No abstract

No abstract

No abstract

SummaryMembrane 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 ( y,_ 2 72 X lo-" N/m) that the non-wetting condition is fulfilled for a number of hydrophobic membranes. As soon as orgamc solutes are present m the solution, the surface tension ;>I> 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 (0 < 90' ) can be calculated. For (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 phase separation phenomena in ternary solutions of polysulfone (PSI) in mixtures of a solvent and a nonsolvent (N,N-dimethylacetamide (DMAc) and water, in most cases) are investigated. The liquid-liquid demixing gap is determined and it is shown that its location in the ternary phase diagram is mainly determined by the PSf-nonsolvent interaction parameter. The critical point in the PSf/DMAc/water system lies at a high polymer concentration of about 8~o by weight. Calorimetric measurements with very concentrated PSf/DMAc/water solutions (prepared through liquid-liquid demixing, polymer concentration of the polymer-rich phase up to 60%) showed no heat effects in the temperature range of -20°C to 50°C. It is suggested that gelation in PSf systems is completely amorphous. The results are incorporated into a discussion of the formation of polysulfone membranes.