F. Larachi

Liquid saturation in cocurrent upflow fixed-bed reactors : a state-of-the-art correlation

On the basis of a large data bank consisting of more than 2600 experimental results published for cocurrent upflow fixed-bed reactors, a state-of-the-art correlation for the prediction of external liquid saturation was proposed. The correlation relied upon combination of dimensional analysis and artificial neural networks which allowed identification of six most expressive dimensionless groups. Robustness of proposed correlation was assessed by testing it on a huge test data file, and the limitations of the literature correlations with regard to their generalization capabilities were demonstrated.

Catalytic oxidation of 4-chloroguaiacol reaction kinetics and catalytic studies

Abstract This paper describes the non-catalytic oxidation and the solid-catalysed oxidation of a chlorinated organo-compound contained in softwood pulp mill effluents. The oxidation of 4-chloroguaiacol was catalysed efficiently using Pt/alumina, manganese/cerium and cobalt/bismuth composite oxide catalysts. Self-inhibition of the parent pollutant, recalcitrance of highly stable organic by-products, and catalyst deactivation were the main causes that prevented full mineralization of the waste-water organic load. A comprehensive homogeneous–heterogeneous deactivation reaction network model was used to account for the distribution of carbon in the liquid, in the gas and on the solid phases. The model combined a two-parallel reaction scheme for the non-catalytic oxidation and a Langmuir–Hinshelwood approach for the catalyst-mediated oxidation.

Catalyst Wetting in Trickle-Flow Reactors: A Phenomenological Model

A phenomenological model was developed to describe the effect of pressure, gas and liquid flow rates on pellet-scale external wetting efficiency in trickle flow reactors. External wetting efficiency was linked to both pressure drop and liquid holdup. Shear slip factor, Ergun creeping flow constant, liquid holdup and two-phase pressure drop required by the model were calculated using a set of hybrid neural network dimensionless correlations based on an extensive trickle flow regime database.

Nu/Sh Correlation for Particle-Liquid Heat and Mass Transfer Coefficients in Trickle Beds Based on Péclet Similarity

Knowledge of the particle to liquid heat and mass transfer coefficients in trickle beds is important, particularly in contexts where exothermic reactions impede liquid replenishment over dried spots in the catalyst bed, or when the transport, especially in liquid-limited reactions, is curbed by excessive liquid–solid interfacial resistance. Although particle–liquid heat and mass transfer coefficients in trickle beds are linked to each other, the known Chilton–Colburn analogy or similar failed to yield a single Nu/Sh correlation to quantify both heat and mass transfer phenomena at the pellet scale. In this work, a single correlation embedding the heat and mass transfer information into a Peclet number was derived and validated over 1259 particle–liquid heat and mass transfer coefficients in trickle beds. Depending on whether a heat or a mass Peclet number was used, the proposed correlation predicted Nu and Sh numbers with average absolute relative errors of 18 and 22%, respectively. In particular, when equal heat and mass Peclet numbers occur, under physically and geometrically similar conditions, the correlation predicts true analogy between heat and mass transfer at the pellet level.

Hydrodynamic Continuum Model for Gas–Liquid Fixed Beds Operating in Trickle Flow and Pre-Loading Regimes

A one-dimensional two-fluid continuum model based on the volume-average mass and momentum balance equations was developed for the prediction of the two-phase pressure drop and the total liquid hold-up in co-current down-flow and counter-current fixed-bed reactors operating respectively in the trickle flow regime and in the pre-loading zone. The slit model drag force closures, as well as the drag closures derived from the modified Kozeny–Carman theory based on a two-dimensional tortuosity model, were adapted. The inertial term in the drag force expressions was corrected to predict satisfactorily the two-phase pressure drops at high pressures. Wall effect functions were incorporated into the drag force equations. Associating the drag forces based on the modified Kozeny–Carman theory and the presently developed continuum model resulted in a fully predictive tool with no adjustable parameter both in co-current down-flow and counter-current flow.