High-pressure investigations on the solubility of anthraquinone dyestuffs in supercritical gases by VIS-spectroscopy .2. 1,4-bis-(n-alkylamino)-9,10-anthraquinones and disperse red 11 in CO2, N2O, and CHF3 up to 180 MPa

Solubilities of 1,4-bis-(n-alkylamino)-9,10-anthraquinone dyestuffs (with alkyl = methyl, butyl, octyl, dodecyl, and hexadecyl) in CO2 and N2O were measured as a function of temperature (310 to 360 K) and pressure (7.5 MPa to 180 MPa). In addition, solubilities of the dyestuff 1,4-diamino-2-methoxyanthraquinone (Disperse Red 11) were studied in CO2, N2O, and CHF3. The concentrations of the saturated solutions were determined using the analytical VIS-spectroscopy method. For 1,4-bis-(methylamino)-9, 10-anthraquinone in CO2, the concentration-pressure solubility isotherms were found to intersect each other. This has been explained by a density effect. For 1,4-bis-(hexadecylamino)-9,10-anthraquinone in CO2 maximum concentrations on some concentration-pressure isotherms exist. The results are discussed in terms of the different properties of CO2 and N2O and differences in the molecular size and the polarity of the dyestuff molecules.