Cellulose Acetate Asymmetric Membranes Research Articles

High performance and antifouling zeolite@polyethersulfone/cellulose acetate asymmetric membrane for efficient separation of oily wastewater

Microfiltration membranes have emerged as a promising alternative for oily wastewater treatment due to their high efficiency, low cost, and ease of operation. In this study, polyethersulfone (PES), cellulose acetate (CA), and 4A zeolite were blended to fabricate asymmetric membranes by the phase inversion technique and examined in oily wastewater treatment. Kerosene was chosen as a model polluting oil. The fabricated pure PES membrane (P), PES membranes incorporating 4A zeolite (ZP), PES membrane blended with CA (PC), and PES/CA blended membranes with 4A zeolite (ZPC) were characterized using field emission scanning electron microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, porosity, and contact angle to study the structure properties of these membranes. The performance of membranes was examined by water permeation, oil permeation flux, oil rejection, flux recovery ratio, and relative flux reduction. The ZPC membranes showed the highest performance in comparison with other prepared membranes. Incorporating 4A zeolite nanoparticles with 0.5 wt% into the PES/CA blended membrane significantly enhanced the microfiltration performance and decreased the contact angle of the P membrane from 70° to 29.8°. The effect of operation parameters such as transmembrane pressure (1–4 bar), feed temperature (25–50 ºC), and concentration of oil feed solution (250–1000 mg/L) on the permeation flux and oil rejection was studied on the PES/CA blended membrane containing 0.5 wt% 4A zeolite (0.5%ZPC). The 0.5%ZPC membrane showed improved porosity of 87.7% and it gave the highest value of pure water flux of 91.1 L/m2.h, oil permeation flux of 75.55 L/m2.h, maximum oil rejection of 98.8%, flux recovery ratio of 97.7%, and relative flux reduction of 21.8%. The permeation flux given by the 0.5%ZPC membrane was improved by about 8 times that of the P membrane. Re-usability studies verified the durability of the blended membranes and their performance in oily wastewater treatment.

Asymmetric membranes for gas separation: interfacial insights and manufacturing.

State-of-the-art gas separation membrane technologies combine the properties of polymers and other materials, such as metal-organic frameworks to yield mixed matrix membranes (MMM). Although, these membranes display an enhanced gas separation performance, when compared to pure polymer membranes; major challenges remain in their structure including, surface defects, uneven filler dispersion and incompatibility of constituting materials. Therefore, to avoid these structural issues posed by today's membrane manufacturing methodologies, we employed electrohydrodynamic emission and solution casting as a hybrid membrane manufacturing method, to produce ZIF-67/cellulose acetate asymmetric membranes with improved gas permeability and selectivity for CO2/N2, CO2/CH4, and O2/N2. Rigorous molecular simulations were used to reveal the key ZIF-67/cellulose acetate interfacial phenomena (e.g., higher density, chain rigidity, etc.) that must be considered when engineering optimum composite membranes. In particular, we demonstrated that the asymmetric configuration effectively leverages these interfacial features to generate membranes superior to MMM. These insights coupled with the proposed manufacturing technique can accelerate the deployment of membranes in sustainable processes such as carbon capture, hydrogen production, and natural gas upgrading.

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.

Effect of coagulant bath on the gas permeation properties of cellulose acetate asymmetric membrane

Membrane based gas separation process technology has been recognized as one of the most efficient and advanced unit operation for gas separation. One of the problems in membrane gas separation is membrane performance. This paper explores the application of cellulose acetate (CA) membrane for natural gas purification and separation by improving its permeability and selectivity. The main interest in this research is to study the effect of quench medium on the gas separation performance towards its physical characteristics and gas separation performance of CA membrane. Cellulose acetate polymer was dissolved in n- methyl-2-pyrrolidone solvent and casted onto a glass plate using a pneumatically controlled casting system with fixed shear rate and solvent evaporation times. The parameter varied was the non-solvent used as quench medium during membrane post treatment that were methanol and n-hexane. The different quench media as post treatment affected the O2 and N2 gas permeation and O2/N2 selectivity as well as the tensile strength of the flat sheet asymmetric membrane. Combination of methanol and n-hexane as quench media gave the best result than the other steps. This solvent exchange step influenced the morphology by producing thin skin layer and thus gives better gas separation performance than other steps

Cellulose Acetate 398-10 Asymmetric Membrane Capsules for Osmotically Regulated Delivery of Acyclovir.

