| 研究生: |
蔡亦逵 Tsai, Yi-Kuei |
|---|---|
| 論文名稱: |
具有富含觸媒液相之固-液-液相間轉移催化技術-醋酸己酯之合成 Solid-Liquid-Liquid Phase-Transfer Catalysis with a Catalyst-rich Liquid Phase - Synthesis of Hexyl Acetate |
| 指導教授: |
蕭旭欽
Hsiao, Hsu-Chin 翁鴻山 Weng, Hung-Shan |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 化學工程學系 Department of Chemical Engineering |
| 論文出版年: | 2006 |
| 畢業學年度: | 94 |
| 語文別: | 中文 |
| 論文頁數: | 110 |
| 中文關鍵詞: | 醋酸己酯 、溴化四正丁基銨 、富含觸媒液相 、固-液-液相間轉移催化 |
| 外文關鍵詞: | catalyst-rich liquid phase, Solid-liquid-liquid phase-transfer catalysis, tetra-n-butylammonium |
| 相關次數: | 點閱:95 下載:1 |
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本論文延續先前之研究,探討一種新穎的固-液-液相間轉移催化技術在醋酸鈉與溴正己烷之醚化反應上的應用,即將一富含觸媒(溴化四正丁基銨, QBr)之液相(簡稱觸媒液相),加入固相反應物醋酸鈉(NaOAc)和有機相反應物溴正己烷(RBr),形成固-液-液相間轉移催化(SLL PTC)反應系統,用以催化RBr和NaOAc反應生成醋酸己酯(ROAc)。藉由本論文進一步分析SLL PTC系統的形成條件,以期找到更佳的批式反應條件,並改良批式重複操作方法達到觸媒重複使用的目的,另外也探討SLL PTC系統內的相轉換情形。
本論文主要分成四個部分:
第一部份是對SLL PTC系統的形成條件作進一步的分析,以瞭解有機相反應物(RBr)與生成物(ROAc)在有機相與觸媒液相中的分佈、固相鹽類醋酸鈉與溴化鈉(NaBr)對觸媒液相的影響、與不同碳數烷類溶劑對催化系統的效應。
第二部分是找出SLL PTC系統中有機相與觸媒液相發生相轉換時有機相體積分率,以瞭解在最佳批式反應條件下,此兩液相在反應過程中的相分佈模式。
第三部份是探討取樣分析方法、觸媒與醋酸鈉用量、有機相反應物與溶劑劑量、觸媒種類、溫度等因素對批式SLL PTC反應結果的效應,以獲得更佳催化效果及更高經濟效益的催化條件。
第四部分是在最佳批式反應條件下,探討重複使用SLL PTC系統中觸媒液相的效果,並改良重複操作方法,重新評估觸媒重複使用的可行性。
由於本實驗的醚化反應是在觸媒液相中進行,因此QOAc之生成速率會影響到整體的反應快慢,但由於SLL PTC中只有少量的水量,因此可溶入鹽類劑量有限,在加入25 mL正庚烷之系統中,最佳反應條件為QBr為0.03 mol,NaOAc為0.04 mol下有最適當反應速率及生成分率,而且使用較低碳數之烷類溶劑與溴化四正丁基銨為觸媒,有益於觸媒液相之生成與ROAc之生成。本實驗中有機相體積遠大於觸媒液相,因此兩液相之分佈情形為有機相包覆觸媒液相。
觸媒重覆使用的實驗中,隨著操作次數增加,RBr之轉化率也隨之遞減,原因有以下三點:(1)反應中生成的NaBr會降低觸媒液相內的Q+OAc-離子對的含量,而降低催化效果,但可加入適量的水分改善;(2)在移除有機相時,有少量的RBr會殘留在反應器中,造成計算時之誤差;(3)在反應過程中觸媒液相之體積不斷增加,造成觸媒液相內的QOAc濃度下降,使得觸媒液相中RBr之反應速率降低。為了改善上述的缺點與偏差,未來可以(1)使用陰離子交換樹酯,以OAc-交換NaBr中Br-;(2)添加適量的水分;(3)以實際參與反應的RBr量計算RBr之轉化率。
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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