Solubility parameter estimation and phase inversion modeling of bentonite-doped polymeric membrane systems

Effects of bentonite concentration on morphology and permeation characteristics of bentonite-doped polysulfone membranes were investigated. Solubility sphere for bentonite was constructed to estimate its solubility parameter. Thermodynamic modeling of phase inversion of this system was carried out using Flory–Huggins theory. The trade-off between thermodynamic and kinetic parameters was used to predict the membrane morphology for bentonite concentration varying from 0 to 5 wt %. The porosity of bentonite-doped membranes decreased up to 3 wt % that increased thereafter. Morphological analysis showed dense cross section with finger-like macrovoids at 3 wt % beyond which it changed to honeycomb structure with large circular voids. Permeability of 3 wt % membrane was the lowest (5.6 × 10⁻¹² m/Pa s) with 95% bovine serum albumin rejection. Contact angle of the membranes decreased from 83 to 66° with bentonite addition making the membrane more hydrophilic. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48450.     

Novel surface modifying macromolecules (SMMs) blended polysulfone gas separation membranes by phase inversion technique

In this article an attempt was made to fabricate defect‐free asymmetric polysulfone (PSf) membranes for the separation of oxygen and nitrogen. The approach is based on the enhanced delayed demixing by blending surface modifying macromolecules (SMMs) in the casting solution and by immersing the cast film in isopropanol for a certain period before it is immersed in water. Different SMMs, including hydrophobic and charged SMMs, were synthesized, characterized, and blended to the host PSf. It was found that the charged SMM could indeed contribute to the removal of defective pores from the skin layer and enhancement of oxygen/nitrogen selectivity. The experimental results were further interpreted based on the shift of the phase boundary line on the polymer/solvent/nonsolvent triangular diagram, which occurred when SMMs were blended to PSf, due to the change in the polymer/nonsolvent interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

In situ study on kinetic behavior during asymmetric membrane formation via phase inversion process using Raman spectroscopy

Asymmetric membrane formation has been studied by using an in situ analysis developed with a Micro Raman spectroscopy, which emphasizes kinetic aspects of the phase inversion process. Changes in composition with time was successfully measured on the gelation bath‐side as well as inside the precipitated phase for the polymer/solvent/nonsolvent system of polysulfone/1‐methyl‐2‐pyrrolidinone/ethanol. The results shows that resulting relative mass transfer rates of solvent and nonsolvent during the phase inversion process strongly influence the final membrane morphologies. In addition, ternary compositions at which phase separation initiates were explored by analyzing the coagulation front. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 135–141, 2000     

共混氧氮分离膜的研究进展

列举了无机、有机氧氮分离膜的研究进展,重点介绍了有机无机共混氧氮分离膜的研究现状、共混膜存在的问题和解决方法以及用于预测共混膜渗透性质的Maxwell模型和其改进形式,并提出了共混氧氮分离膜未来的发展方向.     

Understanding and guiding the phase inversion process for synthesis of solvent resistant nanofiltration membranes

Since its introduction in membrane technology in the 1960's, phase inversion by means of immersion precipitation has been widely studied for the preparation of membranes to be applied in the fields of microfiltration (MF) and ultrafiltration (UF). However, much less knowledge is available about this process in terms of integrally skinned asymmetric nanofiltration membranes, especially for more hydrophobic polymers applied in solvent resistant nanofiltration (SRNF). This review focuses on the preparation aspects of integrally skinned asymmetric membranes to be applied in the field of SRNF via phase inversion. It starts with the explanation of the basic principles of the phase inversion process, covering both thermodynamic and kinetic aspects. Further, it summarizes the parameters that significantly influence final membrane performance and morphology, including polymer type and concentration, casting solvent, additives, evaporation time, and temperature, humidity, membrane thickness, composition, and temperature of coagulation bath and post‐treatment. Literature contained within this review constitutes the core references in the field of SRNF, but also several references on preparation of MF, UF, aqueous NF, and reverse osmosis (RO) membranes have been included to better clarify or illustrate certain aspects of the process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42130.     

聚丙烯腈超滤膜的制备

为了得到高性能的超滤膜,采用相转化法,以聚丙烯腈(PAN)为原料,N-甲基-吡咯烷酮(NMP)为溶剂,制备了聚丙烯腈超滤膜.采用纯水通量以及膜对牛血清蛋白(BSA)的截留率作为评价标准,并使用扫描电镜对膜结构进行表征.研究了聚合物质量分数、添加剂种类、凝胶浴温度、凝胶浴种类对膜性能的影响.研究发现:在一定范围内提高聚合...     

