Γ-alumina Membranes Research Articles

Preparation of high flux mesoporous γ-alumina membranes for whey proteins isolation: Peptizing agent (acetic acid) and binder (PEG) effects

The sol-gel process is a common approach for the fabrication of mesoporous γ-alumina membranes. The viscosity of the sol can significantly affect the membrane thickness as well as its performance. Therefore, it is essential to properly adjust the viscosity of the sol. For this purpose, different compositions of acetic acid and PEG were used as the peptizing agent and the binder, respectively. The findings suggested that if the H+Al3+ ratio is adjusted in the values of 0.4 and 0.6, and PEG is proportionally added, the sols with the viscosity values of 2–3 mPa s will be achieved. The homogenous and defect-free top-layer with thickness of <2 μm were prepared using the mentioned sols by a one-step coating which is also economically important. The performance of the membranes was evaluated by the pure water permeability, PEG rejection tests, and the separation and purification of whey. The membranes exhibited high water permeance (>30 L m−2 h−1.bar−1), and 90% rejection for PEG 4700 Da which was consistent with an ultrafiltration membrane layer. Furthermore, the prepared membranes were examined in a combined ultrafiltration-diafiltration process for purifying the whey proteins from the pre-treated whey through microfiltration. The results showed that the retentate was significantly devoid of lactose, and the protein content was as much as whey protein isolate.

Controlled Nanoconfinement of Polyimide Networks in Mesoporous γ-Alumina Membranes for the Molecular Separation of Organic Dyes

Polyimide networks are key in the development of stable, resilient, and efficient membranes for separation applications under demanding conditions. To this aim, the controlled design of the network’s nanostructure and its properties are needed. However, such control remains a challenge with currently available synthesis methods. Here, we present a simple nanofabrication approach that allows the controlled nanoconfinement, growth, and covalent attachment of polyimide (PI) networks inside the mesopores of γ-alumina layers. The attachment of the PI network on the γ-alumina layer was initiated via different prefunctionalization steps that play a pivotal role in inducing the in situ polymerization reaction at the pore entrance and/or at the inner pore surface. The nanoconfinement was found to be limited to the 1.5 μm-thick γ-alumina supporting layer at maximum, and the resulting hybrid PI/ceramic membranes showed stable performance in a variety of solvents. These PI/ceramic membranes were found to be very efficient in the challenging separation of small organic dye molecules such as Rhodamine B (479 g mol–1) from toxic solvents such as dimethylformamide or dioxane. Therefore, this technique opens up possibilities for a multitude of separations. Moreover, the PI synthesis approach can be applied to other applications that also rely on porosity and stability control, such as for advanced insulation and anticorrosion.

Comparison of ceramic α-alumina and modified γ-alumina membranes for H2 separation

This article provides details of a study that investigates hydrogen (H2) separation, purification and transport behaviour of a ceramic α-alumina membrane and compares it with that of a γ-alumina membrane modified with Boehmite sol.

Hydrolytic stability of PEG-grafted γ-alumina membranes: Alkoxysilane vs phosphonic acid linking groups

Abstract Small polyethylene glycol (PEG) molecules were grafted on ceramic γ-alumina membranes, by making use of organo-alkoxysilanes or organo-phosphonic acids as linking groups. It was proven by FTIR that the short PEG brushes are chemically grafted into the pores of a 5 nm γ-alumina mesoporous support, which results in a decrease of the pore diameter as measured by cyclohexane permporometry (reduction of 2.1 nm). The stability of these PEG-grafted membranes was investigated in water for 216 h. Permeability and liquid state 1H NMR were used to show that PEG-modified membranes with an alkoxysilane linking group degrade rapidly during exposure to water. On the contrary, the phosphonic acid linking group remained grafted on γ-alumina supports for at least 216 h in water. In conclusion, this work shows a promising and simple method for the fabrication in a green solvent (water) of hydrophilic organically-modified ceramic membranes, which can be successfully applied for wastewater treatment.

