Estimation of Hydrogen Bond Distribution in Coal through the Analysis of OH Stretching Bands in Diffuse Reflectance Infrared Spectrum Measured by in-Situ Technique

Abstract

A new method was presented to estimate the strength distribution of hydrogen bonds in coal. The hydrogen bonds include the coal intramolecule hydrogen bonds and coal-water hydrogen bonds formed by hydroxyls in coal. The method analyzes the FTIR spectrum ranging from 2400 to 3700 cm -1 obtained using the in-situ diffuse reflectance IR Fourier transform (DRIFT) technique with neat, undiluted, coal samples. The FTIR spectra during the heat-up of eight coals (seven Argonne premium coals and an Australian brown coal), an ion-exchange resin, and a lignin were measured every 20 °C from room temperature to 300 °C. Each spectrum was divided into six hydrogen-bonded absorption bands by a curve-resolving method, then the amount of hydroxyls contributing to each hydrogen bond was estimated by Beer's law by using different absorptivity for each band. The strength of each hydrogen bond was estimated using a relation presented by Drago et al. that is known as one of the "linear enthalpy-spectroscopic shift relations". Using this analysis method, changes in hydrogen bond distributions (HBD) with increasing temperature were successfully estimated for all the samples examined. By utilizing the HBD the changes in enthalpies associated with the desorption of adsorbed water, the glass transition, and the decomposition of COOH groups were 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.

Beneficiation of Indian coals using Ionic Liquids

“…Some of the acceptor group solvent such as pyridine provides strong hydrogen bonding to swell the coal particles. However, they also fractionate a lesser amount of these hydroxyl groups [9][10][11][12][13][14]. Pseudo solvents such as pyridine and tetracyanoethylene also gave comparable results for coal fractionation.…”

“…The groups are more pronounced for liquefaction process where the interaction of cross-linking of coal surface and solvents play a vital role [4][5][6][7][8]. Low-rank lignite, sub-bituminous and low-volatile bituminous coals are polar in nature and posses oxygencontaining functional groups [9][10][11][12][13][14]. These oxygen-containing functional groups lower the carbon content and thus its calorific value.…”

Effects of mineral matter and temperatures on conversion of carboxylic acids and their derivatives during pyrolysis of brown coals

“…About 20-30 mg coal sample was pressed on the surface of silica and leveled with a spatula, and then the crucible was placed in the center of reaction cell. A mirror, not to adsorb moisture in the atmosphere, was used as the background of infrared measurement [31]. The reaction cell was vacuumized to eliminate the moisture in the atmosphere before the infrared measurement was performed.…”

“…carboxylic acid, esters, carboxylates and anhydrides) during drying of brown coals. Through measuring corresponding peak area of curve-fitted infrared spectra, the technique can be employed to determine apparent aromaticity of coals [26] and quantify aromatic and aliphatic CH groups [27], carbonyl groups [28,29], hydroxyl groups [30] as well as various hydrogen bonds [31] in coals. The works mentioned above demonstrate that the curve-fitting technique is effective for characterization and quantification of functional groups in coals.…”

Production of Metallurgical Coke Utilizing Low-Rank Coals Upgraded by Mild Solvent Treatment

“…In the proposed method, it is expected that the solvent breaks the hydrogen bondings which are thermally weakened above 140°C 10) and pulls the molecules apart by dissolving them to suppress the crosslinking reactions while decomposing oxygen-containing functional groups. Non-polar solvent was chosen in the proposed method because polar solvents which are strongly associated with coal molecules are difficult to be recovered from the product.…”