Integrally skinned polysulfone hollow fiber membranes for pervaporation

From polysulfone as polymer, integrally skinned hollow fiber membranes with a defect-free top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers of ± 1 m have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent

Selectivity as a function of membrane thickness: gas separation and pervaporation

In this article, the pervaporation selectivity as a function of the membrane thickness is studied for the dehydration of acetic acid. From this study, it appeared that the selectivity of polysulfone (PSF), poly(vinyl chloride) (PVC), and polyacrylonitrile (PAN) decreases with decreasing membrane thickness, below a limiting value of about 15 m. However, in the case of gas separation, the selectivity of PSF membranes is independent of the membrane thickness. This phenomenon could not be explained by a difference in membrane morphology, sorption resistance, thermodynamic interaction, or coupling. It is believed that the decrease in selectivity for thin membranes has to be attributed to defects induced during pervaporation. These defects, crazes (and cracks), result from a reduced value of the critical strain, due to sorption of acetic acid/water and stresses between the polymer chains, due to a concentration gradient across the membrane

Poly(vinyl chloride) polyacrylonitrile composite membranes for the dehydration of acetic acid

Composite membranes have been prepared consisting of a poly(vinyl chloride) (PVC) top layer on either a dense polyacrylonitrile (PAN) layer (bi-layer membrane) or a porous PAN support layer (normal composite membrane) and studied with respect to the dehydration of acetic acid. Especially, the influence of the surface porosity of the porous support layer on the selectivity and flux was studied and it was shown that the lower the surface porosity the higher the selectivity of the composite membrane, especially at high acetic acid concentrations in the feed. From the results it can be concluded that the support material does contribute to the selectivity. Despite the low surface porosity relatively high fluxes could be obtained. Using a feed composition of 80/20 wt.% acetic acid/water at 80°C selectivities of 182¿274 and fluxes of 0.56¿0.74 kg/m2-hr were obtained, and with a feed composition of 98/2 acetic acid/water selectivities of 206¿318 and fluxes of 0.14¿0.15 kg/m2-hr were obtained

“JETZT MUSS ICH NUR NOCH ALT WERDEN“ – RISIKOMANAGEMENT ZUR ALTERSSICHERUNG VON LANDWIRTSCHAFTLICHEN BETRIEBSLEITERN

Der auf einer empirischen Erhebung basierende Beitrag behandelt die Alterssicherung deutscher Landwirte unter den Rahmenbedingungen des landwirtschaftlichen Strukturwandels. Vorsorgebedarf, -fähigkeit und -bereitschaft führen in Abhängigkeit von betrieblichen Merkmalen zu unterschiedlichen Sicherungsstrategien. Diese werden unter besonderer Berücksichtigung der Landwirtschaftlichen Altershilfe auf ihre Auswirkungen auf die soziale Lage hin untersucht und mit den Sicherungsstrategien von Altenteilern verglichen. Die Ergebnisse geben keinen Hinweis auf vorhandene oder zukünftig zu erwartende Altersarmut. Verschiedene Vorsorgeinstrumente ergänzen die Landwirtschaftliche Altershilfe als Teilsicherungssystem, das insgesamt positiv bewertet wird.Political Economy, Risk and Uncertainty, Risiko, Landwirtschaft, Alterssicherung.,

Wetting criteria for the applicability of membrane distillation

Membrane distillation can only be applied on liquid mixtures which do not wet a microporous hydrophobic membrane. Solutions of inorganic material in water have such high values of surface tension (γLgreater-or-equal, slanted72x10−3 N/m) that the non-wetting condition is fulfilled for a number of hydrophobic membranes. As soon as organic solutes are present in the solution, the surface tensionγL will be lowered, and if the concentration of organic material becomes too high, wetting of the membrane will occur. By means of theoretical considerations a critical solute concentration or surface tension at which a homogeneous smooth material will be wetted (gq < 90/deg) can be calculated. For a (micro)porous membranes no such theoretical relation can be derived. Therefore, a simple experimental method is described to measure the maximum allowable concentration for a (micro)porous membrane. On the basis of these measurements, the maximum allowable concentration under process conditions can be determined

The CZCS geolocation algorithms

The Coastal Zone Color Scanner (CZCS) on board the Nimbus 7 satellite was designed to measure surface radiance upwelled from the ocean in 6 spectral bands. The CZCS spectrometer obtains its information from a rotating mirror and is timed to collect data when the mirror views the Earth surface between ca. 40 degrees to the left and right of the subsatellite track. Each scan is divided into 1968 picture elements, pixels, of 0.04 degrees scan each. In order to avoid direct reflected Sun glint, the rotating mirror shaft can be tilted so that scans across the subsatellite track up to 20 degrees forward or aft of the point directed beneath the satellite. The CZCS is the first satellite borne instrument to have this tilted scan capability and therefore poses some new problems in locating the Earth surface position of viewed pixels

Single molecule fluorescence: from physical fascination to biological relevance

Confocal fluorescence microscopy is particularly well-known from the beautiful\ud images that have been obtained with this technique from cells. Several cellular\ud components could be nicely visualized simultaneously by staining them with\ud different fluorophores. Not only for ensemble applications but also in single\ud molecule research confocal fluorescence microscopy became a popular technique.\ud In this thesis the possibilities are shown to study a complicated biological process, which is Nucleotide Excision Repair (NER), on the single molecule level with confocal fluorescence microscopy. In chapter one an introduction is given in single molecule fluorescence, properties of fluorescent labels and immobilization methods. Also the NER process is described and the configuration of the confocal fluorescence microscope used