A PA/O-NGO/PPS sandwich composite membrane prepared via multi-step interfacial polymerization for desalination

CFD prediction of concentration polarization phenomena in spacer-filled channels for reverse electrodialysis

Influence of feed flow rate, temperature and feed concentration on concentration polarization effects during separation of water-methyl acetate solutions with high permeable hydrophobic pervaporation PDMS membrane

Forward osmosis (FO), is membrane separation technology in its infancy with various applications such as desalination, power generation, in food industry and others. The technology has shown growing interest due to its numerous advantages and its potential for energy-saving. FO process is, however, still facing important limitations related to efficient membrane and draw agent to achieve higher performances. Water diffusion in FO is driven by the osmotic pressure gradient from a highly concentrated stream (draw solution) to a lower concentration solution (the feed stream) across a semi-permeable membrane. Concentration polarization (CP) phenomena have been reported to be the most important factor causing water flux decline in FO process. Reverse solute flux (RSF) is also considered as a major issue in FO. In this work, an experimental study has been carried out for the evaluation of CP phenomena and RSF in FO process. Ammonium bicarbonate and sodium chloride have been used respectively as draw and feed solutions. Results have shown that dilutive internal concentration polarization phenomena (ICP) induced a draw solution osmotic pressure reduction of 42%. Concentrative external concentration polarization (ECP) effects have shown to affect driving force to a lesser extent, the combined effect of ICP and ECP caused a water decline of 51.5%. A concentration profile based on the obtained results across the FO membrane has been defined.

The role of phase transfer catalysts on properties of polyamide thin-film composite forward osmosis membranes

The main technological problem in the manufacture of electronics on silicon-on-sapphire (SOS) wafers is the high density of defects in the epitaxial silicon layer. The modern method of obtaining ultrathin SOS wafers using solid-phase epitaxial recrystallization (SPER) and pyrogenic thinning that significantly reduce the defect density in these layers. Nevertheless, the influence of the defect density in submicron SOS layers on the structural quality of ultrathin SOS layers remains unclear. In this work, ultrathin (100 nm) SOS wafers were obtained by SPER of submicron (300 nm) SOS wafers with different structural quality. The crystallinity of 300 nm layers before the recrystallization process and ultrathin layers was determined by XRD and TEM. It was found that the smallest values of the FWHM 0.19-0.20° were observed for the ultrathin SOS layers obtained on the basis of 300 nm SOS wafers with the best structural quality. It was shown that the structural perfect near-surface Si layer, which serves as a seed layer in SPER process, and the double implantation regime allow to reduce the linear defect density in the ultrathin SOS layers by ~ 1×104 cm-1.

Tackling membrane wetting is an ongoing challenge for large-scale applications of membrane distillation (MD). Herein, composite Janus MD membranes comprising an ultrathin dense hydrophilic layer are developed by layer-by-layer assembling cationic polyethyleneimine and anionic poly(sodium 4-styrenesulfonate) polyelectrolytes on a hydrophobic polyvinylidene fluoride substrate. Using surfactant-containing saline water as the feed with low surface tension, experiments reveal that the number of polyelectrolyte layers, rather than surface wettability or surface charge, determines the anti-wetting performance of the composite Janus membranes. More deposited layers yield higher wetting resistance. With the aid of positron annihilation spectroscopy, this study, for the first time, demonstrates the origin of the excellent wetting resistance of the composite Janus membranes. The effective pore size of the polyelectrolyte multilayer decreases with an increase in the number of the deposited layer. The membrane with an ultrathin hydrophilic multilayer of 48 nm has a sufficiently small pore size to sieve out surfactant molecules from the feed solution via a size exclusion mechanism, thus protecting the hydrophobic substrate from being wetted by the low-surface-tension feed water. This study may pave the way for developing next-generation anti-wetting Janus membranes for robust membrane distillation.

H2/CO mixture gas separation using composite hollow fiber membranes prepared by interfacial polymerization method

In the present work, a one-dimensional mathematical model is developed to analyze the concentration polarization phenomenon for the separation of gas mixtures in composite hollow fiber membranes. An analytical expression is developed for determining the interfacial concentration at the interface of dense and porous support layers. Further, the model accounts for the non-ideality of the gas mixture. Both co-current and counter-current flow configurations for the separation of hydrogen from a three-component mixture are studied. The effects of feed side pressure and velocity as well as permeability on concentration polarization are probed. It is apparent from this study that the concentration polarization phenomenon significantly affects the separation efficiency at higher permeability values.

