Claudio Olivera-Fuentes

Thermal properties of supercritical carbon dioxide by Monte Carlo simulations

We present simulation results for the volume expansivity, isothermal compressibility, isobaric heat capacity, Joule-Thomson coefficient and speed of sound for carbon dioxide (CO 2 ) in the supercritical region, using the fluctuation method based on Monte Carlo simulations in the isothermal-isobaric ensemble. We model CO 2 as a quadrupolar two-center Lennard-Jones fluid with potential parameters reported in the literature, derived from vapor-liquid equilibria (VLE) of CO 2 . We compare simulation results with an equation of state (EOS) for the two-center Lennard-Jones plus point quadrupole (2CLJQ) fluid and with a multiparametric EOS adjusted to represent CO 2 experimental data. It is concluded that the VLE-based parameters used to model CO 2 as a quadrupolar two-center Lennard-Jones fluid (both simulations and EOS) can be used with confidence for the prediction of thermodynamic properties, including those of industrial interest such as the speed of sound or Joule-Thomson coefficient, for CO 2 in the supercritical region, except in the extended critical region.

HYDRODYNAMICS OF LAMINAR LIQUID JETS. EXPERIMENTAL STUDY AND COMPARISON WITH TWO MODELS

Laminar jets of Newtonian liquids issuing from long vertical cylindrical nozzles and falling freely through stagnant air were studied experimentally for Reynolds numbers between 300 and 1000. Jet diameters were measured from still photographs, and radial distributions of axial velocity were obtained by laser Doppler anemometry. The effect of nozzle diameter, fluid viscosity and surface tension was investigated. The experimental results were compared with numerical solutions of the Protean coordinate model developed by Duda and Vrentas. The boundary layer simplifications were confirmed to be valid only for the downstream region of the jet and for Reynolds numbers greater than 1000. The experimental diameters were also compared with predictions from a form of the Bernoulli equation with a surface tension term. The asymptotic validity of the model was confirmed, provided that the dissipation term arising from fluid viscosity could be neglected. Neither model correlated the jet formation region satisfactorily...

Convective Drying of Gels: Comparison Between Simulated and Experimental Moisture Profiles Obtained by X-ray Microtomography

In this article, internal moisture profiles obtained either by simulation or experimentally during the convective drying of resorcinol-formaldehyde gels are compared. Such a comparison constitutes an attractive way to validate drying simulation models. X-ray microtomography, a powerful 3D imaging technique, coupled to image analysis is used to determine the internal moisture profiles in a nondestructive way. A thermo-hygro-mechanical coupled model is used to simulate the moisture profiles developing during drying. Resorcinol-formaldehyde gels are used because their degree of shrinkage can be easily controlled. Results show a fairly good agreement between experimental and simulated profiles, especially at high moisture contents.

Prediction of the Joule–Thomson inversion curve of air from cubic equations of state

Abstract A modified van der Waals equation of state recommended in the literature for improved prediction of the inversion curve of air is shown to be thermodynamically inconsistent, giving large errors in the critical and two-phase regions. An alternative procedure is presented by means of which the cohesion function of any cubic equation of state can be adjusted to give arbitrarily accurate representation of an experimental inversion curve. New versions of the van der Waals, Redlich–Kwong and Peng–Robinson equations of state are developed based on experimental inversion data of air, and are shown to give better inversion predictions than more complex, multiparameter noncubic equations of state.

Selective hydrogenation of 1,3-butadiene in presence of 1-butene under liquid phase conditions with NiPd/Al2O3 catalysts

The catalytic performance of Al2O3-supported monometallic and bimetallic catalysts in selective hydrogenation of 1,3-butadiene in the presence of 1-butene under liquid phase conditions was studied. Bimetallic catalysts were prepared by the coimpregnation method with the required amounts of the precursors salts [Ni(NO3)2·6H2O and Pd(NH3)4Cl2·H2O] over pellet-form γ-Al2O3 with a constant content of Pd (0.5 wt%) and varying Ni/Pd atomic ratio (0.25, 0.5, 0.75, and 1) obtaining egg-shell profiles of the active components. The catalysts were characterized by X-ray diffraction, temperature-programmed techniques, such as reduction in hydrogen and desorption of ammonia, N2 physisorption, and transmission electron microscopy. The catalytic test showed that the 1,3-butadiene was selectively hydrogenated when bimetallic catalysts were used. The addition of Ni to the Pd-based catalysts suppressed n-butane formation and increased recovery of 1-butene at medium conversion. Therefore, it was observed an improved catalytic performance of the bimetallic catalysts being highest in the case of the 1NiPd/Al2O3.

