Study On The Xenon Enrichment And Gaseous Impurities Removal By Using Polyimide Hollow Fiber Membranes

Radioxenon isotopes monitoring is one of the most important technical means for the On-Site Inspection?OSI?of the Comprehensive Nuclear Test Ban Treaty?CTBT?verification regime.In order to measure environmental xenon,concentrating xenon from large volume air sample is necessary due to its extremely low background concentration.To enrich environmental xenon,hollow fiber membranes were used for gas sample pretreatment to remove the great deal of impurities such as nitrogen,oxygen,carbon dioxide,vapor,etc.An experimental apparatus was developed and analysis methods of each component were established for researching on the performance of impurities removal and xenon enrichment.The effect of temperature,flow rate,stage cut,membranes amount,connective form and gas origin was studied respectively.The results show that the xenon loss rates was minimal when three or four membranes were connected in series.When the stage cut was fixed,the gas flowrate and environmental temperature were hardly influence the performance of membranes.The xenon loss rates of the samples from surface air was a litter higher than that ones from subsurface.The pressure in fibres decreased as the temperature of membranes increased because gas were easy to permeate the walls of fibres.The permeation rates of gas components were not homogeneous along the lognitudinal length of the fibres.High permeable components passed through the walls of the fibers preferentially.On the contrary,low permeable components passed through the walls of the fibers lag behind high permeable components.The polyimide hollow fiber membranes had a positive effect on radon removal.The removal rates of xenon were minimum in this paper,and the permeation rates of these components are as follows: CO₂>H₂O>O₂>Ar>Kr>CH₄>Xe,which is fitted to the reference literatures.Stage cut was the most important factor for the separation performance of hollow fiber membranes.When the stage cut was getting greater,the impurities were removed more thoroughly,and the loss rates of xenon were increasing.When the stage cut was 0.67,the concentrating ratios of xenon were 2.78 in subsurface air and 2.72 in surface air,the xenon loss rates was no more than 10%,and the removal rates of O₂,H₂O and CO₂ were no less than 90%,99% and 99%,respectively.In actual practice,just ensure that the product gas flowrate being 1/ 3 of the feed gas flowrate consistently.In the future,a further research should be done for cascading style of membrane modules and selection of membrane materials.