Cellulose Acetate Reverse Osmosis Membranes Research Articles

Improving water desalination: Sustainable grafted cellulose acetate reverse osmosis membrane from Egyptian cotton

AbstractCellulose diacetate (CDA) and triacetate (CTA) were derived from Egyptian cotton to fabricate reverse osmosis (RO) membranes. The Pphase inversion method was utilized for the production of CDA‐based membranes. Comprehensive characterization of these membranes involved structural, morphologial, and hydrophilic property analyses through techniques such as nuclear magnetic resonance (NMR), infrared spectroscopy, thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements. NMR spectra indicated a degree of substitution of 2.9 for CTA and 2 for CDA. The resulting RO membrane demonstrated a water flux of 6.1 L/m2·h and a salt rejection of 90.3%. Annealing led to an enhanced top layer with reduced defects and macrovoids in the support layer. Moreover, grafting the RO membranes with 15 wt% of 2‐acrylamidopropane‐2‐methyl sulphonic acid improved salt rejection to 96.2% and water flux to 8.7 L/m2.h. These findings underscore the significant performance enhancements achieved through both annealing and grafting processes in RO membranes.

Improved anti-biofouling resistances using novel nanocelluloses/cellulose acetate extracted from rice straw based membranes for water desalination

Cellulose and Nanocellulose acetate (NCA) have attractive novel properties like excellent mechanical properties, rich hydroxyl groups for modification, and natural properties with environmental friendliness. Cellulose was extracted from rice straw wastes as an extra value, then it had been further transformed into NCA using the acidic hydrolysis technique. The structural, crystalline, morphological, were characterized by Fourier transform infrared spectroscopy (FTIR), Proton nuclear magnetic resonance (1HNMR), X-ray diffraction (XRD), Scanning microscopy, respectively. The particle size of the Nanocellulose extracted from rice straw was about 22 nm with a spherical shape. Development membranes were prepared with different concentrations of NCA to improve the performance and the anti-biofouling properties of cellulose acetate reverse osmosis (RO) membranes using a phase inversion technique. The structural of membranes were characterized by FTIR, water contact angle measurements, while the anti-biofouling properties were studied by static protein adsorption. The results indicated the development membrane features a lower contact angle accomplished with exhibits pore-forming ability and enhanced hydrophilicity of prepared membrane, furthermore the development cellulose acetate reverse osmosis (CA-RO) membranes with 40:60% RNCA:CA produced a salt rejection of 97.4% and a water flux of 2.2 L/m2 h. the development membrane have resists effectively protein adsorption and microbial growth showed from the results of Static protein adsorption.

Roles of Sulfites in Reverse Osmosis (RO) Plants and Adverse Effects in RO Operation.

More than 60 years have passed since UCLA first announced the development of an innovative asymmetric cellulose acetate reverse osmosis (RO) membrane in 1960. This innovation opened a gate to use RO for commercial use. RO is now ubiquitous in water treatment and has been used for various applications, including seawater desalination, municipal water treatment, wastewater reuse, ultra-pure water (UPW) production, and industrial process waters, etc. RO is a highly integrated system consisting of a series of unit processes: (1) intake system, (2) pretreatment, (3) RO system, (4) post-treatment, and (5) effluent treatment and discharge system. In each step, a variety of chemicals are used. Among those, sulfites (sodium bisulfite and sodium metabisulfite) have played significant roles in RO, such as dechlorination, preservatives, shock treatment, and sanitization, etc. Sulfites especially became necessary as dechlorinating agents because polyamide hollow-fiber and aromatic thin-film composite RO membranes developed in the late 1960s and 1970s were less tolerable with residual chlorine. In this review, key applications of sulfites are explained in detail. Furthermore, as it is reported that sulfites have some adverse effects on RO membranes and processes, such phenomena will be clarified. In particular, the following two are significant concerns using sulfites: RO membrane oxidation catalyzed by heavy metals and a trigger of biofouling. This review sheds light on the mechanism of membrane oxidation and triggering biofouling by sulfites. Some countermeasures are also introduced to alleviate such problems.

