Aromatic Polyamide Membranes Research Articles

Hybrid organic/inorganic reverse osmosis (RO) membrane for bactericidal anti-fouling. 1. Preparation and characterization of TiO2 nanoparticle self-assembled aromatic polyamide thin-film-composite (TFC) membrane.

Hybrid organic/inorganic reverse osmosis (RO) membranes composed of aromatic polyamide thin films underneath titanium dioxide (TiO2) nanosized particles have been fabricated by a self-assembly process, aiming at breakthrough of biofouling problems. First, positively charged particles of the colloidal TiO2 were synthesized by a sol-gel process, and the diameter of the resulting particles in acidic aqueous solution was estimated to be approximately 2 nm by analyzing the UV-visible absorption characteristics with a quantum mechanical model developed by Brus. Transmission electron microscopy (TEM) further confirmed the formation of the quantum-sized TiO2 particles (approximately 10 nm or less). The TiO2 particles appeared to exist in the crystallographic form of anatase as observed with the X-ray diffraction (XRD) pattern in comparison with those of commercial 100% rutile and commercial 70:30% anatase-to-rutile mixture. The hybrid thin-film-composite (TFC) aromatic polyamide membranes were prepared by self-assembly of the TiO2 nanoparticles on the polymer chains with COOH groups along the surface. They showed improved RO performance in which the water flux even increased, though slightly. Field-emission scanning electron microscopy (FESEM) exhibited the TiO2 nanoparticles well adsorbed onto the surface. X-ray photoelectron spectroscopy (XPS) demonstrated quantitatively that a considerable amount of the adsorbed particles were tightly self-assembled at the expense of the initial loss of those that were loosely bound, and became stabilized even after exposure to the various washing and harsh RO operating conditions. The antibacterial fouling potential of the TiO2 hybrid membrane was examined and verified by measuring the viable numbers and determining the survival ratios of the Escherichia coli (E. coli) as a model bacterium, both with and without UV light illumination. The photocatalytic bactericidal efficiency was remarkably higher for the TiO2 hybrid membrane under UV illumination, compared to that of the same membrane in darkness, as well as those for the neat membranes under either light condition.

Pervaporation of benzene/cyclohexane mixtures through aromatic polyamide membranes

A series of novel aromatic polyamides based on the 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BAPPH) and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPPP) with various aromatic diacids were investigated for pervaporation separation of benzene/cyclohexane binary system. The aromatic polyamide membranes exhibited a benzene-permselectivity for all the feed compositions and the permeation rate increased with increasing benzene in the feed solution. The fluorine-containing polyamide membranes were swollen in benzene but only slightly in cyclohexane. A separation factor toward benzene, a permeation rate, and a pervaporation separation index (PSI) value through the fluorine-containing polyamide membrane (F-3) for a 50 wt.% feed benzene concentration were 4.0, 1470 and 5903 g m −2 h −1, respectively. The permeation rate and the PSI value of fluorine-containing polyamide membranes based on the BAPPH were higher than that of the aromatic polyamide membranes based on the BAPPP.

Four years field experience with fouling resistant reverse osmosis membranes

A novel type of reverse osmosis membrane has been introduced to field operation in 1996, the biofouling resistant (FR) membrane. It is a chemically modified, thin film composite, aromatic polyamide membrane in a tailored spiral wound element construction. When these elements are synergistically coupled with the optimized use of a select biocide, the combination FR technology package has demonstrated dramatic reductions in chemical cleaning frequency. In the meanwhile, many plants have been built and are in operation worldwide. At the same time, the product is being further developed. This poster presents some case histories and field experience with the first two generations of FR membrane during the past four years.

Plasma deposition of acrylamide onto novel aromatic polyamide membrane for pervaporation

Pervaporation of water/ethanol mixtures through acrylamide-plasma graft-aromatic polyamide, AAm- p-aramide, an aramide membrane on which AAm is grafted by plasma polymerization, was investigated in this work. The surface properties of the AAm- p-aramide membranes were characterized by atomic force microscopy, AFM, and contact angle meter. The effects of degree of grafting, feed composition, feed temperature and surface properties on the pervaporation performances were studied. The separation factor and permeation rate of the AAm- p-aramide membranes were higher than that of the unmodified aramide membrane. Optimum pervaporation was obtained by a AAm- p-aramide membrane with a degree of grafting of 20.5% for a 90 wt% ethanol feed concentration, giving a separation factor of 200 and a permeation rate of 325 g/m 2h.

