Quantitative solid-state 13C n.m.r. measurements on cokes, chars and coal tar pitch fractions

Abstract

Bloch decay or single pulse excitation (SPE) 13C n.m.r., generally recognized as the best approach to obtain quantitatively reliable aromaticity values and other skeletal parameters for coals, was applied to partly carbonized coal samples, a biomass char and the toluene-insolubles from a coal tar and a corresponding pitch. As found previously for coals, the aromaticities and non-protonated carbon concentrations were generally higher than those estimated by cross-polarization (CP). Furthermore, in terms of accumulation times, the shorter 13C T 1's of low-temperature chars makes SPE a more efficient technique than for coals. The higher concentrations of paramagnetic centres responsible for the shorter 13C T 1's still result in observability of 75% of the carbon in the chars by the SPE technique. The H C ratios derived from the SPE measurements agree well with those obtained from elemental analysis.