Comparison Between Polydimethylsiloxane and Polyimide-Based Solvent-Resistant Nanofiltration Membranes

Nanofiltration using solvent-resistant membranes has become an important separation technology. Polydimethylsiloxane and polyimide are important materials for preparation of solvent-resistant nanofiltration (SRNF) membranes. In this study, the performance of commercial polydimethylsiloxane and polyimide SRNF membranes (as a trademark of MPF and STARMEM) with molecular weight cutoff values of 200–700 Da was compared in terms of organic solvent preconditioning effect, solvent compatibility, solvent flux, and solute rejection. Organic solvents employed were methanol, toluene, ethyl acetate, dichloromethane, and acetone and the organic solutes in a molecular weight range of 160–850 Da were used. Membrane preconditioning with different organic solvents did not affect membrane performance of the polydimethylsiloxane-based MPF membranes but had a significant influence on the polyimide-based STARMEM membranes. Both MPF and STARMEM membranes are not compatible in dichloromethane. MPF membranes were inert to the organic solvents and had relatively low solvent fluxes. STARMEM membranes were highly swollen in methanol and offered much higher solvent fluxes and attractive NF performance in toluene.     

Investigation on the enhancement of solvent-resistant nanofiltration membrane performance utilizing PDA-UiO-66@CNT as an interlayer

With the growing complexity of separation systems, the application of thin film composite nanofiltration (TFN) membranes in organic solvent separation faces numerous challenges. To augment its solvent stability, an in-situ constructed dopamine hydrogel doped with UiO-66@CNT was developed as an intermediate layer on a polyetherimide (PEI) ultrafiltration membrane. Subsequent interfacial polymerization on this interlayer led to the formation of a solvent-resistant nanofiltration membrane with a vast covalent bond structure, large specific surface area, and enhanced hydrophilicity. Our findings revealed that when the CNT loading in the UiO-66@CNT composite nanoparticles was 2 wt%, the TFN-U₂C₂ membrane exhibited a maximum pure water flux of 126.32 L/(m²·h) and a methanol flux of 45.45 L/(m²·h). The rejection rates for Congo red aqueous and methanol solutions were 96.88% and 92.14%, respectively. The membrane also demonstrated commendable anti-fouling properties. Remarkably, even after 48 h of immersion in various organic solvents, the membrane retained its morphology and separation efficiency. Compared to the TFN-U₂ membrane without CNT addition, the enhancement in separation performance was considerably significant. Hence, this membrane has significant potential for application in treatment of wastewater containing organic solvents and is promising in related fields.     

Polymer membranes for separating organic mixtures

Polyvinyl alcohol (PVA), polyacrylonitrile (PAN), and cellulose ester were respectively chosen as the separation layer and the support in the composite membranes based on the concept of the solubility parameter and the permselectivities for separating ethanol/water mixture, isopropanol/water mixture, and caprolactam/water mixture. The effects of the membrane materials and the construction of the composite membrane on the separation performance were preliminary discussed. The separation performance of the membranes prepared by several making‐membrane techniques, i.e., the polymer solution making‐membrane technique, and the membrane treatment technique (heat treatment, organic solvent modification) were presented. The composite membranes of PVA/PAN and PVA/cellulose acetate, and cellulose triacetate hollow fiber membrane modified, which possess good performance in separating the organic systems, were developed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1160–1164, 2006     

Preparation and properties of polyimide solvent‐resistant nanofiltration membrane obtained by a two‐step method

This study investigated the preparation of polyimide solvent‐resistant nanofiltration membranes by a two‐step method (casting the membrane first and then crosslinking by the thermal imidization method). The influences of polymer concentration, thickness of membranes, temperature of the imidization, phase inversion time and thermal imidization procedure were studied. The membranes with the highest rejection rate of Fast Green FCF (molecular weight 808.86 g mol^?1) were prepared in the following conditions: polymer concentration 13 wt%, phase inversion time 1 h, membrane thickness 150 µm and thermal imidization procedure 200 °C for 2.5 h, 250 °C for 2 h and 300 °C for 2 h in a vacuum environment; the heating rate was 5 °C min^?1. The membrane was stable in most of the solvents tested and the fluxes of some common solvents were equal to or higher than a number of commercial solvent‐resistant nanofiltration membranes. A much higher rejection of dyes in water than in methanol was observed in the filtration experiments and a new way to explain it was developed. Copyright © 2011 Society of Chemical Industry     

