Autothermal pyrolysis of lignocellulosic biomass: Experimental, kinetic, and thermodynamic studies

Abstract

Autothermal pyrolysis that generates in situ heat is a promising way to convert lignocellulosic biomass into value-added products. Autothermal pyrolysis of pinewood under different oxygen concentrations (i.e., 3 %, 5 %, and 10 % O2) was performed in this work. The results showed oxygen addition significantly decreased the selectivity of anhydrosugars in bio-oil by 41.90% at most. Micropores formation in the char was enhanced in the autothermal pyrolysis, and the BET surface area of char obtained under 10 % O2 was 21.9045 m2·g−1. Fraser-Suzuki function was adopted to deconvolute the biomass autothermal pyrolysis process into four pseudo-reactions; namely three degradation reactions of hemicellulose, cellulose, and lignin and a combustion reaction of char residues. The activation energies of three pseudo-degradation reactions decreased after oxygen was introduced, whereas the activation energy of pseudo-combustion reaction of char increased from 69.08 to 88.34–127.47–163.13 kJ·mol−1 as oxygen content increased from 3 % to 10 %. Three major thermodynamic parameters of activation for each pseudo-reaction were also calculated. ΔS‡ results indicated that three pseudo-degradation reactions at the transition state became more ordered at higher oxygen concentration, whereas pseudo-combustion of char showed an opposite trend. The results obtained from this study provide systematic and precise fundamental information for biomass autothermal pyrolysis scale-up.