2- Butanol-water ternary azeotropes

Table 16.21 Ternary azeotrope of n-butyl acetate, -butanol and water...

The ternary azeotrope of n-butyl acetate, n-butanol and water (Table 16.21), which boils at 91 C, also separates so that little solvent is lost in the water phase. 

Qurishi et al., Ladisch, and Phillips and Humphrey discuss some of the issues concerning the separation of the fermenter products. Doherty and Malone" indicate that a two-column distillation system in conjunction with a decanter can be used to separate the heterogeneous binary n-butanol-water azeotrope. Sticklmair and Faii discuss the separation of the ternary acetone-water-n-butanol system in a two-column system. Pucci et al. suggest that the ternary separation can be achieved in a single column in which a side decanter is used to remove the water. 

All these distillations are conducted in the presence of a polymerization inhibitor (200 ppm of hydroquinone or its monoethyl ether), introduced at the irifiix level, and in moderate bottom temperature conditions (100 to 110°C maximum), and hence under reduced pressure if necessary. The different aqueous phases, especially the water extract of the alcohol, are stripped to recover tbe ternary acrylate/alcohol/watcr azeotrope at the top, which is recycled to the extraction step (case of butanol in particular), and a water/alcohol mixture at the bottom, which may be separated by azeotropic distillation. The molar yield of esterification is 90 to 95 per cent in relation to acryfic arid. 

Water and 1-butanol form a heterogeneous azeotrope and an immiscibility gap over a limited region of ternary compositions exists. The stability of the stationary points of the system and the distillation line map modeled by UNIQUAC are shown on Figure 3a. One distillation boundary, miming from methanol (unstable node) to the binary heteroazeotrope (saddle) divides the composition space in two regions. The system belongs to Serafimov s topological class 1.0-2 (Hilmen, 2002). 

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