| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 94 === This thesis presents the results of a continued study on the novel solid-liquid-liquid phase transfer catalysis (SLL PTC), which is adopted for synthesizing n-hexyl acetate (ROAc) from n-hexyl bromide (RBr) and sodium acetate (NaOAc) by using a catalyst-rich liquid phase. The SLL PTC system contains a solid phase (NaOAc), two liquid phases (catalyst-rich liquid phase and organic phase). The phase transfer catalyst used is tetrabutylammonium bromide (QBr). The conditions for forming a solid-liquid-liquid system and the optimal conditions for the esterification of RBr and NaOAc were searched and analyzed. The operating method for reusing the catalyst-rich liquid phase was also improved. Besides, the phase change in the system containing the catalyst-rich liquid phase and organic phase was experimentally observed.
This thesis is mainly divided into four parts. In the first part, the proper conditions to form a solid-liquid-liquid system were searched, the distributions of the organic reactant(RBr) and product(ROAc) between the organic phase and catalyst-rich liquid phase were measured and the effects of the amounts of NaOAc and NaBr in the catalyst-rich liquid phase and the kinds of organic solvents were investigated. The hold-up of organic solvent in the system containing organic phase and catalyst-rich-phase was measured in the second part in order to know when the phase change happened. In the third part, the sampling method was evaluated first, then the effects of the amounts of NaOAc, RBr, QBr and organic solvent, and the kinds of catalysts on the conversion of RBr were investigated to find the optimal operating conditions. The final part dealt with the subject of reusing the catalyst-rich-phase, the best way for reusing the catalyst was found.
Because the main reaction occurred in the catalyst-rich phase, the reaction rate depended on the formation rate of Q+OAc-. A small amount of water should be added into the SLL PTC system for dissolving NaOAc. However, the amount of NaOAc dissolved was limited because only a limited amount of water could be added. When 25 mL of heptane was used as the organic solvent, the optimal amount of QBr and NaOAc added were 0.03 and 0.04 mol, respectively. Using an organic solvent with lower polarity and tetrabutyl ammounium bromide as a catalyst were beneficial for the formation of a catalyst-rich phase. Because the volume of organic phase is much larger than the catalyst-rich liquid phase, the organic phase is always a continuous phase and the catalyst-rich phase is a dispersed phase.
In the experiments of reusing the catalyst-rich liquid phase, the conversion of RBr was found decreasing with the times of reuse. This fact was caused by the following three reasons :(1) NaBr formed during the reaction decreased the amount of ion pair of Q+OAc- resides in the catalyst-rich liquid phase. However, adding a proper amount of water is helpful for mitigating the NaBr effect. (2) Because a small of RBr stayed in the catalyst-rich liquid phase after removing the organic phase, an error in the calculated conversion was thus induced. (3) The increase in the volume of the catalyst-rich liquid phase with the times of reuse would cause the decrease in the concentration of Q+OAc- in the catalyst-rich phase, hence resulted in the decline of conversion in the 2nd and 3rd runs.
To improve the above-mentioned drawbacks and error induced, the following techniques can be adopted. (1) The use of anion exchange resin for exchanging Br- in NaBr with OAc-; (2) The addition of a proper amount of water; (3) The calculation of RBr conversion should be based on the amount of RBr actually taking part in the reaction.
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