Glass-selective extraction of polar, moderately polar, and nonpolar organics from hydrocarbon wastes using subcritical water

The polarity of water drops dramatically when heated under enough pressure to maintain the liquid state. For example, the dielectric constant (epsilon) of water is 80 at ambient temperature, but drops to similar to 30 at 250 degrees C. Thus, low temperature water can be used to extract polar organics, while higher temperature water will extract moderately polar and nonpolar organics. Four samples (a soil, a catalyst, and two sludges) were extracted by subcritical water at different temperatures and pressures. At lower temperatures (50-150 degrees C), phenols and BTEX (benzene, toluene, ethylbenzene, and xylenes) were quantitatively extracted by liquid water, while PAHs (polycyclic aromatic hydrocarbons) and alkanes were not extracted. At 250 or 300 degrees C, liquid water effectively extracted PAHs, but the high molecular weight alkanes (e.g., >C-20) were still not extracted. The quantitative extraction of the high molecular weight alkanes was achieved only by super-heated steam (250 and 300 degrees C at 5 atm) extractions. Class-selective extractions of phenols, alkylbenzenes, PAHs, and alkanes were achieved by simply changing water temperatures (50-300 degrees C) or pressures (5-100 atm). The recoveries of all of the target analytes achieved by subcritical water extraction compare favorably (typically 90-120%) to those of conventional organic solvent extractions.