Membrane module pervaporation

Table 9.2 Typical silicone rubber membrane module pervaporation separation factors (VOC removal from water)...

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. 

Tubular loop reactors, 25 710 Tubular membrane modules, 25 821 Tubular pervaporation modules,... 

Figure 4.9 Derivation of the mass transfer coefficient by Wilson s method. Toluene/water enrichments are plotted as a function of feed solution superficial velocity in pervaporation experiments. Enrichments were measured at different feed solution superficial velocities with spiral-wound membrane modules [15]...

In coupled transport and solvent dehydration by pervaporation, concentration polarization effects are generally modest and controllable, with a concentration polarization modulus of 1.5 or less. In reverse osmosis, the Peclet number of 0.3-0.5 was calculated on the basis of typical fluxes of current reverse osmosis membrane modules, which are 30- to 50-gal/ft2 day. Concentration polarization modulus values in this range are between 1.0 and 1.5. 

Both Mitsui [26] and Sulzer [27] have commercialized these membranes for dehydration of alcohols by pervaporation or vapor/vapor permeation. The membranes are made in tubular form. Extraordinarily high selectivities have been reported for these membranes, and their ceramic nature allows operation at high temperatures, so fluxes are high. These advantages are, however, offset by the costs of the membrane modules, currently in excess of US 3000/m2 of membrane. 

A flow scheme for an integrated distillation-pervaporation plant operating on a 5 % ethanol feed from a fermentation mash is shown in Figure 9.10. The distillation column produces an ethanol stream containing 80-90 % ethanol, which is fed to the pervaporation system. To maximize the vapor pressure difference and the pressure ratio across the membrane, the pervaporation module usually... 

The way membranes (in various forms, i.e., cylindrical, coaxial, flat-sheet, spiral-wound, and hollow fiber, etc.) couple with the bioreactor depends on the role the membrane performs. As with catalytic and pervaporation membrane reactors, the simplest configuration consists of two separate but coupled units, one being the bioreactor the other the membrane module. The biocatalyst (e.g., enzymes, bacteria, yeasts, mammalian cells) could, in this case, be suspended in a solution and continuously circulated through the... 

Pervaporation is used to separate water-organic and organic-organic mixtures that form azeotropes and may be difficult to separate by enhanced distillation. Typical membrane modules cost 30/ft of membrane surface area. 

Pervaporation Membrane surface area, A, ft — C, = 30A Membrane module... 

P. J. Hickey and C. H. Gooding, Modeling spiral wound membrane modules for pervaporative removal of volatile organic compounds from water. J. of Membrane Science, 88 (1994) 47-68. 

The criteria to choose between pervaporation or vapor permeation have been discussed in Section 3.2.6. In Fig. 3.10 the principal features of a standalone vapor-permeation plant are shown. The liquid feed stream from a storage tank is completely evaporated the composition of the vapor entering the membrane modules equals that of the feed entering the evaporator. If the feed is an azeotrope the composition of liquid feed, vapor, and evaporator content are identical. 

A novel membrane module design. Top Cross-sectional view of a membrane-coated channel. Bottom Channel flow pattern. High surface-area modules could reduce the relative cost of pervaporation. The short, narrow, non-uniform, multi-path channels that create higher shear ate formed. The turbulence promoting pathways could go a long way to mitigate fouling in ultrafiltration and microfiltration membrane systems. 

Gagne, I., Matsuura, T., Duvnjak, Z. (2002). Enhanced high fructose syrup production by a hybrid fermentation/pervaporation system using a silicone rubber hollow fiber membrane module. Separation Science and Technology, 37, 2055—2075. 

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