Mechanical properties of tape casted Lanthanum Tungstate for membrane substrate application

Advances in the development of asymmetric membrane concepts require the development of porosity optimized, mechanically reliable substrate materials. The current study focuses on the characterization of the room temperature mechanical properties of tape casted Lanthanum Tungstate of different porosities for membrane substrate applications. Elastic modulus and hardness are assessed using indentation testing. Characteristic strength and Weibull modulus are determined from data obtained using a ball-on-3-balls test that is particularly advantageous for the rather thin tape casted material. Particular emphasis is placed on the effect of the surface composition onto the fracture strength.     

Crosslinked PVDF-HFP-based hydrophobic membranes incorporated with CNF for enhanced stability and permeability in membrane distillation

Over the past decades, numerous materials have emerged as promising amenities for the fabrication of novel membranes. The current study gives insight into a modest and effective method to fabricate a crosslinked poly-vinylidene fluoride-co-hexafluoropropylene membrane with better mechanical properties and permeability for desalination. Poly-vinylidene fluoride-co-hexafluoropropylene membrane was grafted with crosslinked collagen to enhance direct contact membrane distillation used for desalination. Stiffness, rigidity and mechanical properties of the membrane were intensified by incorporating collagen (extracted from eggshells) into the membrane matrix, with glutaraldehyde crosslinkers. Furthermore, to improve water vapor diffusion, immobilized carbon nanofibers (CNF) were integrated in the membrane, casted via phase inversion technique with an optimized controlled approach. The permeate flux of CNF incorporated membrane was as high as 8 LMH, 18% higher than the unmodified poly-vinylidene fluoride-co-hexafluoropropylene membrane at 60 °C, besides minimal salt leakage. The properties of the modified membrane were characterized from its contact angle, morphological structure, surface roughness, dynamic mechanical properties, and water flux. The overall performance of the modified membranes was better than the virgin membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48021.     

Investigation of characteristic and performance of polyvinyl chloride ultrafiltration membranes modified with silica-oriented multi walled carbon nanotubes

The complicated and dynamic nature of membrane fouling is one of the most challenging issues that need to be addressed to obtain an efficient membrane. In this work, silica-oriented multiwalled carbon nanotubes (Si-MWCNTs) are synthesized by the sol–gel method and characterized using several analytical techniques. Novel polyvinyl chloride (PVC) ultrafiltration membranes are fabricated by incorporation of Si-MWCNT nanoparticles at varying loading levels (0–2 wt%) using the phase inversion method. Membrane morphology, chemical composition, thermal behavior, crystallinity, roughness, hydrophilicity, and mechanical strength are characterized and filtration performance is tested to compare the results with those of pristine PVC membranes. The results reveal that the addition of 0.5% Si-MWCNT nanoparticles into the casting solution exhibits the highest flux (400 L/m²h), sodium alginate (SA) rejection rate (96%), and flux recovery ratio (93%) due to having the highest hydrophilicity, an improved structure, and surface properties revealed by surface morphology and bulk property analysis. Furthermore, the results of dynamic mechanical and nanoindentation analyses confirm that mechanical properties such as hardness, Young's modulus, and stiffness of the pristine membrane are significantly improved by the addition of Si-MWCNT nanoparticles.     

In-solution structure formation of poly(vinylidene fluoride) building units influencing on the final membrane characteristics

A systematic study was carried out on the initial casting solutions of asymmetric PVDF ultrafiltration membranes to observe the aggregate structure of polymer building units in solution and the properties of the membranes in terms of microstructure morphology, crystallinity, average pore size, pore-size distribution, total porosity, hydrophobicity, wetting energy, molecular weight cut-off, and permeability. Hydrophobic membrane of higher porosity exhibiting higher flux was obtained from the solution of bigger polymer structural units while the membrane obtained from solution of smaller polymer structural units exhibited relatively rougher and hydrophilic surface and smaller uniform pores with lesser flux.     

