Phase Transfer Characteristics of PTC System with Tetrabutylphosphonium romide as Catalyst

• Main Authors: Wen-Ke Chen, 陳文科
• Other Authors: Chien-Li Chiang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/23672593161127468125

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 91 === 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.