Cellulose Acetate Nanofiltration Membranes Research Articles

Separation of Biobased Carboxylic Acids by Aqueous Phase Nanofiltration

AbstractNanofiltration is an energy efficient separation technology with yet not fully explored potential for in situ product recovery from fermentation solutions. In this work, a commercially available cellulose acetate nanofiltration membrane was investigated to separate different carboxylic acids from glucose in an aqueous solution. The membrane showed a high stability and good separation performance at low pH. Dead‐end and cross‐flow experiments revealed the transferability to real fermentation mixtures and demonstrate the possibility of coupling fermentation with in situ product separation.

Facile Preparation of Positively Charged and Solvent‐Resistant Cellulose Acetate/LSCF Nanofiltration Membranes

AbstractPositively charged nanofiltration membranes often exhibit excellent antibacterial and antifouling properties. Nanofiltration membranes with high solvent resistance also find special applications in industrial waste water separation. Cellulose acetate is used to prepare various separation membranes due to its comprehensive performance. LSCF (La0.6Sr0.4Co0.2Fe0.8O3), a kind of cathode and electrolyte material, shows good conductivity in water solution. The nanosized hydrophilic inorganic additive LSCF is added to the casting solution to improve the performance of cellulose acetate nanofiltration membranes. After reaction with glutaraldehyde and trichloro dihydroxypropyl trimethylammonium chloride (TTAC), the prepared membrane demonstrates positively charged characteristics and excellent solvent resistance.

Cellulose Acetate Membrane with Improved Perm-selectivity through Modification Dope Composition and Solvent Evaporation for Water Softening

Membrane technology has been developed because applicated on several fields. Hence, in this study carried the production of cellulose acetate nano-filtration membranes for water softening. The main objective of this study was determined the effect of solvent evaporation time and the effect of adding PEG to the morphology and perm-selectivity of asymmetry membrane for water treatment. Membranes prepared by dry/wet phase inversion method with variation of solvent evaporation time of 10-15 sec and addition of 2.5-5 wt% PEG in the dope solution. Membrane characterization consists of calculation of membrane flux and rejection with brackish water as a feed, SEM and FTIR analysis. The research concluded that asymmetric cellulose acetate membrane can be made by dry/wet phase inversion method. The results of FTIR analysis showed the larger absorption peaks indicates that the increasing concentrations of PEG addition make the PEG molecular weight and the unit re-CH2-CH2O-greater. The results of SEM analysis exhibited that all the membranes are formed has an asymmetric structure consisting of a thin fine porous structure selective barrier and sub-structure of the porous layer is thicker. Moreover, the addition of PEG, the larger pore of membrane will be formed. Performance optimum membrane was obtained on the composition of 23 wt% cellulose acetate, polyethylene-glycol 5 wt%, 72 wt% acetone and 1 wt% of distilled water in the solvent evaporation time of 25 sec and temperature coagulant at room temperature. Characterization of the optimum membrane were flux 22.33 L/m2/h/bar, 92% rejection for turbidity, rejection for dissolved solids 85 and 81% rejection for ions Ca2+, with modulus young around 12433 N/cm2, respectively.

Study of the Effect of Nanoparticles and Surface Morphology on Reverse Osmosis and Nanofiltration Membrane Productivity

To evaluate the significance of reverse osmosis (RO) and nanofiltration (NF) surface morphology on membrane performance, productivity experiments were conducted using flat-sheet membranes and three different nanoparticles, which included SiO2, TiO2 and CeO2. In this study, the productivity rate was markedly influenced by membrane surface morphology. Atomic force microscopy (AFM) analysis of membrane surfaces revealed that the higher productivity decline rates associated with polyamide RO membranes as compared to that of a cellulose acetate NF membrane was due to the inherent ridge-and-valley morphology of the active layer. The unique polyamide active layer morphology was directly related to the surface roughness, and was found to contribute to particle accumulation in the valleys causing a higher flux decline than in smoother membranes. Extended RO productivity experiments using laboratory grade water and diluted pretreated seawater were conducted to compare the effect that different nanoparticles had on membrane active layers. Membrane flux decline was not affected by particle type when the feed water was laboratory grade water. On the other hand, membrane productivity was affected by particle type when pretreated diluted seawater served as feed water. It was found that CeO2 addition resulted in the least observable flux decline, followed by SiO2 and TiO2. A productivity simulation was conducted by fitting the monitored flux data into a cake growth rate model, where the model was modified using a finite difference method to incorporate surface thickness variation into the analysis. The ratio of cake growth term (k1) and particle back diffusion term (k2) was compared in between different RO and NF membranes. Results indicated that k2 was less significant for surfaces that exhibited a higher roughness. It was concluded that the valley areas of thin-film membrane surfaces have the ability to capture particles, limiting particle back diffusion.

