Transport Modeling of Kinetically Limited Microscale Extraction Systems: Droplet and Supported Liquid Membrane Separations

Abstract

Microfluidic droplet extraction devices can be used to efficiently measure solute phase transfer kinetics in liquid−liquid extraction systems. In this work, a droplet extraction apparatus was constructed using off-the-shelf and custom 3D printed parts for less than 110 USD. The interfacial kinetics of the transfer of Pu(IV) between an aqueous nitric acid phase and a 5 v/v% tridodecylamine (TDA) in toluene phase were characterized by determining the extent of Pu(IV) transfer between phases at different flow rates. Forward interfacial rate constants calculated from this data using an analytical model are 5.6 × 10 −3 mm s −1 under extraction (aqueousto-organic solute transfer) conditions and 3.3 × 10 −3 mm s −1 under stripping (organic-to-aqueous solute transfer) conditions. The analytical model is valid when the rate of solute transfer across the interface between the two liquid phases has pseudo-first-order reversible reaction kinetics and is slow relative to the rate of solute transport to the interface. The change in the outlet concentration with residence time determined using the analytical model was compared with the results of a numerical model accounting for advection/diffusion to the interface in addition to kinetically limited interfacial solute transfer. These calculations revealed that for systems with forward interfacial rate constants greater than approximately 10 −2 mm s −1 , the analytical model must be supplemented with a numerical transport model accounting for an additional advection/diffusion mass transfer resistance. This threshold corresponds to a Damkoḧler number of one. The measured interfacial kinetic rate constants for Pu(IV)/TDA were used in a supported liquid membrane (SLM) numerical model, which showed that the Pu(IV) phase transfer kinetics are fast enough for use in a practical separation.

3D printed field-deployable microfluidic systems for the separation and assay of Pu in nuclear forensics

“…HNO 3 once, and finally reconstituted in 1 mL 3 M HNO 3 for use in the FS-SLM System. The recently purified 238 Pu solution 18 was dried in conc. HNO 3 and reconstituted in 1 mL 3 M HNO 3 .…”

“…Such microsystems have been used to perform chemical separations with high yields and decontamination factors (DFs) for many different applications. [11][12][13][14][15][16][17][18] Flat-sheet supported-liquid membrane (FS-SLM) modules are microfluidic systems in which a semipermeable membrane is placed between two open-faced microfluidic channels, allowing selected species in solution to extract over the membrane from one channel to the other. [19][20][21] Forward and backward extractions can be performed in a single module without the use of a phase separating system.…”