Simplified in-situ tailoring of cross-linked self-doped sulfonated polyaniline (S-PANI) membranes for nanofiltration applications

Sulfonated polyaniline (S-PANI) membranes could have wide-ranging applications due to their electrical tunability, antifouling behaviour and chlorine resistance. However, S-PANI membranes below the ultrafiltration (UF) separation range have not been successfully established. This study presents a scalable approach to produce the first in-situ cross-linked S-PANI membranes at nanofiltration (NF) range. S-PANI membranes were produced by non-solvent induced phase separation (NIPS). The presence of sulfonic groups as polymer cross-linking anchors and controlling the coagulation bath's acidic strength resulted in instant stabilisation of the selective layer, which hindered the solvent/non-solvent exchange rate. This enabled the production of a tailored membrane morphology with a dense skin layer, suppressed macro-voids, reduced porosity, enhanced tensile strength, increased hydrophilicity and solvent stability. S-PANI membranes cast in 3 M HCl(aq) with MWCO≈680 g mol−1 (sucrose octa-acetate) showed a rejection of 99 % for PEG 1000 g mol−1 and 91–100 % for dye solution (MW range of 320–1017 g mol−1) compared to 34 % and 74–85 % rejection for a commercial fluoropolymer membrane (nominal MWCO 1000 g mol−1), respectively. The reported approach is simple and can be applied to design new classes of cross-linked solvent stable S-PANI NF membranes

Exploiting the electrical conductivity of poly-acid doped polyaniline membranes with enhanced durability for organic solvent nanofiltration

We have developed stable organic solvent nanofiltration (OSN) membranes that are electrically conductive. These membranes overcome key issues with current tuneable membranes: molecular weight cut off (MWCO) limited to the UF-range and lack of filtration stability. Polyaniline (PANI) was in-situ doped by poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) using chemical oxidative polymerization that leads to formation of interpolymer complex. The PANI-PAMPSA membranes were prepared by phase inversion method and the pore sizes were shrunk by annealing the membranes at temperatures lower than the crosslinking temperature. The membranes were systematically evaluated using visual and chemical analysis and in-filtration experiments. The developed membranes were solvent stable, reusable, had a denser structure and lower MWCO and there was no thermal crosslinking as seen by IR. The solvent permeance obtained were: 0.46, 0.60 and 0.74 Lm −2 h −1 bar −1 for acetone, 2-propanol and methanol respectively, with MWCO below 300 Da and 266 Da for methanol. For the tuneability investigation, when applying an electrical potential (20 V) in a custom-made cross-flow membrane cell, an increase in MWCO and permeance (10.4% and 55.6%, respectively) was observed. These results show that this simple in-situ doping method with heat treatment can produce promising and stable PANI membranes, for OSN processes in different solvents, with the distinctive feature of in-situ performance control by applying external electrical potential. </p

Flexible electro-responsive in-situ polymer acid doped polyaniline membranes for permeation enhancement and membrane fouling removal

This study investigates the performance of a new electrically tuneable polyaniline (PANI) membrane, and shows that this synthesis method has the potential to address key challenges of small-acid doped PANI membranes, including: acid dopants leaching out during filtration and low mechanical strength. The novel in-situ polymerisation used poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), as polymer acid template leads to the formation of inter-polymer complexes of PANI and polymer acid. The developed membranes were comprehensibly evaluated through visual, chemical, mechanical and filtration studies and compared to small-acid doped membranes (PANI-HCl membranes). The PANI-PAMPSA membranes were smooth, acid leach resistant, had higher tensile strength and showed conductivity three magnitudes higher compared to PANI membrane with post cast doping. The developed membrane showed in-filtration performance stability, electrical tuneability (in-situ control of flux and rejection) and fouling removal characteristics under applied electrical potential. Data obtained by SEM, IR spectroscopy, electrical analysis and cross-flow filtration confirm these results. The overall results showed that the proposed membrane fabrication procedure resulted in a significant improvement in performance across a range of critical parameters, including conductivity, stability, flexibility, permeance and fouling removal with additional advantage of being electrically tuneable

Kinetic resolution of 1-phenylethanol in the spinning mesh disc reactor: Investigating the reactor performance using immobilised lipase catalyst

