Cellulose Triacetate Hollow Fiber Membrane Research Articles

The Optimized Preparation Conditions of Cellulose Triacetate Hollow Fiber Reverse Osmosis Membrane with Response Surface Methodology.

Reverse osmosis (RO) membrane materials play a key role in determining energy consumption. Currently, CTA is regarded as having one of the highest degrees of chlorine resistance among materials in the RO process. The hollow fiber membrane has the advantages of a large membrane surface area and a preparation process without any redundant processes. Herein, response surface methodology with Box-Behnken Design (BBD) was applied for optimizing the preparation conditions of the cellulose triacetate (CTA) hollow fiber RO membrane. There were four preparation parameters, including solid content, spinning temperature, post-treatment temperature, and post-treatment time, which could affect the permeability of the membrane significantly. In this study, the interaction between preparation parameters and permeability (permeate flux and salt rejection) was evaluated by regression equations. Regression equations can be applied to obtain the optimized preparation parameters of hollow fiber RO membranes and reasonably predict and optimize the permeability of the RO membranes. Finally, the optimized preparation conditions were solid content (44%), spinning temperature (167 °C), post-treatment temperature (79 °C), and post-treatment time (23 min), leading to a permeability of 12.029 (L·m-2·h-1) and salt rejection of 90.132%. This study of reinforced that CTA hollow fiber membrane may promote the transformation of the RO membrane industry.

Surface grafting of cellulose triacetate hollow fiber membranes with Ag@ZnO-hyperbranched polyglycerols nanoparticles for constructing antifouling and antibacterial surfaces

In recent years, using novel nanomaterials to improve the antifouling and antibacterial performance of reverse osmosis membranes has received much attention. In this study, hydrophilic Ag@ZnO-hyperbranched polyglycerols nanoparticles were fabricated by ring-opening multibranched polymerization of glycidyl acid with the core-shell Ag@ZnO nanoparticles. The cellulose triacetate composite membranes were prepared by grafting Ag@ZnO-HPGs nanoparticles on the surface of cellulose triacetate membranes. The surface of the nanoparticles with active functional group –OH was confirmed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Surface morphology, charge, and hydrophilicity of the composite membranes were characterized by scanning electron microscope, zeta potential, and contact angle analysis. The results showed that grafting the Ag@ZnO-HPGs nanoparticles onto the cellulose triacetate membrane surface improved the physical and chemical properties of the cellulose triacetate composite membranes. The water flux of cellulose triacetate composite membranes increased while the salt rejection rate to NaCl slightly decreased. Meanwhile, the cellulose triacetate composite membranes showed excellent antifouling properties of having a high flux recovery. The antibacterial performance of the cellulose triacetate composite membrane against E. coli and S. aureus was prominent that the antibacterial rates were 99.50% and 92.38%, and bacterial adhesion rates were as low as 19.12% and 21.35%, respectively.

Preparation of Microfiltration Hollow Fiber Membranes from Cellulose Triacetate by Thermally Induced Phase Separation.

For the first time, self-standing microfiltration (MF) hollow fiber membranes were prepared from cellulose triacetate (CTA) via the thermally induced phase separation (TIPS) method. The resultant membranes were compared with counterparts prepared from cellulose diacetate (CDA) and cellulose acetate propionate (CAP). Extensive solvent screening by considering the Hansen solubility parameters of the polymer and solvent, the polymer’s solubility at high temperature, solidification of the polymer solution at low temperature, viscosity, and processability of the polymeric solution, is the most challenging issue for cellulose membrane preparation. Different phase separation mechanisms were identified for CTA, CDA, and CAP polymer solutions prepared using the screened solvents for membrane preparation. CTA solutions in binary organic solvents possessed the appropriate properties for membrane preparation via liquid–liquid phase separation, followed by a solid–liquid phase separation (polymer crystallization) mechanism. For the prepared CTA hollow fiber membranes, the maximum stress was 3–5 times higher than those of the CDA and CAP membranes. The temperature gap between the cloud point and crystallization onset in the polymer solution plays a crucial role in membrane formation. All of the CTA, CDA, and CAP membranes had a very porous bulk structure with a pore size of ∼100 nm or larger, as well as pores several hundred nanometers in size at the inner surface. Using an air gap distance of 0 mm, the appropriate organic solvents mixed in an optimized ratio, and a solvent for cellulose derivatives as the quench bath media, it was possible to obtain a CTA MF hollow fiber membrane with high pure water permeance and notably high rejection of 100 nm silica nanoparticles. It is expected that these membranes can play a great role in pharmaceutical separation.

