Locating all azeotropes in homogeneous azeotropic systems

A global optimization based approach for finding all homogeneous azeotropes in multicomponent mixtures is presented. The global optimization approach is based on a branch and bound framework in which upper and lower bounds on the solution are refined by successively partitioning the target region into small disjoint rectangles. The objective of such an approach is to locate all global minima since each global minimum corresponds to an homogeneous azeotrope. The global optimization problem is formulated from the thermodynamic criteria for azeotropy, which involve highly nonlinear and nonconvex expressions. The success of this approach depends upon constructing valid convex lower bounds for each nonconvex function in the constraints. The convex lower bounding procedure is demonstrated with the Wilson activity coefficient equation. The global optimization approach is illustrated in an example problem.