Organic Solvent Nanofiltration Membranes Research Articles

Flat Sheet Polybenzimidazole Membranes for Fuel Cell, Gas Separation and Organic Solvent Nanofiltration: A Review

Flat Sheet Polybenzimidazole Membranes for Fuel Cell, Gas Separation and Organic Solvent Nanofiltration: A Review

Influence of in situ silica gel supporting on the pore structure stability of polyacrylonitrile-based thermally crosslinked organic solvent nanofiltration membrane

Influence of in situ silica gel supporting on the pore structure stability of polyacrylonitrile-based thermally crosslinked organic solvent nanofiltration membrane

Ultrahigh-permeance polyamide thin-film composite membranes enabled by interfacial polymerization on a macro-porous substrate toward organic solvent nanofiltration

Organic solvent nanofiltration (OSN) membranes have become a powerful separation platform in a myriad of chemical and pharmaceutical fields owing to their superior merits in high separation efficiency and low energy consuming. Despite extensive progress in exploiting polyamide thin film composite (TFC) membranes for OSN, they are heavily limited by inferior solvent permeability, especially when using conventional low-porous polyimide as TFC substrate. Herein, we report a facile substrate engineering strategy to leverage macro-porous Nylon66 microfiltration membrane to replace the conventional low-porous polyimide substrates for fabricating TFC membranes by interfacial polymerization, enabling high and robust solvent permeability during OSN. Distinct from conventional polyimide, Nylon66 substrates take advantage of their high porosity, macro-porous size and excellent hydrophilicity to realize more monomers storage and uniform monomers distribution, allowing to create crumpled and defect-free polyamide layers. With this method, the polyamide TFC membranes show a 2.1-fold increase in ethanol permeance (up to 16.0 L h−1 m−2 bar−1) meanwhile possessing 98 % rejection of dye, surpassing the most reported TFC membranes. We also demonstrate that the TFC membranes exhibit excellent long-term stability in both polar and non-polar solvent, as well as hold huge promise in the precise separation of dye mixture, pharmaceutical ingredient, and catalyst.

A new class of “structure-by-design” polymer membranes for organic solvent nanofiltration with controllable selectivity

Membrane based separations offer an inexpensive and energy efficient pathway to purification. However, their use is often stifled during separation of organics due to low selectivity. This can be attributed to the inherent limitations of the synthesis methods employed, namely, interfacial polymerization and phase inversion. In this work, a new class of structure-by-design membranes are synthesized by surface modification of crosslinked polyimide using graft polymerization with a series of methacrylate monomers with differing chain lengths and chemistries. Graft polymerization of long chain monomers resulted in increased selectivity (α∼3.7 for 80-20 mol.% MeOH-toluene and α∼6 for 95-5 mol.% toluene-triisopropyl benzene (TIPB) for both test solutions) as a result of increased stiffness and order (using GIWAXS)). The observed selectivities renders these membranes competitive for organic solvent nanofiltration applications. In addition, pure solvent permeabilities were measured. The performance of these membranes was correlated with brush properties such as degree of grafting (using ATR-FTIR), surface polarity (contact angle measurements), stiffness (using QCM-D) and brush configuration in different solvent environments (using MD Simulations). MD simulations demonstrate that in mixtures containing hydrophobic species, polymers with longer hydrophobic side chains well more and form fuller matrices leading to increased solvent accessible surface area. GIWAXS results showed increased order with longer side chain length. These tunable membranes offer promise for organics separation.

