Kinetic Examination of the Pyrolysis of Tritylated Celluloses

Abstract

The Chatterjee method for reaction kinetics by thermogravimetry was applied to two control cellulose samples and to five of their triphenylmethyl ether derivatives, varying in degree of substitution from 0.31 to 0.79 per anhydroglucose unit. The same samples were also examined by the Anderson and Freeman method and by an empirical trial of certain probable orders of reaction in conjunction with the generalized kinetic- reaction formula and the Arrhenius equation. The three methods of treating the data from the thermograms were mutually advantageous from the computational standpoint, requiring relatively small additional mathematical effort in proceeding from one to the other. All methods indicated zero- or low-order reaction at the beginning of pyrolysis (ca. 240°C), followed by first or higher order beginning at about 270°C. The tar phase of the reaction was completed at about 350°C. Usually, only one extended region of first-order decomposition was detected in the control celluloses, but two or more, with di erent Arrhenius parameters, were detected in the ether drivatives. One of the first-order regions, usually the intermediate on with very low activation energy, was associated with scission of the trityl group (285-310°C). In certain cases, the char region (350-500°C) was examined by the same techniques but without discovery of a recognizable kinetic law. 'The results are in substantial agreement with the chain mechanism of cellulose pyrolysis proposed by Chatterjee and Conrad.