Recently there has been considerable interest and activity in crystallizing high value (e.g., pharmaceutical) and/or difficult to crystallize compounds from supercritical fluids (SF). Possible advantages might be extreme size reduction without thermal degradation or chemical contamination. Rapid depressurization results in high supersaturation and causes high nucleation rates, making small crystals. Such processes are termed SF nucleation as there usually is no attempt to grow the crystals. The primary goal of this proposal, which is a continuation of earlier funded work, is to explore and exploit a novel isothermal isobaric method of supersaturation generation (and hence crystallization) in solute-laden SF, namely "salting- out" with high pressure N2 or other non-dissolving, non- interacting inert gases. With CO2 as the main SF solvent, it has been shown that solute precipitation of 0 to ~ 100 percent (benzoic acid as a model system) can be obtained using different N2/CO2 ratios in the final SF mixture. Actual crystallization occurs under isobaric isothermal conditions. Pressure would be reduced ultimately to remove product. SF separation processes involving only CO2 and N2 gases might ultimately prove to be the most cost-effective way of separation and purification of a thermally labile solute mixture.
