Crosslinked polybenzimidazole membranes for organic solvent nanofiltration (OSN): Analysis of crosslinking reaction mechanism and effects of reaction parameters

Influence of Feed Composition on the Separation Factor during Nanofiltration of Organic Acids

In this study, nanofiltration experiments using synthetic solutions containing acetate, butyrate, and lactate are carried out to assess the impact of the feed composition, i.e., feed concentration and feed proportions, on the separation factor of couples of solutes in binary and ternary solutions. In binary solutions, no influence of the solute proportions in the feed was pointed out, whatever the couple of solutes. The separation factor of acetate/butyrate and acetate/lactate was found to decrease with increasing feed concentration, while that of lactate/butyrate remained constant. The separation factors of acetate/lactate and lactate/butyrate were identical in ternary solutions compared to binary ones, showing no impact of the addition of the third solute. In ternary solutions, the presence of lactate decreased the separation factor of acetate/butyrate, but this decrease was not influenced by the proportion of lactate.

Organic Solvent Nanofiltration in Pharmaceutical Applications

Separation and purification in organic solvents are indispensable procedures in pharmaceutical manufacturing. However, they still heavily rely on the conventional separation technologies of distillation and chromatography, resulting in high energy and massive solvent consumption. As an alternative, organic solvent nanofiltration (OSN) offers the benefits of low energy consumption, low solid waste generation, and easy scale-up and incorporation into continuous processes. Thus, there is a growing interest in employing membrane technology in the pharmaceutical area to improve process sustainability and energy efficiency. This Review comprehensively summarizes the recent progress (especially the last 10 years) of organic solvent nanofiltration and its applications in the pharmaceutical industry, including the concentration and purification of active pharmaceutical ingredients, homogeneous catalyst recovery, solvent exchange and recovery, and OSN-assisted peptide/oligonucleotide synthesis. Furthermore, the challenges and future perspectives of membrane technology in pharmaceutical applications are discussed in detail.

Whether membranes developed for organic solvent nanofiltration (OSN) tend to be hydrophilic or hydrophobic? ── a review

In the past few decades, organic solvent nanofiltration (OSN) has attracted numerous researchers and broadly applied in various fields. Unlike conventional nanofiltration, OSN always faced a broad spectrum of solvents including polar solvents and non-polar solvents. Among those recently developed OSN membranes in lab-scale or widely used commercial membranes, researchers preferred to explore intrinsic materials or introduce nanomaterials into membranes to fabricate OSN membranes. However, the hydrophilicity of the membrane surface towards filtration performance was often ignored, which was the key factor in conventional aqueous nanofiltration. The influence of surface hydrophilicity on OSN performance was not studied systematically and thoroughly. Generally speaking, the hydrophilic OSN membranes performed well in the polar solvents while the hydrophobic OSN membranes work well in the non-polar solvent. Many review papers reviewed the basics, problems of the membranes, up-to-date studies, and applications at various levels. In this review, we have focused on the relationship between the surface hydrophilicity of OSN membranes and OSN performances. The history, theory, and mechanism of the OSN process were first recapped, followed by summarizing representative OSN research classified by surface hydrophilicity and types of membrane, which recent OSN research with its contact angles and filtration performance were listed. Finally, from the industrialization perspective, the application progress of hydrophilic and hydrophobic OSN membranes was introduced. We started with history and theory, presented many research and application cases of hydrophilic and hydrophobic OSN membranes, and discussed anticipated progress in the OSN field. Also, we pointed out some future research directions on the hydrophilicity of OSN membranes to deeply develop the effect made by membrane hydrophilicity on OSN performance for future considerations and stepping forward of the OSN industry.

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.

Improving the Separation Properties of Polybenzimidazole Membranes by Adding Acetonitrile for Organic Solvent Nanofiltration

In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries.

