New Class of Synthetic Membranes: Organophilic Pervaporation Brushes for Organics Recovery

Abstract

Isolating and concentrating volatile organics such as fuels and intermediate chemicals from aqueous solutions is important for environmental synthesis and processing. We have prepared a new class of easy-to-synthesize polymeric membranes comprising hydrophobic brush-like structures as a selective layer, and have tested them using pervaporation of isobutanol from water. These brush structures were prepared by graft-induced polymerization of hydrophobic vinyl monomers from light-sensitive poly(ether sulfone) nanofiltration support membranes (grafting from) without initiating agents. Graft-induced tethered polymer chains with multiple C18 alkane side-chains out-performed the industry gold standard silicone rubber membrane with selectivities of α = 10.1 ± 0.9 and 6.7 ± 0.1, respectively, at comparable permeation fluxes of 0.7− 1.0 ± 0.1 L/m 2 -h. Preparation of these brush membranes is simpler and easier to scale-up than current methods of preparing asymmetric and composite membrane structures. These brush structures and this method of preparation have excellent potential for synthesizing selective membranes suitable for large-scale organic−water separations. ■ INTRODUCTIONPressure-driven membrane filtration processes have matured and are now widely accepted in many industries such as in energy, biotechnology, food and beverage, chemical, wastewater, gas fractionation, and desalination due to their low energy requirements and one-phase operation. Although membranes made from metals or ceramics are available, polymeric materials predominate. 1 For over 40 years, both interfacial polymerization 2 and phase inversion 3 have been the predominant methods for preparing composite polymeric and asymmetric membrane structures, respectively. Although these synthesis methods have been very successful, they are both relatively complex and sensitive to small changes in the casting conditions. 4 Many research groups have sought novel synthesis methods for producing synthetic membranes without much success. These membranes suffer from limitations including low porosity (track etched), 5−7 high cost (ceramic or stainless steel), 8 wide pore size distribution (stretched PTFE), 9−11 and low strength (biological), 12 or are difficult to scale-up (zeolite, carbon-nanotubes or graphene oxide). 13−15 Here, we synthesize a new class of synthetic brush hydrophobic polymer membranes, and then test them with a challenging separation: removal of isobutanol from water by pervaporation (PV). 16 To prepare the best performing hydrophobic brush membranes for this separation, we used our unique high throughput platform with 96 filter well plates. 17 The method of preparation involves grafting commercially available vinyl monomers alone or in mixtures to light-sensitive poly(ether sulfone) (PES) nanofiltration membranes, screening for the best performers, and selecting the winners. 18−20 The high throughput platform has also been used with combinatorial chemistry to generate a library of new monomers. 19,21 The newly synthesized hydrophobic-terminat...

Towards cell-free isobutanol production: Development of a novel immobilized enzyme system

“…Our novel hydrophobic brush membrane exhibited a total flux, J , of 0.8 ± 0.15 LMH (L/m 2 h); this is comparable to the fluxes for commercial PDMS membranes Sil5 and Sil20 of J = 0.7 ± 0.06 LMH and 1 ± 0.11 LMH, respectively. However, the selectivity for the brush membrane was α = 10.1 ± 0.86 compared with α = 6.7 ± 0.11 and 6.7 ± 0.05 for Sil5 and Sil20 respectively . This new class of membrane can be utilized with our reaction system to create in situ removal of isobutanol from the system.…”

“…Adsorption, gas stripping, and pervaporation have all been evaluated for n ‐butanol. Below we summarize the main results from a separate paper that focused on the removal of isobutanol (6% (v/v)) from aqueous solution using pervaporation . Membrane materials have a large effect on the efficiency of alcohol removal by the pervaporation (PV) process .…”

“…Below we summarize the main results from a separate paper that focused on the removal of isobutanol (6% (v/v)) from aqueous solution using pervaporation. 30 Membrane materials have a large effect on the efficiency of alcohol removal by the pervaporation (PV) process. 31 By evaluating the properties of the materials, one can determine how diffusivity and sorption properties change.…”

“…However, the selectivity for the brush membrane was a 5 10.1 6 0.86 compared with a 5 6.7 6 0.11 and 6.7 6 0.05 for Sil5 and Sil20 respectively. 30,32 This new class of membrane can be utilized with our reaction system to create in situ removal of isobutanol from the system. The Liao group has employed gas stripping to remove isobutanol from an Escherichia coli fermentation system and obtained final titers of 0.082% (v/v).…”

Structural Properties of the Fluid Mixture Confined by a Semipermeable Membrane: A Density Functional Study

“…In such systems, interactions between fluid-pore and fluid-fluid lead usually to interesting phenomena including laying [2], wetting [3,4], capillary condensation [5] and so on. Actually, among various confining geometries, the semipermeable membrane (SPM) has particular importance due to its ability to model the natural biological membranes and synthetic membranes [6,7]. For instance, the Donnan equilibrium can be conveniently constructed by utilizing of the SPM, across which there exists density difference.…”