Reverse Osmosis Separation Research Articles

Unveiling the pore size change in polyamide membrane using aggregation induced emission

Polyamide (PA) membranes play a crucial role in nanofiltration and reverse osmosis separations, while their pore size is primary to determine the separation performance. Current methods for pore size analysis, such as atomic force microscopy (AFM), positron annihilation spectroscopy (PAS), and the filtration experiment of neutral molecules are time-consuming and lack real-time capabilities. This limitation hinders in-situ monitoring of pore size dynamics under various operating conditions. Therefore, a rapid and real-time method is highly desirable for pore size analysis. This work presents a novel approach for real-time detection of pore size variations in PA membranes under different solvent conditions. It utilizes aggregation-induced emission (AIE) with tetraphenylethylene (TPE) groups covalently linked to the PA polymer chain during interfacial polymerization using 1-(4-Aminophenyl)-1,2,2-triphenylethene as a co-monomer. Fluorescence intensity of the PA membrane serves as an indicator of the confined state of the TPE molecules within the polymer network, thereby reflecting pore size changes under various conditions. The accuracy of the AIE-based approach is validated through complementary analyses such as small-angle X-ray scattering (SAXS) and rejection of dye molecules. The observed consistency between fluorescence variations in the PA membrane and pore size changes under different solvent conditions confirms the effectiveness of this method. This work provides a valuable visual tool for in-situ monitoring of pore size dynamics in polyamide membranes.

Discrimination of Xylene Isomers by Precisely Tuning the Interlayer Spacing of Reduced Graphene Oxide Membrane.

Separating xylene isomers is a challenging task due to their similar physical and chemical properties. In this study, we developed a molecular sieve incorporating a reduced graphene oxide (rGO) membrane for the precise differentiation of xylene isomers. We fabricated GO membranes using a vacuum filtration technique followed by thermal-induced reduction to produce rGO membranes with precisely controllable interlayer spacing. Notably, we could finely tune the interlayer spacing of the rGO membrane from 8.0 to 5.0 Å by simply varying the thermal reduction temperature. We investigated the reverse osmosis separation ability of the rGO membranes for xylene isomers and found that the rGO membrane with an interlayer spacing of 6.1 Å showed a high single component permeance of 0.17 and 0.04 L m-2 h-1 bar-1 for para- and ortho-xylene, respectively, exhibiting clear permselectivity. The separation factor reached 3.4 and 2.8 when 90:10 and 50:50 feed mixtures were used, respectively, with permeance 1 order of magnitude higher than that of current state-of-the-art reverse osmosis membranes. Additionally, the membrane showed negligible permeance and selectivity decay even after continuous operation for more than 5 days, suggesting commendable membrane resistance to solvent swelling and operating pressure.

Analysis of Reverse Osmosis Separation Performances of Ethanol/Water Mixtures and Design of Ethanol Concentration Processes

Analysis of Reverse Osmosis Separation Performances of Ethanol/Water Mixtures and Design of Ethanol Concentration Processes

Membrane Separation of Chicken Byproduct Hydrolysate for Up-Concentration of Bioactive Peptides.

