Pyrolysis kinetics and thermal degradation characteristics of coffee, date seed, and prickly pear wastes and their blends

Abstract

This study's objective was to emphasize the renewable lignocellulosic biomasses' energy potential by thermally describing them. The TG/DTG/DTA procedures were used to examine the thermal pyrolysis behavior of coffee wastes (CW), date seeds (DSM), prickly pears (PP), and two blends (50%CW/50%DSM and 33.3%CW/33.3%DSM/33.3%PP by weight), and their physico-chemical compositions were identified and assessed. The activation energy (E) of all tested samples was predicted using iso-conversional models like Friedman (FR), Starink (ST), Kissinger-Akahira-Sunose (KAS), and Ozawa-Flynn-Wall (OFW), and the frequency factor (A) was calculated based on the acquired (E) values utilizing the chemical reaction mechanisms (C1–C8). SEM, EDX, and FTIR techniques were used to examine the microstructure, mineralogy, and functional group present in the studied samples. Every DTG profile displayed a rightward shift when the heating rate (β) rose to higher temperatures. The difference in the average activation energy (Eav) values between the ST, OFW, and KAS models, except for the blend (1), does not surpass 5 kJ/mole. Increases in the (β) value, particularly for blends, were significantly correlated with increases in the maximum pyrolysis rate (−RP), pyrolysis index (CPI), pyrolysis stability index (RW), and volatile release index (Ddev). The ΔGav discrepancies between the results from all kinetic models for all samples varied from 1 to 7 kJ/mole. A little potential energy barrier was noticed when comparing the (Eav) to the average enthalpy (ΔHav).