Influence of co-solvent on dye solubility in supercritical carbon dioxide

It is experimentally evident that the solubility of non-volatile solid such as disperse dye in supercritical fluid is significantly increased by adding a small amount of co-solvent into the fluid. The phase equilibrium calculation for the ternary system composed of supercritical fluid, solute and co-solvent is established by using the expanded liquid model based on regular solution coupled with Flory–Huggins theory. The solubility of non-volatile solid in mixed fluid including co-solvent is correlated with the liquid model with good accuracy. The model needs only the melting point and heat of fusion for non-volatile solid such as disperse dye that can be measured or be available in literature. But the critical properties and the vapor pressure of the solid that are necessary to estimate the phase equilibrium at high pressure by using an equation of state are not required in this model.