The high temperature (above 400 degrees C typically) of thermal rearrangement reaction often caused pore collapse and skin layer densification of asymmetric hollow fiber, and leading to low gas permeance. To solve this problem, a novel hollow fiber membrane based on phenolphthalein was prepared and undergone a cross-linked thermally rearranged (XTR) treatment. The thermal labile lactone rings from the phenolphthalein moities were employed to cross-link the hollow fiber membrane at sub-Tg. Subsequently, the cross-linked hollow fiber was heated over 400 degrees C and turned into thermally rearranged membrane. The CO2 permeance increased by 70 % when the hollow fiber precursor was first cross-linked at sub-Tg for 2 h. This demonstrated the efficiency of sub-Tg cross-linking, which mitigated the sub-layer collapsing as shown in SEM images. Additionally, by optimizing the hollow fiber spinning condition and the thermal treatment procedure, the CO2 permeance was further increased to 436.22 GPU with a CO2/CH4 selectivity of 30.63, surpassing all TR hollow fiber membranes for CO2/CH4 separation. When used high pressure CO2, CO2/CH4, and CO2/CH4/N-2/ethane/benzene mixed gases as feeds, no significant signs of plasticization were observed. Therefore, the anti-plasticized high performance XTR hollow fiber membrane had a great potential for natural gas purification.

Phenolphthalein-based polyimides and their derivative cross-linked and thermally rearranged polymers (XTR) exhibited attractive gas transport properties. This study attempted to further improve the gas transport performance of XTR polymers by tuning the molecular structures of a phenolphthalein-based diamine, diamino-phenolphthalein (DAP). We synthesized an o-cresolphthalein-based diamine (OCA), which had a similar molecular structure to DAP except that there were two methyl groups on the ortho position to hydroxyl groups of DAP. The OCA monomer reacted with 4,4 '-(hexafluoroisopropyl)phthalic anhydride (6FDA) to form a polyimide, 6FDA-OCA, which was used as a precursor to form XTR polymers by heating in argon. Molecular simulation results indicated that the methyl groups of OCA gave the 6FDA-OCA backbone a lower torsion angle and a higher rotation energy than 6FDA-DAP. This led to a higher T g, better gas transport performance, and better plasticizing resistance of 6FDA-OCA than 6FDA-DAP. After TR reactions, the CO2 permeability of 6FDA-OCA-450 reached 3743 Barrer, which was 60% higher than that of 6FDA-DAP-450, and the ideal selectivity of CO2/CH4 was 18.8, which was slightly higher than the selectivity of 18.6 to 6FDA-DAP. Therefore, the strategy of introducing methyl groups in the benzene ring of phenolphthalein was successful to enhance gas transport properties to phenolphthalein-based polyimides and TR polymers.

Cosolvent-assisted interfacial polymerization, widely researched in the field of separation membranes, is an effective method for enhancing membrane flux. However, the impact of cosolvents on membrane charge properties remains underexplored. Prior research on charge enhanced nanofiltration membranes has predominantly concentrated on unipolar designs, targeting co-ion rejection. This study explores the use of cosolvents to modulate the diffusion behavior of binary aqueous phase monomers: polyethyleneimine, a macromolecular amine, and piperazine, a small-molecule amine. Enhanced differential diffusion of the two monomers toward the interfacial polymerization reaction zone is achieved. By employing precise molecular-scale control, ultrathin polyamide nanofiltration membranes with enhanced Janus charge distributions are successfully fabricated. The polyamide selective layer's charge characteristics display spatial asymmetry, featuring a negatively charged surface and a positively charged backside. This asymmetry yields a zeta potential difference of 48 mV between the upper and lower surfaces, enabling efficient divalent anion rejection and rapid monovalent anion transmembrane passage, thus achieving superior mono/divalent anion selectivity. The membrane exhibits a 99.4 % rejection for Na2SO4 and less than 20 % for NaCl, resulting in a Cl-/SO42- selectivity of 887 and a water flux of 18.0 LMH/bar. This work offers a novel, simple, and efficient approach for fabricating Janus nanofiltration membranes featuring a heterogeneous charge characteristic.

