THERMAL BEHAVIOR OF ENZYMATIC HYDROLYSIS LIGNIN BASED ON TG-FTIR ANALYSIS

摘要

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 degrees C at different heating rates (10, 20, 30, 40 and 50 degrees 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 degrees C), devolatilization of organic volatiles (200-500 degrees C) and char formation (> 500 degrees 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 degrees 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 similar to 400 degrees C. The maximum release rates of H2O, CO2, CO, CH4 and C2H4 took place at 387, 385, 392, 392 and 389 degrees C, respectively. While the maximum rates of evolution of both alkyl groups and oxygen-containing compounds occurred at about 400 degrees 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.