Journal of Membmne Sctence, 1(1976) 271-267 o Elsevler Scientific Publishing Company, Amsterdam - Printed m The Netherlands
APPLICATION OF THE PERVAPORATION PROCESS TO SEPARATE AZEOTROPIC MIXTURES
P. APTEL, N CHALLARD,
J. CUNY and J. NEEL
Ecole Nattonale Supkneure des Industrzes Chrmzques, Znetztut Natzonal Polytechnzque Lormme, I, rue Gmndvdle, 54000 Nancy (France) (Received October 1,1976,
m revised form February 16,1976)
Pervaporatlon through poly(tetrafluoroethylene) films grafted w&h N-vinylpyrrolidone has been successfully used to fractionate positive axeotroprc liquid systems. Selectivlties higher than 10 have often been attamed and daily productions above 100 kg per square meter of membrane can be easily obtained. This procedure can be used for separating water-aprotic solvent, wateticohol and alcohol--alkane constant boiling mixtures. It is shown that a temperature gradient can also be used as the driving force for the transport. By this “thermopervaporation” technique, the condensation of the pervaporate occurs at ambient temperature and an mcrease of the feed temperature leads to an Increase of both selectlvrty and flux.
Introduction and scope Pervaporation is a fractionation process which uses polymeric membranes as separative barriers between the vapor and the liquid phases of a mixture. The mass flux is brought about by mamtaining the downstream side of the membrane at essentially zero vapor pressure. This is done with a vacuum pump or by an mert gas flow. Contrary to other membrane processes, this separation technique requires the vaporization of a part of the liquid charge. It is then necessary to bring mto the system a quantity of energy which is at least equal to the heat of evaporation. It follows that, in general, pervaporation can be of practical use only when the selectivity of the transfer is much higher than for an ordinary vaporization; that is particularly the case for azeotropic mixtures. Neglectmg equipment costs, the evaluation of pervaporation must be made by comparmg the gam in energy due to the higher selectivity with the inherent dxadvantage of the relative slowness of a process which involves transport through a membrane. However, it should be noted that an improvement of the selectivity, at constant flux, both decreases the energy consumption and increases the quantity of hquid charge purified in a given time.
problem of separation of such axeotropic mixtures. It presents several advantages over classical pervaporation. First, only waste heat - z.e. water at a temperature of about 80°C - is required. Secondly, the pervaporate is condensed at ambient temperature with practically no energy consumption. Lastly, as the pervaporate is also a liquid, a continuous multi-stage apparatus can be now more easily designed. References 1 R C. Bmning and R.J. Lee, Separation of azeotroprc mixtures, U.S. Patent 2,963,502 (Sept. 20, 1960). 2 J.W Carter and B. Jagannadhaswamy, Separation of orgamc liqurds by selective permeation through polymeric films, Brrt. Chem. Eng., 9 (1964) 523. 3 V M. Manedova, Z.N. Bagrova, G.P. Bitkova and G.A. Galustjan, Separation of the isopropanol-water azeotrope by permeation through non-porous membrane, Neftepererab. Neftekhim, 10 (1969) 36. 4 M. Fels, Permeation and separation behavior of bmary organic mixtures m polyethylene, AIChE, Symp. Ser., 68 (1972) 49. 5 R.Y. Huang and M. Fels, Separat’ron of organic liquid mixtures by the permeation process wrth graft copolymer membranes, Chem. Eng. Prog., Symp. Ser., 65 (1969) 52. 