Interactions between Pyridine and Coal at the Molecular Level: Insights from Variable-Temperature 1H NMR Studies of Pyridine-Saturated Coal

Abstract

The first systematic, in-situ, variable-temperature 1H NMR study, based on the CRAMPS (combined rotation and multiple-pulse spectroscopy) technique, is reported on pyridine-saturated Argonne premium coals. This work focused on how noncovalent associative interactions are affected at the molecular level by thermal treatment and solvent saturation. With improved proton dipolar-dephasing experiments based on CRAMPS detection, we were able to monitor quantitatively changes of molecular mobility of various molecular structural moieties upon pyridine saturation and temperature variation. It was found that pyridine saturation can dramatically promote fast, random molecular motion with correlation times in the range of 1 μs to 30 ns, even at room temperature, while thermal treatment alone is much less effective in promoting molecular motion even at 230 °C. For pyridine-saturated coal, the molecular mobility of coal can be enhanced further with just a moderate increase in temperature. Correlations between molecula...