Conventional and emerging processes that require the application of multiphase reactors are reviewed with an emphasis on catalytic processes. In the past, catalyst discovery and development preceded and drove the selection and development of an appropriate multiphase reactor type. This sequential approach is increasingly being replaced by a parallel approach to catalyst and reactor selection. Either approach requires quantitative models for the flow patterns, phase contacting, and transport in various multiphase reactor types. This review focuses on these physical parameters for various multiphase reactors. First, fixed-bed reactors are reviewed for gas-phase catalyzed processes with an emphasis on unsteady state operation. Fixed-bed reactors with two-phase flow are treated next. The similarities and differences are outlined between trickle beds with cocurrent gas–liquid downflow, trickle-beds with countercurrent gas–liquid flow, and packed-bubble columns where gas and liquid are contacted in coc...

Multiphase catalytic reactors: a perspective on current knowledge and future trends

A double-slit model developed can predict the frictional two-phase pressure drop, external liquid holdup, pellet-scale external wetting efficiency, and gas–liquid interfacial area in cocurrent downflow trickle-bed reactors operated under partially wetted conditions in the trickle flow regime. The model, an extension of the Holub et al. (1992, 1993) mechanistic pore-scale phenomenological approach, was designed to mimic the actual bed void by two inclined and interconnected slits: wet and dry slit. The external wetting efficiency is linked to both the pressure drop and external liquid holdup. The model also predicts gas–liquid interfacial areas in partially wetted conditions. An extensive trickle-flow regime database including over 1,200 measurements of two-phase pressure drop, liquid holdup, gas–liquid interfacial area and wetting efficiency, published in 1974–1998 on the partial-wetted conditions, was used to validate the modeling approach. Two new improved slip-factor functions were also developed using dimensional analysis and artificial neural networks. High-pressure and -temperature wetting efficiency, liquid holdup, pressure drop, and gas–liquid interfacial area data from the literature on the trickle-flow regime using conventional monosized beds and catalyst bed-dilution conditions were successfully forecasted by the model.

Double‐slit model for partially wetted trickle flow hydrodynamics

Gas}liquid interfacial mass transfer in trickle-bed reactors: state-of-the-art correlations

Meticulous inspection of the literature has unveiled the weakness of several empirical methods for predicting the macroscopic mass- and heat-transfer characteristics relevant to gas−liquid cocurrent downflow and upflow packed-bed reactors. In response, using a wide experimental database consisting of 5279 measurements for trickle beds (downflow) and 1974 measurements for packed bubble columns (upflow), a set of reliable correlations has been recommended for the prediction of the gas−liquid interfacial area (agl), the volumetric liquid- (kla) and gas-side (kga) mass-transfer coefficients, the wall (ηeklw) and bed (ηekls) liquid−solid mass-transfer coefficients, the wall heat-transfer coefficient (hw), the bed effective radial thermal conductivity (λe), and the particle-to-fluid heat-transfer coefficient (hp). Some of these correlations are from the literature, and others have been developed by combining artificial neural networks and dimensional analysis. The accuracy of the proposed correlations surpasses...

http://fs.teledos.gr:2206/%3ERESEARCH%20PUBLICATIONS/CHEMICAL%20ENGINEERING/Mass%20Transfer/Heat%20and%20Mass%20Transfer%20in%20Cocurrent%20Gas-Liquid%20Packed%20Beds.%20Analysis,%20Recommendations,%20and%20New%20Correlati.pdf

Heat and Mass Transfer in Cocurrent Gas−Liquid Packed Beds. Analysis, Recommendations, and New Correlations

A phenomenological description and a semiempirical two-zone model are proposed for the gas−liquid interfacial areas and the volumetric liquid-side mass-transfer coefficients in cocurrent downflow t...

http://fs.teledos.gr:2206/%3ERESEARCH%20PUBLICATIONS/CHEMICAL%20ENGINEERING/Mass%20Transfer/Gas-Liquid%20Interfacial%20Mass%20Transfer%20in%20Trickle-Bed%20Reactors%20at%20Elevated%20Pressures.pdf

Gas-liquid interfacial mass transfer in trickle-bed reactors at elevated pressures

Interfacial area in cocurrent gas-liquid downflow through packed beds is correlated taking into consideration the physical properties of the fluids and the power dissipation in the system. The correlation is tested with the experimental data covering a wide range in system variables including low and high porosity packings, the flow rates of the phases and their physical properties.

D. Venkata Narasaiah

Papers

A correlation for interfacial area in co-current gas-liquid downflow through packed beds