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  • Author or Editor: J. Domínguez x
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Authors: J. Pérez, F. Rodríguez, M. Alonso, M. Oliet and J. Domínguez

Abstract  

The curing kinetics of lignin-novolac and methylolated lignin-novolac resins were studied using non-isothermal methods employing differential scanning calorimetry (DSC) at different heating rates. The Belichmeier, Ozawa and Kissinger methods were applied, which give the kinetic parameters of the curing process studied. In addition, the model-fitting Coats-Redfern method was used to analyze the experimental data. The kinetic study evaluated the effect of the lignin (softwood ammonium lignosulfonate), methylolated or not, on the resin curing process. Results for lignin-novolac and modified lignin-novolac resins were compared with a commercial novolac resin as a reference. When lignosulfonate is modified by methylolation and is incorporated in the novolac resin, there is an important reduction in activation energy. The lignin-novolac showed slightly higher values of activation energy than methylolated-lignin resins, but lower values than commercial resins. This behavior has been attributed to the extra methyol groups introduced by lignosulfonate.

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Abstract  

Both 9mTcO4 - and Rhodamine WT were employed as tracers to record the residence time distribution (RTD) in 5 segments located in the Almendares River in Havana City. Recovery calculations showed the conservative behavior of the 99mTcO4 - under the field conditions studied. The experimental residence time distribution curves from the second segment were convoluted for the d-Dirac injection at the beginning of the section. The spatial behavior of the conservative prompt spills throughout this river section was established for two extreme flow conditions.

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Authors: L. Desdin, O. Dominguez, J. Moreno, L. Alfonso and M. Rodriguez

Abstract  

Determination of boric acid in high nickel content solutions during nickel cathode production was made by measuring the transmission loss of thermal neutrons. According to industrial requirements, adequate accuracy and reproducibility were obtained.

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Authors: J. Domínguez, A. Abreu, R. McCalla, J. Borroto, M. Ortueta and E. Pérez

Abstract  

The infusion rate of a slug of tracer into an anchor agitated 100-liter batch mixer was characterized by a decay rate constant. This constant was then used to define a dimensionless mixing-rate number which was related to the stirrer Reynolds number. This correlationship allows the calculation of time or rotational speed needed to achieve any desired degree of uniformity of the mixture.99mTc was used as radiotracer and the mixing process was followed by a scintillation Nal(Tl) counter situated on the reactor wall near the injection point.

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Authors: M. V. Alonso, M. Oliet, J. C. Domínguez, E. Rojo and F. Rodríguez

Abstract

Resol resins are used in many industrial applications as adhesives and coatings, but few studies have examined their thermal degradation. In this work, the thermal stability and thermal degradation kinetics of phenol–formaldehyde (PF) and lignin–phenol–formaldehyde (LPF) resol resins were studied using thermogravimetric analysis (TG) in air and nitrogen atmospheres in order to understand the steps of degradation and to improve their stabilities in industrial applications. The thermal stability of samples was estimated by measuring the degradation temperature (T d), which was calculated according to the maximum reaction rate criterion. In addition, the ash content was determined at 800 °C in order to compare the thermal stability of the resol resin samples. The results indicate that 30 wt% ammonium lignin sulfonate (lignin derivative) as filler in the formulation of LPF resin improves the thermal stability in comparison with PF commercial resin. The activation energies of degradation of two resol resins show a difference in dependence on mass loss, which allows these resins to be distinguished. In addition, the structural changes of both resins during thermal degradation were studied by Fourier transform infrared spectroscopy (FTIR), with the results indicating that PF resin collapses at 300 °C whereas the LPF resin collapses at 500 °C.

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Summary This paper reports excess molar enthalpies of the binary systems hexane+ethyl benzene, hexane+o-xylene, hexane+m-xylene and hexane+p-xylene at 298.15 K and atmospheric pressure, over the whole composition range. The data was measured directly using a Calvet microcalorimeter. The excess magnitude was correlated to a Redlich-Kister type equation for each mixture. Also, we will discuss the results for the four mixtures studied here and by comparison with the same binary systems but containing propyl propanoate as first component. Finally, we will correlate our results with the Nitta-Chao and the three UNIFAC theoretical approximations.

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Authors: S. Freire, L. Segade, S. García-Garabal, J. Jiménez de Llano, M. Domínguez and E. Jiménez

Abstract  

Excess molar enthalpies for the ternary mixture {propyl propanoate + hexane + chlorobenzene} and the binary mixtures {propyl propanoate + chlorobenzene} and {hexane + chlorobenzene} were determined at the temperature 298.15 K and normal atmospheric pressure. The experimental values were measured using a Calvet microcalorimeter. Excess molar enthalpies obtained were also used to test empirical expressions for estimating ternary properties from binary results.

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Authors: J. Murillo-Hernández, S. López-Ramírez, J. Domínguez, C. Duran-Valencia, I. García-Cruz and J. González-Guevara

Abstract  

A survey on the effect of ionic liquids (ILs) over the thermal stability of a heavy Mexican oil was performed. ILs used were based on [Cnim]+ and [Cnpyr]+ organic cations with FeCl4 metal anion. Mixtures of heavy crude oil (HCO) with ILs show three oxidation zones: low temperature oxidation (LTO), full deposition (FD) and high temperature oxidation (HTO). Thermal stability and mass loss decrease in the LTO zone but increase in the FD and HTO zones for every ILs used. The activation energy of the oxidation is influenced by the ILs in the HTO zone. It decreases when increasing the size of the organic radical substitute in the cation of the ILs while it increases with the presence of hydroxyl groups. The influence of electronic structure and reactivity indexes are rationalized to understand the variations of activation energy obtained of the reaction systems. Among all cations used, cation-3 (IL-3) shows the greater value of HOMO-LUMO gap as well as the lower activation energy.

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