The spinning mesh disc reactor (SMDR) is an innovative catalytic rotating reactor to aid process intensification. In this study, the application of the SMDR has been demonstrated for the enzymatic kinetic resolution of racemic 1-phenyethanol using amano lipase immobilised on wool as a catalyst. Physical characterisation of wool was carried out to confirm the presence of lipase. The reaction was tested for a range of solvents and temperatures for both free and immobilized lipase and the optimised reaction conditions were employed in the SMDR for different flowrates and spinning speeds. The SMDR showed better reaction efficiency compared to the batch reactor: the feed throughput was scaled-up from 10 ml to 250 ml and the productivity increased from 7.05 g l-1 h-1 in batch to 10.92 g l-1 h-1 in the SMDR. An increase in catalyst loading was achieved by adding more lipase cloths and the reaction rate increased from 0.16 mmol min-1 (one cloth) to 0.28 mmol min-1 (three cloths). These results show the first demonstration of novel reactor design for scale-up of enzymatic kinetic resolution using an inexpensive lipase. The SMDR thus shows potential for scale-up and continuous processing for versatile applications in the fine chemicals and pharmaceutical industry.<br/

Process Intensification of Catalysed Henry Reaction using Copper-Wool Catalyst in a Spinning Mesh Disc Reactor

The spinning mesh disc reactor (SMDR) is a novel process intensification technology which uses centrifugal force to drive reaction fluid over a mesh supported catalyst on a rotating disc. The potential of the SMDR for organic synthesis has been demonstrated for the first time for Henry reaction using copper immobilised on woollen cloth mesh. A new protocol for copper immobilisation on wool has been developed producing a superior catalyst to the homogeneous copper triflate system: copper heterogenised on wool afforded a higher batch conversion (85%) (cf. 57% for the homogeneous case) in the same timeframe. In the SMDR, the reaction was more efficient than either homogeneous or heterogeneous batch reaction: with further optimisation the conversion increased from 77% to 93% as the spinning speed of the disc increased from 250 to 450 RPM at a flowrate of 3 ml s-1. There was only a 3% reduction in conversion on re-use of copper wool over 3 cycles under similar experimental conditions indicating that this catalyst is robust. Pure wool was also found to have some catalytic activity for the Henry reaction, giving a maximum conversion of 85% at 450 RPM in the SMDR. However, it deactivated significantly with reuse and therefore cannot be considered a stable, robust catalyst. Overall, the results show that the copper immobilised wool in the SMDR can be used to improve the conversions for the Henry reaction and that there is therefore promise for the SMDR to be extended to other traditional solvent based reactions

Stimuli responsive conductive polyaniline membrane: In-filtration electrical tuneability of flux and MWCO

The membrane performance of conductive polyaniline membrane may be tuned in-situ by applying an external electrical potential. In this study, we focused on the electrical tuneability of polyaniline (PANI) membrane in response to the externally applied potential and also proposed a hypothesis for electrical tuneability in PANI membranes under applied potential. PANI was synthesised via chemical oxidative polymerisation at different polymerisation temperatures (Tpoly) (5 °C, 15 °C and 25 °C) and flat sheet PANI membranes were prepared via non-solvent induced phase separation (NIPS). The influence of electrical tuneability on flux and molecular weight cut-off (MWCO) under external potential during cross-flow filtration was studied. The membrane flux and MWCO were measured for neutrally charged polyethylene glycol (PEG) feed solutions as a function of the applied potential from 0 to 30 V.The results demonstrated that the electrically conductive PANI membranes showed a decrease in permeance and MWCO under the applied potential in the cross-flow filtrations, with a higher applied potential producing to a larger decrease. The PANI membrane (Tpoly = 15 °C) showing the greatest MWCO decrease (down to 2800 g mol−1) at 30 V from 6000 g mol−1 at 0 V. It was hypothesised that the swelling of polymer chains caused the narrowing of pore size of membranes on the application of high external potential and resulted in reduction of membrane flux and MWCO. Overall these results suggest that the electrically conductive PANI membranes can self-regulatively adjust their separation properties in response to electrical stimuli, allowing control over neutrally charged molecules transport beyond the ion based separations under applied potential