Structured Packings for Multiphase Catalytic Reactors

Abstract

Reactor design for multiphase catalytic fixed bed reactors is always based on conflicting objectives. In the past, catalyst discovery and development preceded and motivated the selection of an appropriate multiphase reactor type. This type of sequential approach is increasingly been replaced by a parallel approach to catalyst and reactor selection. In nearly all respects, structured catalysts and reactors have the ability to outperform randomly packed reactors. Structured packings, apart from their advantages of high voidage and low-pressure drop, have the benefit of ease of scale-up and accurate description of the fluid mechanics. In this review we have evaluated the potential of using structured internals for multiphase catalytic reactions, which are currently carried out in randomly packed fixed bed reactors. Characteristics of various structured internals such as monoliths, corrugated sheet or gauze packings, knitted wire packings and foams are discussed in detail. Since designing a structured device for gas-liquid-solid contacting requires a sound knowledge of hydrodynamics and transport phenomena, a concise review of the above-mentioned structured packings and their characteristics based on hydrodynamics and transport phenomena is presented. Existing models (empirical, phenomenological and mechanistic) are outlined with respect to flow regime transition, pressure drop, liquid hold-up, gasliquid interfacial area, gas to liquid mass transfer, liquid to solid mass transfer, residence time distribution (RTD), and heat transfer. The models are critically evaluated, and their limitations are discussed. An overview is given about what information is available, what needs to be evaluated and what kind of existing methodology can be applied in order to arrive at quantitative models for the physical parameters. Last, the structured internals are compared with each other and with randomly packed bed reactors, allowing a rational selection of the preferred packing for a given application.

Selected problems of gas-liquid flow through the channels filled with metal foams

“…A comparison of the heat transfer in the column with various types of packing, conducted by Pangarkar et al [19] demonstrates that metal foams can be put on the list of the category of packings in which the heat transfer occurs with a high intensity. Another advantage resulting from the application of foams in the packed columns (used in the place of other packings) is associated with the decrease of the pressure drop.…”

Microstructured Reactors for Multiphase Reactions: State of the Art

“…Moreover, when applied in the continuous mode, back mixing usually lowers selectivity. 54 Gas-liquid reactions catalyzed by solids represent a very important class of reactions. They may be carried out in either slurry (such as bubble column, stirred tank, and gas-liquid MSR process development and demonstration of industrial production Merck, 17 SK Chemicals, 18 Ampac Fine Chemicals, 19 Phoenix Chemicals, 20 Clariant GmbH, 21 DSM, 16,22,23 Lonza, 24,25 Sigma-Aldrich fluidized configurations) or fixed-bed reactors (trickle bed with cocurrent downflow or cocurrent upflow, segmented bed, and countercurrent gas-liquid arrangements).…”

High-performance monoliths in heterogeneous catalysis with single-phase liquid flow

“…To avoid intrinsic coupling of the characteristic diffusion length (L diff ) inside the fully porous catalyst particles with the characteristic dimension of the flow channels (L flow ) between the particles in a fixed-bed reactor, hierarchically structured monoliths have been used as alternative supports for heterogeneously catalyzed reactions. [5][6][7][8][9] They allow to combine the continuous-flow operational advantages of a fixed-bed over a slurry reactor with a much larger morphological flexibility than for particulate packings. This is illustrated by Fig.…”

“…1 offers a regular structure, i.e., the repeated microchannel pattern of square cells. 5,7 Therefore, structures can be designed with all essential details up to the macroscopic confinement of a catalyst. It offers full control over local environments, including the interplay as well as separate optimization of the intrinsic reaction kinetics, transport phenomena, and hydrodynamics.…”

“…1 have been efficiently used in practical applications, 7 particularly in combination with slug (or Taylor) flow to realize liquid-gas transport that combines low pressure drop with high mass transfer rates (good mixing on slug level) and almost plug-flow behavior (little longitudinal mixing). 5,13 Compared with this solid-liquid-gas and also the wellestablished solid-gas processing, where flow-through pores approach millimeter-dimension to guarantee a high permeability and low energy consumption, the application of monolithic supports for solid-liquid catalysis with single-phase liquid flow still emerges from a niche for low-temperature processes, particularly in the continuous-flow production of pharmaceuticals and fine chemicals. 2,6,8,[14][15][16][17][18][19][20] However, for liquid flow operation, millimeter-sized channels are unsuitable, as they lead to excessive longitudinal mixing (due to the parabolic pore-level flow profile under laminar conditions) and long lateral diffusion times for reactants in the flow channels to reach the external surface area and enter the internal pore space with the active surface.…”