Asymmetric Cellulose Acetate Membranes Research Articles

Optimization of the Asymmetric Cellulose Acetate Membrane Synthesis Variables for Porosity and Pure Water Permeation Flux Using Response Surface Methodology: Microfiltration Application

Membranes play a vital role in membrane-based water treatment processes. Thus, improvement in the membrane fabrication stage can greatly affect the overall performance of these technologies. Accordingly, this study focuses on optimizing the fabrication process of a microfiltration cellulose acetate membrane prepared using a pore-templating method. The effects of synthesis variables and their interactions were investigated using face-centered composite design through response surface methodology (RSM). Calcium carbonate (CaCO3) and glycerin concentrations in the casting solution in addition to evaporation time and hydrochloric acid (HCl) bath time were selected as the independent variables, while the membrane porosity and pure water flux were considered as the response variables. Significant increase in both responses was observed by increasing CaCO3 and glycerin concentrations (P value < 0.05). However, the effect of evaporation time was found to be statistically insignificant on both responses. The effect of the HCl bath time was found to significantly affect the membrane porosity but not the pure water flux. RSM models for both responses were statistically evaluated in terms of the coefficient of determination (R2), and the estimated values (96.74% for the porosity model and 83.85% for the flux model) indicated good fit of the model to the experimental values. Multiple response optimization was employed, and the membrane produced at optimum conditions proved to have good agreement with the predicted values (16.2% error in flux and 3.66% error in porosity). The membrane was successfully applied for paint pigment rejection and oil emulsion rejection, and rejection efficiencies of 95.6% and 80% were achieved for color and oil, respectively, confirming the applicability of the membrane produced at the obtained optimum condition for wastewater treatment.

Design Next Generation Membranes or Rethink the “Old” Asymmetric Membranes?

The first integrally-skinned asymmetric cellulose acetate (CA) membrane for water desalination were developed by Loeb and Sourirajan in the early 1960s at UCLA [...]

The ultrafiltration performance of cellulose acetate asymmetric membranes: a new perspective on the correlation with the infrared spectra

Integral asymmetric cellulose acetate (CA) membranes were casted by phase-inversion with formamide varying content - 22, 30 and 34% - as pore promoter. These membranes, CA-22, CA-30 and CA-34, were analyzed by infrared spectroscopy in attenuated total reflection mode (ATR-FTIR) to investigate the porous membrane matrix influence on the polymer/water/solute interactions and the selective ultrafiltration of salts. The membranes covered a wide range of hydraulic permeabilities, from 3.5 to 81.0 kg.m-2.h-1.bar-1, and of molecular weight cut-offs, from 4.17 to 31.43 kDa. The experimental apparent rejection coefficients of neutral solutes of increasing molecular weight are related to their intrinsic rejection coefficients through the film model. The surface average pore radius, estimated by an iterative algorithm, ranges from 2.1 to 4.5 nm. The tighter membrane, CA-22, displays experimental apparent rejection coefficients to the Na2SO4, CaSO4, MgSO4 of 50% or higher values and this is in contrast with the lower values, between 14 and 18%, to the NaCl, CaCl2 and MgCl2 salts. The ATR-FTIR evidences that in the membranes with larger pores, CA-30 and CA-34, the water molecules are organized with a liquid-water-like structure, in which most molecules are hydrogen bonded to four or to two others; nevertheless, a fraction of water molecules is strongly bonded to the CA carbonyl groups. For the CA-22 membrane, there are more free carbonyl groups and a larger fraction of free water, both able to interact with solutes, such as the hydrated sulphate ions. Therefore, this ultrafiltration membrane has the capability of differentiating anionic species.

