Dehydration of organics

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

Pervaporation is a relatively new process with elements in common with reverse osmosis and gas separation. In pervaporation, a liquid mixture contacts one side of a membrane, and the permeate is removed as a vapor from the other. Currendy, the only industrial application of pervaporation is the dehydration of organic solvents, in particular, the dehydration of 90—95% ethanol solutions, a difficult separation problem because an ethanol—water azeotrope forms at 95% ethanol. However, pervaporation processes are also being developed for the removal of dissolved organics from water and the separation of organic solvent mixtures. These applications are likely to become commercial after the year 2000. 

Dehydration of organics (removal of <1% water) generally feasible by molecular sieving, if kinetic diameter of organic >300 pm. 

For the acid-base catalyzed hydration and dehydration of organic bases, such as pteridine, the equations for and k are ... 

Membranes can also be used to alter the vapor-liquid equilibrium behavior and allow separation of azeotropes. The liquid mixture is fed to one side of the membrane, and the permeate is held under conditions to maintain it in the vapor phase. Most separations use hydrophyllic membranes that preferentially pass water rather than organic material. Thus, pervaporation is commonly used for the dehydration of organic components. 

Pervaporation (PV) partial vapor pressure difference separation of isomers dehydration of organic liquids... 

Pervaporation has become one of the standard membrane technologies with a large number of realized industrial applications. Pervaporation is used for the dehydration of organic compounds, the separation of organic compounds from aqueous solu-... 

Hydrophilic membranes with a preferential permeation of water are mainly used for the dehydration of organic solvents with an emphasis on azeotropic mixtures. Membranes for the removal of small alcohol molecules like methanol and ethanol are also of a hydrophilic nature. 

Hydrophilic polymers are used as selective barriers for dehydration of organic liquids via PV. The selective layer is typically from a glassy polymer chemically... 

Electric endosmose is of technical importance for the dehydration of organic, finely suspended substances containing1 very much water, for example, the drying of peat, according,... 

Dehydration of organics and organic removal from aqueous streams... 

Asada T. Dehydration of organic solvents. Some acmal results of pervaporation plants in Japan. In Backish R. ed.. Proceedings of the Third International Conference on Pervaporation Processes in Chemical Industry. Nancy, France, September 1988 Englewood, NJ Bakish Materials Corporation, 1988 379-386. 

Burshe MC, Netke SA, Sawant SB, Joshi JB, and Pangarkar VG. Pervaporative dehydration of organic solvents. Sep. Sci. Tech. 1997 32(8) 1335-1349. 

Pervaporation and vapor permeation are typical membrane processes with high application potential in chemical industry due to their high efficiency in the separation or the dehydration of organic solvents. Developed initially with organo-polymeric... 

Abstract Two types of membrane are presented free-standing films which are formed from aqueous polyelectrolyte solutions and membranes prepared by alternating electrostatic layer-by-layer assembly of cationic and anionic polyelectrolytes on porous supports. Layer-by-layer assemblies represent versatile membranes suitable for dehydration of organic solvents and ion separation in aqueous solution. The results show that the structuring of the polyelectrolytes in the liquid films and the permeability of the multilayer membranes depends on different internal and environmental parameters, for example molecular weight, polymer charge density, ionic strength, and temperature. 

According to a recent conference given by Prof. Kita [162], the classical synthesis method currently used by Mitsui allows to produce about 250 zeolite membranes per day. Both the LTA and T types (Na K) membranes are now commercial and more than 80 pervaporation and vapor permeation plants are operating in Japan for the dehydration of organic liquids [163]. A typical pervaporation system, similar to the one described in [8], is shown in Fig. 11. One of the most recent applications concerns the production of fuel ethanol from cellulosic biomass by a vapour permeation/ pervaporation combined process. The required heat is only 1 200 kcal per liter of product, i.e. half of that of the classical process. Mitsui has recently installed a bio-ethanol pilot plant based on tubular LTA membranes in Brazil (3 000 liters/day) and a plant with 30 000 liters/day has been erected in India. The operating temperature is 130 °C, the feed is 93 % ethanol, the permeate is water and the membrane selectivity is 10 000. 

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