Pressurized liquid extraction of brazilian coal followed by the extracts characterization by gas chromatography coupled to mass spectrometry

Abstract

This work reports a study on the use of Pressurized Liquid Extraction (PLE) for the selective extraction of organic compounds (aliphatic hydrocarbons-AHs, polycyclic aromatic hydrocarbons-PAHs and polycyclic aromatic compounds-PACs) from high-ash Brazilian coal. A homemade PLE system was built and solvents of different polarities (hexane, toluene and ethanol) were employed to extract the organic compounds from coal samples at a pressure of 10 MPa, under temperatures of 80°C and 200°C and extraction times up to 120 min. The selectivity of the extraction process was evaluated by a well-established methodology employed for the characterization of coal extracts (Preparative Liquid Chromatography-PLC 8). The fractions obtained in the PLC-8 method were dried and, after, quantified by gravimetry. Results showed that the proposed method of extraction was selective for the extraction of AHs using hexane at the temperature of 80°C and for the extraction of PAHs at 200°C. Additionally, the method showed to be selective for the extraction of PACs using ethanol at both studied temperatures. The AHs and PAHs fractions were also analyzed by GC-MS, showing that the first was composed mainly by low molecular weight compounds (<31 carbons) while the second by pyrenes, fluoranthenes, crysenes, benzopyrenes, perylenes and benzofluoranthenes. The present method showed to be a powerful tool for selective extraction of organic compounds from coal samples with simplicity, low quantity of solvent and filling other the requirements to be considered a greener method of extraction.