Structural analysis of functional group and mechanism investigation of caking property of coking coal

Eleven coking coals were used in this study and FT-IR and the caking index tests were carried out. The peak separation and quantitative calculation of FT-IR spectra were performed by using Peakfit software, and the relationship between caking property and typical functional groups of coal was investigated. The results showed that there was a close relationship between caking property and FT-IR spectra of coal, especially in the regions of 3000–2800 and 3700–3000 cm−1. The component with aliphatic structure was a major determinant of coal caking property. Usually, the shorter chain length or the higher branching degree of coal aliphatic structure was, the higher caking property will be. The caking property was codetermined by aliphatic structure and hydrogen bond (including −OH or −NH) and there was a synergic relationship between them. When the condensed degree of structural unit was low and the amount of bridge bonds was higher, the plastic mass based on structural unit with moderate molecular weight can be generated regardless of the coal molecule size. The most dominant sort of binding forces in coal was hydrogen bond. An associative structure even super molecular structure, which was broken and changed into plastic mass during the state of metaplast, was formed when a number of hydrogen bonds were associated together. The existence of plastic mass was beneficial to the transformation of metaplast into semi-coke and further acquisition of well caking property.