Azeotropic ethanol

Fig. 9. Extractive distillation sequence cost as a function of the feed ratio for the production of anhydrous ethanol from azeotropic ethanol using ethylene glvcol at reflux ratios of A, 1.15 r O, 1.2 r and 1.3 r (39). Point A represents a previously pubhshed design for the same mixture (37).

The potential of ILs in fhe field of exfracfive distillation was shown in Refs 126 and 146 for the separation of THF-wafer and ethanol-water azeotropes using [C2Qlm][BFJ. This IL easily breaks the azeotropic ethanol-water phase behavior by interacting selectively with water. 

Fig. 9.—Chromatography on Fuller s Earth Clay of a Fraction from Cuban, Blackstrap Molasses. [The Developer was Azeotropic Ethanol from X to Y, and Etha-nol/Water (90/10) from Y to Z.]...

Go back to the temperature-mole fraction diagram for the isopropyl alcohol-isobutyl alcohol system (Fig. 175). The composition of the vapor is always different from that of the liquid, and we can separate the two compounds. If the composition of the vapor is the same as that of the liquid, that separation is hopeless. Since we ve used the notions of an ideal gas in deriving our equations for the liquid and vapor compositions (Clausius-Clapeyron, Dalton, and Raoult), this azeotropic behavior is said to result from deviation from ideality, specifically deviations from Raoult s law. Although you might invoke certain interactive forces in explaining nonideal behavior, you cannot predict azeotrope formation a priori. Very similar materials form azeotropes (ethanol-water). Very different materials form azeotropes (toluene-water). And they can be either minimum-boiling azeotropes or maximum-boiling azeotropes. 

Another advantage of ETBE is that it can be made from renewable ethanol. This would in turn reduce the dependence on oil imports and create additional markets for agricultural wastes and biomass. The possibility of utilization of azeotropic ethanol (96.5 wt%) or subazeotropic ethanol (80-85 wt%) could increase further the availability, and reduce the cost of ethanol for ETBE production. To sum the advantages of ETBE production ... 

Let s examine the case of breaking the azeotrope ethanol/water with ethylene glycol. The flowsheet was given in Fig. 7.28. The RCM plot is given in Fig. 9.13-left. It can be observed that both products are saddles, which is typical for extractive distillation. 

A convincing application of two columns sequence is the split of the azeotrope ethanol (A) / water (B) with tetrahydrofurane (C), as proposed by Stichlmair (1999). Figure 9.19 depicts qualitatively the split sequencing. The entrainer is a low-boiler forming a minimum azeotrope with water (az nbp 64.2 C) below the boiling point of the original water-ethanol azeotrope (azj, nbp 78.2 °C). There is also an azeotrope tetrahydroftirane-ethanol (az, nbp 65.9 C), but this is not essential. Water and ethanol,... 

The azeotrope ethanol/water can be broken by azeotropic distillation with benzene. Examine by simulation the feasibility of a two-column alternative. Study the influence of different design elements on the achievable purity. 

The ethanol column (C-1) has practically only stripping zone. Fig. 9.31-left shows composition profile both for liquid and vapour phase. The examination of the composition profiles highlights the role of the entrainer. In the zone close to the top the benzene extracts the ethanol in the liquid phase, and as a result increases the volatility of water, so that on lower stages the water is completely removed. In the lower part practically only the binary ethanol/benzene remains. The distillation trajectory starts from the ternary azeotrope, goes along the ethanol/ benzene saddle and terminates in the ethanol vertex. Because the boiling point of the azeotrope ethanol-water is close to the pure ethanol, the profile could easily jump to the ethanol/water azeotrope. Consequently, the design and operation of the column (C-1) is very sensitive. 

Xylans are partially extractable with water from natural cell walls but typically are removed by alkaline solution extraction. To minimize contamination by lignin, the plant or woody material is usually treated with azeotropic ethanol-benzene and the lignin removed by its conversion to halocellulose. The alkaline extract can be neutralized, precipitating the more linear, less acidic xylans. The more acidic, more branched xylan is recovered as a precipitate after addition of ethanol. 

Anhydrous ethanol means an ethyl alcohol that has a purity of >99%, exclusive of added denaturants, meeting the requirements of ASTM D4806. Hydrous (or wet, also sometimes known as azeotropic) ethanol is the most concentrated grade of ethanol that can be produced by simple distillation, without the further dehydration step necessary to produce anhydrous (or dry) ethanol. 

Sections 8.3 and 8.4 Physical Constants of Liquids Fractional Distillation, Azeotropes Ethanol and Fermentation Chemistry... 

The relationship (6.3.182) between the separation factor Uij for the pervaporation process and the separation factors a and a . for the hypothetical thermodynamically equivalent process for Figure 6.3.30(b) can be conceptually illustrated via Figure 6.3.31(a). This figure is based on a similar one from Wijmans and Baker (1993) showing vapor-Uquid equilibrium of the azeotropic ethanol-water system at 60 °C. The plot illustrates total permeate pressure vs. alcohol concentration in the liquid phase (both feed liquid and permeate vapor). Feed liquid having molar concentrations of Cif and Cjf (mole fractions are in equi-... 

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