Experimental analysis and evaluation of the mass transfer process in a trickle-bed reactor

A transient experimental analysis of a three-phase descendent-cocurrent trickle-bed H2O/CH4-Ar/g -Al2O3 system was made using the stimulus-response technique, with the gas phase as a reference. Methane was used as a tracer and injected into the argon feed and the concentration vs time profiles were obtained at the entrance and exit of the bed, which were maintained at 298K and 1.013 10(5) Pa. A mathematical model for the tracer was developed to estimate the axial dispersion overall gas-liquid mass transfer and liquid-solid mass transfer coefficients. Experimental and theoretical results were compared and shown to be in good agreement. The model was validated by two additional experiments, and the values of the coefficients obtained above were confirmed

MASS TRANSFER IN PORE STRUCTURES OF SUPPORTED CATALYSTS

The effects of gas-solid interaction and mass transfer in fixed-bed systems of supported catalysts were analyzed for <FONT FACE="Symbol">g</font> -Al2O3 (support) and Cu/<FONT FACE="Symbol">g</font> -Al2O3 (catalyst) systems. Evaluations of the mass transfer coefficients in the macropores and of the diffusivity in the micropores, as formed by the crystallite agglomerates of the metallic phases, were obtained. Dynamic experiments with gaseous tracers permitted the quantification of the parameters based on models for these two pore structures. With a flow in a range of 18 cm3 s-1 to 39.98 cm3 s-1 at 45oC, 65oC and 100oC, mass transfer coefficients km =4.33x10-4 m s-1 to 7.38x10-4 m s-1 for macropore structures and diffusivities D<FONT FACE="Symbol">m</font> =1.29x10-11 m2 s-1 to 5.35x10-11 m2 s-1 for micropore structures were estimate

On the dynamics of nonequilibrium simple batch distillation processes

The study of the dynamics of a simple batch distillation usually assumes the equilibrium between the liquid and vapour phases. In contrast to that approach, this work considers the analysis of the dynamic behaviour of a nonequilibrium simple batch distillation. A simple batch distillation device is similar to an evapouration unit because no reflux is employed. A mathematical model and their singular points are analysed through the usual technique of linearization followed by the eigenvalues analysis. The stability nature of those points is presented for ideal solutions. Phase plane plots are made to show the occurrence of some unexpected behaviours such as 'dynamic azeotropic points' and 'inversion of the distillation order'. The dependence of these phenomena on the vapour withdrawal flowrate is established for simple batch distillation. (C) 2002 Elsevier Science B.V. All rights reserved.42647548

Caracterização físico-química da superfície de filmes de poli(tereftalato de etileno)

Dentre as diversas técnicas de caracterização superficial de filmes poliméricos, foram utilizadas nos filmes de PET do presente estudo a refratometria, rugosidade, análises de coeficiente de atrito e ângulo de contato. As amostras de filmes de PET analisadas têm 12mim de espessura e compreendem três tipos de estuturas superficiais: filme de homopolímero PET, filme PET com tratamento corona e filme de poli(tereftalato de etileno-co-ciclohexanodimetanol). O filme com tratamento corona apresentou o maior valor de tensão superficial em função da maior parcela dos grupos polares. Resultados de índice de refração indicam que a superfície do filme com copoliéster é menos cristalina que as superfícies dos demais filmes avaliados. A estruturas amorfa e elevado nível de tensão superficial de filmes tratados deverão favorecer a um aumento dos níveis de adesão a tintas e revestimentos