Simulation and Design of a Non-adiabatic Multiphase Microreactor

Abstract

We have identified a novel, multiphase microreactor configuration for the direct fluorination of toluene. With this reactor the fluorine and toluene are separated by a macroporous membrane impregnated with a solid Lewis acid catalyst, which influences the fluorine directly when being absorbed into the liquid phase. Reaction occurs in the membrane adjacent to the gas-phase. According to the literature fluorine is turned into an electrophile in the presence of acidic catalysts improving the selectivity towards monofluorinated products. The direct fluorination of toluene is a very fast and exothermic reaction and therefore heat management is of great importance to avoid thermal runaway. Also, the selectivity of the process deteriorates at elevated temperatures due to increasing radical reactions.To address this issue a detailed model of the heat and mass transfer has been developed. The catalytic membrane is modelled as an idealised system and the porosity, tortuosity and catalytic activity are parameters in a sensitivity analysis to obtain bench-mark values for the reactor performance and the membrane design. The software package FEMLAB has been employed to solve the partial differential equations simultaneously by means of the finite element technique.The performance of the membrane reactor configuration is compared to a falling film microreactor. It is shown that the membrane reactor has great potential to improve the selectivity of the direct fluorination reaction towards mono-fluorinated products by means of a thin solid acid catalyst layer. The influence of the reactor size and the aspect ratio on the temperature in the reaction plane and hot spot formation is studied. With the falling film reactor rising channel size results in increasingly prominent hot spot formation and the selectivity towards monofluorinated products deteriorates. The membrane supports the heat removal because the reaction plane is located inside the solid grid. In this manner the membrane catalyst increases the selectivity of the process and also shifts the optimal operation temperature to higher values towards room temperature. Higher production rate per channel can be achieved requiring less cooling.