Application of Fourier self-deconvolution to the FT-i.r. characterization of coals and their N-methyl 2-pyrrolidinone extraction products

Analysis by Fourier transform infrared (FT-i.r.) spectroscopy of coals and their extraction products, i.e. extracts and residues, gives an insight into the chemical structure of the initial material and changes due to the separation procedure. High quality spectra are obtained for solids by diffuse reflectance FT-i.r. spectroscopy. They also provide rather broad overlapping bands which have to be manipulated to supply useful information. It is shown that Fourier self-deconvolution improves the qualitative and semi quantitative analysis of FT-i.r. spectra of the coals and their N -methyl 2-pyrrolidinone (NMP) extraction products. Several samples of coals (rank ranging from C (wt%, daf) 85.6 to 92.4) were studied. Four spectral regions were selected for discussion: 3100-2800 cm −1 ν(CH ar ), ν(CH ali ); 1750-1600 cm −1 ν(CO), ν(CC ar ); 1260-1034 cm −1 ν(CO); 900-650 cm −1 γ(CH ar ). Several ratios were calculated, including: [ν(CH ar )/ν(CH 2 ,CH 3 )], [ν(CO)/ν(CC)], [ν(CO)/ν(CC)], [γ(CH)(1H)/Σγ(CH)], [γ(CH)(2,3H)/Σγ(CH)] and [γ(CH)(4H)/Σγ(CH)]. These data led to a comparison of the structural characteristics of the coals and of their extraction products. In each case the results are discussed in relation to the various trends observed in the samples, the possible relations with Gieseler fluidity of coals and the sizes of molecular orientations in the relevant cokes obtained by pyrolysis at 1000°C.