Transport effects diagnostic experiments

The presence or significance of interphase transport resistances is confirmed either by conducting diagnostic experiments or by utilizing a well-established criterion. A preliminary set of experiments that must be conducted in laboratory PBRs in order detect the effect of external mass transport is to measure the dependence of the exit conversion Xa on the linear velocity of the fluid through the catalyst bed, u (m/s), which is in fact the velocity of the fluid relative to the catalyst particles [7, 23]. 

The first set of preliminary experiments in a kinetic study carried out in laboratory PBRs should establish the flow conditions at which external transport effects are negligible. The second set of diagnostic experiments conducted should verify the particle size requirements under which intraparticle transport effects are eliminated. A study of intrinsic kinetics must make use of the flow rates and particle sizes that exclude both external and internal transport limitations, respectively. 

In this chapter, we revisit the subject of reaction/transport interactions in heterogeneous catalysts, this time from a quantitative standpoint. The topic must be examined from two perspectives. First, a researcher that is studying the kinetics of a heterogeneous catalytic reaction (or reactions) must ensure that his or her experiments are free of transport effects. In other words, the experiments must be conducted under conditions where intrinsic chemical kinetics determines the reaction rate(s). The researcher may have to make calculations to estimate the magnitude of heat and mass transport influence. He or she may also have to carry out diagnostic experiments in order to define a region of operation where transport does not affect the reaction rate and selectivity. 

Carefully plaimed diagnostic experiments can be used to evaluate the effect of both internal and external transport on catalyst performance. 

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