Stofftrennung durch Membranen

Separation by membranes . The paper reviews membrane processes in general, excluding the electro-membrane processes. The authors' aim is to discuss the aspects common to all membrane processes as well as the essential differences between them. The following processes will be examined: Reverse osmosis, ultrafiltration, gas permeation through porous or diffusion type membranes, pervaporation and liquid membrane techniques. In liquid systems, mass transport at the membrane surface proves to be the limiting factor. Conditions on the permeate side tend to influence flux and quality of the permeate only when a considerable pressure drop occurs. A typical example is that of hollow-fiber modules. It is shown how the permeability and dimensions of the membrane require selective adjustment in order to establish maximum flux.     

Spurenanalyse durch Mikrochromatographie

Trace Analysis by Micro-Chromatography Experiments meant for the micro-chromatographic detection of the trace elements zinc, nickel, manganese, cobalt, copper, iron, molybdenum and vanadium led to the following results. Since it was possible to maintain the conditions of chromatography constant, the Rf-values resulting therefrom are such that the separation of a greater number of elements can be accomplished on one chromatogram. Using a procedure of enrichment, extremely small amounts of elements present can be concentrated to enable visual detection or even quantitative estimation. The most suitable solvent mixture consists of acetone/hydrochloric acid/water, whereby a medium level of water content of about 7% is advantageous. The above procedure is also suitable for the detection of trace elements in oils either after ashing or extraction with complex forming agents.     

Polyurethan-dispersionen durch schmelz-dispergierverfahren

Following a survey of polyurethane ionomers, their technical importance, methods of preparation and characteristics, the methods of preparation of aqueous polyurethane dispersions are presented. Dispersion by strong shearing forces and emulsifiers is compared to the spontaneous dispersion of polyurethane ionomers from organic solution or as liquid isocyanate prepolymers. As a new method for the preparation of polyurethane dispersions, the spontaneous dispersion of ionomer melts with following poly-condensation in two-phase systems is described. The principle is that molten ionic modified polyester or polyether prepolymers containing terminal -NCO groups are reacted with urea to give bisbiuret, methylol groups generated by aqueous formaldehyde in a homogeneous phase, and the plasticised melt of methylolised ionic oligourethane bisbiurets so obtained dispersed in water at 50-130 °C. Thereafter, a formaldehyde poly-condensation forming high-molecular polyurethane polybiuret is achieved by lowering the pH of the dispersion. The reaction takes place in the dispersed phase. The procedure yields from the monomers, simply and without complicated apparatus, emulsifier free aqueous dispersions of ionic polyurethanes. The reactions occurring in the process are discussed.     

Kinetik der aeroben Abwasserreinigung durch Abbau von organischen Verbindungen und durch Nitrifikation

Kinetics of aerobic waste water treatment by degrading organic compounds and by nitrification . Both aerobic degradation of organic substances and nitrification can be described by the double substrate kinetics of Monod; dissolved organic material and ammonium or nitrite are the first substrate and oxygen the second one. The determination of the different kinetic coefficients by evaluation of measurements on a laboratory scale is explained first, and known results are then presented and discussed. Finally, it is demonstrated by two examples, viz. the simultaneous oxidation of carbon and nitrogen compounds and oxygen-limited substrate removal, how reaction kinetic models can be used to obtain important information about the characteristics of the bioreactions.