Estimation of hydrogen bond distribution in coal through the analysis bf OH stretching bands in diffuse reflectance infrared spectrum-measured by in-situ technique

A new method was presented to estimate the strength distribution of hydroge n bonds in coal. The hydrogen bonds include the coal intramolecule hydrogen bonds and coal-water hydrogen bonds formed by hydroxyls in coal. The metho d analyzes the FTIR spectrum ranging from 2400 to 3700 cm(-1) obtained usin g the in-situ diffuse reflectance IR Fourier transform (DRIFT) technique wi th neat, undiluted, coal samples. The FTIR spectra during the heat-up of ei ght coals (seven Argonne premium coals and an Australian brown coal); an io n-exchange resin, and a lignin were measured every 20 degreesC from room te mperature to 300 degreesC. Each spectrum was divided into six hydrogen-bond ed absorption bands by a curve-resolving method, then the amount of hydroxy ls contributing to each hydrogen bond was estimated by Beer's law by using different absorptivity for each band. The strength of each hydrogen bond wa s estimated using a relation presented by Drago et al, that is known as one of the "linear enthalpy-spectroscopic shift relations". Using this analysi s method, changes in hydrogen bond distributions (HBD) with increasing temp erature were successfully estimated for all the samples examined, By utiliz ing the HBD the changes in enthalpies associated with the desorption of ads orbed water, the glass transition, and the decomposition of COOH groups wer e well:estimated. Only FTIR spectra measurements were found to be enough to obtain such enthalpies. This greatly simplified the calculation procedure and increased the accuracy of the enthalpies. The validity: of the proposed in situ FTIR measurement method and the analysis method for obtaining HBD was well clarified.