Mass transfer with complex chemical reaction in gas—liquid ... - ITM

R.D. Vas Bhat et al./Chemical Engineering Science 54 (1999) 137—147 147curve before approaching the final infinite enhancementfactor.Finally, the model presented in this paper has beenused to determine differential selectivity towards the intermediatein the consecutive reaction scheme. Experimentaldata presented previously by Pangarkar andSharma (1974) for the chlorination of p-cresol have beenused for this purpose. As has been reported earlier,a strong influence of mass transfer parameters on theselectivity of the intermediate was observed with selectivityreducing with an increase in Hatta number. In practice,however, a compromise needs to be reached betweenselectivity towards the intermediate on the one hand andconversion on the other. Due to lack of comprehensivedata such as equilibrium constants, the full potential ofthe model could not be exploited.The present model provides a rigorous mathematicalanalysis of the consecutive reaction system under conditionsof unequal diffusivity. With a view of encouragingfurther numerical and/or approximate examination ofthis reaction scheme, a selection of results (obtained withthis model) has been presented in Table 4.AcknowledgementsThe authors wish to thank Akzo Nobel Central Research(the Netherlands) for their financial support tothis investigation and A.P. Higler for his assistance in thenumerical solution of the model.NotationA component A, concentration of componentA, mol mA total A in all forms ("A #D #E ), dimensionless B component B, concentration of component B,mol mB total B in all forms ("B #D ), dimensionless C component C, concentration of componentC, mol mD component D, concentration of componentD, mol mD diffusivity, sub: component, m sE component E, concentration of component E,mol mE enhancement factor, defined by reaction (2b),dimensionlessE final infinite enhancement factor, dimensionlessE intermediate asymptotic enhancement factor,dimensionlessHa Hatta number, defined by reaction (2c), dimensionlessK K k k N r equilibrium constant, sub: reaction number,dimensionlessk /k , dimensionless reaction rate constantsub1: reaction number, sub2: reaction direction,m mol sliquid-side mass transfer coefficient, m sgas flux, mol m sdiffusivity ratio, defined by D /D , sub: component, dimensionlessGreek lettersα loading factor ("A /B ), dimensionless σ differential selectivity, defined by Eq. (5a), dimensionlessζ conversion of p-cresol, defined by Eq. (5b),dimensionlessSubscripts0 initial conditionG, g gas phasei interface¸, l liquid phasered reduced¹ totalAbbreviationsMCPC monochloro-p-cresolDCPC dichloro-p-cresolReferencesDarde, T., Midoux, N., & Charpentier, J.C. (1983). Contribution to theanalysis of the selectivity in gas—liquid reaction part I: literature andtheory. Chem. Engng Commun., 22, 221—241.Darde, T., Midoux, N., & Charpentier, J.C. (1984). Contribution to theanalysis of the selectivity of gas—liquid reactions part II: comparisonof experimental results with model predictions. Chem. Engng Commun.,26, 33—54.DeCoursey, W.J., & Thring, R.W. (1989). Effects of unequal diffusivitieson enhancement factors for reversible and irreversible reaction.Chem. Engng Sci., 44, 1715—1721.Hashimoto, K., Teramoto, M., Nagayasu, T., & Nagata, S. (1968). Theeffects of mass transfer on the selectivity of gas—liquid reactions. J.Chem. Engng (Japan), 1, 132—138.Pangarkar, V.G., & Sharma, M.M. (1974). Consecutive reactions: roleof mass transfer factors. Chem. Engng Sci., 29, 561—569.Teramoto, M., Fujita, S., Kataoka, M., Hashimoto, K., & Nagata, S.(1970). Effect of bubble size on the selectivity of consecutivegas—liquid reactions. J. Chem. Engng (Japan), 3, 79—82.Vas Bhat, R.D., van Swaaij, W.P.M., Kuipers, J.A.M., & Versteeg, G.F.,Mass transfer with complex chemical reaction in gas—liquid systems—partI: consecutive reversible reactions with equal diffusivities.Chem. Engng Sci., 54, 121—136.Vusse, J.G. van de (1966a). Consecutive reactions in heterogeneoussystems I—the effect of mass transfer on selectivity. Chem. EngngSci., 21, 631—643.Vusse, J.G. van de (1966b). Consecutive reactions in heterogeneoussystems II—influence of order of reaction rates on selectivity. Chem.Engng Sci., 21, 645—654.