Preparation and properties of poly(acrylic acid) composite membranes

A new type of membrane has been prepared for hyperfiltration (reverse osmosis) desalination that is essentially a very thin polyelectrolyte membrane. It is prepared by casting an aqueous solution of a polyelectrolyte, specifically poly(acrylic acid) (PAA), directly on one surface of a finely porous support membrane. In hyperfiltration tests, these composite membranes exhibit desalination performance comparable in dilute solutions to that observed with cellulose acetate membranes of the Loeb-Sourirajan type. The water flux through these membranes is linear in the pressure up to 100 atm. Salt rejection is a function of pressure; it is also a function of the concentration of the feed solution and the charge of the counterion, in qualitative agreement with the Donnan ion-exclusion mechanism. Typical long-term results range from water fluxes of 2 × 10^?3 g/cm²-sec (50 gal/ft²-day) and 80% salt rejection to 0.2 × 10^?3 g/cm²-sec (5 gal/ft²-day) and >99.5% salt rejection at 1500 psi with 0.3 wt-% NaCl. These membranes appear to be useful for brackish water desalination.     

Enhanced desalination performance and arsenate removal using semi-aromatic polyamide-based pervaporation membranes by modifying with amino-acids via interfacial polymerization

In this study, the semi-aromatic polyamide membranes were synthesized by the interfacial polymerization between piperazine (PIP) monomers in the water phase and Benzene-1,3,5-tricarbonyl chloride in the organic phase. To further modify the semi-aromatic pervaporation membrane, the two amino acids, glycine, and l -lysine, were mixed with PIP monomers for interfacial polymerization. The morphology and physicochemical properties of the synthesized membranes were analyzed using Fourier transform infrared (FTIR), field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), and contact angle measurements. The results show that the semi-aromatic polyamide membranes modified by the two amino acids possess a higher hydrophilic surface and lower thickness compared to the unmodified membrane. Additionally, the permeation flux of the semi-aromatic polyamide membranes was improved by 18.6% and 38.5% as modified with glycine and l -lysine, respectively, at the operating temperature of 70°C when the rejection of both NaCl and arsenic are higher than 99.8%. Furthermore, the operating temperature significantly influenced the permeation flux, while the salt rejections were insignificantly affected. The permeation flux increases by 3.2- and 4.0-folds for glycine and lysine-modified membranes, respectively, when elevating the feed temperature from 40°C to 70°C. The highest permeation flux of 29.5 kg m⁻² h⁻¹ with a 5 wt% NaCl rejection of 99.8% was obtained at 70°C by using 0.3 wt% l -lysine modified polyamide (PA) membrane. For elimination of 1.5 mg L⁻¹ As solution at the feed temperature of 70°C, such l -lysine modified PA membrane exhibited the permeation flux of 30.5 kg m⁻² h⁻¹ and As rejection of 99.6%, respectively. This work provides a cost-saving, facile, and eco-friendly preparation method for effectively improving the permeation flux while not sacrificing the high rejection of salts of the modified membranes.     

Preparation of reverse osmosis membranes by plasma polymerization of organic compounds

The plasma polymerization of organic compounds was used to prepare a composite reverse osmosis membrane which consists of an ultrathin semipermeable membrane formed by plasma polymerization of an organic compound or compounds and a porous substrate. Many nitrogen-containing compounds (aromatic amines, heteroaromatic compounds, aliphatic amines, and nitriles) were found to yield excellent reverse osmosis membranes by plasma polymerization directly onto porous substrates such as Millipore filters, porous polysulfone filters, and porous glass tubes. Factors involved in the preparation of reverse osmosis membranes by plasma polymerization were investigated and discussed. The plasma polymerized membranes have the following unique features: (1) very stable performance independent of salt concentration and applied pressure (practically no water flux decline was observed with many membranes): (2) salt rejection and water flux both increase with time in the initial stage of reverse osmosis (consequently, the performance of the membrane improves with time of operation); (3) very high salt rejection (over 99%) with high water flux (up to 38 gfd) can be obtained with 3.5% NaCl at 1500 psi (membranes perform equally well under conditions of sea water conversion and brakish water treatment).     

