Abstract
This work presents a general rate model for ion-exchange in column chromatography with the steric massaction isotherm that is suitable for ion-exchange systems involving macromolecules such as large proteins. This comprehensive model considers axial dispersion, interfacial film mass transfer between the bulk-fluid phase and the particle phase, and intraparticle diffusion. The model system has been solved numerically using the finite element method and the orthogonal collocation method with a graphical user interface for Windows based personal computers. The effect of pH is modeled by including buffers, acids, and bases as species in the model system, allowing the induced pH gradients resulted from H+ or OH- sorption by the ion exchanger to be described in the model. Feed profiles of all the species can be specified individually allowing complicated gradient patterns. The software, known as Chromulator-IEX, may be a useful tool for the investigation of ion-exchange chromatography behavior and its scale-up.
Highlights
Downstream processing of a protein product usually takes up the majority of the overall production cost [1]
The model system coupled with the pH expression to calculate the pH value everywhere inside the column successfully simulated the phenomenon of induced pH transitions in ion-exchange chromatography (IEC)
The model and software presented in this work should be useful tools to those involved in the scale-up of ion-exchange chromatography
Summary
Downstream processing of a protein product usually takes up the majority of the overall production cost [1]. For a system with Ns species (including the ion that is used to equilibrate the column initially), Ns(Ns−1)/2 rate constants or Damköhler numbers can be chosen independently of the Ns−1 equilibrium constants. Q1 is the concentration of salt ion sorbed on the ion-exchange resin available for ion exchange after considering the steric hindrance is calculated from the following equation in which σi is the steric factor for species i (excluding the salt, i.e., i≠1), Ns
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