To achieve fuel-grade purity (>= 99.5 wt%), raw bioethanol needs to be purified. Adopting pervaporation membrane for bioethanol enrichment can greatly reduce the energy consumption compared with distillation. However, this requires the membrane having a high flux and high water to ethanol selectivity as well as good stability. In this study, a layer-by-layer self-assembled composite pervaporation membrane was prepared by alternately dip-coating polyallylamine hydrochloride (PAH) and sodium alginate (SA) solutions on the surface of a polyacrylonitrile (PAN) microfiltration membrane. The membrane flux and separation performance under different feed conditions are measured independently, and the results are mutually independent. These tests are conducted as short-term experiments to evaluate the membrane's separation performance under specific feed conditions. By optimizing the concentrations of PAH and SA, best separation performance of the composite membranes was obtained with a flux of 2.02 kg m(-2) h(-1) and a water to ethanol separation factor of 10993 using a 90 % ethanol water solution as feed at 70 degrees C. The composite membrane showed good stability in water. When keeping all other conditions unchanged, the feed ethanol concentration is adjusted to 50 wt%, the membrane flux increase to 12.61 kg m(-)(2) h(-)(1), and the water concentration in the permeate reach 99.7743 wt%.

Researchers have developed pH-stable nanofiltration membranes with polyamine or polyurea selective layers to meet the challenges posed by extreme pH conditions. However, their limited overall separation capacity constrains their effectiveness in alkali resource recovery. In the present study, we report the fabrication of an innovative pH stable nanofiltration membrane via interfacial polymerization between isocyanates and amines. The strategic modulation of isocyanates, varying in molecular structure and reactivity, enabled fine-tuning of the resultant poly(urea-thiourea) selective layer's molecular architecture. 1.8 '' x 12 '' sized spiral wound membrane elements were fabricated and their potential for recovering alkali resources from mercerizing wastewater was evaluated. The membrane elements achieved a COD rejection of 80 %, an OH- permeability of 92 %, with a water flux of 6.5 L/h under 1 MPa. The results underscore their superior comprehensive separation capabilities. These innovative membranes may facilitate impactful pollution mitigation and carbon footprint reduction in the textile industry, by promoting efficient resource recovery and reuse of treated water, thereby promising significant economic and environmental benefits.

Scholarly discourse surrounding the thin film composite organic solvent nanofiltration (TFC OSN) membrane field has largely been dominated by focusing on the optimization of the selective layer. However, this often leaves the porous support layer, with its innate solvent resistance, cost-effectiveness, and superior permeability, in the shadows. This study presents a novel OSN membrane utilizing a polyethylene (PE) battery separator as the porous substrate. The structural affinity between ethylene-vinyl alcohol and PE facilitates efficient hydrophilic modification, which allows for uniform and compact polyamide selective layer formation through interfacial polymerization. The HPE-NF-1.0 membrane exhibits rejections of 99.5%, 96.7%, 100%, and 97.2% for Methyl Orange, Rhodamine B, Congo red, and Rose Bengal, respectively. It also shows a solvent flux of 52.5 LMH in methanol and robust resistance against alcoholic solvents and DMF. Using PE as the porous substrate, we bypass intricate and time-demanding cross-linking processes and complex pore-preservation post-treatments, providing a simplified strategy for TFC OSN membrane fabrication.

Increasing the acid stability and selectivity of nanofiltration (NF) membranes, which are used to treat acidic industrial effluents, is highly beneficial. A series of acid-stable NF membranes featuring polysulfonamide (PSA) separation layers were prepared through interfacial polymerization of branched polyethyleneimine (PEI), polyethylenepolyamine (PPA), and 1,3-benzenedisulfonyl chloride (BDSC) on a porous polyethersulfone (PES) substrate. The optimization of the membrane filtration performance involved analyzing the monomer content in both the aqueous and organic phases and adjusting the PEI-to-PPA ratio, thereby preparing ultrathin PSA layers. The influence of the PSA morphology and structure on the membrane filtration performance was examined. The most effectively optimized sample demonstrated a MgSO4 rejection rate of 95.4 +/- 0.4 % and a water flux of 55.4 +/- 1 L m-2h- 1 at a pressure of 2.0 MPa. The acid stability of the membrane was assessed by examining the permeation, separation, and physicochemical properties before and after undergoing static acid-soaking tests. Following a 5-month exposure to 20 % (w/v) HCl or 20 % (w/v) H2SO4 aqueous solution, the optimal membrane maintained a MgSO4 rejection of 92.6 % at neutral pH, with a permeation flux of 68.2 L m-2h- 1 under 2.0 MPa. Owing to their excellent selectivity, enhanced acid stability, structural controllability, and ease of functionalization, these PSA-NF membranes are promising for use in industries such as mining, semiconductor, and electroplating.

