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See detailPractical Methods for Measuring the Tortuosity of Porous Materials from Binary or Gray-Tone Tomographic Reconstructions
Gommes, Cédric ULg; Bons, Anton-Jan; Blacher, Silvia ULg et al

in AIChE Journal (2009), 55(8), 2000-2012

Two practical methods are proposed to measure the tortuosity of a porous or permeable material from its tomographic reconstruction. The first method is based on the direct measurement of the shortest ... [more ▼]

Two practical methods are proposed to measure the tortuosity of a porous or permeable material from its tomographic reconstruction. The first method is based on the direct measurement of the shortest distance between two points in the pores, and the second is based on the geodesic reconstruction of the pore or permeation space. Unlike the first method, the second can be directly applied to gray-tone tomograms, without the need of a segmentation step. The methods are illustrated with an electron tomogram of clay/plastic nanocomposite, an X-ray microtomogram of sandstone, and a series of model morphologies consisting of penetrable random spheres. For the latter series, the measured tortuosities compare very well with those derived independently from the theoretical effective diffusion coefficients [less ▲]

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See detailModeling of a continuous rotary reactor for carbon nanotube synthesis by catalytic chemical vapor deposition
Pirard, Sophie ULg; Bossuot, Christophe; Pirard, Jean-Paul ULg

in AIChE Journal (2009), 55

The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric ... [more ▼]

The modeling of carbon nanotube production by the CCVD process in a continuous rotary reactor with mobile bed was performed according to a rigorous chemical reaction engineering approach. The geometric, hydrodynamic, physical and physicochemical factors governing the process were analyzed in order to establish the reactor equations. While the study of the hydrodynamic factor suggests a co-current plug-flow approximation, the physical factor mainly deals with the phenomena of transport and the transfer of mass, which can be neglected. Concerning the physicochemical factor, the modeling is based on knowledge of the expression of the initial reaction rate, and takes into account catalytic deactivation as a function of time, according to a sigmoid decreasing law. The reactor modeling allows obtaining the evolution of partial pressure, carbon nanotube production and catalytic deactivation along the reactor for given initial operating conditions. The comparison between experimental and calculated production highlights a very good fit of data. (c) 2009 American Institute of Chemical lEngineers AIChE J, 55: 675-686, 2009 [less ▲]

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See detailDiagnosis of Process Faults in Chemical Systems Using a Local Partial Least Squares Approach
Kruger, Uwe; Dimitriadis, Grigorios ULg

in AIChE Journal (2008), 54(10), 2581-2596

This article discusses the application of partial least squares (PLS) for monitoring complex chemical systems. In relation to existing work, this article proposes the integration of the statistical local ... [more ▼]

This article discusses the application of partial least squares (PLS) for monitoring complex chemical systems. In relation to existing work, this article proposes the integration of the statistical local approach into the PLS framework to monitor changes in the underlying model rather than analyzing the recorded input/output data directly. As discussed in the literature, monitoring changes in model parameters addresses the problems of nonstationary behavior and presents an analogy to model-based approaches. The benefits of the proposed technique are that (i) a detailed mechanistic plant model is not required, (ii) nonstationary process behavior does not produce false alarms, (iii) parameter changes can be non-Gaussian, (iv) Gaussian monitoring statistics can be established to simplify the monitoring task, and (v) fault magnitude and signatures can be estimated. This is demonstrated by a simulation example and the analysis of recorded data from two chemical processes. [less ▲]

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See detailCarbon xerogels as catalyst supports: study of mass transfer
Job, Nathalie ULg; Heinrichs, Benoît ULg; Lambert, Stéphanie ULg et al

in AIChE Journal (2006), 52

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See detailRole of polylelectrolyte charge density in tuning colloidal forces
Abraham, T.; Christendat, D.; Xu, Z. et al

in AIChE Journal (2004), 50(10), 2613-2626

An atomic force microscope was used to study the effects of polymer charge density on surface interactions between similarly charged silica surfaces. Copolymers of acrylamide and acrylic acid of three ... [more ▼]

An atomic force microscope was used to study the effects of polymer charge density on surface interactions between similarly charged silica surfaces. Copolymers of acrylamide and acrylic acid of three different charge densities (f(p) = 15, 40, and 70%) were used The dynamic light-scattering technique was used to obtain the characteristic size of these polymers in solution. Flocculation tests were performed to complement force-distance measurement. At 20 mM KCl and pH similar to 8.0, the low charge density copolymer (f(p) = 15%) caused a purely repulsive force profile between silica surfaces irrespective of the added polymer concentration, suggesting a strong adsorption of the copolymer on the surface. The medium (f(p) = 40%) and high (f(p) = 70%) charge density copolymers, on the other hand, provided an adhesive bridging attraction at low polymer concentrations, but a purely repulsive force at higher polymer concentrations. The range of these repulsive forces, however, was significantly smaller than that measured for the low charge density polymer. The medium and high charge densities exhibit nearly an identical behavior in controlling the intersurface forces, although the forces are different with respect to magnitude. The flocculation tests follow the same trend as that of force-distance data, where a complete, a partial, and no flocculation observed with high, medium, and low charge density polymers, respectively. In all the cases, the range of surface interactions can be correlated with the polymer chain dimension corresponding to the fast diffusion process (individual chains) obtained from dynamic light-scattering measurements. Mean-field models proposed for charged polymers can qualitatively explain both the dependency of bridging interactions on polymer charge density and the dependency of force-distance profiles on added polymer concentrations. Finally, a mean-field model was used quantitatively to account for the measured electrosteric interactions and their dependency on polymer charge density. [less ▲]

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See detailMass transfer in low-density xerogel catalysts
Heinrichs, Benoît ULg; Pirard, Jean-Paul ULg; Schoebrechts, Jean-Paul

in AIChE Journal (2001), 47(8), 1866-1873

Texture and morphology of a Pd-Ag/SiO2 hydrodechlorination low-density xerogel catalyst prepared by a cogelation sot-gel process were characterized in detail to examine mass transfer in such catalysts ... [more ▼]

Texture and morphology of a Pd-Ag/SiO2 hydrodechlorination low-density xerogel catalyst prepared by a cogelation sot-gel process were characterized in detail to examine mass transfer in such catalysts. The catalyst consists of active Pd-Ag nanocrystallites trapped inside elementary 20 nm microporous silica particles arranged in larger aggregates, which constitute the macroscopic pellet. To reach active sites, reactants must first diffuse through large pores located between aggregates of SiO2 Particles and then through smaller pores located between those elementary particles inside the aggregates. Finally, they, diffuse through micropores located inside silica particles. Diffusion in such a "funnel" structure cannot be described assimilating the pellet to a pseudo-continuum. Diffusion should be examined carefully at three levels of decreasing size: the macroscopic pellet, the aggregate of silica particles, and the elementary silica particle. This approach shows that cogelled xerogel catalysts have remarkable mass-transfer properties. [less ▲]

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See detailLiquid distribution images on structured packing by X-ray computed tomography
Marchot, Pierre ULg; Toye, Dominique ULg; Pelsser, A. M. et al

in AIChE Journal (2001), 47(6), 1471-1476

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See detailStatistical hydrodynamics in trickle flow columns
Crine, Michel ULg; Marchot, Pierre ULg; L'Homme, Guy ULg

in AIChE Journal (1992), 38

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