Pervaporation 1,4-dioxane/water

Srinivasa Rao, P., Smitha, B., Sridhar, S., and Krishnaiah, A. (2006) Effect of blending ratio on pervaporative separation of 1,4-dioxane/water mixtures through PVA-PEI membranes. Vacuum, 81, 299-306. 

FIGURE 5.2 Structure of sodium alginate and HEC cross-linked membrane used for pervaporation of water-dioxane and water-THF mixture. (Data from Naidu, V. B. et al., J. Memb. ScL, 260, 131-141, 2005.)... 

Aptel et al. [40] observed a reduction of separation factor as a function of decreasing membrane thickness for grafted polytetrafluoroethylene films using a water/dioxane mixture. They have shown in a different study [41] that transport rate is inversely proportional to thicknes in the pervaporation separation of water through poly(tetra fluoroethylene)-poly(4-vinylpyridine) membranes. 

The different applications of these zeolites in pervaporation include alcohol dehydration water removal in acid solutions organic dehydration separations such as water/ tetrahydrofuran (THF), water/dioxane, or water/dimethyl-formamide (DMF) removal of organics from water and organic/organic separations such as methanol/methyl-tert-butyl ether (MTBE) or p-xylene/o-xylene. In the following subsections, the mechanism of pervaporation in zeolite membranes will be briefly described and we will provide the details about the different applications. 

Efficient enzymatic conversion can be achieved even though most of the reactants are present as solids, provided that there is a liquid phase in which the reaction can occur. This approach has been successfully used for carbohydrate ester synthesis with synthesis of glucose esters of fatty acids between C12 and C18 as typical examples [34]. It is important that the substrates dissolve during the reaction, and often the products precipitate as they are formed, which can be an advantage due to a favourable effect on the equilibrium position. Candida antarctica lipase B is an efficient catalyst in this system and solvents used (in moderate amounts) include ethyl methyl ketone, acetone or dioxane. In order to increase the ester yield, water formed in the reaction can be removed by azeotropic distillation and the solvent (e.g. ethyl metyl ketone) can after condensation be dried by pervaporation, giving a practically useful complete process [35]. 

Performance of sodium alginate membrane and its blend with relatively hydrophilic cellulose derivatives for the separation of water-dioxane mixtures and water-tetrahydrofuran (THF) mixtures have been studied (Naidu et al. 2005) (Figure 5.2). It has been observed that there was a remarkable improvement in pervaporation... 

Naidu, V. B., Rao, K. S. V. K., and Aminabhavi, T. M. 2005. Pervaporation separation of water -I- 1,4-dioxane and water -I- tetrahydrofuran mixtures using sodium alginate and its blend membranes with hydroxyethylcellulose—A comparative study. J. Memb. Sci. 260 131-141. 

Patil, M. B., Veerapur, R. S., Bhat, S. D., Madhnsoodana, C. D., and Aminabhavi, T. M. 2009. Hybrid composite membranes of sodium alginate for pervaporation dehydration of 1,4-dioxane and tetrahydrofuran. Desalination Water Treat. 3 11-20. 

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