Critical evaluation and comparison of fluid distribution systems for industrial scale expanded bed adsorption chromatography columns.

The hydrodynamic properties of an expanded bed contactor with 30 cm or 150 cm internal diameter, which employs a rotating or oscillating fluid distributor, were compared to prototype columns of 60 cm or 150 cm diameter employing local stirring (fixed wall nozzles plus central bottom mounted stirrer) for fluid distribution. Fluid introduction through a rotating fluid distributor was found to give superior hydrodynamic characteristics in the 30 cm and 150 cm diameter column compared to using the local stirrer in both the 60 cm and 150 cm diameter columns. The shortcomings of the local stirring distributor at large scale were apparent: dead zones were present which could not be removed by increasing rotation rates or flow rates, and such changes led to a deterioration in hydrodynamic properties. In contrast, during fluid introduction through a rotating distributor no dead zones were observed, and residence time distribution tests showed that plate numbers remained constant or increased slightly as flow rate was raised from 200 cm h(-1) to 470 cm h(-1). Under the conditions studied, oscillation of the rotating fluid distributor led to increased mixing and poorer performance than rotary movement. The results imply that further improvement in distributor design is needed and careful attention should be given to the trade off between turbulence and adequate fluid distribution.

The use of ion-selective electrodes for evaluating residence time distributions in expanded bed adsorption systems.

The suitability of ion-selective electrodes (ISE) for the determination of residence time distribution (RTD) in turbid, cell-containing fluids was examined. The electrodes were found to give reproducible signals in biomass-containing feedstock with up to 20% wet weight of solids. The enhanced feedstock compatibility of IES, when compared to other tracer sensing devices, allows the study of expanded bed system hydrodynamics under relevant operating conditions. Within the linear range of the corresponding ISE-tracer pair, both examined ISE (Li(+)- or Br(-)-selective) showed to be insensitive against the range of flow rate and pH normally employed during expanded bed adsorption (EBA) of proteins. Analyzing the RTD obtained after a perfect ion tracer pulse in terms of the PDE model (PDE, axially dispersed plug-flow exchanging mass with stagnant zones) gave a quantitative description of the underlying hydrodynamic situation during EBA processing. These data provided a powerful tool to make predictions on the adsorptive global process performance with a defined feedstock type and composition. The link between the hydrodynamic events during feedstock application and the actual process performance was shown when applying intact yeast cell suspensions at different biomass content (up to 7.5% wet weight) and buffer conductivity (5-12 mS) onto an EBA column filled with the adsorbent Streamline Q XL as fluidized phase. On the basis of our experimental results, a guideline for the successful application of the ISE/RTD method to EBA process design is presented.

High gradient magnetic separation versus expanded bed adsorption: a first principle comparison.

A robust new adsorptive separation technique specifically designed for direct product capture from crude bioprocess feedstreams is introduced and compared with the current bench mark technique, expanded bed adsorption. The method employs product adsorption onto sub-micron sized non-porous superparamagnetic supports followed by rapid separation of the 'loaded' adsorbents from the feedstock using high gradient magnetic separation technology. For the recovery of Savinase from a cell-free Bacillus clausii fermentation liquor using bacitracin-linked adsorbents, the integrated magnetic separation system exhibited substantially enhanced productivity over expanded bed adsorption when operated at processing velocities greater than 48 m h(-1). Use of the bacitracin-linked magnetic supports for a single cycle of batch adsorption and subsequent capture by high gradient magnetic separation at a processing rate of 12 m h(-1) resulted in a 2.2-fold higher productivity relative to expanded bed adsorption, while an increase in adsorbent collection rate to 72 m h(-1) raised the productivity to 10.7 times that of expanded bed adsorption. When the number of batch adsorption cycles was then increased to three, significant drops in both magnetic adsorbent consumption (3.6 fold) and filter volume required (1.3 fold) could be achieved at the expense of a reduction in productivity from 10.7 to 4.4 times that of expanded bed adsorption.