Catalyst thickness

Figure 10.20 Effect of radius ratio on conversion of reactant A at reactor exit with (a) constant throughput and constant catalyst thickness and (b) constant throughput and constant catalyst volume. [Akyurtlu et al., 1988]...

Cybulski et al. [39] have studied the performance of a commercial-scale monolith reactor for liquid-phase methanol synthesis by computer simulations. The authors developed a mathematical model of the monolith reactor and investigated the influence of several design parameters for the actual process. Optimal process conditions were derived for the three-phase methanol synthesis. The optimum catalyst thickness for the monolith was found to be of the same order as the particle size for negligible intraparticle diffusion (50-75 p.m). Recirculation of the solvent with decompression was shown to result in higher CO conversion. It was concluded that the performance of a monolith reactor is fully commensurable with slurry columns, autoclaves, and trickle-bed reactors. 

Figure 16 is constructed for = 10 m and = 0.50. The highest STY is obtained for the TBR using the smallest particles possible. The pressure drop is approximately 5 bar, which is close to what can be accepted. Both pressure drop and STYy decrease fast with increasing particle size, and for the 2-mm particles the STYy has dropped below the highest STYy that can be reached with the washcoated MR. For both reactors the selectivity decreases with increasing catalyst thickness. Selectivity is higher for the MR. The diffusion... 

Water-phase PCO studies indicate that there exists an optimum catalyst thickness beyond which no improvement in rate occurs due to mass transfer limitations, once the activation of the catalysts sites by photons is accomplished (18). Rate of diffusion of adsorbates from the interior surface of the adsorbent to the exterior where the reaction takes place limits the overall process. An optimum Ti02 concentration usually occurs at 0.5-1 g/L of Ti02 solution. A much lower optimal Ti02 dosage of 0.1 g/L was achieved in a study where PCO was applied to treat organic-metal wastewater discharged from semiconductor manufacturing facilities (19). 

Figure 7. Effect of catalyst thickness on CO conversion by base metal catalyst...

A detailed example is included here to evaluate thin-film catalytic microreactors as kinetic tools compared with conventional laboratory reactors. Most kinetic studies carried out in laboratory reactors which utilize small catalyst particles and the intrinsic kinetics for rapid reactions could be well hidden by mass and heat transport limitations. Existing criteria for mass and heat transport were estimated for both a microreactor with a thin-film catalyst thickness of 5 pm and a packed-bed laboratory reactor with radii of 2 and 4mm [22]. Based on the calculation of Weitz-Prater... 

In a catalytic plate reactor (CPR), metal plates coated with a suitable catalyst are arranged such that exothermic and endothermic reactions take place in alternate channels (Figure 5.26). These channels typically have a height of the order of millimetres and a catalyst thickness of the order of microns. 

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