A phenolphthalin-based diamine 2-(bis(3-amino-4-hydroxyphenyl)methyl) benzoic acid (AHPBA) was synthesized by a reductive ring-opening reaction of 3,3’-dinitrophenolphthalein. Homopolyimides and copolyimides were prepared by a chemical imidization reaction using 4,4’-hexafluoroisopropylphthalic anhydride (6FDA), AHPBA, and 2,4,6-trimethyl-1,3-phenylenediamine (DAM). These polyimides were post-crosslinked using ethylene glycol to improve their plasticization resistance. Among these polyimides, ester crosslinked 6FDA-APHBA/DAM (1:3) had the best separation performance. After crosslinking, the CO2 and O2 permeabilities increased by 5 times to 500.9, and 106.8 Barrer, respectively, with selectivities to the CO2/CH4 and O2/N2 gas pairs of 29.2 and 4.57, respectively. Moreover, the crosslinked polyimides were not plasticized at 30 atm CO2 pressure. After aging for 60 days, permeability decreased by 10-20% with a slightly increase in selectivity. For CO2/CH4 (1:1) mixed gas separation, a CO2 permeability of 300 Barrer and CO2/CH4 selectivity of 27.68 were achieved at a CO2 partial pressure of 30 atm. These results demonstrated that the AHPBA diamine was suitable for designing high-performance anti-plasticized polyimides.

The petrochemical industry is an important producer of high salinity wastewater, necessitating the efficient separation of salts in zero discharge processes. This study reports the development of an industrially scalable thin film composite nanofiltration membranes that facilitate the effective separation of NaCl/Na2SO4. Employing a one-step functionalization process, the membrane pore distribution is sharpened, and the surface negativity is intensified. Branched polyethyleneimine with abundant reactive amine groups is employed as an aqueous comonomer, leading to the generation of high density grafting active sites. Nucleophilic substitution reaction is employed to functionalize the membrane surface with negatively charged sulfonic acid groups. Simultaneously, large voids within the free volume are filled and the pore size distribution is effectively narrowed. The resultant membranes demonstrate an impressive rejection of 99.5 % for Na2SO4, a selectivity of 163.4 for NaCl/Na2SO4 and a selectivity of 488 for Cl-/SO42-, with a water flux of 45 LMH under 0.5 MPa. The corresponding 8 '' x 40 '' sized spiral wound membrane modules exhibit a NaCl/Na2SO4 selectivity of 100.4 and a Cl-/SO42- selectivity of 258.3, demonstrating high practical applicability. A pilot trial is planned to integrate these novel membrane products into zero discharge processes within the internal chemical enterprises of Sinopec.

Lithium extraction from brine sources such as salt lakes, seawater, and produced water from oil/gas fields is garnering increasing interests from the academic and industrial sectors due to its cost-effectiveness and reduced environmental impact. A critical technological challenge is the efficient separation of Mg 2 + and Li + ions. Many researchers have reported the preparation of positively charged nanofiltration membranes with quaternary ammonium groups, yet investigations about quaternary phosphonium groups are scarce. In this work, positively charged nanofiltration membranes were prepared utilizing polyethyleneimine as the aqueous phase monomer, trimesoyl chloride as the organic phase monomer, and 3-bromopropyl triphenyl phosphonium bromide as the functionalizing monomer. The TFC-P + membranes, enriched with a high density of quaternary phosphonium groups and an enhanced Donnan effect, achieve a MgCl 2 rejection of 98.9 %, a Mg 2 + /Li + selectivity of 81.6, and a water flux of 50 LMH under 0.5 MPa. The membranes possess an enhanced comprehensive separation capability that exceeds that of the majority of nanofiltration membranes documented in scholarly articles. Additionally, the membranes exhibit outstanding anti -fouling and anti -bacterial characteristics, essential for their industrial applications. The preparation method proposed herein is simple and conducive to continuous production processes. In light of the abundant produced water reserves from oil and gas extraction, future work will focus on pilot -scale lithium extraction experiments.

