Calculation Of Continuous Sets Of Fluid State Equilibria At Constant Global Mass Density For Multicomponent Multiphase Chemically Reacting Systems

MOLINA, MATÍAS J.; RODRIGUEZ REARTES, SABRINA BELÉN; ZABALOY MARCELO S

Itaici, Indaiatuba

Congreso; XII Iberoamerican Conference on Phase Equilibria and Fluid Properties for Process Design (Equifase 2022) and X Congresso Brasileiro de Termodinâmica Aplicada (CBTermo, 2022); 2022

University of Campinas

A usual type of experimental study in reacting systems consists of loading a constant volume batch reactor or cell with known amounts of reactants and inert components (specified initial overall composition z0), setting a value for temperature (T), and allowing the system to react until equilibrium is reached. Then, the resulting simultaneous chemical and phase equilibrium (SCPE) pressure and (hopefully) SCPE phase compositions (or other variables) are recorded. Next, the temperature is changed and a new SCPE state is recorded. The resulting curves, which have T as independent variable (e.g., P vs. T, or vaporized fraction vs. T, etcetera), are different projections of a reactive isochore (R-IC), since the total volume (or, more specifically, the global mass density) remains constant for the set of performed experiments. A R-IC may have homogeneous segments and multiphase (heterogeneous) segments. Indeed, a R-IC corresponds to an ideal experiment where SCPE is reached for every set temperature. Clearly, to have the ability of computing complete reactive isochores is of significant practical interest. A set of R-ICs would correspond to a set of batch equilibrium experiments performed using a variable volume reactor. In this work, an algorithm for computing R-ICs over wide ranges of conditions for multicomponent multiphase chemically reacting systems is proposed and validated. The algorithm resorts to a numerical continuation method (NCM) for dealing with potentially high degrees of non-linearity. The models used in this work are of the equation of state type, and the chemical equilibria are accounted for through the stoichiometric approach, which requires to define a set of independent reactions which take place among the components present in the system. According to Duhem’s Theorem, at set initial global composition, it is required to specify two variables for making the equilibrium state become determined. A point of a R-IC is obtained through a reactive flash computation at set global mass density as first specified variable, while the choice of the second specified variable is made, in an automated way, by the NCM. In this work we have allowed the NCM to choose any of the variables of the system as the second specified variable (indeed excluding the global mass density). This makes the NCM very robust. A complete R-IC may include one or more critical points, and it normally has multiphase segments together with homogenous segments. Computation results are presented for a variety of systems, e.g., for a system present in the production of biodiesel in presence of CO2 as inert component (7 components, 3 reactions).