Mass-transfer-controlled reactions modes

Of primary interest for the industrial application of monolith reactors is to compare them with other conventional three-phase reactors. Two main categories of three-phase reactors are slurry reactors, in which the solid catalyst is suspended, and packed-bed reactors, where the solid catalyst is fixed. Generally, the overall rate of reactions is often limited by mass transfer steps. Hence, these steps are usually considered in the choice of reactor type. Furthermore, the heat transfer characteristics of chemical reactors are of essential importance, not only due to energy costs but also due to the control mode of the reactor. In addition, the ease of handling and maintenance of the reactor have a major role in the choice of the reactor type. More extensive treatment of conventional reactors can be found in the works by Gianetto and Silveston [11], Ramachandran and Chaudhari [12], Shah [13,14], Shah and Sharma [15], and Trambouze et al. [16], among others. 

Slurry Process Extra Particle Mass-Transfer Limitations. In a slurry process, very fine catalyst is suspended in a liquid medium, which in the case of an FT process may be the heavier fraction of the liquid product itself. The slurry mode of operation allows effective removal of reaction heat and good temperature control. Because of the small catalyst particles (particle diameter a few hundred micrometers or less), intraparticle diffusion limitation is not a constraining factor for reaction rate. However, compared with a fixed-bed mode of operation the advantage of better catalyst utilization may be offset by the reduced volume of catalyst that can be accommodated in the reactor space. 

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