Effect of the pore sizes of nylon affinity membranes on γ-globulin adsorption

Summary l-Phenylalanine was immobilized on nylon membranes with two pore diameters (0.45 μm and 1 μm), by activation with 1,4-butanediol diglycidyl ether, and the effect of pore size on the affinity adsorption of γ-globulin studied by batch and kinetic methods. Experiment shows that adsorption on both affinity membranes obeys the Freundlich model. The accessible pore volume for adsorption of proteins on the membrane with 0.45 μm diameter pores is less than for that with 1 μm diameter pores. The adsorption capacity of affinity membranes with 1 μm diameter pores is 2.5-fold that of membranes with 0.45 μm diameter pores. Feed-rate has a larger effect on affinity adsorption on the membrane with 0.45 μm diameter pores than on that with 1 μm diameter pores. Small pores on the affinity membrane do not cause broadening of the elution peak. It is concluded that affinity interaction and separation occur mainly in the large pores, and small pore size does not favor improvement of adsorption capacity. γ-Globulin 85.1% pure can be obtained in one step from human plasma by use of the affinity membrane with 0.45 μm diameter pores.     

Influence of polypropylene membrane surface porosity on the performance of membrane distillation process

Two kinds of polypropylene capillary membranes were used in the membrane distillation (MD). These membranes exhibited a similar morphology, but one of them has an additional low porosity layer on the internal surface of capillaries. The changes of membrane performance during MD process of tap water were investigated. The presence of low porosity layer (thickness below 1 μm) caused that the air permeability was reduced from 1.365 to 0.863 dm³/m² s kPa, whereas the MD permeate flux was decreased only by 15%. A significantly larger decline of the flux was caused by CaCO₃ deposit formed during distillation of tap water. This deposit was removed every 30–70 h by rinsing the modules with a 2–5 wt.% HCl. Unfortunately, a repetition of this operation several times resulted in a gradual decline of the maximum permeate flux (distilled water as a feed). However, the module efficiency with the membranes covered by a surface layer of low porosity was found to decreases twice as slowly. The investigations revealed that a low surface porosity does not limit the possibility of surface wetting of polypropylene membranes, but hindered the scale formation inside the pores.     

The influence of polypropylene degradation on the membrane wettability during membrane distillation

In the membrane distillation process only gaseous phase can exist in the membrane pores. The resistance to wettability of capillary polypropylene membranes has been investigated in this work. The SEM-EDS investigations revealed that the pores located up to 100 μm from the membrane surface were filled by the feed during the production of demineralized water over a period of 4500 h. However, the pores located inside the membrane wall were still dry and no feed leakage was observed. Both scaling and polypropylene degradation were indicated as the major reason for partial membrane wettability. The SEM-EDS, XRD and FTIR methods were used for investigations of polypropylene degradation, and material cracking and the presence of hydroxyl and carbonyl groups on the membrane surface has been identified. The membranes irradiated by UV light or stored up to 9 years in air were used to evaluate the membrane wetting caused by the products of polymer oxidation. The membrane samples were soaked in either water or a concentrated solution of NaCl at temperature of 343 K, and their wettability was evaluated on the basis of their variations in the air permeability. It was found that the products of polypropylene oxidation significantly accelerated the degree of wettability during the first 30 days of investigations, but after 60 days the results were similar. The soaked membrane samples wetted faster in NaCl solutions than those soaked in distilled water, which came as a result of the chemical reactions of salt with the hydroxyl and carbonyl groups found on the polypropylene surface.     

Application of vacuum membrane distillation for concentration of organic solutions

Vacuum membrane distillation was used to concentrate organic solutions containing mainly 1,3-propanediol, ethanol and carboxylic acids. The studied solutions were permeates obtained from nanofiltration process applied for the separation of broths from the fermentation of glycerol with the Citrobacter freundii bacteria. The presence of organic solutes decreased the surface tension of permeates to the value of 47 mN m^?1. However, the pores inside the used polypropylene membranes were not wetted by the post-fermentation solutions, and they were concentrated to over five-fold. It was shown that vacuum membrane distillation has over twice higher thermal efficiency compared to that obtained by direct contact membrane distillation.     

