Slow pyrolysis kinetics of apricots stones by thermogravimetric analysis

Thermal degradation and kinetics for apricots stones have been evaluated under dynamic conditions through a Thermogravimetric Analysis (TGA). Slow pyrolysis processes were carried out in presence of nitrogen atmosphere until a temperature of 600 °C was reached. The effect of different heating rate (10 and 20 °C/min) was evaluated. The DTGA (Derivative Thermogravimetric Analysis) plot for the apricot stones clearly shows that the chosen biomass begins to degrade at 200 °C. Moreover, it exhibits three peaks. The first peak of DTGA (100 °C) was due to moisture evaporation, the second peak (284-303°C) was associated with hemicellulose pyrolysis whereas the third peak (348-356°C) was associated to cellulose pyrolysis whose degradation begins at higher temperatures. The biomass mainly volatilized between 200 °C and 400 °C. The total mass loss was of about 58-60% with respect to the initial weight. Mass loss and its rate were strongly affected by the heating rate. Indeed, it was found that an increase in heating rate results in a shift of thermograms to higher temperatures and above all in very different DTGA peaks. An isoconversional differential method, the Friedman method, was used for the determination of the slow pyrolysis energy activation. In the 10-22% conversion range, mainly corresponding to hemicellulose degradation, the apricot stones activation energy has a value of about 110 kJ/mol for both the heating rate evaluated. In the 35-44% conversion range, mainly corresponding to cellulose degradation, the activation energy has a value of 116 kJ/mol and 76 kJ/mol respectively for the heating rate of 10 and 20 °C/min