Journal of Membrane Science最新文献

In the fermentative production of propionic acid (PA), the major problem with batch fermentation systems is the strong inhibitory effect of PA on the production yield; one way to increase the yield is the in-situ removal of PA by using pervaporation. Acetic acid (AA) is the most important by-product in the fermentation; therefore, the membrane should be able to remove selectively PA from an aqueous solution containing AA. Considering that PA is more hydrophobic than AA and their kinetic diameter are 0.480 and 0.436 nm respectively, hydrophobic membranes with main pores in the range of around 0.5–0.6 nm with high permeation are required.

Supported thin Carbon Molecular Sieve Membranes (CMSM) were prepared by the dip coating a porous alumina support into a solution containing resorcinol phenolic resin as carbon source. The hydrophobicity was obtained by carbonizing the polymer at temperatures higher than 750 °C and adding polyvinyl butyral (PVB) as pore forming agent and carbon contributor. PA with 88 % of purity was obtained by pervaporation of an aqueous solution containing 5 % of PA and 5 % of AA using a CMSM carbonized at 850 °C containing 1 % of PVB in the dipping solution.

Polyelectrolyte multilayer nanofiltration (NF) membranes have garnered attention for their potential in Mg²⁺/Li⁺ separation applications, particularly due to their positively charged nature and the versatility offered by the layer-by-layer (LbL) self-assembly technique. However, these membranes often face significant challenges in balancing high ion selectivity with adequate water permeability. Addressing these limitations, this study introduces a novel approach by grafting a zwitterionic material, trimethylamine N-oxide (TMAO), onto polyacrylamide hydrochloride (PAH), creating a new cationic polyelectrolyte (TPAH). By cyclically depositing sodium polystyrene sulfonate (PSS) and TPAH onto a polyethersulfone (PES) substrate, we have successfully fabricated a high-performance NF membrane (i.e., (PSS/TPAH)_n) that demonstrates enhanced Mg²⁺/Li⁺ selectivity with high water permeability. TMAO features shorter distances between its positive and negative charge groups and smaller dipoles compared to other zwitterions. These characteristics enhance its ability to resistance to salt effects and transfer charge from amine oxide to water molecule. Furthermore, the grafting of TMAO enhanced the hydrophilicity of TPAH and regulated the charge distribution of the polyelectrolyte. Compared to the control membrane (PSS/PAH)_n, the optimized membrane (PSS/TPAH)_n showed reduced rejection of LiCl from 60.9 ± 2.7 % to 35.9 ± 1.5 %, while that of MgCl₂ increased from 94.3 ± 1.6 % to 96.1 ± 0.7 %. Additionally, water permeability improved from 9.2 ± 0.9 LMH/bar to 16.1 ± 0.5 LMH/bar. Notably, the membranes exhibited an improved selectivity for Mg²⁺/Li⁺ ions in synthetic saline, reaching a maximum of 30.5 ± 1.5, highlighting its potential for practical separation applications. Density functional theory simulations indicate that TMAO not only enhances Donnan effect and intensify ion dehydration of polyelectrolyte multilayers NF membranes but also increases their hydrophilicity. In general, these polyelectrolyte multilayers NF membranes exhibit considerable promise for multiple applications, such as seawater pretreatment, groundwater softening and lithium extraction.

Sulfonated poly(ether ether ketone) (SPEEK) is widely explored as the proton exchange membrane (PEM). However, it is difficult for it to have both good proton conductivity and vanadium resistance. Herein, the ionic-covalent organic nanosheets (TpTG_Cl) were fabricated and added to the SPEEK matrix. The nitrogen-rich and positive charge porous structure of TpTG_Cl nanosheets endowed the composite membrane with the ability to transfer H⁺ and block V^n + effectively. When the TpTG_Cl weight proportion was 3 %, the ion selectivity of the SP/TpTG-3 is as high as 103.3 × 10³ S min cm⁻³. As expected, the SP/TpTG-3 exhibits outstanding energy efficiency (87.0%–77.4 % at 60–180 mA cm⁻²) and long-cycle stability. The results suggested that the ionic-covalent organic nanosheets afforded opportunities to prepare high performance PEM.

