Chemically modified polybenzimidazole nanofiltration membrane for the separation of electrolytes and cephalexin

A novel chemical modification process has been proposed to prepare polybenzimidazole (PBI) nanofiltration membrane with desirable pore sizes and pore-size distribution. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis have verified the proposed chemical modification reaction between the PBI membrane and p-xylylene dichloride. Depending on the post-treatment process in the p-xylylene dichloride/heptane solution, one can finely control the pure water permeability of the modified membrane. The modified PBI membranes have a decreased effective mean pore size, a narrowed pore size distribution, and demonstrate superior ion rejection performance for liquid separation, especially for the fractionation of multivalent cations and anions from monovalent ions. It is also found that the charge characteristics of PBI membrane may vary with the solution pH, which is reflected by the rejection of NaCl under different pH. Particularly, this modified PBI NF membrane can be employed for the separation and concentration of cephalexin with impressive high rejection rates under a wide range of pH.     

DK2540型工业纳滤膜处理微蚀废液的研究

为了循环利用深圳某电路板厂的微蚀刻废液,首先研究了利用铜粉还原去除废液中的氧化性物质,然后通过用DK2540型工业高脱盐纳滤膜处理,浓缩废液中的铜,回收其中的酸.实验结果为在室温下,桨搅拌速率为300 r/min,投料比n（Cu）∶n（Na2S2O8）=1.2,反应时间70 min时,对过硫酸钠有最高去除率89.37％.在压力4 MPa,进料流量770 L/h时,Cu2＋有最高截留率90.22％,H＋有最高透过率75.68％.对于ρ（铜）=1.55 g/L的废液,可以浓缩ρ（铜）=20 g/L,原液体积减少95％以上.实验表明利用膜法可以实现微蚀废液的循环利用.     

Arsenic removal from drinking water by a “loose” nanofiltration membrane

The removal of arsenic from water by a “loose” nanofiltration (NF) membrane was investigated. Prior to the arsenic removal studies, the loose NF membrane was characterized for molecular weight cut-off and pore size by saccharide retention measurements, and electrokinetic charge by streaming potential measurements. In addition, separation of both single salt and mixed salt electrolyte solutions was studied to investigate the ion transport properties of the membrane. Arsenic rejection experiments included variation of pH, arsenic feed concentration, and presence of background electrolyte. In general, arsenic rejection increased with increasing pH and arsenic feed concentration, and was enhanced in the presence of 0.01 M NaCl. Arsenic was removed 60–90% from synthetic feed waters containing 10, 32, 100, and 316 μg/L As(V), resulting in permeate arsenic concentrations of 4, 6, 10, and 25μg/L, respectively. The behavior of the membrane is consistent with the extended Nernst-Planck equation model predictions for an uncharged membrane where size exclusion controls ion retention. However, separation of Arsenic species was a due to a combination of size exclusion, preferential passage of more mobile ions, and charge exclusion.     

Removal of metal ions from an acidic leachate solution by nanofiltration membranes

This paper presents the feasibility of the application of two commercial nanofiltration (NF) membranes (Desal5 DK and NF-270) in the removal of metal ions from an acidic leachate solution generated from a contaminated soil using H₂SO₄ as a soil washing agent. The experimental results of soil washing indicated that H₂SO₄ is highly effective in removing metal ions from contaminated soil. Following this process, the treatment of this acidic solution by nanofiltration membranes showed good metal ion rejection (between 62% to 100%) where divalent ions were better rejected than monovalent ions. For characterization purposes, the membrane experiments were conducted using K₂SO₄ solutions at different pHs. Membrane performance criteria were evaluated according to membrane permeability and ionic retention in the tank and permeate, taking into account different operating conditions such as pressures, flow rate and pH. These results demonstrated the effectiveness and feasibility of the application of nanofiltration treatments in the cleaning-up of contaminated water residues generated during soil washing processes.     

Separation of acetic acid from dilute aqueous solution by nanofiltration membrane

NF membranes have been prepared from α, β, γ‐cyclodextrin (CD) composite with polysulfone and characterized by pore size, thickness, pure water permeability, contact angle measurement and membrane morphology study. The permeation performances of the prepared membranes have been tested for separation of acetic acid from dilute aqueous solution. Effect of concentration, pressure, flow rate on flux and rejection have been calculated and interpreted. Different permeation models have been tested for experimental values and validated by comparing the values with the experimental data. It has observed that in β‐CD membranes 99% recovery of acetic acid from aqueous solution has been obtained and found to be the best membrane for separation of acetic acid from dilute solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40537.     

