Automatic synthesis of complex separation sequences with recycles

Abstract

This chapter discusses the method for the rapid generation of feasible distillation sequences for a continuous separation of azeotropic mixtures. It allows crossing distillation boundaries by pressure change, by exploiting their curvature, or by liquid–liquid separation in decanters. The method automatically identifies suitable recycling options and calculates recycle mass balances. A few examples of the synthesis of separation schemes for homogeneous and for heterogeneous azeotropic mixtures are presented, where various methods of crossing distillation boundaries are explored and recycles are automatically calculated. The algorithm is general, for any number of components can be applied at any step in the automatic generation of distillation column sequences. In the systematic synthesis of the azeotropic separation schemes, the feasible products is determined first, which can be attained in individual separators for given feed compositions. Then suitable recycling options are identified. There are two types of recycles: (i) primary recycle detected automatically during the synthesis and (2) secondary recycles, where streams are introduced to shift the total feed composition and by doing this, change the functionality of a separation unit. A few examples of synthesis of separation schemes for homogeneous and for heterogeneous azeotropic mixtures were prepared, where crossing distillation boundaries by moving them with pressure change or by liquid–liquid separation in decanters are explored, and proper recycles are automatically calculated.