Measurements and modeling of the solubility of natural phenolic compounds in organic and supercritical solvents


A. Queimada1, J. Baldaia1, F. Mota1 and E. Macedo1

1LSRE/LCM -Laboratory of Separation and Reaction Engineering, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal

Keywords: phase equilibria, CPA EOS, high pressure
property: solubility
material: phenolic compounds

Phenolic compounds are well-known molecules in both industrial and biological processes. Most of natural phenolic compounds are produced by plants and among these several are recognized for their biological activity. Some of these molecules are important antioxidants, others are used as drugs or as intermediates in drug synthesis. Phenolic compounds have also been linked with strong protective effects against some of the most aggressive types of cancer. To separate these molecules from reaction products or natural matrices, a qualitative and quantitative knowledge of their phase equilibria is required.

In this work we will present our most recent measurements of solubility of phenolic compounds (derivatives of hydroxybenzoic and phenylpropenoic acids) in ethyl acetate and alcohols (propanol, isobutanol and 1-butanol). The results to be presented in this communication were obtained at atmospheric pressure using the analytical shake flask method in the temperature range 278.15 – 318.15 K. Gravimetry was used for the quantitative analysis of the saturated phase compositions.

This data together with other literature data were used to assess the applicability of the Cubic-plus-Association equation of state (CPA EoS) to describe the phase equilibria of such molecules. Pure component parameters will be presented and a predictive methodology to obtain them using solely the chemical structure of the phenolic compound will be described. This is an important issue as many of these molecules decompose upon melting and so, there’s no vapor pressure and liquid density data that are the usual inputs to fit these parameters. In this methodology, the cubic term CPA pure component parameters are correlated with the critical temperature, critical pressure and van der Waals volume, obtained from group-contribution techniques. The association parameters are also predicted from the knowledge of the nature, amount and position of the association groups, using information from similar molecules. To test the applicability of the model to higher pressures and supercritical fluid applications, the solubilities in CO2 will also be addressed.

As it will be demonstrated, and following previous works [1-3] where the water solubilities were investigated, the CPA equation of state can be considered as a simple, yet accurate, flexible and highly predictive thermodynamic model.

References
  1. F. L. Mota, A. J. Queimada, S. P. Pinho, E. A. Macedo, Ind. Eng. Chem. Res. 47, 5182 (2008)

  2. F. L. Mota, A. J. Queimada, S. P. Pinho, E. A. Macedo, Fluid Phase Equilibria, 298, 75 (2010)

  3. A. J. Queimada, F. L. Mota, S. P. Pinho, E. A. Macedo, J. Phys. Chem. B 113, 6582 (2009)

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