Counter-current recycle membrane cascades for the separation of the boron isotopes in BF 3

Abstract

Recent research has shown that the stable isotopes of boron ( 10B, 11B) can be separated by permeation of BF 3 gas through modified polymeric and immobilized liquid membranes. Observed separation factors ranged from about α*=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 α* = 1.04-1.07. The calculations show that 95 percent 10B could be produced using simple, ideal counter-current recycle cascades containing from ca. 100 to 290 stages, depending on α* 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.