Comparison of two low-hazard organic solvents as individual and cosolvents for the fabrication of polysulfone membranes

Petroleum-derived solvents commonly used in membrane fabrication are often hazardous and toxic, so the investigation of safer alternatives is important. In this study, two low-hazard solvents, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv® PolarClean) and gamma-valerolactone (GVL), were investigated as sole solvents and as cosolvents to cast polysulfone membranes via nonsolvent induced phase inversion. Normalized viscosity was introduced as an indicator of dope solution homogeneity and was used to compare the required time of mixing to achieve full dissolution of the polymer in the different solvents/solvent mixtures. All dope solutions made with low-hazard solvents were found to be more viscous than those made with traditional solvents, which meant additional mixing time was needed, and that fabricated membranes were morphologically different. With respect to operation, membranes cast from dope solutions containing equal amounts of PolarClean and GVL displayed the most similar flux curves and solute rejection to those made using the traditional solvent tested.     

Deacidification of model vegetable oils using polymeric membranes

Selectivity of polymeric hydrophobic nonporous and hydrophilic nanofiltration (NF) membranes was assessed for the deacidification of model vegetable oils with and without addition of organic solvents. In the model undiluted system, oleic acid permeated preferentially over triacylglycerols in the nonporous membrane, over a wide range of concentrations (?5–70%). The effect of oleic acid concentration on selectivity indicated that the solubility of triacylglycerols in oleic acid played a role in determining the selectivity, besides the solubility and diffusivity of the permeating components. Dilution with hexane improved oil flux by 14‐fold; however, membrane selectivity was completely lost as both triacylglycerols and oleic acid permeated along with the solvent, which clearly showed that the solvent played a greater role than the membrane. Processing of the model oil after diluting with acetone showed that oleic acid was retained less than triacylglycerols by the NF membrane, resulting in higher selectivity (7), indicating its potential. However, the selectivity decreased during successive runs, owing to the gradual loss of hydrophilicity due to polarity conditioning of the membrane. The differences in molecular size, solubility, diffusivity and polarity between triacylglycerols and oleic acid appear insufficient for achieving direct deacidification in terms of reasonable selectivity and throughput with these two membranes. Direct deacidification using membranes still remains as a challenge.     

Asymmetric membranes by wet phase inversion of phenylated polyphenylene

Asymmetric membranes of phenylated polyphenylene were prepared by wet phase inversion. The polyphenylene (M_n = 62 kDa, PD = 2.3) was prepared by Diels–Alder polymerization of 1,4‐bis(tetraphenylcyclopentadienonyl)benzene with 1,4‐diethynylbenzene at 180°C. Solvents and non‐solvents were experimentally identified and solvent : non‐solvent systems were evaluated by the quality of the resulting membranes. Cyclohexanone/n‐butanol (88 : 12) as solvent and n‐butanol as the non‐solvent were found to afford the best asymmetric membranes with minimal defects. Membranes (20–30 µm thick) from coagulating 11.5 wt % polyphenylene from cyclohexanone/n‐butanol in n‐butanol baths exhibited 250–300 nm, non‐porous skins overlaying 20–30 µm of open‐celled, spongiform structure. Due to a relatively high glass transition temperature of 370°C, the phenylated polyphenylene membranes retained their porosity to 200°C higher than polysulfone asymmetric membranes. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Perspective of mixed matrix membranes for carbon capture

Polymeric membrane-based gas separation has found wide applications in industry, such as carbon capture, hydrogen recovery, natural gas sweetening, as well as oxygen enrichment. Commercial gas separation membranes are required to have high gas permeability and selectivity, while being cost-effective to process. Mixed matrix membranes (MMMs) have a composite structure that consists of polymers and fillers, therefore featuring the advantages of both materials. Much effort has been made to improve the gas separation performance of MMMs as well as general membrane properties, such as mechanical strength and thermal stability. This perspective describes potential use of MMMs for carbon capture applications, explores their limitations in fabrication and methods to overcome them, and addresses their performance under industry gas conditions.     

