Bubble columns staged with structured fibrous catalytic layers: Residence time distribution and mass transfer

A new reactor concept for catalyzed three-phase reactions based on the use of woven fibrous materials for bubble columns is suggested. In comparison to conventional multistage bubble columns, the trays are made from woven fibrous catalytic layers. The hydrodynamic parameters such as the residence time distribution (RTD) and the volumetric gas-liquid mass transfer coefficient k(L)a are investigated in an air/water system for different layer structures and different superficial gas (u(g0) < 60 cm/s) and liquid (u(10) < 6 cm/s) velocities. The major reactor design parameters, such as the thread diameter D, the distance between the woven threads w, and the distance between the fibrous layers b, are discussed.

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Volker Höller, Lioubov Kiwi, Albert Renken
2001
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https://infoscience.epfl.ch/record/84711?ln=en

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Mass transfer

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Fluid dynamics

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CFD modelling of liquid–liquid multiphase microstructured reactor: Slug flow generation

Madhvanand Namadeo Kashid, Lioubov Kiwi, Albert Renken

Microreactor technology, an important method of process intensification, offers numerous potential benefits for the process industries. Fluid–fluid reactions with mass transfer limitations have already been advantageously carried out in small-scale geometries. In liquid–liquid microstructured reactors (MSR), alternating uniform slugs of the twophase reaction mixture exhibit well-defined interfacial mass transfer areas and flow patterns. The improved control of highly exothermic and hazardous reactions is also of technical relevance for large-scale production reactors. Two basic mass transfer mechanisms arise: convection within the individual liquid slugs and diffusion between adjacent slugs. The slug size in liquid–liquid MSR defines the interfacial area available for mass transfer and thus the performance of the reactor. There are two possibilities in a slug flow MSR depending on the interaction of the liquids with the solid wall material: a dispersed phase flow in the form of an enclosed slug in the continuous phase (with film—complete wetting of the continuous phase) and an alternate flow of two liquids (without film—partial wetting of the continuous phase). In the present work, a computational fluid dynamics (CFD) methodology is developed to simulate the slug flow in the MSR for both types of flow systems. The results were validated with the experimental results of Tice et al. (J.D. Tice, A.D. Lyon and R.F. Ismagilov, Effects of viscosity on droplet formation and mixing in microfluidic channels, Analytica Chimica Acta 507 (1) (2004), pp. 73–77.).

Elsevier2010

Incremental Model Identification of Gas-Liquid Reaction Systems with Unsteady-State Diffusion

Julien Léo Billeter, Dominique Bonvin, Benoit Till Cretegny, Sriniketh Srinivasan

Identification of kinetic models and estimation of reaction and mass-transfer parameters can be performed using the extent-based identification method, whereby each chemical/physical process is handled separately [1-3]. This method is used here to analyze gas-liquid systems under unsteady-state mass transfer. Such a situation is common in the case of diffusion-controlled reactions and is modeled by the film theory, that is, transferring species accumulate in a liquid film. In both the gas and liquid bulks, mass-balance relations describe the species dynamics as ordinary differential equations (ODE) and serve as boundary conditions for the film. On the other hand, the dynamic accumulation in the film is described by Fick’s second law. The resulting partial differential equation (PDE) system is solved by discretization and rearrangement in ODEs. The estimation of diffusion coefficients follows a two-steps procedure. First, the extents of mass transfer are computed from measurements in the two bulks. Diffusion coefficients are then estimated individually by fitting each extent of mass transfer to the extent obtained by solving the corresponding PDE. Comparison of the estimated diffusion coefficients with their literature values serves to validate the models identified in the two bulks. The estimation of both kinetic parameters and diffusion coefficients is investigated for gas-liquid reaction systems with unsteady-state diffusion. The approach is illustrated with simulated examples. [1] Bhatt et al, Ind. & Eng. Chem. Res. 50, 12960-12974, 2011 [2] Srinivasan et al, Chem. Eng. J. 208, 785-793, 2012 [3] Billeter et al, Anal. Chim. Acta 767, 21-34, 2013

2013