Membrane processes, such as microfiltration, ultrafiltration, and nanofiltration, are increasingly used for various applications in both upstream and downstream processing. Membrane-based processes play a critical role in the field of separation/purification of biotechnological products, including protein production/purification. The possibility of using membranes to separate peptides from a chicken byproduct hydrolysate and the effect of the performed downstream processing on the DPP-IV dipeptidyl peptidase IV (DPP-IV) inhibitory activity of mechanical deboning chicken residue (MDCR) has been investigated. The chicken byproduct hydrolysate was prepared by enzymatic hydrolysis followed by microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) separation. Comparing all separation treatments, hydrolysates processed only by MF and UF show the best DPP-IV inhibition (59.5-60.0% at 1 mg/mL and 34.2-40.7% at 0.5 mg/mL). These samples show dose-responsive behavior. Bioactivity was correlated with molecular weight distribution profiles and average molecular weights. The nanofiltration process notably decrease the inhibitory activity, and these permeates show low DPP-IV inhibition (9.5-21.8% at 1 mg/mL and 3.6-12.1% at 0.5 mg/mL). The size-exclusion chromatography-organic carbon detection-organic nitrogen detection (LC-OCD-OND) analysis confirms that NF and RO would retain the bioactive peptides in the concentrate in comparison to MF and UF. Bioactivity was correlated with molecular weight distribution profiles and average molecular weights. Permeates after ultrafiltration show an IC50 value of 0.75 mg/mL, comparable to other potent DPP-IV inhibitors derived from various food sources, and significantly more potent compared to the microfiltration sample, which shows an IC50 value of 1.04 mg/mL. The average molecular weight of the permeates calculated from the SEC chromatograms was 883 g/mol for UF and 1437 g/mol for MF. Of the four membranes studied, the UF membrane shows the best separation properties with respect to maximizing the yield and up-concentration of the bioactive peptides. Overall, UF was demonstrated to be a feasible technology for the removal of the undesired high-molecular-weight substances and up-concentration of small-molecular-weight bioactive peptides from chicken byproduct hydrolysate. These peptides might exhibit biological activity and could offer several health benefits. There is a high potential for the use of bioactive peptides, and more research in this field can lead to promising results that have significant effects in the food and medical industries.

Bis(triethoxysilyl)ethane (BTESE)-Organosilica Membranes for H2O/DMF Separation in Reverse Osmosis (RO): Evaluation and Correlation of Subnanopores via Nanopermporometry (NPP), Modified Gas Translation (mGT) and RO Performance.

A 40 cm length Bis(triethoxysilyl)ethane (BTESE) membrane having different pore sizes was successfully prepared by changing the number of coating times for gas permeation (GP) and organic solvent reverse osmosis (OSRO) separation study. It was found that BTESE-6 membranes prepared through six-time coating consisted of small-sized pores in the range 0.56 to 0.64 nm estimated using modified Gas Translation (mGT) method and 0.59 to 0.67 nm estimated by nanopermporometry (NPP) method, respectively. These membranes demonstrated a high DMF rejection, RDMF > 95% with total flux, Jv total > 5 kg m-2 h-1 at operating condition feed pressure, Pf: 8 MPa; feed temperature, Tf : 50 °C; and feed flowrate, Qf : 30 mL/min; and they exhibited a high degree selectivity of He/SF6 in the range of ~ 260-3400 at a permeation temperature 200 °C. On the other hand, the larger pore sizes of the BTESE-4 membranes (pore size estimates > 0.76 nm to 1.02 nm) exhibited low DMF rejection and a low degree selectivity of He/SF6 around ~30% and 25, respectively, at the same operating condition as BTESE-6. Both GT and NPP methods can be considered as an indicator of the measurement membrane pore size. From this study, it was found that He and SF6 gases can be some of the potential predictors for water and DMF permeance. Furthermore, by comparing our OSRO membrane with other PV membranes for DMF/H2O separation, our BTESE-6 membranes still exhibited high flux in the range of 3-6 kg m-2 h-1 with a separation factor H2O/DMF in the range of 80-120.

Organic solvent reverse osmosis separations of hydrocarbon-alcohol mixtures using matrimid membranes

The organic solvent reverse osmosis (OSRO) separation of alcohol-hydrocarbon mixtures with Matrimid membranes is studied via experiment as well as modelling with dry glass reference perturbation theory (DGRPT). It is shown that the separation of these mixtures is highly non-ideal, with strong maxima of the separation factors as a function of feed composition. The DGRPT model was fit to pure vapor sorption data, while the Fickian diffusivities were fit from pure liquid permeation data. From this pure component parameterization, the model successfully predicted the highly non-ideal separation behavior observed for mixtures of alcohols and hydrocarbons. Successful application of the model was crucial in the interpretation of the experimental data, conclusively showing that the non-ideal behavior observed in the separations was a result of thermodynamic phenomena.

