Partitioning of some biomolecules at high pressures to aqueous/organic liquid–liquid phases of the carbon dioxide+water+1-propanol system

A completely miscible, binary liquid mixture of water and an organic solvent can reveal a liquid–liquid phase split, when it is pressurised with a ‘near-critical’ gas. The coexisting liquid phases in such a high-pressure three-phase equilibrium can be used to enable an extraction of biomolecules from an aqueous phase into a water-like organic phase. The basic design of such a process requires, at first, information on the behaviour of the phase forming ternary system of ‘near critical’ gas+water+water-soluble organic solvent, at second, experimental data on the partitioning of biomolecules to the coexisting phases and, at third, a method to correlate and predict such phase equilibrium. After a short introduction to the basic phase equilibrium phenomena, experimental results are reported for the partitioning of small amounts of six biomolecules — adenine, caffeine, methyl anthranilate, l-phenylalanine, salicyl alcohol and vanillin — on coexisting liquid phases in high-pressure three-phase vapour–liquid–liquid equilibrium of the ternary system ‘near critical’ carbon dioxide+water+1-propanol at 313 and 333 K. The experimental results for the partition coefficients are correlated with a semi-empirical approach, which combines an equation of state for describing the high-pressure multiphase equilibrium and the UNIQUAC excess Gibbs energy equation for describing the partitioning of the biomolecules.