不同交联剂对PDMS/PVDF纳滤膜溶剂回收性能的影响

以聚二甲基硅氧烷(PDMS)为分离层材料,聚偏氟乙烯(PVDF)超滤膜为底膜,采用正硅酸乙酯(TEOS)、苯基三甲氧基硅烷(PTMOS)、辛基三甲氧基硅烷(OTMOS)、γ-氨基丙基三乙氧基硅烷(APTEOS)4种不同的交联剂对PDMS进行交联,制备了PDMS/PVDF纳滤膜。采用接触角、红外谱图、扫描电镜等对膜的物理和化学结构进行了分析和表征。以大豆油/己烷混合油为实验体系,考察了压力和料液浓度对纳滤膜分离性能的影响。结果表明,纳滤膜的通量随压力线性增长,截留率初始随压力上升较快,随后增幅减慢而趋于稳定。随料液浓度的增加,纳滤膜的通量和截留率都有较大幅度的下降。相比较而言,以TEOS为交联剂所制得的纳滤膜分离性能最佳。大豆油/己烷混合油体系同水溶液体系的渗透特性类似,其渗透压可用van't Hoff方程计算。     

Nanofiltration of single and mixed salt solutions: Analysis of results using principal component analysis (PCA)

The retention of single (NaCl) and mixed (Na₂SO₄ + NaCl) salt solutions by nanofiltration membranes was analysed using principal component analysis (PCA). Seven variables—five different membranes (Desal-5DK, NF 270, NF Filmtec, NF 20 and ESNA-1-LF), flux and salt concentration—were taken into account in the analysis. The dependences of NaCl retention on these variables for single and mixed solutions were evaluated by PCA.Differences and similarities between the obtained results and those from a previous study based on a univariate method were observed. The PCA results from single and mixed salt solution experiments indicated that the NF 20 membrane differs from the others; a finding that is in accordance with earlier observations. The difference could be explained by the fact that the NF 20 membrane was not charged at the filtration pH (6) and by its bigger pore size.For single salt solutions, the results for the NF Filmtec and NF 270 membranes (manufactured by Filmtec) resembled each other when using the PCA method; a finding which could not be shown using a univariate method. These membranes did not resemble each other when filtering mixed salt solutions.Analysis of the results when using the PCA method for the single and mixed salt solutions indicated that the retention of the ESNA-1-LF membrane behaved differently from all the other tested membranes. While a negative retention for NaCl in a mixed solution was observed with the other membranes, the ESNA membrane showed a positive retention which was close to the retention of a reverse osmosis membrane (above 80%).The results showed that both salt concentration and permeate flux had major effects on the salt retentions of the NF 20, NF Filmtec, NF 270 and Desal-5DK membranes.     

Nanofiltration of Magnesium Chloride,Sodium Carbonate,and Calcium Sulphate in Salt Solutions

Abstract

Nanofiltration (NF) membranes have been employed in pre‐treatment unit operations in both thermal and membrane seawater desalination processes. This has resulted in reduction of chemicals used in pretreatment processes as well as lowering the energy consumption and water production cost and, therefore, has led to a more environmentally friendly processes. In order to predict NF membrane performance, a systematic study on the filtration performance of selected commercial NF membranes against brackish water and seawater is required. In this study, three commercial nanofiltration membranes (NF90, NF270, N30F) have been used to treat highly concentrated different salts solutions (MgCl₂, Na₂CO₃, and CaSO₄) at salinity level similar to that of brackish water and seawater. The main parameters studied in this paper are salt concentration and feed pressure. The experimental data were correlated and analysed using the Spiegler‐Kedem model. In particular, the reflection coefficient (σ) of all studied membranes and the solute permeability (P_s) have been determined for all membranes and at different salinity levels of studied salts. All the studied membranes fitted the model well for all investigated salts except the experimental data of MgCl₂ using N30F membrane, which did not fit well at low rejection. The results showed that NF90 produced a high rejection around 97% for all salts with medium permeate flux while NF270 gave a high flux with medium rejection and N30F gave low rejection and flux.     

