Special Kinds of Distillation Processes

Conditions sometimes exist that may make separations by distillation difficult or impractical or may require special techniques. Natural products such as petroleum or products derived from vegetable or animal matter are mixtures of very many chemically unidentified substances. Thermal instability sometimes is a problem. In other cases, vapor-liquid phase equilibria are unfavorable. It is true that distillations have been practiced successfully in some natural product industries, notably petroleum, long before a scientific basis was established, but the designs based on empirical rules are being improved by modern calculation techniques. Even unfavorable vapor-liquid equilibria sometimes can be ameliorated by changes of operating conditions or by chemical additives. Still, it must be recognized that there may be superior separation techniques in some cases, for instance, crystallization, liquid-liquid extraction, supercritical extraction, foam fractionation, dialysis, reverse osmosis, membrane separation, and others. The special distillations exemplified in this section are petroleum, azeotropic, extractive, and molecular distillations. [Pg.410]

Compute optimal t to minimize r3.Then compute new values [Pg.411]

Evaluate condenser and reboiler loads by heat balances if they have not been specified. [Pg.437]

When 13 3, corrections to the Uj, Vij, and 7 are calculated from the nonlinear MESH equations by the Newton-Raphson method. In these equations the enthalpies and equilibrium constants usually are nonlinear functions of the temperatures. [Pg.437]

Employ a process for evaluating the optimum fraction of a calculated correction of each variable to be applied to the next trial. That is, [Pg.437]

The selection process is described by Henley and Seader. The optimally corrected values of /, vy, and 7 are input to Box 4 for the next iteration. [Pg.437]

Conditions sometimes exist that may make separations by distillation difficult or impractical or may require special techniques. Natural products such as petroleum or products derived from vegetable or animal matter are mixtures of very many chemically [Pg.437]

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