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Processing with Supercritical Fluids

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Larger scale processing with supercritical fluids requires optimization of extraction and solute recovery conditions as well as recycle considerations for the processing fluid. As illustrated by the inset figure, the fluid is compressed to the supercritical state where it extracts the substance(s) of interest, followed by decompression of the fluid or adjustment in the fluid's temperature. This process effects separation of the solute(s) from the extracting fluid. The fluid is then recycled to commence the extraction process once again.

Solubility of Naphthalene in CO2To illustrate the above concept (see image above), the changes which occur for a model solute, naphthalene in SC-CO2, are also shown next to the process in the above figure. Here, a solubility of 5.2 mole % is found for naphthalene at a pressure of 300 atmospheres and a temperature of approximately 55°C, parameters corresponding to conditions used in the extraction stage of SFE (E1). Separation of the naphthalene from the compresed CO2 after SFE can then be affected in one of two ways, as shown in the above figure. The separation of the solute from the SC-CO2 can take place at a constant pressure (300 atm) while the temperature is lowered to 20°C, thereby affecting a solubility change of 4.0 mole % (S2). However, an even larger change in naphthalene's solubility in SC-CO2 can be achieved by reducing both the pressure and temperature at the separation staged (S2), by adjusting the pressure to 90 atm and temperature to approximately 45°C. Under these conditions, only 0.1 mole % of naphthalene is left in the SC-CO2 phase.

Organic Solvents The Supercritical Fluid Facility at LANL can measure solute solubilities and miscibility in the supercrtical fluid state by several techniques, including high-pressure optical cell measurements (with video recording). Mass balance calculations can also be facilitated on pilot plant equipment up to 60L extractor capacity, which is designed to measure the total amount of fluid required in the cyclic processing mode. The result can be a useful process devoid of the use of organic solvents and their attendant disposal problem (see image at left).

The staff at LANL's Supercritical Fluids Facility has considerable experience in the design and scale-up of processing equipment to assist clients in developing different scales of production plants as shown by the inset figures on the right. Processing EquipmentThis includes partnering with other equipment vendors or companies specializing in building pilot and production scale plants as well as scaled up toll refining services.

May 21/2008

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