Performance of Nanofiltration Membranes for Solvent Purification in the Oil Industry

The extraction stage of edible oil in the oil industry is commonly performed by using toxic solvents (e.g. hexane) and processes with high energy consumption (e.g. distillation, evaporation) to recover the solvent, which represents around 70–75 wt% in the oil–solvent mixture. In this paper, a membrane-based extraction method using nanofiltration (NF) membranes is presented. Commercial nanofiltration membranes made of different polymers (Desal-DK-polyamide NF from GE-osmonics^®, NF30 polyethersulfone NF from Nadir^®, STARMEM^TM122 polyimide from MET^® and SOLSEP NF030306 silicone base polymer SOLESP^®) were selected and tested to recover the solvent from soybean oil/solvent (10–20–30% w/w oil) mixtures at various separation pressures and constant temperature in a dead-end filtration set up. The selection of the solvent was made in order to compare solvents obtainable from renewable resources, such as ethanol, iso-propanol and acetone, with solvents traditionally used in the industry (i.e. cyclohexane and n-hexane). The structural stability of the membranes towards the different solvents used in this work was verified visually, by the variation of the membrane area and by means of permeate flux assessments. Desal-DK and NF30 showed poor filtration performance and even visible defects after exposure to acetone but a good performance was obtained for the nanofiltration membranes STARMEM^TM122 and SOLSEP NF030306 with ethanol, iso-propanol and acetone. For example, considering a mixture with 30% edible oil in acetone, STARMEM^TM122 shows a flux and oil rejection of 16.8 L m^?2 h and 70%, respectively. For the same conditions, SOLSEP NF030306 exhibited a flux of 4.8 L m^?2 h with 78% rejection, which shows the potential application of nanofiltration membranes in the oil industry.     

Effect of Color and Surfactants on Nanofiltration for the Recovery of Carpet Printing Wastewaters

Abstract

Carpet printing wastewater (CPW) was spiked with metal‐complex dyes at concentrations of 10 and 30 mg/L to investigate the effect of feed color on separation performance of nanofiltration (NF). The rejection was excellent; 98–100% for color and COD under all spiking conditions. Although the flux decline increased with increasing dye concentration, the concentration polarization was the main cause of the flux decline. The effect of surfactants on NF separation performance was also investigated by preparing synthetic wastewaters with dyes and auxiliary chemicals. The presence of a non‐ionic penetrant did not adversely affect the color rejection whereas the COD rejection was reduced from 100% to 91%. Furthermore, fouling became dominant when surfactants were used.     

Performance of Nanofiltration Membranes in the Treatment of Synthetic and Real Seawater

Abstract

Nanofiltration membranes (NF) are being employed in pretreatment unit operations in both thermal and membrane seawater desalination processes and as partial demineralization to seawater. In order to predict NF membrane performance, a systematic study on the filtration performance of selected commercial NF membranes against seawater is presented in this paper. Two commercial nanofiltration membranes (NF90 and NF270) have been investigated in details to study their performance in filtering the salt mixture, synthetic and real seawater in a cross‐flow NF membrane process at a pressure range from 4 to 9 bars. The Spiegler‐Kedem model was used to fit the experimental data of rejection with the permeate flux in order to determine the fitting parameters of the reflection coefficient (σ) and the solute permeability (P_s). The results showed that the rejection increases with pressure for NF90 and slightly increases with pressure for NF270. Also, the NF90 membrane has shown to be able to reject both monovalent and divalent of all investigated mixtures and seawater with very reasonable values but at a relatively low flux. Moreover, it reduced the salinity of investigated seawater from 38 to 25.5 g/L using one stage of the NF membrane at 9 bars. This makes 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. It has also reduced the seawater salinity to 33.6 g/L, but at a very high permeate flux. The SKM model fitted the experimental data of divalent ions in salt mixture and seawater.     

Combined Humic Substance and Heavy Metals Agglomeration,and Membrane Filtration under Saline Conditions

Abstract

Humic substances‐heavy metals complexation combined with membrane filtration is reported. The effects of salinity, humic substances (HS) concentration, heavy metals concentration, and trans‐membrane pressure (TMP) on HS and heavy metals retention using two membranes are studied. Membrane fouling is also studied at the aforementioned conditions. NF270 experienced higher fouling. Moreover, salinity tests showed increasing fouling rate and reduction in membrane retention with increasing salinity level. While increasing HS concentration reduced HS retention and increased heavy metals retention and membrane fouling. Heavy metals concentration reduced the NF270 HS retention, but did not affect the P005F HS retention. In addition, TMP did not affect HS and heavy metals retention nor NF270 fouling, but increased P005F fouling.     

Color and COD retention by nanofiltration membranes

In the present study the application of the nanofiltration process was investigated mainly in the retention ofcolor and chemical oxygen demand (COD) present in textile industry wastewater. Nanofiltration experiments were carried out in a pilot unit, operating in crossflow. Three different types of spiral wound membranes, DK 1073, NF 45 and MPS 31 were used simultaneously in the same unit. The results of the tests showed that for color retention, the values were around 99% for the DK 1073 and NF 45 membranes and the 87% for COD retention for the DK 1073. The permeate flux for the different wastewaters varied from 30.5 to 70 L/h.m². Fouling was observed in all membranes due to the accumulation of molecular species close to the filtering surface. The process was efficient and promising for the reuse of wastewater from this type of industry.     