Fabrication of phenolic resin membrane with polyvinyl alcohol fiber skeleton by electrospinning for organic solvent nanofiltration

As an emerging separation technology, organic solvent nanofiltration (OSN) has shown great potential in the chemical, food, and pharmaceutical industries. Considering the excellent solvent resistance of phenolic resin (PR), it has great potential to be employed for the fabrication of OSN membrane. However, the extremely low permeance due to the highly cross-linked network and limited fabrication strategies still hold back the further application of PR. Herein, we develop a novel method to fabricate PR membrane with polyvinyl alcohol (PVA) fiber skeleton for OSN. This is accomplished through the electrospinning of PVA-resol solution, followed by heating to initiate the cross-linking of resol to form PR. After the further reaction with glutaraldehyde (GA), the PR OSN membrane is finally acquired. Benefiting from the homogeneous mixing of PVA with resol in the electrospinning solution, the formed PVA fibers are uniformly embedded in the PR matrix. The space between PVA fiber skeleton with PR matrix could provide additional channels for the transportation of solvent molecules. Compared with those membranes fabricated by traditional casting methods, the permeance of PR/PVA/GA reported here is significantly improved. The molecular weight cut-off (MWCO) of PR/PVA/GA is about 803 Da based on the rejection curve. Meanwhile, the permeance of acetonitrile about 1.3 Lm-2h-1bar−1 is the highest among the studied solvents, while the values are very low for nonpolar solvents, such as hexane and toluene. Additionally, the obtained membrane exhibits excellent anti-compaction ability and long-term stability. As an alternative to phase inversion and interfacial polymerization, the strategy reported here may provide a new way for the assembly of polymers into nanofiltration membranes for diverse separation applications.

Interfacial polymerization using biobased solvents and their application as desalination and organic solvent nanofiltration membranes

Thin-film composite membranes are widely regarded as more sustainable technologies for desalination and organic solvent nanofiltration. However, the process of fabricating these membranes is not. This is because n-hexane, a toxic and hazardous solvent, or other fossil-derived oily solvents are used as the organic phase to fabricate polyamide selective layers of such membranes. Here we replaced fossil-derived solvents with benign, bio-renewable solvents that possess better environmental, health and safety metrics – cyclopentyl methyl ether (CPME) and 2-methyltetrahydrofuran (2-MeTHF). A fully aromatic polyamide thin film composite (TFC) membrane fabricated via CPME demonstrated a higher NaCl rejection (97.8%), while the same membrane fabricated using n-hexane only presented 92.4% rejection. Meanwhile a semi-aromatic polyamide TFC membrane fabricated with 2-MeTHF showed an ethanol permeance of 9.87 L m−2 h−1 bar−1 and 97.1% RB rejection, 3.7-fold higher than the TFC fabricated using n-hexane. This demonstrated the feasibility and advantages of replacing toxic and hazardous solvents that have long been the standard solvents used in membrane fabrication, with benign alternatives. This work could potentially improve the sustainability of membrane fabrication.

Preparation and performance of thin film composite solvent nanofiltration membrane based on fluorinated diamine monomers

The high perm-selectivity and long-term solvent resistance of organic solvent nanofiltration (OSN) membranes in various solvents pose significant challenges for their development. In this study, ultra-low content mixture of fluorinated diamine (5-trifluoromethyl-1,3-phenylenediamine or 4-trifluoromethyl-1,2-phenylenediamine) and m-phenylenediamine (MPD) as aqueous phase monomers and ultra-low content trimesoyl chloride (TMC) in n-hexane as organic phase monomer were used to perform interfacial polymerization (IP), then followed by crosslinking and solvent activation. By this way, two kinds of ultra-thin and ultra-smooth fluorinated polyamide OSN membranes were achieved. Under optimized conditions, these two kinds of OSN membranes, TFC-5F2,II and TFC-4F1,II, have surface roughness of 2.5 and 3.0 nm, respectively. They show ethanol permeance of 73.9 and 60.9 L m−2 h−1 MPa−1, and RDB rejection of 98.5% and 99.2%, respectively, using 100 mg L−1 rhodamine B / ethanol solution as feed. They show ethyl acetate permeance of 209.4 and 117.0 L m−2 h−1 MPa−1, respectively, and catalyst rejection of 98.2% and 98.8%, respectively, using 50 mg L−1 Jacobsen catalyst/ethyl acetate solution as feed. Meanwhile, they have pure n-hexane permeance of 32.5 and 36.8 L m−2 h−1 MPa−1, respectively. Moreover, they show excellent stability in highly polar solvents, thus have good application prospects in the separation and purification of various organic solvent systems.

