Compartmentalized Droplets for Continuous Flow Liquid–Liquid Interface Catalysis

Abstract

To address the limitations of batch organic-aqueous biphasic catalysis, we develop a conceptually novel method termed Flow Pickering Emulsion, or FPE, to process biphasic reactions in a continuous flow fashion. This method involves the compartmentalization of bulk water into micron-sized droplets based on a water-in-oil Pickering emulsion, which are packed into a column reactor. The compartmentalized water droplets can confine water-soluble catalysts, thus "immobilizing" the catalyst in the column reactor, while the interstices between the droplets allow the organic (oil) phase to flow. Key fundamental principles underpinning this method such as the oil phase flow behavior, the stability of compartmentalized droplets and the confinement capability of these droplets toward water-soluble catalysts are experimentally and theoretically investigated. As a proof of this concept, case studies including a sulfuric acid-catalyzed addition reaction, a heteropolyacid-catalyzed ring opening reaction and an enzyme-catalyzed chiral reaction demonstrate the generality and versatility of the FPE method. Impressively, in addition to the excellent durability, the developed FPE reactions exhibit up to 10-fold reaction efficiency enhancement in comparison to the existing batch reactions, indicating a unique flow interface catalysis effect. This study opens up a new avenue to allow conventional biphasic catalysis reactions to access more sustainable and efficient flow chemistry using an innovative liquid-liquid interface protocol.

The Promises and the Challenges of Biotransformations in Microflow

“…For processing biphasic reactions in a continuous flow fashion, water‐in‐oil Pickering emulsions with water‐soluble enzymes confined in aqueous droplets could be packed into a mesoscale column reactor. Such an approach with water‐“immobilized” enzyme and continuously flowing organic phase was found to lead to a very stable and highly productive biocatalyst use . Another specific multiphase system comprises a mesoscale column bioreactor with monolithic hybrid consisting of microbeads embedded in a matrix for supported ionic liquid phase (SILP) enabling immobilization of enzyme and continuous liquid–liquid contacting.…”

Surfactant Assembly within Pickering Emulsion Droplets for Fabrication of Interior‐Structured Mesoporous Carbon Microspheres

“…This approach mainly involves independent formation of crust and interior architectures.W ater droplets in nanoparticle-stabilized emulsions (Pickering emulsions) are used as spherical templates to grow outer crusts because they are of much higher stability than conventional surfactant-stabilized droplets. [11] Thesurfactant-directed assembly inside the Pickering water droplets is capitalized to create internal structures.S ince nanoparticle emulsifier and surfactants differ significantly in nature,o ur strategy makes it possible to optionally tailor the interior structure of MCMs through changing synthesis conditions,w hile not affecting the outer crust. To the best of our knowledge,f or the first time, surfactant assembly inside Pickering droplets is proposed to synthesize materials although Pickering droplets were previously reported to be used as spherical templates to fabricate polymer microspheres.…”

Submicron Inverse Pickering Emulsions for Highly Efficient and Recyclable Enzymatic Catalysis

“…Pickering emulsions, a type of emulsion that are stabilized by colloidal particles, have attracted tremendous interest for biphasic enzyme catalysis . Compared to conventional surfactant‐stabilized emulsions, Pickering emulsions offer many unique advantages, such as enhanced enzyme stability, simplified product separation, and facile enzyme recycling.…”

“…[8] Pickering emulsions, at ype of emulsion that are stabilized by colloidal particles, have attracted tremendousi nterest for biphasic enzymec atalysis. [9][10][11][12][13][14][15][16][17] Compared to conventional surfactant-stabilized emulsions, Pickering emulsions offer many unique advantages,s uch as enhanced enzyme stability, simplified product separation, and facile enzyme recycling. Pioneering work on the immobilization of enzymesb yu sing Pickering emulsions was accomplished by the groups of Wang and van Hest, who used hydrophobic SiO 2 nanoparticles and polymersomes, respectively,t oe mulsify aqueous solutionso fe nzymes in organic medium.…”