Production of stable isotopes by membrane method

Water enriched with its natural isotopes plays an important role in research and technology. Heavy water (HDO, D2O) is used in nuclear technology and research and the increasing market demand is expected in future if nuclear fusion will be used for energy production. Water enriched in O is used in research and medicine in trace experiments, as is water enriched in O. Recently there appears to be significant market demand for increased production of heavy oxygen (O). Its role is becoming more important as large amounts of heavy oxygen is used for production of F for PET scanning. The method of separation of water isotopomers proposed in the project is thermal evaporation through a porous hydrophobic membrane (membrane distillation). The unit separation factor for the process was determined in experiments carried out with a laboratory apparatus, equipped with PTFE flat sheet membranes. The experiments showed the membrane process is characterized by higher separation factors than distillation of water. Since distillation is now the only commercial method for heavy oxygen production the proposed process has particular importance. In some cases the method can be also applied for a production of heavy water. Preliminary engineering calculations based on cascade theory showed many advantages of membrane permeation. Employing the system of two countercurrent cascades combined in series results in savings in stage number, reflux ratio, and energy demand. The technical and economic evaluation of permeation as compared to other enrichment methods showed the competitiveness of membrane process. The process was experimentally tested with different multistage systems. The method can be applied for a separation of isotopes of hydrogen and oxygen in natural water. It can be used separately or in combination with other separation processes.