Kinetics of Oxidation of Tobacco Char

Abstract

Abstract In this paper, thermal analyses (thermogravimetry, TG: derivative thermogravimetry, DTG: differential scanning calorimetry, DSC) of the tobacco char left after pyrolysis of tobacco shreds were carried out in a nitrogen atmosphere containing given amounts of oxygen under a linear heating or an isothermal condition. The principal object of the present work is to obtain apparent kinetic parameters useful in predicting the overall rate of the tobacco char - oxygen reaction. The TG-DTG-DSC curves obtained under linear heating conditions showed that the oxidation process of the tobacco char apparently consisted of two main steps ( I and II), which were independent of each other. Assuming that a uniform reaction model based on reaction rate - determined processes could be applied to the tobacco char - oxygen reactions in both steps, the oxidation rates for both steps were determined. The results showed that the oxidation rates of both steps could be expressed as: The values of activation energies, E, and pre-exponential factors, Z, for the oxidation reactions in steps I and II were found to be 19-21, 33-40 kcal/mol and 5.9 × 105-5.7x 106, 5.5 × 109 4.5 × 1011/ min atm1/2, respectively. Nomenclature As reactant (solid phase, tobacco char) E activation energy [kcal mol-1, 1 cal = 4.184 J] po2,∞ ambient oxygen partial pressure [atm, 1 atm = 1.013 × 105 Pa] R gas constant [ 1.98 cal mol-1 K-1] T temperature [K] t time [min] W weight loss of tobacco char up to time, t, or temperature, T [mg] Wc weight loss of tobacco char at completion of reaction [mg] Z pre-exponential factor [min-1 atm-m] a fraction of As decomposed at time, t, defined by a = W/Wc