Effect of sol size on nanofiltration performance of a sol-gel derived microporous zirconia membrane

This paper reports the effect of sol size on nanofiltration performances of sol–gel derived microporous zirconia membranes. Microstructure, pure water flux, molecular weight cut-off (MWCO) and salt retention of zirconia membranes derived from zirconia sols with different sizes were characterized. Thermal evolution, phase compo-sition, microstructure and chemical stability of unsupported zirconia membranes (powder) were determined by thermogravimetric and differential thermal analysis, X-ray diffraction, nitrogen adsorption–desorption and static solubility measurements. Results show that nanofiltration performance of zirconia membranes is highly depen-dent on sol size. The sol with an average size of 3.8 nm, which is smaller than the pore size of theγ-Al2O3 support (pore size:5–6 nm), forms a discontinuous zirconia separation layer because of excessive penetration of sol into the support. This zirconia membrane displays a MWCO value towards polyethylene glycol higher than 4000 Da. A smooth and defect-free zirconia membrane with a MWCO value of 1195 Da (pore size:1.75 nm) and relative high retention rates towards MgCl2 (76%) and CaCl2 (64%) was successfully fabricated by dip-coating the sol with an appropriate size of 8.6 nm. Zirconia sol with an average size of 12 nm exhibits colloidal nature and forms a zirconia membrane with a MWCO value of 2332 Da (pore size:2.47 nm). This promising microporous zirconia membrane presents sufficiently high chemical stability in a wide pH range of 1–12.     

Effect of pH on the rejection of inorganic salts and organic compound using nanofiltration membrane

Nanofiltration (NF) has recently received increased attention as a possible tertiary treatment process providing high rejection of solutes and high water flux rate. In this research, solute separation experiments using NF membranes were made with inorganic salts including heavy metal and organic compounds in different pH levels. The rejection of inorganics from feed solution was found to be dependent on the electric charge of membrane as well as the ionic radius and valence of ion. The divalent cation appeared to reduce the potential of negatively charged membrane to lower the rejection of ion. The results of organic compounds showed that the rejection could be estimated from the pKa value and molecular weight of organics, and the pH of the feed solution.     

Economical evaluation of the fluoride removal by nanofiltration

Economic evaluation was carried out for a plant of fluoride removal by nanofiltration having a capacity of 2400 m³/d (100 m³/h) corresponding to a water consumption for 50.000 capita following the Moroccan considerations in rural medium. The design of this plant was carried out for the predetermined optimized conditions corresponding to a recovery rate of 84%, a fluoride rejection of 97.8% and a pressure pump of 10 bar. The capital cost was estimated to 748,003 € and the calculated operating cost to 0.212 €/m³. These costs were briefly compared to other ones.     

Rejection of salt mixtures from high saline by nanofiltration membranes

Nanofiltration (NF) membranes have recently been employed as pretreatment unit operations in seawater desalination processes and as partial demineralization to seawater. The present paper investigates the performance of selected commercial NF membranes to reject salts of high concentrations at salinity levels representative of brackish and sea water. Two commercial nanofiltration membranes (NF90 and NF270) have been investigated in detail to study their performance in filtering aqueous solutions containing different salt mixtures in a cross-flow NF membrane process within the pressure range from 4 to 9 bar. Spiegler-Kedem model (SKM) was used to fit the experimental data of rejection with the permeate flux. The results showed that NF90 membrane was shown to have a distinct ability to reject both monovalent and divalent ions of all investigated mixtures with very reasonable values but with relatively low flux. This will make NF90 more suitable for the application in the pretreatment of desalination processes. On the other hand, NF270 can reject monovalent ions at relatively low values and divalent ions at reasonable values, but at very high permeate flux. The SKM model only fitted well the experimental data of divalent ions in salt mixture. Based on the evaluation of the overall performance of NF90 and NF270 membranes, their distinct ability to reject salts at high salinity from seawater is considered an advantage in the field of pretreatment of seawater feed to desalination units.     

