11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis
11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis
11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
The mass transfer resistances strongly depend on the nature <strong>of</strong> the hydrodynamics inthe contacting device <strong>and</strong> the mode <strong>of</strong> operation. Many devices have been used to studytwo-phase mass transfer at or near the liquid–liquid interface. Hence, the hydrodynamiccharacteristics <strong>of</strong> ion transport through a membrane were presented to evaluate the feasibilitythat this permeation system can be calibrated as a st<strong>and</strong>ardized liquid–liquidsystem for studying the membrane-moderated PT-catalyzed reaction. The individualmass transfer coefficients <strong>and</strong> diffusivities for the aqueous phase, organic phase, <strong>and</strong>membrane phase were determined <strong>and</strong> then correlated in terms <strong>of</strong> the conventional Sh–Re–Sc relationship. The transfer time <strong>of</strong> quaternary salt across the membrane <strong>and</strong> thethickness <strong>of</strong> the hydrodynamic diffusion boundary layer are calculated <strong>and</strong> then the effect<strong>of</strong> environmental flow conditions on the rate <strong>of</strong> membrane permeation can be accuratelyinterpreted [127].The mass transfer <strong>of</strong> quaternary salt from the organic phase into the aqueous phasethrough a lipophilic membrane is indicated in Fig. 3. Assume that the solute activity in thislipophilic membrane is identical to that in the bulk organic solution, then the mass fluxvalues for the individual species are described byN ¼ k o ½QXŠ ½QXŠ i ð57ÞN ¼ k a ½QXŠ i ½QXŠ ð58ÞN ¼ k m ½QXŠ i ½QXŠ ið59ÞThe asterisk denotes the species in the organic phase <strong>and</strong> the membrane phase, respectively.The distribution coefficients <strong>of</strong> quaternary salts between membrane <strong>and</strong> aqueousphase or organic phase are defined asm ¼ ½QXŠ i½QXŠ ið60Þ<strong>and</strong>m ¼ ½QXŠ i½QXŠ ið61ÞFIG. 3Mass transfer <strong>of</strong> the catalyst between two phases <strong>and</strong> membrane.Copyright © 2003 by Taylor & Francis Group, LLC