TG-FTIR and kinetics of devolatilization of Sulcis coal

Abstract The N 2 -pyrolysis of low-rank Sulcis coal was investigated by thermogravimetric techniques (TG/DTG) in the temperature range ambient to 1000 °C under dynamic heating conditions (50, 75, and 100 °C min −1 heating rates). Little differences in the mass losses with heating rates were observed. From thermogravimetric analysis it was established that coal pyrolysis consisted of three main stages: water evaporation; devolatilization of thermally labile and more stable volatiles; and char formation. The evolved gas (EGA) by Fourier transform infrared spectrometry (FTIR) coupled to the thermobalance under 100 °C min −1 heating rate was conducted for the identification of the gaseous species and their evolution profiles during coal thermal degradation. The temperatures of maximum rate of release of H 2 O, CO 2 , CO, COS, C 2 H 4 , as well volatile fragments originating from breaking of covalent bonds such as alkyl and ether groups, were in agreement with the temperature of maximum mass-loss rate around 466 °C. Meanwhile the maximum releasing rates of SO 2 , CH 4 , and NH 3 took place at 330, 575, and 690 °C, respectively. An increase of CO emission intensity at 770 °C was indicating in situ gasification with CO 2 -bearing product of freshly formed char. The kinetic processing of non-isothermal TG data was performed by isoconversional method. In the coal conversion regions α  = 5–40% the apparent activation energies were almost constant suggesting a single-step reaction path. The calculated average E value was 189 kJ mol −1 . A kinetic compensation effect existed between E and ln A : the linear dependence provided an average pre-exponential factor A 0 value of 2 × 10 11  min −1 . With further increase of conversion degree a complex E dependence on α was evident as the coal thermal degradation process underwent a multi-step reactions.