Kinetics of dielectric‐loss microwave degradation of polymers: Lignin

Abstract

Abstract The rate of product formation as well as detailed product composition were measured in the rapid pyrolysis of a 1.3‐cm cylindrical pellet of lignin, a major component of biomass. Volume heating by dielectric‐loss microwave heating resulted in rapid weight loss with an apparent rate coefficient of 1–5 min −1 . Char yield was surprisingly low (33%) owing to the rapid heating rate and high temperature of the pellet. Total gas yield was 38%, of which 12% were simple hydrocarbons and H 2 (both weight percent, of original lignin). Product composition showed extensive secondary reaction at high temperatures evidenced by the significant yields of C 2 H 2 ,H 2 , and condensed aromatics as well as the typical lignin cracking products such as phenols. Poor coupling of microwave energy to lignin required large power settings in order to initiate reaction. Once initiated, the reaction rate was difficult to control because of the exothermic nature of the reactions. Additives of a suitable composition to increase coupling may be a possible solution to this problem and may result in more favorable economics.