Effect of fatty acids on the structure and performance of cellulose acetate nanofiltration membranes in retention of nitroaromatic pesticides

Effects of addition of amphiphilic fatty acids (palmitic, oleic, and linoleic acids) were investigated on morphology and performance of cellulose acetate (CA) nanofiltration membranes. Water contact angle and zeta potential measurements, FTIR-ATR, SEM, AFM, and mechanical tests were applied to characterize the membranes. Performance of the membranes was examined in retention of a series of nitroaromatic pesticides (i.e. nitrophenols as one of the most important pollutants). p-Nitrophenol (PNP), 2,4-dinitrophenol (DNP), 3,5-dinitrosalicylic acid (DNSA), 2-methyl-4,6-dinitrophenol (DNOC), and 4-nitrophenyl phosphate disodium salt hexahydrate (NPP) were selected with different acidity and hydrophobicity as nitroaromatic pesticides. The treated membranes revealed considerably higher pure water flux and permeation compared to CA membrane. Performance of separation was strongly influenced by kind of nitrophenols and solution pH. Rejection of NPP, DNSA, DNP, and DNOC increased by increasing of the solution pH and additives concentration. However, rejection of PNP molecules increased by increment of concentration of additives similar to other nitrophenols, PNP molecules revealed different behavior by alteration in the solution pH. Comparison in efficiency showed that modified membranes upon addition of palmitic acid represent higher rejection of nitrophenols. Performance of the membranes was compared with commercial NF45 membrane proving the superior efficiency of CA modified membranes.

Optimization of cellulose acetate nanofiltration membranes for micropollutant removal via genetic algorithms and high throughput experimentation

Nanofiltration (NF) and reverse osmosis (RO) membranes have a high potential to remove low molecular weight trace contaminants in water that cannot be removed efficiently by conventional biological or physico-chemical treatments. However, membrane performance depends on several parameters involved in membrane synthesis. Multi-parameter optimization strategies, such as genetic algorithms (GAs) are extremely promising to minimize time and material consumption to direct membrane synthesis towards better separation properties (selectivity) of the targeted compounds combined with useful fluxes. Cellulose acetate membranes were prepared via phase inversion. The optimized parameters included compositional (polymer concentration, solvent) and also, for first time when using GA as optimization strategy in membrane synthesis, non-compositional on the level of the membrane synthesis process and post treatment (temperature, annealing time), which have a great impact on membrane performance. Dead-end filtrations were carried out to evaluate the membranes in their potential to retain ibuprofen in water by using high-throughput (HT) experimentation. Ibuprofen was selected as it is one of the smallest molecules among relevant micropollutants present in drinking water. As result, membranes with ibuprofen retention up to 96% and permeabilities in the normal range of cellulose acetate (CA)-based RO membranes were obtained. Thus prepared membranes also showed promising NaCl retention and twice the permeability compared to membranes prepared via a classical parameter-by-parameter optimization.

