Mathematical modelling and computer simulation of aqueous two-phase continuous protein extraction

An extended mathematical model has been developed to describe the continuous, steady state operation of an aqueous two-phase system for protein extraction. The basic model is based on steady state mass balances of the main components and phase equilibrium data. Phase equilibrium (binodial curve) was fitted by an equation that relates poly(ethylene glycol) (PEG) to phase forming salt (e.g phosphate) and added NaCl. Experimental data on the separation of α-amylase from B. subtilis supernatant in a PEG4000/phosphate system was used. The data show the effect of NaCl which was used to carry out the extraction of α-amylase into the PEG phase and back into the salt phase. The partition coefficient of the α-amylase was fitted to a sigmoidal Boltzman curve and gave a very good fit. Two simulations were carried out to show the effect of phase ratio on purification and this was represented in an equilibrium system diagram of material balances. The model has been extended to account for phase separation kinetics and thus aspects of continuous processing. Modelling the rate of settling of the two phases using appropriate correlations has been presented and discussed.