Effects of adsorbent properties on zone spreading in expanded bed chromatography

The mixing performance as well as the adsorption performance in expanded bed chromatography (EBC) was investigated by using various types of adsorption media (average particle size = 100-700 microm, density = 1100-1700 kg/m3, base matrix = hydroxyapatite, styrene-divinylbenzene, cross-linked agarose). The scale down study with 0.8 cm diameter columns was also attempted. Pulse response curves were measured with vitamin B12 as a tracer [Residence time distribution RTD experiments], and the HETP (height equivalent to a theoretical plate or plate height) values were calculated from the peak variance and the peak retention time. The HETP values for different types of packing media tested showed very similar values (0.5-1.0 cm), which did not depend on the flow-rate or the column diameter (0.8-2.6 cm). Dynamic binding capacity (DBC) values of lactic acid on a Dowex anion-exchange resin were determined from breakthrough curve (BTC) measurements for both EBC and fixed bed chromatography (FBC). The DBC values for EBC were similar to those for FBC. When the liquid feed contained insoluble particles (yeast cells) the degree of mixing increased. However, the contribution of the mixing to the total spreading of BTCs for EBC was usually small so that this increase in the mixing did not affect the adsorption performance or the DBC values significantly.