Hollow Fiber Geometry Research Articles

Carbon Molecular Sieve Membranes with Ultra-Thin Selective Skin Layer by Pyrolysis of Porous Hollow Fibers.

Translating carbon molecular sieve (CMS) membranes into highly scalable hollow fiber geometry with ultra-thin selective layer (<1µm) for gas separation remains as great challenge. The porous support layer of precursor hollow fiber membranes is prone to collapse during pyrolysis, which induces thick skin layer (15-50µm) of CMS hollow fiber membranes. Here, a novel strategy is present to obtain an ultra-thin selective skin layer by carbonization of hollow fiber membranes with porous skin. P84-based defect-free CMS hollow fiber membranes with ultra-thin selective skin layer (0.9µm) for gas separation are prepared without any coating or complex chemical pretreatment. Compared with the carbon membranes derived from defect-free fibers, the H2 permeance (93.9 GPU) of CMS membranes derived from the porous fibers increases ≈1353% with comparable selectivity of H2/CH4 (143) and higher H2/N2 (120). Furthermore, the porous fibers are pre-aged near the Tg in N2 conditions before carbonization, and the H2 permeance of the derived CMS hollow fiber membranes reached 147 GPU (increased 2180%). It is a new facile way to prepare CMS hollow fiber membranes with ultra-thin selective layer by porous fibers, demonstrating its versatile potential in gas separation or organic liquids separation.

A novel organic solvent-free method for manufacturing polyethersulfone hollow fiber membranes using melt extrusion

Hollow fiber membranes are traditionally manufactured using the spinning process, which takes advantage of the phase separation/inversion for the creation of a porous structure. In this work, the use of melt extrusion led to the fabrication of hollow fiber membranes without the use of organic solvents. Following post-treatment, the fabricated partially dense fibers are transformed into porous fibers. In detail, ternary blends of polyethersulfone/poly(ethylene glycol)/poly(N-vinyl pyrrolidone) (PESU/PEG/PVP) were developed by combining a solvent-free liquid mixture of PEG/PVP into PESU. Using a single screw extruder, this blend was melted and extruded using an annular slit nozzle where PEG functioned as a plasticizer, i.e., decreased processing temperatures, while PVP aided in retaining the hollow fiber geometry. These hollow fibers were comprised of uniformly closed pores, occurring due to the expansion and formation of bubbles of evaporating PEG nucleated by PVP during extrusion. By immersing these fibers into an aqueous solution of sodium hypochlorite (NaOCl), PEG and PVP were removed, which led to an open porous structure with pore sizes between 100 nm and 1 μm throughout the membrane. The outer surfaces of the hollow fibers were found to contain a higher PVP content than the inner surface. As PVP and PESU are miscible, i.e., blended in a single phase, treatment with NaOCl led to the creation of open pores on the outer surface with pore sizes between 10 and 150 nm, thus deeming the outer surface functional as a separation layer. The effect of blend composition, extrusion settings, and post-treatment parameters on membrane morphology, water flux, thermal characteristics, and tensile strength was studied, while after the modification, near-pristine PESU membranes were pursued. A water-flux of 28 L/h m2 bar and a molecular weight cut-off (MWCO) of 90%, 75%, and 40% for poly(ethylene oxide) of an average of 1000 kDa, 400 kDa, and 100 kDa molecular weight, respectively, proved that via extrusion it is possible to produce hollow fiber membranes for ultrafiltration without the use of organic solvents.

