Methods of Membrane Preparation

The same base material has been used by Rhone-Poulenc Industries to develop Ion-exchange membranes for desalination (21-25). Their research has concentrated on polymers of moderate D.S. and low molecular weight (a restriction imposed by their technique of sulfonatlon which may cause polymer degradation). While their method of membrane preparation Is not entirely clear, it Is evident that the Rhone-Poulenc membranes possess the desired structural asymmetry. In this form the SPSF membranes have proven to be equal to, and In some ways superior to, CA membranes. 

Membrane technology is presently an established part of several industrial processes. Well known is its relevance in the food industry, in the manufacture of dairy products as well as in the automotive industry for the recovery of electropainting baths. Membranes make possible the water supply for millions of people in the world and care for the survival of the large number of people suffering from kidney disease. The chemical industry is a growing field in the application of membranes, which, however, often requires membrane materials with exceptional stability. The first part of the book will discuss the currently available membranes for different processes, which are suitable for the chemical industry. Information on different methods of membrane preparation will be given. Different materials will be compared, taking into account physical characteristics and chemical stability. 

A second method of membrane preparation is based on the thermally-induced phase... 

PS I-activity TFig. 3) is stable over the period of ten days indicating that the drop in the photosynthetic oxygen evolution (Fig. 2) may result from the impairment of reactions around PS II. Indeed the analysis of PS II-HILL-activity reveals an immediate and complete loss during the first day of N-deprivation (data not shown), but this may be caused by the more drastic method of membrane preparation of N-deprived cells. 

After approximately 10 years of development, PBI chemistries and the concomitant manufacturing processes have evolved to produce commercially available MEAs. PBI MEAs can operate rehably without complex water humidification hardware and are able to run at elevated temperatures of 120-180 C due to the physical and chemical robustness of PBI membranes. These higher temperatures improve the electrode kinetics and conductivity of the MEAs, simplify the water and thermal management of the systems, and significantly increase their tolerance to fuel impurities. Membranes cast by a newly developed PPA Process possessed excellent mechanical properties, higher PA/PBI ratios, and enhanced proton conductivities as compared to previous methods of membrane preparation. 

There are different methods to prepare membranes. The principle underlying the membrane preparation is, however, always the same i.e., it is to control the pore size and the pore size distribution at the surface layer and to decrease the thickness of the surface layer. Several methods of membrane preparation are described in the following section. 

Dense homogeneous membranes were prepared using 2 % PPO (high molecular weight with [t ] = 1.79 dL/g in chloroform at 25 °C) solution in TCE solvent. The method of membrane preparation is the same as described in the part of Effect of Solvent. The solvent was evaporated at 22,4 and -10 °C. 

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