Single step fabrication of polymer/silicate porous composite membranes via water-glass induced phase inversion

Water-glass, a low-cost silica precursor solution, is used to produce mostly skinned, polymer–silicate composite membranes with a porous bulk. We explore primarily Nylon 6-10/formic acid dopes where the polymer solvent is an acid, and polysulfone/DMF dope as an example of a polymer dope based on a non-acidic water-miscible solvent. Elemental distribution of silicon in cross sections suggests compositional uniformity of the formed membranes with in some cases 20 wt. % of silicate load. Membranes formed can be used either as separation media or as precursors for compact polymers reinforced with silicate particles.     

The effects of spinning temperature on morphologies and properties of polyethersulfone hollow fiber membranes

Polyethersulfone (PES) hollow fiber membranes were prepared by traditional dry‐wet spinning technique. Scanning electronic microscopy (SEM) was used to characterize membrane morphologies, and the membrane properties were evaluated via bubble point measurements and ultrafiltration experiments. The effects of spinning temperature on the morphologies and properties of PES fibers were investigated in detail. At a high spinning temperature, the obtained membrane structure consisting of a thin skin‐layer and loose sponge‐like sublayer endows PES membrane with not only good permeability, but also high solute rejection. Based on the determination of ternary phase diagrams and light transmittance curves, the relationship of membrane morphologies with thermodynamics and precipitation kinetics of membrane‐forming system was discussed. It was concluded that the morphologies and properties of PES hollow fiber membrane could be conveniently tuned by the adjustment of the spinning temperature and air gap. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microporous anisotropic phase inversion membranes from bisphenol A polycarbonate: Effect of additives to the polymer solution

Phase inversion is a very flexible technique to obtain membranes with a large sort of morphologies. Membrane properties can vary greatly depending on the kind of polymer system used. Bisphenol A polycarbonate (PC) could be used as a phase inversion membrane base polymer, and presents very good properties. Nevertheless, very little information on membrane preparation using PC and the phase inversion process can be found in the literature. In this work flat‐sheet microporous membranes were obtained by the phase inversion process using the immersion precipitation technique. A new polymer system was studied, consisting of polycarbonate, N‐methyl‐2‐pyrrolidone as solvent, water as the nonsolvent, and an additive. The influence of some parameters on membrane morphology, such as polymer solution composition, exposition time before immersion into the precipitation bath, and the kind of additive was investigated. Precipitation was followed using light transmission experiments and membrane morphology was observed through Scanning Electron Microscopy (SEM). The viscosity and cloud points of all polymer solutions were also determined. The results were related to the studied synthesis parameters, using the basic principles of membrane formation by the phase inversion technique, looking forward to establishing criteria to control the morphology of flat‐sheet membranes using polycarbonate as the base polymer. The results showed that both additives were able to increase pore interconnectivity and even suppress macrovoid formation. The decrease in the miscibility region of the polymer system and increase in mass transfer resistance are found to be the determining factors during polymer solution precipitation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3085–3096, 2002     

Method for predicting solubilities of solids in mixed solvents

A method is presented for predicting solubilities of solid solutes in mixed solvents, based on excess Henry's law constants. The basis is statistical mechanical fluctuation solution theory for composition derivatives of solute/solvent infinite dilution activity coefficients. Suitable approximations are made for a single parameter characterizing solute/solvent interactions. Comparisons with available data show that the method is successful in describing a variety of observed mixed solvent solubility behavior, including nearly ideal systems with small excess solubilities, systems with solute‐independent excess solubilities, and systems deviating from these simple rules. Successful predictions for new solvent mixtures can be made using limited data from other mixtures. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Characterization of membrane distillation membranes prepared by phase inversion

In this paper, flat membrane distillation membranes have been successfully manufactured from PVDF/DMAc and PVDF/DMF blends by using phase inversion induced by an immersion precipitation technique. The structure of the membranes is asymmetric with a porous top layer and macrovoids, as assessed by SEM. The existence of MD fluxes in these membranes is established by performing various pure water flux experiments. A maximum in the MD fluxes for a particular value of the polymer content in the casting solution from which the membrane is manufactured has been observed. The dependence of the magnitude of the fluxes on the membrane thickness is also discussed and the influence of temperature polarization evaluated.     