商业正渗透膜的改性及其用于处理焦化废水的研究

正渗透技术是一种新兴的膜分离技术,在处理有机废水方面具有广阔的应用前景。分别对Poten以及HTI商业正渗透膜进行改性,并用于对焦化废水中难降解毒性小分子(吲哚和吡啶)的截留测试。探究了水相单体PIP浓度、膜朝向、汲取液浓度对改性前后两种膜水通量、J_s/J_w比值、有机物截留率的影响,以及改性前后两膜特征参数的变化。结果表明：对Poten膜和HTI膜进行界面聚合改性后,膜水通量以及J_s/J_w比值都不同程度地降低;改性后的两正渗透膜水渗透系数A、盐渗透系数B均降低,而膜结构参数S以及对NaCl和有机物的截留率均提高;其中HTI-IP复合膜对有机物的截留率(81%)明显高于IP-2(改性Poten膜)复合膜;与FO模式相比,IP-2复合膜在PRO模式下(汲取液面向活性层)具有更高的水通量及反向盐通量。此外,在两种膜朝向下,水通量及反向盐通量都随汲取液浓度的增大而增大,但是在FO模式下(料液面向活性层),通量呈现非线性增长。     

Effect of Cyclic Changes in Temperature and Pressure on Permeation Properties of Composite Polyamide Seawater Reverse Osmosis Membranes

The effects of cyclic changes in feed water temperature and pressure on permeate flux, solute rejection, and compaction in spiral wound composite polyamide seawater reverse osmosis membranes were examined with pure water and 4% NaCl solutions. A membrane permeability hysteresis or memory effect due to the up and down temperature and pressure sequences was only seen with the saline water studies. However, the observed changes appeared to be reversible and were consistent with the Spiegler-Kedem/ Film Theory and the Kimura-Sourirajan Analysis/ Film Theory models. The overall results suggest that the net effect on permeance and solute rejection is the consequence of several interactions with feed/operating temperatures affecting membrane porosity and water/solute cluster size, and transmembrane pressure influencing membrane compaction.     

Acrylic acid γ-ray irradiation-grafted nylon 4 membranes

This study was to improve the performances of nylon 4 membranes for washing waste-water treatment of nuclear power plants, e.g., removal of detergent and salt by membranes. The effects of the degree of grafting and ionization on the reverse osmosis performances of acrylic acid (AA)-grafted nylon 4 membranes by γ-ray irradiation modification were investigated. The relationships of operating conditions, such as feed concentrations of salt and detergent, operating temperature, and pressure, and the performances of water flux and solute rejection of the prepared membranes were obtained. Water flux of the prepared membranes was highly sensitive with the operating temperature. It was found that an increase in the operating pressure could increase the water flux and the impaction effect directly. Water flux and salt rejection were significantly improved by both ionized and nonionized AA-grafted nylon 4 membranes compared to ungrafted nylon 4 membranes. Water flux increased rapidly and solute rejection dropped off slightly as the grafted membranes were ionized. The 100% detergent rejection could be obtained by the nonionized AA-grafted nylon 4 membranes with 38.6 and 69.6% degrees of grafting under various operating conditions. Results obtained showed that these modified nylon 4 membranes were usable for washing waste-water treatment of nuclear power plants. © 1993 John Wiley & Sons, Inc.     

Electrolyte removal by mixed matrix membranes based on polyurethane

The membrane processes play a significant role in the water and wastewater treatment to remove dissolved solids, especially electrolytes. In this study, the asymmetric mixed matrix membranes based on polyurethane and SAPO-5 zeolite were used on electrolyte (NaCl) removal from water. Using a low operating pressure, the membrane performances (i.e., pure water permeation, flux and salt rejection) were measured. All membranes were showing an increase in water flux when the pressure was increased. This situation shows that the produced membranes were stable in producing flux and were suitable to be used to proceed for membrane testing process. Based on the results obtained, rejection of salt water increased as the pressure given increased for each membrane. The mixed matrix membranes showed the high rejection for the salt water (NaCl 0.02 M). This shows the good performance in both flux and rejection, and even achieves 98% rejection for the NaCl 0.02 M. Based on the experimental results, it is believed that these mixed matrix membranes are suitable for the electrolytes removal applications.     