Novel Organic Solvent Nanofiltration Approaches for Microbial Biosurfactants Downstream Processing

Glycolipid biosurfactants are the most prominent group of microbial biosurfactants, comprising rhamnolipids, sophorolipids and mannosylerythritol lipids (MELs). Usually, large amounts of hydrophobic substrates (e.g., vegetable oils) are used to achieve high titers (~200 g/L) of a crude product of low purity at values limited to 50-60%, contaminated with unconsumed triacylglycerol and residual free fatty acids and monoacylglycerides. The methods reported for the removal of these contaminants use a mixture of organic solvents, compromising solvent recyclability and increasing final process costs. This study reports, for the first time, an innovative downstream method for MELs, in which 90% of the triacylglycerols are separated from the crude MEL mixture in a first stage and the other lipid derivatives (free fatty acids, mono- and diacylglycerols) are removed by organic solvent nanofiltration (OSN). Three commercially available membranes (GMT-oNF-2, PuraMEm-600 and DuramMem-500) and several homemade membranes, casted from 22, 24 or 26% (w/v) polybenzimidazole (PBI) solutions, were assessed for crude MELs purification by diafiltration. A final purity of 87-90% in the MELs was obtained by filtering two diavolumes of methanol or ethyl acetate solutions through a PBI 26% membrane, resulting in MELs losses of 14.7 ± 6.1% and 15.3 ± 2.2%, respectively. Higher biosurfactant purities can be archived using the PBI 26% membrane at higher DV, but at the cost of higher product losses. Namely, in MeOH, the use of 6 DV leads to losses of 32% for MELs and 18% for sophorolipids. To obtain MELs at reagent grade with purities equal or higher than 97%, a two-sequential cascade filtration approach was implemented using the commercial membrane, GMT-oNF. In such a process, MELs with 98% purity was obtained at the cost of 11.6% MELs losses. Finally, decoloration, important in some applications, was successfully assessed using activated carbon. Overall, this study reports a unique solution for microbial biosurfactants production with minimal product losses, enabling solvent recycling and potentially reducing costs.

Effect of Cross-Linking and Surface Treatment on the Functional Properties of Electrospun Polybenzimidazole Separators for Lithium Metal Batteries

In this work, electrospun PBI separators with a highly porous structure and nanofiber diameter of about 90-150 nm are prepared using a multi-nozzle under controlled conditions for lithium metal batteries. Cross-linking with α, α-dibromo-p-xylene and surface treatment using 4-(chloromethyl) benzoic acid successfully improve the electrochemical as well as mechanical properties of the separators. The resulting separator is endowed with high thermal stability and excellent wettability (1080 to 1150%) with commercial liquid electrolyte than PE and PP (Celgard 2400) separators. Besides, attractive cycling stability and rate capability in LiFePO₄/Li cells are attained with the modified separators. Prominently, CROSSLINK PBI exhibits a stable Coulombic efficiency of more than 99% over 100 charge-discharge cycles at 0.5 C, which is superior to the value of cells using commercial PE and PP (Celgard 2400) separators. The half cells assembled using the CROSSLINK PBI separator can deliver a discharge capacity of 150.3 mAh g^-1 at 0.2 C after 50 cycles corresponding to 88.4% of the theoretical value of LiFePO₄ (170 mAh g^-1). This work offers a worthwhile method to produce thermally stable separators with noteworthy electrochemical performances which opens new possibilities to improve the safe operation of batteries.

Hydroxypropyl-β-cyclodextrin-incorporated Pebax composite membrane for improved permselectivity in organic solvent nanofiltration

Thanks to the characteristic hollow cavity structure and sustainable and nontoxic macrocycle molecule feature, cyclodextrins have been used as building block to fabricate organic solvent nanofiltration (OSN) membranes with enhanced permeability and selectivity. Herein, hydroxypropyl-β-cyclodextrin (HP-β-CD) was incorporated into a poly(ether-block-amide) (Pebax) layer on a polysulfone support, followed by crosslinking with toluene 2,4-diisocyanate to prepare a crosslinked HP-β-CD/Pebax (CHP) membrane. By adjusting the initial HP-β-CD concentration (x) and crosslinking reaction time (y), the microporous structure and surface morphology of CHP x-y (x = 0, 0.25, 0.5, 0.75; y = 5, 10, 15) membranes could be manipulated. The OSN performances of the CHP x-y membranes were evaluated by the removal of dyes in methanol solution. The results revealed that the optimal CHP0.5-10 membrane exhibited a high methanol permeance of 8.7 L m-2 h-1 bar-1, high dye rejection (>96%), and high running stability (at least 336 h), due to the intrinsically microporous structure and surface morphology. This work would inspire the further development of cyclodextrins and other macrocyclic molecules in the preparation of OSN membranes and provide a promising strategy to fabricate state-of-the-art membranes for the efficient separation of organic solvent reclamation and removal of organic pollutants.

