Applications of NMR Methods in Coal Research

Abstract

Publisher Summary This chapter deals with nuclear magnetic resonance (NMR) investigations of the coal structure and the use of NMR spectroscopy methods for the characterization of elementary steps during the interaction of coal surfaces with organic solvents. It particularly emphasizes on low-rank coals, especially brown coals and lignites. The solid state NMR methods of interest are 13C cross-polarization magic-angle spinning (CP-MAS), 13C CP–MAS dipolar dephasing (DD), 13C NMR combined with resolution enhancement procedures or dynamic nuclear polarization, and 1H combined rotation and multiple-pulse spectroscopy (CRAMPS). For a deeper study of coal structure, for e.g., for the definition and investigation of reaction sites in coals, 1H, 13C, 31P double cross-polarization (DCP) MAS NMR technique is used. In this experiment, the 31P nuclei act as a cross-polarization filter. Only carbons with significant 31P–13C dipolar coupling polarize during the second magnetization transfer. In addition, interesting 1H CRAMPS NMR investigations are undertaken with respect to a line decomposition and the influence of water especially on soft brown coal 1H NMR spectra.