Utilisation of a waste biomass, walnut shells, to produce bio-products via pyrolysis: investigation using ISO-conversional and neural network methods

Abstract

This study was conducted to investigate the kinetic, thermodynamics and the reaction mechanism of pyrolysis of native walnut shells of Kashmir, India. Thermal degradation experiments were performed at three heating rates of 10, 25, and 50 K min−1 to calculate the kinetic and thermodynamic parameters, using iso-conversional Kissinger-Akahira-Sunrose (KAS) and Ozawa-Flynn-Wall (OFW) models. The reaction mechanism was predicted by applying Coats-Redfern (CR) method. Moreover, an artificial neural network (ANN) simulation was used to obtain best fit points after comparing the experimental data with the predicted data points. Average activation energy was calculated from the thermogravimetric study was found to be in the range of 146.03–148.89 kJ mol−1, while the Gibbs free energy (ΔG) value for walnut shells was found to be ~180 kJ mol−1. The most appropriate degradation mechanism was found to be based on diffusion and chemical reaction for the temperature range under study. The broad characterisation along with the values of thermodynamic parameters show that the walnut shells can be used as an economical as well as eco-friendly bio-energy feed-stock for pyrolysis. The reaction mechanism of thermal degradation of walnut shells was found to be consisting of two broader zones based on conversion achieved, zone I (0.2 ≤ α ≤ 0.4) and zone II (0.4 ≤ α ≤ 0.8).