Chemistry in Microstructured Reactors

Abstract

The application of microstructured reactors in the chemical process industry has gained significant importance in recent years. Companies that offer not only microstructured reactors, but also entire chemical process plants and services relating to them, are already in existence. In addition, many institutes and universities are active within this field, and process-engineering-oriented reviews and a specialized book are available. Microstructured systems can be applied with particular success in the investigation of highly exothermic and fast reactions. Often the presence of temperature-induced side reactions can be significantly reduced through isothermal operations. Although microstructured reaction techniques have been shown to optimize many synthetic procedures, they have not yet received the attention they deserve in organic chemistry. For this reason, this Review aims to address this by providing an overview of the chemistry in microstructured reactors, grouped into liquid-phase, gas-phase, and gas-liquid reactions.

Design and additive manufacture for flow chemistry

“…It is again believed that this heat transfer is a result of the large surface area to volume ratio associated with microreactor systems. 4 Typically microreactors demonstrate heat transfer coefficients of ~ 10 to 25 kW.m -2 .K -1 which are significantly higher than traditional batch heat exchangers. 4 This effect allows chemists to heat and cool reactions in a highly efficient manner, allowing precise control over reaction thermodynamics.…”

“…2 These reactors typically come in the form of micron-sized channels patterned into the surface of a glass or polymer chip (often referred to as "Lab-on-a-Chip"), 3 or more simply as lengths of tubing typically made from stainless steel, or inert polymers such as polytetrafluoroethylene (PTFE), or polyetheretherketone (PEEK). 4 Reactors can be integrated with other flow accessories via the use of fluidic connectors; compression fittings or ferrules (usually PEEK)…”

“…Typically, microreactors demonstrate a much larger surface area to volume ratio than conventional batch reactors such as round bottom flasks or test tubes, minimising diffusion distances within the reaction. Microreactors with surface area to volume ratios of ~ 10,000 to 50,000 m 2 .m -3 are not uncommon, 4 in comparison to typical batch reactors with surface area to volume ratios of ~ 4 m 2 .m -3 . These values increase exponentially as the internal channel dimensions of a microreactor decrease.…”

“…The outcome for a number of reactions is an increase in reaction yield, purity and selectivity. 4 Small reagent volumes: microfluidic devices often consume fewer reagents than bulk systems to gather the same analytical data. This leads to a considerable reduction in processing cost, particularly when dealing with costly reagents or reactions where only small volumes are available for testing and analysis.…”

“…30 Typically, flow throughout these devices is laminar, with Reynolds numbers being in the range of 1 to 250 depending on channel dimensions and flow rates. 4 Although chip reactors can be used independently or in conjunction with other chip reactors, they are often employed as pre-mixers to larger milliscale "coil" reactors. 32 Microfluidic reactors are often characterised as either active or passive, in reference to the micromixers which they usually contain.…”