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

Accurate description of the critical region by a molecular-based equation of state with a crossover treatment

Consultable des del TDXTítol obtingut de la portada digitalitzadaEl progrés i les millores assolides en el camp industrial han empès els investigadors a buscar eines més refinades per tal de modelar aquests processos amb un major grau de precisió. Les propietats termofísiques són necessàries i el seu coneixement ha de ser molt precís, ja que una predicció poc acurada pot afectar el disseny d'una operació unitària, amb una consegüent pèrdua de rendiment i diners. Actualment, els models teòrics han progressat com a eines modernes que poden proveir a l'usuari d'una quantitat ingent d'informació sobre un fluid de manera ràpida, neta i barata. En qualsevol cas, manca encara un llarg camí per trobar una eina poderosa capaç de calcular el comportament termodinàmic de qualsevol compost en qualsevol condició. Aquest treball utilitza una robusta equació d'estat anomenada soft-SAFT. El nom original prové de la Teoria Estadística de Fluids Associants (SAFT), que és una equació basada en principis de mecànica estadística. Posseeix una molt forta base molecular, proposant un model «físic» per a descriure el compost. Soft-SAFT és una variant de la SAFT original que utilitza un terme de referència basat en una interacció de tipus Lennard-Jones entre les molècules. Malgrat que l'equació prèvia ja havia estat provada de manera exitosa en un conjunt molt variat de treballs, encara fallava en una regió molt important del diagrama de fases: la regió crítica. En aquesta regió, les propietats sofreixen fortes fluctuacions i canvien dràsticament degut a les llargues correlacions que es produeixen entre les molècules. La versió original de la soft-SAFT no pot tenir en compte aquestes fluctuacions de llarg abast perquè està basada en una teoria de camp mig. Tanmateix, aquesta fallida de la teoria ha estat superada introduint un tractament específic de «crossover», que considera les fluctuacions inherents. El procediment està basat en la teoria del grup de renormalització de Wilson (1971) i va ser desenvolupada per White (1992). S'escriu com un joc de relacions recursives on les correlacions entre les molècules són considerades al llarg de vàries iteracions. L'objectiu d'aquest treball de tesi s'ha dedicat a la millora d'una equació d'estat amb base molecular anomenada soft-SAFT afegint el tractament específic de «crossover» mencionat abans. La meta general implica el desenvolupament d'una poderosa eina predictiva aplicable a tot tipus de condicions per càlculs termodinàmics. Un tractament específic per calcular les fluctuacions inherents presents a la regió crítica s'ha implementat dins de la equació. La nova equació, anomenada «crossover soft-SAFT» és utilitzada per estudiar tres famílies diferents d'hidrocarburs: els alcans, els alcanols i els perfluoroalcans, així com les seves mescles entre ells i amb altres compostos, com el diòxid de carboni o l'àcid clorhídric. Els paràmetres moleculars s'optimitzen emprant dades de densitat de líquid i pressió de vapor experimental pels primers vuit membres de cada família. Es proposa una correlació per a cada paràmetre respecte el pes molecular, i els paràmetres s'extrapolen per predir el comportament termodinàmic d'altres membres més pesats de la mateixa família, amb un grau de precisió similar a l'obtingut pels membres més lleugers. Les capacitats calorífiques, la compressibilitat isotèrmica o isentròpica i la velocitat del so han estat també calculats per totes aquestes famílies de compostos, obtenint novament un molt bon acord amb les dades experimentals en la majoria de casos. Els resultats obtinguts per a aquestes propietats resulta molt esperançador ja que aquests càlculs s'han realitzat d'una manera purament predictiva. S'han pogut reproduir les diferents singularitats observades experimentalment en la regió veïna al punt crític, mentre que el càlcul dels exponents crítics universals també ha revelat un acord amb les mesures experimentals. Aquest treball pretén ser un pas endavant en la millora de les eines de modelat molecular per aplicacions enginyerils. Malgrat que la natura sigui sempre sorprenent i difícil de reproduir, l'esforç dedicat a aquesta tasca és prou encoratjador per continuar buscant noves fórmules que ens donin la possibilitat d'acostar-nos una mica més al món real.The progress and the improvements made in the industrial field have pushed the researchers to look for refined tools to model these processes with a higher degree of accuracy. Thermophysical properties are needed and have to be known in a precise way, because an inaccurate prediction may affect the design of a unit property, with a result of a loss in yield and money. Nowadays, the theoretical models have progressed as modern tools that can provide a huge amount of information of a fluid in a rapid, clean and cheap manner. In any case, there is still a long way to find a powerful tool able to calculate the thermodynamic behavior of any compound at any condition. This work uses a robust equation of state called soft-SAFT. The original name comes from the Statistical Associating Fluid Theory (SAFT), which is an equation based on statistical mechanics principles. It has a very strong molecular basis, proposing a «physical» model to describe the compound. Soft-SAFT is a variant of the original SAFT that uses a reference term based on a Lennard-Jones type interaction among the molecules. Although the previous equation had already been successfully tested in many different works, it still failed in a very important region of the phase diagram: the critical region. In that region, the properties suffer strong fluctuations and change drastically due to the long-correlations established among the molecules. The original soft-SAFT version of the equation can not take into account these long-range fluctuations because it is based in a mean-field theory. However, this lack of the theory can be now overcome introducing a specific crossover treatment that considers these inherent fluctuations. The procedure is based in the renormalization group treatment of Wilson (1971) and it was developed by White (1992). It is written as a set of recursive relations where the correlations among the molecules are considered in several iterations. The objective of this thesis work was to improve the molecular-based equation of state named soft-SAFT adding the specific crossover treatment before mentioned. The general aim was to develop a powerful predictive tool applicable under different conditions for thermodynamic calculations. The extended equation, called crossover soft-SAFT is employed to study three different families of hydrocarbons: the n-alkanes, the 1-alkanols and the n-perfluoroalkanes, and their mixtures among them and with other compounds such as carbon dioxide or hydrogen chloride. The molecular parameters are optimized using liquid density and vapor pressure data for the first eight members of each family. A correlation with molecular weight is then proposed, and the parameters are extrapolated to predict the phase behavior of heavier members of the same family, with the same degree of accuracy as that one obtained for the lighter members of the series. Heat capacities, isothermal and isentropic compressibility and the speed of sound have been calculated for these families obtaining very good agreement with experimental data in most of the cases. Results for these properties are very encouraging since calculations were performed in a pure predictive manner. The different singularities experimentally observed in the vicinity of the critical point have been reproduced and the universal critical exponents have also been found in agreement with the experimental measurements. This work intends to be a step forward in the improvement of the molecular modeling tools for engineering applications. Although nature is always surprising and difficult to reproduce, the effort devoted to this task is encouraging enough to continue looking for new formulas that give us the possibility of getting closer to the real world