Investigation on the effects of air gap distance on the formation of cellulose triacetate hollow fiber membrane for CO2 and CH4 gases permeation

CO2 removal is essential for the sweetening process of sour natural gas in order to meet the desired specifications for natural gas to be utilized and transported. CO2 separation from natural gas stream can be achieved through the application of membrane technology which will enable natural gas to be suitable for commercial use. Cellulose triacetate (CTA) is a well-known polymer material for CO2 removal due to its high affinity towards CO2. As compared to flat sheet membranes, hollow fiber configuration is preferable due to its large surface to unit volume ratio and self-supporting characteristics, therefore making it a superior choice compared to other configurations. In this work, fabrication of hollow fiber membranes by employing CTA as a polymer for the separation of CO2 and CH4 gases is focused. During fabrication, the air gap distance was varied from 1 cm to 7 cm. Following that, the morphology of the resulting fibers was investigated by using a scanning electron microscope (SEM). Next, the CO2 and CH4 gas permeation, and CO2/CH4 gas pair selectivity of the resultant HFMs were assessed using a custom-built gas permeation test rig. In addition, post-treatment of HFM with polydimethylsiloxane (PDMS) was also carried out. Then, the gas permeation and gas pair selectivity of the resultant hollow fiber membranes before and after the PDMS coating were compared. The optimum gas permeation performance of CTA HFM was obtained at an air gap distance of 3 cm and a feed pressure of 3 bar as it yielded the highest CO2 permeance of 78.77 GPU and CO2/CH4 gas pair selectivity of 2.80. Whereas for PDMS coated CTA HFM, fibers spun at air gap distance of 1 cm demonstrated the highest CO2 permeance of 14.85 GPU and CO2/CH4 selectivity of 2.54 at feed pressure of 9 bar.

Evaluation of cellulose triacetate hollow fiber membrane for volume reduction of real industrial effluents through an osmotic concentration process: A pilot-scale study

The current article tackles the challenge of reducing wastewater volumes generated from the gas industry. A forward osmosis (FO) pilot unit, deployed as osmotic concentration (OC) process without the draw solution (DS) recovery step, was applied as an option for volume reduction of real industrial effluents. A commercial hollow fiber (HF) FO membrane fabricated from Cellulose Triacetate (CTA) was firstly tested with synthetic feed solution (FS) to investigate the separation properties of the membrane and to identify the optimum operating conditions of the pilot unit. The pilot plant was then challenged with real industrial wastewater for an extended period of operation, primarily to assess membrane-fouling propensities and other performance parameters. Results revealed that according to the operating conditions, the CTA membrane can achieve feed recoveries between 60%–90%, at water fluxes between 2.24-1.65 L.m −2 h −1 (LMH)). The operation at 75% feed recovery was identified as the optimum condition since it showed the lowest specific solute flux (20.93 mmol L −1 ) at a water flux of 1.94 LMH. Outcomes of pilot testing with the real wastewater demonstrated operational stability for over 50 h of continuous operation. The pilot system recovered 75% of the wastewater feed at a stable flux trend with minimal flux decline. Water flux of 1.76 LMH was recorded along with reverse solute flux of 292 mmol h −1 . The water flux was observed to decline slightly by only 5.6%, which was attributed to inorganic scaling on the membrane surface where cleaning with citric acid solution demonstrated efficacy in restoring the initial flux. • The technical viability of osmotic concentration (OC) technology at a pilot scale was appraised. • The performance of a commercial CTA HF membrane was evaluated. • The role of operating conditions in the performance of the pilot unit was examined. • OC pilot unit successfully recovered 75% of real wastewater generated from the gas industry. • Stable flux was observed during 50 h of continuous operation with minimal membrane fouling.