Structure–Function Relationships in Membrane-Based Hydrocarbon Separations Using N-Aryl-Linked Spirocyclic Polymers

The separation of crude oil into its many components by distillation is an energy-intensive process. Membrane-based separations that avoid the use of heat can significantly reduce these energy requirements but are not yet able to obtain sufficiently high levels of molecular discrimination. While we have recently demonstrated initial success in the ability of membranes to fractionate crude oil, a better understanding of the relationship of polymer structure to membrane function will be necessary to design the library of membranes necessary to reduce the energy intensity of separation systems. In this work, we explored structural changes to a polymer, SBAD-1, that has shown exemplary membrane performance. The results suggest that, while aromatic interactions between solute and polymer impart favorable separation properties, polymer backbone rigidity has a much greater effect on membrane performance in organic solvent reverse osmosis separations, and an intermediate degree of rigidity is likely to be optimal.

A model for the separation of complex liquid mixtures with glassy polymer membranes: A thermodynamic perspective

In this work, a new model is developed to predict the separation of organic solvent mixtures with glassy polymer membranes. Particular attention is paid to thermodynamic contributions such as guest solubility and guest-induced polymer swelling, and how these contributions affect the flux in multi-component mixtures. The thermodynamic contributions are complicated by the fact that the membranes are glassy polymers. The thermodynamic aspects of the diffusion problem are calculated using DGRPT (dry glass reference perturbation theory), which extends the non-equilibrium thermodynamics of glassy polymers (NETGP) such that polymer swelling is calculated self-consistently in the theory. The diffusion model for pure fluids diffusing through the membrane is obtained through Maxwell-Stefan equations where the polymer membrane is stationary. The mixture diffusion model is then constructed using a simple diffusivity averaging scheme on this pure fluid result. The model is then shown to accurately predict binary and complex mixture separations in SBAD-1, STARMEM-240, and Torlon membranes. We highlight the ability of the model accurately predict membrane based fractionation of crude oil, using only the sorption isotherms of toluene and octane as input to the model. • A new membrane model was proposed for multicomponent liquid mixtures in glassy polymer membranes. • The role of pressure in liquid phase reverse osmosis separations is discussed. • The model correctly predicts the separation of crude oil using only two experimental sorption isotherms.

Biocidal surfactant-assisted fabrication of thin film composite membranes with excellent and durable anti-biofouling performance

Biofouling is a critical problem for water treatment and desalination membranes because it significantly reduces process efficiency. Here, we present a new facile strategy for the fabrication of anti-biofouling polyamide (PA) thin film composite (TFC) membranes that involves the addition of the biocidal cationic surfactant, benzalkonium chloride (BAC), to an amine monomer solution during interfacial polymerization. The optimal addition of BAC effectively promotes and uniformizes amine diffusion toward the organic phase by reducing organic–aqueous interfacial tension and improving solution wettability on the support, producing a denser and more permeable PA structure. Moreover, BAC was strongly integrated into the PA matrix, presumably via strong chemical interactions between BAC and PA (i.e., electrostatic, hydrophobic, π–π stacking, and cation–π interactions), which enhanced the surface hydrophilicity and anti-bacterial activity of the membrane. Consequently, the BAC-incorporated TFC (BAC-TFC) membrane exhibited significantly enhanced reverse osmosis separation and anti-biofouling performance in comparison with the control TFC membrane. When compared with the conventional surfactant, sodium dodecyl sulfate, BAC resulted in remarkably improved biofouling resistance with comparable performance enhancement. Furthermore, the strong incorporation of BAC into PA led to the long-term durability of the BAC-TFC membrane in terms of its separation and anti-biofouling performance.

Rejection Mechanism of Ionic Solute Removal by Nanofiltration Membranes: An Overview.