Novel Grafted/Crosslinked Cellulose Acetate Membrane with N-isopropylacrylamide/N,N-methylenebisacrylamide for Water Desalination

This work aims to prepare new types of grafted and crosslinked cellulose acetate (CA) reverse osmosis (RO) membranes by phase inversion technique. The grafting and/or crosslinking processes of the pristine CA-RO membrane were conducted using N-isopropylacrylamide (N-IPAAm) and N,N-methylene bisacrylamide (MBAAm), respectively. The grafting/crosslinking mechanism onto the CA-RO membrane surface was proposed. Atomic force microscope (AFM) images of the pure CA-RO and 0.1 wt% N-IPAAm-grafted CA-RO membranes revealed that the surface roughness was 42.99 nm and 11.6 nm, respectively. Scanning electron microscopy (SEM) images of the 0.1 wt% grafted/crosslinked membrane indicated the finger-like macrovoids structure. It was observed that the contact angle of the pristine CA-RO membrane was 66.28° and declined to 49.7° for 0.1 wt % N-IPAAm-grafted CA-RO membrane. The salt rejection of the pristine CA-RO membrane was 93.7% and increased to 98.9% for the grafted 0.1 wt % N-IPAAm/CA-RO membrane. The optimum grafted/crosslinked composition was 0.1 wt %/ 0.013 wt % which produced the salt rejection and water flux of 94% and 3.2 L/m2h at low pressure, respectively. It was concluded that both the grafting and crosslinking processes enhanced the performance of the CA-RO membranes.

Anti-biofouling of 2-acrylamido-2-methylpropane sulfonic acid grafted cellulose acetate membranes used for water desalination

Cellulose acetate based membranes are used for water desalination. Cellulose diacetate (CDA) was prepared from cellulose powder. Reverse osmosis (RO) membranes were prepared on polyester sheets using CDA based through phase inversion technique. The structural, morphological and hydrophilic properties of the prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and contact angle measurements. The FTIR and NMR revealed the presence of the carbonyl groups and degree of substitution (DS) in CDA. Modified membranes by Grafted to improve the performance and the anti-biofouling properties of cellulose acetate reverse osmosis (RO) membranes. The anti-biofouling properties were studied by measurements of static protein adsorption. The effect of grafting the membrane on the salt rejection and water flux was studied using a cross flow RO unit. The results indicated that 15 wt% of 2-acrylamido-2-methylpropanesulfonic acid (AMPS)Grafted membranes have lower adsorption of protein and microbes, in addition to increased salt rejection to 99.24 % and water flux to 17.12 l/m2 h.

Cellulose Acetate Reverse Osmosis Membranes for Desalination: A Short Review

Freshwater scarcity is a critical challenge that human society has to face in the 21st century. Desalination of seawater by reverse osmosis (RO) membranes was regarded as the most promising technology to overcome the challenge given that plenty of potential fresh water resources in oceans. However, the requirements for high desalination efficiency in terms of permeation flux and rejection rate become the bottle-neck which needs to be broken down by developing novel RO membranes with new structure and composition. Cellulose acetate RO membranes exhibited long durability, chlorine resistance, and outstanding desalination efficiency that are worthy of being recalled to address the current shortcomings brought by polyamide RO membranes. In terms of performance enhancement, it is also important to use new ideas and to develop new strategies to modify cellulose acetate RO membranes in response to those complex challenges. Therefore, we focused on the state of the art cellulose acetate RO membranes and discussed the strategies on membrane structural manipulation adjusted by either phase separation or additives, which offered anti-fouling, anti-bacterial, anti-chlorine, durability, and thermo-mechanical properties to the modified membranes associated with the desalination performance, i.e., permeation flux and rejection rate. The relationship between membrane structure and desalination efficiency was investigated and established to guide the development of cellulose acetate RO membranes for desalination.

Synthesis, characterization and excellent antibacterial property of cellulose acetate reverse osmosis membrane via a two-step reaction

In order to improve the antibacterial efficiency and spectrum of cellulose acetate reverse osmosis membrane (CA–RO), both quaternary ammonium and bromoacetyl groups were introduced into cellulose diacetate under mild conditions forming CA–RO with bi-antibacterial groups for seawater desalination. Bromoacetyl bromide and a series of tertiary amine were chosen as the modification agents respectively. The characterization results showed that both two antibacterial groups were successfully introduced with a certain density. The obtaining membrane had a less hydrophilic but more electronegative surface as well as improved mechanical property. The flux values increased firstly and decreased subsequently after twice modifications while the salt rejection rose. The membrane modified with N,N-dimethyloctylamine (DMOA) had the optimal comprehensive performance of flux and salt rejection. The antibacterial testing results indicated that the resulting RO membranes showed high antibacterial efficiency and broad-spectrum. Their bactericidal rates against gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) were more than 99.9%.