Effect of LbL surface modification on characteristics and performances of cellulose acetate nanofiltration membranes

Homemade Cellulose Acetate nanofiltration membranes elaborated by phase inversion were surface modified by adsorption of alternated layers of sodium alginate (ALG) and chitosan (CHI). The membranes were characterised by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive X-ray analysis (EDX) and by contact angle measurements. Separation performances of the prepared membranes are studied with 2 g/L synthetic aqueous solutions in frontal mode, under 15 bar pressure. Morphological characterization showed a formation of a lamellar structure till 15 bilayers followed by a transition to a granular structure. We observed an increase in water and salt fluxes till 20 bilayers. More adsorbed bilayers decrease fluxes. Retention rates of monovalent salts decrease and remain constant by reaching 15 bilayers. However, we observed a constant increase in the retention rate for salts containing divalent ions. Contact angle values showed a decrease till 15 bilayers followed by an increase till 30 bilayers. The correlation of the morphological characterization, contact angle measurements and the separation performances allowed as a better understanding of all the results. The layer-by-layer surface treatment makes CA membranes less sensitive to protein fouling with 15 adsorbed bilayers.

Experimental study on the rejection of salt and dye with cellulose acetate nanofiltration membrane

In this study, the rejections of dye, salt, and dye intermediate by a cellulose acetate (CA) nanofiltration membrane were investigated. The rejections of sodium chloride and sodium sulfate were moderate and declined with the increase of concentration. The rejection of five reactive dyes by a CA nanofiltration membrane was higher than 99.0% at low concentration, and high rejection of five reactive dyes was still achievable at higher dye concentration. However, the rejections of five dye intermediates varied from low to moderate when the molecular weight increased. In the C.I. Reactive Black 5 diafiltration and concentration process, the concentration and constant volume diafiltration mode had a better desalting degree than the constant volume diafiltration and concentration mode. However, the constant volume diafiltration and concentration mode is necessary for C.I. Reactive Blue 13 solution due to its low solubility. This study illustrates that nanofiltration is a promising process for dye desalting and concentrating.

A submerged nanofiltration membrane bioreactor for domestic wastewater treatment: the performance of cellulose acetate nanofiltration membranes for long-term operation

A submerged nanofiltration membrane bioreactor (NF MBR) using cellulose acetate membranes was operated for 240 days to examine the performance of the NF membrane in domestic wastewater treatment. For the first 130 days, dissolved organic carbon (DOC) concentration in the permeates ranged from 0.5 to 2.0 mg/L. The rejection rates of monovalent and divalent ions by the NF membranes varied between 40 and 60% and between 70 and 90%, respectively, for the initial 80 days. The permeate flux increased gradually with decreasing transmembrane pressure (TMP) during the operation. The results of MW distribution and fractionation of dissolved organic matter in the waters demonstrated the increase in membrane pore size and decrease in membrane hydrophobicity over operating time. From the results, the degradation of each water-quality parameter over operation time might be attributed to the qualitative deterioration of the NF membrane caused by the hydrolysis of cellulose acetate, which leads to an increase in pore size and porosity, and decrease in surface charge and hydrophobicity of cellulose acetate membranes.

Surface modification of nanofiltration membranes by ion implantation

This study involves modifying the surface of nanofiltration (NF) membranes by ion implantation for increased salt rejection. F − ions were implanted on the surface of commercially available nanofiltration membranes to increase the negativity of the membrane surfaces. The objective was to increase the Donnan exclusion effect and thus increasing the salt rejection by the modified membranes. A composite polyamide NF membrane (NF 90 Filmtec) and a cellulose acetate NF membrane (SP 28 Osmonics) were implanted with F − ions at two different intensities—1E10 and 5E10 atoms/cm 2. Zeta potential measurements of the unmodified membranes and modified membranes show higher negativity with an increased intensity of ion implantation. Multicomponent salt permeation experiments were performed with the three types of membranes—the unmodified membrane and the two types of modified ones for both NF 90 and SP 28. The results show a decrease of solute flux for all the ions through the modified membranes when compared to that with the unmodified membrane. Initial experiments show no leaching of F − ions into the solution. Therefore, ion implantation on nanofiltration membrane surfaces is a novel technique to increase the salt rejection property of membranes.

