Kinetics of Membrane Flux Decline: The Role of Natural Colloids and Mitigation via Membrane Surface Modification

Applications of membrane technologies for potable water production have been expanding significantly, leading to increased efforts to control membrane fouling, which can significantly reduce membrane performance, increase operating costs, and shorten membrane life. Natural organic matter is ubiquitous in all water supplies and has been implicated as a major contributor to fouling during filtration of natural water. In this review, we discuss factors that influence NOM fouling, including hydrodynamics; properties of the feed constituents such as size, hydrophobicity, charge density and isoelectric point; properties of the membrane including hydrophobicity, charge density, surface roughness, and porosity; and properties of the solution phase such as pH, ionic strength and concentration of metals. We review approaches to identify and mathematically describe fouling kinetics, including effects of pore blockage, cake formation, and osmotic pressure. Finally, we discuss strategies to mitigate fouling, with a focus on strategies that involve a modification of the nanostructure of membrane surfaces, via UV-assisted graft polymerization of hydrophilic monomers to increase surface wettability and reduce interactions between NOM and the membrane surface.     

High throughput screening for rapid development of membranes and membrane processes

The objective of this study was to investigate the feasibility of high throughput (HT) screening techniques for pressure-driven membrane processes. For this purpose, a HT-filtration module, allowing to perform 16 pressure-driven separations simultaneously, was designed. The potential of the developed equipment and of the HT-screening concept in general was validated by demonstrating both the reproducibility of experimental flux and selectivity data, and the scalability of these data between the HT-module and a conventional dead-end filtration set-up. Data were obtained with two solvent resistant nanofiltration (SRNF) membranes: a laboratory-prepared polyimide (PI) and a commercial MPF-50 membrane. The reproducibility of the data was highly encouraging, proving that this HT-approach can be a useful tool to rapidly screen a large array of operational parameters in membrane processes and of synthesis parameters in the development of new membranes.     

Cross-linked polyimide membranes for solvent resistant nanofiltration in aprotic solvents

Solvent stable nanofiltration membranes were prepared through the chemical cross-linking of asymmetric Matrimid^®-based polyimide membranes with p-xylylenediamine. The influence of this straightforward post-treatment on membrane stability, morphology and performance in dimethylformamide (DMF), N-methylpyrrolidinone (NMP), dimethylacetamide (DMAc) and dimethylsulfoxide (DMSO) was thoroughly investigated. With permeabilities up to 5.4 l/m² bar h and rejections up to 98% for low molecular weight dyes in these demanding solvents, optimally performing, truly solvent resistant nanofiltration membranes were obtained. Nanozeolite-filled membranes were prepared in parallel to study the effect of an inorganic filler on the cross-linking reaction and performance in aprotic solvents. The outstanding stability and performance of these membranes and their easy preparation clearly offer vast potential for applications in harsh solvent environments.     

pH stimuli-responsive and fouling resistance PES membrane fabricated by using photochromic spiropyran and spironaphthoxazine nanofillers for pesticide removal

New fouling resistance and stimulus–responsive nanofiltration membranes were fabricated by adding photochromic spiropyran (SPO) and spironaphthoxazine (SNO) nanofillers to the polyethersulfone (PES) matrix via the phase inversion method. The effect of SPO and SNO, as novel photoresponsive molecule nanofillers, were evaluated in terms of membrane morphology, porosity, wettability, pure water flux (PWF), antifouling resistance, and stimulus–responsive properties. All the modified membranes indicated better performance compared to the bare PES. The membrane PWF was notably enhanced from 7.7 kg/m²h for the bare PES up to 18.68 and 20.58 kg/m²h for the 0.1 wt.% SPO and SNO blended membranes, respectively. Also, the 0.1 wt.% of SNO-based PES membrane indicated the best flux recovery ratio compared to the other membranes. The photo stimulus–responsive assessment showed a color change for both SPO and SNO photochromic in membranes. In the case of variable effect investigation, the response surface methodology at three levels (pressure: 4, 5, 6 bar and flow rate: 50, 100, and 150 L/h) was applied. A suitable flux (23.39 kg/m² h) and high removal efficiency (more than 90%) was achieved at optimum conditions. Also, the modified membranes by photochromic materials were sensitive to environmental variables such as acidic and alkaline conditions by changing their color.     

二胺结构对聚酰胺复合纳滤膜性能的影响

分别以邻苯二胺、间苯二胺、对苯二胺为水相单体,均苯三甲酰氯(TMC)为油相单体,聚醚砜超滤膜为基膜,界面聚合法制备了复合纳滤膜.在纳滤膜对Na<,2>SO<,4>,MgSO<,4>,MgCl<,2>和NaCl四种盐的脱盐率中,间苯二胺膜最高,对苯二胺膜居中,邻苯二胺膜最差;在纳滤膜耐氯性能方面,对苯二胺最佳,邻苯二胺居...     

