On the Effect of Enhanced Mass Transfer on Side Reactions in Capillary Microreactors during High‐Temperature Synthesis of an Ionic Liquid

Abstract

Abstract In this work, the high‐temperature production of the imidazolium‐based ionic liquid 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) by means of micro reaction technology was investigated. This reaction is strongly exothermic and a two‐phase liquid/liquid system is formed. Heat and mass transfer limitations can, therefore, have a negative effect on product quality and reaction rate. Here we demonstrate that, even at harsh thermal conditions, the ionic liquid, [BMIM]Br, can be produced at high quality. Side product formation, which usually occurs at elevated temperatures, leading to strong discolorization, can be avoided by enhancing mass transfer in a capillary slug flow. This was done by adjusting the flow rate so that the reaction regime shifted from strongly mass transfer limited to kinetically controlled. Here, the Hatta‐number had been shown to be a suitable measure for defining the minimal flow rate. At 145 °C, [BMIM]Br could be produced continuously within a residence time of 1.3 min and at a space time yield of 1240 kg L –1 day –1 . This successful approach for continuous ionic liquid production with up to a thousand‐fold space time yield compared to batch processes could be easily transferred to other imidazolium‐based ionic liquids.