Microreactors in Organic Chemistry and Catalysis, Second Edition (2013)

1.4. Multifunctional Integration

Some argue that miniaturized tools for both chemical synthesis and analysis need to be integrated onto a single chip in order to gain the true benefits of miniaturization [126], not least because of the problems associated with subsystem interconnectivity, dead volumes, and chip-to-world interfaces. Demonstrations toward such a goal include, for example, a hyphenated mixing reaction channel coupled to a capillary electrophoresis column [127].

As well as miniaturized reactors, microdevices with other functionalities extend the range of functional capabilities that may be achieved when a systems approach is considered [128]. Such microdevices may include mixers, separators, heat exchangers, heaters, coolers, photoreactors, analysis sub-systems, and devices for the application of pulsed electric fields [129]. Therefore, a wide range of processes including extractions (liquid–liquid, liquid–gas, solid-phase enhanced), crystallizations, distillations, purifications, conversions, phase-changes, phase separations, and identifications may be enabled. Thermal conditions may be more readily monitored throughout a microreaction system by employing a distributed reporter such as a thermochromic dye [130] that can report <1 °C temperature variations, albeit over a limited dynamic temperature range.

Interconnects to and between such microdevices for laboratory-scale experimental apparatus have historically been problematical, since a mechanically sound, pressure-resistant, and hermetic juncture with minimal dead volume is usually required. For robust, industry-ready chemical production equipment, stainless-steel fittings are usually employed in microreactor systems. For laboratory-scale apparatus with more delicate chip-based microreactors, a range of microfabricated solutions have been explored [131, 132], resulting in both miniaturized plug-and-play microconnectors [133] and macroscale interface housings. Both adhesive [134] and mechanical [135] solutions have been developed, but it has been reported that the latter have at least an order of magnitude greater strength than the former. More widely, the issues surrounding the packaging and interconnectivity of microfluidics and associated devices have been comprehensively summarized by Velten et al. [136].