Environmental Engineering Reference
In-Depth Information
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0.8
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
Liquid mole fraction of ethanol (-)
FIGURE 13.8
Measured contents of ethanol in water for liquid at equilibrium with vapor
(data from Beebe et al. (1942)).
water mixtures at atmospheric
pressure leads to an azeotropic mixture of 95.6 vol.% ethanol and 4.6 vol.% water.
Figure 13.8 shows the vapor
As mentioned before, distillation of ethanol
-
liquid equilibrium, indicating that, from a certain
ethanol content in the liquid onward, the vapor that is at equilibrium with the liquid
has the same ethanol content as the liquid, so moving that vapor upward in a distil-
lation column and cooling it to form a liquid do not lead anymore to enrichment.
In the simplest scheme of continuous distillation, the feed stream (containing
8.5 vol.% ethanol) is introduced somewhere near the middle of a distillation column,
after preheating to ~100
C. The aforementioned azeotropic mixture leaves the column
at the top, and water with nonvolatile side products leaves the column at the bottom.
The vapor is largely condensed to liquid at the top and mainly recycled to the column
to improve the degree of purification; by analogy, the liquid at the bottom is largely
reboiled. The bottom temperature is ~115
C (so the pressure exceeds atmospheric
pressure), and the top temperature is ~80
C.
In Brazilian practice, separate columns are used for the top and bottom sections, and
additional equipment is used for recovering volatile side products and remaining heat.
-
13.2.8 Economy
The following economic data have been calculated using standardized methods,
although it is not clear to which extent these are valid for the local situation in Brazil.
The total investment for the project is 95,287,000 $, as derived from the purchase
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