High temperature proton exchange membranes (HTPEMs) with multilayered structures based on carbon dots@metal organic framework (CDs@MOF) and Sulfonated Poly(Ether Ketone) (SPEEK) have been prepared with the spin coating technique. In this research, carbon dots (CDs) are self-assembled with metal organic framework (MOF) to form the composite of CDs@MOF. Successive proton conduction channels consisting of CDs@MOF and sulfonated groups in SPEEK facilitate to conduct protons in multilayered structures of the prepared composite membranes. Additionally, CDs@MOF can combine phosphoric acid (PA) molecules deriving from the formed intermolecular hydrogen bonding. The proton conductivity is further improved because of the multilayered structures reducing the proton conduction resistance. Specifically, the (SPEEK/40%CDs@MOF)₃/PA membrane exhibits the maximum proton conductivity of (5.02 ± 0.64) × 10⁻² S/cm at 160 °C. Notably, the proton conductivity can retain 1.53 × 10⁻² S/cm at 80 °C after a 200 h non-stop test. The open circuit voltage peak and power density of a single fuel cell based on the (SPEEK/40%CDs@MOF)₃/PA membrane respectively reach 0.95 V, 258.2 mW/cm² at 100 °C and 0.96 V, 369.9 mW/cm² at 120 °C.

Polyethyleneimine (PEI) nanofiltration (NF) membranes demonstrate remarkable effectiveness in separating lithium and magnesium from salt lakes, attributed to their positively charged surface. However, undesired permeability resulting from densely cross-linked structures limits the further industrial applications and development of PEI NF membranes. Herein, a high permeable Mg²⁺/Li⁺ separation NF membrane with stronger internal and surface positive charge was fabricated using 1-Aminopyridinium iodide (1-AI) for the first time through a capping-grafting synergistic strategy. On the one hand, the monoamine character of 1-AI can realize the end-capping (EC) effect on the acyl chloride monomers in the interfacial polymerization process, which can contribute to a reduction in the cross-linking degree of the membrane. On the other hand, 1-AI with a quaternary ammonium group as the surface grafting (SG) agent can significantly improve the surface positive charge property of the membrane. The synergistic effect of capping-grafting not only rendered the membrane looser and effectively enhanced the surface positive charge of the membrane, but also increased the depth of grafting modification, leading to a notable rise in the internal positive charge of the membrane. After the capping-grafting treatment, the water permeance of the PEI-EC/SG membrane reached 19.8 L·m⁻²·h⁻¹·bar⁻¹, approximately 4.5 times that of the original PEI membrane, while keeping an ideal MgCl₂ rejection rate (97.1%) and exhibiting good Mg²⁺/Li⁺ selectivity (27.7). This work demonstrates the advantages of the capping-grafting synergistic method in regulating membrane structure for improving permeability as well as the surface and internal charge properties of the membrane for enhancing ion selectivity.

In recent years, with the rapid development of new energy vehicles, the demand for lithium resources has been increasing sharply. Positively charged nanofiltration (NF) membranes can accurately separate magnesium ions (Mg²⁺) and lithium ions (Li⁺), which have become an important technology for extracting lithium resources from salt lakes. The introduction of intermediate layer in thin-film composite (TFC) NF membranes could improve the permeability and selectivity for Mg²⁺/Li⁺ separation. However, there is a problem of poor bonding between the intermediate layer and the supporting membranes through the simple physical combination on the membrane surface. Inspired by the controlled growth of succulent plants, the positively charged PA/ZIF-8/PSF composite NF membranes with “multilayer interlocking” structure were prepared successfully based on ZIF-8 layer anchored constrained growth and further interfacial polymerization. The zinc ion ligands of ZIF-8 were pre-anchored on the PSFsolution to provide reaction sites, and the grown ZIF-8 nanoparticles were embedded in the PSFsupporting membrane surface layer. The embedded ZIF-8 nanoparticles can enhance the interface bonding between the PSFsupporting membranes and the ZIF-8 layer. Additionally, the confined growth method can solve the problems of ZIF-8 particle aggregation and poor dispersion. Compared with membranes without ZIF-8 layer, the prepared PA/M − 6 membrane had a high flux of 47.2 L m⁻²h⁻¹, which was 1.82 times that of PA/M-0. Meanwhile, the Mg²⁺/Li⁺ separation factor of the PA/ZIF-8/PSF composite NF membranes could reach 47.6. In particular, the prepared NF membranes exhibited good long-term stability for Mg²⁺/Li⁺ separation.