Electrochemically Facilitated Transport of CO2 between Gas Diffusion Electrodes in Flat and Hollow Fiber Geometries

Electrochemically Facilitated Transport of CO₂ between Gas Diffusion Electrodes in Flat and Hollow Fiber Geometries

Copolyimide asymmetric hollow fiber membranes for high‐pressure natural gas purification

AbstractThe current process to purify contaminated natural gas reserves employs a highly energy‐intensive amine scrubbing technology. To satisfy the growing demand for natural gas coupled with the tight regulations on CO2 emissions, researchers worldwide are investigating the use of polymeric membranes for acid gas removal from natural gas streams, to reduce the energy consumption and carbon emission of the nowadays used technology. Placing a polymeric membrane unit at the upstream of the amine scrubbing column reduces the energy consumption during the regeneration process of saturated amines. Hence, the preparation of polymeric membranes in form of hollow fibers is a key step towards their industrial implementation for natural gas processing. The following study demonstrates the potential separation performance of 6FDA‐Durene/6FDA‐CARDO (5000:5000) in an integrally skinned defect‐free asymmetric hollow fiber geometry. The initial screening studies of the membrane shows good pure‐gas performance as it exhibits CO2/CH4 selectivity coefficients around 28 and CO2 permeance between 310 and 350 GPU. Feed pressures of up to 900 psig and stage cuts ranging from 5% to 20% were tested for a quaternary sweet mixed‐gas feed to assess the membrane performance under operating conditions that mimic those in industrial settings. Mixed‐gas permeance of all gases, and CO2/CH4 selectivity remain somewhat constant as the feed pressure increases up to 900 psig. Both mixed‐gas CO2 permeance and CO2/CH4 selectivity decline as the stage cut increases. As expected, as CO2 recovery is maximized, CO2 purity is minimized and CH4 loss increases with increasing stage cut. As a result of the trade‐off between recovery and purity, the data and analyses reported herein can provide insights into the limitations that certain operating parameters can pose on CO2 separation performance with similar polymeric hollow fiber membranes.

Dealcoholization of Unfiltered and Filtered Lager Beer by Hollow Fiber Polyelectrolyte Multilayer Nanofiltration Membranes-The Effect of Ion Rejection.

Membrane-based beverage dealcoholization is a successful process for producing low- and non-alcoholic beer and represents a fast-growing industry. Polyamide NF and RO membranes are commonly applied for this process. Polyelectrolyte multilayer (PEM) NF membranes are emerging as industrially relevant species, and their unique properties (usually hollow fiber geometry, high and tunable selectivity, low fouling) underlines the importance of testing them in the food industry as well. To test PEM NF membranes for beer dealcoholization at a small pilot scale, we dealcoholized filtered and unfiltered lager beer with the tightest available commercial polyelectrolyte multilayer NF membrane (NX Filtration dNF40), which has a MWCO = 400 Da, which is quite high for these purposes. Dealcoholization is possible with a reasonable flux (10 L/m2h) at low pressures (5-8.6 bar) with a real extract loss of 15-18% and an alcohol passage of ~100%. Inorganic salt passage is high (which is typical for PEM NF membranes), which greatly affected beer flavor. During the dealcoholization process, the membrane underwent changes which substantially increased its salt rejection values (MgSO4 passage decreased fourfold) while permeance loss was minimal (less than 10%). According to our sensory evaluation, the process yielded an acceptable tasting beer which could be greatly enhanced by the addition of the lost salts and glycerol.

Analysis of effective thermal conductivity and tortuosity modeling in membrane distillation simulation

Porous hydrophobic membranes are the main elements in MD (membrane distillation) desalination systems and need to be adequately modeled in terms of transport mechanisms to allow for theoretical assessments toward process design. The objective of this work is twofold. First, illustrate the rational choice of models based on the morphology and structure of a couple of selected membranes for which micrographs and experimental results for distillate mass flux are readily available in the literature. Second, provide a comparative analysis of well-established models for membrane effective thermal conductivity and tortuosity, so as to confirm the adequacy of the proposed model selection path. Theoretical results of the distillate flux were obtained from the numerical simulation of the heat and mass transfer phenomena in the MD process for the DCMD (direct contact membrane distillation) configuration, using a multi-region approach with OpenFOAM @ . The comparative analysis is performed for PVDF membranes with different morphologies in the transversal section, for both flat and hollow fiber geometries. For the membrane with sponge-like morphology, the employment of the parallel-resistance model for the effective thermal conductivity and the fractal tortuosity model, designed for porous media characterized by randomly distributed obstructions in spherical format, led to the best agreement with respect to the experimental data for the distillate flux. On the other hand, for the membrane with macro voids in the cross-section (presence of finger-like channels), asymmetrical morphological structure, and narrow pore size distribution, it was found that the employment of the parallel-resistance model for effective thermal conductivity and the Euclidian-based tortuosity model for the random arrangement of highly interconnected pores provided the best agreement between experimental and theoretical data. The results confirm the appropriate model selection path for effective thermal conductivity and tortuosity in MD simulation by taking into consideration solely the membrane morphology. • A rational choice of membrane distillation (MD) models is considered based on the morphology and structure of the membranes. • A comparison of models for membrane effective thermal conductivity and tortuosity confirms the proposed MD modelling path. • Verifies that membrane surface modification for hydrophobicity enhancement increases distillate mass flux. • Introduces a modified membrane thickness model due to liquid/vapor interface increase in distillate mass flux prediction. • Temperature polarization may overcome the increase in distillate flux due to reduction in diffusion path by pore wetting.

