The Use of Ion-Selective Electrodes for Evaluating Residence Time Distributions in Expanded Bed Adsorption Systems

Abstract

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.

Expanded bed adsorption of bromelain (E.C. 3.4.22.33) from Ananas comosus crude extract

“…Bed voidage was obtained by substitution of data for specific mass (ρ p ) and mass of the adsorbent particles (m P ), cross sectional area of the column (A T ) and bed height (H) into the following equation (Santos et al, 2000;Fernandez-Lahore et al, 2001;Yamamoto et al, 2001):…”

“…Residence Time Distribution Study Figure 4 shows RTD curves for acetone (2.5 % w/v) tracer as it passed through the column bed. Analyzing the RTD obtained after a perfect iontracer pulse (axial dispersion, plug-flow exchange of mass with stagnant zones) gave a quantitative description of the underlying hydrodynamic situation during the EBA process (Fernandez-Lahore et al, 2001). Table 1 shows the RTD results after substitution of data into equations (1) to (3), according to the methodology used by several authors (Santos et al, 2000;Fernandez-Lahore et al, 2001;Yamamoto et al, 2001;Toledo et al, 2006).…”

“…There was a 12-fold increase in axial dispersion when the expansion degree was raised 1.5 fold and a 51-fold increase as its expansion degree increased 2.5 fold. This increase in axial dispersion facilitates the flow of particles and biological material into the bed and increases the interaction of target molecule and adsorbent particles, facilitating the feed of crude extract directly to the bed, avoiding fouling and reducing costs, as the number of pretreatment and pre-purification steps may be reduced, which are the main chromatographic problems (Wheelwright, 1994;Amersham Pharmacia, 1997;Fernandez-Lahore et al, 2001). Table 2 shows the results for Bromelain by expanded bed adsorption on Amberlite IRA 410.…”

“…However, the use of DEAE-cellulose and DEAE-sephacel resins increased the cost of purification of biomolecules. With the use of Amberlite IRA 410 ion-exchange resin and the expanded bed condition, it was possible to obtain pure biological products, such as bromelain, with lower operational cost, thus, decreasing overall process cost (Fernandez-Lahore et al, 2001). The protein and bromelain activity history is presented in Figure 5.…”

“…This technique permits crude feeding into the chromatographic column without initial treatment and, as the bed expands, it increases adsorbent surface contact, making interaction with the target molecule more effective (Roy et al, 1999;Fernandez-Lahore et al, 2001).…”