The petrochemical industry is typically energy -intensive, involving frequent and intricate separation processes. SINOPEC is a globally recognized lubricant manufacturer and distributor, with a substantial production capacity exceeding 1.7 million tonnes in 2022. The dewaxing solvent recovery process in lubricant production necessitates a multi -stage flash and distillation treatment, resulting in substantial energy consumption and high costs. Utilizing organic solvent nanofiltration (OSN) membranes offers a feasible alternative approach to address this issue. A series of thin film composite OSN membranes with varying molecule weight cut-offs were prepared through precise adjustment of the chemical composition and proportion of the organic co -monomers. The application potential of the optimized membranes in the lubricant dewaxing solvent recovery was evaluated using lubricant base oil derived from the actual production line, specifically light deasphalted oil and vacuum cut2. The membrane exhibited a rejection of 99.3 % for light deasphalted oil and 95.6 % for vacuum cut2, with corresponding fluxes of 16.8 and 13.4 LMH under 2 MPa, respectively. Based on this, spiral -wound membrane modules (1.8 '' x 12 '') were fabricated and their suitability for dewaxing solvent recovery was further validated. The fabrication of spiral -wound membrane modules (8 '' x 40 '') is in progress, with intentions to conduct a pilot plant trial on the lubricant oil manufacturing line.

The efficient separation of Mg2+ and Li+ is the crucial step in the process of extracting lithium from salt lake brine. Nanofiltration (NF) membranes exhibit promising application potential in Mg2+/Li+ separation but the Mg2+/Li+ selectively of negatively charged NF membranes prepared by conventional interfacial polymerization process is far from desirable. In this study, a novel positively charged quaternary ammonium bromide, 3-bromopropyl trimethylammonium bromide (BTAB), is grafted on the polyethyleneimine (PEI)/trimesoyl chloride (TMC) NF membrane surface. This is achieved by a chemical reaction known as nucleophilic substitution, which involves the replacement of a bromine atom (-Br) with an amine group. Owing to the enhanced Donnan effects, the BTAB-modified NF membranes exhibit a MgCl2 rejection of up to 99.2 %, while maintaining a water flux of approximately 50 LMH under 5 bar. Meanwhile, the LiCl rejection is only similar to 30 %. The Mg2+/Li+ selectively of the BTAB-modified NF membranes reaches 95.9 when filtrating a simulated brine with a Mg2+/Li+ ratio of 20 (2000 ppm MgCl2 and LiCl mixture), which is a twofold improvement compared with the pristine NF membranes. The working stability of the BTAB-modified NF membranes is confirmed by a 50-h continuous operation process. A two-stage NF treatment is conducted using a simulated East Taijinar salt lake brine, achieving Li2CO3 powder with a purity level of 99.4 %. The nucleophilic substitution reaction between -Br and the amine groups offers a good reference for the surface functionalization of NF membranes.

In the realm of gas purifications, hollow fiber membranes have gained significant prominence due to their unique advantages. However, achieving defect-free membranes poses a considerable challenge. In this study, we addressed this challenge with a novel copolymer, 6FDA-DAM:DAP(2:1), comprising 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,4.6-Trimethy-m-phenylenediamine (DAM), and a phenolphthalein-derived diamine of 3,3 '-diaminophenolphthalein (DAP). We found that defect-free hollow fiber membranes could be prepared when 20 wt% or more ethanol was added in the polymer dope solution, but this led to the formation of oval hollow fibers that would be flattened under high pressure. We solved this limitation by lowering ethanol content to 15 wt%, adding 2 wt% LiNO3, and increasing the air-gap distance. These measures reduced the difference in phase inversion rates between the surface region and the bulk phase of the nascent hollow fiber. The CO2 permeance of this defect-free hollow fiber membrane reached 282 GPU with a CO2/CH4 selectivity of 50.2. Highly permeable defective hollow fiber membranes were also developed using a polymer dope without LiNO3 and a low THF content of 5 wt%. After coated by silicone rubber, CO2 permeance of the membrane reached 554 GPU with a CO2/CH4 selectivity of 45.0. In mixed gas tests, the two membranes exhibited O-2 permeances of approximately 43.3 and 75.3 GPU, with O-2/N-2 selectivities of 5.5 and 5.4, respectively. Their CO2 permeances were 281 and 465 GPU, with CO2/CH4 selectivities of 45 and 41, CO2/N-2 selectivities of 35.7 and 33.3, respectively. These separation performances were among the best of state-of-art polymeric hollow fiber membranes and demonstrated great potential for gas separation applications such as natural gas sweetening, flue gas treatment, and air separation.

