Journal of Membrane Science Letters最新文献

The purification of 1,3-butadiene from C₄ hydrocarbon mixtures currently relies on energy-intensive extractive distillation. In this study, we employed ZIF membranes for this challenging separation for the first time, unveiling their superior capability in isolating 1,3-butadiene from other C₄ hydrocarbons with similar sizes, including 1-butene, isobutene, and n-butane. This strong sieving effect was evident from two types of ZIF-8 membranes: one with low crystallinity fabricated via the all-vapor-phase ligand-induced permselectivation (LIPS) method and another with high crystallinity synthesized through the seeded growth method. The gas permeances decreased with increasing kinetic diameters, following the order of 1,3-butadiene (4.31 Å) > 1-butene (4.46 Å) > n-butane (4.687 Å) > isobutene (4.84 Å). The LIPS-ZIF-8 membrane exhibited a high 1,3-butadiene permeance of approximately 1.43 × 10⁻⁷ mol/m² s Pa (∼430 GPU) and ideal separation factors of 18, 56, and 134 for 1,3-butadiene over 1-butene, n-butane, and isobutene, respectively. In separating four-component C₄ mixtures, these membranes could enrich 1,3-butadiene content from 50% in the feed to 96–98% in the permeate through a single separation step. This unprecedented performance is attributed to differences in C₄ diffusivities that span several orders of magnitude.

A solvent-free post-treatment process known as vapor phase infiltration (VPI) is used to engineer the organic solvent reverse osmosis (OSRO) performance of polymer of intrinsic microporosity 1 (PIM-1) membranes via infiltration of trimethylaluminum (TMA) metal-organic vapor. The infiltration of inorganic aluminum constituents hybridizes the pure polymer PIM-1 into an organic-inorganic material (AlO_xH_y/PIM-1) with enhanced chemical stability. A homogenous distribution of inorganic loading in PIM-1 is achieved due to the reaction-limited infiltration mechanism, and the OSRO performance is enhanced as a result. OSRO separations of ethanol/isooctane mixtures using these membranes are shown to be capable of breaking the azeotropic composition with a separation factor for ethanol over isooctane greater than 5 and an ethanol permeance of 0.1 Lm^–2h^–1bar^–1. Thus, these organic-inorganic hybrid membranes created via VPI show promise as an alternative method for separating azeotropic liquid mixtures.

Polymeric membranes have garnered widespread adoption in applications such as desalination, wastewater treatment, and water reuse. Nevertheless, the current disposal practices for these end-of-life (EoL) polymeric membranes, primarily landfill and incineration, are neither economically nor environmentally sustainable. To address this challenge, we first analyzed the factors leading to the EoL phase for these membranes; an understanding that is critical in developing or selecting appropriate recycling technologies. We further proposed a technological framework to guide recycling choices based on the specific state of the EoL membrane. In cases where the membrane exhibits significant breakage, dissolution using eco-friendly solvents, followed by membrane re-preparation, is recommended. For membranes without substantial breakage, regeneration, upcycling, or downcycling strategies can be deployed based on scenarios. We underscored the crucial role of irrecoverable foulant removal within the regeneration technology. Additionally, the reaction interface must be suitably remediated before the application of upcycling technology to EoL microfiltration/ultrafiltration membranes. The downcycling strategy, facilitated by NaOCl oxidation, is readily applicable to EoL nanofiltration/reverse osmosis membranes. This brief frontier review aims to serve as a valuable reference for recycling end-of-life water treatment polymeric membranes.

