Microfiltration Range Research Articles

Preparação e caracterização de membranas cerâmicas tubulares de mulita

Os produtos cerâmicos são extremamente interessantes no campo das membranas por causa de sua resistência mecânica, inércia química, tempo de vida útil longa e estabilidade térmica. Atualmente as pesquisas estão sendo direcionadas para exploração destes materiais de baixo custo. Este trabalho consiste na preparação de membranas tubulares, obtidas a partir de composição contendo argila, caulim e óxido de alumínio, conformadas pelo processo de extrusão, utilizando diferentes temperaturas na etapa de sinterização para uso em microfiltração. Foi feita caracterização nas massas cerâmicas antes da sinterização, através dos ensaios de análise granulométrica, análise termogravimétrica, análise química e difração de raios X. A análise química mostrou altos teores de SiO2 e de Al2O3 e o ensaio de difração de raios X mostrou a presença de caulinita, quartzo e óxido de alumínio. Foi realizado ensaio de difração de raios X na massa após as sinterizações e os resultados mostraram a presença de mulita, óxido de alumínio e quartzo em todas as sinterizações efetuadas. Com relação ao tamanho e a distribuição destes poros nas membranas, os resultados da micrografia e de porosimetria por intrusão de mercúrio ilustraram a presença de poros em todas as temperaturas de sinterização, com dimensões na faixa de microfiltração. O ensaio de fluxo com escoamento tangencial utilizando água destilada mostrou que a membrana sinterizada a 1300 ºC obteve o maior valor, seguida da de 1250, 1200 e 1150 ºC.

Reducing pollution from the deliming–bating operation in a tannery. Wastewater reuse by microfiltration membranes

This paper presents experimental results from the implementation of two measures aimed at reducing the nitrogen concentration in a tannery wastewater. Specifically, this research has focused on the wastewater from the deliming/bating operations. The proposed measures are the replacement of ammonium salts by carbon dioxide in the deliming process and the reuse of wastewater and chemicals after membrane filtration of the deliming/bating liquor. The experimental study covered different wastewater pretreatment alternatives and experiments with two membranes (with different separation properties): one in the range of microfiltration (MF) and one in the range of the ultrafiltration (UF). Results of the pretreatment study indicated that neither settling nor protein precipitation were feasible. Only a security filtration prior to membrane filtration was recommended. The tested MF membrane was selected due to the higher flux (around 25L/(m2h)) in comparison with the UF membrane. The MF permeate was successfully reused in the deliming/bating process. The delimed leather quality was excellent according to both visual and organoleptic inspection from process technicians and phenolphthalein test, confirming the technical feasibility of the proposal. Globally, the implementation of the above mentioned two measures resulted in 53% total nitrogen reduction.

Development of membrane based technology for the separation of coal from organic solvent

In this work, non-coking coal was extracted using of organic solvent mixture of n-methyl-2-pyrrolidone (NMP) and ethylenediamine (EDA). The coal extraction experiments were carried out at different ratios of coal to organic solvent mixture for 1h under total reflux conditions. The optimum conditions for solvent extraction were determined. Ceramic membrane in microfiltration range was used for recovery of organic solvent from coal organic solvent mixture. Characterization of the prepared inorganic membrane was done in terms of pore size distribution, membrane porosity and chemical stability. Membrane experiments were carried out in batch cell. The mixture of coal and organic solvent obtained after extraction process was passed through ceramic membrane and recovered organic solvent was reused further for extraction process. Same steps were repeated continuously three times. The fabricated ceramic membrane showed solvent recovery of 71%, 68% and 66%, respectively, for successively three stages. The information provided in this study will be helpful to the steel making industries where pure carbon is extracted from coal using energy intensive distillation process. The amount of solvent recovery is quite high in this membrane based technique and will improve the economy of the process in a large extent compared to the existing distillation process.

