Non‐Isothermal Kinetics of Phoenix Dactylifera L. Date Palm Seeds Pyrolysis Using Model Fitting and Iso‐Conversional Model Free Methods

Abstract

AbstractIn this paper, Phoenix dactylifera L. date palm seeds (RDS) were first characterized from a physicochemical point of view, in particular the proximate and ultimate composition, XRD, and SEM–EDX analyses. Based on findings RDS contains 77.4 % of total carbohydrates, 12.8 % of lignin, and a higher heating value (HHV) of 15.88 MJ kg−1. Immuno‐labeling intensity (OD) of non‐cellulosic RDS fraction was also determined thanks to the ELISA technique after the dissolution of polysaccharides in ionic liquid showing the presence of mannans and xyloglucans and the absence of arabinans in date seeds, a significant amount of homogalacturonans were also detected. The thermal decomposition and kinetic of date palm seeds (RDS) using TGA‐DTG, and DSC measurements were then investigated. The RDS samples were heated in the temperature ranges 25–600 °C at 5, 10, 15, and 20 °C/min. The decomposition of hemicelluloses, cellulose, and lignin, active pyrolysis of RDS, was held in a range of temperature 160–450 °C. The kinetic parameters such as activation energy (Ea) and pre‐exponential factor (A) were determined for two degradation steps by using iso‐conversional model‐free methods. The Ea and pre‐exponential factor obtained by the Kissinger method are 212 kJ mol−1 and 7.8×1019 min−1 for the first decomposition interval (I1) and 172 kJ mol−1 and 5.96×1013 min−1 for the second decomposition interval I2. The same average parameters calculated by model‐free methods are 126–156 kJ mol−1 and 180–213 kJ mol−1 and 3.36×1014 and 7.07×1017 min−1 respectively for the first and second intervals of thermal decomposition. Indicating that activation energy decreases in the final stages of the process and that the energy required for hemicelluloses degradation is lower than that of cellulose. The most probable reaction functions have been determined for these two stages, by Coats‐Redfern (CR) and Criado methods, leading to considerably improved calculation performance over the entire conversion range. The pyrolysis reaction models of RDS are described by reaction, second order F2 for cellulose and hemicelluloses. With the Arrhenius parameters obtained from the fitting model of CR, we attempt to reconstruct the temperature‐dependent mass conversion curves and have resulted in generally acceptable results. Based on the Arrhenius parameter values, obtained by the Kissinger equation, the changes in entropy, enthalpy, Gibbs free energy, and lifetime predictions have been estimated for the thermal degradation processes of RDS.