Constructing a tannic-Fe interlayer via a simple in-situ method to enhance the filtration performance of hollow fiber organic solvent nanofiltration membranes

Hollow fiber (HF) organic solvent nanofiltration (OSN) membranes have the advantage of simple production and large packing density, which make them promising for organic solvent recovery. However, current HF OSN membranes still suffer from poor separation performance. To overcome this problem, in this work, we proposed a simple method to in-situ construct a tannic (TA)-Fe interlayer on the surface of an HF ultrafiltration membrane. In this way, we could effectively manipulate the interfacial polymerization (IP) reaction between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), thus successfully boosting the filtration performance of the polyamide (PA) HF OSN membrane. We highlight that TA molecules were enriched on the surface of the HF ultrafiltration membrane during the phase inversion process, which is beneficial for the in-situ construction of a TA-Fe interlayer via immersing this HF substrate in FeCl3 solution. Consequently, we effectively simplified the fabrication procedure for constructing an interlayer. With the aid of the TA-Fe interlayer, the HF OSN membrane obtained higher crosslinking degree and better filtration performance. The optimized HF OSN membrane achieves an ethanol permeance of 14.7 L m−2 h−1 MPa−1 and a Rhodamine B (RDB, 479 Da) rejection of 98.6 %. Additionally, it displays excellent operation stability performance. It remains an ethanol permeance of 8.6 L m−2 h−1 MPa−1 and an RDB rejection of 99.4 % after a continuous cross-flow filtration for over 1000 min. Also, it shows excellent chemical stability performance, corresponding to an extension of less than 4 % after soaking in ethanol for 8 d. This research shows a simple approach for the fabrication of interlayered thin film composite (iTFC) HF OSN membranes.

Novel amino-beta cyclodextrin-based organic solvent nanofiltration membranes with fast and stable solvent transport

To expand industrial utilizations, membranes with fast transport of organic solvents and precision molecular separation, along with strong chemical stability, have great potential for minimizing energy consumption in separation processes. In this study, novel amino-cyclodextrin organic solvent nanofiltration (OSN) membranes containing P84 polymer were successfully fabricated using amino-cyclodextrin and amino-5-guanidinopentanoic acid (DL-A) as monomers through a two-step green modification process. The resulting membranes exhibit high stability in harsh organic solvents, such as dimethylsulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP), with a weight loss of less than 5 % after 30 days of immersion. These membranes also demonstrate rapid solvent transport for both polar solvents, such as methanol (86.56 L m−2 h−1 bar−1), and nonpolar solvents, such as n-hexane (48.97 L m−2 h−1 bar−1), along with high dye rejections. Additionally, the membranes possess rigid nanopores structures and consistent rejections across different pressures and solute concentrations. Most importantly, the newly synthesized amino-cyclodextrin OSN membranes are capable of separating molecules based on their 3D structures, particularly those with relatively similar molecular weights. Comparing to those reported cyclodextrin-based membranes, the newly developed amino-cyclodextrin OSN membranes show significant improvements in permeance for both polar and nonpolar organic solvents, while maintaining comparable dye rejection capabilities. The combination of fast solvent transport, excellent chemical stability, and shape selectivity makes these membranes highly promising for high-performance molecular separation in various industrial applications.

Effect of polymer molecular weight on the long-term process stability of crosslinked polybenzimidazole organic solvent nanofiltration (OSN) membranes

