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Nonequilibrium thermodynamic theory for concentration profiles in liquid extraction
Author(s) -
Hennico Alphonse,
Vermeulen Theodore
Publication year - 1962
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690080327
Subject(s) - raffinate , countercurrent exchange , chemistry , thermodynamics , mass transfer , non equilibrium thermodynamics , supersaturation , mass transfer coefficient , work (physics) , metastability , activity coefficient , extraction (chemistry) , diffusion , spinodal , chromatography , phase (matter) , aqueous solution , physics , organic chemistry
The pattern or profile of concentration change in each of the two countercurrent streams, within a packed extraction column involving a three‐component system, is generally assumed to follow either branch of the mutual‐solubility curve for the system. In the work reported here such concentration profiles have been computed for an idealized extraction. The results show that the raffinate will usually be carried into a metastable condition inside the equilibrium curve, but the extract composition remains appreciably outside the equilibrium curve. In the calculations mass transfer coefficient ratios are held constant at any one steady state condition of operation (called a run ), but are varied in different runs, in order to determine the direction and magnitude of their effects. A modified activity‐gradient, derived both for molecular diffusion and for penetration‐theory conditions, is postulated to govern mass transfer and is used in place of the usual concentration driving potential. Solute depletion, mainly, is found to explain the result for the raffinate phase in much the same way that temperature lowering leads to supersaturation in binary solutions. Solute enrichment is the cause of the extract‐phase behavior.