Microbubble formation using asymmetric Shirasu porous glass (SPG) membranes and porous ceramic membranes—A comparative study

We have recently proposed a new method for generating uniformly sized microbubbles from Shirasu porous glass (SPG) membranes with a narrow pore size distribution. In this study, to obtain a high gas permeation rate through SPG membranes in microbubble formation process, asymmetric SPG membranes were used. At the transmembrane/bubble point pressure ratio of less than 1.50, uniformly sized microbubbles with a bubble/pore diameter ratio of approximately 9 were generated from an asymmetric SPG membrane with a mean pore diameter of 1.58 μm and a skin-layer thickness of 12 ± 2 μm at a gaseous-phase flux of 2.1–24.6 m³ m⁻² h⁻¹, which was much higher than that through a symmetric SPG membrane with the same pore diameter. This is mainly due to the much smaller membrane resistance of the asymmetric SPG membrane. Only 0.27–0.43% of the pores of the asymmetric SPG membrane was active under the same conditions. The proportion of active pores increased with a decrease in the thickness of skin layer. In contrast to the microbubble formation from asymmetric SPG membranes, polydispersed larger bubbles were generated from asymmetric porous ceramic membranes used in this study, due to the surface defects on the skin layer. The surface defects were observed by the scanning electron microscopy and detected by the bubble point method.     

Capillary electrochromatography (CEC) in columns with different inner diameters

Summary Capillaries with different inner diameters (50–250 μm) were packed with the same stationary phase and their electrochromatographic performance was studied. Special focus was put on the currents measured in these capillaries and the necessity of controlling temperature, especially in capillaries of larger inner diameter. With a commercial instrument no loss in plate numbers was observed for a capillary with an I.D. of 180 μm and the corresponding Ohm plot was linear. A test mixture consisting of polar (weakly basic and acidic) and non-polar compounds was separated on packed capillaries with a range of inner diameters. No mass overloading could be observed if sample concentrations up to 5000 ppm were injected. On the other hand, when the injected sample volume exceeds 1% of the packed bed volume a decrease of the separation efficiency occurred. When the capillary I.D. was changed from 50 μm to 180 μm, peak heights and peak areas increased 5 to 6-fold. As a consequence the detection limits of the 180 μm I.D. capillary were 5.6–7.5 times lower than those obtained in a 50 μm I.D. capillary. Dedicated to Professor Dr. Heinz Engelhardt on the occasion of his 65^th birthday.     

Controllable synthesis of β-Mn2V2O7 microtubes and hollow microspheres

β-Mn₂V₂O₇ microtubes with a length of 15–25 μm, 2.5–3.5 μm external diameter, and ∼0.4 μm wall thickness, as well as β-Mn₂V₂O₇ hollow microspheres with an average outer diameter of 2 μm, were successfully synthesized in a suitable molar ratio of NH₄VO₃ and MnCO₃ powders via a hydrothermal process. X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to characterize the products, and the magnetic susceptibility curve was also measured. In the whole process, the concentration of Mn²⁺ cations derived from MnCO₃ dissolution plays a crucial role in the formation of β-Mn₂V₂O₇ microtubes and hollow microspheres.     

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.     

