Distillation sequence azeotropic

Even though the simple distillation process has no practical use as a method for separating mixtures, simple distillation residue curve maps have extremely usehil appHcations. These maps can be used to test the consistency of experimental azeotropic data (16,17,19) to predict the order and content of the cuts in batch distillation (20—22) and, in continuous distillation, to determine whether a given mixture is separable by distillation, identify feasible entrainers/solvents, predict the attainable product compositions, quaHtatively predict the composition profile shape, and synthesize the corresponding distillation sequences (16,23—30). By identifying the limited separations achievable by distillation, residue curve maps are also usehil in synthesizing separation sequences combining distillation with other methods. 

The first step in the synthesis of a homogeneous azeotropic distillation sequence is to determine the separation objective. Eor example, sometimes it is deskable to recover all of the constituents in the mixture as pure components, other times it is sufficient to recover only some of the pure components as products. In other cases an azeotrope may be the desked product. Not every objective is attainable and those that are feasible may requke different distillation sequences. 

Fig. 9. Extractive distillation sequence cost as a function of the feed ratio for the production of anhydrous ethanol from azeotropic ethanol using ethylene glvcol at reflux ratios of A, 1.15 r O, 1.2 r and 1.3 r (39). Point A represents a previously pubhshed design for the same mixture (37).

As mentioned previously, ternaiy mixtures can be represented by 125 different residue curve maps or distillation region diagrams. However, feasible distillation sequences using the first approach can be developed for breaking homogeneous binaiy azeotropes by the addition of a third component only for those more restricted systems that do not have a distillation boundaiy connected to the azeotrope and for which one of the original components is a node. For example, from... 

When liquid mixtures exhibit azeotropic behavior, it presents special challenges for distillation sequencing. At the azeotropic composition, the vapor and liquid are both at the same composition for the mixture. The order of volatility of components changes, depending on which side of the azeotrope the composition occurs. There are three ways of overcoming the constraints imposed by an azeotrope. 

Kubierschky sequence -for azeotropic distillation piSTILLATION, AZEOTROPIC AND EXTRACTIVE] (Vol 8)... 

A second example of the use of liquid-liquid immiscibilities in an azeotropic distillation sequence is the separation of the ethanol-water minimum-boiling homogeneous azeotrope. For this separation, a number of entrainers have been proposed, which are usually chosen to be immiscible with water and form a ternary minimum-boiling... 

The first chapter, by Siirola, reviews the impact of process synthesis in industry and shows how process synthesis fits into the innovation process within industrial manufacturing and research. It also highlights a number of industrial successes leading to substantial energy savings and overall cost reductions. Most of these savings are in the areas of distillation sequences, and examples include heat-integrated separation sequences and separation of azeotropic systems. 

---