[J. Ferment. Technol., Vol. 65, No. 6, 665-674. 1987] Ethanol Stripping by Pervaporation Using Porous PTFE Membrane RONNIE L. CALIBO, MASATOSHI MATSUMURA, JoJ* TAKAHASHI, a n d HIROSHI KATAOKA Institute of Applied Biochemistry, University of Tsukuba, Sakura-mura, Niihari-gun, Ibaraki 305, Japan In a shell-and-tube type of module containing either porous or nonporous tubular membranes, the sweeping action of a flow of inert gas in the shell side was used to strip ethanol from an aqueous ethanol solution flowing countercurrently in the tube side. A calculation of the overall mass transfer coefficient, Kc, of the membrane used was made for this system. In ethanol stripping tests using a module containing poly- tetrafluoroethylene (PTFE) tubular membranes, the K6 was found to be more affected by the liquid flow rate than the gas flow rate. Moreover, the gas side mass transfer coefficient, kc, was estimated to be about 5× 10 -5 mol/cm2.s.atm. The liquid side mass transfer coefficient, kz, on the other hand, was found to increase linearly with the linear velocity of the aqueous solution. Also, at an average solution temperature range of 21 to 32°C, no significant change in the K c was observed. Comparison of the KG of different tubular membranes revealed that the KG of the PTFE membrane was higher than that of polypropylene or silicone membranes under the given experimental con- ditions. Pervaporation is a separation process which employs a membrane to act as a selective barrier between a liquid mixture containing components to be separated and a gas phase to which the extracted components are trans- mitted. The rather broad meaning of the term pervaporation has come to cover several variant methods of executing the process. Most investigations have used a low vacuum pressure in the gas phase to bring about selective separation.X-4) Yuan et al. 5) and Hwang et al.6) used a sweeping flow of gas to remove the vapor permeate. Aptel et al. 7) proposed the use of temperature difference to create a concentration gradient thereby facilitating vapor separation. Generally, cross membrane evaporation and liquid permeation have come to be categorized under pervaporation.8~ Many types of membranes have already been tested for their possible use in pervapo- ration processes. Kimura and Nomurax) have reported high separation coefficients with the use of a silicone membrane in concen- trating organic substances from aqueous mixtures. Saitoh et al.8) were successful in removing ethanol from a fermentation broth using a poly-(tetrafluoroethylene) (PTFE) membrane. However, as do most other researchers, they used fiat membranes, the vapor-liquid contact area per unit separator volume of which is limited. The problem of the small vapor-liquid contact area per unit equipment volume associated with the use of fiat membranes could be improved by the development of equipment utilizing tubular membranes. Accordingly, Hwang and Thormanr) made a continuous membrane column using several silicone rubber capillary tubings. Each of the stripping and enriching columns had an effective interfacial area per unit volume of about 7 cmZ/cmZ. Moreover, separation to a high degree was achieved without the expense and complexity of a multi-staged cascade.