Enhancement of flux and solvent stability of Matrimid® thin‐film composite membranes for organic solvent nanofiltration

The development of high flux and solvent‐stable thin‐film composite (TFC) organic solvent nanofiltration (OSN) membranes was reported. A novel cross‐linked polyimide substrate, consisting of a thin skin layer with minimum solvent transport resistance and a sponge‐like sublayer structure that could withstand membrane compaction under high‐pressure was first fabricated. Then the solvent flux was significantly enhanced without compromising the solute rejection by the coupling effects of (1) the addition of triethylamine/camphorsulfonic acid into the monomer solution, and (2) the combined post‐treatments of glycerol/sodium dodecyl sulphate immersion and dimethyl sulfoxide (DMSO) filtration. Finally, the long‐term stability of the TFC membrane in aprotic solvents such as DMSO was improved by post‐crosslink thermal annealing. The novel TFC OSN membrane developed was found to have superior rejection to tetracycline (MW: 444 g/mol) but was very permeable to alcohols such as methanol (5.12 lm^?2h^?1bar^?1) and aprotic solvents such as dimethylformamide (3.92 lm^?2h^?1bar^?1) and DMSO (3.34 lm^?2h^?1bar^?1). © 2014 American Institute of Chemical Engineers AIChE J, 60: 3623–3633, 2014     

Thin film composite membranes with desirable support layer for MeOH/MTBE pervaporation

A comprehensive study was performed on a new application of thin film composite membranes and selecting a stable sublayer for them as pervaporation membranes in organic solvent separation. For this purpose, four different polymeric sublayers of polyethersulfone (PES), cellulose acetate, polyacrylonitrile, and polyetherimide were prepared, and the interaction of methanol (MeOH) and methyl tert butyl ether (MTBE) with them was investigated. The contact angle results, scanning electron microscopy images, and swelling and mechanical strength measurements obviously displayed the effect of immersion in organic solvents on the sublayers. Finally, a polyamide active layer was subsequently deposited on the PES membrane surface as the stable sublayer via interfacial polymerization based on a multistep statistical optimization strategy involving fractional factorial design and a response surface method. The prepared TFC membranes were tested in the pervaporation of a MeOH/MTBE mixture and exhibited excellent performance compared with the current membranes in this context. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47519.     

Relationship between the separation performances and free volume distributions of polyimide/Ag3O4 composite membranes

First, water, methanol, ethanol, acetone, and methyl t‐butyl ether were used as molecular probes to measure the free volume distribution of a type of polyimide membrane material (HQDEA–DMMDA). The methods were equilibrium swelling and separation membrane technologies. From the Kirchheim theory of free volume distribution, a Gaussian distribution function was determined. The Gaussian distribution function was confirmed with tensile testing and wide‐angle X‐ray diffraction of the polyimide films. Second, polyimide/Ag₃O₄ composite hollow‐fiber membranes were prepared by dry/wet phase inversion. The separation performances of the composite membranes were characterized with a methanol/methyl t‐butyl ether mixture. The change in the separation performances was explained by the free volume distribution function very well. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 871–879, 2005     

Effects of polymer solvents on the performance of cellulose acetate membranes in methanol/methyl tertiary butyl ether separation

The performances of cellulose acetate membranes prepared with casting solutions, with acetone, dimethylformamide (DMF), and N‐methylpyrrolidone (NMP) as solvents, were studied in a series of methanol/methyl tertiary butyl ether separation experiments. The flux and selectivity of the membrane samples were affected by the type of solvent used to prepare the casting solution. The sample with DMF consistently gave the highest selectivity and lowest flux, followed by the samples with NMP and acetone. The differences in the performances were attributed to the effects of the volatility and evaporation rates of the solvents. Scanning electron microscopy and atomic force microscopy techniques were used for comparing the morphologies of the membranes. In addition, we used Raman spectroscopy as a novel technique to study the sorption selectivities of the membrane samples prepared with the three different solvents. In a parallel study, the relation between the polymer concentration in the casting solution and the morphology and performance of the membrane samples was studied. Under similar preparation conditions, the morphology of the membrane changed from being porous to being dense when the membrane was prepared with casting solutions with increasing polymer concentration. Also, the selectivity increased and the permeability decreased with increasing polymer concentration in the casting solution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2882–2895, 2001     

