfully applied to understand the complex degradation mechanism of EHL. Also, such an approach is helpful in achieving a better understanding of the devolatilization process of different types of biomass.