Impacts of temperature on evolution of char structure during pyrolysis of lignin

This study investigated the pyrolysis of lignin pyrolysis in a temperature region from 200 to 800 degrees C, aiming to understand influence of pyrolysis temperature on evolution of structures of the resulting char. The results showed that fusion of the ring structure initiated at 200 degrees C, where the C/H ratio in the char was equal to that in naphthalene (two fused rings). The C/H ratio in the char obtained at 350 degrees C corresponded to that in pyrene (four fused rings), while the char produced at 550 degrees C was equivalent to 20 fused benzene rings in terms of C/H ratio. The increasing pyrolysis temperature also shifted the oxygen-containing functionalities such as the carbonyl, esters, ketones in the bio-oil to the ether functionality that had a higher thermal stability. The DRIFTS study of pyrolysis of lignin showed that drastic changes of the functionalities and the internal structure of the char occurred in a narrow temperature region from 520 to 530 degrees C. The carbonyl functionality and the aliphatic structure were eliminated, and new conjugated pi-bond systems formed. (C) 2019 Elsevier B.V. All rights reserved.