Correlation of separation factor versus permeability for polymeric membranes
نویسنده
چکیده
The separation of gases utlhzmg polymenc membranes has emerged mto a commercially utlhzed unit operation It has been recogmzed m the past decade that the separation factor for gas pairs vanes inversely with the permeablhty of the more permeable gas of the speclflc pair An analysis of the literature data for bmary gas mixtures from the hst of He, Hz, 02, Nz, CH4, and COz reveals an upper bound relatlonshlp for these mixtures The upper bound can be represented by a log-log plot of (Y, (separation factor=P,/P,) versus P, (where P,= permeability of the more permeable gas) Above the lmear upper bound on the log-log plot, virtually no values exist The slope of this hne (n) from the relatlonshlp P,=kac can be related to the difference between the gas molecular diameters Ad,, (d, cl,) where the gas molecular diameter chosen IS the LennardJones kmetlc diameter This relatlonshlp yields lmeanty for a plot of -l/n versus Ad,,, and the hne passes through (0,O) for the x-y plot thus provldmg further venficatlon of thus analysis These results indicate that the dlffuslon coefficient governs the separatmg capqblhtles of polymers for these gas pairs As the polymer molecular spacmg becomes tighter the permeablhty decreases due to decreasmg dlffuslon coefficients, but the separation charactenstlcs are enhanced
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