SOLID-STATE C-13 NMR-STUDY OF THERMALLY UPGRADED LOW-RANK COALS

The results of solid-state C-13 NMR study aimed at evaluating the chemical changes and extent of upgrading achieved id the thermal treatment of two western Canadian low rank coals are discussed. The coals were thermally treated at varying temperatures (200 - 500 degrees C) using different process media (nitrogen, steam and products of combustion). Apparent aromaticity of the two coals was increased after the thermal treatment and increased with treatment temperature. Significant chemical changes, such as loss of the protonated aromatic carbons, quaternary carbons in alkylated rings and aliphatic ethers, were observed at 400 degrees C and above. Condensation and polymerization of the chemical components were also evident. The effect of process medium was found to depend on the coal feed and the treatment temperature.