Formation and characterization of polyamide composite electrospun nanofibrous membranes for salt separation

AbstractCurrently, electrospun nanofibrous membranes (ENMs) are classified in the microfiltration range. In this study, we explored the applicability of using ENMs for nanofiltration (NF) applications through a surface modification approach. A polyamide layer was formed on the surface of the ENMs through interfacial polymerization with two different approaches. In the first approach (approach A), ENMs were soaked in an aqueous phase followed by an organic phase; in the second approach (approach B), we reversed this sequence. This resulted in different surface morphologies over the ENM surface. The best approach B allowed the separation of 80.7% of 2000‐ppm MgSO4 and 67.0% of 2000‐ppm NaCl at a pressure of 70 psig under a dead‐end filtration setup. The fluxes attained were 0.51 and 0.52 L m−2 h−1, respectively. In addition, the effect of the pore size on the formation of a polyamide film was investigated. It was realized that bubble points of 1.8 and 3.4 μm were both able to support the polymer film on its surface, but their separation efficiency differed slightly. These findings suggest that ENMs could be used beyond their current microfiltration stage, and hence, their use could be widened to NF membranes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and characterization of low cost ceramic membranes for micro-filtration applications

Contemporary research in ceramic composites for membrane applications targets the fabrication of stable low cost micro-filtration range membranes. This work reports the fabrication of stable low cost mesoporous membranes deploying subsequent formulations based on kaolin and other suitable low cost materials such as quartz, sodium carbonate, calcium carbonate, boric acid and sodium metasilicate. Incidentally, the processing temperature in this work is about 850–1000 °C instead of 1100 °C which is the usual sintering temperature for inorganic membrane fabrication. The membranes casted as circular disks (52.5 mm diameter and 4.5 mm thickness) were subjected for characterization studies using TGA, XRD, SEM analysis, to evaluate the effect of maximum sintering temperature on membrane structure, porosity and mechanical integrity. Pore size distribution, porosity, average pore size of the membrane along with permeation experiments with both water and air is carried out to study the membrane performance. The average pore size of the membrane is observed to increase from 550 nm to 810 nm when sintering temperature increases from 850 °C to 1000 °C. However, with the increase in temperature from 850 °C to 1000 °C, the membrane porosity is reduced (from 42% to 33%) and flexural strength is increased (from 3 to 8 MPa). The membrane corrosion resistance is found to be unaltered with processing temperature. Based on raw-material prices, the membrane cost is estimated to be $130/m 2. Henceforth, these low cost membranes with good membrane properties are suggested for cheaper application in chemical and biochemical processes using micro-filtration and ultra-filtration techniques.

Modified porous Nafion ®: Membrane characterization and two-phase separations

Perfluorosulfonated ionomer membranes (Nafion ®) were modified by a chemical treatment to increase the permeability of membrane structures. The treatment consisted of a single phase propylene carbonate–water mixture which, in the presence of the sulfonic acid groups of the Nafion ®, yielded CO 2. This CO 2 presumably expanded having the effect of creating larger pores within the Nafion ® framework. The resulting membrane had filtration characteristics in the ultrafiltration–microfiltration range with a maximum flux of ∼10 kg m −2 h at 1.3782 × 10 5 Pa (20 psig). These structures were characterized using flux, solute rejection, neutron scattering and water volume measurements. Further, these membranes were found to be suitable for emulsion separations with the water phase permeating through the membrane. In preliminary results, a water–xylene mixture exhibited a single phase permeate with approximately 60% of the flux of pure water.

Fabrication of poly (ECTFE) membranes via thermally induced phase separation

Poly (ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene with an excellent combination of chemical, thermal and mechanical properties. Although the lack of a suitable solvent for ECTFE precludes membrane casting by conventional room-temperature processes of immersion precipitation or evaporative casting, thermally induced phase separation provides an attractive pathway for membrane fabrication. We have successfully identified three possible latent solvents for ECTFE and have studied the ECTFE-dibutyl phthalate (DBP) polymer-diluent system. ECTFE membranes were fabricated using a TIPS-casting apparatus that allowed control of several important process parameters. ECTFE membranes were characterized via scanning electron microscopy (SEM), porometry and permeation techniques. Results indicated that membranes with continuous pores having diameters in the microfiltration range (0.1–0.5 μm) could be reliably fabricated.

