Splits quasisharp

Figure 5.18. The tangential pinch in rectifying section for the acetone(l)-benzene(2)- chloroform(3) mixture for the split 1,3 2 (a) sharp separation (the tangential-pinch region Regj g not shaded), (b) quasisharp separation. 1, 2, 3, different values of L/V and different iso-f 2 lines (thin hues) SN, saddle-node point.

The example of tangential pinch for four-component mixture is quasisharp separation of azeotropic mixture acetone (l)-benzene (2)-chloroform (3)-toluol (4) of composition Xf (0,350 0,250 0,150 0,250) at intermediate split 1,3(2) 2,4(3) (admixture components heavy and light key are in brackets correspondingly) at the following composition the products xd (0,699 0,001 0,300,0) and xb (0 0,500 10 0,500). The same top product composition, as in the previous example (Fig. 5.18b) of separation of three-component mixture in the top section, is accepted for convenience of analysis. In this case, the boundary elements of top section trajectory bundle, located in face 1-2-3, completely coincides with top section trajectory bundle at separation of previously mentioned three-component mixture. 

At quasisharp separation, possible product composition regions Rego and RegB grow at the decrease of purity of the products. Boundaries found for sharp separation deliberately ensure possible splits for quasisharp separation, but, if it is necessary, the widened boundaries for the set purity can be found. 

Figure 6.14 shows trajectories of the intermediate section for separation 1 1, 2 3 at different modes. Pseudoproduct points ( > — Dj+D) is located at side 1-2, and joining of the intermediate and bottom sections in the mode of minimum reflux goes on in the same way as for the simple column at indirect split. Trajectory of the intermediate section r tears off from side 1-2 in point Sn, and point of side product xd can coincide with point Sn (Fig. 6.14a) or lie at segment 1 - Sri (Fig. 6.14b). The first of these two modes is optimal because the best separation between top and side products (the mode of the best separation) is achieved at this mode. Zones of constant concentrations in the top and intermediate sections arise in point Sri = AC2- Therefore, in the mode of minimum reflux in the intermediate section, there are two zones of constant concentrations. At the reflux bigger than minimum, point 5 1 moves to vertex 2 and at i = oo this point reaches it (i.e., at i = 00, pure component 2 can be obtained in the infinite column as a side product). Therefore, for the colunuis with side withdrawals of the products, the mode of the best separation under minimum reflux corresponds to joining of sections in points 5 1 and of the trajectory bundle of the intermediate section (at sharp separation) or in its vicinity (at quasisharp separation). The trajectory of the column with a side product at minimum reflux at best separation may be described as follows ...

Figure 7.1. Rectifying trajectories at sharp intermediate split and different Xf- (Ki > K2 > K2) (a) rectifying trajectories at quasisharp intermediate spht and different Xf-i...

Figure 7.6. Section trajectories at quasisharp intermediate split for the equimolar pentane(l)-hexane(2)-heptane(3)-octane(4) mixture for L/F=1.3(L/ min> = 0-614, r)D = r]B = 0.99 at different...

Figure 7.9. (a) Section trajectories at quasisharp intermediate split for the equimolar acetone(l)-benzene (2)-chloroform(3)-toluene(4) mixture (L/V = 0.778, Xf i = 1 -b 0 products purity - 0.99), sepa-... 

At reflux bigger than minimum and at separation without distributed components for all feasible quasisharp splits - the direct, the indirect, and the intermediate ones-possible compositions at the trays adjacent to the feed cross-section from above x/ i and below x/fill some segments [x/ i] and [x/] located in the vicinity of... 

At reflux bigger than minimum and at quasisharp separation with distributed component at the set distribution of this component among the products, there is the only one composition at the first tray above the feed cross-section expressed by point X/-1 in the vicinity of separatrix sharp spht region Re p (5/ - - N ) and the only one composition at the first tray below the feed cross-section expressed by point Xf in the vicinity of separatrix sharp split region Reg p - N )- The less sharp is separation the farther from separatrix sharp split trajectory bundles of the sections the composition points in the feed cross-section are located. 

---