Investigation of subbituminous coals by thermogravimetry-mass spectrometry: Part 2. Formation of oxygen- and sulphur-containing products. kinetics of the overall mass loss

Abstract

Results derived from the experiments of Part 1 of this paper (Szabó et al., Thermochimica Acta, 170 (1990) 167) are presented. The mass spectrometric intensities of the oxygen-containing decomposition products, as functions of the temperature, were wide curves with multiple peaks indicating the multiple sources of these compounds. H 2S, COS, CS 2 and CH 3SH evolved mainly in the temperature range of the decomposition of aliphatic structures. Their intensity curves, however, showed a second, sharp peak due to a reaction between iron sulphide, formed from pyrite, and water. SO 2 is believed to be a secondary product of pyrite decomposition. The kinetic evaluation of the mass loss of the sample was based on thermogravimetric results at heating rates of 5,10, 20, 40 and 80°C min −1. Parallel reactions were assumed without any restriction on the distribution of the activation energies and pre-exponential factors. The results indicated that the unimolecular dissociation of the chemical bonds may be rate-determining factors only at higher temperatures, after the evolution of more than 60% of the volatile matter from the sample. Below this region, low activation energies and pre-exponential factors were observed which may be due to diffusion control (at low temperatures) and a radical mechanism (at medium temperatures).