Experimental study on membrane wetting in gas–liquid membrane contacting process for CO2 absorption by single and mixed absorbents

The membrane wetting by the liquid absorbents is an important problem in the operation of gas–liquid membrane contacting process. In order to gain a better understanding on the role of absorbents on membrane wetting, monoethanolamine (MEA, primary amine), diethanolamine (DEA, secondary amine), and 2-amino-2-methyl-1-propanol (AMP, sterically hindred amine) were applied as absorbent solutions. The membrane used for the experiments was the hollow fiber polyvinylidenefluoride (PVDF) membrane. The performance of both single and mixed amine solutions on the CO₂ absorption capacity and membrane wetting potential were investigated. In addition, sodium chloride (NaCl, inorganic salt) and sodium glycinate (SG, organic salt) were added into the MEA aqueous solution to observe CO₂ flux and membrane wetting.The results revealed that the use of MEA solution and SG as absorbents gave highest CO₂ flux. The overall mass transfer coefficients obtained from the experiments also showed the same trend as CO₂ flux, i.e, the values were in the following order: MEA> AMP > DEA. However, the long-term flux was monitored and it was found that MEA also gave lowest flux decline due to the membrane wetting. The use of mixed amine solutions and the addition of NaCl did not help protect the membrane wetting. On the contrary, the addition of SG in to MEA solution can improve flux and resulted in stable CO₂ flux indicating that the membrane wetting was negligible.     

Porous polyethersulfone hollow fiber membrane in gas–liquid contacting processes

Porous polyethersulfone hollow fiber membranes were fabricated via dry–wet phase inversion method with the polymer concentration in the spinning dope either 13 wt% or 15 wt%. The fabricated hollow fiber membranes were characterized by different test methods and the performance of membranes in contactor applications was tested by CO₂ absorption. The mean pore size, effective surface porosity and membrane porosity decreased while the membrane density and Liquid Entry Pressure (LEPw) increased as polymer concentration increased. The CO₂ absorption flux of the fabricated membranes was measured in two cases; i.e. when the absorbent, distilled water, was in the lumen side or in the shell side. The CO₂ flux for the membrane, fabricated from 13 wt% PES solution, was compared with some commercial and in-house made membranes. The former membrane had 111% higher flux than a commercial PTFE membrane.     

Ultrafiltration behaviors of pectin-containing solution extracted from citrus peel on a ZrO<Subscript>2</Subscript> ceramic membrane pilot unit

Ultrafiltration experiments on a solution of pectin, hesperidin, and other mixtures extracted from citrus peels have been performed on a 500 l/min pilot scale crossflow ceramic membrane unit. A 30,000 molecular weight cut-off (MWCO) zirconia (ZrO₂) ceramic membrane with a total effective flow area of 0.5 m² was used in the process. The permeate flux for pure water and hesperidin showed linear relationship with transmembrane pressure (ΔP), but the flux for pectin solutions showed a curvilinear relationship with ΔP and represented a rapid increase with increasing ΔP before leveling-off. Similar behavior was observed by adding different amounts of hesperidin to these pectin solutions, but with much lower permeate flows. The formation of gel layers on the membrane surface is mainly responsible for the lower permeate fluxes. In addition, the permeate flux decrease faster at higher ΔP, since higher ΔP brought bigger flux at lower pectin concentration. Compared with the more than 90% retention rate of macromolecular pectin, pigment and other component have less than 20% retention rate. So, the decolorization, the separation and purification of pectin preparations could be achieved simultaneously through ultrafiltration with a ceramic membrane.     

Effect of crystallinity and swelling on the permeability and selectivity of polymer membranes

The conventional equations describing mass transport through membranes predict proportionality between flux and driving force. Experimental results inconsistent with this prediction are usually attributed to a concentration dependency of the diffusion coefficients of the species involved. It has now been found that, in addition to this effect, simplifications in the models and the neglect of crystallinity and swelling of the membrane material contribute in no small way to the noted deviations. On the basis of the well-known “solution-diffusion” theory a new permeation rate equation has been derived, which accounts for the various shortcomings mentioned and which is capable of predicting the large effects of crystallinity and swelling of the membrane material on permeability. This equation also expresses the mutual effects of permeants on their separation without the introduction of an arbitrary coupling coefficient, which is required in the conventional equations.A simplified procedure is proposed for calculating membrane separation of multicomponent mixtures, which is based on the assumption of an exponential concentration gradient inside the membrane in accordance with reported experimental observations. The exponential form, which differs for each composition and set of conditions, can be calculated from the boundary conditions of the membrane.     