Membrane formation mechanism and permeation properties of a novel porous polyimide membrane

AbstractThe transport properties of a novel porous fluorinated polyimide membrane fabricated by a wet phase inversion process were studied with a stirred dead‐end filtration cell. The porous membrane‐forming solvents were tetrahydrofuran (THF), acetone, N,N‐dimethylacetamide (DMAc), N‐methylpyrrolidone (NMP), N,N‐dimethylformamide (DMF), and dimethylsulfoxide (DMSO). The phase separation phenomena in a ternary system of polyimide/solvent/water were investigated from cloud point curves by a titration method and binary interaction parameters. Solvent–water demixing in the system has been found to play very important roles in determining the structure and surface morphology of the polyimide membrane. The porous fluorinated polyimide membranes showed pore sizes from 4 to 500 nm and permeation properties from ultrafiltration to a microfiltration range. In this study, we particularly focused on fouling of the polyimide membranes, because fouling decreases the flux and increases the resistance. Interestingly, the porous polyimide membrane showed excellent water flux recovery after water cleaning compared with that of the polyethersulfone (PSf) membrane, which suggest that for a 6FDA‐6FAP membrane, the protein–membrane and protein–protein interaction was not so strong compared with those in a PSf membrane. Copyright © 2002 John Wiley & Sons, Ltd.

Factors influencing critical flux in membrane filtration of activated sludge

Membrane filtration of biomass is usually accompanied by significant flux decline due to cake-layer formation and fouling. Crossflow filtration with flux controlled by pumping the permeate can produce stable fluxes if a ‘critical flux’ is not exceeded. Below critical flux the transmembrane pressure is typically very low and increases linearly with imposed flux. Above the critical flux the transmembrane pressure rises rapidly signifying cake-layer formation which is usually accompanied by a continued rise in transmembrane pressure and/or a drop in delivered flux. A range of microfiltration and ultrafiltration membranes with pore sizes from 0.22 to 0.65 µm and molecular weight cut-off of 100 kDa was used. The feed was an activated sludge mixed liquor with concentration in the range of 3–10 g dm−3. The results show that the critical flux depends on feed concentration and crossflow velocity, being higher for higher crossflow velocity or lower feed concentration. Critical flux was also dependent on membrane type, being lower for hydrophobic membranes. Although the transmembrane pressure was higher for the larger pore size membrane, no significant difference in critical flux was observed among different pore size membranes. © 1999 Society of Chemical Industry

Porous latex composite membranes: fabrication and properties

A new class of microfiltration (MF) and ultrafiltration (UF) membranes has been developed. By placing latex particles onto the surface of a microporous substrate and stabilizing the porous array, voids are formed between the particles which provide narrowly distributed pores that serve as separation channels. The size of the interstitial voids in the array is governed by the diameter of the latex particle. This aqueous based technology has advantages relative to other membrane fabrication processes in terms of the high asymmetry of the membranes, the facile adjustment of pore sizes, and the ability to easily modify pore surfaces during the synthesis of particles. A number of approaches were examined for placement of particles and stabilization of latex composite membranes (LCMs). Filtration of particles with reactive surface groups that provide covalent linkages at the contact points in the particle array proved most effective in obtaining stable membranes. These membranes had narrow size distributions in both the UF and MF range and were capable of being cleaned and backflushed. The membranes were characterized in terms of gas permeabilities, pure water permeabilities and electron microscopy. The rejection properties of LCMs were also examined during filtration of monodispersed latex particles and a broadly dispersed dextran mixture.

Mechanism of bacterial and viral transport through microfiltration membranes

Microorganisms such as Qβ, MS2, T4 virus and several bacteria strains in Pseudomonas, Alcaligenes and E-coli groups were filtered with different pore size nuclepore and anopore flat sheet membranes in dead end mode. The obtained rejection results were analyzed with existing pore models in which the rejection is related to the ratio of solute size to pore size. The existing pore models (transport equations) were adjusted to accommodate the microfiltration range particles. The adjusted pore models showed good agreement with the obtained experimental rejection results for virus while the bacteria rejection results showed a deviation. This deviation is partially explained with the wide size distribution of bacteria. The equivalent spherical diameter can be used to represent the virus size while the oval diameter of the cells may be the best possible dimension for bacteria size in membrane filtration. This determination showed the possibility of bacteria cells approaching the membrane pores in their longitudinal direction.