Paper like free-standing hybrid single-walled carbon nanotubes air electrodes for zinc–air batteries

Flexible electrode architectures based on non-functionalized (P2) and functionalized (P3) single-walled carbon nanotubes (SWNTs) were fabricated via a simple vacuum filtration process. A hybrid layer of various compositions of P2- and P3-SWNTs forms free-standing membranes (~80 μm in thickness), and their electrochemical performance was evaluated as an air electrode AEP_2/P3 in zinc–air batteries. Such bifunctionalized air electrodes showed uniform surface morphology with interconnected micron-sized porous structure with high porosity (~70%). The N₂ adsorption isotherms at 77 K are of type IV with BET-specific surface areas of AE_(60/40) and AE_(80/20) to be 130.54 and 158.76 m² g⁻¹, respectively, thus facilitates high active surface area for active oxygen reduction/evolution reactions. BJH pore size distribution of AE_(60/40) and AE_(80/20) shows maximum pores with diameter <15 nm. The zigzag interlaying of the SWNTs imparts mechanical stability and flexibility in zinc–air batteries. Zinc–air batteries with optimized compositions of P2- and P3-SWNTs in air electrode AE_(60/40) had ionic conductivity ~1 × 10⁻² S cm⁻¹ and delivered higher discharge capacity ~300 mAh g⁻¹ as compared to AE_(80/20) composition. The unique properties of AE_(P2/P3) studied in this work would enable flexible air electrode architectures in future metal–air batteries.     

SEM研究PET核孔膜的光接枝聚合

以PET核孔膜为基材 ,二苯甲酮为引发剂 ,采用光接枝方法实现了丙烯酸和丙烯酰胺在核孔膜上的接枝 ,用扫描电镜 (SEM)直接观察了接枝前后膜的表面形貌 ,考察了不同因素对于接枝位置和接枝效果的影响 .发现膜材料本身特性和接枝反应条件对接枝位置和接枝效果有较大影响 .通过光接枝能够实现膜孔的封盖、缩小、填堵等不同的效果 .采用正侧涂布法反应 ,标准直孔 ,特别是小孔径膜 (0 4 μm) ,不利于孔内的接枝 ,接枝主要在膜的表面 ,从而产生孔封盖效应 .双锥形的非标准直孔 ,由于孔壁的受光性好 ,容易发生孔壁上的接枝从而被填充 .大孔径的膜 (5 μm) ,需要加入交联剂才能在孔壁上形成厚的接枝层 .提出了一种新的反应方法 背侧吸附法 ,反应液依靠毛细作用由膜的底部吸入膜孔 ,膜的向光侧表面不存在反应液 ,接枝只发生在膜孔内 ,从而得到很好的填孔效果 .     

Impact of surface forces on wetting of hierarchical surfaces and contact angle hysteresis

The influence of the long-range surface forces on the wetting of multi-scale partially wetted surfaces is discussed. The possibility of partial wetting is stipulated by a specific form of the Derjaguin isotherm. Equilibrium of a liquid meniscus inside a cylindrical capillary is used as a model. The interplay of capillary and disjoining pressures governs the equilibrium of the liquid in the nano- and micrometrically scaled pores constituting the relief of the surface. It is shown that capillaries with a radius smaller than a critical one will be completely filled by water, whereas the larger capillaries will be filled only partially. Thus, small capillaries will show the Wenzel type of wetting behavior, while the same liquid inside the large capillaries will promote the Cassie-Baxter type of wetting. Consideration of disjoining/conjoining pressure allows explaining of the “rose petal effect”, when a high apparent contact angle is accompanied with a high contact angle hysteresis.     

Estimation and Comparison of Pore Charge on Titania and Zirconia Membranes Prepared by Sol-Gel Route Using Zeta Potential Measurement

An attempt has been made to synthesize ceramic titania and zirconia membranes by sol-gel process by filtering respective viscous colloidal sol through microporous alumina support and gelling followed by sintering at 400°C and 470°C respectively. The static charge on the pores of the so formed membranes and the pore size distribution determine the applicability in filtering colloidal solution. The mean pore size from SEM were found to be 0.65 m and 0.54 m for titania and zirconia membranes respectively with 1.47 × 10⁷/cm² as pore density for both. The filtration characteristics during membrane layer formation showed that the membrane layer formation started after 35 minutes in the case of titania membrane and 40 minutes in the case of zirconia membrane. From the gravimetric estimation of water content of the membranes the thickness of the membrane was found out to be 3 m and the porosity was found out to be 0.30 for both the cases. The particle charge density was estimated from the zeta potential and the particle size. The pore charge density was estimated from the particle charge density, pore density, pore diameter and the thickness of the membrane layer. The membrane pore charge density was found to vary between 3 to –1 Coulombs/cm² in the case of titania membrane and 7 to –0.5 Coulombs/cm² in the case of zirconia membrane in the pH range 1–12.     