有机溶剂纳滤膜的润湿性对渗透和分离性能的影响

有机溶剂纳滤是一种绿色、高效、节能的新型膜分离技术,在回收和处理有机溶剂中具有广泛的应用前景。本文采用浸渍法分别将聚合物聚二甲基硅氧烷（PDMS）、嵌段聚醚酰胺（PEBAX2533）和聚乙烯醇（PVA）与聚砜（PS）超滤基膜复合,制备了3种不同润湿性的聚合物耐溶剂纳滤膜,研究了PDMS/PS、PEBAX/PS和PVA/PS复合膜对甲醇、乙醇、异丙醇、正己烷、正庚烷的渗透性能,考察了3种聚合物膜对伊文思蓝/甲醇溶液的有机溶剂纳滤性能。结果表明,有机溶剂在不同润湿性复合膜的渗透和传递性能与溶剂本身的溶度参数、分子量、黏度和极性等有很密切的相关性,溶剂的分子量、黏度、分子动力学直径越小,在同一极性复合膜中渗透通量越大;对伊文思蓝/甲醇溶液的有机溶剂纳滤分离表明,PDMS/PS和PEBAX/PS复合膜的截留率均可达90%以上,通量分别为 58.0L/(m²·h·MPa)和72.2L/(m²·h·MPa);PVA/PS复合膜的截留率为85.1%左右,通量为57.5L/(m²·h·MPa)。     

Thin-film composite membranes for organophilic nanofiltration based on photo-cross-linkable polyimide

This work demonstrates that it is possible to prepare new, competitive thin-film composite (TFC) membranes with a polyolefin ultrafiltration membrane as support and with a non-porous photo-cross-linked polyimide as separation layer for organic solvent nanofiltration. The commercial polyimide Lenzing P84® was modified by a polymer-analogous reaction to introduce side groups with carbon–carbon double bonds to increase its photo-reactivity with respect to cross-linking. Polymer characterization revealed that this was successfully achieved at acceptable level of main chain scission. The higher reactivity of the photo-cross-linkable polyimide had been confirmed by comparison with the original polymer; i.e., shorter gelation times upon UV irradiation, higher suppression of swelling by solvents and complete stability in strong solvents for not cross-linked polyimide such as dimethylformamide (DMF) had been obtained. For films from unmodified and modified polyimide, the degree of swelling in various solvents could be adjusted by UV irradiation time. Photo-cross-linking of the original polyimide did not lead to stability in DMF. TFC membranes had been prepared by polymer solution casting on a polyethylene ultrafiltration membrane, UV irradiation of the liquid film and subsequent solvent evaporation. Polyimide barrier film thicknesses between 10 and 1 μm were obtained by variation of cast film thickness. Performance in organic solvent nanofiltration was analyzed by using hexane, toluene, isopropanol and DMF as well as two dyes with molar masses of ∼300 and ∼1000 g/mol. Permeances of TFC membranes from unmodified polyimide were low (<0.1 L/hm² bar) while rejections of up to 100% for the dye with ∼1000 g/mol could be achieved. TFC membranes from modified and photo-cross-linked polyimide had adjustable separation performance in DMF with a trade-off between permeance and selectivity, in the same range (e.g.: 0.3 L/hm² bar and 97% rejection for the dye with ∼1000 g/mol) as a commercial conventional polyimide membrane tested in parallel. The established membrane preparation method is promising because by tuning the degree of cross-linking of the polymeric barrier layer, the membrane separation performance could be tailored within the same manufacturing process.     

Influence of quench medium on the structure and gas permeation properties of cellulose acetate membranes

Integrally skinned asymmetric cellulose acetate membranes made by the wet phase inversion for removal of CO₂ from natural gas were investigated. The membrane was cast with the membrane-forming systems of cellulose acetate–acetone and quench media, such as methanol, ethanol and isopropanol, respectively, without heat-treating and multistage exchange process. By means of evaluation on separating characteristics of the membrane for CO₂/CH₄, observation of morphologies by scanning electron photomicrographs and analysis of the phase diagrams on the membrane-forming systems, it has shown that the membrane-forming system of cellulose acetate–acetone–methanol is quite suitable to prepare integrally skinned asymmetric cellulose acetate membranes for gas separation with good selectivity CO₂/CH₄ = 30 and flux coefficient = 2.4 × 10⁻⁵ cm³/cm² − s − cm Hg. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1269–1276, 1998     

