Ethanol dehydration of aqueous

In any process, if one component is enriched at the membrane surface, then mass balance dictates that a second component is depleted at the surface. By convention, concentration polarization effects are described by considering the concentration gradient of the minor component. In Figure 4.3(a), concentration polarization in reverse osmosis is represented by the concentration gradient of salt, the minor component rejected by the membrane. In Figure 4.3(b), which illustrates dehydration of aqueous ethanol solutions by pervaporation, concentration polarization is represented by the concentration gradient of water, the minor component that preferentially permeates the membrane. 

In the case of reverse osmosis, the enrichment factors (E and Ea) are less than 1.0, typically about 0.01, because the membrane rejects salt and permeates water. For other processes, such as dehydration of aqueous ethanol by pervaporation, the enrichment factor for water will be greater than 1.0 because the membrane selectively permeates the water. 

Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation... 

Dehydration of Aqueous Ethanol Using n-Pentane as Entrainer... 

Figure 1. Temperature profile for 50 psia column dehydration of aqueous ethanol using n-pentane...

For the azeotropic dehydration of aqueous ethanol mixtures approaching the constant boiling mixture, a brief comparison is shown for the entrainers, n-pentane, benzene, and diethyl ether. Since water is most non-ideal in n-pentane, the driest ethanol is expected to be produced if n-pentane is used. 

C. Black and D. E. Dilsler. Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation. 

B. Bolto, M. Hoang, Z. Xie, A review of membrane selection for the dehydration of aqueous ethanol by pervaporation, Chem. Eng. Process. Process Intensif. 50 (3) (2011) 227-235. 

C. Black and D. E. Ditsler, Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation, in Extractive and Azeotnqnc Distillation, Chap. I, American Chemical Society Advances in Chemistry NO. 115. Washington, DC, 1972. 

Van Ruymbeke (2) A process for dehydrating 95% aqueous ethanol by countercurrent extraction of the vapor with glycerol. 

S. Kato, K. Nagahama, H. Noritomi and H. Asai, Permeation rates of aqueous alcohol solutions in pervaporation through Nation membrane, J. Membr. Sci., 1992, 72, 31-41 V Freger, E. Korin, J. Wisniak and E. Komgold, Transport mechanism in ion-exchange pervaporation membranes Dehydration of water-ethanol mixture by sodium polyethylene sulphonate membranes, J. Membr. Sci., 1997, 133, 255-267. 

It has been proven that the deactivation of the HZSM-5 zeolite used in the transformation of aqueous ethanol into hydrocarbons in the 350-450 °C range is explained by a similar kinetic scheme to that already established for the transformation of aqueous methanol. The kinetic equation, eq. (13), is applicable to all the steps of the kinetic scheme except to ethanol dehydration, which is not affected by catalyst deactivation. Eq. (13) takes into account the effect of concentration of ethene and of the lump of olefins and gasoline in the reaction medium on the deactivation, although ethene is the main coke precursor on the basis of the values of the kinetic constants. The water present in the reaction medium plays an important... 

Another type of inorganic membranes used to the PV separation is a zeolite membrane. Na-type zeolite membranes have been applied for dehydration of aqueous alcohol. Kita et al. [9] reported that a permeation flux of 3kgm h and separation factor (a) over 10 000 isopropyl alcohol aqueous solution (90wt% isopropyl alcohol), which corresponds to much larger flux and selectivity compared with polymeric membranes (normally a 1000 flux <0.1 kgm h h) On the other hand, a silicalite membrane, which is hydrophobic, preferentially permeates alcohol over water, showing a selectivity of 60 and flux of 0.8kgm h - at 5wt% of ethanol at60°C [8). 

For the separation of toluene/cyclohexane mixtures for a 550-h test, the permeation rate was determined by the aromatic component, and the separation factor reached 15-25 at 40 °C. Owing to the low organic solvent composition in the feed, the fluxes of the organic compounds were relatively small. When the same SLM was used for the dehydrations of aqueous 1-propanol and of aqueous ethanol, water was found to be the preferential permeation component (Wang et al., 2009). 

