Experimental transport disguises

Eliminating or Accounting for Transport Disguises, 207 Experimental Reactors, 210... 

One of the more important problems is the accurate measurement of the chemical kinetics especially when heterogeneous catalysts are involved. In such systems, the transport disguises may shadow the true kinetic data and the experimenter must be overly cautious to eliminate them. 

If experimental tests for heat or mass transfer effects cannot be carried out as described above, the criteria assembled in Table 7.2 can be used to confirm the absence of the transport disguises. 

It is always best to operate an experimental reactor under conditions where all diffusional disguises are lifted (by using the criteria listed in the previous section). A less acceptable alternative is to account for them through appropriate effectiveness factors and external transport coefficients. A number of highly sophisticated computer-controlled reactor systems such as the Berty recycle reactor are commercially available. Many of them are available with software and appropriate interfacing that can set and implement the experiments for each of a series of sequential runs (see Mandler et al., 1983), resulting in the emergence of the most acceptable model at the end of the exercise. 

Given an experimental reactor, catalyst pellet size and fluid velocity are usually chosen to eliminate the disguise of intrinsic kinetics by mass and heat transport resistances. To a certain extent, the fluid concentration and temperature can also be used for that purpose. Small pellet sizes and high fluid velocities tend to lower the concentration and temperature differences caused by the resistances. 

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