双组分无机电解质溶液的纳滤膜分离性能

纳滤膜是20世纪90年代问世的新型分离膜,具有两个显著特点：一是其截留分子量介于反渗透膜和超滤膜之间,约为2002000;另一是纳滤膜的表面分离层由聚电解质构成,一般带有负电荷,因此对无机电解质有一定的截留率．     

Scaling analysis of nanofiltration systems fed with saturated calcium sulfate solutions in the presence of carbonate ions

Nanofiltration of saturated calcium sulfate solution of 0.02 mol/L calcium content, with molar ratio ranging from 0.0500 to 2.8 × 10⁻³ was carried out in 6.5 × 10⁻⁴ m² active membrane area laboratory module at 1.2 × 10⁶ Pa transmembrane pressure using the total retentate recycle mode. Permeate mass flow and retentate calcium concentration vs. time and concentration factor (CF) curves allowed identification of calcium sulfate crystallization mechanisms. Though both bulk and surface crystallization mechanisms were identified, they were, however, strongly affected by water quality. A non-fouling CF range up to 2, which is probably due to the existence of metastable supersaturated CaSO₄ solution, was also observed in the case of molar ratio equal to 2.8 × 10^−3. Inorganic scales at the end of each experiment were removed from a NF module, dried at room temperature during 24 h and then examined using the X-ray diffraction method. Gypsum and aragonite were identified as the most common calcium sulfate and calcium carbonate precipitates, respectively. A mixed salt Ca₂(CO₃)(SO₄)·4H₂O (so-called rapidcreekite) was also identified as a result of carbonate and sulfate co-precipitation under low carbonate content conditions.     

Fabrication of anti-fouling polyamide nanofiltration membrane by incorporating streptomycin as a novel co-monomer

Polyamide (PA) thin-film composite (TFC) nanofiltration (NF) membrane has extremely broad application prospects in separation of monovalent/divalent inorganic salts mixed solution. However, membrane fouling is the main obstacle to the application of PA, TFC and NF membrane. Streptomycin (SM) is a hydrophilic antibiotic containing a large number of hydroxyl and amino groups. In this work, the NF membrane was prepared via interfacial polymerization (IP) between trimesoyl chloride (TMC) in the organicphaseand SM/piperazine (PIP) mixture in theaqueousphase. The NF membrane structure and performance were characterized in detail. The results showed that SM successfully participated in the IP. The negative charge and hydrophilicity of membrane surface were improved. The prepared membrane exhibited good anti-adhesion and anti-bacterial performance. Additionally, when the SM concentration was 2%, the prepared membrane exhibited the optimal permselectivity. The water permeance was 89.4 L·m^-2·h^-1·MPa^-1. The rejection of NaCl and Na₂SO₄ were 17.17% and 97.84%, respectively. The NaCl/Na₂SO₄ separation factor of the SM2-PIP/TMC membrane in 1000 mg·L^-1 NaCl and 1000 mg·L^-1 Na₂SO₄ mixed solution was 40, which was 3.3 times that of PIP/TMC membrane. It indicated that SM2-PIP/TMC demonstrated excellent monovalent/divalent salts separation performance. This work provided an easy and effective approach to preparing anti-fouling NF membrane while possessing superior monovalent/divalent salts separation performance.     

Eco-friendly separation and purification of soybean oligosaccharides via nanofiltration technology

Two NF membranes were applied to separate and purify the soybean oligosaccharide (SBOS) from SBOS broth. NF-3A membrane was more appropriate than NF-2A membrane because of its superior separation performance. Constant volume diafiltration mode was used to enhance the purity of SBOS. A difference in the rejection and the yield between the SBOS and other sugars ensured the purity enhancement. Under optimal operation conditions, the yield and the purity of the SBOS could reach up to 83.2% and 77.9%, respectively. Deteriorated membrane performance resulting from the membrane fouling could be recovered via specific chemical cleaning process. NF technology with high-efficiency and eco-friendly properties demonstrates the great potential for SBOS purification in practical application.     

纳滤膜的分离机理及其在染料废水处理中应用

根据纳滤膜分离不同性质的物料，评述了纳滤膜分离机理研究进展。纳滤膜分离非电解质时描述模型有立体阻碍-细孔模型；分离电解质和离子时包括空间电荷模型、固定电荷模型、静电阻碍模型和道南-细孔模型。综述了纳滤膜应用于染料废水处理的现状。     

Rejection of endocrine disrupters contained in biologically treated sewage by nanofiltration

Two commercial nanofiltration membranes, NF-1 (low salt rejection) and NF-3 (medium salt rejection), were used for basic experiments on the rejection of endocrine disrupters of 17βestradiol,p-nonylphenol, bisphenol A and their mixed solution. Nanofiltration membrane experiments were carried out under low trans-membrane pressure of 0.5 MPa as the operating condition. For the two nanofiltration membranes, the rejection factor was high when the pH of each feed solution was not adjusted. Based on the results of the nanofiltration membrane experiments, four commercial nanofiltration membranes-NF-1, NF-2 (medium salt rejection), NF-3 and NF-4 (high salt rejection)-were used for the rejection of endocrine disrupters contained in biologically treated sewage. The biologically treated sewage concentration of 0.039–0.055 μg/Las 17Βestradiol equivalent was reduced by each nanofiltration membrane to 0.026 μg/ L(NF-1), 0.025 μg/L(NF-2), 0.003 μg/L(NF-3) and 0.009 μg/L(NF-4), as 17βestradiol equivalent, respectively. The rejection efficiency of endocrine disrupters showed the same tendency as the TOC rejection efficiency. The permeate flux of nanofiltration membranes was high in the order of NF-1, NF-3, NF-2 and NF-4.     

