Autocatalytic kinetic model for thermogravimetric analysis and composition estimation of biomass and polymeric fractions

Abstract

A comprehensive kinetic model of slow pyrolysis of biomass during a thermogravimetric analysis (TGA) has been developed, including the simulation of variable heating rates, composition estimation and structural analysis of biomass. Biomass was assumed as a matrix of three solid global components (hemicellulose, cellulose and lignin) in which water and oil can be also present.

Kinetics were based on an auto-catalytic model because it can simulate the degradation in cellulosic materials, as the cleavage of the biopolymers produce oligomers that accelerate the further depolymerisation. The reaction pathway followed the Waterloo’s mechanism, which stablishes that all solid compounds decompose into volatiles and charcoal. This mechanism was completed by the vapourization of water and oil, and assuming that the formed charcoal can break into volatiles by a slow reaction. The set was solved by the 8th Runge–Kutta’s method and validated by the Simplex Nelder–Mead and Broyden–Fletcher–Goldfarb–Shanno’s methods. The development of this model has a high interest because it can help to understand how the conversion from biomass to biochemicals takes place.