3 research outputs found
Kinetic compensation effect of isoconversional methods
For experimental data obtained under different reaction/process conditions over
time or temperature, the kinetic compensation effect (KCE) can be expected. Under
dynamic (nonisothermal) conditions, at least two analytical pathways forming the
KCE were found. Constant heating rate (q = const) and variable conversion degrees
(α = var) lead to a vertical source of the KCE, called the isochronal effect. In turn,
for a variable heating rate (q = var) and constant conversion degree (α = const), we
can obtain an isoconversional compensation effect. In isothermal conditions (analyzed
as polyisothermal), the KCE appears only as an isoconversional source of the
compensating effect. The scattering of values for the determined isokinetic temperatures
is evidence of a strong influence of the experimental conditions and the
calculation methodology. The parameters of the Arrhenius law have been shown to
allow the determination of the KCE and further the isokinetic temperature. In turn,
using the Eyring equations for the same parameters, we can determine the enthalpyâ
entropy compensation (EEC) for the activation process and the compensation temperature,
which is often treated as an isokinetic temperature. KCE effects have also
been shown to be able to be amplified or dissipated, but isokinetic temperature is
not a compensating quantity in the literal sense in isoconversional methods because
T
iso
â â. Thus, in isoconversional methods, isoconversional KCE values are characterized
by strong variability of activation energy corresponding to the weak variation
of the pre-exponential factor, which in practice means that lnA â const. This is
completely in line with the classical Arrhenius law