6 R.Y. Huang and V.J.C. Lin, Separation of liquid mixtures by using polymer membranes. I. Permeation of bmary orgamc hqurd mrxtures through polyethylene, J. Appl. Polym SCI., 12 (1968) 2615 7 M. Kucharskr and J Stelmaszek, Separation of hquid mixtures by permeation, Int. Chem. Eng., 7 (1967) 618. 8 F P. McCandless, Separation of aromatics and naphthenes by permeation through modified vmylidene fluoride films, Ind. Eng. Chem., Prod Res. Develop., 12 (1973) 354. 9 L Cabasso, J. Jagur-Grodzmslu and D. Vofsi, A study of permeation of organic solvents through polymeric membranes based on polymeric alloys of polyphosphonates and acetyl cellulose. II. Separation of benzene, cyclohexene and cyclohexane, J. Appl Polym. Scl., 18 (1974) 2137 10 E. Perry and W.F. Strazrk, Process for the separation of diene from organic mixtures, U.S. Patent 3,789,079 (Jan. 29, 1974). 11 F. Vasse, Contrrbutron B l’htude de l’extractron du 1,3-butad&re des coupes pgtrol&es par pervaporatlon a travers des membranes perm&lectives, Th&e de Doct. Ing , Umv. Paris VI, 1974. 12 C.E. Rogers, M. Fels and N N. LI, Separation by permeation through polymer membranes. In N N. Lr (Ed.), Recent Developments m Separation Science, Vol. II, CRC Ress, Cleveland, Ohro, 1972, p 107. 13 J Kubma and J. Stelmaszek, Apphcation of polymer membranes in separatron of azeotroprc and close boiling mixtures, R. Nauk Inst Inz. Chem. Urzadzen Creplnych Pohtech. Wroclaw., 15 (1973). 14 P. Aptel, J. Cuny, J Jozefowlcz, G. Morel and J. Neel, Liquid transport through membranes prepared by graftmg of polar monomers onto poly(tetrafluoroethylene) films. I. Some fractronatrons of liquid mixtures by pervaporatron, J. Appl. Polym Sci., 16 (1972) 1061. 15 P. Aptel, J. Cuny, J. Jozefowrcz, G. Morel and J. Neel, Liquid transport through membranes prepared by grafting of polar monomers onto poly(tetrafluoroethylene) films. II. Some factors determining pervaporation rate and selectivity, J. Appl. Polym. Sm., 18 (1974) 351.
16 P Aptel, J. Cuny, J. Jozefowmz, G. Morel and J. Neel, Liquid transport through membranes prepared by grafting of polar monomers onto poly(tetrafluoroethylene) fdms. III. Steady-state distribution m membrane durmg pervaporation, J. Appl Polym Sm., 18 (1974) 366. 17 A. Chapuo, A.M. Jendrychowska-Bonamour, G Morel and R. Oppelt, Membranes hydrophiles non lomsables obtenues par le greffage radiochimique de la iv-vinylpyrrobdone dans des films de polyt&mfluoroQhyl8ne, Eur. Polym. J., 9 (1973) 847. 18 P Aptel, J Cuny, J. JozefowIcz, G. Morel and J. Neel, Pervaporation 1 travers des films de polyt6trafluoro&hyl&ne modifies par greffage radlochimique de N-vmylpyrrobdone, Eur. Polym J, 9 (1973) 877. 19 F. Hovorka, R.A. Schaeffer and D. Dreisbach, The system dioxane and water, J Amer Chem Sot., 58 (1936) 2264. 20 I Cabasso, J. Jagur-Grodzmski and D. Vofsi, Polymeric alloys of polyphosphonates and acetyl cellulose I. Sorption and diffusion of benzene and cyclohexane, J. Appl Polym SCI ,18 (1974) 2117. 21 N Challard, Fractionnement des azbtropes par pervaporation, These de SpBciahtt(, Umversit~ de Nancy 1, 1974 22 H S. Frank and W.Y. Wen, Structural aspects of ion-solvent Interaction m aqueous solutions a suggested picture of water structure, Disc. Farad Sot., 24 (1957) 133 23 S. Sourualan, Reverse Osmosis, Logos Press Limited, London, 1970. 24 P Aptel, Pervaporation 1 travers des membranes de polytQrafluoro&hyHne modlf&es par greffage de monom&es polaues, These de Doctorat, Universitd de Nancy 1, 1972. 25 S. Yuan and H G Schwartzberg, Mass transfer resistance m cross membrane evaporation mto an, AIChE, Symp. Ser., 68 (1972) 41 26 P. Aptel, unpubbshed results.