Influence of two phase flow on cake layer resistance and flux enhancement in spiral wound and submerged flat sheet microfiltration membrane modules

&lt;p&gt;Gas sparging has emerged as an effective technique for control of particle fouling in different microfiltration membrane processes. However most of the research work carried out has been pertinent to hollow fiber and tubular membrane geometries. A little attention has been paid to evaluate the potentails of gas-liquid two-phase for control of particle fouling in spiral wound and submerged flat sheet microfiltration membranes. This study focuses on control of particle fopuling by gas sparging in open channel spiral wound and submerged flat sheet microfiltration membranes. Commercial yeast was used as test suspension. The Effect of gas sparging on membrane fouling and permeate flux was studied by analysing the cake layer characteristics like cake mass deposition, cake layer thickness and cake porosity. The filtration flux and cake properties under various operating conditions, such as cross-flow velocity, filtration pressure, particle concentration, and sparging intensity are analyzed based on hydrodynamics. The results of this study show that gas sparging is very effective in control of particle fouling for both membrane module geometries. It was found that gas bubbling reduced the deposition of particles on the membrane surface due to which cake layer thickness decreases and resultantly permeate flux increased substantially. The permeate flux increased with increase in gas sparging intensity. A maximum flux enhancement of 170 % and 284 % were observed for spiral wound and flat sheet membranes respectively when gas sparging was applied to the process.&lt;/p&gt;&#x0D;

Effect of Electrolyte and Electrode Configuration on Cu‐Catalyzed Nitric Oxide Reduction to Ammonia

AbstractReduction of nitric oxide was investigated using Cu electrodes in acid and neutral pH conditions. Analysis of Cu discs in stagnant electrolyte by Electrochemical Mass Spectrometry (EC‐MS), revealed the favorable formation of ammonia (and hydrogen) in acidic electrolyte, while N2O and N2 are formed in significant quantities at neutral conditions. Additional performance evaluation of Cu electrodes in hollow fiber geometry, was performed using 10 vol % NO in Ar supplied through the porous electrode structure and off‐line determination of ammonia by 1H NMR spectroscopy. The pH dependent performance of the Cu hollow fiber is in agreement with EC‐MS data at low gas flow rates, showing the highest ammonia selectivity in acidic conditions. However, at relatively high gas flow rates, almost 90 % faradaic efficiency and a NH3 production rate of 400 μmol h−2 cm−2 were obtained in neutral electrolyte at −0.6 V vs RHE, likely due to enhanced availability of NO at the electrode surface, suppressing the hydrogen evolution reaction. This approach shows conversion of waste NO gas to valuable green fertilizer components is possible.

Advances and Applications of Hollow Fiber Nanofiltration Membranes: A Review.

