High-pressure fluid-phase equilibria: Experimental methods and systems investigated (2000-2004)

Major recent advances. Particle formation and design of solid particles and powdery composites with unique properties is at the moment a major development of supercritical fluids (synonyms: dense gasses, dense fluids, high pressure) applications. This review will focus on recent advances and on fundamentals of these processes and their applications.

Particles formation and particle design using supercritical fluids

The melting point depression of semicrystalline polymers exposed to a compressed fluid allows certain biodegradable polymers to be processed in the molten state using carbon dioxide at modest temperatures. Experimental melting temperature ( T m ) data are presented for the aliphatic polyesters, polycaprolactone (PCL) and poly(butylene succinate) (PBS), as a function of the applied pressure of carbon dioxide. The characteristic features of the T m versus P curve – a linear regime at modest P , followed by an abrupt transition to a second regime where T m changes little with P – are interpreted using the Clapeyron equation for two-component, three-phase equilibrium. For PCL and PBS, as well as for other polymers, the slope of the lower pressure linear regime can be quantitatively estimated from the normal T m , the enthalpy of fusion of the polymer, and the Henry's law coefficient for CO 2 dissolved in the melt. The location of the abrupt change in slope is correlated with equivalence of the molar volumes of the compressed fluid and the Kuhn monomer unit of the polymer crystal. The method is also applicable to non-polymeric compounds which have high critical points and low solubility in the compressed fluid.

Carbon dioxide-induced melting point depression of biodegradable semicrystalline polymers

In order to overcome the lack of experimental phase equilibrium data for a deeper understanding of particle formation processes using supercritical fluids, investigations have been carried out in two static equilibrium apparatuses. The first apparatus is designed as a view cell with an inner volume of 1310 cm3 placed in an air-thermostatted chamber, which allows a visual determination of the SLG-line following the first melting point method. The second equilibrium cell of approximately half the inner volume is placed in a water thermostat, which is more efficient for solubility measurements. The SLG-lines of naphthalene with carbon dioxide, trifluoromethane, and a mixture of these two solvents were experimentally determined and additional solubility measurements have been performed. The experimental results are described by means of cubic equations of state, which give, from an engineering point of view, an adequate thermodynamic model for the representation of solubility and SLG-lines.

Phase equilibria of organic solid solutes and supercritical fluids with respect to the RESS process

In this review, available experimental data on the drug confinement in porous matrices via adsorptive precipitation from supercritical fluid solutions with a special emphasis on the drug amorphization is provided. Practical aspects and opportunities for the process optimization are discussed in view of thermodynamic considerations. An attempt is made to elaborate a simplified model that takes into account drug–drug and drug-matrix interactions with the aim of rationalizing the experimental outcomes with respect to the physical state of the confined drug. Potential points of growth and some bottlenecks of the adsorptive precipitation from supercritical solutions are outlined.

Klementina Fukné-Kokot

Papers

Comparison of different methods for determination of the S–L–G equilibrium curve of a solid component in the presence of a compressed gas

Modified freezing method for measuring the gas solubility along the solid–liquid–gas equilibrium line

Influence of the Solid‐Liquid Phase Transition on the Solubility of the Substance under the Pressure of Dense Gas