New polymeric membrane nanofiltration for succinate recovery: a comparative study

Bio-based succinic acid recovery from fermentation broth has remained a challenge in the separation industry due the presence of by-products with similar physicochemical properties. In this work, the selective separation of succinate from succinate model solutions and the actual fermentation broth were investigated using newly fabricated polyimide P84 (PI) nanofiltration (NF) membrane and compared with three types of commercial pressure filtration membranes namely NF1, NF2 and NF270. Results show that PI membrane demonstrated comparable inorganic salt rejections performance as the commercial NF membranes of 86% and 99% for NaCl and Na₂SO₄, respectively. However PI shows much lower surface roughness, beneficial in reducing the fouling effect. PI also demonstrated equivalent performance for succinate permeation flux and retention at high concentration as the commercial membranes. PI exhibited high succinate retention (95%) in actual fermentation broth, equivalent to the commercial membranes (92–99%) and also higher selectivity factor (SF) < 0.14 compared to the NF1 membrane, SF < 0.19. Thus the PI membrane could give better succinate recovery against other carboxylates in the fermentation broth than the commercial membranes.     

Flux,antifouling and separation characteristics enhancement of nanocomposite polyethersulfone mixed-matrix membrane by embedding synthesized hydrophilic adipate ferroxane nanoparticles

Polyethersulfone (PES) nanofiltration (NF) membranes were prepared by blending of synthesized hydrophilic adipate ferroxane nanoparticles (AFNPs) as a novel multifunctional nanofiller via the phase inversion method. The water contact angle measurement indicated the higher hydrophilicity of the NF membranes. The water flux of the membranes improved significantly after the addition of AFNPs, from 10.4 to 32.2 kg/m²h. Antifouling characteristics of AFNPs/PES membranes were improved by increased hydrophilicity and decreased membrane surface roughness. The 0.6 wt% AFNPs/PES membrane exhibited the highest FRR (96%) and the lowest irreversible fouling resistance (6%). The nanofiltration performance of the prepared membranes was evaluated by dye removal and salt retention. The results proved the high dye removal capability of modified membranes (98% rejection) compared with the unfilled PES membrane (89% rejection). The salt retention sequence for membrane with 0.2 wt% of nanoparticles was Na₂SO₄ (70%)>MgSO₄ (60%)>NaCl (18%).     

The influence of degreasing agents used at car washes on the performance of ultrafiltration membranes

The influence of washing chemicals used at car washes on the flux and retention of three ultrafiltration (UF) membranes has been studied. Eleven commercial degreasing agents, two shampoo agents and a wax were included in the investigation. The membrane performance when treating waste water collected at a car wash at different times of the year was also studied. The retention of the different chemicals varied greatly, but there was no significant difference in COD retention among the three UF membranes. The highest flux was observed when treating the alkaline degreasing agents and the shampoo solutions. The flux and COD retention when treating the waste water from the car wash were 30–50 l/m ² h and 60%, respectively. One of the low-retention degreasing agents was treated by nanofiltration (NF). The retention was significantly higher when using NF, but the COD concentration in the permeate was still too high to allow the permeate to be discharged without further treatment.     

Comparison of polyamide nanofiltration and low-pressure reverse osmosis membranes on As(III) rejection under various operational conditions

A nanofiltration (NF) membrane and a low-pressure reverse osmosis (LPRO) membrane both with aromatic polyamide selective layer from the same manufacturer were employed for the comparison of their performances in terms of As(III) rejection and filtration flux under a variety of operational conditions. In addition to the smaller membrane pore size, the LPRO membrane possesses much more dissociable functional groups than the NF membrane. When the feed pH was below the pKa₁ value (9.22) of H₃AsO₃, for which the steric hindrance is the only rejection mechanism, the removal efficiencies by NF and LPRO were about 10% and 65%, respectively. When the feed pH was higher, for which electrostatic effect began to take effect, the removal efficiencies could reach 40% and 90% for NF and LPRO, respectively. The rejection performance of LPRO was marginally affected by the feed As(III) concentration or ionic strength, although ionic strength had a strong effect on the filtration flux. In contrast, feed As(III) concentration and ionic strength had little effect on the filtration flux but great influence on the As(III) rejection performance of NF. The filtration flux was enhanced with the increase of transmembrane pressure for either NF or LPRO. The NF model could predict the general trend of the effects of the filtration flux, the feed water chemistry and its own concentration on As(III) rejection ratio by the NF membrane, but the rejection ratios were over-predicted.     