Thin-film composite (TFC) polyamide (PA) RO membrane modified with a layer of tethered poly(acrylic acid) (PAA) chains displayed intrinsic rejections of nitrate, boron, As(III), and As(V) of 98.0%, 90.7%, 96%, and 99.6%, respectively. The solute permeability coefficients for nitrate, boron, As(III), and As(V) by the SNS-PAA-PA membrane were lower by 31–38%, 49–63%, 57–72% and 87–93% relative to tested commercial membranes. The above results indicate that the SNS-PAA-PA membrane should be suitable for purification of brackish source water contaminated with nitrate, boron, As(III), and As(V) to levels 1219 ppm, 2 ppm, 95 ppb, and 948 ppb, respectively. The study results suggest that there is merit in further exploration of the potential of the present approach for enhancing RO membranes performance for targeted solute removal.

Estimation and correlation of the Hildebrand solubility parameter ($\delta$) of polymers and small molecules is a common practice in membrane material science and is accomplished by experimental and numerical routes. In this paper, we revisit, update, and compare both routes to enhance the accuracy in the determination of $\delta$. Best practices for the experimental determination of polymer solubility parameters are provided, and the viability of Dynamic Light Scattering (DLS) was demonstrated as an alternative to conventional time- and material-consuming techniques, such as Ubbelohde viscometry and swelling measurements. Glassy and rubbery polymers, including high fractional free volume (FFV) microporous polymers such as PIM-1 and poly(1-trimethylsilyl-1-propyne) (PTMSP), are among the samples included in this study with great relevance to membrane science. In an attempt to enhance the accuracy of numerical estimate of polymer solubility parameters via the group contribution method, we provide updated group contribution parameters, along with their uncertainty, according to the technique recently reported by Smith et al. These updated group contribution parameters result in a mean absolute relative error of 9.0% in predicting the solubility parameter on a test set of 40 polymers, which is on par with the average 10% error reported previously. We also show, using machine learning techniques, that augmenting the group contribution model with extra parameters or non-linear relationships does not improve its accuracy. Results of the updated group contribution technique and dynamic light scattering measurements were compared to experimental viscometry on four test polymers, and the difference between the three techniques is compared.

It is a vital technical challenge to extract lithium from salt-lake brine which has very high Mg²⁺ / Li⁺ mass ratio via green and low-cost methods, as these two cations have quite similar ionic hydration radius. Positively charged nanofiltration membranes can separate Li⁺ and Mg²⁺ through Donnan exclusion. In this work, a kind of hollow fiber nanofiltration membrane with positively charged skin layer was successfully fabricated via interfacial polymerization followed by a surface modification with branched polyethyleneimine (BPEI). The resultant membrane has a large number of amine groups, and thus shows positively charged surface with high rejection for divalent cation ions via Donnan exclusion. This gives it very high selectivity for the separation of Li⁺ ions from salt-lake brine. Under optimized conditions, it achieves a water permeance of up to 126.2 L m^-2 h^-1 MPa⁻¹ at a transmembrane pressure difference of 4 bar, and a MgCl₂ rejection of 94.6% with 2000 mg L^-1 aqueous MgCl₂ solution as feed. Meanwhile, it achieves a Mg²⁺ / Li⁺ selectivity of nearly 24 for MgCl₂ and LiCl salt mixture solution with an overall concentration of 2000 mg L^-1 and a Mg²⁺ / Li⁺ mass ratio of 150 : 1 as feed, which is high as compared with most of the literature, demonstrating its potential in the practical application of Mg²⁺ and Li⁺ separation.

The demand of lithium for electric vehicles and energy storage devices is increasing rapidly, thus new sources of lithium (such as seawater and natural or industrial brines), as well as sustainable methods for its recovery, will need to be explored/developed soon. This work presents a novel electromembrane process, called Lithium Membrane Flow Capacitive Deionization (Li-MFCDI), which was tested to recover lithium from a synthetic geothermal brine containing a much higher mass concentration of sodium than lithium (more than 650 times). Specifically, a ceramic lithium-selective membrane was integrated into a flow capacitive deionization (FCDI) cell, which was specifically designed, and 3D printed, to allow simultaneous charging and regeneration of the employed flow electrodes. Despite the extremely high Na⁺/Li⁺ mass ratio in the feed stream, 99.98% of the sodium was rejected and the process selectivity for lithium over other monovalent cations was 141 ± 5.85 for Li⁺/Na⁺ and 46 ± 1.46 for Li⁺/K⁺. The Li-MFCDI process exhibited a stable behaviour over a 7-day test period, and the estimated energy consumption was 16.70 ± 1.63 kWh/kg of Li⁺ recovered in the draw solution. These results demonstrate promising potential of the Li-MFCDI for the sustainable lithium recovery from saline streams.

