INVESTIGATION OF OLIVE STONES PYROLYSIS VIA COUPLED THERMOGRAVIMETRIC ANALYSIS-MASS SPECTROMETRY: THERMAL BEHAVIOR AND KINETIC PARAMETERS

Abstract

The pyrolysis of olive stones was investigated by thermogravimetric analysis-mass spectrometry in nitrogen atmosphere under non-isothermal conditions, at heating rates of 5, 10, 20, and 30 °C/min. According to gas evolution analysis, the thermal degradation of olive stones under inert atmosphere can be divided into four stages. There was only dehydration in the first stage (<200 °C). Most of gas products (CO2, CO, CH4, C2H6 and H2O) were evolved in the second stage in the temperature range 210-407 °C, simultaneously with main mass degradation. Only H2 was produced in the fourth stage at high temperatures (>550 °C). Thermogravimetric analysis results have been utilized to determine kinetic parameters by using a composite procedure involving the iso-conversional method (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose) and the master-plots method. The activation energy values estimated by the Ozawa-Flynn-Wall and the Kissinger-Akahira-Sunose methods are very close, with values of 229.20 kJ/mol and 232.55 kJ/mol, respectively. The master-plots method shows that the most probable reaction mechanism was described by an order n (On) model. The frequency factor was estimated to be A = 5.6x1021 min-1, the kinetic exponent was n = 6.2, and the reaction model function was f(α) = (1-α)6.2.