Characterization of some coals and coal intercalations by high-resolution 1H (BR-24/MAS at 270 MHz) and 13C (CP/MAS) n.m.r. in solids

Abstract

High resolution 1H n.m.r. studies combining the BR-24 multiple-pulse method after BURUM and RHIM with fast magic-angle sample spinning (MAS), and high resolution solid-state 13C n.m.r. measurements with cross polarization (CP) and MAS have been used for investigating: a number of coals of different ranks; GDR soft brown coals characterized by textural differences; and typical intercalations to be found in such soft brown coals. The resolution level of 1H n.m.r. spectra achieved so far at a resonance frequency of 270 MHz permits determination of essential functional groups. The coalification series ranging from soft brown coal to anthracite shows an increase of the aromaticity values ƒ a C and also an increase of the ƒ a H values, which is analogous to the increases in reflectance and carbon content. There are marked differences between the functional groups to be found in detrital and xylite-containing soft brown coals. Tertiary (Miocene) brown coals from the 2nd Lower Lusatian seam (GDR) (i.e. unbedded, poorly bedded, bedded, xylite-containing unbedded, and gelified bedded coals) differ significantly due to variations in micropetrographical composition. Varying amounts of cellulose and lignin are contained in the xylites of the 2nd Lower Lusatian seam. 13C and 1H n.m.r. measurements are employed to determine the main constituents of substances such as pyropissite, retinite, fusite and ‘monkey hairs’ (fossilized rubber).