Effect of Additives during Interfacial Polymerization Reaction for Fabrication of Organic Solvent Nanofiltration (OSN) Membranes

Thin film composite (TFC) membranes is the dominant type of desalination in the field of membrane technology. Most of the TFC membranes are fabricated via interfacial polymerization (IP) technique. The ingenious chemistry of reacting acyl chlorides with diamines at the interface between two immiscible phases was first suggested by Cadotte back in the 1980s, and is still the main chemistry employed now. Researchers have made incremental improvements by incorporating various organic and inorganic additives. However, most of the TFC membrane literature are focused on improving the water desalination performance. Recently, the application spectrum of membrane technology has been expanding from the aqueous environment to harsh solvent environments, now commonly known as Organic Solvent Nanofiltration (OSN) technology. In this work, some of the main additives widely used in the desalination TFC membranes were applied to OSN TFC membranes. It was found that tributyl phosphate (TBP) can improve the solubility of diamine monomer in the organic phase, and sodium dodecyl sulfate (SDS) surfactant can effectively stabilize the IP reaction interface. Employing both TBP and SDS exhibited synergistic effect that improved the membrane permeance and rejection in solvent environments.

Liquid Phase Peptide Synthesis via One-Pot Nanostar Sieving (PEPSTAR)

Herein, a one‐pot liquid phase peptide synthesis featuring iterative addition of amino acids to a “nanostar” support, with organic solvent nanofiltration (OSN) for isolation of the growing peptide after each synthesis cycle is reported. A cycle consists of coupling, Fmoc removal, then sieving out of the reaction by‐products via nanofiltration in a reactor‐separator, or synthesizer apparatus where no phase or material transfers are required between cycles. The three‐armed and monodisperse nanostar facilitates both efficient nanofiltration and real‐time reaction monitoring of each process cycle. This enabled the synthesis of peptides more efficiently while retaining the full benefits of liquid phase synthesis. PEPSTAR was validated initially with the synthesis of enkephalin‐like model penta‐ and decapeptides, then octreotate amide and finally octreotate. The crude purities compared favorably to vendor produced samples from solid phase synthesis.

Thin-Film Composite Nanofiltration Membranes for Non-Polar Solvents

Organic solvent nanofiltration (OSN) has been recognized as an eco-friendly separation system owing to its excellent cost and energy saving efficiency, easy scale-up in the narrow area and mild operation conditions. Membrane properties are the key part in terms of determining the separation efficiency in the OSN system. In this review paper, the recently reported OSN thin-film composite (TFC) membranes were investigated to understand insight of membrane materials and performance. Especially, we highlighted the representative study concepts and materials of the selective layer of OSN TFC membranes for non-polar solvents. The proper choice of monomers and additives for the selective layer forms much more interconnected voids and the enhanced microporosity, which can improve membrane performance of the OSN TFC membrane with reducing the transport resistance. Therefore, this review paper could be an important bridge to connect with the next-generation OSN TFC membranes for non-polar solvents.

Phase Inversion-Induced Porous Polybenzimidazole Fuel Cell Membranes: An Efficient Architecture for High-Temperature Water-Free Proton Transport

To cope with the demand for cleaner alternative energy, polymer electrolyte membrane fuel cells (PEMFCs) have received significant research attention owing to their high-power density, high fuel efficiency, and low polluting by-product. However, the water requirement of these cells has necessitated research on systems that do not require water and/or use other mediums with higher boiling points. In this work, a highly porous meta-polybenzimidazole (m-PBI) membrane was fabricated through the non-solvent induced phase inversion technique and thermal cross-linking for high-temperature PEMFC (HT-PEMFC) applications. Standard non-thermally treated porous membranes are susceptible to phosphoric acid (PA) even at low concentrations and are unsuitable as polymer electrolyte membranes (PEMs). With the porous structure of m-PBI membranes, higher PA uptake and minimal swelling, which is controlled via cross-linking, was achieved. In addition, the membranes exhibited partial asymmetrical morphology and are directly applicable to fuel cell systems without any further modifications. Membranes with insufficient cross-linking resulted in an unstable performance in HT-PEMFC environments. By optimizing thermal treatment, a high-performance membrane with limited swelling and improved proton conductivity was achieved. Finally, the m-PBI membrane exhibited enhanced acid retention, proton conductivity, and fuel cell performance.