Separation of oil constituents in organic solvents using polymeric membranes

Different types of commercial nonporous (reverse osmosis and gas separation) polymeric membranes were screened for their abilities to separate FFA, MG, DG, and TG from a lipase hydrolysate of high-oleic sunflower oil after diluting it with organic solvents (ethanol and hexane). Cellulose acetate (CA) (NIR-1698) membrane gave the largest difference in rejection between FFA and glycerides and high flux in oil/ethanol mixtures. In the hexane system, the values of permeate flux and rejection were generally lower than those in the ethanol system. The silicone-polyimide composite membrane (NTGS-2100) gave the highest flux and rejections of solutes (70.2% for FFA, 94.4% for TG) in oil/hexane mixtures. In the ethanol system with the CA membrane, TG had the highest rejection (98%) followed by DG (90%) and MG and FFA (50–70%) when the oil concentration was varied from 6.3 to 45.8%. A discontinuous diafiltration process (16 batches) using the CA membrane with ethanol changed the composition of the oil from 31∶28∶9∶32 TG/DG/MG/FFA to 65∶30∶1∶4. The results of this study showed that oil constituents can be separated in suitable solvents using appropriate nonporous membranes.     

Isothermal phase diagrams and phase‐inversion behavior of poly(vinylidene fluoride)/solvents/additives/water systems

Isothermal ternary phase diagrams of poly(vinylidene fluoride) (PVDF)/solvents/nonsolvent systems were produced using four different solvents, N,N‐dimethylacetamide (DMAc), 1‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethylformamide (DMF), and triethyl phosphate (TEP), and using water as a nonsolvent. The effects of the additives polyvinylpyrrolidone (PVP, M_w = 10,000), ethanol, and lithium perchlorate (LiClO₄) on the phase‐inversion behavior of PVDF/DMAc/water ternary system were investigated, with additive concentrations of 2 and 6 wt %, at temperatures of 25 and 70°C, respectively. Ethanol, glycerol, and water were used to study the cloud points of 10, 15, and 20 wt % PVDF/DMAc concentrations, at solution temperatures ranging from 30 to 70°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2150–2155, 2003     

Challenges in forming successful mixed matrix membranes with rigid polymeric materials

Mixed matrix materials comprised of molecular sieve domains embedded in processable polymer matrices have the potential to provide membranes with higher permselectivity and equivalent productivity compared to existing membrane materials. It has been shown that successful mixed matrix materials can be formed using relatively low glass transition (T_g) polymers that have a favorable interaction with the sieves. This article extends this earlier work to include the use of more practical rigid matrix polymers with high T_gs that can ultimately be used in forming high‐performance mixed matrix layers for composite membranes. Initial attempts to form mixed matrix materials based on high T_g polymers with a type 4A zeolite resulted in poor adhesion between the polymer and sieve. Correcting this problem was pursued in this study by forming the composite material close to the T_g of the polymer by addition of a plasticizer to match the matrix T_g with the solvent volatility. Forming the films at elevated temperatures presented substantial challenges, and this work discusses overcoming these challenges in detail. With some modifications in the film casting procedure, successful materials were achieved. Promising oxygen/nitrogen transport results are presented for these zeolite 4A–Matrimid®/plasticizer membranes, and this data compares favorably with predictions of the well‐known Maxwell model for composite systems. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 881–890, 2002     

Preparation of polyvinylchloride membranes from solvent mixture by immersion precipitation

In this study, polyvinylchloride (PVC) membranes were prepared through the immersion precipitation method using a mixture of two solvents (tetrahydrofuran (THF) and dimethyl formamide (DMF)), which had different affinities with the nonsolvent (water). Membranes prepared from PVC/THF/water system showed a sponge‐like structure with isolated pores, which were impermeable to water even at a feed pressure of 20 bars, whereas those prepared from PVC/DMF/water exhibited a porous macrovoid containing morphology with a high water flux. The precipitation time and polymer concentration profiles were calculated by using a simple mathematical model and were in good agreement with the experimental findings on PVC/THF/water and PVC/DMF/water systems. By using a mixture of DMF and THF as solvent and changing the mixed solvent composition, membranes with different morphologies from sponge‐like to macrovoid containing were obtained. The membranes showed no water flux below a DMF concentration of 50 wt % and then became increasingly permeable with increasing DMF content in the casting solution. Measurement of the system cloud points showed a linear change of system thermodynamics with variation of the mixed solvent composition. The obtained results showed that although the system thermodynamics could explain the overall behavior of the system, but the local changes such as change of membrane performance from impermeable to permeable at a certain mixed solvent composition could not be explained by the thermodynamics alone. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40206.