Synthesis, characterization and antibacterial properties of reverse osmosis membranes from cellulose bromoacetate

The antibacterial alkyl bromide groups were introduced into cellulose diacetate (CDA) through the esterification between highly active bromoacetyl bromide and hydroxyl groups under mild conditions and the modified cellulose acetate reverse osmosis membrane (Br-CA-RO) was obtained subsequently after phase inversion process. The results of FTIR and 1H-NMR indicated the existence of alkyl bromide groups in the modified CDA powder. The optical density method was used to confirm its antibacterial ability. The chemical structure and morphology characterization demonstrated that the anchoring of bromoacetyl groups as antibacterial part brought out minimal alteration on membrane chemical structure and its asymmetric structure, but the regularity and density of membranes increased with the degree of esterification. The property testing results showed that the whole physical performance was enhanced with the thermal stability getting slightly worse. Both the flux and salt rejection of Br-CA-RO increased after modification and the latter was close to that of cellulose triacetate RO membrane. The dynamic contact antibacterial testing implied that Br-CA-RO showed much higher antibacterial ability than unmodified RO membranes, and its relative bactericidal rates against E. coli (gram negative) and S. aureus (gram positive) were higher than 73.0% and 93.5%, respectively. This method offers a new approach for antibacterial and functional modification of CA-RO membranes.

Reverse osmosis purification: A case study of the Niger Delta region

The Niger Delta region of Nigeria is faced with the problem of drinking water supply. Different methods of water purification were compared and reverse osmosis was considered a choice method for the experiment. Among the region’s brackish water reserves with heavy metal contamination, nickel and cobalt were considered. Model solutions of nickel and cobalt were prepared to mimic the brackish water contamination levels and were purified with cellulose acetate reverse osmosis membrane. Experimental results showed that purifications were more dependent on the overall salt concentrations and not on individual components.

Polymeric Hollow Fibers: State of the Art Review of Their Preparation, Characterization and Applications in Different Research Areas

In this article an attempt is made to review critically the papers published recently on polymeric hollow fibers and hollow fiber membranes. Hollow fiber membranes emerged in early nineteen sixties at almost the same time as the announcement of the cellulose acetate reverse osmosis membrane for seawater desalination by Loeb and Sourirajan. Since then, the hollow fiber technology has progressed along with the industrial membrane separation processes. Today, hollow fiber membranes are being used in every sector of the manufacturing industry, including gas and vapor separation, seawater desalination and waste water treatment. The fabrication of a hollow fiber membrane with a desirable pore–size distribution and performance is not an easy task. There are many factors controlling fiber morphology during the phase inversion process and, at present, we are not able to say that we fully understand the phenomena involved in the fabrication of hollow fibers. Nevertheless, there has been a large amount of knowledge accumulated during the past fifteen years, which has been supported by an equally large amount of efforts by many researchers. This paper attempts to summarize those works. The authors could however look into only those reports which have appeared in scientific journals and few patents, and they are fully aware that there must be much more information that has not surfaced to the journal publication. It is also the authors’ intention to show the future direction including the research topics that have been studied only little or not at all.

Determination of the osmotic pressure of multicomponent solutions in the food industry

This paper is dedicated to the determination of the osmotic pressure of multicomponent solutions using aqueous food substances such as fruit and vegetable juices, whey, and lactose as examples. The determination of osmotic pressure as a critical parameter responsible for the efficiency of the membrane separation of multicomponent aqueous mineral-organic solutions is a problem of considerable current interest. An original method for the determination of the osmotic pressure of complex solutions has been developed. A relationship between the osmotic pressures of fruit and vegetable juices and whey and the concentration of lowmolecular-weight solutes (sugars and salt ions) in them has been revealed. A laboratory system for studying the reverse osmosis process has been developed. Experiments with fresh fruit and vegetable juices, curd whey, cheese whey, and lactose were carried out by a dynamic method with the use of a cellulose acetate reverse osmosis membrane with an asymmetric structure. The characteristics of the initial and final products after ultrafiltration are given. Based on the experimental data, the dependence of the osmotic pressure of fruit and vegetable juices, whey, and lactose on the concentration of dry solutes was plotted. The experimental results are discussed.