Natural gas sweetening using a cellulose triacetate hollow fiber membrane illustrating controlled plasticization benefits

Plasticization is a well-understood drawback of polymer membranes in many applications; however, recent studies have demonstrated surprising advantages of this phenomenon for demanding natural gas sweetening for some glassy polymer dense film membranes. Moving beyond dense film membranes, the current study focuses on cellulose triacetate (CTA) hollow fiber membranes to use the benefits of controlled plasticization for realistic raw natural gas sweetening. Natural gas sweetening can be complicated by co-existence of condensable hydrocarbons, e.g. C2H6, C3H8 and toluene with the main H2S/CO2/CH4 ternary mixture; moreover, the operating temperature and pressure adds another dimension to this important separation. In this study, we consider an aggressive gas composition of high H2S (20 mol.%), low CO2 (5 mol.%), and significant amounts of C2H6 (3 mol.%) and C3H8 (3 mol.%) as well as trace amount of toluene (100–300 ppm) with CH4 comprising the rest of the feed. Various temperatures (35 °C and 50 °C) and pressures (6.9–31.3 bar) are also considered. We show a controlled plasticization benefit for the CTA hollow fiber membrane, with attractive CO2 and H2S permeance (>110 GPU) and selectivity (22–28) for CO2 and H2S over CH4 at 35 °C and 31.3 bar. The current study represents a major step forward in processes for membrane-based natural gas sweetening using practical asymmetric membranes.

Fabrication of Cellulose Triacetate Hollow Fiber Membranes for Forward Osmosis-Nanofiltration.

In this study, hollow fiber membranes for forward osmosis using cellulose triacetate were prepared using the non-solvent phase separation method, and the water purification properties of the prepared membranes were tested. In order to optimize the membrane morphology, which affects the membrane performance, 1,4-dioxane and lithium chloride were used as additives. Using the forward osmosis process, the properties of the membrane were investigated according to changes in the factors such as the salt type, salt concentration, and solution temperature. In the nanofiltration process, the water flux was found to increase and the salt rejection to decrease with increasing air gaps, regardless of the type of salt. In contrast, in the forward osmosis process, the water flux increased and the solute rejection value increased in a manner similar to the increasing concentration of solute.

三酢酸セルロース製中空糸膜の正浸透特性の新規評価法

三酢酸セルロース製中空糸膜の正浸透特性の新規評価法

Effect of chlorine and acid injection on hollow fiber RO for SWRO

Bio-fouling results in deterioration of permeate quality and flux in reverse osmosis (RO) process. Cellulose triacetate hollow fiber membrane used for RO in SWRO has anti-chlorine property that makes technical sense compared to polyamide spiral-wound RO for overcoming bio-fouling. Mode of chlorine injection is the controlling factor of sterilization in SWRO system. This work evaluated the effects of five different modes of chlorine injecting system as well as HCl injection on the performance of HF RO system. In addition, effects of HCl and anti-scalants on anti-scale performance of HF RO system were also investigated, respectively. A brief list of chemical costs under different abovementioned operating conditions was covered in a cost analysis. The results indicated that the injecting mode that employed continuous chlorine with a relatively low concentration of 0.3–0.4 mg/L at pH 5.8–6.2 was preferable in the aspects of total bacterial count (TBC) removal, permeate flow rate, differential pressure, permeability ( P p ), performance factor (η) and chemical costs. HCl injection could improve the sterilization and prevent scaling on the membrane surface efficiently. The expense of anti-scalant (MDC220) was higher than HCl.

