Fractionation of brown coal by sequential high temperature solvent extraction

Separation of brown coal into fractions having rather uniform structure is believed to be one of the promising pretreatment methods for effective utilization of brown coal. The authors have recently presented a new coal fractionation method that can separate a bituminous coal into several fractions having different molecular weight compounds without decomposing the coal. The method extracts coal using a flowing stream of non-polar solvent such as tetralin or 1-methylnaphthalene by increasing the extraction temperature stepwise up to 350 °C. In this study the fractionation method was applied to fractionate a brown coal. Water was used as an extracting solvent in addition to tetralin and 1-methylnaphthalene by intending to utilize inherent water of brown coal as the extraction solvent. An Australian brown coal was successfully fractionated into six fractions by any solvents, but the properties of the fractions were significantly different depending on the extraction solvent. This is because tetralin, 1-methylnaphthalene, and water interacted significantly with the brown coal in different ways even at less than 350 °C. The difference in chemical structure and thermal properties of the fractions were examined in detail through ultimate analysis, 13C NMR, molecular weight distribution, and thermogravimetric and thermomechanical analyses.