Evaluation of the co-pyrolysis of lignin with plastic polymers by TG-FTIR and Py-GC/MS

Lignin extracted from black liquor was co-pyrolyzed with three kinds of plastic polymers (low density polyethylene (LDPE); polycarbonate (PC); polystyrene (PS)), in order to investigate the effect of plastic polymers on the distribution of pyrolysis products (especially monomeric aromatic compounds). TG-FTIR and Py-GC/MS were employed to understand the thermal behavior and identify the typical products from the pyrolysis of individual samples and their mixtures (mass ratio for the mixture: 1:1). For TG-FTIR analysis, the thermal decomposition behavior of lignin-PC mixture exhibits notable difference between the experimental and estimated results over that of lignin-PS mixture and lignin-LDPE mixture. The apparent activation energy for the main conversion zone of co-pyrolysis of lignin with PC (73.08 kJ/mol) is lowest among those of the lignin-plastic mixtures (180.17 kJ/mol for lignin with LDPE and 179.91 kJ/mol for lignin with PS mixtures), suggesting the strongest interaction between lignin and PC. The H2O produced by the decomposition of lignin at low temperature may promote the hydrolytic reaction of PC and the release of CO2. The production of several aromatic compounds assigned to lignin pyrolysis was suppressed by the addition of PC or LDPE, while the formation of monomer aromatic hydrocarbons was notably promoted during the co-pyrolysis of lignin with PS.