Tubular Membrane Filtration with A Side Stream and its Intermittent Backwash Operation

The tubular membrane filtration system is widely applied to solid-liquid separation processes. Any improvements to the filtration module would increase separation efficiency, thus reducing operating costs. In this experiment, PMMA powder with an average particle diameter of 0.8 µm was filtered by a ceramic tubular membrane with an average pore size of 0.2 µm, and the impacts of the operating variables, such as suspension concentration, the filtration pressure, and the crossflow velocity on the permeate flux were discussed. In order to understand the increased permeate flux, the proposed module is comparable to the tubular membrane filtration module, but with an additional side stream under the same filtration mass flow rate. In addition, variations of shear force on the membrane surface are analyzed by CFD simulation, and the influence of backwash operations on the permeate flux is discussed. The results show that the side stream membrane filtration increased the shear force on the membrane surface, reduced fouling on the membrane surface, and increased the permeate flux. Furthermore, a backwash operation with a side stream flow channel could effectively clean the particles deposited in the module, thus, increasing the permeate flux.     

Studies on scaling of membranes in desalination by direct contact membrane distillation: CaCO3 and mixed CaCO3/CaSO4 systems

Scaling of membranes by CaCO₃ and CaSO₄-CaCO₃ is of considerable concern in membrane desalination processes. It is particularly relevant for porous crossflow hollow fiber-based membrane distillation (MD) processes which can achieve high water recovery and can encounter heavy precipitation of scaling salts. Therefore an analysis of the scaling potential for CaCO₃ and mixed CaSO₄-CaCO₃ systems is presented first in terms of the saturation index profiles throughout the crossflow hollow fiber membrane module as a function of the location in the module for feed solutions resulting from high water recovery. Scaling experiments during DCMD with tap water, CaCO₃ and mixed CaSO₄/CaCO₃ were conducted over a wide range of values of saturation index (SI) (10<SI_calcite<64, 1.1<SI_Gypsum<1.5) using porous fluorosilicone coated crossflow hollow fiber membrane desalination modules. The effects of flow rates, flow patterns (cross vs. parallel flow) and the nature of the membrane surface on possible scaling scenarios were further investigated for the scaling salt CaSO₄. Experimental results at high saturation indices show that even when the precipitation rate was fast in the CaCO₃ system at elevated temperatures or high concentrations, no significant loss in water vapor permeation was observed suggesting no effect of scaling on membrane flux. However, for a few of the mixed CaSO₄-CaCO₃ systems, the water vapor flux dropped somewhat. Possible explanations have been provided and a method to solve this problem has been illustrated. Fast feed flow rate resulted in a shortened induction period. Crossflow flow pattern and the nature of the hydrophobic porous coating on the membrane surface were proven to be helpful in developing the resistance to scaling. Results of modeling show that concentration polarization effects are far more important than temperature polarization effects.     

Performance of Composite Membranes of Poly(ether–block–amide) for Dehydration of Ethylene Glycol and Ethanol

Poly(ether–block–amide) (Pebax 2533) membrane was synthesized on a poly(vinylidene fluoride) (PVDF) ultraporous substrate to study the separation of synthetic ethylene glycol/water and ethanol/water mixtures by pervaporation. The membrane was characterized by FTIR spectroscopy, DSC, SEM, and XRD to assess intermolecular interactions, thermal stability, surface morphology, and crystallinity, respectively. Equilibrium sorption studies were carried out in pure liquids and binary alcohol-water mixtures of different compositions to assess polymer-liquid interactions. Pebax 2533 membrane exhibited the requisite potential for dehydration of the alcohols by showing a selectivity of 1254 and water flux of 0.05 kg m^?2 h^?1 for the ethanol azeotrope, whereas the corresponding selectivity for 95% ethylene glycol feed was 978 with a similar flux. The effect of operating parameters such as feed composition and permeate pressure on membrane performance was evaluated. The membrane exhibited considerable feasibility for scale-up with significant potential for alcohol dehydration.     

