Separation sequences

An additional separator is now required (Fig. 4.2a). Again, the unreacted FEED is normally recycled, but the BYPRODUCT must be removed to maintain the overall material balance. An additional complication now arises with two separators because the separation sequence can be changed (see Fig. 4.26). We shall consider separation sequencing in detail in the next chapter. 

Also, if there are two separators, the order of separation can change. The tradeoffs for these two alternative flowsheets will be different. The choice between different separation sequences can be made using the methods described in Chap. 5. However, we should be on guard to the fact that as the reactor conversion changes, the most appropriate sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

We should be on guard for the fact that as the reactor conversion changes, the most appropriate separation sequence also can change. In other words, different separation system structures become appropriate for different reactor conversions. 

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. 

Optimization. Optimi2ation of the design variables is an important yet often neglected step in the design of extractive distillation sequences. The cost of the solvent recovery (qv) step affects the optimi2ation and thus must also be included. Optimi2ation not only yields the most efficient extractive distillation design, it is also a prerequisite for vaUd comparisons with other separation sequences and methods. 

Completing the Separation Sequence. In the remainder of the separation sequence the distiUate stream leaving the azeotropic column, column 2 in Fig. 19a, must be separated into a product stream and a recycle stream so that the entire sequence is closed with respect to the entrainer. 

Ydibierschky Three-Column Sequence. If only simple columns are used, ie, no side-streams, side-rectifiers/strippers etc, then the separation sequence can be completed by adding an entrainer recovery column, column 3 in Figure 19a, to recycle the entrainer, and a preconcentrator column (column 1) to bring the feed to the azeotropic column up to the composition of the binary azeotrope. 

Exploitation of Homogeneous Azeotropes Homogeneous azeotropic distillation refers to a flowsheet structure in which azeotrope formation is exploited or avoided in order to accomplish the desired separation in one or more distillation columns. The azeotropes in the system either do not exhibit two-hquid-phase behavior or the hquid-phase behavior is not or cannot be exploited in the separation sequence. The structure of a particular sequence will depend on the geometry of the residue curve map or distillation region diagram for the feed mixture-entrainer system. Two approaches are possible ... 

Definition of process objectives Generation of separation core structure Selection of separation sequence and unit operations Addition of further units to the process structure Selection of crystallizer type... 

Obviously, the use of purges is not restricted to dealing with impurities. Purges can also be used to deal with byproducts. As with the optimization of reactor conversion, changes in the recycle concentration of impurity might change the most appropriate separation sequence. 

Generation of an initial population of random separation sequences is done first. The sequences describe both which equipment items are used and how they are connected. 

The generation of an initial population of random separation sequences is done first. The sequences describe both in which order the components are separated and which separation method is used. For example the sequence on left in Figure 13 is described by the string 23 12 14 11. The first integer is for the separation method and the second for the heavy key component of the split in the column. The first separation is made by method 2 and the components heavier than no.3 (i.e. 4 and 5) go to bottom. In the next separation method 1 is used and component heavier than 2 (i.e. 3) goes to bottom, etc. 

Applying simulated annealing to separation sequence synthesis... 

Floquet, P. L. Pibouleau and S. Domenech. Separation Sequence Synthesis How to Use a Simulated Annealing Procedure Comput Chemung 18 1141-1148 (1994). 

RIPP separation sequence (removal of insolubles isolation purification polishing), 5 781-782 RISC enzyme, 27 620 Riser termination technologies, 22 685 Risk... 

Electron transfer follows from E12P to Qa, and then a charge-separation sequence such that localised charges reside on the carotenoid and on the quinine (Qb) ... 

These four classes of source materials have given rise to at least 13 coalified products that appear to be optically distinguishable. These 13 products may represent as many as nine separate sequences in which plant substances are altered to coal substances and in which the coal substances are further metamorphosed from one maceral to another. 

The T4 phage tail is assembled in a separate sequence. Six copies of each of three different proteins form a "hub" with hexagonal symmetry (Fig. 7-29). 

In (i), a column separates its feed into products without overlap in the components. An example is the separation of a stream consisting of four components A,B,C, and D via a distillation column, into one product consisting of only A and another product featuring B, C, and D. If all columns are sharp, then the separation sequence is termed as sharp sequence. 

The significant contribution of the utilities to the total cost of a distillation-based separation sequence provides an incentive to synthesize the sequences of distillation columns which feature heat integration alternatives. 

---