THE CHARACTERIZATION OF COALS AND DENSITY SEPARATED COAL FRACTIONS USING FTIR AND MANUAL AND AUTOMATED PETROGRAPHIC ANALYSIS

In the first part of this study density-separated, coal fractions of P oint of Ayr coal were analysed using petrographic techniques and infra red (IR) spectroscopy. Density separations were carried out on the -38 + 20 mu m size fraction using sodium polytungstate as the dense liqui d medium. Petrographic analysis and FTIR analysis, using the diffuse r eflectance technique, were carried out on the density-separated fracti ons. For the FTIR analysis the samples were micronized to give a parti cle size of 2 mu m which leads to a considerable improvement in the qu ality of the recorded spectra without the need for dilution with potas sium bromide. Area measurements of the aromatic (A(Ar)) and aliphatic (A(Al)) CH stretch absorptions together with area ratios of these abso rptions (A(Ar)/A(Al)) were determined for each of the density fraction s and the feed coal. The A(Ar)/A(Al) ratios showed an increase with hi gher density, indicating a change in aromaticity as the density of the fractions is increased. A linear correlation between the area ratios and major maceral analysis was found. The results of this part of the study thus showed that changes in the IR spectrum could be directly re lated to the maceral composition, and that the diffuse reflectance tec hnique could be used to obtain consistent good quality IR spectra of p owdered coals. Using the same FTIR technique the A(Ar)/A(Al) ratios of 29 world coals was found and correlated with maceral analyses of the coal, maceral analysis plus rank and the grey-scale histogram produced during automated, petrographic analysis of the coals using image anal ysis. A poor correlation was obtained between maceral analysis and the A(Ar)/A(Al) ratio. The correlation improved markedly when rank was in cluded, but the best correlation (R-2 = 0.96) was Obtained against the grey-scale histogram. This work indicates that it may be possible to use the diffuse-reflectance FTIR technique as a rapid characterization technique for coal reactivity. (C) 1997 Elsevier Science Ltd.