BEST PRODUCTS OF HOMOGENEOUS AZEOTROPIC DISTILLATIONS

The literature about product boundaries of homogeneous azeotropic dist illation has been reviewed. A method for the calculation of multicompo nent distillation from stage to stage has been developed. The method i s based on balances around the product end of the cascade of equilibri um stages and iterates only the amount of the stream entering the casc ade. By way of linearization of the method for the calculation of mult icomponent distillation from stage to stage at a pinch point, a method for the calculation of separatrixes of distillation has been develope d, which has already been utilized in a method for calculating minimum reflux of real multicomponent distillation (Poellmann et al. Comput C hem Eng (1994) 18 S49). The separatrixes of closed multicomponent dist illation are identical with the product boundaries of closed multicomp onent distillation. A separatrix of open distillation yields only one point of a product boundary of open distillation-its product. A method based on eigenvalue theory has been developed, which makes it possibl e to judge with respect to a pinch point whether the calculation of mu lticomponent distillation from stage to stage initiated at the product has the potential to leave the pinch point. If the pinch point is loc ated on the boundary of the mole fraction space and if the calculation has the potential to leave this boundary, then the product can be rea ched by distillation of mixtures taken out of the interior of the mult icomponent mole fraction space using infinitely many stages. The profi le of reversible multicomponent distillation has been interpreted as a curve in mole fraction space with the temperature as parameter. A sys tem of linear equations for the derivative of the profile of reversibl e multicomponent distillation with respect to the temperature has been given. Numerical integration of this derivative initiated at a point located on the desired profile yields the profile quickly and accurate ly even if the profile exhibits sharp corners. Even if two parts of a profile approach each other very closely, the numerical integration do es not jump onto another part. The inflection points of residue curves have been identified as the bifurcation points of profiles of reversi ble ternary distillation. The envelope of the tangents to residue curv es in their inflection points (Wahnschafft et al. Ind Eng Chem Res (19 92) 31 2345) could be confirmed as the product boundary of reversible ternary distillation. A zero of the determinant of the matrix of coeff icients of the system of linear equations for the calculation of the d erivative of the profile of reversible multicomponent distillation wit h respect to the temperature has been developed as a necessary conditi on for a bifurcation of a profile of reversible multicomponent distill ation. Sufficient for a bifurcation and thus a point of the product bo undary of reversible ternary distillation on an inflection point tange nt is the zero of the determinant, if the determinant is evaluated for the inflection point and for potential products on the tangent. Using the above-mentioned eigenvalue-based method, it could be shown that p roduct which can be reached by reversible multicomponent distillation can also be reached by adiabatic open multicomponent distillation.