Diffusion in a Batch Extraction Cell

The batch extraction cell experiments of Krishna et al. (1985) were discussed at some length in Section 5.6, where it was shown that the diffusion fluxes could be calculated from 

Here we use an effective diffusivity model for the diffusion fluxes 

Example 6,6.1 Multicomponent Diffusion in a Batch Extraction Cell 

In this example we analyze the composition trajectory in the glycerol rich phase (G) of the system glycerol(l)-water(2)--acetone(3) using a pseudobinary model. The initial composition 

DA TA The matrix of multicomponent volumetric mass transfer coefficients [ AT ] is given in Example 5.6.1. as 

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Equation 6.2.3 has exactly the same form as Eq. 5.1.3 for binary systems. This means that we may immediately write down the solution to a multicomponent diffusion problem if we know the solution to the corresponding binary diffusion problem simply by replacing the binary diffusivity by the effective diffusivity. We illustrate the use of the effective diffusivity by reexamining the three applications of the linearized theory from Chapter 5 diffusion in the two bulb diffusion cell, in the Loschmidt tube, and in the batch extraction cell. 

Since thermodynamic nonidealities are of the essence for phase separation in liquid-liquid systems, and such nonidealities contribute to multicomponent interaction effects, it may be expected that liquid-liquid extraction would offer an important test of the theories presented in this book. Here, we present some experimental evidence to show the significance of interaction effects in liquid-liquid extraction. The evidence we present is largely based on experiments carried out in a modified Lewis batch extraction cell (Standart et al., 1975 Sethy and Cullinan, 1975 Cullinan and Ram, 1976 Krishna et al., 1985). The analysis we present here is due to Ej-ishna et al. (1985). The experimental system that will be used to demonstrate multicomponent interaction effects is glycerol(l)-water(2)-acetone(l) this system is of Type I. The analysis presented below is the liquid-liquid analog of the two bulb gas diffusion experiment considered in Section 5.4. 

The mechanisms of CO2 toxicity at near-atmospheric pressures are amplified at the near-critical and supercritical pressures used to achieve sterilization. For example, Spilimbergo et al. (9) examined the mechanism of inactivation of Pseudomonas aeruginosa and B. subtilis at 38-54°C and 5.8-20 MPa in a batch process. Total inactivation of the bacteria was observed when exposed to SCF CO2 at 38°C and 7.4 MPa for 150 s. The mechanism of inactivation is suggested to involve (a) the diffusion of SCF CO2 into the cells leading to a drop in pH and a subsequent loss of activity of key enzymes and (b) the extraction by SCF CO2 of intracellular substances, including phospholipids. Further analysis determined a high solubility of CO2 in model cell membrane phospholipids, suggesting that the enhanced permeability of the membrane in the presence of CO2 contributed to the inactivation of the cells. 

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