Reactivity of Phenol Allylation Using Phase-Transfer Catalysis in Ion-Exchange Membrane Reactor

This study investigates the reactivity of phenol allylation using quaternary ammonium salt as a phase-transfer catalyst in three types of membrane reactors. Optimum reactivity and turnover of phenol allylation were obtained using a respond surface methodology. The contact angle, water content, and degree of crosslinkage were measured to understand the microenvironment in the ion exchange membrane. 1. Introduction Phase-transfer catalytic techniques have been used in manufacturing industry synthesis processes, such as insecticidal and chemical production [1–3]. However, a traditional liquid-liquid phase-transfer catalytic reaction has many disadvantages, because separating the catalyst and purifying the reaction system are difficult. Hence, the liquid-solid-liquid phase-transfer catalyst technique was developed. Although this type of catalyst is easy to use and recover from a solution, the reactant pore diffusion in the catalyst affects the reaction and decreases the reaction rate. A catalyst immobilized in an ion exchange membrane could solve these problems. When a catalyst is immobilized in an inert membrane pore, the catalytic reactivity and separation functions are engineered in a complex system. The membrane technique offers advantages of (i) separating the catalyst from the reaction solution, (ii) maintaining phase separation to minimize the potential of emulsions forming, and (iii) a high surface area per unit volume of the reactor. Furthermore, Zaspalis et al. [4] reported that a reaction using a membrane catalyst could be 10 times more active than a pellet catalyst reaction. Yadav and Mehta [5] presented a theoretical and experimental analysis of capsule membrane phase-transfer catalysis for the alkaline hydrolysis of benzyl chloride to benzyl alcohol. Okahata and Ariga [6] examined the reaction of sodium azide with benzyl bromide in the presence of a capsule membrane with pendant quaternary ammonium groups and polyethylene glycol groups on the outside. A capsule membrane is unsuited to mass industrial production because of the inconvenience of working with capsules. Various methods of preparing ion-exchange membranes for different purposes have been proposed and practiced by industry. One of these methods is copolymerizing divinylbenzene and other vinyl monomers (e.g., styrene, chloromethylstyrene, and vinylpyridine) into a membranous copolymer using the paste method and then introducing ion-exchange groups into the copolymer [7–9]. The polymer solution (which contains polymers with ion-exchange groups and other polymers) is then cast on a flat