Bio-Inspired Robust Membranes Nanoengineered from Interpenetrating Polymer Networks of Polybenzimidazole/Polydopamine

Marine mussel inspired polydopamine (PDA) has received increased attention due to its good thermal and chemical stability as well as strong adhesion on most materials. In this work, high-performance nanofiltration membranes based on interpenetrating polymer networks (IPN) incorporating PDA and polybenzimidazole (PBI) were developed for organic solvent nanofiltration (OSN). Generally, in order to obtain solvent stability, polymers need to be covalently cross-linked under harsh conditions, which inevitably leads to losses in permeability and mechanical flexibility. Surprisingly, by in situ polymerization of dopamine within a PBI support, excellent solvent resistance and permeance of polar aprotic solvents were obtained without covalent cross-linking of the PBI backbone due to the formation of an IPN. The molecular weight cutoff and permeance of the membranes can be fine-tuned by changing the polymerization time. Robust membrane performance was achieved in conventional and emerging green polar aprotic solvents (PAS) in a wide temperature range covering -10 °C to +100 °C. It was successfully demonstrated that the in situ polymerization of PDA-creating an IPN-can provide a simple and green alternative to covalent cross-linking of membranes. To elucidate the nature of the solvent stability, a detailed analysis was performed that revealed that physical entanglement along with strong secondary interaction synergistically enable solvent resistance with as low as 1-3% PDA content.

Zeolitic Imidazolate Framework Membranes for Light Olefin/Paraffin Separation

Propylene/propane and ethylene/ethane separations are performed by energy-intensive distillation processes, and membrane separation may provide substantial energy and capital cost savings. Zeolitic imidazolate frameworks (ZIFs) have emerged as promising membrane materials for olefin/paraffin separation due to their tunable pore size and chemistry property, and excellent chemical and thermal stability. In this review, we summarize the recent advances on ZIF membranes for propylene/propane and ethylene/ethane separations. Membrane fabrication methods such as in situ crystallization, seeded growth, counter-diffusion synthesis, interfacial microfluidic processing, vapor-phase and current-driven synthesis are presented. The gas permeation and separation characteristics and membrane stability are also discussed.

High-Throughput Microfiltration Membranes with Natural Biofouling Reducer Agent for Food Processing

The effect of natural antibiotics Moringa oleifera seeds powder in cellulose acetate membranes as biofouling reducer agent was investigated. Mixed matrix membranes (MMM) were synthesized by adding 100 mesh M. oleifera seeds powder with variation of three concentrations (1 wt%, 2 wt%, and 3 wt%), into a mix polymer solution of CA (cellulose acetate) and two different solvents, i.e., DMF (dimethylformamide) and DMAc (dimethylacetamide). The synthesized membranes morphology was observed under scanning electron microscopy and from the images can be seen that the membranes made of DMAc formed rather large macrovoid as compared to DMF-based membranes. The microstructure affected the water flux through the membranes, in which the DMAc membranes provided a higher flux value and served as high-throughput microfiltration membranes. Antibacterial properties of MMM were tested using Escherichia coli adhesion onto membrane surfaces. The results showed that M. oleifera has been proven to eradicate E. coli activity on the membrane surfaces due to interaction between bacterial cells and phenolic compounds from M. oleifera, through absorption processes involving hydrogen bonds.

An Amphiphilic, Graphitic Buckypaper Capturing Enzyme Biomolecules from Water

The development of carbon nanomaterials for adsorption based removal of organic pollutants from water is a progressive research subject. In this regard, carbon nanomaterials with bifunctionality towards polar and non-polar or even amphiphilic undesired materials are indeed attractive for further study and implementation. Here, we created carbon buckypaper adsorbents comprising amphiphilic (oxygenated amorphous carbon (a-COx)/graphite (G)) nanofilaments that can dynamically adsorb organic biomolecules (i.e., urease enzyme) and thus purify the wastewaters of relevant industries. Given the dynamic conditions of the test, the adsorbent was highly efficient in adsorption of the enzyme (88%) while being permeable to water (4750 L·h−1m−2bar−1); thus, it holds great promise for further development and upscaling. A subsequent citric acid functionalization declined selectivity of the membrane to urease, implying that the biomolecules adsorb mostly via graphitic domains rather than oxidized, polar amorphous carbon ones.