Hollow fiber nanofiltration (NF) membranes have gained increased attention in recent years, partly driven by the availability of alternatives to polyamide-based dense separation layers. Moreover, the global market for NF has been growing steadily in recent years and is expected to grow even faster. Compared to the traditional spiral-wound configuration, the hollow fiber geometry provides advantages such as low fouling tendencies and effective hydraulic cleaning possibilities. The alternatives to polyamide layers are typically chemically more stable and thus allow operation and cleaning at more extreme conditions. Therefore, these new NF membranes are of interest for use in a variety of applications. In this review, we provide an overview of the applications and emerging opportunities for these membranes. Next to municipal wastewater and drinking water processes, we have put special focus on industrial applications where hollow fiber NF membranes are employed under more strenuous conditions or used to recover specific resources or solutes.

Hollow-fiber membranes of block copolymers by melt spinning and selective swelling

Selective swelling of block copolymers has emerged as an efficient strategy to prepare ultrafiltration membranes with well-defined porosities. However, the application of this strategy is only limited to the preparation of flat-sheet membranes so far. Herein, we extend this selective swelling strategy, for the first time, to the preparation of hollow-fiber membranes (HFMs). A mechanically strong copolymer available at large scale, polysulfone-block-poly(ethylene glycol) (PSF-b-PEG), is employed as the membrane-forming polymer. The PSF-b-PEG melt without any diluters or additives exhibits good fluidity, enabling stable and continuous melt spinning of primary hollow fibers with dense fiber walls. Subsequent selective swelling in the mixture of n-propyl alcohol and acetone produces interconnected nanoporosities throughout the fiber walls, thus forming HFMs with PEG chains enriched on the membrane surface. The wall thicknesses as well as pore sizes, and thus the separation performances of the HFMs are tunable by changing the spinning and swelling parameters. In contrast to the strong hydrophobicity of HFMs prepared by cold stretching of polyolfins, our HFMs possess water-wettable surfaces due to the presence of PEG chains, and can be directly used in aqueous milieu. Because of the PSF-based skeleton and homogenous distribution of nanopores, the HFMs exhibit excellent tensile strengths up to 12.5 MPa, much higher than that of HFMs prepared by the commonly used phase inversion processes. Furthermore, the BSA rejection and water permeance of the HFMs currently can be tuned in the range of 29.9–88.2% and 13.7–119.3 L m-2·h-1·bar-1, respectively, by changing the spinning and/or swelling parameters. Their performances are expected to enhance by optimizing the hollow fiber geometries and pore structures. This strategy neither uses any solvents to fluidize the polymer nor produces wastewater, and therefore is a “cleaner” process. This work not only extends the usages of selective swelling, but also establishes a new process to manufacture HFMs.

Polyelectrolyte Complex Tubular Membranes via a Salt Dilution Induced Phase Inversion Process

Tubular membrane geometries are key elements of many industrial filtration applications and artificial organs. Established processes to fabricate polymeric membranes require the use of organic solvents, which are prone to be phased out due to stricter regulations. In the quest of developing solvent‐free alternative fabrication processes, polyelectrolyte complex (PEC) membranes are recently discovered, offering a promising alternative. While flat sheet PEC membranes are successfully fabricated, tubular or hollow fiber geometries remain a material engineering challenge. For the first time, the organic solvent‐free fabrication of PEC tubular membranes in a dry‐jet wet spinning process is demonstrated. The aqueous polymer solution comprising the polyanion—poly(sodium‐4‐styrenesulfonate) (PSS), the polycation—poly(diallyldimethylammonium‐chloride) (PDADMAC), and KBr is extruded with the water‐based bore fluid through a single‐orifice spinneret, passing an air‐gap before immersed into an aqueous coagulation bath. The phase inversion kinetics are influenced to form a defect‐free lumen separation layer through the addition of glycerol to the bore fluid. The resulting tubular membranes show reproducible nanofiltration membrane properties. They have a molecular cut‐off of 320 Da, are positively charged and retain salts with a characteristic salt retention hierarchy. This promising material engineering strategy motivates to continue the quest for smaller tubular dimensions toward hollow fibers.

