Pyrolysis of superfine pulverized coal. Part 1. Mechanisms of methane formation

Highlights: • CH₄ formation mechanisms during superfine pulverized coal pyrolysis are investigated. • The overlapped CH₄ evolution curves are resolved applying the deconvolution method. • Five constituent reaction complexes induced by different functional groups are recognized. • CH₄ formation mechanisms initiated from thermal decompositions of different functionalities are concluded. - Abstract: The superfine pulverized coal has a greater potential for reducing NO_x emissions in the staged and oxy-fuel combustion technologies. The compositions and evolving processes of the volatile species during coal pyrolysis are important for understanding the pyrolysis mechanisms and pollution control strategies. In spite of numerous works focused on the description of coal thermal decomposition, the mechanism of formation reactions for particular gaseous products of coal pyrolysis like CH₄ remains unclear. In this paper, the mechanisms of CH₄ formation during superfine pulverized coal pyrolysis in N₂ and CO₂ atmospheres are investigated under non-isothermal conditions in a fixed-bed reactor. The effects of coal type, particle size and temperature on the evolved CH₄ and its formation mechanisms are analyzed. In addition, the total overlapped CH₄ evolution curves are resolved applying the deconvolution method through numerical analysis. Five constituent reaction complexes induced by different functional groups are recognized. Five CH₄ precursors involving in the CH₄ revolution during coal pyrolysis are confirmed, applying the solid-state ¹³C NMR analysis. Different CH₄ formation mechanisms initiated from the thermal decomposition of the functionalities are concluded, with the products competing for the donatable hydrogen for stabilization