Membrane distillation process

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],... 

Figure 13.13 A schematic illustration of the membrane distillation process showing temperature and water vapor pressure gradients that drive the process...

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...

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,... 

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

FIGURE 2.15 (See color insert following page 588.) Membrane contactor for fruit juice concentration using membrane distillation process. 

The main advantages of the membrane distillation process over conventional distillation are the configuration of the evaporation surface can be made into various membrane modules with a compact area density, mist can be eliminated, and highly pure water can be obtained as product corrosion may be less than that with metal surfaces. 

Considering these merits, the fundamental characteristics of the membrane distillation process have been studied, and progressively, articles by various researchers [32,33,36-39,41,43,44] have provided insights into various process aspects. 

Once the pore size and length I are given to the pore network, one can calculate the effective pressure field (by using iteration method), the temperature field through the network, and its effect on the vapor flux through the membrane. This model takes into account all molecular transport mechanisms based on the kinetic gas theory for a single cylindrical tube and could be applied to all forms of membrane distillation process [61]. 

Vaccum membrane distillation, such as any membrane distillation process, is a thermally driven process in which a feed solution is bought into contact with one side of a microporous membrane and a vacuum is created on the opposite side to create a driving force for transmembrane flux (Figure 19.8). The microporous membrane only acts as a support for a vapor-liquid interface, and does not affect the selectivity associated with the vapor-liquid equilibrium [76]. 

Imdakm, A.O. and Matsuura, T.A. Monte Carlo simulation model for membrane distillation processes Direct contact (MD), J. Membr. Sci., 237, 51, 2004. 

Khayet, M., Godino, P., and Mengual, J.L Thermal boundary layers in sweeping gas membrane distillation processes, AIChEJ, 48(7), 1488, 2002. 

Zakrzewska-Trznadel, G., Chmielewski, A.G., and Miljevic, N., Separation of protium/deuterium and oxygen-16/oxygenl8 by membrane distillation process, J. Membr. Sci, 113, 337, 1996. 

Bausa, J. and W. Marquardt, 2000, Shortcut Design Methods for Hybrid Membrane/Distillation Processes for the Separation of Nonideal Multicomponent Mixtures, Ind. Eng. Chem. Res., 39, 1658-1672. 

Bausa, J. and W. Marquardt, Shortcut design methods for hybrid membrane/distillation processes for the separation of nonideal multicomponent mixtures. Industrial and Engineering Chemistry Research, 2000, 39(6) 1658 1672. 

Xu, L., Rungta, M., Brayden, M.K. et al. (2012) Olefins-selective asymmetric carbon molecular sieve hollow fiber membranes for hybrid membrane-distillation processes for olefin/paraffin separations. Journal of Membrane Science, 423 24, 314—323. 

Khayet, M. and Matsuura, T. 2004. Pervaporation and vacnnm membrane distillation processes Modeling and experiments. 50(8) 1697-1712. 

Huorinated polymers have quite different properties compared to their hydrocarbon counterparts, due to the nature of the C-F bond. They often have a particularly high thermal and chemical stability, insolubility in common organic solvents and resistance to swelling by condensable gases or vapours. Such properties are an advantage for those membrane applications where the separation takes place under harsh conditions. Crystalline perfluoropolymers such as Teflon are extremely stable but their crystalline nature makes them mostly suitable for porous membranes, either for filtration of liquid media, or for instance for membrane distillation processes which take advantage of the... 

Teoh M.M., Bonyadi S., Chung T.S. (2008), Investigation of different hollow fiber module designs for flux enhancement in the membrane distillation process, J. Membr. to., 311,371-379. 

Enzymes can convert lignocellulosic biomass into a suitable fermentation feed-stock for biofuel production. Different yeast strains are used for ethanol production, such as S. diastaticus, Candida sp., S. cerevisiae and K. marxianus, as well as different bacteria such as Zymomonas mobilis. The employment of distillation is desirable for food grade purity of applications other than that of biofuel. In fact, batch fermentation was coupled with a membrane distillation process developed with the application of a membrane distillation bioreactor for ethanol production. Meanwhile,... 

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. 

Another class of applications are aqueous solutions containing low concentrations of a volatile component such as occur in mixtures of ethanoi/waier or trichloroethylene/water. Here also a vacuum can be applied instead of water on the permeate side, resulting in a high driving force (p2 => 0). Becau.se the separation is based on a vapour-liquid equilibrium, the permeate is enriched in the volatile component. Although this process is sometimes referred to as pervaporation it is in fact a membrane distillation process. Membrane distillation can have a distinct advantage over distillation, especially for small-scale applications, because of the large surface area per volume as can be found in hoUow fiber and capillary modules. 

Modelling and Simulation of a Combined Membrane/Distillation Process... 

Synthesis and Characterization of a Novel Hydrophobic Membrane Application for Seawater Desalination with Air Gap Membrane Distillation Process... 

The membrane distillation process can be a feasible alternative to treat contaminated ground waters. 

Several works on the treatment of waters containing As, F" and U with membrane distillation process, are presented in the literature. The main results are reported and discussed in the following sections. 

Islam, A.M. (2005) Membrane distillation process for pure water and removal of arsenic. MSc Thesis. Chalmers University of Technology, Gothenburg, Sweden. 

Yarlagadda, S., Gude, VG., Camacho, L.M., Pinappu, S. Deng, S. (2011) Potable water recovery from As, U, and F contaminated ground waters by direct contact membrane distillation process. Journal of Hazardous Materials, 192, 1388-1394. 

In 2008, Feng and co-workers first demonstrated a PVDF ENM could be used in MD to produce drinking water (NaCl concentration < 280 ppm) from a saline water of NaCl concentration of 6 % by using an air-gap membrane distillation process. The flux rate was comparable to those of commercial MF membranes (5-28 kg/m h) at temperature differences ranging from 25 °C to 83 °C [98]. 

Criscuoli, A., DrioU, E., Capuano, A., Memoli, B., and Andreucci, V. E. (2002). Human plasma ultrafiltrate purification by membrane distillation Process optimisation and evaluation of its possible application on-line. Desalination 147, 147. 

Khayet, M., Khulbe, K. C., and Matsuura, T. (2004c). Characterization of membranes for membrane distillation by atomic force microscopy and estimation of their water vapor transfer coefficients in vacuum membrane distillation process. J. Membr. Sci. 238, 199. 

Srisurichan, S., Jiraratananon, R., and Fane, A. G. (2005). Hunfic acid fouling in the membrane distillation process. Desalination 174, 63. 

---