CHEMICAL ENGINEERING TRANSACTIONS VOL. 43, 2015 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Chief Editors: Sauro Pierucci, Jiří J. Klemeš Copyright © 2015, AIDIC Servizi S.r.l., ISBN 978-88-95608-34-1; ISSN 2283-9216 Modeling of Phase and Chemical Equilibria for Systems Involved in Biodiesel Production Larissa P. Cunico, Reginaldo Guirardello* School of Chemical Engineering, State University of Campinas (UNICAMP), Av. Albert Einstein 500, 13083-852. Campinas- SP. Brazil guira@feq.unicamp.br In recent years, the interest in the use of renewable energy has encouraged the growth of studies into renewable sources, such as the production of biofuels. This work investigates the vapor-liquid equilibrium (VLE), vapor-liquid-liquid equilibrium (VLLE) and liquid-liquid equilibrium (LLE) of binary, ternary, quaternary and pseudo-quaternary systems using an optimization approach for components found in biodiesel production, which consists in vegetable oils, fatty acids, esters and alcohols. A methodology has been developed based on the Gibbs energy minimization and the discretization of the molar fraction domain, which incorporates a thermodynamic model to describe the phase equilibria. This work used the Soave-Redlich- Kwong equation of state (SRK-EOS) for phase equilibria calculation, where the compressibility factor was used to determine the phase present in the system (liquid, vapor or supercritical fluid). The chemical and phase equilibrium problem is solved using linear programming and satisfies the mass balance constraints. It was found that the proposed methodology adequately represents the selected experimental data, with an average absolute deviation of 1.31 % obtained. 1. Introduction The most used energy sources worldwide are still non-renewable, such as oil, coal and natural gas. Factors such as environmental problems encourage the growth of studies in renewable sources such as biofuels. In large development, biodiesel has the main advantages: 1) It is biodegradable and non-toxic; 2) It contributes to the reduction of greenhouse gases, emissions of particulate matter and acid rain. The biodiesel production involves a number of processing steps that require knowledge of chemical or phase equilibrium. When a system is in equilibrium, the Gibbs energy has a minimum value for a given pressure and temperature. The calculation of the correct number of phases in equilibrium and its composition can be divided in two mainly categories: through the equation-solving approach for searching same fugacity or chemical potential in all the present phases in equilibrium, or through the direct minimization of the Gibbs energy (Teh and Rangaiah, 2002). The first approach solves the necessary conditions to guarantee chemical equilibrium, but only one solution minimizes the Gibbs energy and satisfies the second law of thermodynamics. Considering the minimization of Gibbs energy, a common problem observed is the convergence in a global solution and a good estimate of the composition as a starting point is required. This work presents a linear program model formulation for phase and chemical equilibria calculation in quaternary and pseudo-quaternary systems, based on a discretization of the molar fraction domain. The proposed approach can be applied to any thermodynamic model such as equations of state or excess Gibbs energy models. However, in this work, the equation of state of Soave-Redlich-Kwong (SRK-EOS) with the mixing rule of van der Waals two adjustable parameters (VDW-2) was employed. The use of this equation of state allows the calculation of both vapor-liquid equilibrium in elevated conditions of pressure and temperature, vapor-liquid in lower conditions of pressure and temperature, and liquid-liquid equilibrium. In the second part of this work, the performance of the proposed method in predicting phase and chemical DOI: 10.3303/CET1543310 Please cite this article as: Cunico L., Guirardello R., 2015, Modeling of phase and chemical equilibria for systems involved in biodiesel production, Chemical Engineering Transactions, 43, 1855-1860 DOI: 10.3303/CET1543310 1855