A simulation model for membrane affinity chromatography processes

Chromatography represents one of the most important and widely used unit operation in the biotechnology industry. However this technique suffers from several limitations such as high pressure drop, slow mass transfer through the diffusive pores and strong dependence of the binding capacity on flow rate. One of the alternatives that are receiving increasing attention is represented by membrane chromatography, for which it is imperative to develop a reliable simulation model able to describe the process performance in a predictive way. In the present work a novel model is proposed that can describe all the chromatographic steps involved in the membrane affinity chromatography process for protein purification. The mathematical description is based on the species continuity equation coupled with a proper binding kinetic equation, and suitable to describe adequately the dispersion phenomena occurring both in the micro-porous membranes as well as in the extra-column devices used in the system. The model considers specifically all the different chromatographic steps, namely adsorption, washing and elution. Model validation is achieved by comparing simulation results with an extensive set of experimental data which have been obtained for the purification of immunoglobulin G from a cell culture supernatant, using several different innovative affinity membranes and using a broad spectrum of operating conditions. The few relevant fitting parameters of the model were derived from a calibration with experimental affinity cycles performed with pure IgG solutions, then the model is used to describe experimental data obtained in chromatographic cycles carried out with complex feeds as the cell culture supernatant. Simulations reveal a good agreement with experimental data in all the chromatography steps, both in the case of pure IgG solutions and for the cell culture supernatant considered.