Separation factor

The separation factor is a key figure for the change in the composition of a mixture of chemical substances through technical processes, especially separation processes . A high separation factor means a major change in the composition, which is the goal for all of the processes listed. A separation factor of means that there is no change in the composition and the process listed cannot be used to separate the mixture. ${\displaystyle \alpha }$ ${\displaystyle \alpha =1}$

The separation factor is usually given as a value , but from a mathematical point of view, the reciprocal value describes the same separation factor (e.g. a separation factor is synonymous with the separation factor ). ${\displaystyle \alpha >1}$ ${\displaystyle \alpha =0,2}$ ${\displaystyle \alpha =5}$

rectification

The separation factor in rectification describes the ratio of the pure substance vapor pressures of two components (ideal separation factor) or the ratio of the vapor pressures multiplied by their activity coefficients (real separation factor):

${\displaystyle \alpha _{12}\,=\,{\frac {P_{1}^{S}}{P_{2}^{S}}}}$ (ideal separation factor)

${\displaystyle \alpha _{12}\,=\,{\frac {\gamma _{1}\cdot P_{1}^{S}}{\gamma _{2}\cdot P_{2}^{S}}}}$ (real separation factor)

γ: activity coefficient
P ^S : saturation vapor pressure of the pure substance

A separation factor that deviates significantly from 1 allows a mixture to be separated by multiple evaporation. A separation factor of 1 means azeotropy and material separation is no longer possible due to rectification.

extraction

During extraction , a mixture of substances is separated into two immiscible phases due to the different solubility of the substances. The separation factor is the ratio of the distribution coefficients .

Membrane process

The separation factor describes the ratio of the activities (in a first approximation of the concentrations ) of components on the sides of semi-permeable, semi-permeable membranes . It is also known as the sieving coefficient and is calculated using the equation:

${\displaystyle S={\frac {C_{p}}{C_{f}}}}$

C _f and C _p are the concentrations in the feed and permeate .

Isotope separation

In the case of isotope separation , for example uranium enrichment , the separation factor describes the ratio of the concentrations of an isotope before and after the enrichment.

Chromatography

In chromatography, the separation factor describes the relationship between the retention times of two substances. ${\displaystyle t_{R}}$

${\displaystyle \alpha _{12}\,=\,{\frac {t_{R}^{1}}{t_{R}^{2}}}}$

or

${\displaystyle \alpha _{12}\,=\,{\frac {t_{R}^{1}-t_{0}}{t_{R}^{2}-t_{0}}}}$

with , the dead time (flow time without interactions with the stationary phase) and t ¹ _R > t ² _R ${\displaystyle t_{0}}$