The importance of polymer molecular weight on the long-term performance of polybenzimidazole (PBI) membranes in organic solvents was investigated. PBI membranes were manufactured from two different polymer molecular weights: the standard molecular weight of PBI polymer, used almost universally across literature for organic solvent stable membranes (∼27,000 g mol-1), and an untested ∼ two-fold higher molecular weight (∼60,000 g mol-1). After crosslinking, all PBI membranes were chemically and mechanically stable. However, during continuous long-term pressurised filtration in DMF, the standard molecular weight PBI membranes suffered slow permeance decline over time. This was attributed to rearrangement of the crosslinked polymer chains. Increasing the extent of crosslinking reduced the rate of membrane permeance decline but did not provide a fully process stable membrane. Using a higher molecular weight PBI, and a similar extent of crosslinking, resulted in a membrane with constant permeance and excellent process stability, even during continuous DMF filtration at 120 °C. This was attributed to the increased interchain interactions and entanglement in the high molecular weight polymer, which reduced the rate of chain rearrangement and compaction. This work demonstrates the importance of polymer molecular weight for reducing membrane compaction and providing process stability in organic solvents.

Machine Learning-Assisted Design of Thin-Film Composite Membranes for Solvent Recovery.

Organic solvents are extensively utilized in industries as raw materials, reaction media, and cleaning agents. It is crucial to efficiently recover solvents for environmental protection and sustainable manufacturing. Recently, organic solvent nanofiltration (OSN) has emerged as an energy-efficient membrane technology for solvent recovery; however, current OSN membranes are largely fabricated by trial-and-error methods. In this study, for the first time, we develop a machine learning (ML) approach to design new thin-film composite membranes for solvent recovery. The monomers used in interfacial polymerization, along with membrane, solvent and solute properties, are featurized to train ML models via gradient boosting regression. The ML models demonstrate high accuracy in predicting OSN performance including solvent permeance and solute rejection. Subsequently, 167 new membranes are designed from 40 monomers and their OSN performance is predicted by the ML models for common solvents (methanol, acetone, dimethylformamide, and n-hexane). New top-performing membranes are identified with methanol permeance superior to that of existing membranes. Particularly, nitrogen-containing heterocyclic monomers are found to enhance microporosity and contribute to higher permeance. Finally, one new membrane is experimentally synthesized and tested to validate the ML predictions. Based on the chemical structures of monomers, the ML approach developed here provides a bottom-up strategy toward the rational design of new membranes for high-performance solvent recovery and many other technologically important applications.

Ultra-thin PTMSP nanocomposite membranes incorporated with functionalized MoS2 nanosheets for pharmaceutical concentration and solvent recovery

Organic solvent nanofiltration (OSN) membranes with enhanced separation performance and excellent structure stability are of great benefit in recovering organic solvent and concentrating molecules in pharmaceutical industry. In this study, we developed a smooth and ultra-thin nanocomposite membrane by incorporating sodium dodecylbenzene sulfonate (SDBS) functionalized molybdenum sulfide (MoS2) nanosheets into an ultra-thin poly-trimethylsilylpropyne (PTMSP) skin layer on polysulfone (PSf) substrate via a facile solution coating method. The two-dimensional (2D) SDBS-MoS2 with improved compatibility was employed to provide selective channels for solvent permeation while reducing defect cavities to increase solute rejection. The resulting membrane exhibited a significantly improved methanol permeance of up to 8.38 L m−2 h−1 bar−1, signifying a noteworthy 56 % increment compared to the pristine membrane. Additionally, the RB rejection increased from 95.05 % to 97.72 %. The as-prepared membrane also demonstrated favorable long-term stability and efficient molecules separation capabilities in the pharmaceutical industry. This work demonstrated that the compatibility and dispersibility of 2D MoS2 could be improved by adding SDBS, resulting in a SDBS-MoS2-PTMSP membrane with excellent OSN performance and outstanding long-term stability, making it highly promising for industrial applications.

A novel organic solvent nanofiltration membrane prepared via green mild and simple crosslinking process

Organic solvent nanofiltration (OSN) is a new type of organic fluid separation technology that can greatly reduce energy consumption compared with traditional distillation techniques. However, the development and application of OSN are restricted by the high manufacturing cost of solvent resistant membranes, including expensive materials and complex post-treatment process. In this paper, a low-cost polyaryletherketone bearing amino group synthesized from industrial raw material phenolphthalein was proposed, and then the crosslinked polyaryletherketone membrane with remarkable stability in polar aprotic solvent was prepared by green, mild and simple crosslinking method. The separation accuracy of the membrane can be easily adjusted from ultrafiltration to nanofiltration by altering the composition of the cast solution. In addition, the prepared membrane can be operated in DMF for 120 h, which indicated the excellent stability of the membrane, even for hash polar aprotic solvents. Therefore, this work demonstrates a novel low-cost solvent resistant membrane material that is promising for OSN applications.