Preparation of an Asymmetric Membrane from Sugarcane Bagasse Using DMSO as Green Solvent

Asymmetric cellulose acetate membranes have been successfully fabricated by phase inversion, using sugarcane bagasse (SB) as the starting material. SB is a raw material with high potential to produce cellulose derivatives due to its structure and morphology. Cellulose was extracted from SB by pretreatment with solutions of 5 wt% NaOH, 0.5 wt% EDTA; then bleached with 2 wt% H2O2. Cellulose acetate (CA) was prepared by the reaction between extracted cellulose with acetic anhydride, and H2SO4 as a catalyst. The obtained CA exhibited a high degree of substitution (2.81), determined with 1H-NMR spectroscopy and titration. The functional groups and thermal analysis of the extracted cellulose and the synthesized CA have been investigated by Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The change in the crystallinity of the extracted cellulose and CA was evaluated by X-ray diffraction (XRD) spectroscopy. Asymmetric membranes were fabricated using dimethyl sulfoxide (DMSO) as the solvent, with a casting thickness of 250 µm. The obtained membranes were studied by scanning electron microscopy (SEM), DSC and atomic force microscopy (AFM). The hydrophilicity of the membranes was evaluated, as demonstrated by the measurement of water contact angle (WCA) and water content. Furthermore, the antifouling properties of membranes were also investigated.

Enhancement of separation performance of asymmetric cellulose acetate membrane for produced water treatment using response surface methodology

Produced water is the wastewater generated from the process of exploration in oil and gas production, which needs special treatment. A membrane with cellulose acetate is widely used for produced water treatment, but further developments and improvements are still required. Therefore, it is important to determine the factors of separation efficiency of an ultrathin cellulose acetate membrane by assessing the influence of the composition of the dope solution. The response surface methodology was employed to determine the optimal conditions for this application. The investigations were conducted by varying the cellulose acetate polymer concentration at 18-20 wt.%, polyethylene glycol 4000 at 2-3 wt.% and nonsolvent addition at 3-5 wt.%. The evaluation of membrane performance for the produced water treatment was performed in a dead-end filtration cell with permeate water flux and rejection parameters for turbidity, total dissolved solids, Ca2+, Mg2+ and sulfides of produced water upstream and downstream of the membrane. The optimal composition of the dope solution was: 19 wt.% of cellulose acetate, 3 wt.% of polyethylene glycol, and 5.67 wt.% of non-solvent.

Modeling of CO2/CH4 gas mixture permeation and CO2 induced plasticization through an asymmetric cellulose acetate membrane

A mathematical model for permeation and diffusion of mixed gases in glassy polymeric membranes in the presence of plasticization was derived.

Characterization of commercial RO membranes for the concentration of ammonia converted to ammonium sulfate from anaerobic digesters

Commercially available thin film composite (TFC) polyamide membrane (GE AG) and asymmetric cellulose acetate membrane (GE CE) have been characterized using different concentrations of ammonium sulfate, up to 40g·l−1, in order to determine their suitability for the concentration of ammonium as ammonium sulfate from anaerobic digester digestate. At the manufacturer specified pressures of 1550kPa and 2900kPa, the solvent permeances for the GE AG and the GE CE membranes were found to be 2.1×10−5 and 7.4×10−6l·m−2·h−1·Pa−1, respectively. These permeances were practically independent of feed concentration. At the same time, both membranes showed excellent solute rejections, which decreased slightly with feed concentration, but were generally greater than 0.99. Consequently, the lower pressure GE AG membranes were considered to be more suitable for the separation of ammonium sulfate, and they were further tested at pressures exceeding the manufacturer specified value. These experiments revealed a slight decrease in solvent permeance for up to 17%, as well as a slight decrease in solute rejection, which was 0.97 or greater. Given these results, both membranes studied in this research are suitable for future investigations; first using multi-ion aqueous solutions and then pre-treated anaerobic digester digestate.

Studies of thermal annealing and dope composition on the enhancement of separation performance cellulose acetate membrane for brackish water treatment from Jepara

