Effects of porous media on extraction kinetics: Is the membrane really a limiting factor?

Abstract

Porous media in extraction and especially pertraction are often suspected to add unnecessary diffusive resistance and considerably slow down extraction kinetics. This work presents a miniaturized pertraction device and simulation of diffusive and reactive solute transport. Kinetics are experimentally observed and numerically fitted. Reaction rates-or solute transfer rates-are estimated via this fit on a numerical basis. The work shows that the diffusive resistance created by a porous medium is prevalent only at low distribution coefficients. At high distribution coefficients as is the case of quasi all industrial processes, the porous membrane does not interfere with overall kinetics. Instead, the diffusive resistance is shared between the feed and extraction phases, and the interface transfer, depending on the value of the transfer rate. Overall, this work can be generalize as enabling the measurement of solute transfer rates at the liquid-liquid interface, a key parameter in pertraction and membrane separation which is difficult to measure using classic methods of extraction.

A microfluidic study of synergic liquid–liquid extraction of rare earth elements

“…1 and previously described in detail, as well as validated, elsewhere. 32,33 Typically, the oil Fig. 1 (A) Photograph of the experimental bench with (from top to bottom): a syringe pump modified to accommodate two syringes; aqueous (blue liquid) and organic (yellow liquid) syringes; a microfluidic extraction ship (labeled ''2''; aqueous and organic output sample septum vials; and a valve; artificial food colouring in water is used to enable better visualisation.…”

“…The thickness of this membrane was previously optimised to 30 mm so as to: (i) be easy to handle and (ii) not become the limiting factor in the mass transfer kinetics. 33 Connectors between the microfluidic ship and PTFE tubing were made of a stainlesssteel tubing sealed with epoxy resin (Fig. 2).…”

“…Our validated microfluidic liquid-liquid extraction procedure can be summarized as follows: 32,33 the first step of any of our microfluidic extractions consisted in loading the aqueous and oil phases -classically an extractant at predetermined composition and a ''diluent'' -into gas-tight 5 mL glass syringes equipped with a PTFE plunger (Hamilton Bonaduz, syringe 1005TLL). Then, both syringes were placed on a syringe pump (NE1000, New Era Pump Systems, modified to enable simultaneous use of two syringes) to deliver desired flow rates and injection volumes.…”

“…Importantly, we recently reported that the use of a thin membrane to separate the two phases, such as the one used here, is not a limiting factor, hence it does not modify extraction kinetics. 33 To compare our microfluidic extraction results with those of standard approaches, we measured extraction efficiencies for various molar fractions of microfluidic extraction experiments and systematically reproduced these using the macroscopic standard so-called ''batch method'' in flasks.…”

“…In a preliminary paper, we have shown that the presence of a membrane may not limit the transfer observed and can be considered as an alternative to the most popular strategy based on droplets. 33 In this paper we report on the interest of chemical analysis of all four microfluidic channels (aqueous/oil, in & out), which enables accurate measurements of the concentration ratio [Ion] out / [Ion] in (both in water and oil). We show that such a microfluidic study, here applied to a very promising synergic system formed by two different extracting molecules, 34 allows for: (i) classical yield measurements, but also, for the first time to the best of our knowledge; (ii) the measurement of Gibbs free energies of transfer reactions and thus not only for Winsor II but also Winsor III data points.…”