Polymer membranes for separating organic mixtures

AbstractPolyvinyl alcohol (PVA), polyacrylonitrile (PAN), and cellulose ester were respectively chosen as the separation layer and the support in the composite membranes based on the concept of the solubility parameter and the permselectivities for separating ethanol/water mixture, isopropanol/water mixture, and caprolactam/water mixture. The effects of the membrane materials and the construction of the composite membrane on the separation performance were preliminary discussed. The separation performance of the membranes prepared by several making‐membrane techniques, i.e., the polymer solution making‐membrane technique, and the membrane treatment technique (heat treatment, organic solvent modification) were presented. The composite membranes of PVA/PAN and PVA/cellulose acetate, and cellulose triacetate hollow fiber membrane modified, which possess good performance in separating the organic systems, were developed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1160–1164, 2006

Importance of asymmetric structure in determining mass transport characteristics of hollow fiber hemodialyzers

Most synthetic hemodialysis membranes have an asymmetric structure consisting of a thin semi-permeable skin and a more open support structure. The impact of this asymmetric structure on the transport characteristics of hemodialysis membranes has not been appreciated. Experimental data were obtained for solute clearance and sieving through asymmetric polysulfone membranes and homogeneous cellulose triacetate hollow fiber membranes. The clearance of urea and the large molecular weight dextrans were greater for the cellulose triacetate membrane compared to the polysulfone, but the clearance of the smaller molecular weight dextrans was slightly greater for the polysulfone dialyzer. The sieving coefficients for the asymmetric membrane were uniformly smaller than those for the homogeneous membrane, although this effect was dramatically reduced at very small filtration velocities. These results were in good agreement with theoretical calculations based on a two-layer model for the asymmetric membrane and available hydrodynamic descriptions of hindered solute transport.

Solvent treatment of CTA hollow fiber membrane and its pervaporation performance for organic/organic mixture

Cellulose triacetate (CTA) hollow fiber membrane used to separate methanol/methyl tert-butyl ether (MTBE) by pervaporation (PV) has been prepared from CTA hollow fiber reverse osmosis (RO) membrane for desalination of brackish water with high salinity. Acetone was selected as a modification agent of CTA membrane. PV performance depended on the solvent concentration, the treatment time and modification temperature of CTA RO hollow fiber membrane soaked in the aqueous acetone. The results show that CTA hollow fiber membrane modified with the solvent has a superior performance both the separation factor and the permeate flux in the PV experiment conditions.

Modified performance of cellulose triacetate hollow fiber membrane

Cellulose triacetate (CTA) hollow fiber membrane for reverse osmosis (RO) desalination of brackish water with high salinity has been modified for pervaporation (PV) membrane of separating organic/organic mixture. The experiments presented that modified performance of CTA hollow fiber membrane treated by the organic solvent was affected by the modifying conditions. PV performance of CTA hollow fiber membrane modified mainly depends on the concentration of the modifying agent and the treatment time of CTA hollow fiber membrane in the aqueous acetone. The results showed that the membrane treated respectively by 5% acetone aqueous solution possesses a good PV separation performance, i.e. the separation factor 1998 and the permeate flux 45.1 (g/m 2.h). It was exhibited from scanning electron microscope (SEM) photograph were produced. The structural changes from porous, defect to non-porous, even on the membrane surface and turn from asymmetric membrane of two layers consisting of the active and the support into the homogeneous membrane of single layer in the cross section of the membrane would indicated why the original RO membrane can become that of PV by means of modification treatment.

New chlorine-resistant polyamide reverse osmosis membrane with hollow fiber configuration

New asymmetric hollow fiber reverse osmosis (RO) membrane was developed from a new chlorine-resistant copolyamide [4T-PIP(30)] with a piperazine moiety by a conventional phase-separation method. The new 4T-PIP(30) hollow fiber membrane has the same low-pressure RO performance as cellulose triacetate hollow fiber membrane (FR = 205 L/m2 day, Rj = 99.6%) and superior chlorine resistance as well as pH resistance to conventional aramid RO membranes. Structural analysis and viscoelastic study revealed that the new hollow fiber consisted of a top skin, dense layer, and microporous layer, and that it began to decrease its elasticity at 80°C in water, which is possibly related to its good and stable RO performance around room temperature. Several kinds of RO modules were made from the new hollow fiber membranes, for which RO performances were stable for 2 years in chlorinated feed water desalination (the free residual chlorine ranged from 0.l to 1.1 mg/L). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 517–527, 2001