Two-dimensional spectroscopic analysis of sulphur group and pyrite transformations in coal coking

An accurate description of the sulphur migration process and mechanism is essential for guiding the selection and development of desulphurisation technology during the coking process, to increase the desulphurisation efficiency in the use of high-sulphur coking coal and decrease the sulphur content in the produced coke. However, the identified sulphur transformation mechanism in coal pyrolysis is not entirely applicable to the coking process due to variations in atmosphere, temperature and pressure. This work used numerous characterisation techniques in conjunction with experiments to quantitatively evaluate the transformation mechanism of both organic and inorganic sulphur throughout the coking process. The bond-breaking order of functional groups in sulphur during coking was obtained by the two-dimensional correlation spectroscopy analysis. The results show that desulphurisation in the coking process mainly occurs below 600 °C and 72.8% of sulphur in coal is retained in coke. Among them, FeS 2 and sulphoxide are completely removed while sulphides are reduced by 67.9%. The content of sulphone increases by 46.1% because of the transformation of sulphoxide. Thiophenes and sulphates increase by 32.5% and 33.9%, respectively, as a result of the inorganic sulphur transformation and secondary reactions of sulphur-containing gases above 500 °C. Through Noda's theorem, the bond-breaking sequence of sulphur-containing functional groups in coal during the coking process is obtained as follows: Fe–S bond → thiol C–S bond → alkyl sulphide C–S bond → thiol–SH → aliphatic C–S bond → thioether C–S bond → sulphoxide S=O bond → sulphone, sulphoxide C–S bond. By clarifying the desulphurisation characteristics of different sulphur forms, suggestions and ideas for the development of desulphurisation technology of coking coal are put forward, which is helpful for the wide utilisation of high-sulphur coal.