THE EXACT PENETRATION MODEL OF DIFFUSION IN MULTICOMPONENT IDEAL GAS MIXTURES. ANALYTICAL AND NUMERICAL SOLUTIONS

An exact analytical solution is derived for the penetration model of diffusion in multicomponent ideal gas mixtures at constant pressure and temperature. It takes the form of a matrizant solution to the continuity and Maxwell-Stefan equations transformed by introduction of a similarity variable, and includes as special cases the corresponding binary and linearized theory solutions Direct numerical implementation of the analytical solution is computationally inefficient, but an alternative finite-difference algorithm is developed in which the transformed equations are solved by Eulers method with a simple shooting technique. Sample calculations are reported for two ternary diffusion problems It is concluded on the basis of the theoretical and numerical results that the linearized theory predictions should provide an excellent approximation to the exact solution of the penetration model.

Three-Parameter Corresponding-States Correlations for Joule–Thomson Inversion Curves

In the present work, the Lee–Kesler (LK) and Boublík–Alder–Chen–Kreglewski (BACK) equations of state were used to compute Joule–Thomson inversion curves for nonsimple fluids. Comparisons with available data showed that predictions were quite reliable and could be used in place of experimental values. Two sets of corresponding-states correlations were developed, giving reduced inversion pressures and densities as functions of reduced temperature and acentric factor. The LK-based correlations are valid for Tr≤4.0, giving an average absolute deviation (AAD) of 4.5% for pressures. The BACK-based correlations are valid up to the maximum inversion temperature and give a 6.7% AAD for pressures. Respective volume AADs are 12.0 and 8.0% in the high-density region.

MULTICOMPONENT FUGACITY COEFFICIENTS AND RESIDUAL PROPERTIES FROM PRESSURE-EXPLICIT EQUATIONS OF STATE

Abstract A procedure presented by Szarawara and Gawdzik (1989) for development of expressions for the fugacity coefficients of components of a fluid mixture from cubic equations of state (EOS) is extended to the generation of similar formulas for the residual enthalpy and entropy, and is shown to relate to a more fundamental Helmholtz energy approach. The method is not limited to cubic EOS, but applies in general to any pressure-explicit EOS with parameters dependent on temperature and composition. A general step-by-step application sequence is presented. The method is illustrated with three examples: the Benedict—Webb—Rubin and Benedict—Webb—Rubin—Starling EOS, the general class of perturbed hard-core models (with the Carnahan—Starling—van der Waals EOS as a particular case), and a generalized four-parameter cubic EOS of the Schmidt—Wenzel type. The existence of a common functional form for all the residual properties from each of these EOS is demonstrated. The method is highly flexible, making it straightforward to insert different temperature functions and mixing rules into a given EOS model, or to explore new combinations of volume functions taken from different models.

Promoting effect of ceria on the performance of NiPd/CeO2–Al2O3 catalysts for the selective hydrogenation of 1,3-butadiene in the presence of 1-butene

The removal of traces of highly unsaturated compounds, such as 1,3-butadiene, from olefin feedstocks via selective hydrogenation is of particular importance because the oligomerization of these impurities produces deactivation and an increased pressure drop across the catalytic beds used in the polymerization processes. The present work focuses on the selective hydrogenation of 1,3-butadiene in the presence of 1-butene using (xCeO2-)Al2O3-supported NiPd catalysts (x = 0, 1, 2, and 3 wt% CeO2) in both liquid and gas conditions. The samples were characterized by XRD, N2 physisorption, Zeta potential, H2-TPR, NH3-TPD, HRTEM and STEM-HAADF. Modifying the catalysts with CeO2 resulted in an increase of 1,3-butadiene conversion, an enhancement of 1-butene selectivity and a decrease of butane production under liquid phase conditions. In contrast, in the gas phase both the Ce-modified and unmodified catalysts behaved similarly: while the fresh catalysts showed similar reactivity to that found in liquid phase conditions, the reacted and thermally pretreated catalysts showed increased reactivity, leading to full hydrogenation up to butane. The improvements observed under liquid phase conditions may be related to modification of the acid strength with increasing CeO2 loading, which would increase the adsorption of 1,3-butadiene and diminish the further hydrogenation of 1-butene. Optimal activity and selectivity were observed for the catalyst with an Ni/Pd atomic ratio of 1, and loadings of 0.5 wt% Pd and 3.0 wt% CeO2.