Pervaporation ethanol/water mixture

Fig. 42. Integrated distillation/pervaporation plant for ethanol recovery from fermentors. The distillation columns concentrate the ethanol—water mixture from 5 to 80%. The pervaporation membrane produces a 99.5% ethanol product stream and a 40—50% ethanol stream that is sent back to the distillation...

Pervaporation. Pervaporation differs from the other membrane processes described so far in that the phase-state on one side of the membrane is different from that on the other side. The term pervaporation is a combination of the words permselective and evaporation. The feed to the membrane module is a mixture (e.g. ethanol-water mixture) at a pressure high enough to maintain it in the liquid phase. The liquid mixture is contacted with a dense membrane. The other side of the membrane is maintained at a pressure at or below the dew point of the permeate, thus maintaining it in the vapor phase. The permeate side is often held under vacuum conditions. Pervaporation is potentially useful when separating mixtures that form azeotropes (e.g. ethanol-water mixture). One of the ways to change the vapor-liquid equilibrium to overcome azeotropic behavior is to place a membrane between the vapor and liquid phases. Temperatures are restricted to below 100°C, and as with other liquid membrane processes, feed pretreatment and membrane cleaning are necessary. 

The catalytic esterification of ethanol and acetic acid to ethyl acetate and water has been taken as a representative example to emphasize the potential advantages of the application of membrane technology compared with conventional distillation [48], see Fig. 13.6. From the McCabe-Thiele diagram for the separation of ethanol-water mixtures it follows that pervaporation can reach high water selectivities at the azeotropic point in contrast to the distillation process. Considering the economic evaluation of membrane-assisted esterifications compared with the conventional distillation technique, a decrease of 75% in energy input and 50% lower investment and operation costs can be calculated. The characteristics of the membrane and the module design mainly determine the investment costs of membrane processes, whereas the operational costs are influenced by the hfetime of the membranes. 

Y.F. Xu, R.Y.M. Huang, Pervaporation separation of ethanol-water mixtures using ionically crosslinked blended poly(acrylic acid) (PAA)-nylon 6 membranes, J. Appl. Polym. Sci. 36 (1988) 1121— 1128. 

R.Y. Huang, C.K. Yeom, Pervaporation separation of aqueous mixtures using crosslinked poly(vinyl alcohol) (PVA). Part II. Permeation of ethanol-water mixtures, J. Membr. Sci. 51 (1990) 273-292. 

Y.M. Sun, T.L. Huang, Pervaporation of ethanol-water mixtures through temperature sensitive poly(vinyl alcohol-g-u-isopropyacrylamide) membranes, J. Membr. Sci. 110 (1996) 211-218. 

Figure 9.9 Comparison of separation of ethanol/water mixtures by distillation and by three pervaporation membranes cellulose triacetate (CTA), an anionic polyelectrolyte membrane, and GFT s poly(vinyl alcohol) (PVA) membrane [40]...

FIG. 22-23 Comparison of two types of pervaporation membranes to distillation of ethanol-water mixtures. (SOURCE Redrawn from Ref. 24.)... 

Alginate hydrogel membranes, crosslinked with EIX2, can be used in the pervaporation separation of ethanol-water mixtures. ... 

The mass flow is effected by keeping the downstream side of the membrane at reduced pressure. The performance of membranes for the pervaporation of ethanol-water mixtures is evaluated by the separation factor a H and the specific permeation rate R. is defined as follows ... 

Another application of substituted polyacetylenes is in the pervaporation of the ethanol-water mixture. Pervaporation is a method for separating liquid mixtures by evacuating the downstream side of the separation membrane (29). The performance of a membrane is evaluated by the separation factor (a) and the specific permeation rate (R). 

Sano T., Yangishita H., Kiyozumi K., Mizukami F. and Haraya K., Separation of ethanol-water mixture by silicalite membrane on pervaporation, 7. Membr. ScL 95 221 (1994). 

A good example of separation on the basis of affinity is the separation of alcohol/ water mixtures using a hydrophobic, silicalite membrane. Pervaporation of an ethanol/ water mixture through such a membrane resulted the removal of the alcohol from the mixture [16]. The separation selectivities achieved are between 10 and 60, depending on temperature and the alcohol content in the feed. In this way azeotropes can be broken. The reason for this is that the principle of separation, namely, differences in adsorptive behavior, is different from separation based on vapor pressure differences, used in distillation. Another example of such a separation is the pervaporation of an acetic acid/water mixture through a silicalite membrane, resulting in the removal of acetic acid [17]. 

Lee KH, Kim HK, and Rhim JW. Pervaporation separation of binary organic-aqueous Uquids mixtures using crosslinked PVA membranes III ethanol-water mixture. J. App. Poly. Sci. 1995 58(10) 1707-1712. 

Takegami S, Tujii S, and Yamada H. Pervaporation of ethanol-water mixtures using novel hydrophobic membranes containing polydimethylsiloxane. Jpn. J. Poly. Sci. Tech. 1992 49(12) 981-991. 

Permeate compositions for pervaporation of ethanol-water mixtures. Example 26.3... 

