Pyrolysis characteristics and kinetics of lignin: effect of starting lignins

To elucidate the impact of starting lignins on pyrolysis characteristics and kinetics of lignin, seven lignins were pyrolyzed on a thermogravimetric (TG) analyzer. Results show that hardwood lignins showed derivative thermogravimetric (DTG) curves with one weight loss peak, softwood lignin showed a curve with two weight loss peaks, while grass lignins showed curves with a main weight loss peak and a shoulder peak. The average apparent activation energy (Ea) obtained with Starink model-free method varied greatly across the lignins. Prepared under mild conditions, the Ea values followed the order as grass lignin > hardwood lignin > softwood lignin. The most probable mechanism functions (MPMF) determined by Coats-Redfern model-fitting method also depended upon the lignins. This work shows that the slow pyrolysis behavior of lignin and the kinetic parameters are tightly related to its structure which depended greatly upon the biomass sources and isolation methods. More weak linkage structures, like β − O − 4 linkage, ferulates, and p-coumarates, could lead to the lower activation energy.