Pervaporation membrane

Driving force for the rate of separation concentration gradient in the vapor pressure. 

Membrane asymmetric homogeneous or microporous (polyacrylonitrile, cellulose acetate, polyamide, polysuUbne,) composite of a homogeneous polymer film on microporous substructure (cellulose acetate, polyamide, polysulfone, polyimide, polyvinyl alcohol). Usual pore 0.1-0.2 pm. 

1 [tm PVA water methanol ethanol other organics Silicone rubber methanol ethanol aldehydes ketones water paraffins olefins 

Cellulose esters aromatics paraffins olefins paraffins dienes olefins n-paraffins branch low molar mass paraffins high molar mass paraffins. Capacity/unit feed 1.5 kg/s. 

Feed temperature = dose to the normal boiling temperature usually 50-100 °C. Permeate conditions pressure 0.5-2 kPa absolute with condenser temperatures -20 to -t30 °C. 

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Pervaporation has been commercialized for two appHcations. The first and most developed is the separation of water from concentrated alcohol solutions. GFT of Neunkirchen, Germany, the leader in this field, installed their first important plant in 1982. More than 100 plants have been installed by GFT for this appHcation (90). The second appHcation is the separation of small amounts of organic solvents from contaminated water (91). In both of these apphcations, organics are separated from water. This separation is relatively easy, because organic compounds and water, due to their difference in polarity, exhibit distinct membrane permeation properties. The separation is also amenable to membrane pervaporation because the feed solutions are relatively nonaggressive and do not chemically degrade the membrane. 

Membrane Porosity Separation membranes run a gamut of porosity (see Fig. 22-48). Polymeric and metallic gas separation membranes, electrodialysis membranes, pervaporation membranes, and reverse osmosis membranes are nonporous, although there is hnger-ing controversy over the nonporosity of the latter. Porous membranes are used for microfiltration and ultrafiltratiou. Nanofiltration membranes are probably charged porous structures. 

Hubert, Fleming L., Consider Membrane Pervaporation, Chemical Engineeiing Frogress, July 1992, p. 46. 

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

Pervaporation Membranes Pervaporation has a long history, and many materials have found use in pervaporation experiments. Cellulosic-based materials have given way to polyvinyl alcohol and blends of polyvinyl alcohol and acrylics in commercial water-removing membranes. These membranes are typically solution cast (from... 

Many other methods for separating isotopes have been described. A partial list includes membrane and membrane pervaporation, thermal diffusion of liquids, mass diffusion, electrolysis and electro-migration, differential precipitation, solvent extraction, biological microbial enrichment, and more. Although not discussed in... 

Hennepe, H.j.C., Bargeman, D., Mulder, M.H.V., and Smolders, C.A. (1987) Zeolite-filled silicone rubber membranes part 1. membrane pervaporation and pervaporation results. J. Membr. Sd., 35 (1), 39-55. 

M.S.K. Chen, G.S. Markiewicz and K.G. Venugopal, Development of Membrane Pervaporation TRIM Process for Methanol Recovery from CH3OII/MTBE/C4 Mixtures, in Membrane Separations in Chemical Engineering, AIChE Symposium Series Number 272, A.E. Fouda, J.D. Hazlett, T. Matsuura and J. Johnson (eds), AIChE, New York, NY, p. 85 (1989). 

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). 

Membrane pervaporation (permselective evaporation of liquid molecules) is the term used to describe the extraction of volatile organics from an aqueous matrix to a gas phase through a semipermeable membrane. 

Process Descriptions Selectively permeable membranes have an increasingly wide range of uses and configurations as the need for more advanced pollution control systems are required. There are four major types of membrane systems (1) pervaporation (2) reverse osmosis (RO) (3) gas absorption and (4) gas adsorption. Only membrane pervaporation is currently commercialized. 

Membrane Pervaporation Since 1987, membrane pervaporation has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate liquid hydrocarbons to yield a high-... 

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]. 

Shabtai Y, Chaimonitz S, Freeman A, Katchalski KE, Linder C, Nemas M, Perry M, and Kedem O. Continuous ethanol production by immobilized yeast reactor with membrane pervaporation unit. Biotech. Bioengg. 1991 38 869-876. 

Zwijnenberg HJ, Koops GH, and Wessling N. Solar driven membrane pervaporation for desalination processes. J. Memb. Sci. 2005 250 (l-2) 235-246. 

Effect of Polyimide DSDA-TrMPD/ODA/DEB Chemical Composition (the Content of Amine Coreagents), Cross-Linking of Polyimide and Addition of Tetracyanoethylene (TCNE) to the Polymer on the Membrane Pervaporation Properties... 

Yang D, Majumdar S, Kovenklioglu S, and Sirkar KK. Hollow fiber contained liquid membrane pervaporation system for the removal of toxic volatile organics from wastewater. J Mem Sci, 1995 103(3) 195-210. 

Sirkar KK, Yang D, Majumdar S, Kovenklioglu S, and Sengupta A. Hollow fiber-containing liquid membrane pervaporation for removal of volatile organic compounds from aqueous solution. Patent No. US 5637224 Kind A Date 19970610. 

Maier, G. Gas separation with polymer membranes. Angewandte Chemie 1998,37, 2961-2974. Feng, X. Huang, R.Y.M. Liquid separation by membrane pervaporation. Industrial Engineering Chemistry Research, 1997, 36, 1048-1066. Moskvin, L.N. Niskitina, T.G. Membrane methods of substance separation in analytical chemistry. Journal of Analytical Chemistry 2004, 59 (1), 2-16. 

Pervaporation is a membrane process in which a liquid is maintained on the feed side of a membrane and permeate is removed as a vapor on the downstream side of the membrane. Pervaporation is used, because of its low energy consumption and low cost, to separate dissolved organics from water, purify waste water or volatile chemicals, and break azeotropes. Pervaporation plants range from processing a few grams per hour up to thousands of tons per year. For waste water treatment flow of less than 76 L min pervaporation is more cost-effective than other treatment options, such as chemical oxidation, ultraviolet destruction, air stripping followed by carbon adsorption, steam stripping, or distillation/incineration [262]. 

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