Introduction To Extractive Distillation

Multistage distillation under continuous, steady-state operating conditions is widely used in practice to separate a variety of mixtures. Table 13-7, taken from the study of Mix, Dweck, Weinberg, and Armstrong [Am. Inst. Chem. Eng. J. Symp. Ser. 76, 192, 10 (1980)] lists key components for 27 industrial distillation processes. The design of multiequi-librium-stage columns can be accomplished by graphical techniques when the feed mixture contains only two components. The x-y diagram

[McCabe and Thiele, Ind. Eng. Chem., 17, 605 (1925)] utilizes only equilibrium and mole-balance relationships but approaches rigorous-ness only for those systems in which energy effects on vapor and liquid rates leaving the stages are negligible. The enthalpy-concentration diagram [Ponchon, Tech. Mod., 13, 20, 55 (1921); and Savarit, Arts Metiers, 65,142, 178, 241, 266, 307 (1922)] utilizes the energy balance also and is rigorous when enough calorimetric data are available to construct the diagram without assumptions.

TABLE 13-7 Key Components for Distillation Processes of Industrial Importance

Key components

Typical number of trays

Hydrocarbon systems Ethylene-ethane Propylene-propane Propyne-1-3-butadiene 1-3 Butadiene-vinyl acetylene Benzene-toluene Benzene-ethyl benzene Benzene-diethyl benzene Toluene-ethyl benzene Toluene-xylenes Ethyl benzene-styrene o-Xylene-m-xylene

Organic systems

Methanol-formaldehyde Dichloroethane-trichloroethane Acetic acid-acetic anhydride Acetic anhydride-ethylene diacetate Vinyl acetate-ethyl acetate Ethylene glycol-diethylene glycol Cumene-phenol Phenol-acetophenone

Aqueous systems HCN-water Acetic acid-water Methanol-water Ethanol-water Isopropanol-water Vinyl acetate-water Ethylene oxide-water Ethylene glycol-water

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