Membranes becoming more widely available for aqueous—organic separations some successful industrial appHcations reported for dehydrations and removal of alcohols (ethanol and above) from water. 

Cupric chloride or copper(II) chloride [7447-39 ], CUCI2, is usually prepared by dehydration of the dihydrate at 120°C. The anhydrous product is a dehquescent, monoclinic yellow crystal that forms the blue-green orthohombic, bipyramidal dihydrate in moist air. Both products are available commercially. The dihydrate can be prepared by reaction of copper carbonate, hydroxide, or oxide and hydrochloric acid followed by crystallization. The commercial preparation uses a tower packed with copper. An aqueous solution of copper(II) chloride is circulated through the tower and chlorine gas is sparged into the bottom of the tower to effect oxidation of the copper metal. Hydrochloric acid or hydrogen chloride is used to prevent hydrolysis of the copper(II) (11,12). Copper(II) chloride is very soluble in water and soluble in methanol, ethanol, and acetone. 

Volkov (1994) has given a state-of-the-art review on pervaporation. A number of industrial plants exist for dehydration of ethanol-water and (.vwpropanol-water azeotropes, dehydration of ethyl acetate, etc. There is considerable potential in removing dissolved water from benzene by pervaporation. The recovery of dis.solved organics like CH2CI2, CHCI3, CCI4, etc. from aqueous waste streams also lends itself for pervaporation and pilot plants already exist. 

Classical Aldol. Aldol reaction is an important reaction for creating carbon-carbon bonds. The condensation reactions of active methylene compounds such as acetophenone or cyclohexanone with aryl aldehydes under basic or acidic conditions gave good yields of aldols along with the dehydration compounds in water.237 The presence of surfactants led mainly to the dehydration reactions. The most common solvents for aldol reactions are ethanol, aqueous ethanol, and water.238 The two-phase system, aqueous sodium hydroxide-ether, has been found to be excellent for the condensation reactions of reactive aliphatic aldehydes.239... 

For example, the reaction of nitronates (123) with a zinc copper pair in ethanol followed by treatment of the intermediate with aqueous ammonium chloride a to give an equilibrium mixture of ketoximes (124) and their cyclic esters 125. Heating of this mixture b affords pyocoles (126). Successive treatment of nitronates (123) with boron trifluoride etherate and water c affords 1,4-diketones (127). Catalytic hydrogenation of acyl nitronates (123) over platinum dioxide d or 5% rhodium on aluminum oxide e gives a-hydroxypyrrolidines (128) or pyrrolidines 129, respectively. Finally, smooth dehydration of a-hydroxypyrrolidines (128) into pyrrolines (130f) can be performed. 

In comparison, photolysis of 83 in protic solvents such as methanol, ethanol, and water yields 84 as expected, but 84 forms mainly 87 rather than 85. Furthermore, in these solvents, the transient absorption (Amax 425 nm) due to 84 decays not with a second-order rate law but by biexponential decay. For example, the decay of transient absorption of 84 (A ax 420 nm) in water at pH 7 had rate constants of 2 x 10 and 3 x lO s Subsequent to the decay of 84, a transient absorption was formed with Amax 330 nm and a weak absorption band at 740 nm. However, this transient was formed much slower than 84 decayed. The absorption at 330 nm was described as a biexponential growth with rate constants of 584 and 21 s h The authors assigned this absorption to 88. Since 84 and 88 do not form and decay at the same rate, the authors theorized that 84 decays into 87, which then furnishes 88. Even though intermediate 87 does not absorb in the near UV, the authors characterized it with time-resolved IR spectroscopy. The authors demonstrated that, in hexane and a strongly acidic or basic aqueous solution, the photorelease from 83 goes through the formation of 87, whereas in near neutral aqueous solution, formation of 85 predominates. The authors concluded that the dehydration of intermediates 85 and... 

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