(271e) Optimal Synthesis of Azeotropic Reactive Distillation Networks

In this work, we present a methodology for the global optimization of azeotropic reactive distillation (RD) networks, through the Infinite DimensionAl State-space (IDEAS) approach. The IDEAS conceptual framework gives rise to an Infinite linear program (ILP). The solution of a series of finite dimensional linear programs is the values that converge to the infinite program's infimum. The proposed optimal design methodology is demonstrated in a case study involving reactive distillation-based synthesis of Isopropyl acetate from acetic acid and Isopropanol. This system is particularly interesting because it involves three binary, one ternary and one ?reactive? azeotrope. An acid catalyzed esterification reaction occurs:

CH3COOH + iso-C3H¬7OH CH¬3COOC3H7 + H2O

A detailed reactive flash distillation model that accounts for vapor/liquid phase equilibrium (VLE) and liquid phase kinetics is used in the IDEAS context. It employs a VLE thermodynamic model based on modified Raoult's law, with an NRTL equation consisting of binary interaction parameters to model the non-ideality of the liquid phase. Despite the complex and the nonlinear nature of the underlying thermodynamic and kinetic model, the IDEAS approach yields nevertheless a linear program formulation of the global minimum capital cost. Capital cost is considered proportional to a weighted linear combination of the liquid hold-up and plate area.

The long standing question of whether pure isopropyl acetate can be produced is equivalently formulated as the feasibility of the IDEAS ILP. Namely, a reactive flash distillation network that can deliver pure isopropyl acetate as product exists if the IDEAS problem is feasible. The specs can be easily incorporated as linear constraints in the ILP formulation.