Effect of an Initiating Additive of CuSO4 on Changes in the Characteristics of Brown Coal Oxidation and Pyrolysis

Аннотация

The oxidation and pyrolysis of brown coal containing 5 wt % CuSO₄ as an initiating additive was studied. The experiment was performed by thermogravimetry at a heating rate of 2.5 K/min in an atmosphere of air and nitrogen. The process characteristics in the pyrolysis and oxidation mode were evaluated, and the activation energy of the process was determined by the Coats–Redfern method. It was established that the addition of the initiating agent CuSO₄ led to a significant decrease in the initial temperature of oxidation and pyrolysis processes to shift the reaction toward the low-temperature region. Maximum changes in the reaction initiation temperatures in the oxidation (ΔT_i) and (ΔT_d) pyrolysis modes were 35 and 50°С, respectively. It was established that the introduction of CuSO₄ led to a decrease in the activation energy of oxidation by 7.1 kJ/mol, and ΔE_a was 10 kJ/mol for the pyrolysis process. A decrease in the residence times of a sample within the limits of the sublimation of volatile substances was observed: Δt_i was 12 min for oxidation, and Δt_d was 18 min for pyrolysis. According to mass-spectrometric analysis data, the presence of SO₂ (peaks at 230 and 320°C) was detected in the oxidation and pyrolysis reaction products of modified samples; this was explained by the chemical interaction of copper sulfate with brown coal components.