Characterization by 13C CP/MAS n.m.r. spectroscopy of the structural changes in coals after chemical treatments

13C CP/MAS spectra have been used for the characterization of two different coal types and their derived products, obtained after mild and severe treatment. The carbon aromaticity (faC) was determined by fitting signal areas in CP/MAS spectra to an expression that describes the evolution of carbon magnetization with the experimental contact time. Proper modification of the CP/MAS pulse sequence allows separation of protonated and non-protonated carbons. This technique is used to determine the carbon aromaticity of the non-protonated carbons. This parameter is related, together with the faC, to the coal structure. Our results are compared with literature data for both coal types.