Phase transfer catalysis (PTC) is an important method in synthetic two-phase chemistry. Stable liquidÀliquid hydrodynamic flow in a microtube reactor offers considerable benefits over the conventional batch reactors. In this work, we attempted to conduct a two-phase organic solvent/aqueous sodium hydroxide solution PTC Wittig reaction of benzyltriphenylphosphonium bromide and oand p-methoxybenzaldehydes in a microtube reactor under reproducible slug-flow pattern. Stable operating conditions and a defined specific interfacial area are crucial to study the interaction between kinetics and mass transfer effects. A strong impact of aqueous-to-organic (AO) phase volumetric flow ratio on the specific interfacial area and consequently on mass transfer between phases was observed. The increase of the specific interfacial area causes a higher overall reaction rate at the same residence time when 0.1 M sodium hydroxide solution was used, which confirms that mass transfer has an influence on the overall reaction rate. Increasing the aqueous sodium hydroxide solution concentration at the organicÀwater interface increased mass transport. At defined conditions, when the surface-to-volume ratio and concentration of OH À ions were adequate, reaction kinetics came to be the rate-limiting step.
A liquid-liquid phase transfer catalyzed (PTC) esterification reaction of 4-t-butylphenol in aqueous phase (1 M sodium hydroxide solution) and 4-methoxybenzoyl chloride in organic phase (dichloromethane) in a microchannel under parallel laminar flow conditions was studied in this work. Tetrabutylammonium bromide was used as the PTC. Stable liquid-liquid hydrodynamic flow and a defined specific interfacial area in a microreactor offer considerable benefits over conventional batch reactors and are crucial to study interactions between kinetics and mass transfer effects. Mentioned features were used to develop a 3D mathematical model considering convection in the flow direction, diffusion in all spatial directions, and reactions in organic and aqueous phases. Results have shown a much higher mass transfer rate of the PTC between both phases as the one predicted by the 3D mathematical model. It may be assumed that the instability of parallel flow, along with the mass transfer of catalyst between both phases, causes rippling and erratic pulsation at the interface which then leads to interfacial convection and increased mass transfer rates. With a proposed correlation for mass transfer enhancement due to interfacial convection, all the experimental data were successfully predicted by the model.
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