Preparation and characterization of nanofiltration membranes fabricated from poly(amidesulfonamide), and their application in water–oil separation

Nanofiltration membranes prepared from selected types of poly(amidesulfonamide) (PASA) targeted to retain either sucrose, raffinose, or β‐cyclodextrin were fabricated in conditions deduced from a chemometric method. Membrane performance was characterized by the permeation of solutions containing 1000 ppm carbohydrates and metal ions. To demonstrate the dependence of the membrane properties on the polymer structure, the separation characteristics of a series of four PASA homopolymers and four PASA copolymers were established. The results allowed us to screen out several promising PASA materials for the NF separation process. In addition, the superiority of the PASA materials, characterized by excellent retention and high flux rate, was evident from the results of a study comparing it with polysulfonamide, poly(ether amide), and commercially available regenerated cellulose. As a means of pollution control, the PASA NF membranes have been proven to be effective in removing oil from oily wastewater. Under an operating pressure of 2–3 psi, a constant flux of 5 L m^?2 h^?1 and 99.6% retention of a solution of 5000 ppm olive oil could be achieved with the PASA membranes over a period of 430 h. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1803–1810, 2003     

Correlation between retention and adsorption of phenolic compounds in nanofiltration membranes

Equilibrium adsorption experiments of phenol, 3-chlorophenol, 4-chlorophenol, and 3-nitrophenol aqueous solutions on NF90 membrane were conducted to obtain the corresponding adsorption isotherms at 25 ºC. Single-compound solutions with concentration ranging from 0.1 to 8 mmol L^− 1 were used. Freundlich and Langmuir models were compared to the experimental isotherms and their characteristic parameters were obtained from linear fits. In addition, the adsorptive behaviour of twelve aqueous phenolic compounds on the NF90 membrane was studied in order to investigate the relationship between adsorption and retention of selected solutes. An inverse correlation between the adsorbed amount, at the same equilibrium concentration (1 mmol L^− 1), and retention was found. The influence of the molecular hydrophobicity and dipole moment of phenolic compounds on membrane adsorption, solute retention and water flux decline was also investigated.     

Nanofiltration of Hormone Mimicking Trace Organic Contaminants

Abstract

The removal mechanisms of three hormone mimicking organic compounds by nanofiltration (NF) membranes have been examined. Two NF membranes having different pore sizes were used in laboratory‐scale nanofiltration experiments with feed solutions spiked with a hormone mimicking compound—nonylphenol, tert‐butylphenol, or bisphenol A. Retention of the compounds was determined at various solution chemistries, namely aqueous solution pH, ionic strength, and presence of natural organic matter. The nanofiltration behavior of the selected hormone mimicking compounds appears similar to that of natural hormones as reported in our previous work. While the solution pH can dramatically influence the retention of hormone mimicking compounds by a loose NF membrane, ionic strength does not affect the nanofiltration of such contaminants. However, in the presence of natural organic matter in the feed solution, ionic strength appears to play a significant role in solute‐solute and solute‐membrane interactions, resulting in increased retention due to partitioning of the hormone mimicking compounds onto organic matter at a higher ionic strength.     

Preparation and characterization of a novel positively charged nanofiltration membrane based on polysulfone

The goal of this study was to prepare positively charged nanofiltration (NF) membranes to remove cations from aqueous solutions. A composite NF membrane was fabricated by the modification of a polysulfone ultrafiltration support. The active top layer was formed by the interfacial crosslinking polymerization of poly(ethylene imine) (PEI) with p‐xylene dichloride (XDC). Then, it was quaternized by methyl iodide (MI) to form a perpetually positively charged layer. The chemical and morphological changes of the membrane surfaces were studied by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy. To optimize the membrane operation, the PEI solution concentration, PEI coating time, XDC concentration, crosslinking time, and MI concentration were optimized. Consequently, high water flux (5.4 L m^?2 h^?1 bar^?1) and CaCl₂ rejection (94%) values were obtained for the composite membranes at 4 bars and 30°C. The rejections of the NF membrane for different salt solutions, obtained from pH testing, followed the order Na₂SO₄ < MgSO₄ < NaCl < CaCl₂. The molecular weight cutoff was calculated by the retention of poly(ethylene glycol) solutions with different molecular weights, and finally, the stoke radius was calculated as 1.47 nm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41988.     

