Solubility of beta-carotene in ethanol- and triolein-modified CO2

Abstract

Modification of an experimental device and methodology improved speed and reproducibility of measurement of solubility of beta-carotene in pure and modified SuperCritical (SC) CO2 at (313 to 333) K. Solubilities of beta-carotene in pure CO2 at (17 to 34) MPa ranged (0.17 to 1.06) mu mol/mol and agreed with values reported in literature. The solubility of beta-carotene in CO2 modified with (1.2 to 1.6) % mol ethanol increased by a factor of 1.7 to 3.0 as compared to its solubility in pure CO2 under equivalent conditions. The concentration of triolein in equilibrated ternary (CO2 + beta-carotene + triolein) mixtures having excess triolein reached values (0.01 to 0.39) mmol/mol corresponding to its solubility in pure SC CO2 under equivalent conditions. Under these conditions, the solubility of beta-carotene in triolein-modified CO2 increased by a factor of up to 4.0 in relation with its solubility in pure CO2 at comparable system temperature and pressure, reaching an uppermost value of 3.3 mu mol/mol at 333 K and 32 MPa. Unlike in the case of ethanol, where enhancements in solubility where relatively independent on system conditions, solubility enhancements using triolein as co-solvent increased markedly with system pressure, being larger than using (1.2 to 1.6)% mol ethanol at about (24 to 28) MPa, depending on system temperature. The increase in the solubility beta-carotene in SC CO2 as a result of using ethanol or triolein as co-solvent apparently does not depend on the increase in density associated with the dissolution of the co-solvent in CO2. Enhancements may be due to an increase in the polarizability of SC CO2, which possibly growths markedly as triolein dissolves in it when the system pressure becomes higher.