Properties of cellulose acetate nanofiltration membranes. Application to brackish water desalination

In this work, we report about cellulose acetate nanofiltration (NF) membrane preparation according to the phase inversion process. Pore size was monitored by using dope solutions of two polymer concentrations (20 and 22 wt−%) and annealing temperatures from 60–80°C. Membrane characterization included a morphologic analysis using scanning electron microscopy (SEM) and hydraulic permeability ( L p 0) determined from pure water filtration. SEM cross-section micrographs exhibited the expected asymmetric structure with more opened sub-layer morphology for nanofilters prepared using the lower annealing temperatures. The L p 0 values indicative of the pore size increased by decreasing the polymer concentration in dope solutions and the temperature during the annealing operation. Desalting efficiency of the obtained nanofilters was first evaluated through the filtration of synthetic solutions containing 500–2000 ppm of NaCl using a dead end process. The variation of salt rejection vs. the permeation rate allowed us to determine the operating conditions corresponding to the optimal material performances as shown by the plateau related to limit rejection. Desalination experiments for two Tunisian brackish waters with a salt content between 3500 and 4000 ppm were carried out under a transmembrane pressure of 16 bar. Annealed membranes at 75 and 80°C showed the better performances.

Characterization and identification of rejection mechanisms in nanofiltration membranes using extended Nernst–Planck model

Nanofiltration (NF) membranes have found increasing applications especially in water and wastewater treatment. In order to predict and optimize the performance of NF membranes, the membranes need to be characterized properly in terms of their structural parameters such as pore radius (r p) and effective thickness (Δx/A k) as well as the effective charge density (X d). In this work, three cellulose acetate NF membranes were fabricated to different properties and were characterized using a model based on the extended Nernst–Planck equation. The results show that the variations of r p, Δx/A k and X d are quite distinct between the three membranes. The membranes were found to have r p>1.2 nm and high X d. Thus the rejection mechanism depends very much on the Donnan effect rather than the steric effect. The high rejection of several negatively charged organics and salts confirmed this finding. Apart from being effective, this method of characterization offers a cheaper alternative in understanding NF membranes.

Effect of hydrodynamic conditions on fractionation of β-lactoglobulin tryptic peptides using nanofiltration membranes

Fractionation of a β-lactoglobulin (β-LG) peptide mixture by nanofiltration (NF) membranes was investigated. Peptide mixture was prepared by tryptic hydrolysis of commercial β-LG followed by ultrafiltration (UF) for enzyme removal. The peptide mixture (permeate) was further fractionated using an Osmonics-SG13 cellulose acetate NF membrane with a molecular weight cut-off (MWCO) of 2500 g mol −1. The effect of hydrodynamic parameters on a “resistance-in-series” model and transmission of tracer peptides was studied at 0.5 wt.% hydrolysate concentration by varying the operating pressure (0.200 and 0.500 MPa), recirculation rate (0.17 and 0.29 m s −1), and recirculation time (30 and 120 min). A detailed comparison on individual peptide transmission revealed that increasing recirculation time to 120 min, at lower recirculation rates, greatly affected peptides β-LG 102–105 and β-LG 142–148 at both operating pressures. Our results are indicative of important changes in NF selectivity as affected by hydrodynamic conditions and recirculation time via possible peptide–peptide interactions occurring in the so-called weakly attached layer.

A novel application of a submerged nanofiltration membrane bioreactor (NF MBR) for wastewater treatment

Nanofiltration (NF) membrane technology has made rapid progress and then extended its application fields. It has obtained in particular the good results in the removal of organic and inorganic matters or microbes in the water and wastewater. To investigate the applicability and characteristics of NF membrane, the membrane bioreactor (MBR) using the cellulose acetate NF membrane was performed to treat synthetic wastewater. A hollow-fiber-type cellulose acetate membrane was chosen to get enough water productivity regardless of its biodegradability. As a result of the experiments, enough water productivity was obtained for 60 days without fatal fouling and membrane cleaning. This raised the applicability of cellulose acetate membrane to the MBR system. Electrolytes were not accumulated in the bioreactor, as its rejection was also low. This enabled the NF MBR to be operated under a low suction pressure and prevented from inhibition against microorganisms, whose activity might be deteriorated by high salt concentration. Nitrification and denitrification happened simultaneously and this might be achieved by the module configuration. The phosphorus was not removed with the loose NF membrane. According to AFM investigation, the cellulose acetate membrane after 71 days has larger voids because of the biodegradation.