Oriented ionic covalent organic framework membranes for efficient organic solvent nanofiltration

Developing effective organic solvent nanofiltration (OSN) membranes to separate molecular solutes from organic solvents is highly desired yet requires a suitable material platform and an in-depth investigation of membrane selectivity. Herein, an oriented ionic covalent organic framework membrane (oi-COM) was fabricated, which features well-ordered channels that are vertically aligned towards the membrane surface and lined with abundant sulfonate groups. Filtration experiments of multifarious organic solvents and solutes with different charges and molecular sizes were conducted. The oi-COM exhibited above 99% rejection for negatively charged dye (Evans blue), much higher than that for positively charged dye with similar molecular size, while maintaining high solvent permeance for ethanol of 63 L m−2 h−1 bar−1. These results demonstrated the significance of electrostatic repulsion effect in membrane selectivity, providing insights for the design of high-performance OSN membranes.

Regenerated cellulose membranes for efficient separation of organic mixtures

Organic solvent nanofiltration (OSN) is a low-carbon technology for organic mixture separation that usually relies on non-renewable fossil-derived membranes. Cellulose, a biomass material with extensive sources and superior resistance to organic solvents, holds great promise in engineering OSN membranes. Here we studied the mass transport and separation properties of regenerated cellulose membranes (RCMs), which were made from wood pulp using ionic liquid as solvent by phase inversion method. By regulating membrane thickness from 150 μm to 350 μm, the solvent permeance and solute rejection can be finely tuned. The 350-μm-thick RCM membrane (RCM-350) displays better compaction resistance than the thinner ones and harvests high solute rejection with ethanol permeance reaching ∼ 30 L m−2 h−1 bar−1, outperforming the state-of-the-art polymeric membranes and showing long-term stability during cross-flow OSN. When used for solute separation, the RCM-350 membrane provides molecular selectivity of up to 294 and 68 for Alcian blue/Rifampicin and Alcian blue/Tetracycline mixtures, respectively, which depends on the mixture composition. Our findings reveal the potential of regenerated natural cellulose as a high-performance and sustainable alternative membrane material for separating organic mixtures.

Solution-processable poly(ether-ether-ketone) membranes for organic solvent nanofiltration: from dye separation to pharmaceutical purification

Through polymer engineering, the membrane properties can be considerably changed and its performance can be improved. Organic solvent nanofiltration (OSN) membranes require polymers with good solution processability to facilitate membrane preparation. However, the resultant membranes should have excellent solvent resistance. Poly(ether-ether-ketone) (PEEK) is a potential polymer for OSN applications because of its high thermal stability and excellent solvent resistance. However, commercial PEEK has limited solution processability, and its fabrication requires a harsh acidic environment. Herein, two customized PEEKs were synthesized by incorporating methyl (–CH3) and sulfonyl (SO2) groups into the polymer backbone. The membranes were prepared by phase inversion using N-methyl-2-pyrrolidone (NMP) and TamiSolve as a green alternative. The effects of the polymer structure, green solvent, and crosslinking on the membrane morphology, chemical and mechanical stability, as well as separation performance have been examined. The molecular interaction between organic solvents and PEEKs were investigated through molecular dynamic simulations and density functional theory. The molecular weight cutoff (MWCO) values of the membranes were 540–768 g mol−1, with a high corresponding permeance of 8.2–20 L m−2 h−1 bar−1 in acetone. The long-term stability of membranes was successfully demonstrated over two weeks through a continuous crossflow filtration using acetone under a pressure of 30 bar. The membranes demonstrated excellent active pharmaceutical ingredient purification through the removal a 2-methoxyethoxymethyl chloride (125 g mol−1) carcinogenic impurity from roxithromycin (837 g mol−1).

