Bubble and Dew Point Calculations in Multicomponent and Multireactive Mixtures

A. Bonilla-Petriciolet, A. Acosta-Martínez, U. I. Bravo-Sánchez and J. G. Segovia-Hernández

Abstract
Bubble and dew point calculations are useful in chemical engineering and play an important role in the study of separation equipments for non-reactive and reactive mixtures. To the best of the authors’s knowledge, few methods have been proposed for these calculations in systems with several chemical reactions. The objective of this paper is to introduce new conditions for performing bubble and dew point calculations in reactive mixtures. We have developed these conditions based on the application of transformed variables of Ung and Doherty (1995). Using these transformed variables, the solution space is restricted to compositions that are already at chemical equilibrium and by consequence the problem dimension is also reduced. The reliability and efficiency of three equation-solving methods are tested and compared using our equilibrium conditions: a) a simultaneous equation-solving approach using Newton method (SESN), b) an equation-decoupling approach using successive substitution method (EDSS) and c) an optimization approach using the stochastic optimization method Simulated Annealing (OSA). Our results indicated that even for simple reactive systems, bubble and dew point calculations are challenging for classical equation-solving methods and require robust strategies. We conclude that OSA and EDSS methods are reliable to locate bubble and dew points in reactive systems. EDSS is more efficient than OSA; however, OSA does not need initial guesses and is more suitable for difficult problems.

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Keywords
chemical equilibrium, phase equilibrium, bubble point, dew point, Global optimization, equation-solving method comparison