steady state extraction

https://doi.org/10.1351/goldbook.10188

State of a continuous process operating in such a way that the concentration of solutes in exit streams remains constant with respect to time for constant feed concentrations, even though the two phases are not necessarily in thermodynamic equilibrium in any part of the process.

Note: The term equilibrium should not be used to describe this situation.
Source:
PAC, 2016, 88, 517. (Glossary of terms used in extraction (IUPAC Recommendations 2016)) on page 526 [Terms] [Paper]