在不互溶的兩液相反應系統，反應受限於兩相的界面，以致反應速率慢，產率甚低。若添加相轉移觸媒，其可在兩液相間來回穿梭，因而提高催化反應效率，且具有反應條件溫和、觸媒用量少、加速反應速率、提高產率與具選擇性等特色。所以，相轉移觸媒催化反應系統的研究，一直是化工界研究的重點。
另一方面，由於相間轉移觸媒反應系統牽涉到兩不互溶的液相，因此相轉換特性為研究該系統穩定性的重要依據。系統的相轉換特性包括連續相和分散相在系統內的動態行為，包括分散相的 Hold Up，分散相液滴的大小，以及在何種條件下，連續相和分散相會產生相轉換。相轉換是指含油相與水相的系統，在持續的攪拌下，水/油乳化(W/O) 與油/水乳化 (O/W) 的型態突然的轉變。這些相轉換特性都會影響系統的反應行為。
一般來說，在相轉移觸媒反應的相關應用與研究中，大多是以四級銨鹽為主，但是四級銨鹽在某些極端的條件下會發生 Hofmann Degradation 現象，比如說強鹼或者是高溫。比較起來，四級磷鹽的效率並不會遜色於四級銨鹽，且四級磷鹽在這些條件下比四級銨鹽更來得穩定，因此在工業上的應用有一定的價值。
本論文以溴化四丁基磷做為相轉換觸媒，催化有機相中的苯甲醯氯與水相中的酚鈉合成苯甲酸苯酯，來探討四級磷鹽的濃度與反應物的濃度對於系統物性、相轉換特性和遲滯相轉換時間的影響。由實驗結果發現，在只添加觸媒的反應系統中，攪拌速率增加會使得水相容易成為連續相，也就是說，系統傾向於形成 O/W 乳化。而由於 O/W 乳化態較穩定而使得 O/W → W/O 型式的相轉換較難以發生。而在物性、相轉換 Hold Up、液滴結合時間與遲滯相轉換的時間等特性，所得結果皆與使用四級銨鹽相轉觸媒的結果大致相似。相較於四級銨鹽或者是反相相轉換觸媒的系統，添加溴化四丁基磷後的相轉換 Hold Up 較高，顯示添加四級磷鹽後更容易形成 O/W 乳化態。
對於有質傳現象或者是化學反應的系統，隨著反應物濃度的增加，其 W/O → O/W 的相轉換 Hold Up 會有增加的趨勢。但反應物濃度大到某一程度時，相轉換 Hold Up 反而下降，這是因為分散特性更加複雜所致。在 O/W → W/O 的系統，則大多觀察不到相轉換的發生。
在測定液滴結合時間 (Tc) 方面，當觸媒濃度提高或者是轉速增加，O/W 形式的分散會很穩定，使得 Tc 變大。在可觀察到相轉換的系統中，W/O → O/W 的 Tc 值皆大於 O/W → W/O 之 Tc 值。
在遲滯相轉換時間 (Td) 方面，當 Hold Up 越大，Td 值越小。在發生質傳現象或者是化學反應時，在 O/W → W/O 的系統，雖然注入分散相後馬上發生相轉，但是在某些系統，會有 W/O 變回 O/W 的現象產生。

For an immiscible two-phase system, the chemical reactions occur only in the interface, hence the reaction rate is very slow and the yield is low. If phase-transfer catalyst (PTC) was added, it could transport the reactants between the water phase and the organic phase. It was found that the reaction rate could be greatly enhanced. In addition, phase-transfer catalysis has many merits such as small amounts of catalyst, mild conditions for the chemical reactions, greater reaction rate, higher yield and selectivity. Consequently, the researches of phase-transfer catalysis are the emphasis of chemical engineering industries.
On the other hand, for the system with two immiscible phases, characteristics of phase-inversion are the major concerns from the view point of the stability of tsystem. The dispersion characteristics embrace the dynamic behaviors of the continuous phase and the dispersion phase in the system, hold up and droplet size of the dispersion phase, and the conditions which may cause the phase-inversion. Phase-inversion refers to the phenomenon that an agitated emulsion of oil droplets in water (O/W) changes its type immediately, and becomes an emulsion of water droplets in oil (W/O), and vice versa. These characteristics of phase-inversion will affect the reaction rate of the system.
In general, quaternary ammonium salts have been used in the majority of reported phase-transfer reactions and dissertations, but quaternary phosphonium salts can be equally effective, and may be preferred under some extreme conditions of high temperature or concentrated base when Hofmann Degradation occur. As the result, quaternary phosphonium salts have specific value in the industrial applications.
In this thesis, we use the synthesis of phenyl benzoate from benzoyl choride in the organic phase and sodium phenolate in the water phase with tetrabutylphosphonium bromide as the catalyst to study the variations of the physical properties, characteristics of phase-inversion and delayed inversion time of the systems upon changing the PTC concentrations and reactant concentrations. In the systems which PTC added only, we found that it tends to help water becoming continuous phase when agitated speed increased, i.e. it tends to form an O/W emulsion. Therefore, the occurrence of O/W→W/O is more difficult. In this test, the results of the physical properties, characteristics of phase-inversion, droplet coalescence time and delayed inversion time of systems are similar to those obtained by using quaternary ammonium salts. Comparatively speaking, the hold up of phase-inversion of systems with tetrabutylphosphonium bromide added is higher than those with quaternary ammonium salts or inverse phase-transfer catalyst added. It shows that it is easier to form an O/W emulsion after quaternary phosphonium salts are added.
With regard to those systems which mass transfer or chemical reaction occur, the increasing of the reactant concentrations tends to increase the hold up of the W/O→O/W type phase-inversion. However, the dispersion characteristics become more complicated with higher concentrations of the reactants, we found that the phase-inversion hold up decrease at higher concentrations. In the O/W→W/O type, we could not observe the happening of phase-inversion for the most parts of the experiments.
For the coalescing time of droplets, when the reactant concentrations or agitated speed is increased, the dispersion of O/W type is stable and higher Tc value could be obtained. For the systems which the phase-inversion could be observe, the value of Tc of the W/O→O/W type are always larger than O/W→W/O type.
For the delayed inversion time, the larger the hold up of phase-inversion is, the smaller the Td value. Systems which accompany with mass transfer or chemical reaction, for the O/W→W/O type system, in some cases, in spite of the happening of phase-inversion, nevertheless, it reversed from W/O to O/W.

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