Pressurized Liquid Extraction of Brazilian Coal Followed by the Extracts Characterization by Gas Chromatography Coupled to Mass Spectrometry.

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 degrees C and 200 degrees 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 degrees C and for the extraction of PAHs at 200 degrees 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.