Molecular separation using poly (styrene-co-maleic anhydride) grafted to γ-alumina: Surface versus pore modification

Here, we report the covalent coupling of poly (styrene-co-maleic anhydride) onto γ-alumina to develop high-performance organic solvent nanofiltration (OSN) membranes. A high molecular weight (Mw) alternating copolymer of maleic anhydride (MA) and styrene (St) was synthesized and directly grafted to the γ-alumina membrane, while commercially available low Mw random copolymers of St and MA were also investigated. We show that solute rejection and membrane permeability strongly depend on the nature of the applied copolymer. In particular, the Mw of the copolymer applied is potentially the key for improving the membrane performance. When a high Mw copolymer was applied, the grafted layer covered the surface of the membrane. This results in membranes with significantly improved rejection, while maintaining a high permeability. In contrast, we observed pore grafting by applying low Mw copolymers, which resulted in membranes with slightly higher rejection and dramatically lower permeability compared to unmodified membrane. The best results were obtained by grafting γ-alumina with a high Mw alternating copolymer. These membranes showed a solute rejection of 98% for Sudan Black B (457 g mol−1) in toluene, while the permeability remained high at 2.9 L m−2 h−1 bar−1.

Transport of liquid and supercritical CO2 and selected organic solvents through surface modified mesoporous γ-alumina and titania membranes

ABSTRACTThe permeation of liquid and supercritical CO2 and the organic solvents toluene, heptane, and 1-propanol were investigated in unmodified hydrophilic and modified hydrophobic mesoporous γ-alumina and titania tubular ceramic membranes. These ceramic membranes are solvent resistant, thermally stable, and hydrophilic in nature. Viscosity-corrected solvent flux was used to evaluate the applicability of Darcy’s law, which is governed by convective transport. The permeability coefficients were dependent on solvent type due to unique solvent–membrane interactions, which is a deviation from Darcy’s law. Surface chemistry of modified membranes was evaluated using contact angle measurements, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and Energy Dispersive X-ray Spectroscopy.

Influence of the intermediate layer on the hydrothermal stability of sol-gel derived hybrid silica membranes

The hydrothermal stability of microporous silica hybrid sol-gel derived membranes is often only tested for either the mesoporous intermediate membrane layer or the microporous separation layer. In this work an investigation is done on the interaction between the intermediate γ-alumina layer and the hybrid (BTESE-derived) silica separation layer during hydrothermal treatment. Although bare γ-alumina is degraded during a hydrothermal treatment, a coating of hydrophobic BTESE on γ-alumina retains its gas separation performance, albeit with a lower mechanical adhesion between the hybrid silica separation layer and the γ-alumina intermediate layer. Applying a monoaluminumphosphate (MAP) coating between the α-alumina support and the γ-alumina layer stabilizes the γ-alumina membrane. A BTESE coating on a MAP modified γ-alumina membrane did not show any signs of delamination after hydrothermal testing. Moreover, a significant increase in the H2/N2 (perm)selectivity, factor 3, was observed for these membranes.

Design of Phosphonated Imidazolium-Based Ionic Liquids Grafted on γ-Alumina: Potential Model for Hybrid Membranes.

Imidazolium bromide-based ionic liquids bearing phosphonyl groups on the cationic part were synthesized and grafted on γ-alumina (γ-Al2O3) powders. These powders were prepared as companion samples of conventional mesoporous γ-alumina membranes, in order to favor a possible transfer of the results to supported membrane materials, which could be used for CO2 separation applications. Effective grafting was demonstrated using energy dispersive X-ray spectrometry (EDX), N2 adsorption measurements, fourier transform infrared spectroscopy (FTIR), and special attention was paid to 31P and 13C solid state nuclear magnetic resonance spectroscopy (NMR).

Catalysts with Cerium in a Membrane Reactor for the Removal of Formaldehyde Pollutant from Water Effluents.

We report the synthesis of cerium oxide, cobalt oxide, mixed cerium, and cobalt oxides and a Ce–Co/Al2O3 membrane, which are employed as catalysts for the catalytic wet oxidation (CWO) reaction process and the removal of formaldehyde from industrial effluents. Formaldehyde is present in numerous waste streams from the chemical industry in a concentration low enough to make its recovery not economically justified but high enough to create an environmental hazard. Common biological degradation methods do not work for formaldehyde, a highly toxic but refractory, low biodegradability substance. The CWO reaction is a recent, promising alternative that also permits much lower temperature and pressure conditions than other oxidation processes, resulting in economic benefits. The CWO reaction employing Ce- and Co-containing catalysts was carried out inside a slurry batch reactor and a membrane reactor. Experimental results are reported. Next, a mixed Ce–Co oxide film was supported on an γ-alumina membrane used in a catalytic membrane reactor to compare formaldehyde removal between both types of systems. Catalytic materials with cerium and with a relatively large amount of cerium favored the transformation of formaldehyde. Cerium was present as cerianite in the catalytic materials, as indicated by X-ray diffraction patterns.

