liquidtoliquid

Liquid-to-liquid, often written as liquidto liquid in some texts, is a term used in physical chemistry and chemical engineering to describe processes that involve the transfer of solutes or energy across the interface between two immiscible liquid phases. The concept is central to liquid-liquid extraction and solvent partitioning, where a solute preferentially distributes between an aqueous phase and an organic phase.

In a typical liquid-liquid extraction, a feed solution is contacted with a second immiscible solvent. The solute moves between phases according to a distribution ratio, D, and the efficiency depends on interfacial area, mixing intensity, and physical properties like density and viscosity. Equipment designs include stirred-tank extractors and packed-column contactors; mass transfer is described by diffusion through a liquid film and by convective mixing.

Interfacial phenomena such as interfacial tension, emulsion stability, and droplet breakup govern the formation of dispersed phases and the rate of mass transfer. Models use activity coefficients to describe solute behavior in each phase; correlations such as Sherwood, Reynolds, and Schmidt numbers help scale lab results to industrial equipment.

Applications span metal extraction (e.g., solvent extraction of copper and rare earths), purification of pharmaceuticals, and environmental remediation, including removal of organics from water. The term can also appear in contexts outside chemical engineering as a brand name or project identifier, but in scientific literature it generally refers to interfacial transfer between two liquids.

Because "liquid-to-liquid" is not a single standardized concept, definitions vary by discipline; the umbrella covers physical processes at liquid interfaces as well as practical separation technologies.