Solvent-Free Synthesis of [DMIM]DMP Ionic Liquid in a Microreactor and Scale-Up Aspects

High-temperature, solvent-free, and continuous flow synthesis of dimethyl-imidazolium-dimethylphosphate ([DMIM]DMP) in a microreactor is reported for the first time. The microreactor comprises a 750 μm diameter microbore tube connected to a 750 μm diameter opposed T-microfluidic junction. Systematic experiments are conducted to determine the effect of residence time, reaction temperature, and flow velocity on the yield of the ionic liquid product. The yield is found to increase with an increase in residence time (for constant velocity) and an increase in reaction temperature. The product yield is observed to first reduce, reach a minimum, and then increase with an increase in flow velocity (for constant residence time). A residence time of 9.59 min and a reaction temperature of 160 °C are found to be the optimal conditions for complete conversion of 1-methylimidazole to [DMIM]DMP. The corresponding values of the production rate and space–time-yield are 0.2 kg/day and 1.52 × 105 kg/(day m3). A comparison of two different microfluidic junction designs─an opposed T-junction and a commercial split-and-recombine micromixer─is reported. Finally, based on the experimental data on the product yield, the kinetic parameters for [DMIM]DMP synthesis are determined. A laminar flow reactor model is used to estimate the kinetic parameters. A one-dimensional (1D) dispersed plug flow model is developed, validated, and then used to freeze an optimal scaled-up reactor configuration for processing 10 kg/h 1-methylimidazole, which corresponds to a production rate of 27.1 kg/h of the ionic liquid.