A 3-zone model for protein adsorption kinetics in expanded beds

Vortex flow reactor assessment for the purification of monoclonal antibodies from unclarified broths

The vortex flow reactor (VFR) can be used in many chemical engineering applications. This paper assesses its novel use in the purification of monoclonal antibodies from cell broth. To this end, the IgG2a antibody was purified from the unclarified fermentation broth of transgenic mouse 55/6 hybridoma cells. Visual experiments showed that the VFR worked in the laminar vortices flow regime and the vortices displaced slightly faster than the axial flow. The VFR has the advantage of creating two sorts of flows: axial flow to produce the expanded bed and an extra vortex flow to avoid channeling and stabilize the expanded bed, the hydrodynamic behavior of which is plug flow with an experimental Pèclet number higher than 20. The pH was adjusted in the untreated fermentation broth, which was directly introduced into the reactor thus reducing the number of stages. The IgG2a purification was carried out in a single device via two steps: antibody adsorption in the expanded bed and antibody elution in the settled bed using Streamline rProtein A. A thirty-fold increase in the high-purity antibody concentration was achieved at the top of the pH5 elution peak with a total recovery of 93.1% (w/w) between elution peaks pH 5 and 3.

Mathematical modelling of expanded bed adsorption - a perspective on in silico process design

Expanded bed adsorption (EBA) emerged in the early 1990s in an attempt to integrate the clarification, capture and initial product concentration/purification process. Several mathematical models have been put forward to describe its operation. However, none of the models developed specifically for EBA allows simultaneous prediction of bed hydrodynamics, mass transfer/adsorption and (unwanted) interactions and fouling. This currently limits the development and early optimization of EBA-based separation processes. In multiphase reactor engineering, the use of multiphase computational fluid dynamics has been shown to improve fundamental understanding of fluidized beds. To advance EBA technology, a combination of particle, equipment and process scale models should be used. By employing a cascade of multiscale simulations, the various challenges EBA currently faces can be addressed. This allows for optimal design and selection of equipment, materials and process conditions, and reduces risks and development times of downstream processes involving EBA. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evaluation and characterization of axial distribution in expanded bed: II. Liquid mixing and local effective axial dispersion

Expanded bed adsorption (EBA) is a promising technology to capture proteins directly from unclarified feedstock. In order to better understand liquid mixing along the bed height in expanded beds, an in-bed sampling method was used to measure residence time distribution at different bed heights. A 2cm diameter nozzle column was tested with agarose raw beads (3% crosslinked agarose containing tungsten carbide). Two settled bed heights (11.5 and 23.1cm) with different expansion factors (1.4-2.6) were investigated and the number of theoretical plates (N), the height equivalent of theoretical plate (HETP) and the local effective axial dispersion coefficient (Dax) were calculated for each bed height-defined zone. The effects of expansion factor, settled bed height and mobile phase were evaluated. The results showed that N increased with the increase of expansion factors, but Dax was unaffected under fixed bed heights. Dax and HETP were found similar as a function of relative bed height for two settled bed heights tested. Higher mobile phase viscosity resulted in stronger axial dispersion. In addition, the local effective Dax under the expansion factor near 2.0 had a different profile which showed minimum values at 0.6-0.8 relative bed height, and the potential mechanism was discussed. These results would be useful for the characterization of axial dispersion and modeling protein adsorption in expanded beds under varying operation conditions.

Evaluation and characterization of axial distribution in expanded bed. I. Bead size, bead density and local bed voidage

