Trickle-bed reactors mass transfer in

Liquid-solid mass transfer in trickle-bed reactors... 

I. Iliuta, A. Ortiz-Arroys, F. Larachi, B.P.A. Grandjean and G. Wild, Hydrodynamics and mass transfer in trickle-bed reactors an overview, Chem. Engng. Science, 54 (1999) 5329-5337. 

F. Larachi, M. Cassanello and A. Laurent, Gas-liquid interfacial mass transfer in trickle-bed reactors at elevated pressures, Ind. Engng. Chem. Res., 37 (1998) 718-734. 

Iliuta I, Larachi F, Grandjean BPA, Wild G. Gas-Uquid interfacial mass transfer in trickle-bed reactors state-of-the-art correlations. Chem. Eng. Sci. 1999 54 5633. 

Herskowitz, M., R. G. Carbonell and J. M. Smith. Effectiveness Factors and Mass Transfer in Trickle-Bed Reactors. 

Turek, F.and R. Lange. Mass Transfer in Trickle-Bed Reactors at Low Reynolds Nuntoer. Chem. Eng. Sci. 36 (1981) 569-579. Turpin, J. L. and R. L. Huntington. Prediction of Pressure Drop for Two-Phase, Two-Component Concurrent Flow in Packed Beds. AICHE J. 13 (1967) 1196-1202,... 

Specchia, V., G, Baldi and A. Gianetto, "Solid-Liquid Mass Transfer in Trickle Bed Reactors", Proc, 4th ISCRE, (1976) 656-662 Heidelberg, Germany,... 

Cocurrent packed columns - Trickle-bed reactgr. Cocurrent gas-liquid flow in packed beds, packing being either catalytic or inert, is advantageously employed in the petroleum and chemical industries. Successful modeling of mass transfer in packed-bed reactors requires careful study of the three-pliase hydrodynamics - fluid flow patterns, pressure drops, and liquid holdup. 

The reaction is carried out using a Pt/Al203 catalyst [11,12]. Information on this reaction when conducted in trickle-bed reactors is available, comprising flow-pattern maps, kinetic data, mass transfer data and energy dissipation data (see original citations in [11]). 

In multiphase reactors we frequently exploit the density differences between phases to produce relative motions between phases for better contacting and higher mass transfer rates. As an example, in trickle bed reactors (Chapter 12) liquids flow by gravity down a packed bed filled with catalyst, while gases are pumped up through the reactor in countercurrent flow so that they may react together on the catalyst surface. 

In packed-bed reactors, the catalyst is fully wetted, whereas the heat and mass transfer efficiency is higher than that observed in trickle-bed reactors. However, low operation efficiency may appear due to backmixing of the liquid phase. Moreover, high liquid-phase residence times can result in the occurrence of homogeneous side reactions. 

Failing to identify the limiting reactant can lead to failure in the scale-up of trickle-bed reactors (Dudukovic, 1999). Gas-limited reactions occur when the gaseous reactant is slightly soluble in the liquid and at moderate operating pressures. For liquid-limited reactions, concurrent upflow is preferred (packed bubble columns) as it provides for complete catalyst wetting and thus enhances the mass transfer from the liquid phase to the catalyst. On the other hand, for gas reactions, concurrent downflow operation (trickle-bed reactors), especially at partially wetted conditions, is preferred as it facilitates the mass transfer from the gas phase to the catalyst. The differences between upflow and downflow conditions disappear by the addition of fines (see Section 3.7.3, Wetting efficiency in trickle-bed reactors). 

N. Midoux, B.I. Morsi, M. Purwasasmita, A. Laurent and J.C. Charpentier, Interfacial area and liquid-side mass transfer coefficient in trickle-bed reactors operating with organic liquids, Chem. Engng. Science, 39 (1984) 781-794. 

The above discussion on previous experimental studies in trickle-bed reactors suggests that both liquid-solid contacting and mass transfer limitations play a role in affecting trickle-bed reactor performance. Except for a few isolated cases, the reactor models proposed in the literature for gaseous reactant limiting reactions have not incorporated particle-scale incomplete contacting as paft of their development. For cases where it was used, this parameter served as an adjustable constant to match the observed conversion versus liquid mass velocity data so that the true predictive ability of the model... 

Fundamentals The basic reaction and transport steps in trickle bed reactors are similar to those in slurry reactors. The main differences are the correlations used to determine the mass transfer coefficients. In addition, if there is more than one component in the gas phase (e.g., liquid has a high vapor pressure or one of the entering gases is inert), there is one additional transport step in the gas phase. Figure 12-17shows the various transport steps in trickle bed reactors. Following our analysis for slurry reactors we develop the equations for the rate of transport of each step. The steps involving reactant A in the gas phase are... 

Nigam, K.D.P. Iliuta, I. Larachi, F. Liquid back-mixing and mass transfer effects in trickle-bed reactors filled with porous catalyst particles. Chem. Eng. Process. 2002, 41, 365. 

Liquid-solid. Transport between the liquid and solid (catalyst) phases in trickle-bed reactors is at least a first cousin to transport in more conventional fixed beds, and our understanding of the liquid phase mass-transfer coefficient here benefits from the decades of research devoted to that topic. A good correlation was reported as far back as 1948 by Van Krevelen and Krekels [D.W. Van Krevelen and J.T.C. Krekels, Rec. Trav. Chim. Pays-Bas, 67, 512 (1948)], who proposed... 

One often finds that either external or intraparticle mass transfer effects are significant in trickle bed reactors. Although the treatments of these topics outlined in Sections 12.3 and 12.4 are in general applicable to trickle bed reactors, analyses specific to such reactors have been reviewed by Gianetto and Specchia (3). 

Most common in practice is a trickling flow that occurs at relatively low gas and liquid flow rates. Under these conditions in trickle-bed reactors (TBRs) complete liquid films around the particles would break up into partial films, rivulets and droplets and a so-called partial wetting trickling regime exist. It is easier for hydrogen to enter the no wetted or very thin wetted part of partially wetted catalyst pellets because the mass-transfer resistance between a gas and the particle sur-... 

---