Solubility of an acid dye in supercritical carbon dioxide by ion-pairing with dodecyltrimethylammonium bromide

In this study, solubility of Acid Red 57 (AR57), which is an anionic dye, in supercritical CO2 was investigated using an ion-pairing with dodecyltrimethylammonium (DTMA) bromide. The measurements of AR57 and AR57-DTMA in supercritical CO2 without/with methanol as a modifier solvent were carried out at temperatures from 45 to 100 °C and pressures from 250 to 325 bar. Although AR57 is insoluble in supercritical CO2 even with methanol as a modifier solvent, AR57-DTMA can dissolve in methanol modified supercritical CO2. The hydrophobic ion-pairing provides a possibility for the solubility of hydrophilic dye in supercritical CO2. The solubilities of AR57-DTMA were measured in methanol modified supercritical CO2 and the results were correlated by using a semi-empirical equation.