Studies on Hydrodynamic Distribution of Two Immiscible Solvent Phases in Rotating Coils

Abstract

Hydrodynamic distribution of two immiscible solvent phases in rotating coils was studied with a simple rotary device. Experiments were performed with 1–2 cm I.D. glass coils, either nontreated or silicone coated, ranging in helical diameter from 2.5 to 20 cm. In general two solvent phases display characteristic four-stage distribution according to the applied rpm governed by interplay between the Archimedean screw force and radial centrifugal force. Under slow rotation the two solvent phases are evenly distributed on the head side of the coil by the Archimedean screw effect (Stage I). As the rotational speed is increased, one phase, usually the heavier phase, tends to dominate on the head side of the coil and at a critical rpm the two solvent phases are completely separated in the coil, one phase entirely occupying the head side and the other phase the tail side (Stage II). At this stage, high interfacial tension binary systems such as chloroform/water disclosed a typical effect of solvent-wall interaction in a narrow-bore coil in such a way that the aqueous phase distributed on the head side in the untreated coil whereas the nonaqueous phase occupied the head side in the silicone-coated coil. With further increase of rpm, the unilateral phase distribution declines through variety of distribution patterns (Stage III) and finally a strong radial centrifugal force field generated by rotation establishes hydrostatic phase distribution through the coil (Stage IV). The present studies may provide valuable clues for understanding the mechanism of unilateral phase distribution in the rotating coil.