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Permeation Flux (permeation + flux)
Selected AbstractsPerfluorosulfonic acid,Tetraethoxysilane/polyacrylonitrile (PFSA-TEOS/PAN) hollow fiber composite membranes prepared for pervaporation dehydration of ethyl acetate,water solutionsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Hai-Kuan Yuan Abstract Preparation of organic-inorganic composite membranes and their pervaporation (PV) permeation and separation characteristics for the aqueous solution of ethyl acetate were described. Polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane as support membrane, the mixtures of perfluorosulfonic acid (PFSA) and tetraethoxysilane (TEOS) by the sol-gel reaction as the coating solution, the PFSA-TEOS/PAN hollow fiber composite membranes by the different annealing conditions were prepared. The swelling of PFSA in ethyl acetate aqueous solutions was inhibited with addition of TEOS. The PFSA-TEOS/PAN composite membranes containing up to 30 wt % TEOS in coating solution exhibited high selectivity towards water, then the selectivity decreased and permeation flux increased with increasing the TEOS concentration more than 30 wt %. When the PFSA-TEOS/PAN composite membranes were annealed, the separation factor increased with increasing annealing temperature and time. Higher annealing temperature and longer annealing time promoted the crosslinking reaction between PFSA and TEOS in PFSA-TEOS/PAN composite membranes, leading to the enhanced selectivity towards water. For the PFSA/PAN and PFSA-TEOS/PAN composite membrane with 5 and 30 wt % TEOS annealed at 90°C for 12 h, their PV performance of aqueous solution 98 wt % ethyl acetate were as follows: the separation factors were 30.8, 254 and 496, while their permeation flux were 1430, 513 and 205 g/m2 h at 40°C, respectively. In addition, the PV performance of PFSA-TEOS/PAN composite membranes was investigated at different feed solution temperature and concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Pervaporation characteristics and structure of poly(vinyl alcohol)/poly(ethylene glycol)/tetraethoxysilane hybrid membranesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Li Yi Ye Abstract Poly(vinyl alcohol) (PVA) blended with poly(ethylene glycol) (PEG) was crosslinked with tetraethoxysilane (TEOS) to prepare organic,inorganic PVA/PEG/TEOS hybrid membranes. The membranes were then used for the dehydration of ethanol by pervaporation (PV). The physicochemical structure of the hybrid membranes was studied with Fourier transform infrared spectra (FT-IR), wide-angle X-ray diffraction WXRD, and scanning electron microscopy (SEM). PVA and PEG were crosslinked with TEOS, and the crosslinking density increased with increases in the TEOS content, annealing temperature, and time. The water permselectivity of the hybrid membranes increased with increasing annealing temperature or time; however, the permeation fluxes decreased at the same time. SEM pictures showed that phase separation took place in the hybrid membranes when the TEOS content was greater than 15 wt %. The water permselectivity increased with the addition of TEOS and reached the maximum at 10 wt % TEOS. The water permselectivity decreased, whereas the permeation flux increased, with an increase in the feed water content or feed temperature. The hybrid membrane that was annealed at 130°C for 12 h exhibited high permselectivity with a separation factor of 300 and a permeation flux of 0.046 kg m,2 h,1 in PV of 15 wt % water in ethanol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Oxygen permeability and structural stability of a novel tantalum-doped perovskite BaCo0.7Fe0.2Ta0.1O3,,AICHE JOURNAL, Issue 3 2010Huixia Luo Abstract Dense BaCo0.7Fe0.2Ta0.1O3,, (BCFT) perovskite membranes were successfully synthesized by a simple solid state reaction. In situ high-temperature X-ray diffraction indicated the good structure stability and phase reversibility of BCFT at high temperatures. The thermal expansion coefficient (TEC) of BCFT was determined to amount 1.02 × 10,5 K,1, which is smaller than those of Ba0.5Sr0.5Co0.8Fe0.2O3,, (BSCF) (1.15 × 10,5 K,1), SrCo0.8Fe0.2O3,, (SCF) (1.79 × 10,5 K,1), and BaCo0.4Fe0.4Zr0.2O3,, (BCFZ) (1.03 × 10,5 K,1). It can be seen that the introduction of Ta ions into the perovskite framework could effectively lower the TEC. Thickness dependence studies of oxygen permeation through the BCFT membrane indicated that the oxygen permeation process was controlled by bulk diffusion. A membrane reactor made from BCFT was successfully operated for the partial oxidation of methane to syngas at 900°C for 400 h without failure and with the relatively high, stable oxygen permeation flux of about 16.8 ml/min cm2. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Evaluation of mixed-conducting lanthanum-strontium-cobaltite ceramic membrane for oxygen separationAICHE JOURNAL, Issue 10 2009Lei Ge Abstract In this study, La0.4Sr0.6CoO3-, (LSC) oxide was synthesized via an EDTA-citrate complexing process and its application as a mixed-conducting ceramic membrane for oxygen separation was systematically investigated. The phase structure of the powder and microstructure of the membrane were characterized by XRD and SEM, respectively. The optimum condition for membrane sintering was developed based on SEM and four-probe DC electrical conductivity characterizations. The oxygen permeation fluxes at various temperatures and oxygen partial pressure gradients were measured by gas chromatography method. Fundamental equations of oxygen permeation and transport resistance through mixed conducting membrane were developed. The oxygen bulk diffusion coefficient (Dv) and surface exchange coefficient (Kex) for LSC membrane were derived by model regression. The importance of surface exchange kinetics at each side of the membrane on oxygen permeation flux under different oxygen partial pressure gradients and temperatures were quantitatively distinguished from the oxygen bulk diffusion. The maximum oxygen flux achieved based on 1.6-mm-thick La0.4Sr0.6CoO3-, membrane was ,4.0 × 10,7 mol cm,2 s,1at 950°C. However, calculation results show theoretical oxygen fluxes as high as 2.98 × 10,5 mol cm,2 s,1 through a 5-,m-thick LSC membrane with ideal surface modification when operating at 950°C for air separation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Performance study of heptane reforming in the dense ceramic membrane reactorsAICHE JOURNAL, Issue 1 2008Wenliang Zhu Abstract Heptane reforming was investigated in three dense ceramic membrane reactors, where the membranes were modified differently with reforming catalyst. Each reactor displayed distinctive catalytic behavior. The reactor with a bare membrane showed low catalytic activity and low oxygen permeation flux (JO2), but gave stable performance. The left two membranes reactors modified with catalyst both displayed shift processes at the preliminary stage of membrane reaction, not only in JO2 but also in the selectivity of all products. Moreover, the membrane reactor with more catalyst gave higher performance in the case of JO2 and CO selectivity. The observed shift phenomena are due to the activation of catalyst on the membrane surface, and the different amounts of catalyst produce different impaction on the membrane reactions. On the basis of the results in three membrane reactors, a reaction pathway of hydrocarbon reforming in dense ceramic membrane reactor is proposed. Being some different from combustion and reforming mechanism (CRR), hydrocarbon reforming in dense ceramic membrane reactor has its own characteristics. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Hydrogen separation of methyltriethoxysilane templating silica membraneAICHE JOURNAL, Issue 12 2007Jong-Ho Moon Abstract Hydrogen separation on microporous methyltriethoxysilane-templating silica composite/,-alumina membranes (below MTES membrane) was studied using three binary gas mixtures: H2/N2, H2/CO2, and H2/CH4. The characteristics of unsteady and steady-state permeation/separation on the MTES membrane were compared to each other. Although permeation flux in the H2/N2 mixture was comparatively low, H2 selectivity was high (H2/N2 SF , 30,60). On the contrary, the H2/CO2 mixture showed high permeation flux but low H2 selectivity (H2/CO2 SF , 1.5,6.5). The H2/CH4 mixture showed a large difference between permselectivity (28,48) and separation factor (10,22). Results from this study revealed that it was difficult to predict the separation factor using the one-component permeation ratio (permselectivity) over the experimental range tested. These separation characteristics could be primarily ascribed to the molecular size and structure of each gas, which likely contributed to steric hindrance or molecular sieving within the membrane pore. In addition, the adsorption affinity of each molecule on the membrane surface acted as a key factor in separation performance because it significantly influenced surface diffusion. The generalized Maxwell-Stefan model incorporating the dust gas model, and the Langmuir model could successfully predict the transient and steady-state permeation/separation. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Delivery of nerve growth factor to brain via intranasal administration and enhancement of brain uptakeJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2009Siva Ram Kiran Vaka Abstract The main objective of the study was to investigate the efficacy of chitosan to facilitate brain bioavailability of intranasally administered nerve growth factor (NGF). In vitro permeability studies and electrical resistance studies were carried out across the bovine olfactory epithelium using Franz diffusion cells. The bioavailability of intranasally administered NGF in rat hippocampus was determined by carrying out brain microdialysis in Sprague,Dawley rats. The in vitro permeation flux across the olfactory epithelium of NGF solution without chitosan (control) was found to be 0.37,±,0.06 ng/cm2/h. In presence of increasing concentration of chitosan (0.1%, 0.25%, and 0.5%, w/v) the permeation flux of NGF was found to be 2.01,±,0.12, 3.88,±,0.19, and 4.12,±,0.21 ng/cm2/h respectively. Trans-olfactory epithelial electrical resistance decreased ,34.50,±,4.06% in presence of 0.25% (w/v) chitosan. The Cmax in rats administered with 0.25% (w/v) chitosan and NGF was 1008.62,±,130.02 pg/mL, which was significantly higher than that for rats administered with NGF only 97.38,±,10.66 pg/mL. There was ,14-fold increase in the bioavailability of intranasally administered NGF with chitosan than without chitosan. Chitosan can enhance the brain bioavailability of intranasally administered NGF. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:3640,3646, 2009 [source] Combined strategies for enhancing the transdermal absorption of midazolam through human skinJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 9 2010Cristina Balaguer-Fernández Abstract Objectives, Midazolam administration by intravenous or intramuscular injection produces pain and stress. For this reason, alternative methods of administration have been proposed. The transdermal administration of midazolam could improve patient comfort, which is especially important for children in the pre-operative period. We aimed to assess the effect of iontophoresis and chemical percutaneous enhancers applied individually and together, to determine if a synergistic effect is achieved when both enhancement techniques are simultaneously employed. Methods, This work reports the characterization of the passive diffusion of midazolam hydrochloride through human skin in vitro and evaluates the effect of iontophoresis application and chemical percutaneous enhancers on said diffusion when employed both individually and in combination. Key findings, Percutaneous absorption assays demonstrated that the physical technique of iontophoresis, when applied alone, moderately increased midazolam hydrochloride permeation flux through human skin, producing a similar effect to that obtained with R -(+)-limonene chemical enhancer. Among the strategies assayed, it was observed that Azone produced the most pronounced enhancement effect when applied separately. The combination of pre-treatment with Azone and iontophoresis exhibited a higher capacity for enhancing the transdermal flux of midazolam through human skin than Azone alone. Conclusions, In conclusion, when applied individually, Azone exhibited the greatest enhancement effect on the transdermal diffusion of midazolam of the various strategies assayed. The combination of Azone and iontophoresis produce the highest transdermal steady-state flux of midazolam but no synergic effect was achieved when the two enhancement strategies were applied in combination, showing that although selecting the best conditions for iontophoresis application, it is less effective for augmenting the transdermal delivery of midazolam than the chemical enhancer Azone. [source] Influence of magnesium aluminium silicate on rheological, release and permeation characteristics of diclofenac sodium aqueous gels in-vitroJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2005Thaned Pongjanyakul The effect of magnesium aluminium silicate (MAS) on rheological, release and permeation characteristics of diclofenac sodium (DS) aqueous gels was investigated. DS aqueous gels were prepared using various gelling agents, such as 15% w/w poloxamer 407 (PM407), 1% w/w hydroxypropylmethylcellulose (HPMC), and 1% w/w high and low viscosity grades of sodium alginate (HV-SA and LV-SA, respectively). Different amounts of MAS (0.5, 1.0 and 1.5% w/w) were incorporated into the DS gels. Incorporation of MAS into the DS gels prepared using SA or PM407 caused a statistical increase in viscosity (P<0.05) and a shift from Newtonian flow to pseudoplastic flow with thixotropic property. The DS release rates of these composite gels were significantly decreased (P<0.05) when compared with the