Commercial nanofiltration (NF) membranes based on polyamides may experience a decline in permeation performance after prolonged operation. The short lifespan of NF membranes will lead to waste and additional carbon emissions. Thus, rejuvenating membranes and extending their lifespan seem more meaningful than investigating new materials. In this paper, polyamide NF membranes were modified with various polyphenol monomers to improve their permeation performance. The effects of different polyphenols on pore size, surface morphology, and permeation performance of the NF membranes were thoroughly investigated. After modification with tannic acid, the NF membrane exhibits improved salt rejection while experiencing an acceptable decrease in water flux. It should be noted that the commercial NF membrane element fabricated by Koch can recover its Na2SO4 rejection from 83.0% to 94.2% and demonstrate long-term stability after rejuvenation with tannic acid. Combined with the environmental friendliness of polyphenols, this straightforward modification method has the potential for prolonging the operational lifespan of industrial NF membrane products.

Polyimides containing lactone rings can be thermo-oxidatively cross-linked to enhance gas separation properties and antiplasticization performance. Degradation of the lactone ring at high temperature is crucial to generate free radicals for cross-linking. Determining the thermal stability of the lactone ring is required to set an appropriate heating protocol for thermal cross-linking. To elucidate the relation between polymer structure and the thermal stability of the lactone ring, we prepared two phenolphthalein-based diamines, AMPB and AHPB. These diamines were reacted with 6FDA and DAM to form three copolyimides using azeotropic distillation and chemical imidization. This was used to design copolyimides containing lactone rings and different ortho functional groups including -OH, -OCH3, and -OOCCH3. By characterizing the physiochemical properties of these copolyimides and performing molecular simulations, we discovered that the stronger the electron-donating ability of the ortho groups, the higher the temperature at which the lactone ring began to degrade. Copolyimides with a relatively weak electron-donating groups, -OH and -OOCCH3, could be oxidatively cross-linked at 275 degrees C, while the copolyimide with a -OCH3 group could be only cross-linked at a temperature above 325 degrees C. Moreover, the gas separation property, mechanical properties, and plasticization resistance were improved after cross-linking.

Thermally rearranged (TR) polymers have good gas separation property, but the high TR temperature often caused pore collapsing and embrittlement of hollow fiber. We designed two copolyimides by reacting a TR-able 3,3 '-diaminophenolphthalein (DAP), and two non-TR able diamines, 2,4,6-trimethyl-m-phenylenediamine (DAM) and diethyl-toluene diamine (DETDA) with hexafluoroisopropylidene diphthalic anhydride (6FDA) using azeotropic distillation. The bulky DAM and DETDA diamines and the hydrogen bonding provided by the OH groups of DAP enabled high glass transition temperatures of Co-PI-DAM and Co-PI-DETDA copolyimides so that the thermal cross-linking and TR reaction realized at sub-T-g. Moreover, compared with the 6FDA-DAP polyimide, copolymerization greatly improved the tensile strength from 35 to 75 MPa (Co-PI-DAM). The cross-linked TR polymers exhibited high separation performance to CO2/CH4 and were not plasticized by CO2 at 30 atm. The two copolyimides show great potential for fabricating TR hollow fiber membranes.