The study was aimed at developing cellulose acetate asymmetric membrane capsules (AMCs) of acyclovir for its controlled delivery at the absorption site. The AMCs were prepared by phase inversion technique using wet process. A 23 full factorial design assessed the effect of independent variables (level(s) of polymer, pore former, and osmogen) on the cumulative drug release from AMCs. The buoyant optimized formulation F7 (low level of cellulose acetate; high levels of both glycerol and sodium lauryl sulphate) displayed maximum drug release of 97.88 ± 0.77% in 8 h that was independent of variation in agitational intensity and intentional defect on the cellulose acetate AMC. The in vitro data best fitted zero-order kinetics (r 2 = 0.9898). SEM micrograph of the transverse section confirmed the asymmetric nature of the cellulose acetate capsular membrane. Statistical analysis by Design Expert software indicated no interaction between the independent variables confirming the efficiency of the design in estimating the effects of variables on drug release. The optimized formulation F7 (desirability = 0.871) displayed sustenance of drug release over the drug packed in AMC in pure state proving the superiority of osmotically active formulation. Conclusively the AMCs have potential for controlled release of acyclovir at its absorption site.

An ATR-FTIR study of water in cellulose acetate membranes prepared by phase inversion

The state of water in the active layer of a series of cellulose acetate asymmetric membranes, prepared by the phase inversion process, was investigated using attenuated total reflection infrared spectroscopy (ATR-FTIR). The relative amount of water present in the active layer depends on the inherent surface or skin layer morphology; the more permeable ultrafiltration asymmetric membranes contain more water compared to the less permeable nanofiltration / reverse osmosis asymmetric membranes studied. Lightly clustered water species, weakly hydrogen-bonded to the polymer hydroxyl groups, predominate in the skin layer of the reverse osmosis membranes whereas the ultrafiltration membranes contain predominantly bulk-like water cluster. During the rehydration of the dried membrane, either with liquid water or in a constant relative humidity environment, the size of the water clusters and the extent of the water-water interactions in these clusters increase as more water is sorbed by the active layer. This difference in the state of water (amount and type of water species) present in the skin layer evidences the heterogeneous morphology of the active layers for a series of cellulose acetate asymmetric membranes prepared by the phase inversion technique.

Dielectric properties of cellulose acetate reverse osmosis membranes in aqueous salt solutions

The dielectric properties were studied of cellulose acetate asymmetric membranes in aqueous electrolyte solutions. The value of the membrane capacitance was 395 nF/cm 2, which was attributed to the dense layer in the asymmetric membrane. The thickness of the dense layer was calculated to be 27 nm from the value of the membrane capacitance. The membrane conductance depended on the type of electrolyte, while the membrane capacitance remained almost unchanged irrespective of the kind of electrolyte. The dependence of membrane conductance on the type of electrolyte showed that more highly hydrated ions were only capable of permeating the membrane with more difficulty.

Ｎ，Ｎ‐ジメチルアセトアミド水溶液の逆浸透濃縮

Reverse osmotic concentration of aqueous N, N-dimethylacetamide solutions was carried out, using cellulose acetate asymmetric membranes and composite membranes : PEC-1000, NS-100 and FT-30. Separation of N, N-dimethylacetamide and solution flux through the membranes were measured in the following ranges : concentrations, 1 to 7 wt%, operating pressures, 2.94 to 6.86MPa. PEC-1000 membranes show the best performance among the membranes tested. Its separation was above 99.5% and the best was 99.95% at 1wt%, 7MPa. At the same experimental condition, separation of FT-30 BW was 92%, FT-30 SW 94%, NS-100 P 1700 86%, NS-100 P 3500 95%, CA heat treated at 90°C 93%, 87°C 74%, and 85°C 76%.An analysis of data with Spiegler-Kedem's transport model was carried out to obtain membrane constants such as reflection coefficient σ, solute and hydraulic permeabilities w and Lp, and concentration induced compaction coefficients for ω and Lp, βs and βv, . Values of a for PEC-1000 are 1.0. FT-30 shows the largest value of βv, and cellulose acetates are the smallest.Energy and membrane area required using PEC-1000 were calculated to concentrate aqueous N, N-dimethylacetamide solution from 0.6wt% to 5.1wt% and 9.7wt% by reverse osmosis. The energy per kilogram of concentrated N, N-dimethylacetamide is proportional to operating pressure and slightly depends on final concentration and concentration polarization, and is found 0.25 to 0.55 kwh /kg-DMAc. The membrane area is inversely proportional to the operating pressure and found 0.52 m2/kg-DM Ac/day to concentrate upto 9.7wt%, at 5 MPa, and no concentration polarization.

