Periodic Reporting for period 1 - SHIPMENT (Sustainable and HIgh Performance MEmbranes via iNTerfacial complexation (SHIPMENT))
Periodo di rendicontazione: 2022-05-01 al 2023-10-31
Membrane technology is a very sustainable approach to separation, as it requires much less energy than conventional separation approaches. However, the sustainable image of membranes becomes substantially tarnished when you realize that nearly all membranes are prepared using large quantities of toxic and unsustainable aprotic solvents (NMP, DMF, etc.). Moreover, these aprotic solvents are under serious scrutiny by governments, with the European Union recently agreeing on substantial restrictions for these solvents. To secure the future of membrane technology, it becomes critical to develop more sustainable approaches to membrane fabrication. An Aqueous Phase Separation (APS) technique has recently been proposed by the group of the PI, Membrane Surface Science (MSuS), as a green and sustainable alternative to the currently dominant non-solvent induced phase separation (NIPS) process.APS utilizes polyelectrolytes such as poly(sodium 4-styrenesulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDADMAC), poly(allyl amine hydrochloride) (PAH), and polyethyleneimine (PEI) to obtain sustainable polyelectrolyte complex (PEC) membranes in a completely water-based process. The structure and morphology of these APS membranes can easily be controlled to produce excellent separation properties. Although APS membranes show high solute retentions, the water permeability is much lower than NIPS membranes now utilized for the same application. For example, APS based nanofiltration (NF) membranes showed pure water permeability in the range of ~1–4 L·m–2·h–1·bar–1¸ while the permeability of most commercial NF membranes lie in the range of 5–20 L·m–2·h–1·bar–1.The lower water permeability of the existing APS membranes is now the major obstacle preventing their commercial production and large scale industrial acceptance. This originates from the fact that the separation in case of APS membranes is performed by the same material that gives the membrane its mechanical strength. Indeed, the water permeability is significantly compromised when utilizing dense and mechanically strong membranes, while more swollen an permeable materials are simply took weak. For NIPS based membranes this problem is typically alleviated by coating a thin layer of dense and selective material on top of a porous support membrane either by interfacial polymerization (IP) or dip-coating. But this second step is laborious and again relies on dangerous and harmful organic solvents, for example n-hexane, a known neurotoxin. In this project, we have studied an advanced APS procedure, employing Interfacial Complexation (IC) during the phase inversion step, to produce composite membranes in a highly sustainable one-step approach that will lead to the required high performances i.e. excellent permeability and solute retentions.
We have studied the APS system based on two strong polyelectrolytes, PDADMAC and PSS, where coagulation is induced through a sudden decrease in salt concentration. The focus was on a system in a charge ratio of 1:1, so an equal amount of positive and negative groups, allowing for a charge neutral and strong polyelectrolyte complex. But during the coagulation step we bring the outside layer of the membrane in contact with either a PDADMAC or a PSS solution, leading to an excess of positive or negative charges in the eventual active separation layer. The membranes were succesfully produced and gave relevant separation properties, although not as good as hoped, alo the reproducibility was not always perfects. Still, we moved on from the initial flat sheet membranes to more complex (and more promising) hollow fibre membranes. These were also succesfully made, although also there reproducibility issues were observed.
Overall, we have thus studied a completely new method to make membranes with a gradient in PE ratio in the polyelectrolyte complex membranes.
Overall, we have thus studied a completely new method to make membranes with a gradient in PE ratio in the polyelectrolyte complex membranes.
By far the largest application of polymeric membranes is in the production of drinking water, treatment of wastewater, and kidney dialyzers. Water supply boards, the wastewater treatment companies, and biomedical companies are the largest markets for polymeric membranes. Currently, these companies utilize composite polymeric membranes that are produced via NIPS approach which utilizes huge amounts of reprotoxic organic solvents. Furthermore, the coating process to obtain the final membrane is laborious, requires additional specialized equipment, and also uses harmful organic solvents.[The APS-IC approach, proposed here, is completely unique in that it retains the key strengths of APS, i.e. sustainability and the control over the structure, but now with an additional tuning parameter to obtain composite membranes in a single-step approach without using any additional equipment. At the same time, the IC approach opens the door to a whole new generation of advanced sustainable composite membranes originating from new recipes and novel materials that can be used for densifying the top layer, with functionalities that could not be achieved by traditional NIPS or even with APS. The APS-IC composite membranes with thin dense separation layers could then be used by drinking water production companies to for example, desalinate water and help tackle water scarcity issues impacting our drinking and irrigation water supplies. These types of membranes can also be used by water treatment plants to remove micropollutants from our surface and drinking water supplies. The APS-IC approach opens up the possibility to produce composite APS membranes in a one-step approach that can rival the traditional NIPS membranes in terms of performance and provides direct incentives to the industry for adapting the APS membrane production approach for commercial membrane production. \
Still, did project has shown a good direction to fullow, but has not yet achieved the full potential of the APS-IC approach, more research is first needed. We are in contact with companies interested in further commercialization of this approach.
Still, did project has shown a good direction to fullow, but has not yet achieved the full potential of the APS-IC approach, more research is first needed. We are in contact with companies interested in further commercialization of this approach.