The purpose of this model is to simulate extraction in a multi-stage mixer-settler extractor. In the biochemical process industries, extraction is primarily used in the recovery and purification of antibiotics and other low to medium molecular weight products.
● Mixer-Settler Extraction Procedure
Material balances can be done based on component splits or partition coefficients. In the former case, the user specifies the fraction of each component that ends up in the top or bottom exit stream. The figure below shows a schematic representation of the multiple extraction stages in the case that partition coefficients are used.
In the above representation, L and H are the volumetric flowrates and yi and xi are the component concentrations at stage i in the light and heavy phase, respectively. Two streams that exit from a stage are assumed to be at equilibrium described by a partition coefficient Ki = yi/xi. By considering the material balances around each stage with the assumption of constant volumetric flowrates for the heavy and light phases, one can derive the following equation for the concentration of (Belter, Cussler and Hu, 1988):
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eq. (A.217) |
where:
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eq. (A.218) |
Notice that partition coefficients refer exclusively to non-solvent components. To model solvent miscibility in two-solvent systems, the solubility of each solvent (of the light or heavy phase) in the other solvent should be specified. For single-solvent systems (e.g., aqueous two-phase systems used in biotechnology for the recovery and purification of proteins and other biological molecules), the user must specify the split of the single solvent between the two phases.
In Design Mode, the sizing of the mixer and settler tanks is based on the volumetric throughput the corresponding residence time that is specified by the user. If the operating throughput exceeds the maximum, the program assumes multiple units operating in parallel with a total throughput equal to the calculated. In rating mode, the size of the mixer and settler tank is provided by the user and the program calculates the corresponding residence times.
1. Belter, P. A., E. L. Cussler, and Wei-Shou Hu (1988). Bioseparations - Downstream Processing for Biotechnology, John Wiley & Sons.
The interface of this operation has the following tabs:
● Oper. Cond’s, see Mixer-Settler Extraction: Oper. Conds Tab
● Mat. Balance, see Mixer-Settler Extraction: Material Balance Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab
