Commercial Cellulose Triacetate Membrane Research Articles

Support-free assembled molecular layer by layer - HPAN forward osmosis membranes

The internal concentration polymerization (ICP) phenomenon may hinder the flux of forward osmosis (FO) membranes. The mitigation of ICP can be achieved by employing a porous support layer structure. Nevertheless, conventional interfacial polymerization (IP) methods encounter challenges in establishing a dense selective layer upon a highly porous support layer. In this study, the support-free assembled molecular layer-by-layer (SF-mLbL) was suggested to manufacture the thin-film composite (TFC) membrane by combining the separately fabricated polyamide (PA) selective layer with a tunable thickness and the highly porous support layer. The SF-mLbL (8 wt%) membrane had a higher water flux and selectivity (43.52 ± 0.89 LMH/0.15 ± 0.01 g L−1) than those (10.34 ± 0.48 LMH/0.75 ± 0.02 g L−1 and 7.41 ± 0.18 LMH/0.81 ± 0.01 g L−1) of IP-PA and commercial cellulose triacetate membranes as 0.5 M NaCl draw solution in FO mode. Consequently, the SF-mLbL membranes exhibited significant improvement in the FO process with well-balanced permselectivity.

Demonstration of Power Generation from Fertilizer Solutions via Pressure-Retarded Osmosis

HighlightsMechanical work can be generated from fertilizer via pressure-retarded osmosis.Laboratory tests show up to 5 Wh of energy recovered per kg of fertilizer.Tradeoffs between energy recovery and power generation are demonstrated.Maintaining power above 5 W m-2 is reasonable given current membrane technology.Abstract. Large amounts of energy are released when concentrated fertilizers are diluted in water. In this study, we demonstrate the use of fertilizer to generate useful mechanical work via pressure-retarded osmosis (PRO). A number of common single solutes and fertilizer blends were analyzed using both experimental and numerical methods. Laboratory test trials showed energy recovery of up to 5 Wh kg-1 of fertilizer and power of up 6 W m-2 of membrane area given commercial cellulose triacetate membranes. A drop in power was demonstrated throughout the fertilizer PRO batch process, and the resulting tradeoffs between energy recovery and power density are discussed. Simulation results suggest that high-performance membranes can be used to maintain elevated power above 5 W m-2 throughout the batch process, while recovering approximately 5 Wh kg-1. The loss of valuable fertilizer via leakage to the feed stream was found to be less than 1% of the initial fertilizer mass, suggesting that this non-ideal dynamic can be reasonably minimized. Implications at the food-energy-water nexus are discussed. Keywords: Fertilizer osmosis, Forward osmosis, Fertilizer energy, Food-energy-water nexus.

Preparation of thin-film composite membranes supported with electrospun nanofibers for desalination by forward osmosis

Abstract. The forward osmosis (FO) process has been considered to be a viable option for water desalination in comparison to the traditional processes like reverse osmosis, regarding energy consumption and economical operation. In this work, a polyacrylonitrile (PAN) nanofiber support layer was prepared using the electrospinning process as a modern method. Then, an interfacial polymerization reaction between m-phenylenediamine (MPD) and trimesoyl chloride (TMC) was carried out to generate a polyamide selective thin-film composite (TFC) membrane on the support layer. The TFC membrane was tested in FO mode (feed solution facing the active layer) using the standard methodology and compared to a commercially available cellulose triacetate membrane (CTA). The synthesized membrane showed a high performance in terms of water flux (16 Lm −2 h−1) but traded the salt rejection (4 gm−2 h−1) compared with the commercial CTA membrane (water flux = 13 Lm−2 h−1 and salt rejection = 3 gm−2 h−1) at no applied pressure and room temperature. Scanning electron microscopy (SEM), contact angle, mechanical properties, porosity, and performance characterizations were conducted to examine the membrane.

Surface modification of FO membrane by plasma-grafting polymerization to minimize protein fouling

The aim of this study was to compared the effect of two plasma gases, Argon (Ar) and carbon dioxide (CO2), in the acrylic acid (AAc) grafting modification of a commercial cellulose triacetate (CTA) membrane to improve water flux and anti-protein fouling properties in forward osmosis (FO) for protein recovery application. The successful grafting polymerization was evaluated by measuring the grafting yield and water contact angle, X-ray photoelectron spectroscopy (XPS) analysis, Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) analysis. The contact angle of the CTA membrane was decreased from 64.0° to 37.1° and 36.4° by CO2 and Ar plasma gas treatment, respectively, which indicated an increase in hydrophilicity. The FO experiments were carried out in a lab-scale filtration apparatus. The effects of interfacial characteristics between membrane surfaces and model protein and polysaccharide foulants on flux decline and reversibility of foulants were compared. Ar gas was able to provide more free radicals and plasma electrons on the membrane surfaces, thus it was more effective than CO2 in increasing water flux and also decreased reverse salt flux and fouling tendency. The modified membranes had excellent anti-protein fouling properties, which makes them suitable for protein recovery applications. Using the Ar plasma modified membranes, tuna protein was concentrated from 4.5 % to 10.7 %, and excellent maintenance of water flux was achieved.

Pilot scale concentration of cheese whey by forward osmosis: A short-cut method for evaluating the effective pressure driving force

Cheese whey was concentrated to a concentration factor of 2.7 in a pilot scale forward osmosis filtration system, using a commercial cellulose triacetate membrane in a spiral-wound configuration. The whey was concentrated in a batch mode, using sodium chloride as the draw solution at initial osmotic pressures of 53–75 bar. During the process, flux was shown to reduce due to the simultaneous decrease in the bulk osmotic pressure of the draw solution, increase in the bulk osmotic pressure of the whey and the effect of concentration polarisation on both sides of the membrane. The flux is known to be driven by the effective osmotic pressures of whey and the draw solution on the surface of the membrane active layer. A short-cut approach that requires minimal information in advance about the osmotic pressure of whey and the geometry of the filtration system was implemented, enabling the determination of these effective osmotic pressures. The results obtained were shown to be in agreement with the fundamental forward osmosis flux model. The short-cut approach can be utilised for estimating effective osmotic pressures of other liquid food streams to be concentrated by forward osmosis, without the need of external measurements.

Direct preparation of dialysate from tap water via osmotic dilution

Preparation of dialysate for hemodialysis (or dialysis) requires dilution of the dialysis concentrate with purified water. Present practice contains two steps: first to purify water, and then water is transported to clinic to mix with the dialysate concentrate before treatment. As a new forward osmosis dialysis hybrid process, based on osmotic dilution, is evaluated for decentralized health care systems. A commercial cellulose triacetate (CTA) and a tailor-made thin film composite (TFC) polyamide FO membranes were examined. The rejection of salts in tap water by the FO membranes was investigated, and the real rejections of various ions as a function of permeate flux were well described by using a irreversible thermodynamic model. The hollow fiber TFC FO membrane showed higher water flux and lower reverse salt flux than the CTA membrane in diluting process. Both steric hindrance and electrostatic repulsion explained the rejection behavior of the membranes to the ions. Higher rejections of anions were obtained than cations, which was attributed to the anions selection characteristics of the membranes. No obvious foulings or scalings were observed in a relatively long time osmotic dilution process over 5 repeated cycles. The stable, high efficient osmotic dilution process in hemodialysis holds a strong promise in reducing the consumption of purified water or even eliminating the water purification step. This work provides a potentially new platform hemodialysis which can be portable and implementable away from major hospitals and major clinics.

Low-Energy Membrane Process for Concentration of Stick Water.

This communication describes the application of forward osmosis (FO) to concentrate stick water, a nutrient-rich water byproduct of meat rendering operations. The objectives of the study were to carry out a set of batch FO runs in concentration mode to determine the maximum achievable stick water concentration and to perform a preliminary cost analysis for operating a FO/reverse osmosis membrane separation process for comparison to an evaporative concentration process. The study examined the roles of feed and draw solution stir rates, temperature, feed concentration, and draw solution ionic strength on flux using commercial cellulose triacetate membranes. Results show that FO could concentrate the stick water up to 45 wt %; however, concentrations above about 30 wt % would be difficult to process through conventional membrane configurations. Preliminary operating cost estimations show that the energy cost of the FO process is about 5.3% of the energy costs for a single-effect thermal evaporation process; and, assuming a 2-year membrane lifetime, the total operating cost using FO membranes was estimated to be about 23.1% of the operating cost using such a thermal evaporation process.

Transport of Components in the Separation of Ethanol from Aqueous Dilute Solutions by Forward Osmosis

Membrane-based technologies have been considered for separation of ethanol/water mixtures as an alternative to thermal based separations. In this work, we consider forward osmosis (FO) for ethanol separation from aqueous solutions using commercial cellulose triacetate (CTA) and thin film composite (TFC) forward osmosis membranes. Aqueous solutions containing ethanol were used as feed solution and sodium chloride was used as osmotic agent for the tests. The total permeate flux and the reverse salt flux are increased with the increase of the osmotic pressure difference, while the ethanol–water separation factor is decreased. CTA and TFC membranes presented similar total permeate fluxes (from 4 to 8 kg m–2 h–1), but CTA presented lower reverse salt flux (below 5 g m–2 h–1) and higher separation factor (αethanol–water between 1 and 2). Additional tests using reverse osmosis (RO) were conducted to compare with the FO results.

Application of a nanofibrous composite membrane to the fertilizer-driven forward osmosis process for irrigation water use

ABSTRACTIn this study, we fabricated a nanofibrous composite (NFC) membrane as a substrate to produce forward osmosis (FO) membranes, and we also assessed the use of liquid fertilizer as a draw solution for the FO process in order to produce agricultural irrigation water. Commercial cellulose triacetate (CTA) and thin-film composite (TFC) FO membranes were included in this study. Under FO tests, the NFC, CTA, and TFC membranes achieved initial osmotic water flux values of 35.31, 6.85, and 3.31 L/m2·h and final osmotic water flux values of 12.62, 6.31, and 3.85 L/m2 h, respectively. The reason for the high osmotic water flux of the NFC membrane is because its nanofiber layer has low tortuosity, high porosity, and a low thickness, resulting in a reduction in the internal concentration polarization phenomenon. When liquid fertilizer was used as the draw solution, the water flux values in the FO experiments for the NFC, CTA, and TFC membranes were 15.54, 5.46, and 2.54 L/m2 h. Finally, our results revealed that the FO process using liquid fertilizer as a draw solution can be applied to produce agricultural irrigation water from brackish water and the newly fabricated NFC membrane can be applied to the FO process.

Synthesis and Performance of Polyamide Forward Osmosis Membrane for Natural Organic Matter (NOM) Removal

Forward Osmosis (FO) polyamide thin-film composite membranes have been prepared by interfacial polymerization using commercial UF polyethersulfoneas membrane support. Different interfacial polymerization times (10s, 30s and 60s) in the organic solution containing trimesoyl chloride (TMC) at constant mphenylenediamine (MPD) concentration (2% w/v) were studied. The synthesized polyamide membranes then tested for treatment of natural organic matter (NOM) and compared to commercial Cellulose TriAcetate (CTA) membrane. It was found that membrane prepared with higher reaction time (30s and 60s) exhibited better membrane performance (flux and humic acid removal) over commercial CTA membrane.

A novel ethanol dehydration process by forward osmosis

Bioethanol, one of the alternative energy sources, has drawn increasing attention as a potential solution of energy crisis and global warming. However, the current ethanol dehydration processes are still energy intensive. In this study, the feasibility of ethanol dehydration by forward osmosis (FO) was systematically investigated using a commercial cellulose triacetate membrane containing a dense film (active layer) and a porous substrate. The results showed that water can be removed from ethanol solutions to potentially produce an ethanol solution of 90wt%. The ethanol concentration and membrane orientation have significant impact on the membrane performance in term of membrane flux, reverse salt flux and forward ethanol flux. For instance, higher total fluxes and lower reverse salt flux when the active layer faces the draw (salt) solution instead of the porous substrate. However, the forward ethanol flux is significantly high in both of the orientations, being 1420–2249gh−1m−2 at the 75% ethanol feed concentration. The membrane durability study over the 30days of exposure in 30% and absolute ethanol solutions indicates that the membrane performance deteriorates which is caused by the membrane active layer undergoing chemical modification. The results provide a general proof of concept and scientific understanding into the FO dehydration process and FO membrane development.

Impacts of operating conditions and solution chemistry on osmotic membrane structure and performance

Herein, we report on changes in the performance of a commercial cellulose triacetate (CTA) membrane, imparted by varied operating conditions and solution chemistries. Changes to feed and draw solution flow rate did not significantly alter the CTA membrane's water permeability, salt permeability, or membrane structural parameter when operated with the membrane skin layer facing the draw solution (PRO-mode). However, water and salt permeability increased with increasing feed or draw solution temperature, while the membrane structural parameter decreased with increasing draw solution, possibly due to changes in polymer intermolecular interactions. High ionic strength draw solutions may de-swell the CTA membrane via charge neutralization, which resulted in lower water permeability, higher salt permeability, and lower structural parameter. This observed trend was further exacerbated by the presence of divalent cations which tends to swell the polymer to a greater extent. Finally, the calculated CTA membrane's structural parameter was lower and less sensitive to external factors when operated in PRO-mode, but highly sensitive to the same factors when the skin layer faced the feed solution (FO-mode), presumably due to swelling/de-swelling of the saturated porous substructure by the draw solution. This is a first attempt aimed at systematically evaluating the changes in performance of the CTA membrane due to operating conditions and solution chemistry, shedding new insight into the possible advantages and disadvantages of this material in certain applications.