Phase equilibria in near-critical solutions: binary and ternary mixtures of carbon dioxide and certain solutes and the occurrence of two-phase holes

摘要

Ternary mixtures can be used as model systems for some important applications in super- and near-critical fluid technology, which increasingly find their way into laboratories and industry. In contrary to gases, which, in general, have very poor solubility properties, near- and supercritical gases can be used as solvents for various substances, operating at moderate temperatures. At present, some distinct separation processes already make use of the advantages that supercritical fluid technology has to offer. Supercritical fluid extraction (SFE) is based on the fact that, near the critical point of the solvent, its properties, like the density, and with it, the ability for selectively dissolving non-volatile (e.g. organic) substances, change rapidly with only slight variations of pressure. This can form the basis for many powerful separation processes, but also makes eficient process control necessary, which is a challenge for engineers. In addition, the phase behavior of the mixture of substances involved has to be known very accurately. This often acaused problems in the past, since pahse behavior in the critical region was considered to be too complicated to control. Today, research has provided much more insight into the phase behavior of mixtures in the critical region and former difficulties have partly become opportunities for the development of new, more efficient separation and production processes.