(8d) Quaternary Phase Segmented Flow Format for Biphasic Reactions

Continuous flow microreactors offer lab scale process development with directly scalable numbered up design.One limitation of these systems is that the conditions necessary for many reactions have a high propensity towards reactor fouling, leading to limited operation lifetime and challenging inline process monitoring. To date, there is not a viable technique for studying biphasic reactive systems. In response, we have developed new multi-phase flow format for continuous operation of biphasic chemical processes and accurate optical monitoring. As a case study of biphasic reactions, we adapted ligand exchange and sulfide capping of cadmium selenide (CdSe) quantum dots.^] This multi-phase flow format features a novel quaternary phase segmented flow regime (QSF), which allows for the use of two immiscible reactive phases. The reactive droplets are carried by an inert gaseous carrier phase and encapsulated by fluorinated oil to ensure the reactive phase never contact the microreactor wall. The robustness of this design was evaluated by comparing the viable operational envelop to other segmented flow formats . Across 1,500 automated experiments, the range of viable fluid velocities (u_D) and toluene to formamide ratios (R₁) was tested, and QSF formed stable flow across the entire parameter space and showed no visible reactor fouling. We then profiled the exchange kinetics through residence time studies. We found complete phase transfer and ligand exchange occurred after 16 minutes, but when the reactor tubing was exposed to a UV light source, the exchange time could be reduced to 4 minutes with a 2.5 times photoluminescence intensity increase.^[2]This work details a novel flow regime for microfluidic reactors with immediate applications in biphasic reaction studies spanning both nanoscience and chemistry and enables the use of high fouling biphasic chemistries.

[2] React. Chem. Eng. 2021,6, 1367-1375