Development of aromatic polyamide membranes for pervaporation and vapor permeation

The pervaporation and vapor permeation performances of a series of fluorine-containing aromatic polyamide membranes for various alcohol mixtures were investigated. Compared with pervaporation, vapor permeation effectively increases the permselectivity of water. The solubility of alcohol in an aromatic membrane is higher than that of water, but the diffusivity of water across the membrane is higher than that of the alcohols. In addition, the relationship between the polymer structure and pervaporation performance was obtained. It was found that the permeation rate can be increased by the introduction of bulky substituted groups and arylene ether groups into the polymer backbone.

Improve RO system performance and reduce operating cost with FILMTEC fouling-resistant (FR) elements

A new generation of chemically modified, FILMTEC thin-film composite, aromatic polyamide membrane elements has been introduced that exhibits reduced rates for bacterial adhesion, longer induction periods before biofilm start developing, and extended operating times between chemical cleanings. When these biofouling-resistant (FR) elements are coupled with the optimized use of selected biocides to prevent biofilm growth, a significant reduction in chemical cleaning frequency is achieved. This paper reviews biofouling in membrane systems and describes the development of the FR elements through full-scale field trials over about 3 years, focusing in the improvement achieved in mitigating the negative effects of biofouling on the performance of reverse osmosis plants. Some economic guidelines are given to estimate the potential value of FR technology.

Separation of Organic Pollutants by Reverse Osmosis and Nanofiltration Membranes: Mathematical Models and Experimental Verification

Predictive reverse osmosis (RO) models have been well-developed for many systems. However, the applications to dilute organic−water systems require the modification of transport models and the understanding of solute−polymer interactions. Studies with various substituted, nonionized phenolic compounds showed that these could cause substantial membrane water flux drop, even in dilute solutions with negligible osmotic pressure. Further, the organics could significantly adsorb on the cross-linked aromatic polyamide active layer. In some cases, even concentrations as low as 0.2 mM, 2,4-dinitrophenol (solution in particle-free, double-distilled water) can cause as much as a 70% flux drop with an aromatic polyamide membrane. Two models are presented in this paper: a modified steady-state solution diffusion model and an unsteady-state diffusion adsorption model which are able to predict flux and permeate concentrations from a single RO experiment. Further, the development of these models allows for the understa...

Preparation of aromatic polyamide membrane for alcohol dehydration by pervaporation

Two aromatic polyamide membranes were synthesized by direct polycondensation of 5-t-butyl isophthalic acid with 2,2-bis[4-(4-aminophenoxy)phenyl]hexfluoropropane, (F-aramide), and with 2,2-bis[4-(4-aminophenoxy)- phenyl]propane, (H-aramide), in a solution containing triphenyl phosphite, pyridine and N-methyl-2-pyrrolidinone. The effects of feed composition, feed temperature, and the molar volume of the feed alcohol on pervaporation performance were investigated. The separation factor and the permeation rate increased with increasing ethanol concentration in the feed for both aromatic polyamide membranes. The separation factor of the H-aramide membrane was higher than that of the F-aramide for pervaporation of water/ethanol solution. For the H-aramide membrane, a separation factor of 60 and a permeation rate of 293 g m −2h −1 were obtained when the concentration in the feed was 90 wt% and the feed temperature was maintained at 25°C.

Permeation of apple aroma compounds in reverse osmosis

Abstract This work studies the permeation of apple juice aroma compounds through a reverse osmosis spiral wound aromatic polyamide membrane of 99.2% NaCl rejection. A model solution of apple juice aroma was used as feed. Experiments were carried out at different transmembrane pressures (1.5–3.5 MPa) and feed flows (200–600 l/h; Reynolds numbers between 100 and 300). Temperature was set at 25°C. Rejection was observed to increase with transmembrane pressure and feed flow. The preferential sorption-capillary flow model was used to estimate the experimental rejection using only data on the permeation of a solute taken as reference (NaCl) and on the permeation of pure water. Good agreement between experimental and estimated rejection was found for the most hydrophilic aroma compounds, while a slightly higher rejection than the experimental one was predicted for the least hydrophilic compounds.

