| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 90 === Two phase transfer catalysis techniques were employed in this study, one is tri-liquid-liquid-phase catalysis technique in which soluble tetra-ammonium salt (tetra-n-propylammonium bromide Pr4NBr and tetra-n-butylammonium bromide Bu4NBr) were used as the phase transter catalysts, the other is liquid-liquid-solid (i.e. triphase) catalysis technique in which insoluble polymer-supported catalyst was utilized. In the preparation of the polymer-supported catalyst (triphase catalyst) tributylamine was immobilized on chloromethylated polystyrene polymer. With organic product allyl phenyl ether (ROPh) as solvent, we made use of allyl bromide (the organic reactant, RBr) and sodium phenolate (the aqueous reactant, NaOPh) to synthesize allyl phenyl ether. By this way, we can get the pure allyl phenyl ether without separation and purification if all the allyl bromide is converted. Thus, we can save the operation cost, and need not to dispose the waste solvent. It will correspond with the ‘green chemistry’. At the end of this study, the feasibilities and two catalysis techniques were evaluated and compared by operating in continuous-flow stirred vessel reactor (CFSVR).
This thesis is composed of three parts. In the first part, the feasibilities of using Pr4NBr and Bu4NBr as the phase transfer catalysts for the tri-liquid-phase reaction in a continuous-flow reactor were evaluated basing on whether a third liquid phase will be formed or not. Then, using Pr4NBr as the catalyst, the tri-liquid-phase catalytic reaction was carried out under different operating conditions by means of a continuous-flow stirred vessel reactor. The performance of prepared polymer-supported catalyst was evaluated by using it as a triphase catalyst repeatedly in a batch reactor under different operating conditions in the second part. The tri-liquid-phase and liquid-liquid-solid catalytic systems were compared in the last part.
In the first part, the etherification reaction was carried out with the tri-liquid-phase method, the effects of operating variables, including the most suitable volume of allyl phenyl ether for helping the tri-liquid-phase and mole fraction of Pr4NBr on the conversion of RBr, and the repeated batch operations on the distribution of Pr4NBr or Bu4NBr in various phase were investigated first. After that we investigate the effects of agitation speed, inlet flow rate, reaction temperature, inlet molar ratio of reactant, the number of stages in the extractor and the kinds of catalysts on the performance of CFSVR. Experiment results show that the tri-liquid-phase catalytic system that was formed by the using Pr4NBr as a catalyst and equal amount of allyl phenyl ether and pure water was suitable for being operated in a continuous-flow reactor. When the mole fraction of Pr4NBr was 0.5, most of the catalysts concentrate on the third-liquid phase. Although the catalytic activity of Pr4NBr is lower than Bu4NBr, however, its loss rate is lower when both were used as the catalysts in repeated batch operations. When total volume of inlet fluid is larger than the volume of reactor, the system can reach a steady state. The interfacial mass transfer resistance can be neglected when the agitation speed is beyond 600 rpm. A higher conversion of RBr can be obtained when the inlet flow rate is 1 ml/min. The higher the temperature is, the higher the conversion gets and the more stable more stable the third-liquid phase is. In order to prevent the loss of that the third-liquid phase resulting from agitation, we installed a packed bed or baffles under the continuous-flow reactor, and observed individual. The result shows that the reactor with a packed bed can keep the catalyst loss rate of aqueous being lower. However, the droplet of the third-liquid phase easily stayed under the packed bed rather than go back to the reaction area. Therefore, the reaction is more appropriately carried out in the continuous-flow reactor that has baffles. The more stages the extractor has, the better the effect of extraction is. The effect of extraction will be similar if there is little amount of Pr4N+ among organic phase outlet. Feeding with equal organic-to-aqueous reactant molar ratio can keep the catalyst loss rate lower than unequal reactant molar ratio inlet. Because of lower lipophilicity, Pr4NBr was more suitable to be used as the phase transfer catalyst to run this tri-liquid-phase catalytic reaction than Bu4NBr.
In the second part, the etherification reaction was carried out with the liquid-liquid-solid method. Several factors which influence the conversion of RBr is discussed. The factors include agitation speed, volumetric ratio of organic solvent and water, reaction temperature, amount of catalysts, amount of aqueous and organic reactants, amount of salts, amount of tri-n-butylamines and stability of catalyst. Experimental results show that the interfacial mass transfer resistance can be neglected when the agitation speed is beyond 200 rpm. High conversion of RBr will be obtained when the volume of organic solvent and water are equal. Raising the temperature can promote the conversion. But RBr will vaporize and the catalyst will be worsened when the temperature is too high. As a result, the appropriate temperature is 50℃. An amount of 5.4 meq catalyst is economic and cost-effective. When using more NaoPh than RBr, the reaction is pseudo-first-order irreversible reaction. As this time, a higher conversion of RBr comes into effect. Existence of salts restrains the activity of catalyst. The extent of inhibition depends on the amount of salts. Two reasons will cause the decrease of catalyst activity. One is that the activity site on the polymeric support will fall down because of Hofmann elimination reaction. The other is that the force of agitation will destroy the structure of catalyst. The tri-n-butylamine which falls from support can react with organic reactant and form the tetra-alkylamine salt. The tri-n-butylamine salt has catalytic activity but is lower than the form that the tri-n-butylamine fixes on the support.
The performances of the tri-phase system and liquid-liquid-solid system are compared in the last part. The comparison is based on four items, namely, catalytic effect, stability of catalysts, the operation of continuous-flow reactor and the procedure of preparing catalysts. Because of the high dispersion and bigger interfacial area, the tri-liquid phase catalyst has better catalytic effect. On the other hand, the tri-liquid phase catalyst is cheaper than the triphase catalyst hence it is more cost-effective. Although the tri-liquid phase catalyst will dissolve in organic and aqueous phase and flow away with outlet, the stability of catalyst is still better than triphase catalyst. The operation of continuous-flow reactor with liquid-liquid-solid catalyst is simpler due to the fact that we don’t have to extract the catalyst from the organic phase. The procedure of preparing polymer-supported catalysts is complicated and the reproducibility is not as well as the formation of a third liquid phase in the tri-liquid phase system.
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