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High-pressure reverse osmosis (HPRO) holds promise as a technology for the energy-efficient desalination of hypersaline brine (≥70 g/L total dissolved solids). In this work, we examined the effects of membrane compaction for four types of thin-film composite (TFC) RO membranes from DuPont Water Solutions (XLE, BW30, SW30HR, and XUS180808) using a crossflow filtration setup. The membranes were tested at a maximum applied pressure (ΔP) of 200 bar using a seawater desalination brine feed solution (70 g/L NaCl) to simulate conditions encountered in HPRO processes. Post-compaction membrane characterization revealed the densification of the support and selective layers of the TFC membranes (42–61% decrease in thicknesses and 15–22% reduction in polyamide heights, respectively) with respect to their pristine analogues. We also performed a mechanical strength analysis of the support layers that revealed the inverse relationship between the Young's modulus and magnitude of support layer compression. Our results suggest that support layers with a tensile strength ≥7 MPa and a Young's modulus ≥130 MPa are necessary to fabricate mechanically robust TFC membranes for HPRO application. In terms of desalination performance, the least compact-resistant membrane, XLE, displayed a drastic drop in water permeability and salt rejection from 1.63 L m−2 h−1 bar−1 and 97.5% in seawater RO test (ΔP: 55 bar, 35 g/L NaCl feed solution) to 0.39 L m−2 h−1 bar−1 and 95.0% in HPRO test (ΔP: 200 bar, 70 g/L NaCl feed solution). On the other hand, the most compact-resistant membrane, XUS180808, showed the least decline from 0.60 L m−2 h−1 bar−1 and 99.4% in seawater RO test to 0.35 L m−2 h−1 bar−1 and 99.2% in HPRO test. Overall, all four membranes showed irreversible decline in performance after HPRO tests whereby they could not regain their original permeability values at lower pressures (<200 bar). [Display omitted] • TFC membranes were tested in HPRO for brine desalination (ΔP: 200 bar; feed: 70 g/L NaCl). • Best-performing membrane showed a permeability of 0.35 L m−2 h−1 bar−1 (99.2 % rejection). • Compacted membranes displayed a densified support layer (42–61 % decrease in thickness). • Support layers with tensile strength ≥7 MPa and modulus ≥130 MPa are suitable for HPRO. • Nanovoids were preserved in the compacted polyamide layers (∼20 % decrease in height). [ABSTRACT FROM AUTHOR]

Thin film composite (TFC) polyamide (PA) membranes experience compaction at high pressure applications, resulting in the reduction in water permeability. However, the compaction mechanism is still unclear especially for different PA morphologies and substrate structures. In this work, we systematically studied the compaction of TFC PA membranes with different structures and morphologies. We first examined 2 main types of commercial reverse osmosis (RO) membranes: brackish water RO and seawater RO membranes. After that, we synthesised four types of TFC membranes with tailored PA and substrate structures to further understand the compaction behaviors. TFC membrane with a PA layer of low protuberances or nodules and dense substrate showed excellent resistance against high pressure (50 bar), with only a slight irreversible decrease of 2.1–3.5% in water permeability when retested at 5 bar. However, the PA layer of high protuberances experienced significant compaction even when it was supported by a similar dense substrate. The permeability of the TFC membrane decreased ∼10% as a result of the decrease in the effective area of the active layer. On the other hand, the TFC membrane with a PA layer of low protuberances formed atop a loose substrate showed a greater decrease (∼18.5%) in water permeability. The densified skin layer and collapsed macro-voids within the loose substrate resulted in a ∼40% decrease in the overall height of the PA layer and a 65% decline in substrate surface porosity, respectively, which are identified as the reasons for the reducing water permeability. Notably, the water-salt selectivity of this particular membrane was seriously deteriorated after compaction due to the presence of subtle defects in the PA layer caused by the drastic deformation of the loose substrate. This work deepens the understanding of the compaction behaviors of TFC PA membranes, providing a clear fundamental guidance on designing membranes applied at high operating pressures. [Display omitted] • The compaction of TFC PA membranes with different PA and substrate structures at 50-bar hydraulic pressure was investigated. • The high protuberances on the PA layer were compressed at 50 bar, resulting in an apparent decline in water permeability. • A porous substrate resulted in the decreases of water permeability and selectivity simultaneously after membrane compaction. • A TFC membrane with a low-protuberance PA layer and dense substrate is suitable for use in high-pressure processes. [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [ABSTRACT FROM AUTHOR]