Preparation and characterization of multilayer mesoporous γ-alumina membrane obtained via sol-gel using new precursors

AbstractIn this paper, a mesoporous γ-alumina membrane coated on a macroporous α-alumina support via sol-gel method has been reported. A crack-free γ-alumina membrane was obtained by adding PVA to the alumina solution and optimum parameters of roughness, temperature and porosity were achieved. The support was dip-coated in different solutions using two new different solvents with different particle size distributions. Using these two solvents led to the uniform distribution of pore size in the final membrane. The alumina sols showed particle size distributions in the range of 20 to 55 nm which was measured by a DLS Zeta Sizer. X-ray diffraction technique, atomic force microscopy and scanning electron microscopy were used to characterize the membrane layer. XRD and DTA data for the γ-alumina membrane showed its thermal stability up to around 600 °C. The thickness of the mesoporous γ-alumina membrane was about 4 μm with 16 nm of surface roughness and 5 nm pore size. The resultant crack-free mesoporous membrane shows that the membrane preparation procedure was optimum. In this work, it has been investigated the performance of γ-alumina membranes for single gas permeation and separation of binary gas mixtures.

RETRACTED: Preparation and characterization of multilayer mesoporous alumina nano membrane via sol–gel method using new precursors

Abstract In the present study, a mesoporous γ-alumina layer was coated on a macroporous α-alumina support via sol–gel method to produce a multilayer mesoporous alumina membrane with high performance. Different parameters like homogeneity of colloidal solution, additive, working temperature, roughness of the membrane surface, membrane thickness and porosity of the membrane were analyzed. Two types of new different solvents and additives were considered and compared to have a perfect colloidal sol. A crack-free γ-alumina membrane was obtained by adding Poly Vinyl Alcohol to the alumina solution in an optimum conditions. In order to investigate the thermal stability of the membrane, it was dried and heated up to 600 °C. The alumina sols showed particle size distributions in the range of 20–55 nm which was measured by a DLS zeta sizer. The roughness of the sub-layers was measured using a Roughness Checker and density and porosity were measured based on Archimedes principle. X-ray diffraction technique (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to characterize the membrane layer. The thickness of the produced mesoporous membrane was about 4 µm with 16 nm of surface roughness and 5 nm pore size.

Inorganic Membranes for the Recovery of Effluent from Municipal Wastewater Treatment Plants

Effluent from the secondary treatment of municipal wastewater was treated with membrane filtration to reduce its toxicity. Five different inorganic membranes were tested, namely, an α-alumina microfiltration membrane, an anatase titania ultrafiltration membrane, a γ-alumina nanofiltration membrane, an amorphous titania nanofiltration membrane, and an amorphous hybrid organo-silica membrane. The permeabilities and selectivities (color, UV254-absorbing components, conductivity and inorganic nitrogen compounds) of the membranes were determined, and the γ-alumina nanofiltration membrane was found to be the most promising membrane for the treatment of the effluent. The effluent flux was measured to be approximately 40 L m–2 h–1 for the γ-alumina nanofiltration membrane, and it removed nearly 75% of the UV254-absorbing components and 15% of the ions. It also removed 40% of the CuCl and 25% of the CuSO4 from the spiked effluent. The fouling resistance was less pronounced for the γ-alumina membrane compared with ...

Performance of zeolite membrane (ZSM-5/γ-Alumina) in the oil/water separation process

There are several technologies for the treatment of oily wastewater generated by the oil industry, not only to separate the emulsified oil in water, but also to reduce its concentration in the aqueous effluent. Among the processes of separation, the separation using membranes should be highlighted when they become an effective material and it also resistant to high temperatures, have good corrosion resistance, easy to clean, and have long life operation, among others. This work aims to synthesize the material (ZSM-5, γ-alumina membrane, and zeolite membrane ZSM-5/γ-alumina) and to evaluate the membranes in the oil/water separation in a continuous flow system. From the XRD results of the individual materials, it can be observed the formation of all the characteristic peaks for each material. The EDX analysis of zeolite ZSM-5 showed the formation of this material with a Si/Al = 19. From the SEM image of these materials, it can be seen that the surface of the γ-alumina is completely covered with ZSM-5 zeolite crystals. The oil/water removing, using ZSM-5 γ-alumina membrane, showed high retention of the oil, obtaining a higher performance in relation to γ-alumina membrane. This reveals that the insertion of ZSM-5/γ-alumina in the material makes that this new material acquires a lower porosity, obtained by decreasing the passage of oil molecules through the membrane structure.