The toxicity of heavy metals can cause water pollution and has harmful effects on human health and the environment. Various methods are used to overcome this pressing issue and each method has its own advantages and disadvantages. Membrane filtration technology such as nanofiltration (NF) produces high quality water and has a very small footprint, which results in lower energy usage. Nanofiltration is a membrane-based separation technique based on the reverse osmosis separation process developed in the 1980s. NF membranes have a pore size of 1 nm and molecular weight cut off (MWCO) of 300 to 500 Da. The properties of NF membranes are unique since the surface charge of the membranes is dependent on the functional groups of the membrane. The rejection mechanism of NF membrane is unique as it is a combination of various rejection mechanisms such as steric hindrance, electric exclusion, dielectric effect, and hydration mechanism. However, these mechanisms have not been studied in-depth due to their complexity. There are also many factors contributing to the rejection of NF membrane. Many junior researchers would face difficulty in studying NF membrane. Therefore, this paper is designed for researchers new to the field, and will briefly review the rejection mechanisms of NF membrane by both sieving and non-sieving separation processes. This mini-review aims to provide new researchers with a general understanding of the concept of the separation process of charged membranes.

Organic solvent reverse osmosis using CuAAC-crosslinked molecularly-mixed composite membranes

Molecularly-mixed composite membranes (MMCMs) incorporating amorphous scrambled porous organic cages (ASPOCs) are a rapidly emerging membrane class that are characterized by the formation of a solid solution due to a high degree of homogeneity that is not observed in other classes of polymer-particle composites. Molecular-level mixing overcomes many of the performance/processing issues typically encountered with two phase composite materials. However, chemical stabilization of the polymer matrix can deactivate the ASPOC cages. Here, we illustrate an alternative method of crosslinking Matrimid® in MMCMs using the copper catalyzed azide alkyne cycloaddition (CuAAC) click reaction. We fabricated thin film composite membranes and benchmarked them in a crossflow permeation system with standard styrene oligomers dissolved in a variety of organic solvents as well as an exemplar organic solvent reverse osmosis separation. We found that the presence of ASPOC increased both permeance and styrene dimer separation factor by up to 79% and 154%, respectively, over crosslinked Matrimid depending on the solvent, although the separation factor decreased at higher ASPOC loadings. The crosslinked MMCMs were challenged with a solvent-solvent separation in an organic solvent reverse osmosis modality and were able to effectively purify toluene from triisopropylbenzene. This work provides experimental observations needed to understand the mass transport processes occurring in MMCMs and highlights their separation performance and scale-up potential.

Hypoglycemic effect of low-sugar juice derived from Hovenia dulcis on type 1 diabetes mellitus rats.

Fruit juice is usually rich in monosaccharides and disaccharides. A reverse osmosis separation machine was used to remove monosaccharides and disaccharides from Hovenia dulcis fruit juice, leaving behind most of the bioactive substances in a low-sugar fruit juice (LSFJ), so as to provide a more effective treatment for diabetic patients. This study was carried out with type1 diabetes mellitus model induced with high dose of streptozotocin (60 mg kg-1 ), and oral administration of LSFJ for 4 weeks. LSFJ treatment led to significant gain in body weight and increased serum insulin level, insulin-like growth factor-1 level, blood urea nitrogen level, creatinine level, and hepatic glycogen level. Meanwhile, fasting blood glucose, fructosamine level, and glucose tolerance were also observably enhanced. Additional, LSFJ treatment significantly improved lipid metabolism, islet quality, and islet oxidative stress. The messenger RNA levels of glucose metabolism genes in the pancreas of diabetic rats decreased in the diabetes model group, whereas messenger RNA expression of these genes was significantly increased with LSFJ treatment. These findings indicate that LSFJ can improve symptoms associated with type 1 diabetes mellitus. The research also suggests new strategies for diabetes prevention and treatment. © 2021 Society of Chemical Industry.