Size selective sampling using mobile, 3D nanoporous membranes

We describe the fabrication of 3D membranes with precisely patterned surface nanoporosity and their utilization in size selective sampling. The membranes were self-assembled as porous cubes from lithographically fabricated 2D templates (Leong et al., Langmuir 23:8747–8751, 2007) with face dimensions of 200 μm, volumes of 8 nL, and monodisperse pores ranging in size from approximately 10 μm to 100 nm. As opposed to conventional sampling and filtration schemes where fluid is moved across a static membrane, we demonstrate sampling by instead moving the 3D nanoporous membrane through the fluid. This new scheme allows for straightforward sampling in small volumes, with little to no loss. Membranes with five porous faces and one open face were moved through fluids to sample and retain nanoscale beads and cells based on pore size. Additionally, cells retained within the membranes were subsequently cultured and multiplied using standard cell culture protocols upon retrieval. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Osmotic distillation of oily feeds

This paper describes the development of modified hydrophobic membranes for osmotic distillation (OD) which are tolerant to oily feeds. Three commercial membranes were chosen as substrates including the Celgard 2500, Millipore GVSP and the UPVP. The focus has been on using PVA coatings which were found to have an insignificant effect on flux.For concentrated sucrose solutions, flux was reduced significantly by viscosity-related concentration polarisation effects. The presence of the coating did not increase this effect, suggesting that the flux limitation mostly occurred adjacent to the feed-side of the laminate and not within the top-layer or inside the pores.The laminate membrane is a necessity for oily feeds since the uncoated membranes were promptly wetted out even for low concentration of oil (limonene) dispersion in water. The laminate membranes were all stable in oil emulsions when tested for periods up to 24 h; i.e. the membranes did not wet out during flux measurement and no visual damage nor coating detachment was observed for laminates. These observations confirm the efficacy of having coated membranes for OD of oily feeds.     

Determination of N-acetyl-L-cysteine by flow-injection potentiometry

A multi-purpose tubular flow-through sensor was constructed with an AgI-based membrane. The membrane was prepared by pressing silver salts (AgI, Ag₂S) and powdered Teflon. This membrane was incorporated in the tubular flow-through sensor body. A 2-mm diameter hole was drilled through the center of the tubular sensor and the membrane, thus determining the active sensor volume of about 4 μL. The tubular sensor with reference electrode was placed into a complex flow-injection system and used for the flow-through determination of N-acetyl-L-cysteine, (NAC), in perchloric acid medium, pH = l. Linear dependence was established between the recorded signal height and the concentration of NAC in the injected sample. The recorded change in potential for a decade change in concentration, 62 mV {p (NAC)}^–1, in the concentration range from 1 × 10^–4 to 1 × 10^–1 mol L^–1, was based on the formation mechanism of the sparingly soluble deposit between silver and NAC on the surface of the sensitive part of the membrane. Received: 7 July 1997 / Revised: 22 September 1997 / Accepted: 26 September 1997     

Size effect and mechanochemical contraction of the Si(100) specimens

Variation of thickness of specimens of single crystalline silicon Si(100) prepared by scribing of the water of 100 mm diameter to parts of smaller size under atmospheric conditions is studied. It is shown that the thickness of specimens having small surface (∼1 cm²) decreases after scribing by 0.8–1.0% (with the error of measurements < 0.3%). The observed decrease in the thickness is explained by the effect of sorption of vapors of atmospheric moisture in micropores with the decrease in the external surface of specimens of Si(100) (the sorbostriction phenomenon).     

