11. Interfacial Mechanism and Kinetics of Phase-Transfer Catalysis

The mass transfer rates of catalysts between two phases are difficultly realized due tothe difficult identification of the active catalyst during the reaction [57,112–115]. Masstransfer coupled rapid reactions subjected to LLPTC have been studied extensively[58,63,69,115,116]. Mass transfer rates of catalysts in the reaction of 2,4,6-tribromophenoland tetra-n-butylammonium bromide in a solution of KOH were determined [57,114].Evans and Palmer [50] first consider theoretically the effect of diffusion and masstransfer in two well-mixed bulk phases of uniform composition separated by a uniformstagnant mass transfer layer at the interface. They studied the effect of the Damko¨ hlernumber, organic reaction equilibrium rate constant, reactant feed-rate ratio, flow rate ofthe organic phase, and the organic reaction reactivity on conversion. Chen et al. [53]derived algebraic expressions for the interphase flux of QY and QX. The reaction parameterswere estimated from experimental data using a two-stage method of optimal parameters.Naik and Doraiswamy [117] reported that future research should be directedtowards the use of a membrane module as a combination reactor and separator unitwith the membrane serving not merely to carry out the PT-catalyzed reaction, but alsosimultaneously and selectively to recover the organic product. Stanley and Quinn [118]reported the use of a membrane reactor for performing PT-catalytic reactions andincluded theoretical models and calculations to predict the kinetic behavior of the system.Matson [119] investigated the commercial feasibility of such membrane systems. However,the characterization of hydrodynamic phenomena in PT-catalyzed reactions has not beenattempted.Rushton et al. [120] developed a method for measuring the mass transfer coefficient.However, their method can only be used in systems with unity distribution ratio. Asai etal. [121] measured the liquid–liquid mass transfer coefficients in an agitated vessel with aflat interface. In their later work [122,123] on the alkaline hydrolysis of n-butyl acetate andoxidation of benzyl alcohol in an agitated vessel, the overall reaction rate of PTC withmass transfer at a flat interface was analyzed. The observed overall reaction rate wasconcluded to be proportional to the interfacial concentration of the actual reactant.Wang and Yang [57] investigated the dynamic behavior of PT-catalyzed reactions bydetermining the parameters accounting for mass transfer and the kinetics in a twophasesystem. The film theory was applied to interpret the behavior of PTC. The overallmass transfer coefficients of QX (or QY) from an agitated mixture of QX (or QY) werefirst calculated in known qualities of water and the organic solvent by using a simplecorrelation:"lnC QXþV C # QX1V!mQXC QX;i m QXV C QX;i V þ 1 ¼ K QX At ð56ÞThe overall mass transfer coefficient of QX was obtained by plotting the term on the lefthandside of Eq. (56) versus time. Yang et al. [124] developed a mathematical modelconcerning mass transfer in a single droplet to describe the dispersed phase system.They measured the distribution coefficient and the mass transfer coefficient of a PTcatalytic intermediate between two phases.Also, the diffusion boundary layer resistances on either side of the membrane filter inmembrane transport processes have been extensively examined [125,126]. Most of thesestudies deal with cases wherein solute diffuses across a membrane filter separating twoaqueous phases with different concentrations. However, the individual film mass transfercoefficients in both liquid phases are unavailable.Copyright © 2003 by Taylor & Francis Group, LLC