Organic solvent mixture separation during reverse osmosis and nanofiltration by a perfluorodioxole copolymer membrane

Highly selective separation of one organic solvent from its mixture with another organic solvent by reverse osmosis will be very useful. Using a 1.67 μm thick film of a particular variety of a glassy amorphous copolymer, perfluoro-2,2-dimethyl-1,3-dioxole copolymerized with tetrafluoroethylene, (PDD-TFE), supported on an e-PTFE support, organic solvent reverse osmosis (OSRO) separations of a number of types of binary organic solvent mixtures were studied. A few studies employed a 0.6 μm thick film of the same copolymer variety designated CMS-7. The feed pressures were varied between 1000 and 5000 kPa; most of the data involved 2500–3500 kPa. Different types of solvent mixtures were studied (similar classes mentioned together): ethanol-NMP, ethanol-dimethylsulfoxide (DMSO); methanol-DMSO, methanol-NMP; toluene-methanol, toluene-N-Methyl-2-pyrrolidone (NMP), toluene-dimethylformamide (DMF); heptane-dodecane; heptane-ethanol. In quite a few cases, a pure solvent was obtained as permeate; the permeate flux could be as much as 3.5 L/m2-hr depending on the feed composition and pressure. Since this behavior is unusual in reverse osmosis, mixture sorption studies were implemented. Mixture sorption data of various mixtures in the copolymer show exclusive sorption by the species showing up as the pure permeate under certain conditions. These and other observed OSRO permeation rate and sorption behavior in the perfluoro-copolymers explain the basis for such extraordinary selectivity for quite a few systems.To illustrate OSRO-facilitated solvent-exchange in organic solvent nanofiltration, studies were carried out also to retain the dye Oil Blue N using the following binary solvent mixtures: toluene-NMP; methanol-NMP. These and other potential applications of highly selective OSRO have been discussed.

Rationally designed in-situ fabrication of thin film nanocomposite membranes with enhanced desalination and anti-biofouling performance

Silver nanoparticle (AgNP)-incorporated thin film nanocomposite (Ag-TFN) membranes with enhanced reverse osmosis (RO) separation and anti-biofouling performance were fabricated via a rationally designed in-situ hybridization technique based on the dual action of reactant materials: (1) m-phenylenediamine (MPD) monomer, conventionally employed to form a polyamide (PA) selective layer, can also reduce Ag precursors (AgNO3) to form AgNPs; (2) sodium dodecyl sulfate (SDS) surfactant, widely used to facilitate PA formation, can also stabilize AgNPs and transfer them to the interface where the PA layer is formed. The simple addition of AgNO3 to an MPD solution containing SDS during interfacial polymerization enabled the simultaneous formation of the PA layer and AgNPs, which led to the uniform incorporation of AgNPs into the PA matrix, creating the PA-AgNP interfacial free volume (nanovoids) without impairing PA crosslinking. Hence, the Ag-TFN membrane exhibited remarkably higher water permeance with similar NaCl rejection in comparison with the pristine thin film composite (TFC) and commercial membranes, mainly owing to its enhanced interfacial free volume and increased hydrophilicity. The Ag-TFN membrane also exhibited better anti-biofouling performance than control TFC owing to the antibacterial ability of AgNPs and reinforced anti-adhesion enabled by its reduced surface roughness and enhanced surface hydrophilicity.

