separationslag

Separationslag, also spelled separation lag, is a term used in the study of separation processes to describe a temporal delay between the onset of a driving force for separation and the observable separation of mixture components. In practice, when a gradient, pressure difference, electric field, or flow is applied to a system, the components do not separate instantaneously; instead, a lag period occurs during which concentration profiles adjust due to finite mass transport, sorption kinetics, and phase equilibria.

Causes include finite diffusion rates, adsorption-desorption kinetics on interfaces or membranes, internal transport resistance, and mixing due to convective flows. The magnitude of the lag depends on diffusion coefficients, system geometry, temperature, solvent properties, and the selectivity of the separating medium. External factors such as temperature fluctuations and operating conditions can also influence the duration of the lag.

Separationslag is commonly discussed in chromatography, electrophoresis, membrane separations, and gas separation, where designers must account for transient behavior in process start-up, switchovers, or pulsed operation. It can be reduced by increasing driving force, shortening diffusion paths, using highly selective media, or implementing flow patterns that minimize boundary-layer effects, though this may incur trade-offs with other performance metrics.

Measurement of a separation lag often involves time-resolved sampling or noninvasive monitoring to track concentration changes, enabling estimation of transfer coefficients and lag times. The term is not universally standardized; some authors refer to transient response, propagation delay, or diffusion-limited transfer instead.