Bridging the gap between lab-scale and commercial dimensions of hollow fiber nanofiltration membranes

The development of nanofiltration membranes with hollow fiber geometry is a relatively young field of research in membrane science with only limited, but quickly growing, availability on a commercial scale. These membranes offer promising properties for application in water treatment such as high fouling resistance and low cost compared to Reverse Osmosis membranes. Major differences are found in dimension and operating conditions of hollow fiber nanofiltration membranes used in academia and on an industrial scale. To allow for adequate comparison and prediction of membrane performance, the effect of fiber dimension and operating conditions on process performance needs to be properly understood. A systematic experimental study on MgSO4 retention by hollow fiber nanofiltration membranes was performed to investigate the effect of fiber length and operational conditions on membrane performance. A significant drop in the retention of MgSO4 was observed for 1.5 m long fibers in flux ranges of 20 LMH when reducing crossflow velocity to 0.1 m/s. Transport models were used to describe and predict this behavior. We show that the commonly used mass transport models under predict this decrease in retention. Using different theoretical transport models for the hollow fiber feed phase and reducing dimensional resolution from 2D to 1D and 0D allows for the identification of limitations of the commonly applied analytical mass transfer correlations. To accommodate for this discrepancy found between experimental results and model predictions, a correction factor was derived using the 2D model to specifically account for deviations of these correlations at high permeate recovery values. Our newly developed model makes it possible to accurately predict full scale membrane performance solely based on measured done on small scale membranes, an important precondition for the further development of dense hollow fiber based membranes and processes.

Mathematical modeling of CO2 separation using different diameter hollow fiber membranes

This research presents a 2D mass-transfer simulation model using computational fluid dynamics (CFD) for separation of CO2 from a binary gas mixture of CO2/CH4 by means of polytetrafluoroethylene (PTFE) hollow fiber membrane contactor (HFMC). Governing equations with their corresponding boundary conditions are solved using COMSOL Multiphysics and the results are validated against reported experimental data. Convection and diffusion flux vectors and concentration gradient of CO2 species in the radial and axial directions of the HFMC are investigated. This study provides an opportunity to investigate the effects of gas and liquid cross flow velocities on the overall performance of membrane contacting system. The results demonstrate that increasing the liquid phase velocity improves the CO2 absorption performance of the membrane system, while increasing the gas mixture velocity deteriorates the CO2 separation of the system. The impact of hollow fiber geometry on the removal of CO2 is investigated and the results indicate that hollow fibers with smaller inner diameter provides higher effective mass-transfer area and therefore superior CO2 removal performance. Furthermore, the modeling predictions for the CO2 removal are in good agreement with the experimental data under various ratios of gas to liquid velocity. The PTFE hollow fiber membrane contacting system showed a great potential for separation of CO2 from gas mixtures.

Experimental and modeling study on fouling of hollow-fiber membranes by fine dust aerosol particles

This work aimed to study the pressure drop evolution of hollow-fiber membranes (HFMs) during aerosol loading. We tested two types of polypropylene HFMs varying in inner fiber diameter with an ASHRAE A2 test dust. Data was recorded including pressure drop, flowrate/permeate velocity and accumulated mass of particles until reaching the final pressure drop. The results showed a slow pressure drop increase even when loaded with extremely high (units of g/m3) dust concentrations. The membranes were easily cleanable simply by shaking, with a minimal residual pressure drop. The particle loading profile (pressure drop/dust load curve) was dependent on the inner diameter of hollow fibers and permeate velocity. The loading profile of a new HFM was independent of dust concentration. However, when a regenerated membrane was used, the dependence on the dust concentration was obvious. The same was true for the fouling rate, which was higher for the regenerated membrane. Theoretical and empirical models for dust cake pressure drop were in a strong disagreement with experiment data. In practical applications, they will be rather limited to a very specific low volume, or short-term high volume filtrations due to the higher pressure drops caused by the hollow-fiber geometry.

