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|標題:||Synergism Effects of Trialkylamine on Esterification of Sodium Salicylate in Third- Liquid Phase-Transfer Catalysis
|關鍵字:||相間轉移觸媒;Phase-transfer catalysic;第三液相;三級胺;固體觸媒;四級銨鹽;界面張力;觸媒再生及回收;Third-liquid phase;Trialkylamine;Solid catalysts;Tetraalkylammonium salts;Interfacial tension;Recovering of catalysts||出版社:||化學工程學系||摘要:||
首先，針對三級胺之固體觸媒對三液相系統之影響，加入固體觸媒其表面吸附水相反應物，且固體觸媒懸浮於第三液相內，因此可攜帶水相反應物至第三液相，提高反應速率至0.027 min-1左右。探討因素包括不同三級胺官能基之固體觸媒、固體觸媒用量、固體觸媒高分子擔體之交聯度和粒徑，另外，固-液-液系統之反應速率遠小於第三液相系統。轉速超過300 rpm可忽略質傳阻力。
加入液態之三級胺於第三液相系統中，三級胺會在有機相與有機相反應物形成四級銨鹽質傳至第三液相，藉著四級銨鹽本身的性質改變第三液相性質及第三液相與有機相之間的界面張力，使得反應速率產生一些變化。故三級胺之四級銨鹽生成量多寡會影響反應速率及界面張力，不同種類三級胺使界面張力改變程度有所不同，加入親水性三乙基胺之界面張力隨三級胺用量從8.92 mN/m提升至10.88 mN/m，而加入親油性三辛基胺，其界面張力從8.92 mN/m減少至4.14mN/m，探討四級銨鹽生成量之因素有不同三級胺種類，溫度效應，以及三級胺種類與用量會影響界面張力。另外，此反應為可逆反應，藉著生成四級銨鹽之平衡常數對溫度倒數之關係圖得到不同三級胺生成四級銨鹽之焓變化量：三辛基胺之：8.21 (kcal/mol)，三己基胺：6.37 (kcal/mol)，三丁基胺：5.61 (kcal/mol)，三乙基胺：2.32 (kcal/mol)。
本文亦探討三級胺在三液相催化酯化反應之反應動力學。在動力學探討變數中，當攪拌速率超過250 rpm時，可忽略質傳阻力，產物在有機相與第三液相的分佈係數為1.02定值。不同三級胺種類的影響，以三乙基胺之反應速率最低，其產率約74.67%左右。三己基胺和三辛基胺之反應速率最高，產率值約為86.47%左右，而不加三級胺之反應其產率約83.58%左右。若單純只加三辛基胺而不加相間轉移觸媒，其反應速率很低，產率40%左右。當溫度提高，加入三級胺使有機相與第三液相之間的界面張力改變，反應對溫度的敏感性明顯地變化。加入三種三級胺之活化能數值為三丁基胺：16.79 (kcal/mol)；三己基胺：17.52 (kcal/mol)；三辛基胺：18.98 (kcal/mol)。加入三級胺於第三液相系統中，反應速率隨著回收次數增加而沒有任何變化。
The cocatalyst effects of trialkylamines on the esterification of sodium salicylate with benzyl bromide in a third-liquid phase-transfer catalyzed system were investigated. The types of trialkylamine included solid catalysts which trialkylamine was loaded on polymer supports and trialkylamine reacted to become tetraalkylammoniun salts with benzyl bromide. The outline of this thesis included the cocatalyst effects of solid catalysts in third-liquid phase, the formation reaction of tetraalkylamine of trialkylamine and interfacial tensions between third-liquid phase and organic phase in tri-liquid system, and the kinetics of esterification with tetraalkylammonium salts of trialkylamine in tri-lquid system.
For effects of solid catalysts of trialkylamine in tri-liquid system, sodium salicylate was absorbed on the surface of solid catalysts, which suspended in third-liquid phase, to carry about sodium salicylate into third-liquid phase and to raise reaction rate to about 0.027 min-1. The factors include different function groups of trialkylamine loaded on supports, amounts of solid catalysts, degree of crosslinking and particle size of solid catalysts. Additionally, reaction rates of solid-liquid-liquid catalyzed system were smaller than third-liquid phase catalyzed system by neglecting mass transfer resistance when agitation speed exceeded 300 rpm.
Adding trialkylamines into third-liquid phase, trialkylamines reacted to tetraalkylammoniun salts with benzyl bromide in organic phase and transferred into third-liquid phase. With properties of tetraalkylammoniun salts changing the property of third-liquid phase and interfacial tension between third-liquid phase and organic phase, the reaction rates were changed. So the amount of formation of tetraalkylammoniun salts influenced reaction rate and interfacial tensions, and the factors included different types of trialkylamine and temperature, moreover, the types and amounts of trialkylamine also influenced interfacial tension. By adding triethylamine, the interfacial tension between third-liquid phase and organic phase was from 8.92 mN/m to 10.88 mN/m with increasing amount of triethylamine, and the interfacial tension was from 8.92 mN/m to 4.14 mN/m with increasing amount of trioctylamine by adding trioctylamine. In addition, this reaction was reversible, and the enthalpy obtained by changing different types of trialkylamine forming tetraalkylammoniun salts from the relationship of the equilibrium constant for forming tetraalkylammoniun salts and temperature were: trioctylamine: 8.21 (kcal/mol); trihexylamine: 6.37 (kcal/mol); tributylamine: 5.61 (kcal/mol); triethylamine: 2.32 (kcal/mol).
The reaction mechanism and kinetic model was proposed and validated from the experimental results. When the agitation speed exceeded 250 rpm, the mass transfer resistance at the third-liquid interface could be ignored, and the distribution constant of product between third-liquid pahse and organic phase was 1.02. For the effects of different types of trialkylamine, the reaction rate by adding triethylamine was the lowest to give 74.67% of the yield, and the reaction rates by adding trihexylamine and trioctylamine were higher to give the yield 86.47%, and the yield without adding trialkylamine was 83.58%. If only adding trioctylamine and without adding tetrabutylphosphonium bromide, the reaction rate was the lowest and the product yield was about 40%. When increasing temperature, the interfacial tension between organic phase and third-liquid phase was changed by adding trialkylamine, the sensitivity of reaction rate to temperature was obviously changed, and the activation energy for three trialkylamines were: tributylamine: 16.79 (kcal/mol); trihexylamine: 17.52 (kcal/mol); trioctylamine: 18.98 (kcal/mol). By adding trialkylamine in third-liquid phase catalyzed system, the reaction rate had only very little changing with the recovering order of catalysts.
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