Effect of turbulence induced shear on continuous synthesis of imidazolium ionic liquid 1-butyl-3-methylimidazolium bromide ([BMIM]Br) in a high shear rate Taylor-Couette flow reactor

The preparation methods are crucial for successful synthesis of ionic liquids. The present study has employed a Taylor-Couette Flow Reactor (TCFR) to generate local high shear flow to investigate the effects of turbulence induced shear rate (changing the inner cylinder rotational speed), reaction temperature and feed flowrate on the conversion rate, reaction rate, production yield, and space-time yield (STY) for a typical ionic liquid (Imidazolium Ionic Liquid 1-Butyl-3-Methylimidazolium Bromide ([BMIM]Br)) synthesis. Main finding is that production rate (PR) of the ionic liquid decreases with increasing the residence time, but increases with a higher shear rate by controlling the reaction temperature within 80–85 °C. There exist strong correlations among the PR, STY of the ionic liquid and local turbulence-induced shear rate in the TCFR. Comparisons on the synthesis performance by adopting different reactors, the TCFR, microreactor, and high shear mixer (HSM), were also conducted. It has been demonstrated that the PR and STY obtained using the TCFR increases when taking a higher reaction temperature, with the STY being six times greater than that of using the microreactor and HSM. The study has clearly shown that reducing the retention time of 1-methylimidazole and carefully controlling radial temperature variation in the TCFR can produce a pure, colorless product of [BMIM]Br. The results of CFD modelling on hydrodynamics in the TCFR using the Reynolds Stress Model (RSM) affirm that when the mean shear increases, the local turbulence-induced shear in the TCFR significantly intensifies, beneficial to the early stage of the ionic liquid synthesis.