The fundamentals of chemical reaction kinetics
will be presented with the purpose of building, starting with elementary reactions,
complex mechanisms. These mechanisms consisting of many elementary reactions can be used
with existing software (discussed later) to make predictions on the performance of
chemical reactors with special consideration to the formation of trace species. The focus
will be on homogeneous processes taking place in the gas phase. The majority of the
material presented in this manuscript is based on the author’s own research
(Gargurevich, 1997).
Both in past and present literature dealing with the design of chemical reactors, there is
an oversimplification of the chemical reaction models, with the use of global mechanisms
consisting of a few reactions with empirically determined reaction rates (Worstell, 2001;
Arakawa et al., 1998). For example, the rate of consumption of reactant A by B to form
product C, represented by the overall reaction (1) below, is presented in the form of
Equation (2),
(1)
(2)
where Ae is the pre-exponential factor, E an empirically determined activation
energy, and a and b, the exponents of the reactant concentrations that are able to
represent the concentration dependence over a range of conditions also empirically
determined.
Unfortunately, these oversimplified mechanisms, to give an example, may not be able to
accurately predict the formation of toxic products present in very small concentrations
because depending on conditions their formation is dependent on complex chemistry
involving stable and radical species, as well as reaction temperature. There is a need
then to arrive at more complex mechanisms consisting of elementary reactions that are
relevant to the consumption of the reactants, formation of intermediate species and
products, and any other chemical species of interest (Senkan, 1992).