The structure with a selective nanofiltration (NF) layer on top of a catalytic ultrafiltration (UF) membrane provides the possibility of treating micropollutants (MPs) by both rejection and degradation. However, such a dense selective layer unavoidably induces a formation of a highly concentrated retentate and a low utilization of the oxidant due to its rejection. A different membrane orientation is expected to solve the problems mentioned above since the concentrated MPs can be degraded within the catalytic support, and the rejection of the oxidants can be avoided when the pressure is applied from the porous support side. However, the resulting complex concentration polymerization (CP) effects are not well understood, and the effects of the following concentration changes of the MPs and the oxidants around the catalyst within the porous support membrane are unclear as well. In this work, three polyelectrolyte multilayers with different selectivity were fabricated on PES@CoFe2O4 catalytic UF membranes by sequential dip-coating. Concentration polarization models are utilized to predict the concentrations of naproxen and peroxymonosulfate (PMS) within the porous catalytic support under different membrane orientations. The results of naproxen removal after adding PMS show that a higher naproxen removal can be obtained with a higher concentration ratio of PMS to naproxen (cPMS/cNPX). Moreover, it is shown that the MPs in the feed solution can be degraded in a catalysis-separation sequence, exhibiting the potential of rejecting and simultaneously degrading MPs. However, the coating of a selective polyelectrolyte multilayer on the catalytic UF membranes also causes lower accessibility of PMS and naproxen to the catalysts embedded within the polymeric membranes, resulting in the decline of degradation efficiency. By coating only one side of the membranes, this negative effect caused by the polyelectrolyte coating can be mitigated. Overall, a 97% removal of naproxen on the permeate side and a 12% degradation of naproxen on the feed side were observed with the one-side-coated membranes under a catalysis-separation sequence. This work highlights the key role that concentration polarization can play in the degradation efficiency of naproxen in catalytic NF membranes, providing valuable guidance for the design of further improved catalytic membranes.

An ultrathin nanofibrous composite nanofiltration (NF) membrane was developed through controlled interfacial copolymerization where an electrospun sulfonated poly(ether sulfone) (SPES) nanofibrous membrane serves as the substrate and 2,5-diaminobenzenesulfonic acid (2,5-DABSA) and piperazine (PIP) serve as aqueous phase monomers. The integration of the electrostatic interaction and hydrogen bonding between SPES nanofibers and PIP/2,5-DABSA triggered the controlled diffusion rate of monomers into the organic phase, resulting in the fabrication of an ultrathin polyamide barrier layer (∼56 nm). Additionally, a polyamide structure was created through the ternary interfacial copolymerization of PIP/2,5-DABSA and trimesoyl chloride (TMC), which offers high permeability to the composite NF membrane. Meanwhile, the -SO3H groups on 2,5-DABSA issued highly negative charges to the polyamide barrier layer, leading to a significant improvement in the rejection ratio against SO42- and fouling resistance against bovine serum albumin. The impact of 2,5-DABSA monomer on the cross-linking degree and pore size distribution of the polyamide barrier layer was investigated by optimizing the proportion of PIP and 2,5-DABSA monomers in the interfacial polymerization (IP) process. The ion selectivity and robustness of the composite NF membrane was determined and compared with conventional and commercial NF membranes comprehensively. Molecular dynamics simulations were conducted to demonstrate the mechanism of the controlled diffusion of monomers; the cross-linking degree and fractional free volume of the polyamide barrier layer were also evaluated. The NF-M(1:1) composite membrane exhibited a significant enhancement in the permeation flux as 137.4 L/m2·h at 0.5 MPa, which was 4 times higher than that of conventional NF membranes, while maintaining excellent divalent salt rejection against Na2SO4 at 99.4%, compared with 98.0% of the conventional NF membrane, effectively breaking through the trade-off effect in the long-term filtration performance.

Computational fluid dynamics study on concentration polarization phenomena in silica membrane reactor during methanol steam reforming

Lab scale assessment of power generation using pressure retarded osmosis from wastewater treatment plants in the state of Kuwait

Diffusional phenomena in membrane separation processes

Effect of poly-dispersed nanostructures on concentration polarization phenomena in ion exchange membranes

Construction of PTFE/PI-PI/PANI-PA composite nanofibrous membrane for efficient photothermal membrane distillation and VOCs interception