Multiobjective Optimization Applied to the Integration of Polyamide and Cellulose Acetate Reverse Osmosis Membranes in Hybrid Cascades for Ultrapurification of Wet Chemicals

The present work is focused on three main aims. The first one is the comparison of commercial polyamide (BE from Woongjin Chemical) and cellulose acetate (CE from GE Osmonics) reverse osmosis membranes when applied to the ultrapurification of aqueous hydrogen peroxide solutions. The second one is the search for possible advantages of combination of both types of membranes, which show quite different characteristics, under a hybrid cascade configuration. The results demonstrated that the employment of only polyamide membrane cascades is more competitive than hybrid systems for this application. The third one is the analysis of the influence of the product quality over the optimal economic cascades. The polyamide membrane systems were then formulated adding product quality metrics to economic criteria to afford a bicriteria nonlinear programming (NLP) problem. The Pareto solutions to the multiobjective problem were generated via the epsilon constraint method. On the one hand, maximum economic profit solutions corresponded with the configurations applying bypass. On the other hand, maximum quality solutions were obtained by low recovery rates (specifically in the last stages of the cascade).

Surface modification of commercial cellulose acetate membranes using surface-initiated polymerization of 2-hydroxyethyl methacrylate to improve membrane surface biofouling resistance

To improve biofouling resistance, cellulose acetate (CA) reverse osmosis membranes were modified by reacting surface hydroxyl groups with an atom transfer radical polymerization (ATRP) initiator, 2-bromoisobutyryl bromide, followed by polymeric grafting of 2-hydroxyethyl methacrylate (pHEMA) using activators regenerated by electron transfer (ARGET) ATRP. Thermogravimetric analysis (TGA), atomic force microscopy (AFM) and water contact angle (WCA) measurements of pristine and modified membranes were performed to measure and compare the amount of polymer deposited, the surface morphology and the hydrophilicity of the surfaces, respectively. Roughness and hydrophilicity increased with graft density. The biofouling resistance of pHEMA-modified membranes immersed in seawater aquarium tanks was compared to pristine membranes and the effect of pHEMA coating on water flux and NaCl rejection was measured. Based on stirred-cell and aquaria experiments, pHEMA-modified membranes with low graft density showed just a 6% decrease in salt rejection and water flux relative to pristine CA membranes, and a 24% improvement in resistance to seawater microbial biofouling.

Cellulose Acetate Reverse Osmosis Membranes Made by Phase Inversion Method: Effects of a Shear Treatment Applied to the Casting Solution on the Membrane Structure and Performance

A mixture of equal parts of cellulose diacetate and cellulose triacetate was dissolved in dipropylene glycol and exposed to shear stresses of varying intensity on a three-roll calander. Asymmetric reverse osmosis membranes were prepared from these materials by the phase-inversion method. Reverse osmosis tests in a dead-end module provided membrane performance data. A structure analysis was performed by scanning electron microscopy and the microstructure of the membranes was investigated by differential scanning calorimetry and X-ray diffraction. It was observed that increasing shear times as well as shear rates reduced the salt rejection while the permeate flux was escalating. The size-exclusion chromatography analysis showed a strong decrease of M w and M z at a constant M n indicating the degradation of the higher molar mass macromolecules. Since the physical structure of the membranes was not affected and a change in polymorphism could not be related to the variations in the reverse osmosis performance the reduced salt rejection should be caused by this degradation process, supposedly through affecting the material's diffusion properties by changing the fractional free volume.

Influence to the performance of cellulose acetate reverse osmosis membranes by fibers addition

AbstractThe asymmetric membranes based on cellulose acetate are mainly applied for separations in aqueous systems and in reverse osmosis processes, although they can also be used in the so‐called salinity process of energy generation. These applications require membranes with considerable water permeability and high salt rejection. In this paper the improvements resulting from the addition of two different types of fibers on the permeability performance of the membranes (water permeability and salt rejection) as well as on mechanical properties are presented. Concerning the water permeability and salt rejection, the influence of four different contents of cellulosic fibers (CF) and anionic diethylaminoethyl cellulose (DEAE) fibers has been studied and the optimum value was chosen after measuring water permeability and salt rejection of the membranes. To study the mechanical performance, membranes with six different contents of these two types of fibers were produced. Both permeability and mechanical test results obtained for membranes with different contents of fibers were compared with the ones for the membranes produced from the same solution but without fibers. In terms of permeability tests, the membranes with 0.5 wt % CF fibers present the best results, with water permeability 22.8% higher than the membrane without fibers, while the salt rejection only decreases by 7.3%. Concerning the mechanical properties, the best membrane would be the one with 3 wt % CF fibers, however the membrane with 0.5 wt % CF fibers still present a toughness 18.9% higher than the membrane without fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Cellulose acetate reverse osmosis membranes: Optimization of the composition

