COUNTERCURRENT RECYCLE MEMBRANE CASCADES FOR THE SEPARATION OF THE BORON ISOTOPES IN BF3

Recent research has shown that the stable isotopes of boron (B-13, B-11) can be separated by permeation of BF3 gas through modified polymeric and immobilized liquid membranes. Observed separation factors ranged from about alpha* = 1.02-1.09. The present paper investigates membrane cascade requirements to separate the boron isotopes if suitable membranes could be fabricated which exhibit separation factors in the mid-range of those observed, i.e. at alpha* = 1.04-1.07. The calculations show that 95 percent B-10 could be produced using simple, ideal counter-current recycle cascades containing from ca. 100 to 290 stages, depending on alpha* and overall cut. Constant recycle ratio and "squared-off" cascades require fewer stages but have larger area and compressor duty requirements. A properly designed "squared-off" cascade approaches the performance of an ideal cascade and may be a practical alternative to the ideal cascade which would require a different area and compressor size for each stage.