Pervaporation is a method of separating liquid mixtures, especially ethanol-water mixtures, withtheuseofapolymermembrane. Poly(TMSP)membranehasprovedhighlypermselective for ethanol in the ethanol-water pervaporation. Thus, the separation factor, a(EtOH/ H2O), reaches 17 at 10 wt% ethanol in the feed. This value is similar to that for poly(dimethylsiloxane), a well-known ethanol-permselective membrane. In contrast, other substituted poly acetylenes are nonpermselective or rather water-permselective. On the basis of its excellent adsorptivity for organic compounds, poly(TMSP) has been applied to a regenerate column packing which removes trace organic solvents from water ". ... 

Combinations of distillation and pervaporation (membrane separation with a vapor permeate stream) have been applied to many separation problems. One example is the separation of ethanol-water mixtures. Ethanol and water form an azeotrope and therefore conventional distillation is not feasible. Using a combination including pervaporation, pure ethanol and water can be obtained as can be seen from Fig. 3.2-10. Water can be obtained from the bottom of the distillation column. The distillate stream consists of the azeotropic mixture which is fed into the pervaporation unit The highly selective polyvinyl alcohol membrane is capable of separating water from ethanol. Pure ethanol can be obtained from the retentate, and the permeate stream, which consists of ethanol and water, is recycled into the distillation column. 

Sano. T. Yanagishita, H. Kiyozumi, U. Mizukami. F. Separation of ethanol/water mixture by siiicalite membrane on pervaporation. J. Mernbr. Sci. 1994, 95. 221-228. 

A study of the pervaporation separation of ethanol/water mixtures by polydimethylsiloxane (PDMS) membranes filled with phosphazene nanotubes showed selectivity favoring water over ethanol, which corresponds to the behavior of the host polymer. The nanotubes were reported to increase permeation flux and selectivity. This conclusion was further supported by the use of a TFE/phenoxy/2-allylphenoxy phosphazene host in place of PDMS. Phosphazenes also can be used as a cross-linker for traditional organic polymers to impart greater performance in the separation of water and ethanol. In this work, poly(vinyl alcohol) membranes were cross-linked with cyclotriphosphazene substituted with 4-hydroxybenzaldehyde... 

Mulder MHV, Smolders CA. 1984. The mechanism of separation of ethanol/water mixture by pervaporation. I. Calculation of concentration profiles. J. Membr. Sci. 17 289-307. 

Sano T, Yanagishita H, Kiyozumi Y, Mizukami F, Haraya K. Separation of ethanol-water mixture by siheahte membrane on pervaporation. J Membr Sci 1994 95 221-228. 

The pervaporation dehydration study of isopropanol-water and ethanol-water mixtures was carried out by Moon et al. [90]. The two-ply dense composite membranes were prepared using successive castings of sodium alginate and CS solutions. The membranes showed improved mechanical strength, flux, and separation factor. The three factors like polymer type contacting the feed stream, NaOH treatment, and type of cross-linking agent decide the flux and separation factor of the two-ply membrane system. 

Pandey and Shahi [98] prepared functionalized silica (sodium 2-formylbenzenesulfonatepolysiloxane [SBAPTS])-NSBC (modified CS derivative A,0-sulfonic acid benzyl CS, Figure 16.16) hybrid membranes by sol-gel technique followed by cross-linking using formaldehyde for pervaporation separation of water/ethanol azeotrope. The prepared hybrid membrane was assessed to be very suitable for the separation of water from azeotrope of water-ethanol with 5282 selectivity and 0.59 L/m h total flux at 30°C in ethanol/ water mixture (90 wt.%). 

Chen, W.J., Aranda, P. and Martin, C.R. 1995. Pervaporation separation of ethanol/water mixtures by polystyrenesulfonate/alnmina composite membranes. 107 ... 

Claes, S., Vandezande, R, Mullens, S. et al. 2010. High flux composite PTMSP-silica nanohybrid membranes for the pervaporation of ethanol/water mixtures, 351 ... 

Li, G., Zhang, W., Yang, J. and Wang, X. 2007. Time-dependence of pervaporation performance for the separation of ethanol/water mixtures through poly(vinyl alcohol) membrane. 306(2) 337-344. 

Neidlinger, H.H., Schissel, P.O. and Orth, R.A. 1987. Pervaporation separation of ethanol-water mixtures using polyethylenimine composite membranes. US 06/746592. 

Pera-Titus, M., Fite, C., Sabastian, V., Lorente, F., Llorens, J. and Cunill, F. 2008. Modeling pervaporation of ethanol/water mixtures within real zeolite NaA membranes, fnd. Ene. Chem. Res. 47(9) 3213-3224. 

Zhan, X., Li, J.D., Chen, J. and Huang, J.Q. 2009a. Pervaporation of ethanol/water mixtures with high flux by zeolite-filled PDMS/PVDF composite membranes. 

E2. We wish to use pervaporation to increase the ethanol concentration in an ethanol water mixture to 98.5 wt %. The feed from the distillation column to the pervaporation unit is 90 wt % ethanol. 

Uragami, T. and Takigawa, K. 1990. Permeation and separation characteristics of ethanol-water mixtures through chitosan derivative membranes by pervaporation and evapomeation. Polymer 31 668-672. 

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