AbstractMembranes based on cellulose acetate for reverse osmosis can possibly be applied to the so‐called salinity process of energy generation and water desalinization. The requirements for membranes for these two different applications are a relatively high water flux and low salt permeability. In this article, we present the optimization of the composition of such membranes. We started by producing membranes with a patented casting solution with the following composition: 45.77 wt % dioxane, 17.61 wt % acetone, and 8.45 wt % acetic acid (solvents); 14.09 wt % methanol (nonsolvent); and 7.04 wt % cellulose diacetate and 7.04 wt % cellulose triacetate. The membranes produced with this solution were analyzed comparatively, with the membranes obtained by the introduction of modifications to the following parameters: the solvent mix, the nonsolvent mix, the proportion of cellulose diacetate and cellulose triacetate in the casting solution, and the addition of reinforcing cellulose fibers. The results led us to conclude that the best membrane formulation had the following composition: 45.77 wt % dioxane, 17.61 wt % acetone, and 8.45 wt % acetic acid (solvents); 4.22 wt % cellulose triacetate and 9.86 wt % cellulose diacetate (polymers); 14.09 wt % methanol (nonsolvent); and 0.5 wt % cellulose fibers (with respect to the total polymer content). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4052–4058, 2006

Microbiological damage of cellulose acetate RO membranes

Based on the data presented in this study, microorganisms can degrade wet cellulose acetate (CA) reverse osmosis (RO) membranes during shutdown periods or under storage conditions. Fungal (and perhaps bacterial) metabolism of the membranes was measured from CA membranes using the 14 C isotope. Using uniformly labeled 14 C cellulose as the starting compound, CA polymer was synthesized, casting solutions were made, and CA membranes were produced. After inoculating membrane samples with the microorganisms, the metabolism of the membranes was confirmed by measuring isotopically enriched carbon dioxide gas produced either by the respiration under aerobic or anaerobic conditions using the Krebs metabolic cycle or by fermentation. Results show that the dense zone of the asymmetric membrane, where desalting occurs, could be compromised in 3 months or less. Membrane samples that were treated by sanding and hydrolyzing the surface to simulate a “used” membrane, degraded at a faster rate than new membranes. Removing oxygen from the system failed to slow or stop the rate of growth. Data showed that no “special” fungus from the RO industry is unique in degrading CA membrane. Instead, all organisms tested degraded these membranes, including microorganisms found in the biofilms from a field RO system and microorganisms present as laboratory contaminates.

Effect of hydrolysis on porosity of cellulose acetate reverse osmosis membranes

Effect of hydrolysis on porosity of cellulose acetate reverse osmosis membranes

Effect of hydrolysis on porosity of cellulose acetate reverse osmosis membranes

AbstractThe alkaline hydrolysis of asymmetric cellulose acetate membranes was investigated. The changes of cellulose triacetate and cellulose diacetate membrane performances caused by hydrolysis of the membrane material were measured, and the data were analyzed in terms of pore size distributions and effective number of pores in the upper membrane layer before and after hydrolysis. The resulting membranes rejection factors decrease of 10–25%, and a noticeable permeation rates increase were caused by closing of a part of the smallest “network” membrane pores and by increasing the size of the other pores. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1768–1775, 2001

Separation of nutmeg essential oil and dense CO 2 with a cellulose acetate reverse osmosis membrane

The association of membrane separation processes to the supercritical fluid extraction of essential oils from vegetable matrices can be an alternative to the reduction of recompression costs derived from the depressurization step necessary for the recovering of the extracts. In this work, a cellulose acetate reverse osmosis membrane was applied to perform the separation of nutmeg essential oil and dense carbon dioxide. The effects of feed stream essential oil concentration, temperature and transmembrane pressure on essential oil retention and CO 2 permeability were investigated. The average retention of essential oil by the membrane was of 96.4% and it was not affected significantly by any of the process variables. The CO 2 flux was linearly proportional to the transmembrane pressure applied and decreased as the essential oil concentration in the feed stream increased. The membrane presented good CO 2 permeability and resisted well to the severe pressure conditions applied.