Thermal behavior and kinetic analysis of torrefied coconut fiber pyrolysis

Abstract

The present work discusses the effect of mild torrefaction on coconut fiber pyrolysis kinetics. Firstly, it was evaluated by statistical experimental design (473–523 K, 15–45 min) in the fixed bed reactor. The results showed a reduction of volatile matter content and atomic ratios of hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C), and an increase in heating values. Secondly, the thermal decomposition was quantified by thermogravimetric analysis, in which the hemicellulose fraction was partially removed after torrefaction. Thirdly, the activation energy was determined by two isoconversional methods (single-step reaction) obtaining a variation from 184 to 238 kJ/mol. Fourthly, the kinetics of thermal decomposition of the torrefied sample was well-described (average deviation <3%) by three independent parallel reactions scheme assuming first-order reactions with activation energies of 99.5, 203.2 and 45.4 kJ/mol for hemicellulose, cellulose, and lignin, respectively. Finally, these kinetic parameters remained constant at different heating rates, providing more reliable information, which can be used to model the pyrolysis of coconut fiber in future works.