The Effect of Pulsed Direct Current Field on the Membrane Flux of a New Style of Membrane Bioreactor

The effect of a pulsed direct current electric field on the membrane flux of an antifouling Membrane Bioreactor (MBR) designed and built in the laboratory was studied. The results showed that a pulsed direct current electric field had a significant effect on the membrane flux. The average membrane flux when using a pulse direct current electric field was between that of a steady electric field and that of no electric current under a trans‐membrane pressure drop of ΔP = 0.1 MPa and a pulsed direct current electric field strength of 20 V/cm. There was an optimum value of pulse intensity and pulse duration for the membrane flux. The shorter the pulse interval time was, the higher the frequency of power‐on, and the higher the average stable membrane flux of the MBR. This may have resulted from the fact that charged coarse particles and colloids account for 80 % of COD_cr and BOD₅ in urban domestic sewage. These particles and colloids moved away from the membrane surface at a certain electrical field strength, gradually thinning the particle sedimentary layer, reducing the membrane filtration resistance, and increasing the membrane flux significantly. However, the formation of a sedimentary layer on the membrane surface needed a significant amount of time and an appropriate pulse frequency while the MBR is powered on. This could save energy while keeping the membrane clean.     

表面偏析法制备用于乙醇渗透蒸发脱水的整体PVA-PES复合膜(英文)

A facile surface segregation method was utilized to fabricate poly(vinyl alcohol)-polyethersulfone (PVA-PES) composite membranes. PVA and PES were first dissolved in dimethyl sulfoxide (DMSO), then casted on a glass plate and immersed in a coagulation bath. During the phase inversion process in coagulation bath, PVA spontaneously segregated to the polymer solution/coagulation bath interface. The enriched PVA on the surface was further crosslinked by glutaraldehyde. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) confirmed the integral and asymmetric membrane structure with a dense PVA-enriched surface and a porous PES-enriched support, as well as the surface enrichment of PVA. The coverage fraction of the membrane surface by PVA reached up to 86.8% when the PVA content in the membrane recipe was 16.7% (by mass). The water contact angle decreased with the increase of PVA content. The effect of co-agulation bath type on membrane structure was analyzed. The membrane pervaporation performance was evaluated by varying the PVA content, the annealing temperature, feed concentration and operation temperature. The mem-brane exhibited a fairly good ethanol dehydration capacity and long-term operational stability.     

Gradient crystallinity and its influence on the poly(vinylidene fluoride)/poly(methyl methacrylate) membrane-derived by immersion precipitation method

Herein, phase inversion poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) microporous membranes were prepared at various PMMA concentration by immersion precipitation method. Increment in the PMMA concentration has a significant influence in the PVDF membrane crystallinity, which is studied by differential scanning calorimeter, X-ray diffractometer, and small-angle X-ray scattering analyses. Properties such as membrane bulk structure, porosity, hydrophilicity, mechanical stability, and water flux vary in terms of PMMA concentration. Porosity is increased, and tensile strength decreased when PMMA concentration is beyond 30 wt %. Thermodynamic instability during the liquid to solid phase separation and variation in the crystallinity has an intense effect on these membrane properties. Then, 70/30 blend membrane selected as optimum composition owing to the high porosity and pure water flux compared to other compositions. This membrane is modified with a composite filler derived from the graphene oxide and titanate crosslinked by chitosan. The antibacterial, antifouling, and bovine serum albumin separation studies reveal that the developed nanocomposite membrane is a potential candidate for the separation application. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48677.     

Influence of the membrane structure on the composition of the deposit-layer during processing of microbial suspensions.

The performance of a microfiltration (MF) membrane was compared with an anisotropic ultrafiltration (UF) membrane during cell harvesting of E. coli. The microfiltration membrane has very high surface porosity and thus very high water flux. When challenged with E. coli fermentation broth the MF membrane exhibited a much higher rate of initial flux decline and gave lower steady state flux than the UF membrane. Transmission Electron Microscopy was used to examine the nature of the deposits on the remaining membrane surface after use. The cake on the MF membrane was composed of E. coli cells densely packed into a biofilm while the deposit on the UF membrane was very thin and composed of macromolecules and fibrils and only few cells. These results showed that under cross-flow conditions cells were washed away from the smooth surface of the UF membrane but not from the surface of MF membrane.     