分离有机/有机混合物的PVA、CA系列膜及其渗透汽化性能研究(Ⅰ)膜材料与成膜工艺

依据溶度参数原则和分离甲基叔丁基醚(MTBE)/甲醇(MeOH)混合物的选择渗透性,选择了聚乙烯醇(PVA)为复合膜的分离层材料,聚丙烯腈(PAN)、醋酸纤维素(CA)系列为支撑层的膜材料.初步讨论了膜材料和复合膜结构对分离性能的影响,给出了用不同成膜工艺制备的膜性能,获得了可用于有机/有机体系分离的性能优良的PVA/PAN和PVA/CA复合膜,以及CTA中空纤维渗透汽化膜.     

Cellulose acetate–silica fume membrane: characterization and application for separation of starch and maltose

Maltose is one of the starch derivatives. Maltose can be produced by starch hydrolysis using any kind of hydrolytic process. One of the methods to separate a mixture of both compounds is using porous membrane. In this research, a novel type of hybrid membrane was prepared from a mixture of cellulose acetate and silica fume. Silica fume is widely used in the domain of construction as cement material, whereas in this research silica fume was successfully used as membrane material. Various compositions of membrane dope solutions were prepared for obtaining the membranes used for separation of starch and maltose. Such synthesized membranes demonstrate a good performance in separation processes. The best performance is achieved when the composition of cellulose acetate in membrane dope solution is 15 % (w/w) in N,N-dimethylacetamide solvent and the mass ratio between cellulose acetate and silica fume is 4:1. For this composition, the rejection of membranes towards starch and maltose is 87 and 2 %, respectively, at working pressure of 3 bar and compaction time of 2 h. Infrared spectrum indicates no new peaks are found compared to raw materials’ spectral peaks. Thus, it can be concluded that the interaction between the cellulose acetate and silica fume is merely a physical type. From the observation of cross-sectional SEM images, we can remark that the morphology of such a membrane is porous. X-ray diffractogram indicates that the synthesized membranes are amorphous.     

Separation and Polychromatic Identification of Some Amino Acids Present in Carrot Protein

Abstract

An efficient one dimensional thin-layer chromatography separation of seven amino acids known to be present in carrot was developed. The thin-layer plates were coated with an adsorbent of microcrystalline cellulose. Several solvent systems were evaluated with a butanol, acetone, water, dicyclohexane solvent giving a good separation of the amino acids. Detection was accomplished by spraying with ninhydrin.     

The effect of short air exposure periods on the performance of cellulose acetate membranes from casting solutions with high cellulose acetate content

Highly productive cellulose acetate membranes were cast under conditions of very short air exposure periods from cellulose acetate–acetone–formamide casting solutions having a high cellulose acetate (CA) content and lying close to the phase boundary. Air exposure periods as short as 0.05 sec were used with CA content up to 32 wt-%. Membranes from a casting solution containing 30 wt-% cellulose acetate (E-398-3), 45 wt-% acetone, and 25 wt-% formamide perform as well as membranes from other compositions at all salt rejection levels for a 0.5 wt-% NaCl feed at 600 psig. Partial replacement of acetone by dioxane in the casting solution substantially increases the water flux from membranes cast with short air exposure periods at any given salt rejection level below 96% salt rejection. Addition of small amounts of ZnCl₂ to nondioxane casting solutions with 32 wt-% CA improves membrane performances remarkably for lower salt rejection levels, while the improvement in performance of membranes from 30 wt-% CA casting solutions with dioxane due to ZnCl₂ addition is marginal. Variation in air exposure from 0.05 to 2 sec results in minor performance variations in the membranes having any of these compositions. With air exposure periods beyond 2–3 sec, membrane fluxes drop drastically. The concept of a thinner skin satisfactorily explains the improvement in mixed solvent systems, whereas ZnCl₂ acts as a swelling salt. A Kimura-Sourirajan-type membrane performance plot indicates that for a 0.5 wt-% NaCl feed at 600 psig, membranes of the present work perform as well as the best performing membranes reported in the literature for conversion of brackish water.     