Modeling of spiral wound membranes for gas separations. Part I: An iterative 2D permeation model

Membranes are excellent alternatives for gas separations due to their low installation and maintenance costs. In industrial environment, membranes are usually organized in modules with spiral-wound or hollow fiber geometries. Because of their wide range of applications, the development of reliable mathematical models for industrial membrane operations is encouraged. In the present work, a mathematical model is proposed to describe gas separations in spiral-wound membranes, based on a phenomenological approach. The proposed model was validated in four case studies of common separations: (i) ammonia; (ii) hydrogen; (iii) CO2 from natural gas and (iv) CO2 from flue gas. It is shown that the proposed model is able to represent the analyzed phenomena accurately. The robustness and good performance of the model for several operation conditions were evaluated through sensitivity analyses. In addition, a novel numerical approach is proposed to solve the analyzed mathematical model. The proposed procedure presents good efficiency and accuracy and is faster and more efficient than the well-known shooting method, largely employed to perform membrane simulations, allowing the use of the model in real time applications.

Aquaporin-Containing Proteopolymersomes in Polyelectrolyte Multilayer Membranes.

The field of membranes saw huge developments in the last decades with the introduction of both polyelectrolyte multilayer (PEM)-based membranes and biomimetic membranes. In this work, we combine these two promising systems and demonstrate that proteopolymersomes (PP+) with the incorporated aquaporin protein can be distributed in a controlled fashion using PEMs, even on the inner surface of a hollow fiber membrane. In this way, various proteopolymersome multilayers (PPMs) are fabricated using PP+ as the positively charged species in combination with the polyanions poly(styrene 4-sulfonate) (PSS) and poly(acrylic acid) (PAA). It is shown by reflectometry through alternately adsorbing the polyanions and PP+ that, for both PAA and PSS, a good layer growth is possible. However, when the multilayers are imaged by SEM, the PAA-based PPMs show dewetting, whereas vesicular structures can only be clearly observed in and on the PSS-based PPMs. In addition, membrane permeability decreases upon coating the PPMs to 2.6 L∙m−2∙h−1∙bar−1 for PAA/PP+ and 7.7 L∙m−2∙h−1∙bar−1 for PSS/PP+. Salt retentions show that PAA/PP+ layers are defective (salt retentions <10% and high molecular weight cut-off (MWCO)), in line with the observed dewetting behavior, while PPMs based on PSS show 80% MgSO4 retention in combination with a low MWCO. The PSS/PP+ membranes show a Donnan-exclusion behavior with moderate MgCl2 retention (50%–55%) and high Na2SO4 retention (85%–90%) indicating a high amount of negative charge present within the PPMs. The corresponding PEMs, on the other hand, are predominately positively charged with MgCl2 retention of 97%–98% and Na2SO4 retention of 57%–80%. This means that the charge inside the multilayer and, thus, its separation behavior can be changed when PP+ is used instead of a polycation. When comparing the PPM membranes to the literature, similar performances are observed with other biomimetic membranes that are not based on interfacial polymerization, but these are the only ones prepared using a desired hollow fiber geometry. Combining PEMs and biomimetic approaches can, thus, lead to relevant membranes, especially adding to the versatility of both systems.

Electrical swing adsorption on functionalized hollow fibers

Temperature swing adsorption (TSA) is a favorable adsorption technique when applied for capturing CO2 but limited by long cycle times and low concentrations of the recovered adsorbate. Direct heating of the adsorbent can mitigate these drawbacks. Combined with the beneficial mass transfer of a hollow fiber geometry it offers a powerful sorption process. In this study, we combine the advantages of direct heating and the benefits of the hollow fiber geometry in electrically conducting hybrid hollow fibers. Two different solid sorbents are manufactured and characterized: polyethylenimine-impregnated silicon carbide fibers (SiC-PEI) and fibers consisting of a carbon nanotube matrix with dispersed zeolite particles (CNT-zeolite). Both fibers exhibit Joule heating properties and high adsorption capacities. The CO2 uptake, CO2 isotherms, and the kinetic behavior are examined. The maximum CO2 uptakes at 30 °C and 15 vol% CO2 are 8.3 mg/gfiber for SiC-PEI and 102.2 mg/gfiber for CNT-zeolite. A lab-scale module is designed and used to determine the CO2 capacity of a fiber bundle. The energy requirement to heat such a fiber bundle from ambient temperature to 80 °C is 3.1 J/gFiberK (SiC-PEI) and 15.8 J/gFiberK (CNT-zeolite). To investigate the suitability of the fibers for real process applicability, a mathematical model is established and simulation results are presented and discussed. The two different approaches prove to be viable options for CO2 separation. They are not limited to CO2 capture but can be expanded to other gas separation tasks.

