| 1. |
- Andersson, Charlotte, et al.
(författare)
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Effects of exposure to water and ethanol on silicalite-1 membranes
- 2008
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 313:1-2, s. 120-126
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Tidskriftsartikel (refereegranskat)abstract
- The effects of long exposures to ethanol, water and 0.1 M aqueous solutions of ammonia, sodium hydroxide, tetrapropylammonium hydroxide (TPAOH) and hydrochloric acid on thin TPA-silicalite-1 membranes were studied. Single gas permeation experiments, porosimetry and scanning electron microscopy were used to characterize the membranes. It was found that a short exposure (24 h) will only dissolve synthesis residues and will not affect membrane quality negatively. The only medium that had an effect after 24 h was sodium hydroxide, which almost dissolved the film completely. After exposing TPA-silicalite-1 membranes for 30 days in the various liquids, the membrane quality decreased in the order ethanol < 0.1 M hydrochloric acid < 0.1 M TPAOH < water < 0.1 M ammonia < 0.1 M sodium hydroxide due to dissolution of the silicalite-1 crystals. This study has shown that prolonged exposure to aqueous solutions will lead to dissolution of silicalite-1 crystals causing an increase in micro- and mesopores in the film. The amount and size of the pores will depend on the pH of the aqueous medium. Higher pH gives a higher dissolution and hence more non-zeolitic pores in the silicalite-1 film. Ethanol has no effect on the dissolution of the zeolite film even after 30 days. This finding has an effect in membrane preparation and in several membrane applications such as pervaporation and separation of hydrocarbons isomer mixtures.
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| 2. |
- Butylina, Svetlana, et al.
(författare)
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Fractionation of whey-derived peptides using a combination of ultrafiltration and nanofiltration
- 2006
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Ingår i: Journal of Membrane Science. - : Elsevier. - 0376-7388 .- 1873-3123. ; 280:1-2, s. 418-426
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the fractionation and further isolation and characterisation of peptides and proteins present in sweet whey by means of ultrafiltration using a regenerated cellulose membrane with a nominal molar mass cut-off value of 10 kg/mol and nanofiltration through sulphonated polyether sulphone membrane with a cut-off of 1 kg/mol. The concentration of whey proteins was done below the critical flux. The sieving coefficients for the whey components (proteins, lactose and salts) were estimated. Whey proteins were completely rejected by the ultrafiltration membrane. Size exclusion chromatography (SEC) and matrix-assisted laser desorption ionisation time-of-flight (MALDI-TOF) mass spectrometry were used to evaluate the molar masses of the peptide fractions that were present in the whey permeates. Nanofiltration of whey permeates obtained after ultrafiltration was conducted at two pH values (9.5 and 3.0) that corresponded to the different charged states of the membrane and of the peptides. The transmission of peptides, amino acids and lactose was found to be mainly affected by the permeability of the fouling layer. The selectivity of the nanofiltration membranes toward peptides compared to lactose was calculated as 0.82 and 6.81 at pH 9.5 and 3.0, respectively.
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| 3. |
- Dong, Qian
(författare)
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An experimental method to identify various oxygen species transported in oxides
- 2007
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Ingår i: Journal of Membrane Science. - : Elsevier. - 0376-7388 .- 1873-3123. ; 306:1-2, s. 166-172
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen transport in oxides can take place in molecular, atomic and ionic form. An experimental method is described which separates the contributions of molecules, atoms and ions to the overall oxygen transport in oxides. The method comprises gas phase analysis and the use of oxygen isotopes O-16 and O-18. In the general case, exposure to non-equilibrated O-2 containing 60-70% O-18 is optimal to obtain the highest accuracy in the measurement. The method is exemplified by distinguishing non-ionic (molecular and atomic) oxygen transport from ionic oxygen transport in a commercial yttria-stabilized zirconia (YSZ) sample in the temperature range of 600-900 degrees C. There is approximately 35% molecular, 20% atomic transport and 45% ionic oxygen transport in YSZ at 600 degrees C. It is found that the fraction percent of non-ionic oxygen transport decreases with increasing temperature, and ionic oxygen transport increases sharply with increasing temperature.
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| 4. |
- Gualtieri, Magdalena Lassinantti, et al.
(författare)
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Crack formation in α-alumina supported MFI zeolite membranes studied by in situ high temperature synchrotron powder diffraction
- 2007
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 290:1-2, s. 95-104
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Tidskriftsartikel (refereegranskat)abstract
- Cracks are frequently formed in α-alumina supported MFI membranes during calcination. To better understand crack formation, in situ powder diffraction data were collected during calcination of a type of MFI membrane (ca. 1800 nm thick) which is known to crack reproducibly. In addition, data for MFI powder and a blank support were also collected. Both a synchrotron radiation facility and an in-house instrument were used. The unit cell parameters were determined with the Rietveld method, and the strain in the direction perpendicular to the film surface was calculated for the film as well as for the support. The microstrain in the support was also estimated. Based on the results obtained here, a model for crack formation in this type of MFI membrane was proposed. The lack of cracks in other types of MFI membranes (ca. 500 nm) prepared in our laboratory is also explained by the model. In thicker MFI films, the crystals are well intergrown. During heating, the MFI crystals contract and the α-alumina support expands. Consequently, a thermal stress develops in the composite which eventually leads to formation of cracks in the film and structural defects in the support. In thinner films, the crystals are less well intergrown and the thermal expansion mismatch leads to opening of grain boundaries rather than cracks.
