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Subcritical Water Processing

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Phase Diagram for WaterComplementing supercritical carbon dioxide (SC-CO2) as a natural processing agent is the use of water in its subcritical state (i.e., water held in its liquid state above its normal atmospheric boiling point by the application of pressure). This is in contrast to using HO in its supercritical state (see image at left, click image to see larger version) at a very high temperature/pressure where H2O exhibits hydrocarbon-like properties and can be used for the destruction of organic matter constituting hazardous waste. As shown (thumbnail image below right),Properties of Water as it Approaches the Critical Point application of an increase in the temperature of water held under pressure results in a decrease in its dielectric constant, which is similar to those exhibited by solvents such as methanol, ethanol, or acetonitrile. Therefore, subcritical water can be used as a selective extraction solvent or reaction media to yield unique extracts or products, such as anthocyanine from grapes and berries.

Commercial SC-CO2 Unit Modified for use with Subcritical Water The staff in the Supercritical Fluids Facility at LANL has experience in designing equipment for subcritical water processing (see image on left) as well as utilizing analytical scale equipment such as an ASE (Accelerated Solvent Extraction) instrumentation (see image below) equipment to screen the efficiency of subcritical solvents for extraction, fractionation, or as a reaction medium. Reactions conducted in subcritical water can be particularly effectiveDionex Accelerated Solvent Extraction (ASE) Unit when applied for the selective degradation of biomass as well as modifying the properties of materials, such as producing specific particle sizes and morphologies.

May 21/2008

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