(174h) Prediction and Modeling of Solubility Phenomena in Subcritical Fluids Using An Extended Solubility Parameter Approach

Srinivas, K., University of Arkansas
Hansen, C. M., Charles M. Hansen Consulting
King, J. W., University of Arkansas

There has been a growing interest in use of sub-critical fluids in extraction and/or reactive processing of natural products. Subcritical water and hydroethanolic solvents under compression above their boiling points are currently being used both in the extraction of pharmacological/nutraceutical components as well as for biomass/bioenergy conversion applications. The first step towards design and optimization of such systems is the assessment of physicochemical properties of solutes in sub-critical solvents. In the past, we have previously correlated solute solubility in subcritical fluids using different solubility models like those of Clifford-Hawthorne[1] and delValle et. al.[2]. As an extension of these studies, we have investigated the applicability of modified solubility parameter approaches including the Hansen 3-dimensional solubility parameters and the RED theory. As to be expected, the dispersion, polar and hydrogen bonding partial solubility parameter components of subcritical solvents decrease with temperature to varying degrees. There exists insufficient experimental data for the partial solubility parameters of certain complex structural solutes in the literature. Hence, group contribution methods and suitable equations based on molecular properties were used to calculate the partial solubility parameters for such solutes. Relative Energy Difference (RED) numbers reflects the affinity of the solutes for subcritical fluids depending on their values at various temperatures. A SPHERE[3] software program can be used to generate three dimensional solubility parameter spheroid maps that can help in studying the interactions between the solutes and the subcritical solvent. The above approach when coupled with a group contribution method and/or a statistical thermodynamic-based or corresponding states approach can be used to estimate solubility parameter trends in subcritical fluid media. These trends coupled with the study of the temperature and pressure dependence on the partial solubility parameters of structurally-complex solutes and pressurized/subcritical solvents can be used for modeling extraction or reaction selectivity of solutes in subcritical solvents.

[1] Anthony A. Clifford and Steven B. Hawthorne, ?Processes in Subcritical Water?, Super Green 2002, Proceedings of the 1st International Symposium on Supercritical Fluid Technology for Energy and Environment Applications, Kyung Hee University, Suwon, Korea, November 3-6,2002, pp. 21-29.

[2] Jose M del Valle, Juan C. de la Fuente and Jerry W. King, ?Correlation for the Variations with Temperatura of Solute Solubilities in Hot, Pressurized Water?, Equiphase Conference, Morelia, Michoacán, México, October 21-25, 2006 (To be published).

[3] Charles M. Hansen, ?Hansen Solubility Parameters: A User's Handbook?, CRC Press, Boca Raton, FL, 1999.