Organic and inorganic sulphur compounds releases from high-pyrite coal pyrolysis in H2, N2 and CO2: Test case Chinese LZ coal

•A high-pyrite coal was chosen to study the thermal effect of N2, H2 and CO2 atmospheres.•Different gases resulted in specific decompositions/changes of both organic and inorganic sulphur.•The effect of CO2 atmosphere on sulphur compound formation was evaluated in more details.

The effects of different atmospheres on the distribution of organic and inorganic sulphur compounds during high-pyrite coal pyrolysis were investigated. Sulphur compound releases were determined by atmospheric pressure-temperature programmed reduction (AP-TPR) “on-line” coupled with MS and AP-TPR “off-line” coupled with TD-GC/MS, which is a reliable technique for coal sulphur characterization. The results show that the decomposition of both organic and inorganic sulphur is different in the three applied atmospheres: H2, N2 and CO2. In H2, most sulphur from LZ coal is hydrogenated/reduced to H2S, decomposition of inorganic sulphur (pyrite and sulphates) has a great effect on the formation of H2S. It not only enhances the intensity of its m/z 34 signal but also shifts the peak maximum of its profile to a higher temperature, even without a returning to the base line. In inert N2 gas, as expected, hydrogenation of some sulphur compounds such as less-reactive di-aryl sulphur species and simple thiophenic structures are highly limited. The dominant peak of m/z 34 can also be related to the reduction of pyrite. In CO2, coal sulphur is mainly converted into SO2/SO, because CO2 is a more reactive gas and rather acts as an oxidizing agent. Decomposition of organic sulphonic acids occurs before 500 °C and of sulphonics/sulphoxides after 500 °C. The decomposition of sulphates and pyrite is better detectable in CO2 than in inert gas atmosphere. After 800 °C char gasification in CO2 results in further decomposition of sulphur compounds and lower sulphur retention.