Membrane is an alternative technology of water treatment with filtration principle that is being widely developed and used for water treatment. The main objective of this study was to make an asymmetric membrane using cellulose acetate polymer and study the effect of additive and annealing treatment on the morphology structure and performance of cellulose acetate membranes in brackish water treatment. Asymmetric membranes for brackish water treatment were casted using a casting machine process from dope solutions containing cellulose acetates and acetone as a solvent. Membranes was prepared by phase inversion method with variation of polyethylene glycol (PEG) concentration of 1 and 5 wt% and with thermal annealing at 60 o C in 10 seconds and without thermal annealing behavior. Membrane characterization consists of calculation of membrane flux and rejection with brackish water as a feed from Jepara. The research concluded that asymmetric cellulose acetate membrane can be made by dry/wet phase inversion method. The more added concentration of PEG will be resulted the larger pore of membrane. Meanwhile the higher temperature and the longer time of annealing treatment, the skin layer of membrane become denser. Membrane with the composition of 18 wt% cellulose acetate, 5 wt% PEG, 1 wt% distilled water, with heat treatment at temperature of 60 o C for 10 seconds is obtained optimal performance.

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.

Enhanced Separation Performance of Cellulose Acetate Membrane For Brackish Water Separation Using Modification of Additives and Thermal Annealing

Membrane is an alternative technology of water treatment with filtration principle that is being widely developed and used for water treatment. The main objective of this study was to make an asymmetric membrane using cellulose acetate polymer and study the effect of additive and annealing treatment on the morphology structure and performance of cellulose acetate membranes in brackish water treatment. Asymmetric membranes for brackish water treatment were casted using a casting machine process from dope solutions containing cellulose acetates and acetone as a solvent. Membranes was prepared by phase inversion method with variation of polyethylene glycol (PEG) concentration of 1, 3, and 5wt% and the annealing temperature at 60oC and 70oC for 5, 10, and 15 seconds. 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 more added concentration of PEG will be resulted the larger pore of membrane. Meanwhile the higher temperature and the longer time of annealing treatment, the skin layer of membrane become denser. Membrane with the composition of 18 wt% cellulose acetate, 5 wt% PEG, 1 wt% distilled water, with heat treatment at temperature of 70oC for 15 seconds is obtained optimal performance: flux 6.52 L.m -2 .h -1 .bar -1 , 71% of total dissolved solid (TDS) rejection, 63.75% of turbidity rejection, 52.9% rejection of Ca2+, and 41.9% rejection of Mg 2+

Pressure Retarded Osmosis and Forward Osmosis Membranes: Materials and Methods

In the past four decades, membrane development has occurred based on the demand in pressure driven processes. However, in the last decade, the interest in osmotically driven processes, such as forward osmosis (FO) and pressure retarded osmosis (PRO), has increased. The preparation of customized membranes is essential for the development of these technologies. Recently, several very promising membrane preparation methods for FO/PRO applications have emerged. Preparation of thin film composite (TFC) membranes with a customized polysulfone (PSf) support, electorspun support, TFC membranes on hydrophilic support and hollow fiber membranes have been reported for FO/PRO applications. These novel methods allow the use of other materials than the traditional asymmetric cellulose acetate (CA) membranes and TFC polyamide/polysulfone membranes. This review provides an outline of the membrane requirements for FO/PRO and the new methods and materials in membrane preparation.

Positron annihilation spectroscopic study on fine-structure characterization and ethanol dehydration by pervaporation for interfacially polymerized composite membranes

In this study, polyamide (PA) composite membranes (DMDPA–TMC/CA, NTEA–TMC/CA, DETA–TMC/CA) were prepared through the interfacial polymerization reaction between a trimesoyl chloride (TMC) and each of the following three amines: 3,3-diamino-N-methyl-dipropylamine (DMDPA), nitrilotriethylamine (NTEA), and diethylenetriamine (DETA), on the surface of an asymmetric cellulose acetate (CA) membrane. The effects of the amine chemical structure and the interfacial polymerization conditions on the dehydration of an aqueous ethanol solution by pervaporation were investigated. To characterize the swelling behavior and the resulting free volume variation in the interfacially polymerized PA layers, the PA membranes in dry and wet (with aqueous ethanol solution) conditions were probed by positron annihilation lifetime spectroscopy (PALS). The difference between the o-Ps lifetime in the wet and that in the dry condition (Δτ3=τ3w–τ3d) of the interfacially polymerized PA membranes increased in the following order: DETA–TMC<DMDPA–TMC<NTEA–TMC. The swelling effect induced by the aqueous ethanol solution was restricted by the crosslinking structure in the PA layer. This result corresponded well with that of the XPS analysis. The DETA–TMC/CA composite membrane prepared using the desirable interfacial polymerization conditions (immersion in the aqueous solution of 0.5wt% DETA for 10s, and contact with the organic solution of 0.5wt% TMC for 5s) exhibited the following desirable pervaporation performance in dehydrating an aqueous solution of 90wt% ethanol at 25°C: a permeation flux of 1220g/m2h and a water concentration in permeate of 98.4wt%. It was also found that the DETA–TMC/CA composite membrane exhibited superior performance compared to the composite membranes discussed in the literature.