Expanded bed adsorption (EBA) is an innovative chromatography technology that allows the adsorption of target proteins directly from unclarified feedstock, and the most important property of an expanded bed is the perfectly classified fluidization of resin beads in the column. Due to the variation of both size and density of bulk resin beads, the axial distributions of bead size, bead density and bed voidage are the inherent characteristics of an expanded bed. However, the understanding on these properties is quite limited. In this study, raw beads (3% crosslinked agarose containing tungsten carbide) and 2cm-diameter nozzle column were used as the model system and mean bead size, bead density and local bed voidage along the bed height were measured systematically with the in-bed sampling method for two settled bed heights (11.5 and 23.1cm) and different expansion factors (1.4-2.6). With the increase of bed height, mean bead size and wet density of the beads decreased from 140 to 90μm and from 4 to 2g/ml, respectively. The local bed voidage increased from 0.6 to 0.9 with the increasing bed height. The relative bed height and relative bed voidage were introduced to describe the general rule of axial distribution. Some empirical equations were used to correlate the mean bead size, bead density and local bed voidage along the bed height with the standard deviations of 10.6%, 6.1% and 5.5, respectively. In addition, a general equation was proposed to predict the axial distributions of bead size, bead density and local bed voidage in the column with standard deviations less than 10% for most of the experimental data, which would be useful for the characterization of resin beads distribution in an expanded bed under varying operation conditions.

Mathematical modeling and simulation of inulinase adsorption in expanded bed column

A mathematical model for an expanded bed column was developed to predict breakthrough curves for inulinase adsorption on Streamline SP ion-exchange adsorbent, using a crude fermentative broth with cells as the feedstock. The kinetics and mass transfer parameters were estimated using the PSO (particle swarm optimization) heuristic algorithm. The parameters were estimated for each expansion degree (ED) using three breakthrough curves at initial inulinase concentrations of 65.6UmL(-1). In sequence, the model parameters for an ED of 2.5 were validated using the breakthrough curve at an initial concentration of 114.4UmL(-1). The applicability of the validated model in process optimization was investigated, using the model as a process simulator and experimental design methodology to optimize the column and process efficiencies. The results demonstrated the usefulness of this methodology for expanded bed adsorption processes.

Expanded bed adsorption/desorption of proteins with Streamline Direct CST I adsorbent

Streamline Direct CST I is a new type of ion exchanger with multi-modal functional groups, specially designed for an expanded bed adsorption (EBA) process, which can capture directly the proteins from the high ionic strength feedstocks with a high binding capacity. In this study, an experimental study is carried out for two-component proteins (BSA and myoglobin) competitive adsorption and desorption in an expanded bed packed with Streamline Direct CST I. Based on the measurements of the single- and two-component bovine serum albumin (BSA)/myoglobin adsorption isotherm on Streamline Direct CST I, the binding and elution conditions for the whole EBA process are selected; and then frontal analysis for a longer timescale and column displacement experiments in a fixed bed (XK16/20 column) are carried out to evaluate the two-component proteins (BSA and myoglobin) competitive adsorption and displacement on Streamline Direct CST I. Finally, the feasibility of capturing both BSA and myoglobin by an expanded bed packed with Streamline Direct CST I is addressed in a Streamline 50 column packed with 300 mL Streamline Direct CST I.

Predictive modeling of protein adsorption along the bed height by taking into account the axial nonuniform liquid dispersion and particle classification in expanded beds

Expanded bed adsorption (EBA) is a special chromatography technique with perfect classification of adsorbent particles in the column, thus the performance of protein adsorption in expanded beds is particular, obviously nonuniform and complex along the column. Detailed description of the complex adsorption kinetics of proteins in expanded bed is essential for better analyzing of adsorptive mechanisms, the design of chromatographic processes and the optimization of operation parameters of EBA processes. In this work, a theoretical model for the prediction of protein adsorption kinetics in expanded beds was developed by taking into account the classified distribution of adsorbent particles along the bed height, the nonuniform behaviors of axial liquid dispersion, the axial variation of local bed voidage as well as the axial changes of target component mass transfer. The model was solved using the implicit finite difference scheme combining with the orthogonal collocation method, and then applied to predict the breakthrough behaviors of bovine serum albumin (BSA) on Streamline DEAE and lysozyme on Streamline SP along the bed height in expanded beds under various conditions. In addition, the experiments of front adsorption of BSA on Streamline DEAE at different axial column positions were carried out to reveal the adsorption kinetics of BSA along the bed height in a 20 mm I.D. expanded bed, and the influences of liquid velocity and feed concentration on the breakthrough behaviors were also analyzed. The breakthrough behaviors predicted by the present model were compared with the experimental data obtained in this work and in the literature published. The agreement between the prediction and the experimental breakthrough curves is satisfied.