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Fluorous membrane-based separations and reactions

Yang, Yanhong (2011) Fluorous membrane-based separations and reactions. Doctoral Dissertation, University of Pittsburgh.

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    Abstract

    Porous alumina membranes were rendered compatible with fluorous liquids by surface modification with a carboxylic acid terminated perfluoropolyether (Krytox 157FSH). FTIR and contact angle measurements demonstrate the success of the modification.Fluorous liquids are readily imbibed by modified alumina membranes, resulting in fluorous supported liquid membranes. Fluorine-containing organic solutes are selectively transported through the fluorous supported liquid membranes. Selectivity is defined as the permeability of a fluorous tagged solute over an analogous organic compound. The membrane modification conditions (reagents, concentrations, reaction time) were optimized to maximize the selectivity. The membrane pore size affects the solute permeabilities and selectivities.Two series of homologous esters of perfluoroalkanoic acids with different organic moieties were studied. Permeability increased for both series as the perfluoroalkyl chain was lengthened. This shows that the difference in permeabilities is dominated by partitioning rather than diffusion. We further measured the partition coefficients of the homologs. The free energy of transfer of a ¨CCF2¨C group (ethanol to perfluorinated solvents) is -1.1 kJ/mol. The experimental values of the partition coefficients are well correlated with the ¡®mobile order and disorder¡¯ theory. This provides an easy way to estimate partition coefficients in any biphasic system, even for solvents that are fluorous mixtures. Diffusion coefficients were determined from permeabilities and partition coefficients based on the solution-diffusion model of permeability. Measured values are satisfactorily related to the Stokes-Einstein equation, especially for higher homologs. This investigation enables the prediction of transport properties of the fluorous supported alumina membranes.Krytox 157FSH, which is virtually insoluble in any but fluorous solvents, was deposited on the fluorous-modified alumina membranes. FTIR shows the presence of the H-bond-based carboxylic acid dimers for these adsorbed Krytox 157FSH molecules. The carboxylate groups of Krytox 157FSH extract cations from aqueous solutions.

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    Details

    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmail
    Committee ChairWeber, Stephen G.sweber@pitt.edu
    Committee MemberKoide, Kazunorikoide@pitt.edu
    Committee MemberEnick, Robert M.rme@pitt.edu
    Committee MemberAmemiya, Shigeruamemiya@pitt.edu
    Title: Fluorous membrane-based separations and reactions
    Status: Unpublished
    Abstract: Porous alumina membranes were rendered compatible with fluorous liquids by surface modification with a carboxylic acid terminated perfluoropolyether (Krytox 157FSH). FTIR and contact angle measurements demonstrate the success of the modification.Fluorous liquids are readily imbibed by modified alumina membranes, resulting in fluorous supported liquid membranes. Fluorine-containing organic solutes are selectively transported through the fluorous supported liquid membranes. Selectivity is defined as the permeability of a fluorous tagged solute over an analogous organic compound. The membrane modification conditions (reagents, concentrations, reaction time) were optimized to maximize the selectivity. The membrane pore size affects the solute permeabilities and selectivities.Two series of homologous esters of perfluoroalkanoic acids with different organic moieties were studied. Permeability increased for both series as the perfluoroalkyl chain was lengthened. This shows that the difference in permeabilities is dominated by partitioning rather than diffusion. We further measured the partition coefficients of the homologs. The free energy of transfer of a ¨CCF2¨C group (ethanol to perfluorinated solvents) is -1.1 kJ/mol. The experimental values of the partition coefficients are well correlated with the ¡®mobile order and disorder¡¯ theory. This provides an easy way to estimate partition coefficients in any biphasic system, even for solvents that are fluorous mixtures. Diffusion coefficients were determined from permeabilities and partition coefficients based on the solution-diffusion model of permeability. Measured values are satisfactorily related to the Stokes-Einstein equation, especially for higher homologs. This investigation enables the prediction of transport properties of the fluorous supported alumina membranes.Krytox 157FSH, which is virtually insoluble in any but fluorous solvents, was deposited on the fluorous-modified alumina membranes. FTIR shows the presence of the H-bond-based carboxylic acid dimers for these adsorbed Krytox 157FSH molecules. The carboxylate groups of Krytox 157FSH extract cations from aqueous solutions.
    Date: 01 July 2011
    Date Type: Completion
    Defense Date: 22 February 2011
    Approval Date: 01 July 2011
    Submission Date: 08 March 2011
    Access Restriction: No restriction; Release the ETD for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    URN: etd-03082011-092358
    Uncontrolled Keywords: diffusion; free energy of transfer; membrane transport; partition coefficient; permeability; surface modification
    Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
    Date Deposited: 10 Nov 2011 14:32
    Last Modified: 24 Feb 2012 13:53
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-03082011-092358/, etd-03082011-092358

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