Nanoscale characteristics of the polyamide layer are key towards the high desalination performance of thin-film composite reverse osmosis (TFC-RO) membranes. Further advancements in the performance of TFC membranes necessitate a comprehensive understanding of the desired polyamide characteristics and its formation mechanisms. Empirical evidence has shown that the properties of the support layer is as equally important as the interfacial polymerization (IP) conditions in the fabrication of high permselectivity TFC membranes for desalination. Herein, we discuss the properties of polyamide layers formed using identical IP conditions over support membranes of different polymers and chemistries (polyethersulfone, polyetherimide and polysulfone) under fairly similar surface pore properties. The characteristics of the polyamide layers formed thereon displayed different physicochemical properties. It is postulated that the support membrane chemistry actually affects the IP reaction and polyamide formation by controlling the amine diffusion speed as well as the breadth of the IP reaction zone (i.e., the region between the interface and the furthest point in which the reaction occurs). Transmission electron microscopy analyses further revealed the nanoscale differences in the polyamide layer (heights ranging from 50 to 200 nm), including intrinsic thickness of basal layer (~10–35 nm) and leaf-like top layer (~20–85 nm), as well as the presence of nanovoids. Finally, we propose a conceptual model to underline the role of support membrane chemistry in the IP reaction, and consequently the formation mechanism of the nanoscale polyamide features. The mechanistic insights from this study are expected to provide more understanding towards a better control over the fabrication of polyamide layers for TFC membranes. The findings in this work are also expected to facilitate tailoring polyamide layers for specific osmotically driven processes. [Display omitted] • Support membrane chemistry affects MPD diffusion and partitioning extent in IP. • TEM and SEM analyses revealed changes in the polyamide (PA) nanoscale morphology. • PA layer of TFC-PES membrane was thin and smooth without any nanovoids. • PA layer of TFC-PSf membrane had thick base, thin leaves and multi-layer nanovoids. • PA layer of TFC-PEI membrane had thin basal layer with clumpy roof-like top layer. [ABSTRACT FROM AUTHOR]

Seawater reverse osmosis (SWRO) is the key technology driving an energy-efficient and cost-effective desalination process. At the center of this technology are the thin film composite (TFC) membranes, which not only promise a stable operation but also high separation performances. The objective of this review is to consolidate recent advances in SWRO membranes from the standpoint of membrane materials, fabrication methodologies and applications. First, the thermodynamic limit and energy consumption of SWRO desalination are reviewed, before we discuss the current status of SWRO membranes, highlighting the four main challenges to date – permselective tradeoff, relatively low single-pass boron rejection, membrane fouling and poor chlorine resistance. Thereafter, a comprehensive review of the membrane development is presented. We examine findings reported in research papers and patents, and various methods to achieve SWRO membranes of higher permselectivity, boron rejection, and chlorine resistance as well as lower fouling propensity. Key insights from the membrane industry are also furnished. Then, we put together an outlook, featuring our perspectives on SWRO membrane development. Empirical data in this review are collated into an upper-bound relationship, which is tailored specifically for SWRO membranes and expected to provide benchmarking for future SWRO membrane development. Since the traits of SWRO membranes are unique from those of brackish water RO (BWRO) membranes, we also distinguish the methods used for SWRO membrane fabrication to help zero in on the correct strategies, and provide insights for advancing new membrane designs. Overall, this review sums up the current state-of-the-art SWRO membranes, looking at the array of fabrication methods used thus far, and putting into perspective critical strategies to realize the next-generation TFC membranes that can address the future demands of SWRO and deliver a more competitive desalination process. [Display omitted] • Recent advances in SWRO membrane are collated from papers and industrial patents. • Current status and future outlook of SWRO membrane industry are discussed. • A permselectivity upper bound is established specifically for SWRO membranes. • The upper bound is given by A/B = 46.75 A −1.72 (A/B in bar−1 and A in Lm−2h−1 bar−1). • A roadmap for SWRO membrane fabrication is proposed (short/long-term strategies). [ABSTRACT FROM AUTHOR]