Pyrolysis kinetics and activation thermodynamic parameters of exhausted coffee residue and coffee husk using thermogravimetric analysis

Abstract

Exhausted coffee residue (ECR) and coffee husk (CH) are potential feedstock for energy production through thermochemical and biochemical conversion processes. Kinetic study of ECR and CH is essential for the design and optimization of different thermochemical conversion processes. In this study, four different iso‐conversional methods were employed in the estimation of the activation energy (EA) and pre‐exponential factor (A). The methods used includes Flynn‐Wall‐Ozawa (FWO), Kissinger‐Akahira‐Sunose (KAS), Kissinger’s method, and the Friedman method. Data from the thermogravimetric/derivative thermogravimetric analysis (TGA/DTG) at varying heating rates of 5‐20°C/min in an inert environment were used in this study. It was observed that the heating rate influences the pyrolysis parameters such as peak temperature, maximum degradation rate and initial decomposition temperature. The activation energy for ECR using the FWO method was in the range of 62.3‐102.4 kJ · mol−1. Likewise, the KAS and Friedman methods yielded activation energy between 51.3‐93.3 kJ · mol−1 and 10.6‐122.7 kJ · mol−1, respectively. In addition, the activation energy calculated for CH using FWO, KAS, and Friedman methods were shown to range from 39.1‐140.6 kJ · mol−1, 27.7‐131.6 kJ · mol−1, and 24.9‐111.2 kJ · mol−1, respectively.