On-line monitoring of breakthrough curves within an expanded bed adsorber

Abstract

By abstracting samples of the liquid phase from various positions along the height of an expanded bed, it has been possible to monitor the breakthrough pro®les of adsorbing components during the application of feedstock. Similarly, the concentration pro®les of the subsequent washing and elution procedures were also followed. The procedure involves the abstraction of liquid samples from the voids of the expanded bed using a specially modi®ed column and assaying the levels of proteins in the withdrawn stream by on-line rapid chromatographic monitoring. Studies of the residence time distribution showed that the modi®cations to the expanded bed did not cause additional mixing and dispersion. Breakthrough pro®les have been measured in a simple single component system and in a complex feedstock in which the adsorption of lysozyme from skimmed cows' milk was monitored. The system shows promise for the on-line control and monitoring of expanded bed adsorption separations, together with providing additional insight into the hydrodynamic and adsorption/desorption processes that occur during bioseparations using expanded bed adsorption. IntroductionOn-line monitoring and control of adsorption separations can have dramatic effects on process optimisation and ef®ciency [1±6]. Parameters critical to the ef®cient operation of the different stages of such a process include: Adsorption/loading stage. Ideally the duration of this phase should be such that the required component just starts to break through the column at a low level. Operation for longer periods results in wasteful loss of that component in the bed ef¯uent as it is no longer captured ef®ciently by the bed, whereas operation for shorter periods results in under-utilisation of the adsorption capacity of the adsorbent and hence the productivity of the bed is not as high as possible.Washing stage. During the washing phase, it is helpful to monitor the removal of certain key components from the bed. This ensures that the wash is continued for a suf®-cient period to ensure adequate removal of contaminants whilst minimising the consumption of wash buffer and possible loss of the required component as a result of the reversible nature of the adsorption process. Elution stage. During the elution phase, it is important to be able to detect the start and end of the peak containing the component of interest. This enables the required product to be collected in the minimum volume and at the highest yield. On-line knowledge of the levels of other eluting components allows fractions of the highest purity to be collected.Traditionally, the required information has been acquired by assaying the levels of key components in the ef¯uent stream from the bed. However, particularly for the monitoring of the loading stage of the procedure, this is inef®cient as the information obtained re¯ects the situation solely at the bed exit, rather than the more general situation within the bed. If control and termination of loading is based on detection of the level of breakthrough of the required ...

Experimental measurement of particle size distribution and voidage in an expanded bed adsorption system

“…This has been enabled by the adaptation of a glass column for the expanded bed system that has side ports at 5-cm vertical intervals to enable samples to be taken from the bed while the system is running. A number of studies report on the use of such a sampling method for the removal of liquid from within the column during a typical run (Willoughby et al, 1999;Chase et al, 1999) in order to consider product breakthrough and binding characteristics.…”

Use of dimensionless residence time to study variations in breakthrough behaviour in expanded beds formed from varied particle size distributions

“…Although expanded bed adsorption (EBA) has been well noted in the literature, little consideration has been given to the behaviour of matrix particles of different sizes during product breakthrough. Previously, Willoughby et al (2000a,b), Bruce and Chase (1999, 2001, and Chase et al (1999) studied various aspects of expanded bed behaviour and, in particular, used in-bed sampling and on-line monitoring to consider the breakthrough of products and contaminants along the axis of the bed. Of particular interest was the observation (Willoughby et al, 2000b) that the largest particles (those that remained in the bottom third of the bed during expansion) were seen to provide over 60% of the binding capacity of the column in a typical 10% product breakthrough loading strategy.…”

The use of rapid on-line monitoring of products and contaminants from within an expanded bed to control separations exhibiting fast breakthrough characteristics and to maximize productivity

“…Recently, workers have reported on the use of in-column sampling for EBA control (Chase et al, 1999). In this case the breakthrough was very slow (over 4 h for C/C 0 ‫ס‬ 0.1 at the top of column loading at 200 cm/h) which enabled a small-scale method of packed-bed chromatographic analysis to be used for monitoring of the product and control of the EBA.…”