Structural analysis of lignin residue from black liquor and its thermal performance in thermogravimetric-Fourier transform infrared spectroscopy

Structural characteristics of benzene-ethanol-extracted lignin (BEL) and acetone-extracted lignin (AL) precipitated from black liquor were identified by elemental analysis, FOR, C-13 NMR, and H-1 NMR, while the thermal behaviors were examined with thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR). The frequency of beta-O-4 bonds per 100 C9 monomeric units was 28 and 17 for BEL and AL Two-stage pyrolysis processes were observed for the two lignins. The mass loss rate of the initial solvent evolution stage (110-180 degrees C) of BEL was greater than that of AL The two lignins presented slightly different mass loss curves and evolution profiles of gases in the main pyrolysis stage (280-500 degrees C). A global kinetic model was proposed for lignin pyrolysis and activation energies of 39.5 and 38.8 kJ/mol was obtained for BEL and AL The results enhance understanding of lignin pyrolysis and facilitate commercial utilization of black-liquor lignin. (C) 2012 Elsevier Ltd. All rights reserved.