Examinando por Autor "Suárez, Inmaculada"

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Engineered PP impact copolymers in a single reactor as efficient method for determining their structure and properties
(Elsevier, 2021) Pastor-García, María Teresa; Suárez, Inmaculada; Expósito, María Teresa; Coto, Baudilio; García-Muñoz, Rafael A.
Impact polypropylene (PP) copolymers (IPCs) are important materials for many commercial applications. These materials are usually synthetized through different methods involving two consecutive reactions in the same phase or in different phases. Here, a laboratory-scale synthesis method based on a sequential liquid- and gas-phase two-step process in a single reactor is developed. Propylene homopolymers and IPCs were synthesized with varying amounts of comonomers and hydrogen. The IPC materials obtained were fully characterized via analytical temperature rising elution fractionation (TREF), differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (13C NMR), gel permeation chromatography with an infrared detector (GPC-IR5), Charpy impact, scanning electron microscopy (SEM), and cross-fractionation chromatography (CFC). The addition of only ethylene to the second step in the absence of hydrogen led to the creation of an ethylene-propylene (EP) copolymer with similar impact strength to that of a propylene homopolymer. The addition of hydrogen to the first step dramatically shortened the length of the PP chains and inhibited catalytic active centers that led to EP copolymer synthesis. This material exhibited very low molecular weight, low ethylene incorporation, and rubbery phases irregularly distributed along the isotactic polypropylene (iPP) matrix, resulting in the formation of an EP copolymer material with poor impact properties. IPCs synthesized without hydrogen and with a 50/50 (v/v) mixture of propylene/ethylene monomers in the second step enhance ethylene incorporation, facilitating adequate homogeneous and heterogeneous ethylene distribution and resulting in a high increment of amorphous ethylene-propylene-rubber (EPR) domains, which remarkably improves impact properties. Additionally, a criterion based on the ratio between EEE and EPE + PEP triads ranging between 1 and 2 was also established to predict the impact resistance of any heterophasic PP. Fractionation of the optimal sample provided a detailed understanding about the microstructure of this copolymer through the study of the molecular weight and composition of the fractions via GPC-IR, analytical TREF, and DSC measurements. Finally, the liquid–gas-phase two-step IPC material was compared, by means of SEM and CFC measurements, with synthesized IPC using liquid–liquid-phase two-step polymerization, and the results showed that the range of EP composition as well as ethylene distribution in the molar mass molecules of the IPCs was correlated to their mechanical behavior. This proves that crystalline families composed of high-molecular-weight EP copolymers in the liquid–gas-phase process can act as a compatibilizing agent between the iPP matrix and the elastomeric rubbery phase, allowing one to improve the impact resistance of the IPC, more so than that of IPCs obtained in the gas–gas and liquid–liquid phases. The results indicate that the synthesis of IPC resins in a single reactor is an efficient experimental method for fundamental research on IPCs.
Experimental data and modeling of viscosities and densities of pyrene + toluene + heptane mixtures at T = (293.15 to 343.15) K
(Elsevier, 2023) Tenorio, Maria José; Suárez, Inmaculada; Díaz Magdaleno, Julia; González, Miguel A.; Coto, Baudilio
Oil mixtures are a complex system that remains unclear. Its study is particularly challenging due to the many variables involved in their properties. These include, for instance, the compositions of the mixture and the nature of their compounds. To simplify the study of these systems, it is proposed to model them with simpler mixtures, as in the case of using hydrocarbon mixtures to describe the behavior of crude oil. Two mixtures have been prepared; the one hand, a binary mixture of pyrene in toluene, and on the other hand, a ternary mixture of pyrene in toluene/heptane has been prepared. Their densities and dynamic and kinematic viscosities have been measured from (293.15 to 343.15) K at atmospheric pressure. The compositions of binary and ternary systems are 1.0, 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0 % weight fraction of pyrene. In the case of ternary systems, several toluene/heptane mass ratios have been studied, from 0.1 to 10. This article presents new experimental results of density and viscosity for the mixtures studied. Therefore, a theoretical study has been carried out to describe experimental data. Viscosity models, such as Ideal, Refutas, Ratcliff, UNIFAC-Visco, and Krieger, have been checked and, in some cases, have been modified to analyze the dependence of viscosity on temperature, composition, and possible association of pyrene. Standard deviations for each model and system have been calculated. Modified Ratcliff and Krieger models presented an excellent agreement with experiments.