Calculation of alcohol‐acetone‐cellulose acetate ternary phase diagram and their relevance to membrane formation

ABSTRACT Alcohol‐acetone‐cellulose acetate phase diagrams incorporated with methanol, ethanol, and isopropanol as nonsolvents are calculated according to a new form of the Flory–Huggins equation. Nonsolvent–cellulose acetate interaction parameters are measured by swelling experiments. Concentration‐dependent nonsolvent–solvent interaction parameters are obtained by vapor–liquid equilibrium and the Wilson equation. It is shown that alcohol is a week coagulant compared with water, and water > methanol > ethanol > isopropanol for cellulose acetate. The phase diagrams characteristic of acetone‐cellulose acetate combined with water, methanol, ethanol, and isopropanol as nonsolvents is different, which leads to the different morphological structure of a cellulose acetate membrane. The structure of a water coagulated membrane has large macrovoids from liquid–liquid phase separation. A methanol coagulated membrane has a honeycomb‐like structure from spinodal microphase separation. An ethanol or isopropanol coagulated membrane has a thicker, dense top layer from the delay time phase separation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1650–1657, 2001     

用于脱除C5及MTBE中甲醇的渗透汽化膜研究

Several pervaporation membranes, cellulose acetate (CA), polyvinylbutyral (PVB), poly(MMA-co-AA), MMA-AA-BA, CA/PVB blend and CA/poly(MMA-co-AA) blend, were prepared, and their pervaporation properties were evaluated by separation of methanol/C5 or methanol/MTBE (methyl tert-butyl ether). The results shows that the CA composite membrane has a high separation performance (flux Jmenthanol =350g.m-2.h-1 and separation factor a > 400) for methanol/C5 mixtures, and the pervaporation characteristics of MMA-AA-BA copolymer membranes changes with the ratio of copolymer. For CA/poly(MMA-co-AA) blend membrane, the pervaporation performance is improved in comparison with CA or poly(MMA-co-AA) membrane. From the experiment of CA/PVB blend membranes for methanol/MTBE mixture, it is found that the compatibility of blends may affect the separation features of blend membrane.     

Studies on Cellulose Acetate/Low Cyclic Dimmer Polysulfone Blend Ultrafiltration Membranes and their Applications

Abstract

Flat sheet ultrafiltration membranes from cellulose acetate (CA)/low cyclic dimer polysulfone (LCD PSf) were prepared by a phase inversion method. N, N′‐Dimethyl formamide and different molecular weight of polyethylene glycol (PEG 200, PEG 400, and PEG 600) were used as solvent and pore‐forming additive, respectively. The membranes were characterized in terms of pure water flux, water content, porosity, membrane hydraulic resistance, and morphology. The pure water flux was found to reach the highest value of 181.82 Lm^?2h^?1 at 5 wt.% PEG of 600 molecular weight and 10 wt.% LCD PSf content in the blended solution for membrane preparation. SEM micrographs indicated that the addition of PEG into the CA/LCD PSf solution changes the inner structure of the membrane. The influence of filtration time and applied pressure on membrane permeability was examined by copper/polyethylenimine complex rejection studies. With increase in filtration time, the rejection of the copper/polyethylenimine complex decreased and the results were discussed.     

Studies on the solvent exchange technique for making dry cellulose acetate membranes for the separation of gaseous mixtures

The effect of the pore size on the surface of the water-wet reverse osmosis membrane and the solvents used in the solvent exchange process on the pore size of the resulting dry cellulose acetate membrane was studied with respect to the separation of a CO₂/CH₄ mixture. It has been found that there is a critical pore size on the surface of wet membrane that results in the smallest pore size on the dry membrane and, consequently, in the highest separation factor. Such critical pore sizes become greater when the boiling point of the second solvent is increased.     

Surface Force-Pore Flow Model in Predicting Separation and Concentration of Polyhydric Alcohols in Aqueous Solutions Using Cellulose Acetate Membranes

Abstract

The reverse osmosis separation and concentration of polyhydric alcohols were experimentally tested by using cellulose acetate membranes of different average pore sizes. An attempt was made to predict membrane performance data, such as the solute separation and the product permeation rate, on the basis of the surface force-pore flow model, and the results were tested by experimental values. The processing capacities of the membranes were also calculated.