Pressurized fluid extraction of coal

Three Argonne Premium Coals (Upper-Freeport, Pittsburgh #8, and Lewiston-Stockton) were extracted with benzene in both Soxhlet and pressurized fluid extraction (PFE) systems. The extracts were compared on the basis of dry mass yield and hydrocarbon profiles as obtained by gas chromatography/mass spectrometry. The dry mass yields (wt%, daf) indicated no difference by either method for the Upper-Freeport coal, but statistically different yields were obtained for the Pittsburgh #8 and Lewiston-Stockton coals. In this study, PFE required ∼90 vol.% less solvent compared to Soxhlet extraction. The gas chromatograms obtained from the Soxhlet extracts contained solvent contaminant peaks as dominant peaks, which were not observed in chromatograms of the PFE extracts. No thermal degradation, as indicated by excess phenolic compound concentrations, was noted in any of the PFE extracts.