Membranes for water-in-oil (W/O) emulsion separation require high emulsion permeance, oil purity selectivity, high water-fouling resistance, and reusability. Therefore, a functional membrane structure that satisfies these needs is required. Herein, we describe the effective modification of a membrane surface by forming functional silica particles on a porous polyketone (PK) membrane to form a hierarchical membrane structure with enhanced roughness and superhydrophobicity. We also demonstrate the potential application of the membrane for W/O emulsion separation based on enhanced performance and fouling resistance. Membranes were fabricated by forming silica particles on a porous PK membrane by a sol–gel method using tetraethoxysilane (TEOS). By modifying these silica particles with fluoroalkyl silane (FAS), a superhydrophobic membrane with a high contact angle of up to 162° was fabricated. The resulting FAS-modified membrane had higher permeance with regard to a toluene W/O emulsion than an unmodified PK membrane or a commercially available polyvinylidene fluoride (PVDF) membrane. It was possible to recycle the FAS-modified membrane by simply washing it in toluene to remove external fouling. This effective membrane surface modification helps to enhance both emulsion permeance and fouling resistance during W/O emulsion separation.

It is useful to be able to predict the potential economic performance of new membrane materials and the associated configurations of equipment which would give the best possible performance with these materials. In this study we propose a systematic search of ranges of different possible membrane properties. The properties varied here include the CO₂ permeance and the CO₂/CH₄ selectivity, and a 2D grid with different values of each property is investigated. For each individual combination of properties a superstructure optimization is used to find the configuration and operating pressures which minimize the cost of biogas upgrading. Applying this to every point in the grid gives a surface of upgrading costs across the ranges of possible CO₂ permeances and selectivities. Subsequently a correlation equation is fitted to this data which can be used to predict the potential economic performance of future possible materials within this range. In general the upgrading costs reduce when either of these parameters are increased but for different reasons. Higher permeances allow smaller area of membranes to be used allowing lower membrane costs while higher selectivities reduce the need for recycling and associated compression costs. The selectivity, in particular, is found to strongly affect the optimal configuration with high selectivities allowing for designs without recycling while lower selectivities force the process to include recycling streams in order to meet recovery and purity targets. It is expected that the proposed correlation could be used to quickly evaluate the economic performance of new materials as they are being developed and tested.

Despite the excellent separation performance of organic-inorganic hybrid membranes, such as mixed-matrix membranes, their commercial application remains challenging due to difficulties in uniformly dispersing inorganic fillers and achieving good interfacial contact over large areas. In this paper, we present high-performance, thin-film composite (TFC) membranes made from low-cost, all-organic materials using a commercially attractive and straightforward process for CO₂ capture. The TFC membranes were prepared on a porous polysulfone support using 2,4,6-triaminopyrimidine (TAP) dispersed in comb-shaped polymerized poly(oxyethylene methacrylate) (PPOEM), synthesized through a free radical polymerization process. The organic filler TAP functioned as a hydrogen bond inducer, controlling the free volume and reducing gas diffusivity, thereby enhancing CO₂ selectivity over larger gases such as N₂ and CH₄. Incorporating 2 wt% TAP significantly improved separation performance by primarily reducing N₂ and CH₄ permeances, achieving a CO₂ permeance of 1140 GPU, with CO₂/N₂ and CO₂/CH₄ selectivities of 43.3 and 15.0, respectively. The achieved performance significantly surpassed that of Pebax-based membranes and successfully met the target criteria for post-combustion CO₂ capture. Variations in free volume, molecule aggregation, hydrogen bonding, and interaction energies between gases and membranes were thoroughly investigated via molecular dynamic (MD) simulations. This high-performance TFC membrane, created through simple and facile methods using entirely organic materials, achieves commercial standards for post-combustion CO₂ capture.