Extraction of aromatic and polyaromatic compounds with NMP: experimental and model description
(Elsevier, 2021) Coto, Baudilio; Suárez, Inmaculada; Tenorio, Maria José; Huerga, Isabel
Optimization of the extraction process for reducing aromatic and/or polyaromatic compounds is of primary interest in crude oil refining. Several solvents are described for carrying out such operations (furfural, N-methyl-pyrrolidone -NMP-, dimethyl-sulfoxide -DMSO-, …) and experimental data and model description are required for the correct design of the separation operations and the optimization of the conditions. In this work, liquid-liquid equilibria (LLE) data were determined for oil multicomponent mixtures formed by n-dodecane + mono-aromatic + poly-aromatic with NMP at ambient temperature (298.15 K) and pressure and covering a wide range of the solvent/oil ratios. A new analytical method based on NMR was developed, calibrated, and tested to fully determine the composition of equilibrium phases despite the high number of compounds. Obtained values for distribution constants and selectivities are higher than one and ranging 1-15, respectively, for aromatic compounds and even higher for polyaromatic components. Thus NMP appears as a suitable solvent for carrying both separations. The experimental data were predicted by several versions of the UNIFAC model, including the UNIFAC, modified UNIFAC (Dortmund), modified UNIFAC (NIST), and UNIFAC, including fitting parameters. Overall, modified UNIFAC (Dortmund) yields the best results, even when deviations obtained for some of the compositions are around 40% of the value, and simulations carried out with such models should be considered cautiously
Liquid-Liquid Extraction of polyaromatic compounds with ionic liquid. A theoretical and experimental approach
(Elsevier, 2022) Arenas-Fernández, Plácido; Suárez, Inmaculada; Coto, Baudilio
Recent legislation worldwide aims to reduce the levels of polyaromatics compounds in lubricant bases due to their harmful effect on health. Ionic liquids have obtained broad interest as green recyclable extractants. Here, we presented new experimental data of liquid-liquid extraction implementing ionic liquids for the removal of aromatics compounds of synthetic crude oil in a 1:1 mass/mass ratio for temperatures ranging from 303.15 to 293.15 K. Selectivity and distribution constant data are obtained to know the extractive potential of each ionic liquid. To support the experimental results, several computational calculations have been performed. First, two predictive thermodynamic models COSMO-SAC and UNIFAC, have been applied, and the reliability of both models has been compared with experimental results. The results show that using UNIFAC is more accurate than using COSMO to predict extraction behavior. Second, the extractive process has been studied using molecular dynamics. This tool allows us to understand better how the extraction process occurs and the molecules’ situation when they reach equilibrium. It is shown that the cation of the ionic liquid is the primary driver of liquid–liquid extraction. In addition, molecular dynamics will enable a qualitative comparison between the performance of ionic liquids and the experimental results. It is a helpful tool to save time and material resources before laboratory experimentation.
Viscosities and Densities of Binary and Ternary Mixtures of Aliphatic and Polyaromatic Hydrocarbons: Pyrene +1-Methylnaphthalene + Dodecane at T = (293.15 to 343.15) K. Experiment and Modeling
(American Chemical Society, 2024-03-18) Tenorio, María José; González, Miguel A.; Magdaleno, Julia D.; Suárez, Inmaculada; Coto, Baudilio
This work presents new experimental viscosity and density data for aromatic and polyaromatic compounds in binary and ternary pyrene, 1-methylnaphthalene, and dodecane mixtures. The lack of experimental viscosity data for these mixtures requires the development of a new database, which is vital for understanding the behavior of mixtures in more complex systems, such as asphaltenes and fuels. The mixtures proposed in this work have been measured over a temperature range of (293.15 to 343.15) K at atmospheric pressure. Several mixture compositions have been studied at these conditions: 1.0, 2.5, 5.0, 7.5, 10.0, 12.5, and 15.0% pyrene mass fraction. The concentration of pyrene correlates with an increase in the viscosity and density values. At the lowest temperature in binary mixtures, the corresponding values reach 4.4217 mPa·s for viscosity and 1.0447 × 103 kg·m–3 for density, respectively. In ternary mixtures, the introduction of dodecane leads to the lowest maximum values of 3.5555 mPa·s for viscosity and 1.0112 × 103 kg·m–3 for density at the same temperature. The experimental data have been employed for the specific modification of viscosity models. These modifications could facilitate the prediction of the viscosity of mixtures that are more complex than those presented in this work. Various viscosity models have been employed, such as Linear, Ratcliff and Khan, modified UNIFAC-Visco, and Krieger–Dougherty. The settings in the models used reliably reproduce the experiment reliably. However, the Ratcliff model agrees excellently with the experiment, having a low standard deviation (2.0%) compared to other models. Furthermore, a model based on the equation of state of Guo is proposed to predict the viscosity values by modifying the specific parameters and adjusting them to the mixtures proposed in this work. The results from this study are compared to previous work, where pyrene, toluene, and heptane mixtures were analyzed. In this case, we find that the decrease of aggregation grade in the present systems is predicted by the model fixed in this work.