In this work, the successful fabrication of polymeric hollow fiber (HF) and flat sheet (FS) membranes was examined by employing γ-butyrolactone (GBL)-a green and environmentally friendly solvent- for the polymer's dissolution following the principles of green chemistry and sustainability regarding the membrane preparation. In addition, the ternary phase diagram of the P84/GBL/water was constructed and the viscosity of dope solution was measured for different concentrations and temperatures. Their morphological characteristics of the prepared polyimide membranes were investigated through SEM analysis. CO₂/CH₄ separation measurements under continuous flow were performed to evaluate the efficiency of the membranes for a binary 10/90 vol.% CO₂/CH₄ gas mixture. The developed green HF and FS membranes exhibited comparable, and in some cases even superior, performance compared to membranes prepared using the conventional and highly toxic NMP solvent, making them highly promising candidates for CO₂/CH₄ separation, with a real mixture separation factor of ∼58.

Molybdenum disulfide (MoS₂) has been fabricated into thin-film composite (TFC) membranes for dye desalination due to its excellent underwater stability and tunable interlay spacing. However, it remains challenging to synthesize thin layers of MoS₂ with high water permeance and high dye rejection due to the difficulty in fabricating large crystalline sheets or exfoliation. Herein, we report a scalable method coupling bottom-up hydrothermal synthesis and top-down ultrasonic exfoliation to obtain well-dispersed MoS₂ nanosheets and a vacuum filtration method to prepare ultrathin membranes (thickness: 30 – 60 nm) for dye desalination. The MoS₂ nanosheets and membranes are thoroughly characterized for their chemistries and nanostructures. The membrane with 60-nm MoS₂ exhibits water permeance of 32 LMH/bar, Na₂SO₄ rejection of 2.3%, and Direct Red-80 rejection of 99.0%. The MoS₂ membranes exhibit dye desalination performance superior to state-of-the-art commercial polyamide membranes and many leading membranes based on two-dimensional materials.

Polyamide (PA) reverse osmosis membranes are commonly employed in seawater desalination owing to their effective salt rejection and water permeability; however, the elimination of small and neutral boron molecules from seawater remains a significant hurdle in energy-efficient and cost-effective desalination processes. In this work, a seawater reverse osmosis (SWRO) membrane with powerful boron removal competence was designed by adopting an in-situ rapid integration protocol, which utilized aliphatic amines as hydrophobic barriers by bonding the residual chloride groups upon the membrane surface and as molecular plugs by embedding in the PA networks. Consequently, it resulted in a notable improvement in the rejection of neutral boron molecules due to enhanced steric hindrance caused by immobilized amine plugs and synergistically tunned hydrophobic interactions. The permeability coefficient of boron decreased from 4.8 to 0.9 L m⁻² h⁻¹, and the boron rejection increased from 80.7 to 90.5% under the modification conditions with the optimal type and concentration of amines, while displaying a NaCl rejection of 99.8% and an acceptable water permeability of 0.55 L m⁻² h⁻¹ bar⁻¹. Meanwhile, the alteration of membrane chemical compositions and structure properties was kept to a minimum. This study offers intuitive insights into the critical roles played by the aliphatic amines in the selective layer of the membrane for the removal of neutral boron molecules and salts, thereby enabling the fabrication of highly selective SWRO membranes, which may have significant implications for more efficient membrane-based seawater desalination and boron removal.