High performance Polyfil II microfiltration range

High performance Polyfil II microfiltration range

Mechanism of bacterial and viral transport through microfiltration membranes

Microorganisms such as Qβ, MS2, T4 virus and several bacteria strains in Pseudomonas, Alcaligenes and E-coli groups were filtered with different pore size nuclepore and anopore flat sheet membranes in dead end mode. The obtained rejection results were analyzed with existing pore models in which the rejection is related to the ratio of solute size to pore size. The existing pore models (transport equations) were adjusted to accommodate the microfiltration range particles. The adjusted pore models showed good agreement with the obtained experimental rejection results for virus while the bacteria rejection results showed a deviation. This deviation is partially explained with the wide size distribution of bacteria. The equivalent spherical diameter can be used to represent the virus size while the oval diameter of the cells may be the best possible dimension for bacteria size in membrane filtration. This determination showed the possibility of bacteria cells approaching the membrane pores in their longitudinal direction.

Membrane filtration as a tool in biotechnical down-stream processing

A summary is given of DDS RO's range of ultrafiltration, microfiltration, and reverse osmosis membranes and modules as well as their applications within biotechnology and down-stream processing: enzymes, xanthan gum, and an unspecified, microbiologically produced organic acid.

Removal of endotoxin from water by microfiltration through a microporous polyethylene hollow-fiber membrane.

The microporous polyethylene hollow-fiber membrane has a unique microfibrile structure throughout its depth and has been found to possess the functions of filtration and adsorption of endotoxin in water. The membrane has a maximum pore diameter of approximately 0.04 micron, a diameter which is within the range of microfiltration. Approximately 10 and 20% of the endotoxin in tap water and subterranean water, respectively, was smaller than 0.025 micron. Endotoxin in these water sources was efficiently removed by the microporous polyethylene hollow-fiber membrane. Escherichia coli O113 culture broth contained 26.4% of endotoxin smaller than 0.025 micron which was also removed. Endotoxin was leaked into the filtrate only when endotoxin samples were successively passed through the membrane. These results indicate that endotoxin smaller than the pore size of the membrane was adsorbed and then leaked into the filtrate because of a reduction in binding sites. Dissociation of 3H-labeled endotoxin from the membrane was performed, resulting in the removal of endotoxin associated with the membrane by alcoholic alkali at 78% efficiency.

Rückdifferenzierung als Voraussetzung ontogenetischer Entwicklung.

The main purpose of this research is to synthesize porous ceramic membrane based on alkali-activated blast furnace slag and achieve optimal synthesis conditions for removing over 90% petroleum compounds and flux in the range of microfiltration (MF) and ultrafiltration (UF). The method applied for membrane synthesis is simple, environmentally friendly, and economical. The blast furnace slag as the main starting material was used to fabricate these free sintering and self-supported ceramic membranes. The L9 orthogonal array of the Taguchi method was employed to determine the optimum conditions of three controlling factors, i.e. hydraulic pressing pressure, alkali-activated blast furnace slag drying time, and pressing time in three levels. Morphology and filtration performance of the synthesized membranes were characterized via SEM images using Image-j software, total porosity determination, and pore size study using bubble point method. Cross-flow filtration of 75 ppm gas oil in water emulsion was performed and COD analysis of permeate was then monitored. Distribution of synthesis parameters and their influences on the membrane fabrication process were investigated using analysis of variance (ANOVA). According to the results, drying time and hydraulic pressing pressure were known as the most effective parameters on COD and permeation flux. Two optimal membranes for COD removal and permeation flux were identified in hydraulic pressing pressure, drying time and pressing time of (400 bar, 6 h, 5 min) and (225 bar, 8 h, 30 min), respectively. COD optimal UF membrane with an average pore size of 0.07 µm and 100% removal of gas oil and permeation flux optimal MF membrane with an average pore size of 0.66 µm and pure water permeation flux of 1960 kg/m2 h were introduced.