r

Recovery of a component: The fraction of a component in permeate divided by its content in the feedstock.

Recycle: An element of membrane apparatus that provides return of permeate or retenetate (concentrate) into any stage of technological process.

Recycle: Return of permeate or retenetate (concentrate) into the stream of the mixture to be separated.

Regeneration of membranes: Regeneration of the starting parameters of membranes after or in the process of its exploitation.

Reinforcing of membranes: Introduction of reinforcing elements such as nets or meshes, non-woven cloth, etc. into membrane wit the aim of improving mechanical properties of the membranes.

Rejection curve; Dependence of the rejecting ability of a membrane on the molecular mass rejected components or their molecular size.

Rejection factor, R: Parameter equal to one minus the ratio the concentrations of a component (i) on the downstream and upstream sides of a membrane {Note 1: R = 1-[(c_i)downstream/(c_i)upstream]} [Note 2: concentrations may be either in the bulk ("Apparent Rejection Factor”) or at the membrane surface ("Intrinsic Rejection Factor")] [Note 3: rejection factor refers to a local relationship between upstream and downstream concentrations while retention factor and relative recovery refers to feed and retentate or permeate leaving the module].

Relative recovery, η_n,B (substance efficiency): Amount-of-substance of a component В collected in a useful product, η_B,out divided by the amount-of-substance of that component entering the process, η_B,in: η_η,B = η_B,out/η_B,in [Note: in membrane separations, the useful product may be either the retained material (or retentate) or the permeated material (or permeate)].

Resource of membrane or Membrane life-time: Life time of a membrane before its replacement.

Retentate (raffinate): Stream that has been depleted of penetrants that leaves the membrane modules without passing through the membrane to the downstream.

Retention factor, r_F: Parameter defined as one minus the ratio of permeate concentration to the retentate concentration of a component (i) {Note 1:r_F = 1 - [(с_i)_p / (c_i)_r]} [Note 2. "p" and "r" refer to permeate and retentate.

Reverse osmosis membrane: Membrane with the pores having the size less than 5 nm used in baromembrane process of reverse osmosis for separation of solutions of low molecular mass compounds.

Reverse osmosis: Liquid-phase pressure-driven separation process in which applied transmembrane pressure causes selective movement of solvent against its osmotic pressure difference.