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| 5. |
- Hedlund, Jonas, et al.
(författare)
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Permporometry analysis of zeolite membranes
- 2009
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 345:1-2, s. 276-287
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Tidskriftsartikel (refereegranskat)abstract
- In permporometry analysis of zeolite membranes, the permeance of a non-adsorbing gas, such as helium, is measured as a function of pressure of a strongly adsorbing compound, such as n-hexane in the case of silicalite-1 membranes. The adsorbing compound effectively blocks the transport of the non-adsorbing gas already at very low activity of the adsorbing compound. The plot of the permeance of the non-adsorbing gas as a function of relative pressure of the adsorbing compound is denoted a permporometry pattern. The present work is based on experimental data for a number of thin MFI membranes with a film thickness ranging from 300 to 1800 nm. An adsorption-branch permporometry experiment is simple and straightforward and after activation of the membrane by removing adsorbed species at 300 °C in a flow of dry gas, a full permporometry pattern is recorded within about 7 h for such membranes. It is shown how the distribution of flow-through defects can be estimated from the permporometry pattern using a simple model for permeation based on Knudsen diffusion. The estimated defect distribution is supported by SEM observations. In addition, the permeance of the non-adsorbing gas through defects measured in permporometry can be used to predict the permeance of molecules diffusing through defects in the membrane in mixture separation experiments and also indicate the separation factor. For instance, the helium permeance through defects in an MFI membrane measured by helium/n-hexane permporometry at room temperature can be used to estimate the permeance of 2,2-dimethylbutane (DMB) in a mixture separation experiment at a higher temperature with a feed containing both DMB and n-hexane by assuming Knudsen diffusion for both helium and DMB in the defects. Also, the separation factor αn-hexane/DMB in a mixture separation experiment at a certain temperature with an MFI membrane with a given defect distribution can be estimated from n-hexane/helium permporometry data recorded at the same temperature through an empirical correlation. In summary, adsorption-branch permporometry is a very effective tool for analysis of thin zeolite membranes, that in short time gives data that can be used to estimate the distribution of flow-through defects in the membrane and to estimate the transport of large molecules through defects in separation experiments and also estimate separation performance.
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| 6. |
- Nilsson, Mattias, et al.
(författare)
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The influence of pH, salt and temperature on nanofiltration performance
- 2008
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 312:1-2, s. 97-106
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Tidskriftsartikel (refereegranskat)abstract
- The influence of pH, KCl and temperature on the performance of an Alfa Laval NFT-50 nanofiltration membrane was evaluated by glucose and KCl retention measurements at constant flux. It was found that at constant temperature an increase in pH in the absence of KCl reduced the water permeability, and this was correlated to the electroviscous effect. The selectivity decreased with increasing KCl concentration and the decrease became more evident with increasing pH. The decrease in selectivity could be related to membrane swelling, and it appears that pH had no effect on swelling other than enhancing the effect of KCl. The influence of KCl and pH on membrane performance was evaluated as a function of temperature after reaching steady state at 50 °C. The degree of swelling was higher at 50 °C than at 20 °C, due to an increase in polymer flexibility with increasing temperature. The decrease in selectivity with increasing temperature was less for KCl than for glucose, showing that the charge effect was influenced less by temperature than diffusion through the membrane.
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| 7. |
- Nilsson, Mattias, et al.
(författare)
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The influence of sodium chloride on mass transfer in a polyamide nanofiltration membrane at elevated temperatures
- 2006
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 280:1-2, s. 928-936
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Tidskriftsartikel (refereegranskat)abstract
- The influence of temperature (20-50 degrees C) and NaCl on mass transfer of pure water and glucose solution (0.0055 M) using an Alfa Laval NFT-50 nanotiltration membrane has been investigated. Addition of 0.017 M NaCl(aq) increased the membrane permeability in comparison to measurements with pure water. Performing cyclic temperature variations using a membrane pre-treated with 0.20 M NaC](aq) caused the membrane permeability to decrease for each time a new maximum temperature was reached. After NaCl pre-treatment, the relative flux decline measured over 4 h was found to be greater for glucose than for water, and the rate of the flux decline for both water and glucose increased with temperature (20-50 degrees C). The permeability was found to be unaffected by the pressure if the membrane had previously been rinsed at a lower pressure but at a higher temperature. Changes in permeability due to the presence of NaCl could be related to interactions in the active polymer layer of the membrane. MgCl2 pre-treatment influenced the membrane permeability less that NaCl pre-treatment. (c) 2006 Elsevier B.V. All rights reserved.
