Nada Miljevic

Separation of protium/deuterium and oxygen-16/oxygen-18 by membrane distillation

Abstract An attempt to explain the significant isotope effect of deuterium and heavy oxygen observed in the MD process was undertaken. A study of the transport mechanism through porous PTFE membranes showed that membrane mass transfer coefficients can be well estimated from the molecular diffusion model or from the combination of Knudsen and molecular diffusion models. the existence of a diffusion isotope effect in membrane distillation enhances the separation factors for H 2 O HDO and H 2 16 O H 2 18 O enrichment. The discussion of the nature of the isotope effect in MD is presented.

Membrane Distillation Employed for Separation of Water Isotopic Compounds

Abstract An attempt to apply membrane distillation (MD) for the enrichment of water isotopic compounds was made. The process was conducted as a direct-contact MD with flat-sheet microporous, hydrophobic polytetrafluoroethylene (PTFE) membranes in the temperature range 323–353K. The distillate condensation was carried out directly into a stream of cooling water. The comparison between calculated Rayleigh distillation curves and the results of permeation experiments demonstrated the MD process to be more efficient than simple distillation for enrichment of the heavy isotopes in water.

INVESTIGATION OF THE SEPARATION FACTOR BETWEEN LIGHT AND HEAVY WATER IN THE LIQUID/VAPOR MEMBRANE PERMEATION PROCESS

Abstract Results of measurements of the separation factor between light and heavy water during membrane permeation are presented. In these experiments the membrane separated the liquid and vapor phases. Measurements were made between 20 and 90°C at downstream pressures (vapor chamber) of 6, 160 and 460 Torr. Two different cellulosic membranes, “Cuprophan 150 M” and “Tomofan I”, were employed. The isotopic composition of hydrogen in the two phases was analyzed by isotope ratio mass spectrometry. The separation factors, α, and their temperature dependences for both membranes are reported.

CASCADES FOR NATURAL WATER ENRICHMENT IN DEUTERIUM AND OXYGEN-18 USING MEMBRANE PERMEATION

Abstract Heavy isotope enrichment of water using a hydrophobic membrane permeation process is described. Simple and ordinary countercurrent cascades will not be of practical interest because of high energy demand. A better solution is to employ a double countercurrent cascade, reutilizing part of the heat of condensation.

Isotope effects in aqueous systems. X. Boiling point elevations for NaCl solutions in H2O and D2O

Solvent isotope effects on the osmotic coefficients of NaCl solutions in H2O or D2O have been determined by an ebulliometric technique at 100°C.