Thermochemical decomposition of coffee ground residues by TG-MS: a kinetic study

A thermogravimetric analyser coupled to a mass spectrometer, for evolved gas analysis, were employed to perform pyrolysis tests at heating rates (5–100 °C/min) and at maximum temperature of 500 °C to determine kinetic parameters of thermochemical decomposition of the biopolymers comprising coffee ground residues. During the pyrolysis process, the maximum decomposition rate of each biomass component increased linearly with the heating rate used. The slope increased with the biopolymer reactivity in the following sequence: hemicellulose > celluose > lignin. Accordingly, kinetic parameters for any of these individual biopolymers in CGR were estimated using the model-free isoconversional dynamic methods Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) models. The average value for the apparent activation energy of the individual biopolymers (hemicellulose, cellulose and lignin) in CGR calculated by KAS and FWO methods were estimated as 214, 241 and 266 kJ/mol, respectively; whilst for the CGR as a whole it was 242 kJ/mol. The two model-free isoconversional dynamic methods have been shown to be useful tools for assessment of biomass pyrolysis kinetic parameters, as they can provide Ea values for use in reactor design models.