Distillation is the most widely used separation technique in the chemical and petroleum industry. However not all liquid mixtures are amenable to ordinary fractional distillation. When the components of the system have low relative volatilities (1.00 < <1.05). Separation becomes difficult and expansive because a large number of trays are required and, usually a high reflex ratio as well. Both equipment and utilities costs increase markedly and the operation can become uneconomical. In other cases the formation of a binary azeotrope may make it impossible to produce nearly pure products by ordinary fractionation. In that cases "azeotropic distillation" is performed by adding a third component called an entrainer which changes the relative volatilities of the original components and thus facilities their separation.
[...] Azeotropic distillation requires significant preliminary work including: Choosing the solvent Developing or finding necessary data Preliminary Screening Computer simulation Small Scale testing. The analysis of process dynamics is carried out in a combination of modeling, simulation and experimental studies on the hand. Simulations are used to fix experimental conditions, which facilitate reproducibility in spite of the high sensitivity and which dead to meaningful results. On the other hand experiments are carried out to decide whether it is necessary to develop a more detailed model or whether it is possible to introduce simplifying modeling assumptions. [...]
[...] Nontoxic of low talent heat of vaporization of low freezing point to facilitate storage and outdoor handling, and. of low viscosity to provide high tray efficiencies. Azeotropic distillation systems show a very high sensitivity to small changes in the operating conditions or requirements. To mention just a few; small changes in bottoms products purity specs can significantly impact the column temperature profile and entrainer requirements. Small changes in the reflux ratio can dramatically changes the temperature profile. Small fluctuations in pressure can move the overhead composition outside the heterogeneous region, thus causing column failure. [...]
[...] Stage and Reflux Requirement: In azeotropic distillation, the extraneous material the “entrainer” may be charged to the column with the feed or with the reflux. When the entrainer is charged with the feed the operations are essentially the same as in ordinary single-feed multi-component distillation, except that the relative volatilities of the several components may charge substantially through the column. When the entrainer is charged with the reflux the operation constitutes a special case of a two-feed operation. The operation of typical azeotropic-distillation for a binary feed is shown below figure. [...]
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