Interlaboratory studies of highly permeable thin‐film composite polyamide nanofiltration membrane

The aim of this paper is to survey interlaboratory studies of performance data to produce highly permeable thin‐film composite (TFC) polyamide nanofiltration (NF) membrane in the form of flat sheet at bench scale. TFC polyamide NF membranes were fabricated via interfacial polymerization of 1,3‐phenylenediamine and trimesoyl chloride on porous polyethersulfone (PES) membrane. The NF membranes were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross‐flow filtration. The AFM and SEM analyses indicated that a rough and dense film was formed on the PES support membrane. The permeability and NaCl rejection of the NF membrane prepared at the presence of camphor sulfonic acid as pH regulator and triethylamine as accelerator in the aqueous solution were 21 l m^?2 h^?1 and 70%, respectively. In order to estimate the repeatability and reproducibility standard deviations, the development of an interlaboratory study was conducted by measurements of permeation flux and salt rejection of the synthesized membranes. Repeatability standard deviation of the permeation flux data for the membrane based on optimum formulation was 1.99, and reproducibility standard deviation was 3.55. Also based on this trend, repeatability standard deviation of the salt rejection data was 1.57, and reproducibility standard deviation was 4.11. The American Society for Testing and Materials standard E691‐05 was used for data validation of the repeatability and reproducibility standard deviations and consistency statistics. Copyright © 2011 John Wiley & Sons, Ltd.     

Batchwise and Continuous Organophilic Nanofiltration of Grubbs‐Type Olefin Metathesis Catalysts

Retained : An N‐heterocyclic carbene with eight cyclohexyl groups (see figure) provides increased electron density for a highly active olefin metathesis catalyst as well as sufficient steric bulk to allow the efficient separation of such a complex from the organic products in the solvent‐resistant nanofiltration.

     

Membrane processes used for separation of effluents from wire productions

Metal wires are produced from different metals using drawing methods. The metal used influences both the technology applied and the composition of effluents generated during wires production. Ultrafiltration and nanofiltration are used for the separation of waste emulsions from cable factories. Membrane distillation was proposed for the treatment of acidic saline wastewater generated during steel wire manufacturing (etching). The possibility of the previously mentioned processes application for water reuse is presented. The application of poly(vinylidene fluoride) (PVDF) membranes (FP 100) with the molecular weight cut-off (MWCO) of 100 kDa in the ultrafiltration process resulted in the reduction of 99 % of oil and lubricants in the treated emulsions and allowed complete removal of suspended solids and colloidal substances. Such pre-treated emulsion was subsequently purified by nanofiltration (NF-90-2540) and a 98 % rejection of copper ions was achieved, resulting in a decrease of the permeate electrical conductivity from 3200 μS cm⁻¹ to 260 μS cm⁻¹. The obtained permeate was suitable for preparation of fresh oil emulsion utilized for lubrication in the wire drawing process. The spent etching baths (from steel wire production), which mainly contained FeSO₄ and about 1 mass % of sulfuric acid, were separated by membrane distillation. The obtained permeates were: clean water with electrical conductivity at a level of 3–5 μS cm⁻¹. Concentrates (190–200 g of Fe per L) from the MD process were cooled to 295 K, which enabled the FeSO₄ crystallization. Application of the above-mentioned membrane processes allows producing high quality product water, over 90 % of water was recovered from the treated wastewaters. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Polymeric Membrane Nanofiltration and Its Application to Separations in the Chemical Industries

The application of membrane technology, particularly water-based nanofiltration, as a separation process in the chemical industries has increased tremendously in recent years. However, the use of membranes capable of molecular separation in non-aqueous systems (e.g. nanofiltration) is a relatively new and growing application of membrane technology. The main challenge in applying polymeric nanofiltration membranes to non-aqueous systems is that the polymers developed for water-based applications are not suitable. Polyimide is a particularly interesting polymer as it has excellent chemical resistance, and membranes produced from it provide desirable separation properties – i.e. economically viable flux and good separation of nanoscale molecules. Various research works have shown that commercial polyimide organic solvent nanofiltration (OSN) membranes, trademark STARMEM™, 1 are robust and suitable for performing molecular separations. This work will discuss in detail the use of STARMEM™ in a pharmaceutical application. The EIC-OSN process was developed for separating the enantiomers of chiral compounds in pharmaceutical applications. High optical purity (94.9%) of (S)-phenylethanol from rac-phenylethanol was achieved through the use of STARMEM™122. Process simulation of the ideal eutomer-distomer system predicted that the highest theoretical resolvability from this process would be 99.2%. Other application areas of OSN are varied, including purification and fractionation in the natural products industry, homogeneous catalyst recovery, monomer separation from oligomers, etc. Currently, OSN is used in a small number of processes including a very large petrochemical application, but it has the potential to be applied to a wide range of separations across the full spectrum of the chemical industries.     

紫外辐照接枝制备亲水性两性纳滤膜

通过紫外辐照在酚酞基聚芳醚酮(PEK-C)超滤膜表面引发自由基共聚反应, 依次接枝二甲基二烯丙基氯化铵(DADMAC)和对苯乙烯磺酸钠(SSS), 制成亲水性、表面载有两种不同电荷的纳滤膜. 通过测定膜的纯水通量和对不同盐溶液表观截留率的变化, 系统研究了单体浓度和接枝时间对膜的分离性能的影响. 结果表明, 用这种方法制成的亲水性两性纳滤膜对盐溶液的截留作用与两种单体在接枝液中的浓度和接枝时间有关. 膜对由高价同离子和高价反离子组成的盐表现出优良的截留作用.