Sharp distillation region

Trajectory Tear-Off Regions and Sharp Distillation Regions... 

As for the top and bottom sections, working trajectory bundle of the intermediate section should be located in a sharp distillation region where the order of the components is the same as at the trajectory tear-off region i.e. segment... 

Joining condition at minimum reflux for split with distributed component feed cross-section composition point for one column s section must belong to the sep-aratrix min-r ux region and the other to the separatrix sharp distillation region for given product points and reflux ratio and satisfy the material balance in feed cross-section x/ i e andxf e Reg or Xf.i and... 

The first split is sharp. The process takes place in two distillation regions, but the concentration profiles do not cross the simple distillation border. 

The main difference between the azeotropic mixtures (and also nonideal zeo-tropic mixtures) and the ideal ones are that, to determine possible sphts of an azeotropic mixture, special analysis is required. The availability of a few distillation regions under the infinite reflux Reg can result in sharp separation becoming completely impossible or in a decrease in sharp splits number. Let s note that for ideal mixtures the fine of possible products compositions atR = ooandiV=oo and set feed composition goes partially inside the concentration simplex and partially along its boundary elements. For azeotropic mixtures, this line can go along the boundary elements of the distillation region (Fig. 3.6a, line 2). 

For the sake of briefness, we call the first of these conditions the term of connectedness. It has general nature - it can be applied to mixtures with any number of components and azeotropes. Moreover, the term of connectedness embraces not only sharp splits, when the product points lie in the boundary elements of the concentration simplex, but also the semisharp and nonsharp splits, when the product points lie in the boundary elements of the distillation region. 

The diagrams of reversible distillation were constructed for some types of three-component azeotropic mixtures. It is interesting that some types of mixtures with one binary azeotrope and with two distillation regions [types 3 and 5 according to classification (Gurikov, 1958)] permit sharp separation into component and binary zeotropic mixture at some feed compositions. The mixture acetone(l)-benzene(2)-chloroform(3) is an example of such mixture. 

For splits with distributed components, sharp split regions of two sections are different (Fig. 5.10). Reversible distillation regions Regf and RegJ, which are discussed in Chapter 4, are a particular case of sharp split regions (in this case, component h is absent in overhead and component / is absent in bottom). 

Comparison of the calculated trajectories of a two-section column (Fig. 6.16b) with those of one-section column (Fig. 6.16c) shows a sharp difference between them. Trajectory of the one-section column lies completely in the distillation region Regf containing isopropanol. This trajectory does not have points of sharp twist that are quasizones of constant concentrations ... 

Figure 7.13. Section separatrix sharp split regions for extractive distillation of ideal four-...

As one can see in Fig. 4.2, the trajectory of each section at sharp reversible distillation consists of two parts the part, located inside the (n -1) component boundary element C i of concentration simplex, lying between the product point Xd or xb and the tear-off point of the trajectory from this boundary element x[, and the part located inside concentration simplex C , lying between the tear-off point of the trajectory and the feed point xp. Only the second part should be located inside a region of reversible distillation Reg y orRegJ g, and product point Xd or xb can lie outside this region. 

Therefore, Eqs. (4.19) and (4.20) allow determination of the boundaries of the possible product composition region Reg, or Reg at sharp reversible distillation in (n - l)-component boundary elements C i of the concentration simplex. 

It follows from the aforesaid that sharp separation in a reversible distillation column is feasible only if the liquid-vapor tie-line of feeding is directed to the possible product composition region Reg at the boundary element C i of the concentration simplex and from region Reg at other boundary element... 

Figure 4.16. Bundles of sharp reversible stripping trajectories in region reversible distillation Regjigy j for the acetone(l)-benzene(2)-chloroform(3)-tolnene(4) mixture (a) node is component 1, (b) node is azeotrope 13, and (c) nodes are component 1 and azeotrope 13.

I. Define the main notions (1) region of reversible distillation of top Reg g bottom Reg -e, and intermediate sections Reg g (2) regions of trajectory tear-off Reg and Reg (3) region of possible product points of sharp reversible distillation Reg, Reg, and Reg and (4) node of trajectory bundle of reversible distillation Nrev-... 

The analysis carried out above (see Figs. 6.8 and 6.9) allows for a general conclusion about dimensionality, structure, and evolution of trajectory bundles (regions) of intermediate section at sharp extractive distillation for any multicomponent mixtures. 

The location of intermediate sections trajectories of columns with two feeds, including those at extractive, heteroazeotropic, and heteroextractive distillation, has fundamental distinctions from that of section trajectories of the simple columns. At sharp extractive or heteroextractive distillation, pseudoproduct point x), of the intermediate section should be located at the continuation of the boundary element, to which components of top product and of entrainer belong. If this condition is valid, the whole trajectory bundle of the intermediate section including trajectory tear-off point x[ from the mentioned boundary element is located in the region Reg where the top product components are more volatile and the entrainer components are less volatile than the rest of components. The trajectory tear-off point of the intermediate section is the stable node x[ = A+). The conditions of intermediate section trajectory tear-off in different points of trajectory tear-off region Reg allow to determine limit modes of extractive distillation for each mixture - the mode of minimum flow rate of the entrainer min, and for the... 

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