Process intensification using microreactor

Cecilia, R., Kunz, U. and Turek, T. (2007). Possibilities of process intensification using microwaves applied to catalytic microreactors. Chemical Engineering and Processing, Vol. 46, pp. 870-881. 

Companies like Clariant and Merck use microreactors for production, and they are obviously convinced that the ultimate development of process intensification leads to microreaction technology. In contrast to other companies, Clariant... 

Several recent reviews have discussed the fundaments and applications of PI concepts. Doble [16] has discussed the concept of a green reactor, for example, how process intensification could be achieved by microreactor technology using very high forces, ultra-high pressures, electrical fields, ultrasonics, surfactant-based separations, shorter diffusion and conduction pathways, flow field and fluid microstmcture interactions, and/or size-dependent phenomena. 

These hmitations, which are associated with the use of molecular oxygen, might be overcome by the use of microreactor technology [7-15]. Due to their small inner dimensions, microreactors provide both high safety and enhanced process intensification [16-18]. The high surface-to-volume ratio properties of microchannels (inner diameter 100-1000 pm) are highly beneficial, especially for multiphase reactions. In addition to enhanced gas-hquid interfacial transfer, intense recirculation within the hquid slugs allows for fast renewal of the interfaces... 

Three examples of new designs of single-injection MSR and one example of multi-injection reactor applied for fast and exothermic liquid phase reactions are presented. Finally, it is demonstrated that the process intensification has been achieved using these microreactors. 

There are already many examples of advances ofPSE embedding sustainabihty aspects as part of the process development cycle. Continuous microreactors from Coming utilized for fine chemicals and pharmaceuticals [97], continuous formulation processes, process intensification demonstrated in several processes [98], and life cycle assessment evaluations integrated into process development [99], to mention a few. However, a more widespread uptake is needed, so they are used routinely. 

Most of these substitution reactions have already been investigated in microstruc-tured reactors, some of them more intensively than others. Researchers were in particular interested in finding routes to process optimization and process intensification compared with macroscopic processes by making use of the improved heat and mass transfer characteristic of microstmctured reactors. In this context, microreactors turned out to be efficient tools for systematic and fast parameter screenings under conditions of continuous processing, consuming only small amounts of chemicals. 

As approaches to high-throughput experimentation, process intensification and process optimization continue to develop and show value to the researcher, then the engineer or the analytical chemist will be under increased pressure to use microanalysis tools. This will be to evaluate the operations of the microreactors (such as diagnostics of the microchaimels and composition of the reactor). The results of these applications will be seen in distributed manufacturing approaches and number-up versus scale-up of processes. These successes in engineering will also increase the demand for the effective use of microanalytical instrumentation. 

Another study [7] was reported based on process intensification via novel process windows [19], which permitted a reduction in the reaction time required of up to three orders of magnitude. For this reason, synthesis in a microreactor becomes competitive compared with the batch process. Otherwise, when using the conventional operating conditions, synthesis in a microreactor would generate formidably higher costs. 

Future Trends in Reactor Technology The technical reactors introduced here so far are those used today in common industrial processes. Of course, research and development activities in past decades have led to new reactor concepts that may have advantages with respect to process intensification, higher selectivities, and safety and environmental aspects. Such novel developments in catalytic reactor technology are, for example, monolithic reactors for multiphase reactions, microreactors to improve mass and heat transfer, membrane reactors to overcome thermodynamic and kinetic constraints, or multifunctional reactors combining a chemical reaction with heat transfer or with the separation in one instead of two units. It is beyond the scope of this textbook to cover all the details of these new fascinating reactor concepts, but for those who are interested in a brief outline we summarize important aspects in Section 4.10.8. 

Gas-liquid-solid processes are possible by using either waD-coated catalyst or mini-packed beds. Numerous applications have demonstrated process intensification in terms of selectivity, space-time yield, and safety by use of gas-liquid microreactors, including fluorinations, chlorination, hydrogenations, sulfonations, photooxidations, and so on. This is achieved by enhanced mass transfer via the interface and through formation of thin liquid layers, which also give better transfer and allow conducting photochemical reactions more efficiently. Operation is now possible in new process windows with very aggressive reactants such as elemental fluorine or even under explosive conditions. 

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