Modeling the vapor-liquid equilibrium and association of nitrogen dioxide/dinitrogen tetroxide and its mixtures with carbon dioxide

We have used in this work the crossover soft-SAFT equation of state to model nitrogen dioxide/dinitrogen tetraoxide (NO2/N2O4), carbon dioxide (CO2) and their mixtures. The prediction of the vapor – liquid equilibrium of this mixture is of utmost importance to correctly assess the NO2 monomer amount that is the oxidizing agent of vegetal macromolecules in the CO2 + NO2 / N2O4 reacting medium under supercritical conditions. The quadrupolar effect was explicitly considered when modeling carbon dioxide, enabling to obtain an excellent description of the vapor-liquid equilibria diagrams. NO2 was modeled as a self associating molecule with a single association site to account for the strong associating character of the NO2 molecule. Again, the vapor-liquid equilibrium of NO2 was correctly modeled. The molecular parameters were tested by accurately predicting the very few available experimental data outside the phase equilibrium. Soft-SAFT was also able to predict the degree of dimerization of NO2 (mimicking the real NO2/N2O4 situation), in good agreement with experimental data. Finally, CO2 and NO2 pure compound parameters were used to predict the vapor – liquid coexistence of the CO2 + NO2 / N2O4 mixture at different temperatures. Experimental pressure – CO2 mass fraction isotherms recently measured were well described using a unique binary parameter, independent of the temperature, proving that the soft-SAFT model is able to capture the non-ideal behavior of the mixture

Soft-SAFT modeling of vapour liquid equilibria of nitriles and their mixtures

Nitriles are strong polar compounds showing a highly non-ideal behavior, which makes them challenging systems from a modeling point of view; in spite of this, accurate predictions for the vapor-liquid equilibria of these systems are needed, as some of them, like acetonitrile (CH3CN) and propionitrile (C2H5CN), play an important role as organic solvents in several industrial processes. This work deals with the calculation of the vapor - liquid equilibria (VLE) of nitriles and their mixtures by using the crossover soft-SAFT Equation of State (EoS). Both polar and associating interactions are taken into account in a single association term in the crossover soft-SAFT equation, while the crossover term allows for accurate calculations both far from and close to the critical point. Molecular parameters for acetonitrile, propionitrile and n-butyronitrile (C3H7CN) are regressed from experimental data. Their transferability is tested by the calculation of the VLE of heavier linear nitriles, namely, valeronitrile (C4H9CN) and hexanonitrile (C5H11CN), not included in the fitting procedure. Crossover soft-SAFT results are in excellent agreement with experimental data for the whole range of thermodynamic conditions investigated, proving the robustness of the approach. Parameters transferability has also been used to describe the isomers n-butyronitrile and i-butyronitrile. Finally, the nitriles soft-SAFT model is further tested in VLE calculation of mixtures with benzene, carbon tetrachloride and carbon dioxide, which proved to be satisfactory as well

Phase Behavior of strongly associating systems

The modeling of associating fluids has been an active area of research for several decades. Attention has gradually shifted from the so called chemical theories, where molecular association is treated as a chemical reaction, to molecular models where association naturally arises from strong attractive intermolecular forces; among the last ones the Statistical Associating Fluid Theory (SAFT) and related approaches are becoming very popular. We will present calculations performed with the soft-SAFT EoS [F.J. Blas and L.F. Vega, Ind. Eng. Chem. Res. 37 (1998) 660-674.] to simulate the equilibrium thermodynamic properties of the acetic acid and the nitriles family (two classes of strongly associating compounds) as well as their mixtures[K. Jackowski and E. Wielogorska, Journal of Molecular Structure355 (1995) 287-290.]. Carboxylic acids form stable double hydrogen bridged dimers which in the gas phase exist in equilibrium with the monomers. Molecular association in liquid phase of the nitriles family is interesting as they are important organic solvents which are soluble in water without any limits. Pure-component molecular parameters are obtained by fitting the equation to available experimental data. The equation enables to search for physical trends, allowing the transferability of the parameters. The complex behavior of these mixtures is also investigated with the same approach