Influence of chemical speciation on the separation of metal ions from chelating agents by nanofiltration membranes

The simultaneous separation of various metal ions (nickel, copper, calcium, and iron) from chelating agents (EDTA and citric acid) in water streams using Nanofiltration membranes is analyzed. Assuming that multiply-charged species are highly rejected, chemical speciation computations reproduce the observed patterns of metal and ligand rejection at different pH values and concentrations. The separation of metal ions from citric acid is achieved in acidic conditions, where multiply-charged free metal ions and neutral or singly charged free chelating species are abundant. Overall, speciation studies help to evaluate the applicability of Nanofiltration for recycling chelating agents used for metal extraction.     

Effect of SPEEK content on the morphological and electrical properties of PES/SPEEK blend nanofiltration membranes

Polyethersulfone (PES)/poly (ether ether ketone) (SPEEK) blends nanofiltration membrane at different SPEEK contents were prepared using a simple dry-jet wet spinning technique. The SPEEK polymer with fixed sulfonation degree was used for membrane preparation and characterized using FTIR and nuclear magnetic resonance (NMR) spectrometer. The morphological and electrical properties of the blends membrane were deduced based on the combination of irreversible thermodynamic model, steric-hindrance pore model (SHP) and Teorell-Meyer-Sievers model (TMS). The modeling results have been analyzed and discussed. The effect of SPEEK content on the blend properties was further studied in detail by FTIR, DSC and TGA and the results were discussed.     

Selective separation of contaminants from paper mill effluent using nanofiltration

Biologically treated newsprint mill effluent containing 57 mg L⁻¹ DOC and 1430 TDS was used in a screening study of nine commercial NF membranes for use as pretreatment for reverse osmosis in an end of pipe water recycling application. A salt-organic-separation (SOS) efficiency factor was developed to help rank the performance of the membranes. The SOS measures the ratio of the sum of the percentage rejection of organics and divalent cations over the percentage rejection of monvalents. It can be used to discriminate between NF membranes that are not too permeable to divalent cations or organics in which case the NF permeate will have a high chlorine demand due to the carryover of organics, or too retentive in which case all the material in the effluent will be retained and fouling problems are likely to occur. The optimum SOS efficiently for this study appeared to range from 3.5 to 5.6 for six membranes, DK, HPA-150, ESNA1-LF2, DL, TFC-SR2 and NF-270, which were categorised as membranes with an intermediate rejection. Out of these membranes ESNA1-LF2, TFC-SR2 and NF-270 were capable of operating up to 90% recovery with high permeabilities ranging from 17.7 to 22.3 L m⁻² h⁻¹ bar⁻¹.     

Membrane Concentration and Separation of L-Aspartic Acid and L-Phenylalanine Derivatives in Organic Solvents

Abstract

The concentration and separation of the amino acids N-benzyloxycarbonyl L-aspartic acid and L-phenylalanine methyl ester hydrochloride in organic solvents have been investigated using reverse osmosis membranes of two types of cellulose acetate, a nanofiltration membrane of polyamide-polyphenylene sulfone (PA-PPSO) composite and a gas separation membrane of polyimide composite in a stirred batch cell. The organic solvents used included primary, secondary, and tertiary alcohols, an ester, and a ketone. There were significant variations in permeate flux, solute rejection, and membrane stability. Usually the rejection of both amino acids was similar; however, certain membrane-solvent combinations gave significantly different levels of rejection. The highest rejection of amino acids (～0.94) at the lowest pressure of 0.5 MPa was obtained with the PA-PPSO membrane using methanol as a solvent. The cellulose acetate membranes gave reasonable rejection and fluxes but the membrane stability was very poor. The performance of the polyimide composite membrane was good with ethanol but poor with other solvents. The PA-PPSO membrane with methanol as solvent appeared the most promising combination, and the separation performance according to concentration polarization was discussed.