Experimental Investigation on the Separation of Bentonite using Ceramic Membranes: Effect of Turbulence Promoters

Abstract

The static turbulence promoters presented in this work are designed to enhance filtration within tubular ceramic membranes of 0.5 micron pore size. Permeate flux enhancement still remains a topical problem during tangential crossflow filtration. The decline in flux with time is due to the usual phenomena of concentration polarization and membrane fouling, operating parameters including the system pressures, feed composition, membrane type and configuration, and the hydrodynamics within the membrane module. Solute accumulates on the membrane surface and forms a high concentration gel layer, thus increasing the effective membrane thickness and reduces its hydraulic permeability. Turbulence promoters of varying pitch lengths have been incorporated into the work to ultimately reduce the deposition of bentonite particles on the membrane surface during microfiltration. Yeast suspensions have previously been used as feed suspensions in order to compare the effectiveness of the turbulence promoters with an organic foulant. The objective of this work was to investigate the influence of static promoter geometry on flux sustainability enhancement during bentonite suspension filtration. All experiments have been conducted on a tubular ceramic membrane and the experimental membrane rig as shown in this paper. The effects of feed concentration, feed temperature, system pressures, and crossflow rates on the membrane flux sustainability were investigated. It was found that the promoters greatly improved flux sustainability and membrane efficiency over time and in some cases, a loss of 3% in membrane efficiency was realized with turbulence promoters at higher feed temperatures. The use of the turbulence promoter caused a large scouring of the membrane surface and membrane cleaning was significantly improved compared to the experiments without the promoters.     

膜生物反应器中膜的污染与清洗

通过不同清洗方法对膜通量恢复效果的评价以及对污染膜和各步清洗后对膜表面和断面形貌的观察，对膜生物反应器工艺中的膜污染特征和膜污染进行了研究。结果表明，清水冲洗能消除纤维膜之间淤积的污泥和膜表面松散的污染层，次氯酸钠可以清除膜表面的微生物和有机污染物，而硫酸和柠檬酸能清除膜上的无机物垢。在膜外表面的污染物主要为生物膜和凝胶层污染，而膜内表面的污染物主要为滋生的微生物和无机污染物。对应各步清洗后膜通量的恢复，可以推出，在试验的工艺条件下，无机物污染对膜过滤阻力的影响较大。在此基础上．为延缓膜污染对膜生物反应器提出三点建议．     

陶瓷膜污染的超声波辅助清洗

膜污染的控制和膜的清洗再生是膜应用的关键,研究了采用超声波辅助清洗被乳化液污染的氧化锆陶瓷膜。结果表明：超声波的功率、超声清洗时间及膜污染程度等对清洗效果均有影响,超声功率越高,清洗后水通量的恢复率越高,超声清洗时间在20 min左右比较适宜。超声波对膜表面的污染清洗效果较好,对膜孔内堵塞清洗效果相对较弱,超声辅助化学清洗可有效恢复膜通量。     

PAC-UF处理含蛋白质类溶液过程中的膜污染研究

使用粉末活性炭(PAC)-超滤(UF)组合工艺处理牛血清白蛋白(BSA)溶液,研究了不同PAC投量下组合工艺的膜污染情况。结果表明,PAC本身对膜污染无明显贡献,PAC吸附BSA后使得膜通量急剧下降;PAC对改善BSA溶液通过超滤的膜通量和膜污染阻力均有一个最佳投加值;PAC在膜表面形成的滤饼层对膜通量改善作用明显;PAC滤饼层主要形成可逆污染,而水中BSA则是不可逆膜污染。     

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al₂O₃) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al₂O₃ powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al₂O₃ hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al₂O₃ hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al₂O₃/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al₂O₃/PES ratios and sintering temperature. When the Al₂O₃/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m²·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m²·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al₂O₃ hollow fiber membrane retained its’asymmetric structure even after the sintering process.