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Abstract: Athin layer of colloidal silicalite was coated on a macroporous alumina substrate to improve the effectiveness in loading and supporting ionic liquid (IL) membrane on macroporous ceramic substrate. The [bmim][BF4] IL and CO2 gas separation were used as the model system in this research. The colloidal silicalite top layer enabled the formation of a pinhole-free IL membrane with significantly reduced load of IL as compared to the bare alumina substrate because the former had a smaller and more uniform inter-particle pore size than the latter. The supported IL membrane was extensively studied for CO2 separation in conditions relevant to coal combustion flue gases. The silicalite-supported IL membrane achieved a CO2/N2 permselectivity of ~24 with CO2 permeance of ~1.0×10-8 mol/m2·s·Pa in dry conditions at 26˚C and reached a CO2/N2 separation factor of ~18 with CO2 permeance of ~1.56×10-8 mol/m2·s·Pa for a feed mixture containing ~11% CO2 and ~9% water vapor at 50oC. This supported IL membrane exhibited excellent stability under a 5-bar transmembrane pressure at 103˚C and chemical resistance to H2O, SO2, and air (O2). Results of this study also indicated that, in order to fully realize the advantages of using the colloidal silicalite support for IL membranes, it is necessary to develop macroporous ceramic supports with optimized pore size distribution so that the IL film can be retained in the micron-thin silicalite layer without penetrating into the base substrate. Keywords: Colloidal silicalite, ionic liquid, membrane, carbon dioxide, separation. Download Full Article |
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Abstract: Modeling of CO2/CH4 separation using SAPO-34 tubular membrane was performed by computational fluid dynamics. The Maxwell-Stefan equations and Langmuir isotherms were used to describe the permeate flux through the membrane and the adsorption-diffusion, respectively. Three-dimensional Navier-Stokes momentum balances in feed and permeate side coupled with adsorption-diffusion equations from the membrane were simultaneously solved by ANSYS FLUENT software. The velocity and concentration profiles were determined in both feed and permeate sides. There was a good agreement between simulation and experimental results and root mean square deviation for CH4 and CO2 are 0.13 and 0.1 (mmol m-2 s-1), respectively. The concentration polarization effect was observed in the results. The effect of the process variables were investigated to find out the most influential parameters in permeation and purity. The impact of operating conditions on separation were studied and showed that for enhancement of separation efficiency of CO2 from CH4, feed pressure, feed flow rate and tube radius and number of membrane modules in series should be increased, whereas flow configuration has less significant effect. Keywords: Computational fluid dynamic, tubular zeolite membrane, CO2/CH4 separation, SAPO-34, Adsorption-diffusion mechanismv. |
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Abstract: An air sweep pervaporation process with thin anion-exchange hollow fibers was investigated for various water-organic solvent mixtures at different operating conditions. It was found that flux and separation factor increased with a decrease of the dielectric constant of the organic solvent. When the temperature of the process was increased, the flux increased. At feed temperatures of 65–70°C it was possible to reduce the water concentration in a 3–10% isopropyl alcohol (IPA) solution to 0.5%. The energy requirement for decreasing the water concentration in IPA from 3–10% to 0.5% was 100–225 kWh ton-1. Keywords: Solvent dehydration, pervaporation, anion exchange hollow fibers, dielectric constant. Download Full Article |
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Abstract: The control of surface roughness of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS) and cellulose (CE) membranes was attempted by changing the rate of nonsolvent influx in the phase inversion process. PVDF and CE were chosen to represent membranes of high hydrophobicity and hydrophilicity, respectively, while PES and PS were chosen to represent membranes of intermediate hydrophobicity/-philicity. The concentration of sodium chloride (NaCl) in the aqueous coagulation medium was increased from 0 to 1.9 mol/L to decrease the rate of nonsolvent (water) influx in the solvent/nonsolvent exchange process. As well, the effect of polymer concentration and solvent on the surface roughness was investigated with respect to PVDF and PES. It was observed that the membrane surface roughness increased and decreased, respectively, for the hydrophobic PVDF and hydrophilic CE membrane as the rate of nonsolvent influx was decreased. For the PES and PS membranes of intermediate hydrophilic/-philicity, no significant roughness change was observed. The surface roughness tended to increase as the solution viscosity decreased. It was also observed that the pattern wave length of the hydrophobic membrane did not change significantly while that of the hydrophilic membrane increased significantly as the solvent influx rate was reduced. This trend is predictable by considering the shrinking or swelling of the cast polymer solution during the solvent/nonsolvent exchange process. Keywords: Surface roughness, pattern wave length, hydrophobicity/-philicity, AFM, nonsolvent influx rate, membrane..Download Full Article |
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Abstract: It appeared that malic acid solubilized both Al3+ and Cr3+ in aqueous solutions at all pH-values in 0.1 M NaNO3 at 25 oC. The detailed potentiometric measurements indicated that these free tri-valent metal ions released a net of three protons (3H+’s) into the solution. Free malic acid released a net of (2H+’s) into the solution from the two carboxylates. However, in the presence of metal ions malic acid effectively releases a net of three protons (3H+’s) into the solution; two from the two carboxylates and the third from the alcoholic group. The reaction mixture of Al3+:malic acid indicated the formation of a dimeric species. The proposed structure of this dimeric species is in good agreement with what has been shown in the literature. We are presenting a dimeric species that may play an important role in malate transportation across cell membrane. Formation of the Al3+-malic acid complexes cover the span of a total of 400 mV; from +250 mV to -150 mV. The Cr3+-malic acid reaction mixture indicated the formation of a dimeric species as well. Keywords: Aqueous solutions, Dimeric species, Malic acid, Al3+, Cr3+, and Speciation diagrams.Download Full Article |