Solid-State 13C NMR of Pyridine-Swollen Coal

Abstract

We have studied the solid-state 13 C CP/MAS NMR spectra of pyridine-swollen coal. The coal used in this study were Upper Freeport (UF, C 88 wt %), Wyodak (WY, C 75 wt %), and Yallourn (YL, C 65 wt %). Each coal was immersed in pyridine for 0 (momentarily) or 1 h. For UF coal, the spectra of the coal immersed in pyridine were the same as the fresh coal and pyridine peaks were not observed. So, most of the pyridine molecules in UF coal were thought to be in a mobile state. For WY and YL coal, it became clear from solid-state 13 C CP/MAS NMR that pyridine connected with coal in the form of hydrogen bonding. For WY coal, α- and β-carbons' peaks of pyridine were observed at 0 h after immersion and all carbons' peaks were observed at 1 h after immersion. This was because the efficiency of cross polarization for γ-carbon of pyridine in coal was different from α- and β-carbons. For YL coal, all carbons' peaks of pyridine were observed at both 0 and 1 h after immersion. The swelling of YL coal at 0 h after pyridine immersion seemed to be enough for the effective cross polarization for γ-carbon of pyridine. The T 1 H of pyridine-swollen coal was also measured. The T 1 H of UF coal decreased, while the T 1 H of WY and YL coal increased with the pyridine immersion. The change of the T 1 H of coal was followed by the change of molecular mobility of coal. WY and YL coal showed an increase in the T 1 H with pyridine immersion, since these coals were at around ωτc 1 originally and moved to the ωτc 1 region originally and stayed in that region even after solvent immersion.