Effects of polyethylene glycol on the structure and filtration performance of thin-film PA-Psf composite forward osmosis membranes

In forward osmosis, internal concentration polarization is related to the properties (e.g., hydrophilicity, porosity, structural resistant) of membrane support layer. In this work, polyethylene glycol with a low molecular weight of 400 Da was introduced as a support layer additive during the fabrication of thin-film polyamide-polysulfone composite forward osmosis membranes. The forward osmosis performances including water flux and reverse salt flux of the membranes were tested in the mode of AL-FS where the membrane active layer faced toward feed solution. Results showed that the addition of polyethylene glycol would reduce internal concentration polarization and improve membrane performance in forward osmosis by means of enhancing membrane hydrophilicity and changing pore morphologies of membrane support layer. The membrane prepared with 6 wt.% polyethylene glycol was found to exhibit the highest water flux of 47.4 Lm^?2h^?1 with a reverse salt flux of 7.6 gm^?2h^?1 when using DI water and 2.0 M NaCl as the feed and the draw solution, respectively, indicating an optimal polyethylene glycol dosage of 6 wt.% in this work.     

An interpolymer anionic composite reverse osmosis membrane derived from poly(vinyl alcohol) and poly(styrene sulfonic acid)

An interpolymer anionic composite membrane for reverse osmosis was prepared from poly(vinyl alcohol) and poly(styrene sulfonic acid). The effects of composition of a casting solution, heat-curing periods, and casting thickness on the reverse osmosis performance of resulted membranes have been examined. A mixture of water and ethyl alcohol (12/7, wt %) was found to be a proper solvent for casting an interpolymer membrane on the supporter. The composite membrane was formed by casting the polymer solution in ultrathin film on a microporous polypropylene supporter, evaporating the solvent, and heat-curing at 120°C for a proper period. the optimum composition of a casting solution was as follows: wt % of poly(vinyl alcohol)/poly(styrene sulfonic acid)/solvent was 3/2/95. The membrane heat-cured at 120°C for 2 h has a good performance for reverse osmosis, viz., water flux of 9.1–28.4 L/m².h at salt rejection level of 88.1–93.4% under applied pressure of 80 kg/cm² with 0.5% NaCl aqueous solution. The formation mechanism of a water-insoluble membrane was discussed.     

Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300^°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90^°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013     

Relation between salt rejection and electrokinetic properties on Shirasu porous glass (SPG) membranes with nano-order uniform pores

The salt rejection by Shirasu porous glass (SPG) membranes having nano-order uniform pores was investigated for understanding the electrokinetic mechanism resulting from the surface charge developed on the membrane when in contact with salt solutions. Due to the dissociation of the hydroxyl groups such as silanol groups on the membrane surface, the membrane was negatively charged over a pH range of 3–10 from electrophoretic measurements. Cross-flow filtration experiments showed that up to 63% of NaCl was rejected by an SPG membrane having a mean pore diameters of 33 nm in a 1 mol m⁻³ NaCl solution at pH 7 under a transmembrane pressure of 74 kPa, even though the pore diameter is much larger than the ion diameter. This is a consequence of the electrostatic repulsive interaction between the co-ions (Cl⁻ ions) and the membrane surface. At the same pH, the rejection factor of NaCl decreased with increasing salt concentration due to an increase in the ionic strength. More negative charge on the membrane surface at higher pH resulted in higher rejection factors of NaCl for a fixed salt concentration. Higher rejection factors of NaCl by SPG membranes with smaller pore sizes for a fixed concentration are due to the higher ratio of the thickness of the electric double layer (Debye length) to the pore radius. The SPG membrane showed a salt rejection sequence: Na₂SO₄, NaCl and CaCl₂ at the same pH. This is because divalent anions (SO₄²⁻) are more strongly repelled by the negatively charged membrane, while divalent cations (Ca²⁺) adsorb specifically onto the membrane surface than monovalent cations (Na⁺). The salt rejection factor increased with increasing permeate volume flux. Due to the stronger acidity of the membrane materials, SPG membranes had a higher rejection factor and a lower isoelectric point (IEP < 3) than ceramic membranes.     