Polyethylene Battery Separator as a Porous Support for Thin Film Composite Organic Solvent Nanofiltration Membranes

Organic solvent nanofiltration (OSN) has made significant advances recently, and it is now possible to fabricate thin film composite (TFC) membranes with a selective layer thickness below 10 nm that gives ultrafast solvent permeance. However, such high permeance is inadvertently limited by the support membrane beneath the selective layer, and thus there is an urgent need to develop a suitable support to maximize TFC performance. In this work, we employed a commercially available polyethylene (PE) battery separator as a porous support to fabricate high performance TFC OSN membranes. To deposit a uniform polyamide selective layer onto the porous support via interfacial polymerization, the PE support was hydrophilized with O₂ plasma and the reaction efficiency was optimized using a surfactant. Owing to the high surface porosity of the PE support and the high permselectivity of the PA layer, the PE-supported TFC membrane outperformed the previously reported OSN membranes and its performance exceeded the current performance upper bound. A solvent activation step dramatically improved the solvent permeance by 5-fold while maintaining nanoseparation properties. In addition to the superior OSN performance, the commercial availability of the PE support and simplified TFC fabrication protocol would make the PE-supported OSN membranes commercially attractive.

Do Wet-Dry Ratio and Fe-Mn System Affect Oxidation-Reduction Potential Nonlinearly in the Subsurface Wastewater Infiltration Systems?

To understand characteristics of on-line oxidation-reduction potential (ORP) in a subsurface wastewater infiltration system (SWIS) under different intermittent influent conditions, ORP among five matrix depths at wet-dry ratios (R_wds) of 2:1, 1:1 and 1:2 with a hydraulic load of 0.10 m³·(m²·d)^-1 were monitored. Results showed that the optimal R_wd for the SWIS was 1:1. In that case, ORP at 40 and 65 cm depths changed significantly, by 529 mV and 261 mV, respectively, from the inflow period to the dry period, which was conducive to the recovery of the oxidation environment. It was concluded that ORP varied nonlinearly in strongly aerobic and hypoxic environment. Wastewater was fed into the SWIS at 80 cm and dissolved oxygen diffused at the initial period of one cycle. As a consequence, ORP at 65 cm increased with water content increasing. However, ORP at 40 and 95 cm displayed inverse trends. Moreover, results showed that ORP decreased with Fe²⁺ and Mn²⁺ increasing under aerobic conditions (p < 0.05) because Fe²⁺ and Mn²⁺ moved with wastewater flow. Effluent met reuse requirements and no clogging was found in the SWIS during the operation.

A New Method for the Process Division and Effect Evaluation of Coagulation Based on Particle Size Fractal Dimension

To divide, control, and predict the effects of the coagulation process in water treatment, a characteristic analysis of the change in particle size distribution (particle number and fractal dimension) during aided coagulation with hydrated MnO2 was performed. The results showed that the process of coagulation could be divided into three characteristic stages based on the first derivative of the particle size fractal dimension. In the primary stage, most of the microflocs aggregated to form small flocs; in the growth stage, most of the small flocs aggregated to form large flocs; and in the stable stage, some large flocs broke apart and reformed. The first derivative of the particle size fractal dimension had a good linear relationship with the coagulation time in the primary stage and growth stage, and its slope had a power function relationship with the particle number in settled water; the first derivative could thus be used to evaluate the coagulation effect. In the stable stage, the rate of change in particle size fractal dimension fluctuated along the fitted line, and the mean residual sum of squares had a linear relation with the particle number in settled water; therefore, this parameter could be used as an indicator of the coagulation effect.