Interlayered thin film nanocomposite nanofiltration (TFNi-NF) membranes have the potential to overcome the permeability and selectivity limitations of conventional NF membranes. This work is the first attempt to construct the polyvinyl alcohol/attapulgite (PVA/ATP) nanocomposite interlayer by chemical cross-linking between PVA and glutaraldehyde (GA) in which the nanomaterial ATP was connected with covalent bonds. Meanwhile, the support layer of the NF membranes was chosen to be a microporous membrane with high porosity and a three-dimensional (3D) network porous structure prepared by the innovative atomization-assisted non-solvent induced phase separation (AA-NIPS) method, greatly enhancing the water transport channels. The ATP acted as a multifunctional regulator to tune the porous structure of the PVA/ATP nanocomposite interlayer through physicochemical interactions. By manipulating monomer diffusion behavior, a dense polyamide (PA) layer with only 12 nm in thickness was prepared, leading to enhanced permeability and rejection for divalent ions. In addition, the structure and performance of the TFNi-NF membranes are highly tunable by changing the ATP loading. The prepared TFNi-NF membranes have shown great potential for seawater desalination and the separation and purification of aqueous electrolytes.

In this study, a multi-layer pervaporation composite membrane was prepared by spray-coating a hydrophilic layer consisting of poly(allylamine hydrochloride) (PAH)/polyvinyl alcohol (PVA)/trimesic acid (BTA) onto a polyethersulfone (PES) porous substrate. The presence of amine groups facilitated the transport of water molecules, enabling the composite membrane to exhibit excellent water/ethanol separation properties. When a feed solution consisting of 90 ​wt% ethanol and 10 ​wt% water was dehydrated using the PV membrane at 70 ​°C, a flux of 1.46 ​kg ​m−2 ​h−1 with a water/ethanol separation factor of 3300 was realized. In addition, after coating a 267 ​nm silicone rubber layer on top of the membrane, the separation factor was further increased by 70.79 % to 5285, while the flux was slightly decreased by 12.33 % to 1.28 ​kg ​m−2 ​h−1. This was because the hydrophobic silicone rubber layer reduced the water swelling effect of the selective layer and hindered the permeation of ethanol-water coupling molecules, resulting in a reduction in the ethanol flux of the composite membrane and an improvement in the separation factor. This simple but effective method to improve dehydration properties was very useful for fabricating PV composite membranes.

Nanofiltration has gained increasing attention in lithium extraction from salt lake brine with high Mg2+/Li+ ratio. However, conventional nanofiltration membranes with negatively charged surfaces suffer from low Mg2+/Li+ selectivity. Herein, positive nanofiltration membranes with high charge density were fabricated via a two-step charge enhancement strategy. High concentration of polyethylenimine was used as the aqueous monomer to ensure the abundant amino groups on the membrane surface. To further enhance the electro-positivity, 2, 3-epoxypropyl trimethyl ammonium chloride was grafted through ring-opening reactions. The as-obtained membranes demonstrated positive zeta potentials over a large pH range (3-10), leading to significantly strengthened Donnan exclusion for Mg2+. The membrane rejection to MgCl2 was up to 99.3% while the rejection to LiCl was only -30%. The Mg2+/Li + separation factor was 167 when filtration simulated brine with a Mg2+/Li+ ratio of 20 (2000 ppm MgCl2 and LiCl mixture), which is the highest value achieved among polyamide-based nanofiltration membranes. In addition, the membranes exhibited good stability in 40 h' continuous testing. The modification strategy proposed in the present work is highly compatible with current industrial membrane preparation processes and easy to scale up with cost effectiveness.

It is highly desired to improve the safety and stability of ultrafiltration (UF) membranes for biotechnology, medicine and food processing by eliminating the use of chemical additives during the membrane preparation process. In this work, a series of high-performance polyacrylonitrile (PAN) UF membranes were prepared continuously by the atomization-assisted nonsolvent induced phase separation (AA-NIPS) method. The pore structure and surface properties of the membranes can be precisely tailored, requiring no chemical additives. The prepared UF membranes are composed of a sublayer of highly interconnected three-dimensional (3D) network structure and a smooth surface layer of uniform small pore structure with a narrow pore size distribution. Compared to UF membranes prepared by the NIPS method, the PAN UF membranes exhibit enhanced water flux and antifouling properties as well as a well-preserved high rejection to bovine serum albumin (BSA). With different atomization pretreatment times, the pure water fluxes of the UF membranes increased by 41 %similar to 100 %. The AA-NIPS method employed in the present work can effectively modify the porous structure of the membranes without introducing pore-forming additives. The good separation performance, structural controllability, and easy functionalization of the UF membranes make them a promising candidate to be applied in many fields, especially in biotechnology, medicine, and food processing.