Effect of sonochemical synthesized TiO2 nanoparticles and coagulation bath temperature on morphology, thermal stability and pure water flux of asymmetric cellulose acetate membranes prepared via phase inversion method

In this study, asymmetric pure CA and CA/ TiO2 composite membranes were prepared via phase inversion by dispersing TiO2 nanopaticles in the CA casting solutions induced by immersion precipitation in water coagulation bath. TiO2 nanoparticles, which were synthesized by the sonochemical method, were added into the casting solution with different concentrations. Effects of TiO2 nanoparticles concentration (0 wt. %, 5wt.%, 10wt.%, 15wt.%, 20wt.% and 25wt.%) and coagulation bath temperature (CBT= 25?C, 50?C and 75?C) on morphology, thermal stability and pure water flux (PWF) of the prepared membranes were studied and discussed. Increasing TiO2 concentration in the casting solution film along with higher CBT resulted in increasing the membrane thickness, water content (WC), membrane porosity and pure water flux (PWF), also these changes facilitate macrovoids formation. Thermal gravimetric analysis (TGA) shows that thermal stability of the composite membranes were improved by the addition of TiO2 nanopaticles. Also TGA results indicated that increasing CBT in each TiO2 concentration leads to the decreasing of decomposition temperature (Td) of hybrid membranes.

Concentration of Bio-Ethanol through Cellulose Ester Membranes during Temperature-Difference Controlled Evapomeation

To evaluate the high-performance of membrane materials in the concentration of an aqueous solution of dilute bioethanol under temperature-difference controlled evapomeation (TDEV), asymmetric porous cellulose nitrate (CN) and cellulose acetate (CA) membranes were prepared by a phase inversion method. In the concentration of dilute ethanol under TDEV, these membranes showed a high permeation rate and high ethanol/water selectivity. In membranes with almost the similar pore size, the ethanol/water selectivity was considerably higher for the CN membrane than the corresponding CA membrane. This result suggested that the affinity between the membrane material and the permeant is an important factor in the separation selectivity.

One-step fabrication and analysis of an asymmetric cellulose acetate membrane for heat and moisture recovery

A one-step approach is employed to prepare an asymmetric cellulose acetate (CA) membrane that is used for total heat recovery (heat and moisture recovery). The process only involves a cheap raw material of CA, an environmental friendly solvent acetic acid and an additive deionized water. A porous support layer and a dense skin layer are formed simultaneously during the solvent and coagulant medium exchange. Investigations found that the approach is successful in making membranes for heat and moisture recovery. The new membranes have high moisture permeability. Moreover, the permeation of other unwanted gases like CO 2 is effectively prohibited. Analysis found that the optimum solution compositions for casting membranes are: acetic acid to deionized water ratio 70:30. The approach provides an environmental friendly yet economical solution for preparing membranes for heat and moisture recovery.

SEM study of the morphology of asymmetric cellulose acetate membranes produced from recycled agro-industrial residues: sugarcane bagasse and mango seeds

Cellulose, obtained both from sugarcane bagasse and mango seeds, was used for synthesizing cellulose acetate in order to produce asymmetric membranes. These were compared to membranes of commercial cellulose acetate (Rhodia). All produced membranes were asymmetric, characterized by the presence of a dense skin and a porous support. Differences regarding the morphology of the surfaces as well as of the porous support can be noticed. Scanning Electron Microscopy (SEM) showed that the morphology of the superficial layer, responsible for transport, depends on the different lignin content of the starting material and also on the viscosity average molecular weight of the cellulose acetates produced from sugarcane bagasse, mango seed, and Rhodia’s commercial cellulose acetate.

