Pyrolysis Characteristics and Reaction Mechanisms of Pine Needles

Pyrolysis has been considered as a promising method to utilize biomass by thermal cracking for energy or feedstock. In order to provide guidance for thermochemical process management of pine needle utilization by pyrolysis, the pyrolysis kinetics and reaction mechanism of one typical pine needle are investigated employing thermogravimetric analysis in nitrogen in the present study. Multi kinetics methods including model-free method and model-fitting method are adopted. Results indicate that one peak and three shoulders occur in the reaction rate curves. The maximum reaction rates decrease with the increasing of heating rates, and the average reaction rate of the whole process is 0.0021 K^-1. The pyrolysis process of pine needles in nitrogen may be divided into four stages in the conversion rate range of 0~0.1, 0.1~0.5, 0.5~0.75, and 0.75~1, which may be mainly resulted by the reaction of the extractives, hemicellulose, cellulose, and lignin, respectively. The reaction mechanisms of stages I, II, and III may be regarded as random nucleation and nuclei growth, but the reaction mechanism of stage IV may be chemical reaction. The average value of activation energy and logarithm of the pre-exponential factor for the whole pyrolysis process is 215.99 kJ mol^-1 and 38.75 min^-1, respectively.