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The reaction-diffusion performance for the Fischer-Tropsch reaction in a single cobalt catalyst particle is analysed, comprising the Langmuir-Hinshelwood rate expression proposed by Yates and Satterfield and a variable chain growth parameter a, dependent on temperature and syngas composition (H 2 /CO ratio). The goal is to explore regions of favourable operating conditions for maximized C 5+ productivity from the perspective of intra-particle diffusion limitations, which strongly affect the selectivity and activity. The results demonstrate the deteriorating effect of an increasing H 2 /CO ratio profile towards the centre of the catalyst particle on the local chain growth probability, arising from intrinsically unbalanced diffusivities and consumption ratios of H 2 and CO. The C 5+ space time yield, a combination of catalyst activity and selectivity, can be increased with a factor 3 (small catalyst particle, d cat = 50 mm) to 10 (large catalyst particle, d cat = 2.0 mm) by lowering the bulk H 2 /CO ratio from 2 to 1, and increasing temperature from 500 K to 530 K. For further maximization of the C 5+ space time yield under these conditions (H 2 /CO = 1, T = 530 K) it seems more effective to focus catalyst development on improving the activity rather than selectivity. Furthermore, directions for optimal reactor operation conditions are indicated.

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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 This type of sequential approach is increasingly been replaced by a parallel approach to catalyst and reactor selection.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.

Atomic layer deposition (ALD) is a promising technique for coating micrometer-and nanometer-sized particles. Due to the self-terminating nature of the ALD half-reactions, the coating thickness can be controlled to the atomic level by choosing the number of cycles in which the half-reactions are repeated. This technique is performed in a fluidized bed reactor, under atmospheric pressure. LiMn 2 O 4 particles (primary particles 200 À 500 nm in diameter) are coated with Al 2 O 3 to various thicknesses, ranging from 5 ALD cycles to 28 ALD cycles. The resulting coatings are homogeneous, and the individual particles are coated, rather than the agglomerates as a whole; however there are indications of some build-up of water -mainly in poresthat may be related to the use of atmospheric pressure. Quantitative characterization of the coating is difficult due to the powdered substrate.

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Gas flow pulsation was employed to improve the drying of porous pharmaceutical granules in a cylindrical fluidized bed. In our approach, a fraction of the total flow was oscillating intermittently and periodically, typically at 3 Hz during 2 min and remaining constant during the other 2 min of each 4 min cycle. It was found that such pulsation-assisted fluidization not only shortened the total drying time but also enhanced homogeneity. A transition in fluidization behavior, reflected by a distinct transition in the bed dominant frequencies, was observed.

The goal of the described project is to design mixtures of particles with optimal fluidization properties. Using high-throughput experimentation, a novel approach to study hydrodynamics in fluidized beds, the relevant properties can be obtained in a limited period of time. This approach is demonstrated by assessing the influence of particle size distribution on fluidized bed hydrodynamics of Geldart A powders. By manipulating the width of the particle size distribution of alumina powder, the bubble diameter is reduced up to 40%. The addition of fines to a given particle size distribution also decreases the bubble diameter up to 40%, whereas the addition of coarse particles hardly influences the bubble size. At low gas velocities, the bubble size was found to increase with fines addition or increasing standard deviation. V