eq. (A.239)
In differential extractors, solutes are transferred from one phase to the other continuously, but never fast enough to reach equilibrium. The result is significant product isolation, but without the potentially tedious settling times which characterize the staged extractors.
● Differential Extraction Procedure
The analysis of the differential extractor depends on three key equations. The first one is the statement of equilibrium:
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eq. (A.239) |
where x* is the concentration in the heavy phase which would be in equilibrium with the concentration y in the light phase at a certain position in the column. K is the partition coefficient of the product component between the two phases. The second key equation is a mass balance:
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eq. (A.240) |
where L and H are the volumetric flowrates of the light and heavy phase respectively. The index 0 denotes the concentration of the product component in the entering streams. The last key equation for the analysis of the differential extractor is:
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eq. (A.241) |
where dz is the differential height of the extractor over which the mass transfer takes place, k is the mass transfer coefficient, S is the surface area per unit volume, A is the cross sectional area of the extractor, and x is the concentration of the product in the heavy phase.
In Design Mode, the user specifies the product recovery yield and the above equations are used to calculate the number of transfer units (NTU), and height of a transfer unit (HTU) and consequently the height of the column. The column diameter is calculated by dividing the overall throughput by the flux of combined streams. If the calculated diameter exceeds the maximum, the program assumes multiple units operating in parallel with a total cross sectional area equal to the calculated. In Rating Mode, the user specifies the dimensions of the column and the above equations are used to calculate the product recovery yield and the compositions of the outlet streams.
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 Differential 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
