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Distillation Membrane

Another thermally driven membrane process is membrane distillation. Here, a porous membrane separates two liquids which do not wet it. If the liquids differ in temperature, the resulting vapour pressure differencecauses vapour molecules to permeate from the high-temperature (high vapour pressure) side to the low-temperature (low vapour pressure) side. The basic concept of membrane distillation will be described below. [Pg.365]

Membrane distillation is a process in which two liquids or solutions at different temperatures are separated by a porous membrane. The liquids or solutions must not wet the membrane otherwise the pores will be filled immediately as a result of capillary forces. This implies that non-wettable porous hydrophobic membranes must be used in the case of aqueous solutions. A schematic representation of a membrane distillation process is given in figure VI - 48. [Pg.365]

When the phases contain pure water and there is no temperature difference, the system is in equilibrium and no transport occurs. If the temperature of one of the two phases is higher than that of the other, a temperature diflerence exists across the membrane, resulting in a vapour pressure difference. Thus, vapour molecules will transport through the pores of the membrane from the high vapour pressure side to the low vapour pressure side. Such transport occurs in a sequence of three steps  [Pg.365]

Membrane distillation is one of the membrane processes in which the membrane is not directly involved in separation. The only function of the membrane is to act as a barrier between the two phases. Selectivity is completely determined by the vapour-liquid equilibrium involved. This means that the component with the highest partial pressure will show the highest permeation rate. Thus, in the case of an etbanol/water mixture where the membrane is not wetted at low ethanol concentrations, both components will be transported through the membrane but the permeation rate of ethanol will always be relatively higher. With salt solutions, for example NaCl in water, only water has a vapour pressure, i.e. the vapour pressure of NaCl can be neglected, which means that only water will permeate through the membrane and consequently very high selectivities are obtained. [Pg.366]

The transpon of volatile components through the membrane can be described by phenomenological equations in which the flux is proportional to the driving force, i.e. the temperature difference across the membrane. The temperature difference results in a vapour pressure difference (temperature and vapour pressure are related according to the Antoine equation [Pg.366]


Definitions Following the practice presented under Gas-Separation Membranes, distillation notation is used. Literature articles often use mass fraction instead of mole fraction, but the substitution of one to the other is easily made. [Pg.2054]

Hyperfiltration (Reverse Osmosis) is a form of membrane distillation or desalination (desalting) operating with membrane pore sizes of perhaps 1 to 10 Angstrom units. The various individual RO component technologies have improved tremendously over the last 20 to 25 years, and resistance to fouling and permeate output rates have benefited. Nevertheless, all RO plants remain susceptible to the risk of fouling, and adequate pretreatment and operation is essential to minimize this problem. [Pg.360]

Membrane absorption Membrane distillation Adsorptive distillation... [Pg.248]

A number of other desalination processes, such as freezing, membrane distillation, and solar humidification, have been used to desalt saline waters. Based on their commercial success, these processes can be considered as minor desalination processes. [Pg.477]

A variety of desalting technologies has been developed over the last 40 years. Based on their commercial success, they can be classified into major (viz., multistage flash distillation, MSFD multiple-effect distillation, MED vapor compression, VC ED RO) and minor (i.e., freezing, membrane distillation solar humidification) processes. [Pg.305]

The third application area for pervaporation is the separation of organic/organic mixtures. The competitive technology is generally distillation, a well-established and familiar technology. However, a number of azeotropic and close-boiling organic mixtures cannot be efficiently separated by distillation pervaporation can be used to separate these mixtures, often as a combination membrane-distillation process. Lipnizki et al. have recently reviewed the most important applications [53],... [Pg.383]

Liquid-liquid contactor with two miscible liquids (membrane distillation) to remove pure water from a salt solution (31-33)... [Pg.501]

Liquid/Liquid Membrane Contactors (Membrane Distillation)... [Pg.506]

The most important example of liquid/liquid membrane contactors is membrane distillation, shown schematically in Figure 13.13. In this process, a warm, salt-containing solution is maintained on one side of the membrane and a cool pure distillate on the other. The hydrophobic microporous membrane is not wetted by either solution and forms a vapor gap between the two solutions. Because the solutions are at different temperatures, their vapor pressures are different as a result, water vapor flows across the membrane. The water vapor flux is proportional to the vapor pressure difference between the warm feed and the cold permeate. Because of the exponential rise in vapor pressure with temperature, the flux increases dramatically as the temperature difference across the membrane is increased. Dissolved salts in the feed solution decrease the vapor pressure driving force, but this effect is small unless the salt concentration is very high. Some typical results illustrating the dependence of flux on the temperature and vapor pressure difference across a membrane are shown in Figure 13.14. [Pg.506]

Figure 13.13 A schematic illustration of the membrane distillation process showing temperature and water vapor pressure gradients that drive the process... Figure 13.13 A schematic illustration of the membrane distillation process showing temperature and water vapor pressure gradients that drive the process...
Membrane distillation offers a number of advantages over alternative pressure-driven processes such as reverse osmosis. Because the process is driven by temperature gradients, low-grade waste heat can be used and expensive high-pressure pumps are not required. Membrane fluxes are comparable to reverse osmosis fluxes, so membrane areas are not excessive. Finally, the process is still effective with slightly reduced fluxes even for very concentrated solutions. This is an advantage over reverse osmosis, in which the feed solution osmotic pressure places a practical limit on the concentration of a salt in the feed solution to be processed. [Pg.507]

