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

Abstract

This work demonstrates an experimental method for studying breakthrough behaviour in expanded beds. The behaviour of beds made with differently sized particles were studied at varying flowrates. The use of a dimensionless residence time measurement allowed a more valid comparison of breakthrough characteristics in expanded bed operation by compensating for the changes in bed volume that occur during expansion. We demonstrate that bed breakthrough behaviour can be compared directly even when the beds contain different-sized particles and hence have different expanded volumes. By utilising this concept we demonstrate that, in the case of the Alcohol Dehydrogenase (ADH) / STREAMLINE Phenyl system used here, there was little or no variation in ADH breakthrough behaviour between beds of differently sized particles operating at flowrates above 100 cm/h. This suggests that the higher specific surface area and hence binding capacity of smaller particles is negated in this case due to mass transfer limitations and the increase in system void volume even at normal operating flowrates of 200 -300 cm/h. B 2004 Wiley Periodicals, Inc.

A study of the influence of yeast cell debris on protein and α‐glucosidase adsorption at various zones within the expanded bed using In‐Bed sampling

“…Thus, the adsorbent in the bed, above zone I (85% of the bed) could be utilised efficiently by increasing the concentration of the enzyme in the feed. Gardner et al (2004) observed that the total binding capacity of ADH as determined by the finite bath method was 1.94 mg/mL for larger particles ($140-250 mm) and 3.8 mg/mL for smaller particles ($110-200 mm). They proposed that the higher matrix surface area offered by the smaller adsorbent particles was responsible for the higher binding capacity for ADH.…”

“…The efficient adsorption of a product at any particular zone within the expanded bed also depends on the size of the molecule. The significance of the size of the product molecule on binding efficiency has been noted for b-galactosidase (Clemmitt and Chase, 2000), ADH (Gardner et al, 2004) and lysozyme (Bruce and Chase, 2001). Thus the adsorption of a target molecule in any particular zone within an expanded bed will depend on the size of the product, the concentration of the product in the feed and the amount of intact and partially broken cells in the feed that could potentially block the binding sites.…”

“…However, the increased voidage in the top zone results in an increased liquid phase residence time. Gardner et al (2004) found that there was no delay or difference in the breakthrough of alcohol dehydrogenase (ADH) between expanded beds composed of either smaller or larger adsorbent particles, and postulated that the higher external surface area offered by the smaller particles is counteracted by the increased void volume and hence high mass transfer resistance due to the increased path length for diffusion. The efficient adsorption of a product at any particular zone within the expanded bed also depends on the size of the molecule.…”

Residence Time Theory

“…[94][95][96] Biochemical processes use the same intellectual base of RTD theory as petrochemical applications, but there is a greater emphasis on separations rather than reactions. 97,98 Chromatography is dependent on differences in mean residence time. 99 Size exclusion separations exploit differences in the volume that is available to molecules of different sizes, 100 giving mean residence times that are, more or less, proportional to molecular weight.…”

Too big to bind? Will the purification of large and complex therapeutic targets spell the beginning of the end for column chromatography?

“…Remove the ability to do this and the bead functions as a solid sphere, leading to the potential capacity of the unit operation being drastically reduced. Research has already suggested1 that the kinetics and capacity of chromatography resins are affected unfavourably by larger proteins in comparison with smaller ones, and this effect will increase significantly with yet larger targets. At the extreme, cellular targets are likely to be of the same order of magnitude in terms of size as the chromatography beads themselves, a situation that will lead to extremely poor capacity if conventional chromatography beads are used in their purification.…”