control gels. This was due to an interaction between MAS and PM407 or SA, and adsorption of DS onto MAS particles. Moreover, a longer lag time and no change in DS permeation flux were found when MAS was added to the gels. The findings suggest that the rheological characteristics of gels prepared using PM407 or SA could be improved by incorporating MAS. However, the use of MAS could retard the DS release and extend the lag time of DS permeation. [source] Synthesis and Properties of 6FDA-MDA Copolyimide Membranes: Effects of Diamines and Dianhydrides on Gas Separation and Pervaporation PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2007Shude Xiao Abstract 6FDA-MDA-based polyimides were synthesized from a one-step polycondensation of 6FDA and MDA with other diamines and dianhydrides. The polyimides were characterized by GPC, FT-IR and NMR, and dense membranes were prepared from their solutions for gas separation and pervaporation. Gas separation and pervaporation properties were investigated using the linear moiety contribution method. The moiety contribution factors were used to analyze the effects of the dianhydride and diamine monomers on gas permselectivity and pervaporation permeation flux. It was shown that the steric effects and flexibility of the monomers and the interactions between the membrane and the penetrants accounted for the differences in separation properties. [source] State of the art of carbon molecular sieves supported on tubular ceramics for gas separation applicationsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Kelly Briceño Abstract During recent years, research into alternative power generation and less polluting vehicles has been directed towards the fabrication of compact and efficient devices using hydrogen fuel cells. As a compact viable proposal, membrane reactors (MR) have been studied as means of providing a fuel cell with an on-board supply device for pure hydrogen streams obtained by reforming hydrocarbons. However, the development of MRs is strongly dependant on the membrane having high permeation flux and high selectivity ratios towards H2 in a mixture of gases. To meet this need, carbon membranes are proposed materials, which have pores that are the same size as the kinetic diameters of syngases. These would provide an alternative to polymers, metals and ceramics in MR applications. Moreover, a tubular shape is a highly recommended configuration for achieving a compact and large reaction surface area. However, it is not easy to obtain a supported and amorphous carbon layer from polymer pyrolysis because the fabrication methods, the type of precursor material, characteristics of the support and pyrolysis conditions are all closely connected. The combination of all these factors and the stability problems of carbon membranes have limited the use of carbon molecular sieves (CMS) in large-scale applications. This review attempts to provide an overview of the use of carbon membranes in MRs for gas separation. It also reviews the advances in the materials, fabrication methods and characterisation techniques of specific supported carbon molecular sieve membranes that have been supported on tubular carriers so they can take advantage of the high permeation and selectivity values previously reported for unsupported CMS. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of metal-support interface on hydrogen permeation through palladium membranesAICHE JOURNAL, Issue 3 2009Ke Zhang Abstract Thin palladium membranes of different thicknesses were prepared on sol-gel derived mesoporous ,-alumina/,-alumina and yttria-stabilized zirconia/,-alumina supports by a method combining sputter deposition and electroless plating. The effect of metal-support interface on hydrogen transport permeation properties was investigated by comparing hydrogen permeation data for these membranes measured under different conditions. Hydrogen permeation fluxes for the Pd/,-Al2O3/,-Al2O3 membranes are significantly smaller than those for the Pd/YSZ/,-Al2O3 membranes under similar conditions. As the palladium membrane thickness increases, the difference in permeation fluxes between these two groups of membranes decreases and the pressure exponent for permeation flux approaches 0.5 from 1. Analysis of the permeation data with a permeation model shows that both groups of membranes have similar hydrogen permeability for bulk diffusion, but the Pd/,-Al2O3/,-Al2O3 membranes exhibit a much lower surface reaction rate constant with higher activation energy, due possibly to the formation of Pd-Al alloy, than the Pd/YSZ/,-Al2O3 membranes. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] | |||||||||||||