Pyrolysis kinetics of chitin by non-isothermal thermogravimetry

Abstract

The TGA studies of a pyrolytic decomposition of chitin obtained from arctic krill were carried out. The investigation was made at the temperature ranging from 30 to 1000 °C (303–1273 K) in the argon atmosphere at four heating rates β = 2.5, 5, 10 and 20 K min −1. Two methods were used for the determination of kinetic reaction parameters: the first one involving linear regression (Kissinger's method) and the other one with the use of nonlinear regression. On the basis of isoconversion analysis of DTG curves, and literature data concerning the materials of a structure similar to chitin, four reaction groups were specified in the tested range of temperatures. A comparison of TG and DTG curves, both experimental and generated on the basis of parameters obtained, was used as a test for the correctness of calculations. Kinetic parameters obtained by the Kissinger method described process kinetics insufficiently and they were used as the starting values in the parameter estimation by the nonlinear regression method. The calculations were made for the scheme of four independent parallel reactions and four consecutive nth order reactions. Kinetic parameters E, k 0 and n obtained in this way provided a correct representation of the process kinetics although for the last group of reactions the high reaction orders ( n = 4–5) were obtained for the two schemes of reactions. To this group at above 380 °C corresponds a mild mass loss on the TG curve. It was hypothesized, and confirmed by numerical simulation calculations, that in the region described by a high order of reaction, many reactions of first order with slightly different activation energies can take place.