Effectiveness of pretreatment on kinetic and thermodynamic parameters during the thermal degradation of coffee pulp biowaste material

Abstract

This work aimed to elucidate the influence of pretreatment by a steam explosion in an alkaline condition of coffee pulps (CP) waste material during the thermal degradation on the kinetic, physicochemical, and thermodynamic parameters. Characterizations such as thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, Fourier transform infrared, and Raman spectroscopies were performed on untreated and treated materials (CP@B). Thermal degradations occurred in the 25–800 °C temperature range at heating rates of 10, 15, and 20 K/min in a nitrogen atmosphere. Kinetic and thermodynamic parameters were evaluated using Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink models. The most probable mechanism for the thermal degradation of both materials was determined using the Coats–Redfern model. The activation energy was estimated between 66.58 and 69.84 kJ/mol (FWO), 57.31 and 67.76 kJ/mol (KAS), and 58.02 and 68.56 kJ/mol (Starink) for untreated and treated material, respectively. The Gibbs free energy obtained was 146.95 and 153.17 kJ/mol for the FWO model, 135.79 and 152.18 kJ/mol using the KAS model, and 134.6 and 142.08 for the Starink model corresponding to untreated and treated coffee pulps, respectively. Through thermal analysis, this work showed the bioenergetic potential of coffee pulps subjected to pretreatment by steam explosion in an alkaline condition for the production of second-generation biofuel.