Controlled multistep synthesis in a three-phase droplet reactor

TLDR

Channel fouling hampers continuous flow chemistry, but droplet chemistry isolates reactions from channel walls; however, adding reagents to existing droplets is difficult, limiting droplet chemistry to simple reactions. The authors present a method for repeatedly adding controlled amounts of reagents to droplets. Reagents are injected into a multiphase stream of carrier liquid, droplets, and inert gas that keeps droplets evenly spaced and prevents new droplet formation. The method enables multistep reactions, demonstrated by a five‑stage quantum‑dot synthesis where particle growth is maintained by successive feedstock additions.

Abstract

Channel-fouling is a pervasive problem in continuous flow chemistry, causing poor product control and reactor failure. Droplet chemistry, in which the reaction mixture flows as discrete droplets inside an immiscible carrier liquid, prevents fouling by isolating the reaction from the channel walls. Unfortunately, the difficulty of controllably adding new reagents to an existing droplet stream has largely restricted droplet chemistry to simple reactions in which all reagents are supplied at the time of droplet formation. Here we describe an effective method for repeatedly adding controlled quantities of reagents to droplets. The reagents are injected into a multiphase fluid stream, comprising the carrier liquid, droplets of the reaction mixture and an inert gas that maintains a uniform droplet spacing and suppresses new droplet formation. The method, which is suited to many multistep reactions, is applied to a five-stage quantum dot synthesis wherein particle growth is sustained by repeatedly adding fresh feedstock.