Development of hollow fiber membranes with alumina and waste of quartzite

The development of ceramic membranes with different geometries and compositions extends the possibilities of industrial applications, inducing advantages in terms of increased permeability, membrane area by volume module and chemical, thermal and mechanical resistance. The use of low-cost raw materials is a trend that has grown in scientific research. The aim of this work is to prepare membranes with hollow fiber geometry from alumina and residue of quartzite, by the technique of immersion precipitation in distilled water from a mixture of ceramic mass with a solution of polyethersulfone and, synthesized in temperatures of 1100 oC to 1500 °C. The hollow fiber membranes were characterized by chemical analysis, X-ray diffraction, particle size distribution, scanning electron microscopy, apparent porosity, flexural strength and permeated water flow by the membranes. The results indicated that the sintering temperature has direct influence on the formation of the mullite phase, and the properties of apparent porosity and permeate flow. The higher the sintering temperature (1400-1500 ° C) increase the formation of the mullite phase, the lower the porosity, as well as the lower the permeate water flow in the membranes. However, there was increase in flexural strength in the hollow fiber membranes with high temperature.

Preparation and pervaporation performance of vinyl-functionalized silica membranes

Pervaporation using hydrophobic membranes to separate azeotropic and thermally degradable mixtures, and organics from aqueous solutions with low concentrations has attracted attention. On the other hand, distillation, which is the conventional and commercialized separation method, is unsuitable for the separation of these mixtures. In this study, an α-alumina substrate coated with a γ-alumina layer in both hollow fiber and tubular geometries was used for preparation of vinyl-functionalized silica (VFS) membranes by the sol-gel method using vinyltrimethoxysilane as the silica precursor. Silica functionalized with vinyl groups shows excellent affinity for ethyl acetate (EA) based on Hansen solubility parameters [1]. The VFS membrane prepared on a tubular alumina substrate at 453K showed the EA flux of 0.85kgm–2h–1 and separation factor of 77.3 for pervaporation of a 5% (mass fraction) EA aqueous solution at 295K. An α-alumina hollow fiber was further used instead of the conventional tubular substrate to improve the EA flux. The hollow fiber-supported VFS membrane has a flux of 2.53kgm–2h–1, which is three times higher than that prepared on the tubular-substrate, and a separation factor of 81.5 for the pervaporation of a 5% (mass fraction) EA from aqueous solution at 295K. The fluxes of methyl acetate and methyl ethyl ketone for the hollow fiber-supported VFS membrane are also about three times higher than those obtained for tube-supported VFS membranes.

Continuous Production of Macroporous Films: an Alternative to Breath Figure Assembly

Despite the need for sophisticated instrumentation, breath figure assembly (BFA) methods are restricted to produce macroporous films on a tiny scale so far. The current study narrates the fabrication of macroporous films in hollow fiber geometry which extends to adopt the method for continuous production of isoporous surfaces from commercially available low-priced polymer materials. The fabrication of the films in the hollow fiber geometry is carried out by a co-centric quadruple orifice spinneret through which four different liquids are co-extruded simultaneously: bore fluid (to fill the lumen of the fiber), support layer solution, glycerol, and an isoporous film forming solution through the outer most orifice. The extruded entities plunge into a coagulation bath after passing a definite air gap. The implementation of the concept of diffuse-in, droplet formation, and then condense-out behavior of glycerol in a co-extrusion method of hollow fiber spinning makes macroporous film formation possible in an interminable way sidestepping the use of breath figure assembly method. Moreover, the continuous film formation by the proposed mechanism is also authenticated in flat sheet geometry by employing two casting blades in a casting machine. The structure of the films is analyzed by scanning electron microscopy (SEM).