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| 8. |
- Saha, N. K., et al.
(författare)
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Performance evaluation of thin film composite polyamide nanofiltration membrane with variation in monomer type
- 2009
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Ingår i: Journal of Membrane Science. - 0376-7388 .- 1873-3123. ; 342:1-2, s. 60-69
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Tidskriftsartikel (refereegranskat)abstract
- This work investigated the effect of variation in polyamide structure of thin film composite nanofiltration membranes resulting from variation in monomers on flux and rejection properties. Membranes from various combinations of monomers have been prepared including mixture of diamines or acid chlorides. The physicochemical characteristics of the membranes thus obtained were determined by infra-red spectroscopy, SEM, AFM, contact angle measurement and molecular model analysis. Attempts have been made to correlate the observed flux and rejection properties of the membranes with their physicochemical properties. It has been observed that polyamide structure influences flux and rejection of membranes to a great extent. (c) 2009 Elsevier B.V. All rights reserved.
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| 9. |
- Salazar-Alvarez, G., et al.
(författare)
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Transport characterisation of a PIM system used for the extraction of Pb(II) using D2EHPA as carrier
- 2005
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388 .- 1873-3123. ; 250:02-jan, s. 247-257
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Tidskriftsartikel (refereegranskat)abstract
- The facilitated transport of lead(II) through polymeric inclusion membranes consisting of cellulose triacetate as polymeric support, his(2-ethylhexyl)-phosphoric acid (D2EHPA) as carrier, and tris-(2-butoxyethyl)phosphate as plasticiser (TBEP), is investigated. The influence of some of the aqueous and membrane components on the permeability of Pb(II) was studied. The maximum flux obtained with these membranes is 3.5 x 10(-6) mol m(-2) s(-1), which is of the same order of magnitude of those reported for supported liquid membranes and is in the upper range of those reported for polymeric inclusion membranes. Aqueous and membranes resistances were determined from a model that describes the transport mechanism across the membranes using the stoichiometric relationship Ph R(2)2HR and the extraction equilibrium constant value of 6.2 x 10(-4) determined independently by solid-liquid extraction. An activation energy of I I kJ mol(-1) was also determined for Pb(II) migration, which suggest that the transport of Pb(II) is controlled by a membrane diffusion mechanism. Membrane characterisation was per-formed using several techniques including atomic force microscopy, scanning electron microscopy coupled with energy-dispersive spectroscopy, and thermal analysis.
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| 10. |
- Belkhouche, Nasr-Eddine, et al.
(författare)
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Study of new organophosphorus derivates carriers on the selective recovery of M(II) and M(III) metals, using supported liquid membrane extraction
- 2006
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388. ; 284:1-2, s. 398-405
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies different organophosphorus extractants for the selective recovery of metal ions such as Cu (II), Co (II), Ni (II), Ph (II), Fe (III), Cd (II) from effluents resulting from the metal finishing at the time of industry process. In a first step, a commercial extractant such as di(2-ethylhexyl)phosphoric acid (D2EHPA) was used as carrier for SLM extraction. Combining D2EHPA and TOPO (tri-octylphosphine oxide) leads to enhanced extraction of Cu (II), Ni (II) and Co (II). The influence of other critical parameters such as pH, ionic strength and mass transfer resistance of the feed was investigated as well as the diffusion of metal ions and membrane permeation. D2EHPA showed good extraction efficiency for Ph (II) (91%) in the mixture, whereas it is lower for Cu (II) (9%). When TOPO was added to D2EHPA, the extraction efficiency of copper increases up to 57%. In a second step, new organophosphorus extractants, synthesized by microwave irradiation, were tested in SLM extraction of metal ions. Di[p-(1, 1 ',3,3 '-tetramethylbutyl)phenyl] phosphoric acid (DOPPA) and 1, 12-(4,9-dioxatrisdecanyl)diphosphonic acid (DOTDDA), selectively extracted Cu (II) and Co (II) (100%) from Fe (III), Cd (II), Ph (II) and Ni (II) in the mixture (0%), whereas methylenediphosphonic acid (MDPA) is a good carrier for Cd (II) (83%), Ph (II) (69%) and Ni (II) (63%) extraction. However 1,1 3-diamino-4,7,10-trioxatridecanyltetramethylene phosphonic acid (DATOMPA) is useful for extraction of trace metals (Fe (III); 72%). For a selective extraction of Co (II) and Cu (II) from other metals, DOPPA shows the highest extraction efficiency for these two cations, whereas the rest of heavy metals tested are not extracted.
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