Columns with fixed beds of immobilized enzymes or other proteins are commonly used in affinity chromatography and as reactors for continuous operation. Most carrier particles for protein immobilization are deformable or compressible by application of pressure. For non-compressible beds at low Reynolds-numbers, < 10, the pressure drop p is a linear function of flow rate; and the flow resistance is constant. With deformable particles in fixed beds p is a non-linear function of bed height h and volumetric flow rate v (1). This is shown in Fig. 1 where the flow resistance increased with p, finally leading to instability and occlusion. It is evident that at p ≅ 100 mbar the pressure drop increased very rapidly with the flow rate, and occlusion occured beyond about 500 mbar. The maximal flow rate depended on h as expected. Reproducibility was difficult, depending on pretreatment and hysteresis. The flow through a compressible bed must take into account varying hydraulic radii rh in the flow path, caused by particle deformation.
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