Effect of PEG additive and coagulation bath temperature on the morphology, permeability and thermal/chemical stability of asymmetric CA membranes

In this study, asymmetric cellulose acetate (CA) membranes were prepared from polymeric blend of CA–PEG/1-methyl-2-pyrrolidone (NMP) system via phase inversion induced by immersion precipitation in water coagulation bath. Effects of PEG concentration (0 wt.%, 5 wt.% and 10 wt.%) and coagulation bath temperature (CBT = 0 °C and 25 °C) on morphology, pure water permeation flux (PWF) and thermal/chemical stability of the prepared membranes were studied and discussed. Rejection of the developed CA membranes was quantified using human serum albumin (HSA) solution. Increasing PEG concentration in the cast solution film along with higher CBT results in increasing the membrane thickness, pure water flux (PWF) and HSA transmission, also these changes facilitate macrovoids formation (even with the size of more than 50 µm) in the membrane sublayer. On the other hand, increasing PEG concentration along with reduction of CBT results in increasing the thermal/chemical stability of the prepared membranes. Presence of low molecular weight PEG additive in the cast solution film increases porosity/permeability and simultaneously thermal/chemical stability of the prepared membranes. On the other hand, using cold coagulation bath despite of increasing the thermal/chemical stability of the prepared membranes results in reduction of membranes porosity/permeability.

Impacts of membrane properties on reactive dye removal from dye/salt mixtures by asymmetric cellulose acetate and composite polyamide nanofiltration membranes

This paper aims to study fundamentally the impacts of membrane properties on the reactive dye removal from dye/salt mixtures by nanofiltration membranes. To begin with, two types of nanofiltration membranes of similar pore size, namely asymmetric cellulose acetate membrane and thin-film composite polyamide membrane were fabricated, and their key physical, chemical and performance properties were characterized. After that, these resultant membranes were employed to perform dye removal experiments with aqueous solutions of reactive black 5 and NaCl under different operational parameters. The dye removal rate and steady permeate flux were determined and correlated with the measured membrane properties. It was found that there were significant differences between the dye removal performances of the two membranes, and that the membrane properties played an important role in dye removal rate, stable permeate flux and their change behaviors under operational conditions. Surface charge was the most influential property for dye removal efficiency at low dye and salt concentration, while surface roughness was the most influential membrane property at high dye concentration or salt concentration. Additionally, the most influential membrane property which determines the change behavior of dye removal efficiency with pressure and cross-flow velocity was pure water permeability and surface roughness, respectively.

Cellulose acetate (CA)/polyvinylpyrrolidone (PVP) blend asymmetric membranes: Preparation, morphology and performance

Abstract Cellulose acetate (CA) membranes are widely used for reverse osmosis (RO) and ultrafiltration (UF) applications. In this study, asymmetric CA membranes were synthesized using phase inversion method. CA with molecular weight of 52,000, polyvinylpyrrolidone (PVP) with molecular weight of 15,000 and 1-methyl-2-pyrrolidone (NMP) were used as polymer, additive and solvent, respectively. The effects of PVP concentration (at 0, 3 and 6 wt.%) and coagulation bath temperature (CBT at 0, 25 and 50 °C) on morphology, contact angle and permeability of the prepared membranes were studied and discussed. It was found out that the effects of PVP concentration and CBT depend on their values.

Effect of production conditions on morphology and permeability of asymmetric cellulose acetate membranes

Membranes are widely used in wastewater treatment. In this study, cellulose acetate (CA) (M w = 52,000) was mixed with polyethylene glycol (PEG) (M w = 400) as an additive in N-methyl-2-pyrrolidone as a solvent. The phase inversion method was used for preparation of flat sheet membranes. Effects of CA and PEG concentrations and also coagulation bath temperature on the membrane morphology were discussed in terms of membrane thickness and cross section structure. Pure water permeation flux of the membranes was also measured.