Theoretical foundations of the use of the transcritical state in extraction, separation, and concentration processes. Pathways of transcritical superextraction

The physicochemical foundations of known fluid supercritical extraction processes and of essentially new transcritical extraction processes in liquid-liquid systems, and in ultramicrogeterogeneous systems with subtransitional dispersed phase in micellar and liquid-crystalline transitions, are discussed via a unified approach based on conclusions of the modern fluctuation theory of phase transitions. It is shown that regions of enhanced selectivity of the phase redistribution exist on the path to the critical point both under supercritical and under subcritical conditions, and that a subcritical selectivity maximum is possible only if the system contains a region in which the classical theory of critical phenomena is applicable. In the selective extraction into both the subcritical and the supercritical phases a weak, universal (physical) selectivity, may be accompanied and complemented by stronger specific chemical effects leading to selective complex formation. It is shown that the chemical reaction in the homogeneous phase can be treated as a first-order phase transition close to a second-order phase transition, and accordingly we observe a universal physical superextraction into this phase. The bibliography includes 79 references.