Journal of Membrane Science, 1(1976) 333-353 o Elsevler Sclentlfrc Publishing Company, Amsterdam - Printed m The Netherlands
SELECTIVE PERMEATION THROUGH MODIFIED POLYVINYLIDENE FLUORIDE MEMBRANES
and F P McCANDLESS
Dept of Chemwal Engmeenng, (USA) (Received October 1,1976,
Montana State Unrverstty, Bozeman, Montana 59715
m revrsed form March 29.1976)
Several sulfones were tested as modifiers m polyvmyhdene fluoridebased membranes to improve the selectivity with respect to SO, An 18 wt % sulfolene (dhydrothiophene 1,ldroxrde) membrane was found to grve the best separation of SO, at all the conditions of temperature and pressure studled The permeability coefficients for SO, were found to be about four orders of magmtude greater than those for N,, CO, Ar, O,, methane, ethane, ethylene, and 1,3 butadrene, about 3 orders of magnitude greater than for H,, and about two orders of magnitude greater than for CO, In the separation of mixtures of SO, from N, and CO, from H,, best results were obtamed at lower temperatures and at higher values of the partral pressures of SO, and Co, usmg an 18 percent sulfolene membrane A 96 6 vol % SO, permeate was obtained for an exhaust gas SO, concentration of 6.6% m nitrogen with permeate fluxes of about 1 x lo-’ cc (SIP)/ cm’ aec at 0” C and 316 psra upstream pressure The best separatron of CO, from H, gave a permeate cornpositron of 68.0% for an exhaust composrtron of 42.0% with a permeate flux of about 0 9 x lo-’ cc(STP)/cm’ set at 0” C and 733 psla upstream pressure Strong plastrcrzmg effects of the sorbed gases in the membrane were detected which tended to decrease the membrane selectrvlty wrth respect to SO, and CO,.
Introduction and background The permeability coefficient of a vapor or gas 1s considered to be a function of both the solubility and dlffuslvity coefficients. Thus, membrane selectivity can be determmed by the relative solubilitles of the components of a mixture to be separated usmg the film. The solublllty of vapors and gases can be greatly mfluenced by the mcluslon of high solubihty chemicals as plasticizers in relatively impermeable polymers [1,2]. Because of the high solubrlity of SO2 m certam sulfones it seemed reasonable to investigate the effect of different sulfones on the separation of SO? from other gases by permeation. This study was undertaken to optimize the separation of SO2 from nitrogen by mcorporation of a sulfone in a polyvinyhdine fluoride membrane and to determine the permeability
*Present address Yacmuentos
Petrohferos Fiicales Bolivlanos, Cgsrlla 401, La Paz, Bohvla
to different gases. For this system, the permeability coefficients for SO2 and CO2 exhibit a complicated non-linear behavior which probably can be adequately explamed by the solubllity of SO2 and CO2 m the sulfolene. Other gases includmg 02, Hz, CH, , GH,, C&H, and 1,3-butadiene also exhibit an exponential dependence of the permeability coefficient on pressure. This is unhke the behavior of CO, NP and Ar which have permeability coefficients mdependent of pressure. This indicates a strong mteraction between solute gas and the membrane system for all but the latter gases with the non-ideahty being much stronger for SO2 and C02. It would be interestmg to compare the permeation data with data on-the solubllity of the various gases m the solid sulfolene but unfortunately these data are not available. This type of study 1s planned for the future. The permanence of the membrane modification due to sulfolene addition has not been determmed but deterioration with time would be expected, especially with prolonged operation at higher temperatures.
References 1 F P McCandleas, Separation of aromatics and naphthenes by permeation through modified vmylidene fluoride films, Ind. Eng. Chem. Process. Des. Develop., 12 (1973) 364 2 R Seibel and F P McCandleas, Separation of sulphur dioxide and nitrogen by permeation through a sulfolane plaaticlzed vinylidene fluoride film, Ind. Eng. Chem. Process. Dee Develop., 13 (1974) 76 3 R A Klttila, DMF, Dimethylformamide Chenucal Uses. E.1 DuPont de Nemours and Company, Wilmmgton, Delaware, 1967. 4 V M Stannett, R L. Sxwarc, J.A. Rhangara, J.A. Meyer, A W Meyers and C.E Rogers, Permeability of plastic films and coated paper to gases and vapors, Technical Association of the Pulp and Paper Industry, (TAPPI Monograph Series, No. 23), New York, 1962.