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Palladium-doped silica materials with SiCH3 groups were fabricated by sol-gel method under various calcination atmospheres and membranes were made thereof by coating process. The results showed that air atmosphere can lead to the partial oxidation of metallic Pd0 to PdO while N2 and H2 atmospheres can effectively prevent metallic Pd0 from being oxidized. H2 atmosphere is proved to be a more prominent way to slow down the decomposition of organic SiCH3 group than N2 and air atmospheres. The surface area, micropore volume and porosity of palladium-doped silica membrane material calcined in H2 atmosphere are much higher than those calcined in N2 atmosphere. Compared with N2 atmosphere, the palladium-doped silica membranes calcined in H2 atmosphere showed higher H2 permeability and H2/CO2 selectivity before and after the steam exposure. The apparent activation energy of H2 permeation through the palladium-doped silica membrane calcined under H2 atmosphere (2.51 ± 0.05 kJ/mol) was slightly lower than that calcined under N2 atmosphere (2.84 ± 0.04 kJ/mol). Calcination atmosphere plays some role in membrane performance, which has greater influence on the permeance than on the gas permselectivity. Calcination under H2 atmosphere is well conducive to improve the gas permeance and H2 permselectivity of palladium-doped silica membrane.
Der ultraschnelle Mechanismus der Alken-Hydrosylilierung lässt sich von den Flüssigsiliconen (LSRs) auf VNB-EPDM-Mischungen übertragen. In der Verarbeitung würde diese für VNB-EPDM die Wettbewerbsfähigkeit hinsichtlich realisierbarer kürzester Zykluszeiten und neue Marktsegmente alternativ zu den LSR-Materialien eröffnen, u.a. in speziellen Dichtungsanwendungen. Peroxidisch vernetzte EPDM-Mischungen können in wässrig-sauren und wässrig-alkalischen Medien eine bessere chemische Beständigkeit als LSR-Materialien bieten. Sie sind duch die radikalische Vernetzung in der Kinetik aber im Vergleich zu additionsvernetzbaren Elastomeren als deutlich träger einzustufen. Ein weiterer Aspekt ist die Permeationsbeständigkeit gegenüber Gasen und Lösemitteldämpfen, die in dieser Arbeit näher untersucht worden ist. In dieser Eigenschaft unterscheiden sich VNB-EPDM und LSR deutlich voneinander. Mit der Bestimmung von zeit- und temperaturabhängigen Permeationsraten von n-Hexan-Lösemitteldämpfen erfolgt ein Vergleich beider Elastomerklassen. Auf die Theorie der Gaspermeation und der sogenannten Pervaporation wird grundlegend eingegangen und zusätzlich der weitere Einfluss von Rezepturbestandteilen beleuchtet. Des Weiteren werden stationäre Permeationskoeffizienten für die Lösemittel-Dampf-Evaporation berechnet, indem die Ausprägung des Quelldrucks im Inneren der Elastomerwerkstoffe durch signifikante Volumenquellungen als eigentliche Triebkraft herangeszogen wird.
Polycaprolactone (PCL) was electrospun with the addition of arginine (Arg), an α-amino acid that accelerates the haeling process. The efficient needleless electrospinning technique was used for the fabrication of the nanofibrous layers. The materials produced consisted mainly of fibers with diameters of between 200 and 400 nm. Moreover, both microfibers and beads were present within the layers. Higher bead sized were observed with the increased addition of arginine.
Long-term stability of membranes in membrane distillation operation is a problem nowadays which prevents the industrial breakthrough of this separation process. Fouling or slow pore wetting are the basic reasons for this.
Membrane distillation membranes were made by NIPS process rendering the membrane asymmetrically to achieve low permeation resistance and pores which can be over coated with polyelectrolyte polymers thus leading to thermopervaporation membranes. Those membranes prohibit pore wetting and may strongly reduce resorption of organic substances on for membrane distillation typically used hydrophobic surfaces thus leading to longterm operation stability in dewatering including stable membrane cleaning.
Asymmetric PVDF membranes have been coated with cation exchange polyelectrolyte leading to a very thin, defect-free layer which has a high permeation rate for water due to the domain structure of phase-separated hydrophilic and hydrophobic three-dimensional structures.
A vapor permeation processes for the separation of aromatic compounds from aliphatic compounds
(2014)
A number of rubbery and glassy membranes have been prepared and evaluated in vapor permeation experiments for separation of aromatic/aliphatic mixtures, using 5/95 (wt:wt) toluene/methylcyclohexane (MCH) as a model solution. Candidate membranes that met the required toluene/MCH selectivity of ≥ 10 were identified. The stability of the candidate membranes was tested by cycling the experiment between higher toluene concentrations and the original 5 wt% level. The best membrane produced has a toluene permeance of 280 gpu and a toluene/MCH selectivity of 13 when tested with a vapor feed of the model mixture at its boiling point and at atmospheric pressure. When a series of related membrane materials are compared, there is a sharp trade-off between membrane permeance and membrane selectivity. A process design study based on the experimental results was conducted. The best preliminary membrane design uses 45% of the energy of a conventional distillation process.
In thermopervaporation the same economically favorable driving force as in membrane distillation, i.e., a temperature difference between feed and permeate for the transport, is used but with non-porous thin-film composite membranes. Membrane pores cannot be wetted and long-term operational stability can be achieved with the appropriate coating layer, but normally with a decrease of the flux compared to membrane distillation with porous hydrophobic membranes.
Porous asymmetric PVDF membranes were made to achieve low permeation resistance and pores which could be overcoated with polyelectrolyte polymers. This coating prohibits pore wetting and strongly reduces adsorption of organic substances.
Those membranes showed a high permeation rate for water due to a structure of phase-separated hydrophilic and hydrophobic three-dimensional domains. The permeation rates of these composite membranes for water is between 6 and 12 l/(h m²) at a feed temperature of 60 °C and permeate at a temperature of 40 °C of a 2% saline solution feed depending on the operational parameters. This is only a slight reduction of 10–15% in permeation rate compared to membrane distillation with porous hydrophobic membranes.
In whey dewatering experiment this membrane showed a constant performance over 4 days in intermittent operation mode and stability in cleaning with strong alkaline solution.