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Kinetics for Esterification of Sodium Benzoate over Immobilized Phase-Transfer Catalysts
|關鍵字:||Phase-Transfer Catalysis;相間轉移觸媒;Kinetics;Esterification;Immobilized Catalyst;Regeneration and Recycle of Catalyst;動力學;酯化反應;固定化觸媒;觸媒再生及回收||出版社:||化學工程學系||摘要:||
The kinetics for SN2 nucleophilic substitution reaction of sodium benzoate with benzyl bromide catalyzed by immobilized phase-transfer catalyst was investigated. The support of solid phase-transfer catalyst was prepared from the copolymerization of polystyrene and chloromethylstyrene. Different functional groups were used as the active centers, such as trialkylamines, trioctylphosphine or triphenylphosphine, and that was immobilized onto the surface of the macroporous or microporous catalysts.
In solid-liquid-liquid system, the product yield was obtained above 86% within 3 hr of reaction using small amount of solid catalyst with the properties of 1.38% divinylbenzene crosslinked, particle size of 40-80 mesh ,tributylamine activated, and macropore-mouth type, and the overall reaction rate decreased with increasing the mean particle size. This demonstrates that the esterification of sodium benzoate is controlled by the combination of intraparticle diffusion and intrinsic reaction under triphase conditions. Moreover, the characteristics and structure of the catalyst support also affect the catalytic efficiency. With the same degree of crosslinking, macroporous catalyst with tributylamine activated has higher activities than microporous catalyst does. The effects of operating parameters, including agitation speed, reaction temperature, amounts of catalyst, types of solvents, molar ratio of reactants, type of phase-transfer catalysts, volume ratio of aqueous, and so on, were all performed to find the optimal reaction conditions. With increasing of agitation speed, reaction temperature and amounts of catalyst, the reaction rate increased. The catalytic efficiency of functional group used as trioctylphosphine was best than trialkylamines.
The ion-exchange reaction is one of the fundamental process of solid-liquid-liquid triphase reactions. We also proceed the ion-exchange reaction by triphase catalysts for sodium benzoate solution to know the formation and variation of the active intermediate (PhCOOQ) during the reaction. After induction period in 3 minutes, the active intermediate of the solid catalyst with 1.38% divinylbenzene crosslinked and macroporous type was also observed to keep at a near constant concentration. With increasing of cross-linking level, the formation of the active intermediate decreased.A kinetic model was developed to describe this esterification conducted in the solid-liquid-liquid triphase system, and the experimental data were well described by the pseudo-first-order kinetics.
Eventually, the methods of reuse and regeneration of the catalyst was also explored to reach the purpose of lowering processing cost and saving resources.
|Appears in Collections:||化學工程學系所|
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