Fabrication and structural tailoring of reverse osmosis membranes using β-cyclodextrin-cored star polymers

Here, we designed a new chemistry of fouling-resistant reverse osmosis (RO) membranes using a star polymer (CD-PAH) comprising multiple linear polymer (poly(acryloyl hydrazide), PAH) arms grafted onto a β-cyclodextrin (β-CD) core. The well-defined structure of the β-CD-cored star polymer enabled us to systematically synthesize CD-PAHs with different arm lengths, which were assembled into membrane selective layers via a layered interfacial polymerization technique. Increasing the PAH arm length of CD-PAH enhanced the inter-chain entanglement of PAH arms and thus the crosslinking reaction efficiency by providing a higher density of the crosslinkable amine groups of densely-packed PAH arms. Hence, longer PAH arms of CD-PAH resulted in an enhancement in NaCl rejection with a reduction in the water permeance of the CD-PAH-assembled (CD-TFC) membrane. Importantly, the CD-TFC membranes prepared using CD-PAHs with longer PAH arms exhibited RO separation performance comparable to that of a commercial RO membrane, which is not feasible by other reported branch-structured macromolecules. Furthermore, the CD-TFC membrane displayed lower organic fouling with a higher rinsing efficiency than a commercial RO membrane, because of its more negatively charged and hydrophilic surface combined with its smoother surface, overcoming a performance-fouling trade-off.

Experimental study and modeling of organic solvent reverse osmosis separations through organosilica membranes

AbstractExceptionally stable, mechanically robust, and highly methanol‐selective organosilica membranes, including Bis(triethoxysiyl)acetylene (BTESA), fluorine‐doped bis(triethoxysiyl) methane (F‐BTESM), and Cetyltrimethylammonium chloride‐etched bis(trimethoxysiyl)hexane (CTAC‐BTMSH), were prepared and utilized for organic solvent reverse osmosis (OSRO) separations. The BTESA membrane showed optimal separation performance regarding methanol/toluene and possessed the highest levels of both permeation flux and rejection. Continuous measurements were performed to highlight the molecule size/shape discrimination of BTESA membranes using compounds such as methanol/methyl acetate, methanol/dimethyl carbonate (DMC) and methanol/methyl tert‐butyl ether (MTBE). Also, a generalized solution‐diffusion model was successful in predicting the permeation behaviors through organosilica membranes when used in an OSRO modality, and proved to be capable of accurate predictions on pressure‐dependent permeation flux and rejection for a wide range of feed concentrations (0–55 wt%) and pressures (2–14 MPa). This study lends important insight for the development of organosilica membranes and process design for the energy‐efficient OSRO separation of organic liquids.

Efficiency assessment of Ultra-filtration pretreatment prior to Reverse Osmosis separation of contaminated natural water

Efficiency assessment of Ultra-filtration pretreatment prior to Reverse Osmosis separation of contaminated natural water

Optimization of Membrane Reverse Osmosis separation for Aqueous media characterized by High mineralization

Optimization of Membrane Reverse Osmosis separation for Aqueous media characterized by High mineralization

Flux Equations for Osmotically Moderated Sorption–Diffusion Transport in Rigid Microporous Membranes

The development of non-aqueous reverse osmosis separations via the use of rigid microporous membrane materials suggests that the flux equations originally developed for swellable polymeric membrane...

Torlon® hollow fiber membranes for organic solvent reverse osmosis separation of complex aromatic hydrocarbon mixtures

AbstractDefect‐free polyamide‐imide (Torlon®) hollow fiber membranes were fabricated to investigate the potential for polymer‐based organic solvent reverse osmosis (OSRO) separations. The quality of the membranes was assessed by gas permeation, and the membranes were found to be defect‐free. Low molecular weight cut‐offs of ~180 g/mol were obtained using a complex mixture of aromatic hydrocarbons relevant to refinery separations. We demonstrate bulk OSRO‐type separations of 80/20 (mol%) mixtures of toluene and 1,3,5‐triisopropylbenzene (TIPB, 204 g/mol). At an upstream pressure of 80–90 bar, we find that the permeate concentration was approximately 98.5–99.0 mol% toluene and that the TIPB rejection coefficient was approximately 90% in the permeate. We observed low solvent permeances of 0.01 L/m2 hr bar, which can be attributed to the low OSRO driving forces and the low permeability of Torlon®. The membranes were found to provide stable performance up to pressures of 95 bar and temperatures of 60°C.