Measurement and modelling of the solubility of solids in mixtures of common solvents and compressed gases

• Published in: The Journal of supercritical fluids 2004-12, Vol.32 (1), p.79-87
• Main Authors: Wubbolts, F.E., Bruinsma, O.S.L., van Rosmalen, G.M.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Precipitation; Solubility; Solvent; Supercritical
• ISSN: 0896-8446; 1872-8162
• DOI: 10.1016/j.supflu.2004.02.004

The solubility of many solids in a compressed gas like carbon dioxide is low and it is therefore less suitable as a solvent. Instead, it can be used as an anti-solvent to crystallise a solute from a solution. For the evaluation and design of crystallisation processes solubility data of solids in mixtures of a solvent and carbon dioxide is crucial. While the vapour–liquid equilibrium data of solvents and CO 2 are usually available, the solubility of solids in a mixture of a common solvent and CO 2 are not. A method and equipment are presented to measure the solubility of solids in mixtures of CO 2 and a solvent at a constant temperature and pressure. The systems studied were p-acetamido phenol + ethanol + CO 2 and cholesterol + diethyl ether + CO 2. In both systems the solubilities were measured at about 295 K, 7 MPa and at 315 K, 10 MPa. For data correlation a method was developed with a solubility model that is based on the Peng–Robinson equation of state. This method for the measurement of the solubility in pressurised systems is a practical alternative for techniques that require analysis of the equilibrium composition. The measured solubilities were successfully correlated with the solubility model as well as with a simple explicit equation.