Permselectivities of aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation

The separation of water/alcohol mixtures was carried out using a series of fluorine-containing aromatic polyamide membranes. Aromatic polyamides were prepared by direct polycondensation of fluorine-containing diamine (2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, BAPPH) and various aromatic diacids. The separation factor toward water increased when the feed ethanol concentration was increased. The solubility of ethanol in aromatic polyamide membrane is higher than that of the water, but the diffusivity of water across the membrane is higher than that of alcohols. A separation factor of 83 and a permeation rate of 262 g/m2h with a 90 wt% feed ethanol concentration at 25 °C was obtained.

Synthesis and evaluation of aromatic polyamide membranes for desalination in reverse-osmosis technique

Reverse-osmosis membrane-grade aromatic polyamides have been synthesized by reacting 3,5-diaminobenzoic acid separately with three different acylchlorides, viz. isophthaloyl chloride, terephthaloyl chloride, and 4,4′-diphenyldicarboxylic acid chloride. Using these polyamides, asymmetric membranes were developed and characterized for various physical parameters, such as Staverman coefficient, membrane potential, and percent salt rejection using sodium chloride solution under high pressure. The effects of pressure, feed concentration, and feed flow rate have been studied on membrane transport parameters, viz. pure water permeability constant, product rate, solute transport parameter, and separation factor. The effects of annealing temperature and solvent evaporation time on the performance of the membranes were also studied. The analysis of the reverse-osmosis data revealed that the membranes prepared from the 3,5-diaminobenzoic acid and 4,4′-diphenyldicarboxylic acid chloride are superior to the membranes prepared from other polymeric materials. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 643–653, 1997

Waste water treatment using reverse osmosis: real osmotic pressure and chemical functionality as influencing parameters on the retention of carboxylic acids in multi-component systems

The influence of chemical functionality in carboxylic acids and osmotic pressure of multi-component solutions on the retention in the reverse osmosis process are discussed. Therefore formic-, acetic-, propionic-, glycolic-, acrylic- and methoxyacetic acid ( target substances) were combined with one or two other carboxylic acids ( active substances), chosen out of a pool of 16. All investigations were carried out with an aromatic polyamide membrane and the operating conditions were kept constant. Although the combination of all effects is extremely complex, the experiments showed that the influence on the retention of a substance equate as an outcome of molecular mass, acidity, functionality and spatial requirement. The influence of functionality in the active substances could be further divided into an additional carboxylic group, double bond and aromaticity. The calculation of the osmotic pressure demonstrated that there was no observable difference between the real and ideal one when the solution contained the same number of components. Therefore it can be concluded that in this study the osmotic pressure has no influence on the retention of the target substance.

Selective separation of water from aqueous alcohol solution through fluorine-containing aromatic polyamide membranes by pervaporation

For dehydrating aqueous alcohol solution by pervaporation, a fluorine-containing aromatic polyamide membrane was synthesized. The fluorine-containing polyamides were prepared by direct polycondensation of 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, BAPPH, with various aromatic diacids by triphenyl phosphite and pyridine in N-methyl-2-pyrrolidinone. The novel aromatic polyamides were examined by elemental analysis, FTIR, and X-ray diffraction. The aromatic polyamides were crystalline except (A-B 2). The effects of feed composition, degree of swelling, and the molecular size of alcohols on pervaporation performances were investigated. Water molecules preferentially permeate through the aromatic polyamide membranes. A separation for water of 36 and a 383 g/m 2h permeation rate with a 90 wt% feed ethanol concentration was obtained.

Electrical Properties of Modified Aromatic Polyamide Membranes

The effects of chemical structure on the values of different electrical parameters measured with novel aromatic polyamide (aramid) membranes were studied. Poly-(isophthalamides) containing pendant groups were considered since they can be transformed into dense membranes, suitable for the determination of characteristic transport parameters such as ion transport numbers, electrical resistances and capacitances. Measurements were carried out with the membranes in contact with different NaCl and MgCl2 solutions. Results show that resistance values are strongly dependent on concentration, but membrane capacitance is almost constant for the whole range of concentrations studied (10−3 < C(N) < 5 × 102). The ionic permeabilities in the membrane were determined from membrane potential and resistance results. The presence of polar side substituents causes lower resistivity in modified polyamides compared with the unsubstituted parent, and the higher the polarity of the substitutent, the lower the resistivity. This trend is valid for both NaCl and MgCl2 solutions.