Modeling water flux and salt rejection of mesoporous γ-alumina and microporous organosilica membranes

The water and ion transport through a mesoporous γ-alumina membrane and a microporous organosilica membrane was simulated using the extended Nernst–Planck equation combined with models for Donnan, steric and dielectric interfacial exclusion mechanisms. Due to the surface charge within the pore, the electroviscous effect was introduced in the model. The modified model fits well the rejection and permeability data for both membranes. The organosilica membrane shows a higher selectivity compared to the γ-alumina membrane, but the permeate flux is lower. At low ionic strength the electroviscous effect lowers the water flux through the γ-alumina membrane. The electroviscous effect is negligible for the organosilica membrane because its absolute surface potential (~20mV) is low compared to the γ-alumina membrane (~60mV). The simulation shows that the electroviscous effect should be included for the membranes with high surface potential (>20mV) and a pore size below 2–5 times of the electroviscous double layer thickness.

PDMS grafting of mesoporous γ-alumina membranes for nanofiltration of organic solvents

In this paper grafting of mesoporous γ-alumina membranes with monovinyl terminated polydimethylsiloxane (PDMS), using 3-mercaptopropyltriethoxysilane (MPTES) as a linking agent, is described. The grafting performance of the organic moieties on γ-alumina powders was studied by FTIR. Contact angle measurements and solvent permeability tests were used to characterize the membrane properties. The results indicated that grafting reactions were successfully carried out. The toluene permeability of the membrane was reduced from 5.3 to 2.1L/m2hbar after grafting with the polymer. No degradation of the membrane material was observed after chemical stability tests in toluene for 6 days at room temperature and at elevated temperatures (up to 90°C).

Preparation and Characterization of Single Layer Ultra Filtration Alumina Membrane Directly over Porous Clay-Alumina Tubular and Capillary Support for Textile Effluent Treatment

Clay-alumina porous tubular supports of 8/6 mm for outside diameter/inside diameter (OD/ID) were prepared by extrusion and sintering at 1450°C for 110 min to obtain an average pore size of 1 µm and porosity of 40%. Slip casting slurry was prepared by peptization of boehmite (AlO(OH)) powder with 1.5 N nitric acid and mixing it with γ-Al2O3 powder of 40 nm particle size along with PVA and PEG in determined weight percentage. Clay alumina porous support tubes of 3.1/1.9 and 8/6 mm (OD/ID) were coated with the slip casting slurry and sintered at 550°C for 60 min to obtain γ-alumina membrane directly over the supports in a single step. The membrane layer prepared over both the support tubes were without any intermediate layer. The membranes presented a pore diameter distribution centered at 7.0 nm on 3.1/1.9 mm (OD/ID) and 5.5 nm on 8/6 mm (OD/ID) supports, which was in ultrafiltration (UF) range. The prepared UF membranes were studied for treatment of bio-treated synthetic and real textile effluent in the side stream mode. About 98% decolorization of synthetic dye solution and 95.6% colour removal of real textile effluent were obtained by the combined effect of UF membrane and bioreactor.

Development of a PDMS-grafted alumina membrane and its evaluation as solvent resistant nanofiltration membrane

A new solvent resistant nanofiltration (SRNF) membrane is developed by grafting a PDMS polymer into the pores of a 5nm γ-alumina ceramic membrane. These PDMS-grafted γ-alumina membranes were attained through a two-step synthesis. The linking agent, 3-aminopropyltriethoxysilane (APTES), was first applied on a ceramic membrane either by a vapor phase or a solution phase method, followed by grafting of an epoxy-terminated PDMS. Through this route it was possible to tune the pore size and to engineer the surface chemistry (e.g. hydrophobicity) of ceramic membranes in favor of non-polar organic solvent permeation. Reproducible results were obtained for filtration experiments with hexane, toluene and isopropanol (IPA). As expected, higher permeabilities were found for non-polar solvents than for more polar solvents (resp. 4.8±0.1lm−2h−1bar−1 for hexane, 3.1±0.5lm−2h−1bar−1 for toluene and 0.54±0.04lm−2h−1bar−1 for IPA). A Molecular Weight Cut Off (MWCO) of 500±10Da was determined. Stability tests in hexane, toluene and IPA have shown that these newly developed membranes were stable in all these solvents during testing periods of up to 170 days.

