Page 172 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

Reaction Kinetics Information: This information is reaction specific and must be obtained
experimentally. The overall kinetics may involve homogeneous and heterogeneous reactions both catalytic
and noncatalytic. The expressions are often complex.

Before a process is commercialized, reaction kinetics information, such as space velocity and residence
times, must be obtained for different temperatures and pressures from pilot plant studies. Such data are
necessary to design the reactor. At this point, we are not interested in the reactor design, and hence

specific kinetics expressions have not been included in Table 6.6 and are not necessary for the following
analysis.

The analysis of the reactor takes place in two parts.

a. Evaluation of the special conditions from the thermodynamic point of view. This assumes that
chemical equilibrium is reached and provides a limiting case.
b. Evaluation of the special conditions from the kinetics point of view. This accounts for the
limitations imposed by reaction kinetics, mass transfer, and heat transfer.

If a process is unattractive under equilibrium (thermodynamic) conditions, analysis of the kinetics is not
necessary. For processes in which the equilibrium conditions give favorable results, further study is
necessary. The reason for this is that conditions that favor high equilibrium conversion may be
unfavorable from the standpoint of reaction kinetics.

Thermodynamic Considerations. We consider the use of high-temperature, high-pressure, and non-