Role of membrane surface morphology in colloidal fouling of cellulose acetate and composite aromatic polyamide reverse osmosis membranes

Laboratory-scale colloidal fouling tests, comparing the fouling behavior of cellulose acetate and aromatic polyamide thin-film composite reverse osmosis (RO) membranes, are reported. Fouling of both membranes was studied at identical initial permeation rates so that the effect of the transverse hydrodynamic force (permeation drag) on the fouling of both membranes is comparable. Results showed a significantly higher fouling rate for the thin-film composite membranes compared to that for the cellulose acetate membranes. Addition of an anionic surfactant (sodium dodecyl sulfate, SDS) to mask variations in chemical and electrokinetic surface characteristics of the cellulose acetate and aromatic polyamide membranes resulted in only a small change in the fouling behavior. The higher fouling rate for the thin-film composite membranes is attributed to surface roughness which is inherent in interfacially polymerized aromatic polyamide composite membranes. AFM and SEM images of the two membrane surfaces strongly support this conclusion. These surface images reveal that the thin-film composite membrane exhibits large-scale surface roughness of ridge-and-valley structure, while the cellulose acetate membrane surface is relatively smooth.

Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes. II. Pervaporation performances for ethanol/water mixture

Pervaporation of ethanol/water mixtures through symmetric dense aromatic polyamide membranes was investigated. The membrane structure was controlled by varying the solvent evaporation time before gelation. The membranes were water-selective and the selectivity increased with an increase in the solvent evaporation time. On the other hand, the water flux as well as the ethanol flux decreased with an increase in the evaporation time. These results were consistent with the morphology change of the membrane which takes place with solvent evaporation : the decrease in the channel size. The effects of the downstream pressure on the pervaporation performances were also studied for membranes with different solvent evaporation times. The ethanol concentration in the permeate side increased with an increase in the downstream pressure to certain point, showed a maximum there, then decreased thereafter. The water flux decreased with an increase in the downstream pressure for all membranes studied ; the dependence was expressed by a parabolic curve in the lower pressure range. The ethanol flux also decreased with an increase in the downstream pressure for the membrane with shorter evaporation time, while this flux was slightly affected by the downstream pressure for the membrane with longer evaporation time.

Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes. II. Pervaporation performances for ethanol/water mixture

Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes. II. Pervaporation performances for ethanol/water mixture

The influence of intermolecular interactions on the selectivity of several organic acids in aqueous multicomponent systems during reverse osmosis

This work investigates the extent to which the rejection of a target substance is influenced by the addition of other substances. The alteration effects on the permeation of acetic acid through a aromatic polyamide membrane when combined with one of 27 further organic acids was studied. The operating conditions were kept constant during all investigations. It was found that the retention of a target substance was dependant on the other compounds in particular aromatics and short-chained monocarboxylic and dicarboxylic acids. Acids which significant influenced acetic acid retention were additionally combined with other target substances, formic and propionic acid. The results showed that, in general, it is only possible to increase the direction of the target substances rejection, a higher rejection can only be increased, a lower rejection can only be decreased. These results were used to create and investigate quaternary solutions which showed that, in principle, it is possible to intensify the increasing effect of retention. Using the experiment data it should be possible to determine the separation capacity by concentration complex mixtures through reverse osmosis (RO).

95/05831 Gas separation by silicone-coated dry asymmetric aromatic polyamide membranes

95/05831 Gas separation by silicone-coated dry asymmetric aromatic polyamide membranes

Effect of evaporation time on the pervaporation characteristics through homogeneous aromatic polyamide membranes. I. Pure water permeation and membrane characterization by sorption measurements

AbstractThe pervaporation of pure water through homogeneous aromatic polyamide membranes was investigated. The structure of the prepared membranes was controlled by varying the solvent evaporation times before the gelation step from 5 min to 240 min. The permeation flux of pure water decreased rapidly when the solvent evaporation time increased from 5 min to 30 min, and the decrease was rather moderate at higher evaporation times. Vapor and liquid sorption measurements were used to characterize the membranes. The amount of vapor sorption at a given relative pressure increased with an increase in the solvent evaporation time. The specific surface area of the membranes, calculated from the vapor sorption isotherm, increased with evaporation time up to 30 min, and remained constant thereafter. Liquid sorption volume, on the other hand, decreased monotonically with an increase in evaporation time. The formation of channels in the membrane is used to explain the morphology change during the solvent evaporation. The increase in the solvent evaporation time gradually increases the number of the channels in the membrane and decreases their average size. Good correlation was observed between the average size of the channels (represented by the ratio of specific volume to the specific surface area) and the parameters associated with pervaporation transport. © 1995 John Wiley &amp; Sons, Inc.