Two dimensional 1H magnetic resonance relaxometry-based analyses of Argonne premium coals

Abstract

1H magnetic resonance (MR) is a useful technique for determining molecular structure of coals. Most previous MR studies were based on one-dimensional 1H magnetic resonance relaxometry. Two-dimensional (2D) 1H magnetic resonance relaxation correlation methods, T1–T2* and T1ρ–T2*, were used to evaluate Argonne premium coals, including Beulah-Zap (BZ), Wyodak-Anderson (WA), Pittsburgh #8 (PIT), Upper Freeport (UF), and Pochontas #3 (POC) coals as received. Samples were also measured after oxidization at low temperature (110 and 210 °C). From the 2D relaxation correlations, various hydrogen-containing components were distinguished and characterized. The change of hydrogen during low temperature oxidation was analyzed, and the hydrogen content estimated. The technique captured significant differences between low rank coals (BZ and WA) and high rank coals (PIT, UF, and POC). The order of T1/T2* ratios is aliphatic hydrogen > aromatic hydrogen > hydrogen- and oxygen-containing functional groups > moisture in BZ and WA coals. The PIT, UF, and POC coals mainly contain aromatic hydrogens. The T1–T2* and T1ρ–T2* spectra of BZ and WA coals change significantly during low temperature oxidation. Our new MR method provides new insight into coal behaviour.