| Summary: | 碩士 === 國立中興大學 === 化學工程學系 === 93 === The present study is to investigate the kinetics of synthesizing o-hydroxybenzoic acid benzyl ester in a continuous flow reactor via third-liquid phase transfer catalysis. This reactor was designed in such a way that the third-liquid phase was kept in middle part of the reactor with both aqueous phase and organic phase flowing through. The conditions of forming the third-liquid phase include different concentrations of aqueous reactants, inorganic salts, and catalysts, and the optimal condition to form the catalytic intermediate in the third-liquid phase was found. Adding an excess of water the volume of third-liquid will disappear. The operating parameters include aqueous reactants, inorganic slats, agaitation speed organic reactans, phase transfer catalyst, and different of temperature on the reaction, and space time.
In this system, the reaction conditions of agaitation speed at 300 rpm, catalyst tetrabutylphosphonium bromide ( TBPB ) at 0.025 mol and at 70℃, the product yield greater than 82.43% was obtained. The apparent activation energy in heptane was obtained 8.91 kcal/mol using tetrabutylphosphoium bromide as the catalyst and a higher temperature is to facilitating to form the third-liquid phase.
The yield of o-hydroxybenzoic acid benzyl ester increases with the space time for the aqueous phase and organic phase both controlling at 0.3 ml/min. It is found that the minimum quantity of TBPB required to form the third –liquid is dependent on the amounts of NaBr added, and the volume of third-liquid generated increases with increasing catalyst used. The reaction rate will be decreased in an excess of catalyst at 0.025mol. The experimental data were well described by the proposed kinetic model.
Adding trialkylamines are also investigated at different reaction conditions in the continuous flow reactor. Trialkyamines first reacted to form tetraalkylammonium salts with benzyl bromide in organic phase and then transferred into the third liquid phase. Adding tralkylamies well effects volume of third liquid phase, reaction rate and changing properties of the third-liquid phase. By increasing temperature, the reaction rate will be faster and get a higher product yield for tri-ethylamine, due to its easy reaction with the aqueous reactant to form the catalytic intermediate and good for this esterification reacation.
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