High performance flow-focusing droplet microreactor. Extractive separation of rare earths as case of study

This work advances the knowledge of the design and manufacture of microdroplet reactors for reactive liquid–liquid systems assisted by advanced simulation techniques (CFD). The mathematical model is based on the integrated analysis of the fluid dynamics for multiphase systems, passive mixing of reactants inside and outside the microdroplet and interfacial reaction rate. To validate the results obtained with the predictive model a spiral microdevice with droplet generation using flow-focusing geometry has been designed and fabricated by additive manufacturing. First, the influence of fluid flowrate, hold-up and viscosity on the droplets frequency and size has been evaluated with the model and assessed experimentally. Next, the performance in the separation of a binary Dysprosium-Lanthanum system has been tested, working with a dispersed aqueous phase containing the rare earth elements (REEs) solution and a continuous organic phase constituted of a solution of the extractant Cyanex® 572 in Shellsol® D70. The extraction experiments have been conducted at residence times between 3 and 60 s to generate aqueous phase monodispersed droplets with high interfacial area that varies between 61.4 and 49.2 cm2·cm−3 depending on the operating conditions. At pH 1, 90 % of dysprosium has been extracted, and almost complete separation of both REEs has been achieved. Very good agreement between simulated and experimental results has been reached with an error lower than 12 %. Therefore, here we provide the tools to design and predict the microdroplet enhanced performance of extractive liquid–liquid microreactors.