Double Azeotropy: calculations with Newton-like methods and continuous GRASP (C-GRASP)

Abstract

Azeotropy is a thermodynamic phenomenon where a boiling liquid produces a vapour with identical composition. This situation is a challenge for separation engineering, since distillation processes explore the differences among relative volatilities and, thus, an azeotrope can be a barrier for the separation. In binary mixtures, the azeotropy calculation problem is characterised by a 2 × 2 non-linear system with pressure or temperature and a molar fraction as unknowns. An interesting and rare case is the so-called double azeotropy, when this non-linear system has two solutions, corresponding to two distinct azeotropes. In this paper, we present some numerical aspects of double azeotropy using classical approaches (Newton’s methods with globalisation techniques) and a new non-linear optimisation algorithm (the C-GRASP method).