Figure 13.15 Flow scheme and performance data for a membrane distillation process for the production of water from salt solutions [31]. Feed salt solution is heated to 100 °C and passed counter-current to cool distillate that enters at 42 °C. The distillate product is almost salt-free as shown by its low conductivity. The distillate flux is almost constant up to salt concentrations as high as 20 % NaCI. Reprinted from J. Membr. Sci. 39, K. Schneider, W. Holz, R. Wollbeck and S. Ripperger, Membranes and Modules for Transmembrane Distillation, p. 25. Copyright 1988, with permission from Elsevier... Figure 13.15 Flow scheme and performance data for a membrane distillation process for the production of water from salt solutions [31]. Feed salt solution is heated to 100 °C and passed counter-current to cool distillate that enters at 42 °C. The distillate product is almost salt-free as shown by its low conductivity. The distillate flux is almost constant up to salt concentrations as high as 20 % NaCI. Reprinted from J. Membr. Sci. 39, K. Schneider, W. Holz, R. Wollbeck and S. Ripperger, Membranes and Modules for Transmembrane Distillation, p. 25. Copyright 1988, with permission from Elsevier...
In membrane distillation, two liquids (usually two aqueous solutions) held at different temperatures are mechanically separated by a hydrophobic membrane. Vapors are transported via the membrane from the hot solution to the cold one. The most important (potential) applications of membrane distillation are in water desalination and water decontamination (77-79). Other possible fields of application include recovery of alcohols (e.g., ethanol, 2,3-butanediol) from fermentation broths (80), concentration of oil-water emulsions (81), and removal of water from azeotropic mixtures (82). Membrane (pervaporation) units can also be coupled with conventional distillation columns, for instance, in esterifications or in production of olefins, to split the azeotrope (83,84). [Pg.37]

Membrane distillation is considered a promising separation method applicable primarily in environmental technologies. In membrane distillation a microporous and hydrophobic membrane separates aqueous solutions at different temperatures and compositions, as shown in Figure 9. The temperature difference existing across the membrane results in a vapor pressure difference. The molecules are transported through the pores of the membrane from the high-vapor-pressure side to the low-vapor-pressure side. At least one side of the membrane remains in contact with the liquid phase. Benefits offered by membrane distillation include (202) ... [Pg.290]

Membrane distillation systems may be classified into four different categories (203) ... [Pg.291]

Direct contact membrane distillation (DCMD), in which the membrane is in direct contact with the liquid phase on both sides... [Pg.291]

Air-gap membrane distillation (AGMD), in which an air gap is interposed between the membrane and the condensation surface... [Pg.291]

Vacuum membrane distillation (VMD), in which the vapor phase is evacuated from the liquid through the membrane and the condensation takes place in a separate apparatus... [Pg.291]

Sweeping-gas membrane distillation (SGMD), in which a stripping gas, instead of vacuum, is used as a carrier... [Pg.291]

Currently, the most important application area for membrane distillation is water desalination technology. Figure 10 shows one of the water desalination processes developed by a Japanese organization, the Water Re-Use Promotion Center, in cooperation with Takenaka Corporation and Organo Corporation (204). The process uses solar energy and can therefore be installed at locations without an electricity supply. Other application areas for membrane distillation reported in the literature are summarized in Table 8. [Pg.291]

On the other hand, a pervaporation membrane can be coupled with a conventional distillation column, resulting in a hybrid membrane/distillation process (228,229). Some of the investigated applications of such hybrid pervaporation membrane/distillation systems are shown in Table 9. In hybrid pervaporation/ distillation systems, the membrane units can be installed on the overhead vapor of the distillation column, as shown in Figure 13a for the case of propylene/ propane splitting (234), or they can be installed on the feed to the distillation column,... [Pg.292]

Figure 10 Scheme of the demonstration test plant for water desalination using solar energy and membrane distillation. (Courtesy CADDET, Center for Renewable Energy, Harwell, UK). [Pg.293]

In 2002, Drioli and coworkers (304) investigated a process for obtaining protein crystals by means of membrane crystallization, which actually combines membrane distillation and crystallization techniques. The solvent evaporates at the membrane interface, migrates through the pores of the membrane, and condenses on the opposite side of the membrane. The reported preliminary results indicate interesting potentialities of this new method with respect to macromole-cular crystallization. [Pg.303]

CADDET Center for Renewable Energy. A Solar Desalination System Using the Membrane Distillation Process. Technical Brochure No. 46, 2001. [Pg.315]

TNO Environment, Energy and Process Innovation. Memstill Membrane Distillation. Technical information brochure, 2002. [Pg.316]

For serum replacement (6), the latex is confined in a cell with a uniform-pore-size Nuclepore filtration membrane. Distilled, deionized water is pumped through the latex until the conductance of the effluent stream is about the same as that of the distilled, deionized water. This serum replacement removes the adsorbed emulsifier and solute electrolyte quantitatively and allows recovery of the serum in a form suitable for further analysis however, it does not+replace the Na+ and K counterions of the surface groups with Vl ions. To do this, dilute hydrochloric acid (ca. 10 N) is pumped through the latex, followed by distilled, deionized water to remove the excess acid. The latex is then titrated conductometrically to determine the surface charge. [Pg.71]


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