Deposition of toxic metal particles on rough nanofiltration membranes

Two nanofiltration (NF90 and Nano-Pro-3012) membranes were investigated for their capacity to remove metal ions. This study presents the effect of membrane roughness on the removal of toxic metal ions during dead end membrane filtration. Atomic force microscopy, scanning electron microscopy, WSXM software and ImageJ were used to characterize the roughness of the membranes. Gradual decrease in filtration permeate flux was observed as foulants accumulated at the interface of the membranes; filtration permeate flux varied from 20 L/m²/h to 14 L/m²/h and 11 L/m²/h to 6 L/m²/h for NF90 and Nano-Pro-3012, respectively. NF90 membrane was more prone to fouling than the Nano-Pro-3012 membrane: the percentage flux reduction was higher for NF90 (3.6%) than Nano-Pro-3012 (0.98%). The bearing ratio of the fouled NF90 exhibited a high peak of 7.09 nm than the fouled Nano-Pro-3012 with the peak of 6.8 nm.     

Novel charged chitosan composite nanofiltration membranes containing chiral mesogenic group

To improve the performance of nanofiltration (NF) membranes, a chiral mesogenic compound, a positively charged compound, and a negatively charged compound were grafted to chitosan, respectively. Series of novel composite NF membranes were prepared by over‐coating the polysulfone ultrafiltration membrane with the mixture of chitosan and modified chitosan. The chiral mesogenic compound, the positively charged compound, the negatively compound and their chitosan derivatives were characterized by infrared spectrophotometer, differential scanning calorimetry, polarized optical microscope; the structure of the membrane was characterized by scanning electron microscopy. The performance of composite NF membranes was strictly related to the novel compounds grafted to chitosan and its composition. The rejection reached the maximum of 95.7% for CaCl₂ with P_2‐7 composite NF membrane, corresponding flux was 3155 Lm^?2h^?1. The rejection reached the maximum of 93% for Na₂SO₄ with P_3‐5 composite NF membrane, corresponding flux was 3879 Lm^?2h^?1. Comparing with conventional NF membranes, the membranes were used in low pressure with high flux, especially for the separation of high‐valence ions from solution. The membranes were typical charged NF membranes. POLYM. ENG. SCI., 57:22–30, 2017. © 2016 Society of Plastics Engineers     

Treatment of Leather Plant Effluent by Membrane Separation Processes

Abstract

A scheme is proposed for the treatment of the leather plant effluent using membrane based separation processes. The effluent coming out from the various upstream units of the leather plant (except chrome tanning) are combined and a two step pressure driven membrane processes involving nanofiltration (NF) and reverse osmosis (RO) are adopted after a pretreatment consisting of gravity settling, coagulation, and cloth filtration. The entire membrane separation scheme is validated by conducting experiments under a continuous cross flow mode. A detailed parametric study for cross flow experiments is investigated to observe the effects of the operating conditions, i.e., the transmembrane pressure drop and the cross flow velocity on the permeate flux and quality for both NF and RO. Using a combination of osmotic pressure and solution diffusion model for both NF and RO, the effective osmotic pressure coefficient, solute diffusivity, and the solute permeability through the membrane are obtained by optimizing the experimental permeate flux and concentration (in terms of total dissolved solids) values for this complex industrial effluent. The BOD and COD values of the finally treated effluent are well within the permissible limits (in India).     

Recovery and recycle of tannins in the leather industry by nanofiltration membranes

The aim of this work was the study of the application of membrane concentration to exhausted tanning baths from vegetable tannage operations in order to increase the tannin/non‐tannin (T/NT) ratio and obtain recyclable material. For this purpose four samples of tanning baths at different T/NT ratios (from 0.7 to 1.4) were processed using six different types of membranes which ranged from reverse osmosis (RO) to nanofiltration (NF). The membrane module Fluid Systems TFC S 2540 gave the best results in terms of permeate flux and also in terms of increased T/NT ratio in the retentate (from 1.4 to 1.7). In order to compare the permeate flux reduction with time (J_t) for the different modules, the osmotic pressure differences (Δπ) between permeate and retentate were estimated by electrical conductivity measures. The fouling phenomena for the different membranes in the processing of each sample were evaluated by comparing the pressures required to obtain the same VRF (volume reduction factor), NPF (normalized permeate flux) and membrane performances with tap water before and after tannin concentration. The retention of tannins, which are polyphenols capable of significant hydrogen bonding, was found to be governed by the chemistry of the interactions between their complexes and the polyamide membrane material. Copyright © 2004 Society of Chemical Industry