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Effects of Multisolute Steric Interactions on Membrane Partition Coefficients
Matthew J. Lazzara1, Daniel Blankschtein, William M. Deen
1Department of Chemical Engineering, Cambridge, Massachusetts, 02139
Journal of Colloid and Interface Science
|June 13, 2001
Summary
This study explores how solute size impacts partition coefficients in separations. It found that mixtures of different-sized solutes or fibers significantly alter partition coefficients compared to uniform systems.
Area of Science:
- Separation science
- Physical chemistry
- Materials science
Background:
- The partition coefficient is crucial for membrane and chromatographic separations, representing solute distribution between phases.
- Previous studies examined dilute solutions and uniform-sized spherical solutes in concentrated solutions.
- Concentrated solutions show increased partition coefficients due to steric interactions.
Purpose of the Study:
- To theoretically investigate the effects of solute size and shape on partition coefficients in porous and fibrous media for concentrated mixtures.
- To extend existing models by incorporating excluded volume effects for non-uniform systems.
Main Methods:
- Utilized an excluded volume approach to model steric interactions between solute molecules and with pore/fiber walls.
- Calculated partition coefficients by summing excluded volumes for solute molecules, considering their finite size and the presence of other solutes and obstacles.
- Extended calculations to include mixtures of spherical solutes, spheroidal solutes, and heterogeneous fibrous media.
Main Results:
- For binary mixtures of spherical solutes, any second solute increased the partition coefficient of the first, with smaller solutes having a greater effect.
- When total solute volume fraction was constant, increasing smaller second solutes raised the first solute's partition coefficient, while increasing larger second solutes lowered it.
- In heterogeneous fibrous media, smaller fibers decreased partition coefficients, whereas larger fibers increased them, for a constant total fiber volume fraction.
Conclusions:
- The excluded volume theory accurately models steric effects in concentrated solute mixtures.
- Heterogeneities, such as mixtures of solute sizes or fiber sizes, significantly influence partition coefficients.
- These findings are critical for optimizing separation processes involving complex mixtures and non-uniform materials.