Microstructure, strength and CO2 separation characteristics of α-alumina supported γ-alumina thin film membrane

In this work, a mesoporous γ-Al2O3 membrane was synthesised on an α-Al2O3 substrate by a sol–gel dip coating process. The membranes were characterised using SEM, field emission SEM, X-ray diffractometry and N2 adsorption/desorption measurements (Brunauer–Emmett–Teller analyses). The characterisation results revealed that a flawless γ-alumina membrane layer with 3·5 μm thickness and 2·1 nm average pore size was achieved. Subsequent separation tests indicated that CO2 could be separated from N2 by the mesoporous γ-Al2O3 membrane. In spite of the difficulties of the separation, the optimised microstructure achieved for the prepared membrane led to desirable and regular permeation behaviour. It was also observed that separation could be more efficient in high pressure permeation conditions. The prepared substrate fulfilled the required strength and permeability for the thin γ-Al2O3 membrane film under these conditions. Accordingly, an optimised completely ceramic membrane structure, applicable for CO2 separation applications, was achieved.

The transport of gases in a mesoporous γ-alumina supported membrane

We investigate the low pressure diffusion of several gases in a disordered mesoporous γ-alumina membrane of pore diameter 10.4nm, coated on a macroporous α-alumina tubular support. Transport data for the uncoated support is also separately obtained and interpreted using the conventional slip flow correlation with a single representative pore size, and with effective medium theory while considering the entire pore size distribution. It is shown that the conventional correlation based on a single pore size yields significant anomalies in the tortuosity and pressure profile for all gases, which are eliminated on using the effective medium theory, demonstrating the importance of considering the pore size distribution (PSD). These anomalies lead to failure of the correlation for the membrane layer. The effective medium theory is also extended to the disordered membrane layer, using the classical slip flow model and a version corrected for finite molecular size, as well as the Oscillator Model developed in this laboratory. All the diffusion models fitted the experimental data accurately, without the artifacts observed with the commonly used single pore size model. The results make evident the importance of correctly taking the pressure profile into account, in any investigation for a multi-layered supported membrane (i.e. with a macroporous support and a mesoporous membrane layer). It is seen that the slip flow model leads to significantly higher apparent diffusivities than the Oscillator flow model at small pore sizes. Nevertheless, the performance of all three diffusion models is comparable, and it is not possible to distinguish between them for the large pore diameter of 10.4nm of the mesoporous γ-alumina membrane layer. The results unequivocally show that it is critical to consider the full PSD for each layer rather than using a single representative pore size in modeling membrane transport, and in interpreting experimental permeability data.

Preparation, characterization and microstructural optimization of a thin γ-alumina membrane on a porous stainless steel substrate

► A mesoporous γ-Al 2 O 3 membrane was synthesized on conventional α-Al 2 O 3 substrates. ► γ-Al 2 O 3 membrane was potential for CO 2 separation at high pressure test conditions. ► Thus, it was required to provide the membrane layer with more strength. ► α-Alumina substrate was substituted with porous stainless steel. ► A stainless steel supported α-Al 2 O 3 membrane with better properties was synthesized. In this work, a supported mesoporous (MEP) γ-Al 2 O 3 membrane was synthesized on conventional α-Al 2 O 3 substrates by sol–gel dip coating process. In the following, the preparation of a novel metallic–ceramic composite membrane was studied, which incorporated desirable properties of both ceramic membrane and porous metallic substrate. For this purpose, mesoporous alumina membrane layer was developed on a porous 316L stainless steel substrate. The substrate was prepared by loose powder sintering and modified by soaking–rolling and fast drying method. The prepared membranes were characterized using scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and N 2 -adsorption/desorption measurements (BET analyses). The results revealed that a defect-free γ-alumina membrane with 2.1 nm average pore size can be produced. Permeation tests with N 2 gas revealed that the stainless steel substrate had 40 times more permeability than conventionally used alumina support. Additionally, single gas permeation of γ-alumina membrane for CO 2 and N 2 was compared. It was observed that CO 2 could be separated from N 2 by the MEP γ-Al 2 O 3 membrane in high pressure permeation condition, where stainless steel presents superior mechanical strength than alumina as a substrate.