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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: This aim of this work was to investigate the effects of mass transfer in three commercially available frontal nanofiltration systems (Amicon, Sterlitech and Membranology) using the rejection of uncharged poly ethylene glycol (molecular weight 3400) at different pressures and stirrer speeds using a 4000 MWCO membrane. The real rejection was calculated from the observed rejection using the infinite rejection method and a comparison was made between experimentally obtained mass transfer coefficients and those obtained from commonly used ultrafiltration theory. A new mass transfer correlation was proposed that is more appropriate to account for the increased mass transfer effects observed with the larger pressures of nanofiltration. This new correlation is defined as NSh = φ(NRe)n (NSc)0.33 [1+[JV/ωr]X] is only a minor modification to existing theory and has an accuracy suitable for engineering design purposes. Keywords: Mass transfer, Concentration polarisation, Equipment characterisation, Frontal filtration, Nanofiltration.Download Full Article |
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Abstract: Electrochemical Performance of DMFC was studied under the effect of various operating parameters like temperature, methanol concentration and relative humidity (RH) for the synthesized silica immobilized phosphotungstic acid-poly(vinyl alcohol) (Si-PWA/PVA) nanocomposite membrane (thickness 80-100 µm). The optimized 1.5 Si-PWA/PVA membrane showed good electrochemical properties (transport number: 0.92 and IEC: 0.90 meq/g) with excellent mechanical strength, thermal and chemical stability. Open circuit voltage (OCV) decay was significantly lower in comparison to Nafion-117. Maximum power density (45.7 mWcm-2)was obtained at 60oC cell temperature. DMFC performance exhibited better performance even at higher methanol concentration (2 M) demonstrating lower concentration over potential. The appreciable rise in the peak power density observed at higher relative humidity (90%) showed good water stability of the membrane. Performance of the DMFC with the synthesized composite membrane was comparable to the state of the art Nafion-117. Keywords: Nanocomposite membrane, Membrane electrode assembly, proton conductivity, methanol crossover, over-potential.Download Full Article |
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Abstract: Model for concentration profile at the mechanism of shear- induced back migration has been proposed. The model is based on the following assumptions: (1) Flow is assumed to be isothermal, incompressible, fully developed and steady– state. The model implies the position dependence of transverse velocity and shear rate; (2) Dispersed phase consists of rigid bodies characterized by identity variables and particle- size distribution; (3) Back migration being non- diffusive in nature is characterized by certain kinetic behavior. The migration of particle is determined by shear- induced force (moving force) and drag forces (resistance force); (4)The migration of particles was assumed to occur within the zone referred to as shear-diffusion migration zone. Migration zone ranges from membrane to its threshold value at the upper boundary where the state of pseudo-equilibrium takes place; Vector sum of the forces acting the particle (shear and drag forces) ranges from its maximum value at the surface of membrane to zero at the upper boundary of migration zone where the state of pseudo-equilibrium takes place; (5) The driving force being degree of deviation from the state of equilibrium was expressed as the difference between local shear rate and its threshold value at the upper boundary of migration zone; Transport mechanisms such as Brownian diffusion, inertial lift, interaction based on Van der Waals or electrostatic forces, combined effects of particle-particle and particle–membrane interactions are outside the scope of the model. The proposed model has the following possible implications: (A) It can be used for quantitative estimation of the probability of fouling caused by different fractions at existing hydrodynamic conditions; (B) The model allows analyzing the impact of hydrodynamic conditions (such as shear stress and transverse velocity) on the probability of fouling caused by certain dispersed fraction; (C) It allows estimation of the threshold value of the shear rate specific for the certain fraction that should be exceed in order to prevent accumulation of this fraction; (D) Proposed model permits analyzing the influence of shear rate at the surface of membrane on the transverse concentration distribution; (E) The model can be used for quantitative analysis of CP distribution of individual fraction while considering poly-disperse systems as soon as any fraction is characterized by its individual migrating behavior. Keywords: Shear-induced diffusion, concentration polarization, cross-flow microfiltration, modeling.Download Full Article |
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Abstract: Graphene and its derivatives have got increasingly application interests emanating from its unique properties. This work reports silver-graphene oxide sheets (Ag-GO) composite synthesis and then incorporated into Polyethersulfone (PES) casting solution. The composite casting mixtures were cast via phase inversion method. Graphene and its derivatives were characterised by ATR/FTIR, Raman, XRD and TEM. The morphology and performance of the neat PES and composite PES membranes were characterised by SEM, AFM, CA, permeation flux, protein (BSA) rejection, antifouling and antibacterial tests. The composite membranes exhibited a slightly higher permeation flux and then gradual decreased compared to neat PES membranes. However, the antifouling tests revealed that the composite membranes with Ag particles showed a preferable antifouling performance. The antibacterial tests confirmed that the composite membranes exhibited a effective antibacterial performance against both gram-positive (E. coli) and gram-negative (S. Aureus) strains. Keywords: Graphene derivativies, Polyethersulfone, silver particles, antibacterial effect.Download Full Article |