Ｎ，Ｎ‐ジメチルホルムアミド水溶液の逆浸透濃縮

Reverse osmotic concentration of aqueous N, N-dimethylformamide solutions was carried out, using cellulose acetate asymmetric membrane and composite membranes (PEC-1000, NS-100 and FT-30). Separation of N, N-dimethylformamide and flux through the membrane were measured within the following ranges : concentrations ; 1-10 wt %, operating pressure ; 3.29-6.86 MPa.PEC-1000 membrane shows the best performance among the membranes tested. Its separation for every condition was above 98.5% and was 99.2% at 5wt%, 5MPa. At the same experimental condition, separation of FT-30 BW was 88%, FT-30 SW 73%, NS-100 p1700 94%, NS-100 p3500 96%, cellulose acetate heat treated at 90°C 73%, 87°C 65% and 85°C 60%.An analysis of data with Spiegler-Kedem's transport model was carried out to obtain membrane constants such as reflection coefficient σ, solute and hydraulic permeabilities ω and Lp, and solute induced compaction coefficients for ω and Lp, βs and βv. Values of σ for composite membrane are 1.0. FT-30 shows the largest value of βv and solute v and cellulose acetate membranes are the smallest.Energy and membrane area required using best membrane PEC-1000 were calculated to concentrate N, N-dimethylformamide from 0.5w% to 10.5wt% by reverse osmosis. The energy per one kilogram of concentrated N, N-dimethylformamide is proportional to operating pressure and slightly depends on final concentration and concentration polarization and is found 0.3 to 0.7 kWh/kg-DMF. The membrane area is inversely proportional to the operating pressure and found 0.65 [m3/kg-DMF/day] for 5MPa, at no concentration polarization.

両性膜の透過性 Ｉ 両性膜の作製方法

Amphoteric ion-exchange composite membranes were prepared by forming ultra-thin layer of partially quarternized polymer of partially chloromethylated polystyrene, on a porous polyvinylchloride support membrane, and by introducing cross-linkages and sulfonic acid groups intothe ultra-thin layer through dipping the composite membrane into concentrated sulfuric acid.The membrane thus prepared exhibited a similar permselectivity to saccharose as the cellulose acetate asymmetric membrane, but very low permselectivity to sodium chloride.

両性膜の透過性 ＩＩ 無機塩，有機酸アミノ酸の選択透過性

The permselectivities of the amphoteric ion-exchange composite membrane to inorganic salts, organic acids and amino acids were examined in single solute aqueous solutions and mixed aqueous solutions of the organic compound and salt.The permselectivity to each solute in single solutions was resembled to that of the cellulose acetate asymmetric membrane;that is, the rejection of insrganic salts becomes large for cations with higher valencies, and organic acids and amino acids in charged state were impermeable. However, we observed districtly the piezo-dialytic behavior with the mixed solutes.These results shows the possibility that the concentration and the purification of the organic compounds could be made simultaneously and quite effectively by using the amphoteric ion-exchange membranes.

Theoretical and experimental analysis of an immobilized enzyme membrane reactor

The unsteady state behavior of an immobilized enzyme membrane reactor has been analyzed both theoretically and experimentally. The reacting system considered is sucrose hydrolysis by invertase (EC 3.2.1.26). Enzyme immobilization has been obtained by ultrafiltering co-cross-linked invertase through a cellulose acetate asymmetric membrane. On the basis of the proposed mathematical model, the steady state behavior of the system can be dealt with in terms of a continuous stirred tank reactor

A study of the structure of reverse osmosis membranes by means of the scanning electron microscope

SUMMARYReverse osmosis, or hyperfiltration, is a desalination process that uses membranes through which brackish or sea water is passed under pressure. The desalination properties of the cellulose acetate reverse‐osmosis membranes are due to their particular structure.A study was made of the structure of the Loeb‐Sourirajan type cellulose acetate membranes by means of the scanning electron microscope (SEM). The specimens were prepared as follows: the samples were freeze‐dried and then fractured by applying a bending stress at liquid nitrogen temperature.Different results were obtained depending on which of the two surfaces of the membrane had been subject to bending stress. The scanning micrographs of membrane cross‐sections confirmed (Gittens et al., 1973), a three‐layer structure of the membranes: a first dense layer which is responsible for desalination, a second layer, and a porous sub‐layer which is a very good natural support for the dense one. The asymmetric morphology of the membrane was correlated with its particular transport properties. A study was also made of the influence that the conditions of preparation exerted on the structure of cellulose acetate asymmetric membranes; the micrographs confirmed that the evaporation step has a marked effect on the membrane morphology. The technique has been extended to observe the recently perfected, anisotropic polyamide membranes.