The field of membrane separations has its own terminology, described by Kronos [1]. I have collected some vocabulary terms described using his description. The scientific membrane field terminology is different from the chemical engineering field terminology. I connect the two fields by using the chemical engineering term equivalent to the membrane field term.
Membrane Filtration
In membrane filtration a component, or several components, are filtered from the feed stream, to stay on the feed side of the membrane. This membrane filtration belongs to the chemical engineering unit operation filtration.
Membrane Separation
In membrane separation the desired pure product selectively diffuses through the membrane, while all other components stays on the feed side of the membrane. This then results in a very pure product stream.
Permeate
The component diffusing through the membrane is called permeate. This is in general the main product stream. The outlet chamber is called the permeate chamber.
Retentate
The mixture of all other components staying on the feed side of the membrane is called retentate. The feed side chamber is called the retentate chamber.
Dead-end Membrane Separation
In dead-end membrane separation the retentate side chamber is closed at one end. So that only diffusion and flow through the membrane layer can occur. After some time, the operation has to stop and the material at the retentate side is removed. This is in chemical engineering terms a batch operation.
Tangential Membrane Separation
In tangential membrane separation the feed flows tangentially along the membrane surface through the retentate chamber and leaves at the retentate side exit, while the desired pure component diffuses through the membrane layer to the permeate side. So, this is a continuous operation.
Reference [1] Koros WJ, Ma YH, Shimidzu T. Terminology for membranes and membrane processes. J. Membr. Sci. 1996 Nov 13;120(2):149-59.