A CHEMICAL AND SOLID-STATE F-19 MAS NMR INVESTIGATION OF OXYGEN FUNCTIONALITY IN LIGNITE - THE FLUORINATION OF LOW-RANK COAL WITH DIETHYLAMINOSULFUR TRIFLUORIDE

The oxygen functionality in low-rank coals can be converted into their fluoride equivalents by treatment of the coal with diethylaminosulfur trifluoride (DAST). The generated fluoride functional groups are identified by solid-state F-19 MAS NMR spectroscopy. The presence and nature of oxygen functionality is inferred from these species. Resolution in the F-19 chemical shift dimension of solid-state F-19 NMR spectra of DAST-treated coals is sufficient to allow the differentiation of primary and secondary fluorides and to distinguish aromatic and aliphatic carboxylic acid fluorides. By virtue of high F-19 nuclear sensitivity and isotopic abundance, F-19 MAS NMR permits the detection of functional groups at part per thousand level. This work reports the first clear evidence for the presence of low concentrations of primary and secondary alcohols in lignite, and for the separate identification of aliphatic and aromatic carboxylic acid functions in this coal.