INTERFEROMETRIC MEASUREMENT OF CONCENTRATION POLARIZATION PROFILE FOR DISSOLVED SPECIES IN UNSTIRRED BATCH HYPERFILTRATION (REVERSE OSMOSIS)

Using a high pressure test cell with windows, laser interference patterns in a 62 mg/1 NaCl solution adjacent to the membrane were photographed after the establishment of steady state for 30 atm. constant applied pressure. The mathematical solution of the concentration profile was, with ray tracing, analytically fitted to the experimental interference pattern. From this analysis at 28 ± l°C and 30 atm. pressure, an intrinsic sail rejection of R - 0.86 ± 0.02 and reduced permeation flux of v - 100 cm^?1 for the DDS-990 cellulose acetate membrane was obtained. Limitations of the method, sensitivity and accuracy of the results are also discussed.     

Analysis of transport phenomena in cellulose diacetate membranes IV. Dependence of membrane desalination properties on annealing temperature: a Molecular Analysis

Using NaCl aqueous solutions, the volume flux and the salt rejection of various cellulose acetate membranes annealed at different temperatures, were determined from hyperfiltration experiments performed at 25°C and pressure up to 60 atm. Additional determinations including membrane hydration characteristics and dialysis-osmosis transport coefficients permitted analysis of the observed desalination properties in terms of polymer-polymer, polymer-water and water-water interactions.Whatever the membrane and the applied pressure both sharp decrease in volume flux and increase in salt rejection can be qualitatively explained by a decrease in the free water content of the membrane and an increase in the ratio of polymer-polymer to polymer-water hydrogen bonding. Practical efficiency of the heat-treatment depends on the formation conditions of the ascast membranes, owing to different sensitivity to pressure effects of each type of membrane structure.     

Using nanocomposite materials technology to understand and control reverse osmosis membrane compaction

Composite reverse osmosis (RO) membranes were formed by interfacial polymerization of polyamide thin films over pure polysulfone and nanocomposite-polysulfone support membranes. Nanocomposite support membranes were formed from amorphous non-porous silica and crystalline microporous zeolite nanoparticles. For each hand-cast membrane, water flux and NaCl rejection were monitored over time at two different applied pressures. Nanocomposite-polysulfone supported RO membranes generally had higher initial permeability and experienced less flux decline due to compaction than pure polysulfone supported membranes. In addition, observed salt rejection tended to increase as flux declined from compaction. Cross-sectional SEM images verified significant reduction in thickness of pure polysulfone supports, whereas nanocomposites better resisted compaction due to enhanced mechanical stability imparted by the nanoparticles. A conceptual model was proposed to explain the mechanistic relationship between support membrane compaction and observed changes in water flux and salt rejection. As the support membrane compacts, skin layer pore constriction increased the effective path length for diffusion through the composite membranes, which reduced both water and salt permeability identically. However, experimental salt permeability tended to decline to a greater extent than water permeability; hence, the observed changes in flux and rejection might also be related to structural changes in the polyamide thin film.     

Flux decline during ultrafiltration of kraft black liquor using different flow modules: a comparative study

Ultrafiltration of black liquor was studied in three different modules, namely, radial cross flow, rectangular cross flow and stirred cell over a wide range of operating conditions. Effects of different cut-off membranes on the permeate flux and observed rejection were also studied in the stirred cell module. Effects of operating conditions, e.g. pressure difference, Reynolds number and feed concentration on the permeate flux and observed rejection were also investigated. Such comparative study may be useful to select a suitable module, membrane and a set of optimum operating conditions to achieve a desired quantity and quality of permeate flux. A comparative analysis of flux decline for different modules is also presented using a simple resistance-in-series model.     

COD Removal from Concentrated Wastewater Using Membranes

Membranes can be used for wastewater treatment. The selection of the appropriate membrane depends on a number of factors, such as waste characteristics, nature of materials present in the wastewater, concentration, temperature, pH, etc. If the wastewater contains low molecular weight organics, reverse osmosis (RO) is the best treatment process. RO membranes allow solvent (water) to pass and prevent the transport of organics, either completely or partially. In this study, raw wastewater from an alcohol manufacturing plant was treated using a RO process. The chemical oxygen demand (COD) of the wastewater was between 35000-40000 mg/l due to the presence of organic components. Eight polymeric membranes (e.g. FT30, PVD, DSII, DS, BW30, 37100, 3750 and NF45) were used in total. None of the membranes were able to reduce COD to a desirable level (i.e. less than 200 mg/l) in one step. However a two-step process could be designed for wastewater treatment. Based on data obtained for flux and rejection, the NF45 nanofiltration membrane exhibited the best performance. A high volume of fluid can pass through the NF45 membrane because of its high porosity. The flux of this membrane (i.e. 15 kg/m².h) was higher than the reverse osmosis membranes tested. The NF45 membrane decreased COD to a greater extent than the other membranes tested (52%). While the PVD membrane showed better efficiency compared to the other reverse osmosis membranes, probably because of its material of construction and configuration.     