Screening of Commercial Organic Solvent Nanofiltration Membranes for Purification of Plastic Waste Pyrolysis Liquids.

Increasing consumption rates of plastics, combined with the waste generated from their production, leads to several environmental problems. Presently, plastic recycling takes account of only about 10% of the plastic waste, which is achieved mainly through mechanical recycling. Chemical recycling methods, such as pyrolysis, could significantly increase overall recycling rates and reduce the need for the production of fossil-based chemicals. Produced pyrolysis oil can be used for the production of benzene, toluene and xylene (BTX) through catalytic upgrading or for the production of alkanes if used directly. Separation of high-value components in pyrolysis oil derived from plastic waste through traditional separation methods can be energy intensive. Organic solvent nanofiltration has been recognised as an alternative with very low energy consumption, as separation is not based on a phase transition. This work focuses on the screening of several (semi-) commercially available membranes using a simplified model mixture of pyrolysis oil obtained from plastics. Based on membrane performance, a selection of membranes was used to treat a feedstock obtained from the direct pyrolysis of plastics. This work shows that currently, commercial OSN membranes have promising separation performance on model mixtures while showing insufficient and non-selective separation at very low flux for complex mixtures derived from the pyrolysis of plastics. This indicates that OSN is indeed a promising technology but that membranes should likely be tailored to this specific application.

Carbon-doped metal oxide interfacial nanofilms for ultrafast and precise separation of molecules.

Membranes with molecular-sized, high-density nanopores, which are stable under industrially relevant conditions, are needed to decrease energy consumption for separations. Interfacial polymerization has demonstrated its potential for large-scale production of organic membranes, such as polyamide desalination membranes. We report an analogous ultrafast interfacial process to generate inorganic, nanoporous carbon-doped metal oxide (CDTO) nanofilms for precise molecular separation. For a given pore size, these nanofilms have 2 to 10 times higher pore density (assuming the same tortuosity) than reported and commercial organic solvent nanofiltration membranes, yielding ultra-high solvent permeance, even if they are thicker. Owing to exceptional mechanical, chemical, and thermal stabilities, CDTO nanofilms with designable, rigid nanopores exhibited long-term stable and efficient organic separation under harsh conditions.

Construction of highly permeable organic solvent nanofiltration membrane via β-cyclodextrin assisted interfacial polymerization

As the key of organic solvent nanofiltration (OSN) technology, OSN membranes could effectively retain small molecules with molecular weight between 200 and 1000 Dalton (Da), but they still face some problems such as low solvent permeance. In this work, we fabricated a poly(amide-ester) selective layer on polyimide substrate surface by introducing β-cyclodextrin (β-CD) into the aqueous phase solution to assist the interfacial polymerization reaction between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), followed by cross-linking and solvent activation treatment. Thus, we successfully fabricated a kind of thin film composite (TFC) membrane with high selective permeability for OSN. We emphasized that extra-low contents were employed for both MPD and β-CD, which were 0.05 wt% and 50 mg L−1, respectively. The effect of β-CD content on the pore size, surface shape, surface hydrophilicity, surface chemistry, filtration performance, as well as durability performance of the OSN membrane was studied in depth. β-CD endows the selective layer with better hydrophilicity and larger pore size. The optimized OSN membrane possesses a Rhodamine B (RDB, 479 Da) rejection of 99.2 % and an ethanol permeance of 70.6 L m−2 h−1 MPa−1. Furthermore, the optimized OSN membrane remains above 99 % RDB rejection after being immersed in DMF at 25 °C for 1000 h, which demonstrates its superb solvent resistance. Additionally, the optimized OSN membrane exhibits outstanding long-time performance and possesses a rejection of 98 % for Jacobsen catalyst during more than 106 h semi-continuous filtration using Jacobsen catalyst/ethyl acetate solution as feed, indicating its vast potential in the recovery of catalyst.

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review.

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.