Liquid membrane pervaporation

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. 

See also Arsenic. Flow Injection Analysis Environmental and Agricultural Applications. Membrane Techniques Dialysis and Reverse Osmosis Ultrafiltration Liquid Membranes Pervaporation. Selenium. Sulfur. 

Dialysis and Reverse Osmosis Ultrafiltration Liquid Membranes Pervaporation... 

Key words wastewater, membrane operations, supported liquid membranes, pervaporation, membrane bioreactors, complexation... 

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). 

An survey of recent developments in membrane processes, involving reverse osmosis (RO), ultrafiltration (UF), microfiltration (MF), electrodialysis (ED), dialysis (D), pervaporation (Pr), gas permeation (GP), and emulsion liquid membrane (ELM), has been provided by Sirkar (1997). 

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. 

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... 

Figure 19.3 schematically describes in more detail the transport phenomena occurring during pervaporation. First, solutes partition into the membrane material according to the thermodynamic equilibrium at the liquid-membrane interface (Fig. 19.3a), followed by diffusion across the membrane material owing to the concentration gradient (Fig. 19.3b). A vacuum or carrier gas stream promotes then continuous desorption of the molecules reaching the permeate side of the membrane (Fig. 19.3c), maintaining in this way a concentration gradient across the membrane and hence a continuous transmembrane flux of compounds.

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). 

Separation of products from the reaction mixture In situ product removal from enzymatic reactor via a nanofiltration or ultrafiltration membrane Removal of selected enantiomer via a liquid membrane Removal of water in esterification reactions via a pervaporation membrane... 

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. 

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-... 

Wodzki R and Szczepanski P. Integrated hybrid liquid membrane systems—membrane extraction and pertraction coupled to a pervaporation process. J Mem Sci, 2002 197(1-2) 297-308. 

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. 

Figure 5.9 Scheme of the MHS[FLM-PV] multimembrane hybrid system (1) cation-exchange membranes, (2) flowing liquid membrane, (5) vacuum system, (6) pervapora-tion unit, (7) pervaporation membranes, (8) contactor, (9) feed solution, and (10) stripping solution. From Ref. [29] with permission. 

MHS with pervaporation of water from LM (MHS-PV) is presented in Fig. 5.9. Contrary to the simple MHS with an agitated bulk liquid membrane, separated from the feed and strip solutions by flat hydrophobic or hydrophilic or ion-exchange membranes, the MHS-PV system exploits a Hquid membrane continuously flowing between the two flat cation-exchange and two pervaporation membranes. To couple the separation and pervaporation processes, the LM is simultaneously pumped through the MHS and PV modules. The pervaporation membranes are placed on stainless steel porous supports. Aqueous feed and strip solutions are intensively agitated. 

IzakP, Kbckerhng M, KraglU(2006) Solute transport from aqueous mixture through supported ionic liquid membrane by pervaporation. Desalination 199 96-98... 

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]. 

Groot et al [3.86] investigated the technical feasibility of five reactive separation technologies (fermentation coupled to stripping, adsorption, liquid-liquid extraction, pervaporation, and membrane solvent extraction). They concluded that liquid-liquid extraction and pervaporation reactive separation processes show the greatest potential, with PVMBR systems particularly attractive due to their operational simplicity. Membranes utilized include silicone [3.76, 3.77, 3.74, 3.87, 3.75, 3.85, 3.88], supported liquid membrane systems [3.87, 3.89], polypropylene [3.70], and silicalite filled PDMS membranes [3.90, 3.91]. The results with PVMBR systems have been very promising. 

Membranes for Liquid-Liquid Extraction Pervaporation Reverse Osmosis Symbols Problems References... 

Pervaporation is a special case of gas separations in that it is a concentration driven process. The feed mixture is supplied as a liquid to the membrane and the permeate is recovered as a vapor on the low pressure side of the membrane. Pervaporation finds application in dehydration as well as the separation of a variety of liquid mixtures. A discussion of pervaporation is beyond the scope of this review. 

Recently much attention has been paid to ceramic membranes exhibiting a nanoporous structure with the aim of new membrane processes for the nanofiltration of liquids [26], pervaporation [27], gas separation [27,28], or catalysis... 

Other interactions in a membrane internal nanospace. The first is evaporation through a nonporous membrane (pervaporation). Interaction of separating components with a polymer in a membrane internal nanospace, in some cases, moves liquid-vapor equilibrium and removes azeotropic points. 

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