Assessment of a Thermally Modified Cellulose Acetate Forward‐Osmosis Membrane Using Response Surface Methodology

Cellulose acetate (CA) flat sheet membranes were fabricated and evaluated in a forward‐osmosis process. Effects of CA concentration, coagulation bath temperature, and annealing thermal treatment on both membrane structure and performance were investigated. NaCl rejection of the optimum membrane was determined utilizing a reverse‐osmosis setup based on conductivity measurements. Two validated models were obtained by means of response surface methodology based on Box‐Behnken design. The optimum operating pressure, temperature, and draw solution concentration were assessed as well.     

Cellulose triacetate membranes for seawater desalination

Experimental data on reverse osmosis using a sodium chloride solution by cellulose triacetate membranes are presented. The investigation involved studies on the composition of membrane casting solutions and their effects on the performance. A higher polymer concentration (11–13%) is found suitable for production of a uniform and highly salt rejecting membrane. Salt rejection of 99.0% and 4–5 GFD product water flux were obtained at 1000 psi operating pressure using 30,000 ppm TDS seawater in the initial experiments.     

Spinning-assist layer-by-layer assembled polysulfonamide membrane for reverse osmosis from naphthalene-1,3,6-trisulfonylchloride and piperazine

Polysulfonamide (PSA), with its chemical stability and acid-resistance, is seen as a potential material for reverse osmosis. However, the present PSA thin film composite membranes fabricated via prevailing interfacial polymerization (IP) approach generally exhibited nonfavored desalination performance. In this work, PSA membrane was assembled via spinning-assist layer-by-layer (sLbL) on a poly(vinyl alcohol) modified polyethersulfone substrate. Fabrication was carried out through sequential interfacial reaction between naphthalene-1,3,6-trisufonylchloride and piperazine by alternately dipping and drying the substrate in two monomer phases. Morphology, chemical composition, surface charge distribution as well as surface hydrophilicity were investigated as a function of repeated cycles. The sLbL assembly approach implemented facile control over membrane properties with well-organized selective layer thickness growth and twofold to threefold reduced surface roughness. As measured from spectroscopic ellipsometry, the sLbL assembled membranes exhibited a linear thickness growth at ~2.72 nm per layer. Performance test indicated that the salt rejection and water flux showed a trade-off pattern with increasing layer number. The PSA membrane with five layers showed a preferable NaCl rejection of 95.7 ± 0.4% with a water flux of 12.4 ± 0.9 L m⁻² h⁻¹ at 10 bar, whereas the IP membrane exhibited only 58% and a 22.12 L m⁻² h⁻¹ flux. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47138.     

Air Separation through Modified Ethyl Cellulose Thin Film Supported on Porous Polyethersulfone

Abstract

Composite membranes for air separation were prepared from a liquid crystal DYC-modified ethyl cellulose (EC) thin film ranging in thickness from 1 to 7 μm and a porous polyethersulfone support with a thickness of 120 μm. The effects of DYC/EC (9/91) solution concentration, water, and operating parameters such as temperature, pressure, and time on the air-separation properties of the composite membranes were examined by a constant pressure—variable volume method. The permeate flux and oxygen concentration of the oxygen-enriched air (OEA) through the membranes increase significantly with increasing operating pressure difference. With decreasing casting solution concentration, or with increasing humidity around the membranes or operating temperature, the OEA flux increases greatly while the oxygen concentration sometimes decrease slightly. An increase in the operating time leads to an OEA flux decline, but the oxygen concentration rose when the operating time was varied for 70 hours. However, a further increase of the operating time from 70 to 500 hours does not lead to further changes of the OEA flux and oxygen concentrations. A thin-film composite membrane exhibits a slightly lower oxygen concentration accompanied by a very significant enhancement in the OEA flux and membrane stability compared to a homogeneous dense membrane of the same materials.