Synthesis of tungsten oxides with cellular structure

Being exposed to hydrochloric acid vapor, solutions of a surfactant and sodium tungstate form tungstic-acid-based materials with a structure representing a system of interpenetrating hollow spheres 2–8 μm in diameter constructed from lamellar H₂WO₄ crystals with a thickness of 80–200 nm. The reduction of the tungstic-acid-based material with hydrogen gives rise to the formation of a material based on tungsten(IV) oxide (WO₂), which retains the initial structure. The adsorption capacity of the tungstic-acid-based materials is determined with respect to benzene. The specific surface area of the obtained materials is 60–110 m²/g.     

Construction and evaluation of PVC and sol–gel sensor membranes based on Mn(III)TPP-Cl. Application to valproate determination in pharmaceutical preparations

The construction and general performance of new valproate-selective electrodes based on manganese(III) tetraphenylporphyrin [Mn(III)TPP-Cl], as an ionophore, are presented. The ionophore was incorporated into PVC and ceramic membranes (sol–gel) based on methyltriethoxysilane. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives in PVC membranes were investigated concerning their influence on the slope, response time, selectivity and lifetime of the electrodes. The PVC membrane without additive and the sol–gel membrane presented slopes and practical limits of detection of −60.8 mV dec⁻¹ and 5x10⁻⁶ mol l⁻¹ and −60.3 mV dec⁻¹ and 1×10⁻⁴ mol l⁻¹, respectively. The sol–gel membranes displayed higher selectivity for valproate when compared with PVC membranes. These two types of electrodes were coupled to a sequential-injection analysis (SIA) system for the direct determination of valproate in pharmaceutical formulations. The association of Mn(III)TPP-Cl with the sol–gel support inserted in a SIA system provided potentiometric sensors with an analytical range of 1x10⁻³–5x10⁻² mol l⁻¹, with a sample rate of 55 samples per hour and a sample and carrier consumption of 140 and 2,500 μl per determination, respectively.     

Ethanol production in a membrane bioreactor

Pilot plant trials were conducted in a corn wet mill with a 7000-L membrane recycle bioreactor (MRB) that integrated ceramic microfiltration membranes in a semi-closed loop configuration with a stirred-tank reactor. Residence times of 7.5–10 h with ethanol outputs of 10–11.5% (v/v) were obtained when the cell concentration was 60–100 g/L drywt of yeast, equivalent to about 10⁹−10¹⁰ cells/mL. The performance of the membrane was dependent on the startup mode and pressure management techniques. A steady flux of 70 L/(m²·h) could be maintained for several days before cleaning was necessary. The benefits of the MRB include better productivity; a clear productstream containing no particulates or yeast cells, which should improve subsequent stripping and distillation operations; and substantially reduced stillage handling. The capital cost of the MRB is $21–$34/(m³·yr) ($0.08–$0.13/[gal·yr]) of ethanol capacity. Operating cost, including depreciation, energy, membrane replacement, maintenance, labor, and cleaning, is $4.5–9/m³ ($0.017–$0.034/gal) of ethanol.     

Formation of thin YSZ electrolyte films by electrophoretic deposition on porous cathodes

The structure, dispersity, stability, and electrophoretic deposition (EPD) of suspensions of spherical ZrO₂ stabilized Y₂O₃ (YSZ) nanoparticles with a mean size of 10.9 nm onto the porous surface of La_0.6Sr_0.4MnO₃ (LSM) with a pore size of 3–20 μm were studied by electron microscopy, photon correlation spectroscopy, and electroacoustical analysis. The optimum conditions of deposition were attained by using a mixed isopropanol-acetylacetone dispersion medium, which provided the aggregative stability of the suspension with 95% individual particles. The maximum pore size on the covered surface should be up to 0.5 μm if nanoparticles with a mean diameter of 10–20 nm are used. When the pores are larger, the EPD of YSZ will be effective if an additional intermediate LSM layer is formed by EPD to provide the required pore size.