Ionic liquids are a promising class of solvents. They have been developed as an alternative to classic organic solvents for separation of industrially relevant organic mixtures. This can be attributed to their high thermal stability, low volatility, and good separability properties. Generally, ionic liquids comprise of cations and anions thus the considerably high flexibility in their design. Currently, the application of ionic liquids in chemical synthesis is mainly used in their characterization as green solvents. This, however, does not take into consideration the environmental impact of the ionic liquid manufacturing process. Additionally, the production processes should highly improve material and energy efficiency for higher output. Therefore, effective methods for investigating ionic liquid synthesis are highly desirable.
Recently, reaction kinetics have been investigated in the microreactors under suitable conditions which have proved to be an efficient approach for the optimization of the reaction parameters. Unlike in the batch processes, transfer of heat and mass in the microstructured devices is suitable for solvent-free synthesis. This is due to efficient heat removal that ensures high product quality and effective handling of the dispersed product phase that is often witnessed in solvent free-ionic liquid synthesis. Therefore, process development for continuous synthesis of solvent-free ionic liquids is highly desirable.
To this note, a group of researchers: Dr. Sebastian Schwolow, Benedikt Mutsch and Professor Thorsten Röder from the Institute of Chemical Process Engineering together with Professor Norbert Kockmann from the TU Dortmund University assessed the process development for solvent-free continuous synthesis of 1-butyl-3-methyl-imidazolium bromide. Fundamentally, the experiment was set-up in a microreactor device. Briefly, the authors commenced their work by deriving a model for the liquid-liquid two-phase system taking into consideration the heat and mass transfer. Next, the influence of mass and heat transfer coefficients on the conversion and temperature of the flow reactor was evaluated based on the parameter variations simulations. The main objective was to develop a process with high productivity and maximum material efficiency. The work is currently published in the research journal, Reaction Chemistry and Engineering.
The research team observed that the reaction rate highly depended on the high-conversion range. Therefore, the highest temperature range was used to avoid the need for long residence time in the flow reactor. Additionally, a stability criterion was used determine the stability diagrams from the calculated temperature profiles. Based on the diagrams, the operation stability was achieved and effectiveness of different set-ups predicted. Despite some simplifying assumptions, a good agreement between the simulated and experimental data was observed.
In summary, the German scientists successfully looked at the solvent-free synthesis of the ionic liquid in a microreactor setup. The obtained results enhanced our understanding of the interaction between the reaction and mass transfer. Furthermore, the advantage of the kinetic model for developing a channel design reaction-specific optimized reactor was demonstrated. The study will advance the design and synthesis of more efficient ionic liquid for desired applications.
Schwolow, S., Mutsch, B., Kockmann, N., & Röder, T. (2019). Model-based scale-up and reactor design for solvent-free synthesis of an ionic liquid in a millistructured flow reactor. Reaction Chemistry & Engineering, 4(3), 523-536.Go To Reaction Chemistry & Engineering