Combining soft-SAFT and COSMO-RS modeling tools to assess the CO2-SO2 separation using phosphonium-based ionic liquids

The development of efficient CO2 separation techniques from post-combustion flue gases is a key area of research to green-house gas control. However, CO2 capture is typically affected by the presence of other acid impurities, such as traces of SO2. In that sense, this work assesses CO2 separation from a CO2/SO2 mixture with a set of phosphonium-based ILs. Two different modeling tools, soft-SAFT and COSMO-RS, have been used cooperatively to study the CO2 gas separation on ILs. From one side, the soft-SAFT equation of state, which has been employed for the first time in this family of ILs, has been used to effectively reproduce the absorption properties of these promising CO2 absorbents in a wide range of pressures/temperatures. Additionally, COSMO-RS, employed to evaluate the charge distribution so as to develop representative models for soft-SAFT, has been capable of reproducing the low-pressure absorption region in a purely predictive way. In both cases, the enthalpy and entropy of dissolution and the selectivity of the mixtures are predicted. Also, several ternary diagrams have been built to analyze different acid gas compositions

Functionalization of fluorinated ionic liquids: A combined experimental-theoretical study

FCT/MCTES (Portugal), through: grant SFRH/BD/130965/2017 (M.LF.); Investigador FCT 2014 (IF/00190/2014 to A.B.P. and IF/00210/2014 to J.M.M.A.); projects PTDC/EQU-EQU/29737/2017, PTDC/QEQ-FTT/3289/2014 and IF/00210/2014/CP1244/CT0003. Associate Laboratory for Green Chemistry-LAQV, financed by national funds from FCT/MCTES (UID/QUI/50006/2019). projects 2018-LC-01 and 2019-URL-IR1rQ-011, from Obra Social "la Caixa" and by Khalifa University through project RCII-2018-0024.We present new experimental and modelling data concerning imidazolium based-FILs synthesized with a hydroxyl group in the end of the cationic hydrogenated side chain and compared them with the analogous non-functionalized FILs in order to verify their suitability in the biomedical field. The thermophysical and thermodynamic properties of the neat compounds and the self-aggregation behaviour of FILs in aqueous solutions were measured and compared with theoretical results from the soft-SAFT equation of state, in good agreement with each other. Results showed that the presence of the hydroxyl group increases the density and viscosity of pure compounds and aqueous mixtures, whereas the thermal stability, melting, free volume, ionicity and self-aggregation behaviour decrease. These properties are improved with respect to the conventional perfluorosurfactants for the desired application, due to the full miscibility in water and the promising improved biocompatibility.authorsversionpublishe

Screening of Ionic Liquids and Deep Eutectic Solvents for Physical CO2Absorption by Soft-SAFT Using Key Performance Indicators

RC2-2019-007 PID2019108014RB-C21 SFRH/BD/130965/2017 UID/QUI/50006/2019The efficient screening of solvents for CO2 capture requires a reliable and robust equation of state to characterize and compare their thermophysical behavior for the desired application. In this work, the potentiality of 14 ionic liquids (ILs) and 7 deep eutectic solvents (DESs) for CO2 capture was examined using soft-SAFT as a modeling tool for the screening of these solvents based on key process indicators, namely, cyclic working capacity, enthalpy of desorption, and CO2 diffusion coefficient. Once the models were assessed versus experimental data, soft-SAFT was used as a predictive tool to calculate the thermophysical properties needed for evaluating their performance. Results demonstrate that under the same operating conditions, ILs have a far superior performance than DESs primarily in terms of amount of CO2 captured, being at least two-folds more than that captured using DESs. The screening tool revealed that among all the examined solvents and conditions, [C4 py][NTf2] is the most promising solvent for physical CO2 capture. The collection of the acquired results confirms the reliability of the soft-SAFT EoS as an attractive and valuable screening tool for CO2 capture and process modeling.publishersversionpublishe