Optimal Design of a Two-Stage Membrane System for Hydrogen Separation in Refining Processes

This paper fits into the process system engineering field by addressing the optimization of a two-stage membrane system for H2 separation in refinery processes. To this end, a nonlinear mathematical programming (NLP) model is developed to simultaneously optimize the size of each membrane stage (membrane area, heat transfer area, and installed power for compressors and vacuum pumps) and operating conditions (flow rates, pressures, temperatures, and compositions) to achieve desired target levels of H2 product purity and H2 recovery at a minimum total annual cost. Optimal configuration and process design are obtained from a model which embeds different operating modes and process configurations. For instance, the following candidate ways to create the driving force across the membrane are embedded: (a) compression of both feed and/or permeate streams, or (b) vacuum application in permeate streams, or (c) a combination of (a) and (b). In addition, the potential selection of an expansion turbine to recover energy from the retentate stream (energy recovery system) is also embedded. For a H2 product purity of 0.90 and H2 recovery of 90%, a minimum total annual cost of 1.764 M$·year−1 was obtained for treating 100 kmol·h−1 with 0.18, 0.16, 0.62, and 0.04 mole fraction of H2, CO, N2, CO2, respectively. The optimal solution selected a combination of compression and vacuum to create the driving force and removed the expansion turbine. Afterwards, this optimal solution was compared in terms of costs, process-unit sizes, and operating conditions to the following two sub-optimal solutions: (i) no vacuum in permeate stream is applied, and (ii) the expansion turbine is included into the process. The comparison showed that the latter (ii) has the highest total annual cost (TAC) value, which is around 7% higher than the former (i) and 24% higher than the found optimal solution. Finally, a sensitivity analysis to investigate the influence of the desired H2 product purity and H2 recovery is presented. Opposite cost-based trade-offs between total membrane area and total electric power were observed with the variations of these two model parameters. This paper contributes a valuable decision-support tool in the process system engineering field for designing, simulating, and optimizing membrane-based systems for H2 separation in a particular industrial case; and the presented optimization results provide useful guidelines to assist in selecting the optimal configuration and operating mode.

Advances in Organic Solvent Nanofiltration Rely on Physical Chemistry and Polymer Chemistry

The vast majority of industrial chemical synthesis occurs in organic solution. Solute concentration and solvent recovery consume ~50% of the energy required to produce chemicals and pose problems that are as relevant as the synthesis process itself. Separation and purification processes often involve a phase change and, as such, they are highly energy-intensive. However, novel, energy-efficient technologies based on polymer membranes are emerging as a viable alternative to thermal processes. Despite organic solvent nanofiltration (OSN) could revolutionize the chemical, petrochemical, food and pharmaceutical industry, its development is still in its infancy for two reasons: (i) the lack of fundamental knowledge of elemental transport phenomena in OSN membranes, and (ii) the instability of traditional polymer materials in chemically challenging environments. While the latter issue has been partially solved, the former was not addressed at all. Moreover, the few data available about solute and solvent transport in OSN membranes are often interpreted using inappropriate theoretical tools, which contributes to the spread of misleading conclusions in the literature. In this review we provide the state of the art of organic solvent nanofiltration using polymeric membranes. First, theoretical models useful to interpret experimental data are discussed and some misleading conclusions commonly reported in the literature are highlighted. Then, currently available materials are reviewed. Finally, materials that could revolutionize OSN in the future are identified. Among the possible applications of OSN, isomers separation could open a new era in chemical engineering and polymer science in the years to come.

Polysulfone/Polyamide-SiO₂ Composite Membrane with High Permeance for Organic Solvent Nanofiltration

To improve the filtration performance and properties of organic solvent nanofiltration (OSN) membranes, we firstly introduce nanoporous silica (SiO₂) particles into the polyamide (PA) active layer of polysulfone (PSf) membrane via an interfacial polymerization process. Results from the study revealed that introduction of SiO₂ influenced the properties of PSf/PA-SiO₂ composite membranes by changing the surface roughness and hydrophilicity. Moreover, results also indicated that nanoporous SiO₂ modified membranes showed an improved performance of alcohols solvent permeance. The PSf/PA-SiO₂ composite membrane modified by 0.025 wt % of SiO₂ reached a permeance of 3.29 L m⁻² h⁻¹ bar⁻¹ for methanol and 0.42 L m⁻² h⁻¹ bar⁻¹ for ethanol, which were 20.0% and 13.5% higher than the control PSf membrane (permeance of 2.74 L m⁻² h⁻¹ bar⁻¹ for methanol and 0.37 L m⁻² h⁻¹ bar⁻¹ for ethanol). Conclusively, we demonstrated that the increase of membrane hydrophilicity and roughness were major factors contributing to the improved alcohols solvent permeance of the membranes.