Determination of the solubilities of dyestuffs in near- and supercritical fluids by a static method up to 180 MPa

Solubilities of the synthetic dyestuff 1,4-bis-(octylamino)-9,10-anthraquin one in CO2, N2O, CClF3, and SF6 and additionally of the natural dyestuff al l-trans beta-carotene in CO2 and N2O were measured by a static analytical s et-up consisting of a high-pressure autoclave coupled to a UV/VIS-spectroph otometer. In the case of 1,4-bis-(octylamino)-9,10-anthraquinone isotherms were recorded for temperatures from 282 to 341 K and over a pressure range from 6 to 110 MPa, whereas for all-trans beta-carotene experiments both on solubility and solubility kinetics were carried out in the temperature and pressure ranges from 308 to 350 K and 8 to 180 MPa, respectively. For both substances it could be found that solubility normally increases with rising temperature at a constant solvent density and equally with rising solvent densities at a given temperature. N2O proved to be the best solvent, follow ed by CO2. At solvent densities corresponding to normal liquids, however, t he curvature of the solubility isotherms (plot concentration versus density ) changed its sign and as a consequence solubility maxima were observed for the systems 1,4-bis-(octylamino)-9, 10-anthraquinone + SF6 and beta-carote ne + CO2. Additionally, beta-carotene showed a temperature dependent all-tr ans to cis isomerization at supercritical conditions and even thermal decom position with further increasing temperatures. (C) 1999 Elsevier Science B. V. All rights reserved.