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

La morfología como herramienta de comprensión lectora

Los lenguajes se encuentran en permanente estado de cambio para satisfacer las necesidades de sus hablantes. En el campo de la ecología, los cambios en el medio ambiente han producido el enriquecimiento del léxico del idioma inglés a través de diversos procesos de creación de nuevas palabras. Numerosos autores (Yule, 2006; Aronoff, 2011; Biber et al., 1999) coinciden en que la composición y la derivación morfológica son los procesos utilizados con mayor frecuencia en la construcción de neologismos. El objetivo de este trabajo es analizar el enriquecimiento del léxico del idioma inglés a través de la derivación morfológica. Debido al alcance de este trabajo, nos hemos limitado a los procesos de derivación nominal que resulten en sustantivos deverbales. El corpus de este trabajo está compuesto por 30 artículos periodísticos en inglés que versan sobre ecología. Los resultados de este trabajo, sumados a los hallazgos de trabajos anteriores, indican que el léxico del campo de la ecología se ha incrementado recientemente a través de sustantivos deverbales. Consideramos que nuestros hallazgos podrían contribuir a la enseñanza de la lengua inglesa como L2 y a la enseñanza de estrategias de comprensión lectora de inglés para propósitos específicos.All languages are constantly changing in order to satisfy the speakers’ needs. In the ecological field, the changes have contributed to the enrichment of the English vocabulary through different morphological processes to create new lexemes. Many authors (Yule, 2006; Aronoff, 2011; Biber et al., 1999) believe that two of the most frequently used word formation processes are: composition and derivation to form neologisms. The main objective of this paper is to analyze the enrichment of the English lexicon by the derivational process. In order to focus on one grammatical category, this work encompasses the derivation of nouns that results in nouns with a verb as the base. The corpus of this research includes thirty articles in English that are widely recognized and refer to ecological topics. The results of this paper indicate that the English lexicon related with environmental issues have recently increased through derivation. These findings can contribute to the teaching of English as a second language and of comprehension strategies so that students can improve their reading skills

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

Las TIC alteraron el paratexto de los artículos de investigación científica.

Este trabajo pretende demostrar que la revolución tecnológica que comenzó a fines del siglo pasado y la consecuente introducción de las tecnologías de la información y de la comunicación (TIC) al proceso de investigación han producido Transformaciones en algunos aspectos textuales de los artículos de investigación científica (AI), género que nuestros alumnos universitarios deben dominar para participar exitosamente en la comunidad académico-científica. Desde el marco teórico de la Teoría del Género (Dudley Evans, 1984; Swales, 1990, 1996, 2004; Hyland, 2004; Yakhonotova, 2002 b, 2006), esta investigación plantea un análisis diacrónico de los cambios textuales experimentados por los títulos y los datos autoriales de los AI en respuesta a los avances en el contexto tecnológico en el que se producen los mismos. El corpus está compuesto por 40 AI pertenecientes al área de la lingüística escritos en inglés, 20 de ellos publicados con anterioridad y 20 con posterioridad a la incorporación de las TIC. Los resultados de este trabajo, junto con los hallazgos de trabajos anteriores, indican que hay una relación directa entre la incorporación de las TIC al proceso de investigación y las modificaciones que se observan en las convenciones genéricas del AI a través del tiempo.https://rdu.unc.edu.ar/handle/11086/2312Fil: Llovell Curia, Magdalena. Universidad Nacional de Córdoba. Facultad de Lenguas; Argentina.Fil: Guerrero Prompto, Lucía. Universidad Nacional de Córdoba. Facultad de Lenguas; Argentina.Lingüístic

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