Bed height monitoring and control for expanded bed chromatography

Abstract

The height of a stable expanded bed depends upon the physical properties of the inlet liquid of which viscosity, density and flow rate have the most significant influence. A change in any of these parameters will subject the top of the bed to fluctuations and effective control would require monitoring the position of the top of the bed. In this work, the use of an LED based sensor configuration for providing information on the movement of the top of the bed in terms of its direction and rate of change is described. The information is incorporated in two different algorithms for pump control for appropriate adjustment of flow rate to counter the observed changes. The effectiveness of the sensor assembly and control algorithm was evaluated by testing the system on an expanded bed subject to a step change in the viscosity of the inlet irrigating liquid. The algorithm was further evaluated under scale-up and excellent control could be achieved using the protocol developed as a result of the high correlation of the expansion characteristics at the different scales.