Expanded Bed Adsorption – Challenges and Advances in Column and Process Design

T he concept of chromatography in Expanded Bed Adsorption (EBA) was first proposed in early 90s. The initial advantage of the idea was to be able to directly process particulate containing biological feedstocks for target products, while still maintaining sufficiently high separation efficiency that is usually enjoyed only by the traditional chromatography columns. EBA could potentially replace several traditional unit operations combined, namely centrifugation, filtration, and capture chromatography. EBA can significantly shorten the overall processing time, increase the overall yield, and save both capital investment and operating cost for many biological purification processes Figure 1. EBA is different from the fluidized bed used in the traditional chemical industry. The media beads are only intended to be fluidized in their local area, instead of a full mixing stage as in a fluidized bed, to provide reasonably high separation efficiency (plate count). A typical EBA operation involves the following steps: bed stabilization/equilibration, sample loading, washing, elution, regeneration and cleaning, and re-equilibration as shown in Figure 2. The settled EBA bed is first expanded by applying upward flow that is sufficiently fast to fluidize the media beads. Particulate containing feedstock will be directly applied into the column after equilibration. The target proteins or smaller molecules will be binded to the EBA absorbent while other contaminants such as Nucleotide and lipids pass through. A wash will be applied using fresh buffer to remove the loosely bound contaminant molecules after the sample loading. Elution step is usually run as a packed bed by lowering the top adaptor and applying downward flow. The target proteins or molecules that were binding on the adsorbent will be eluted from the column and collected. The column will then be cleaned/regenerated using stronger agents such as sodium hydroxide and re-equilibrated using the starting buffer for the next loading cycle.