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

摘要

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 CO2 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 CO2 and a solvent at a constant temperature and pressure.The systems studied were p-acetamido phenol + ethanol + CO_2 and cholesterol + diethyl ether + CO2.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.