Kissinger-Akahira-Sunose (KAS) Analysis

Kissinger-Akahira-Sunose (KAS) Analysis is the model-free (isoconversional) method of kinetic analysis calculating dependence of activation energy E(α) on degree of conversion α for dynamic experiments with different constant heating rates β.

Kissinger-Akahira-Sunose method is different from Kissinger method.

It is always necessary to check if this model-free method is valid to be used and is applicable because of restrictions of model-free methods.

Kissinger-Akahira-Sunose analysis belongs to the group of integral model-free methods where firstly, the integral of main kinetic equation Eq. (1) must be found then the series is created and finally the logarithm must be taken:

Integral for Kissinger-Akahira-Sunose analysis:

Right integral in equation has the series for z=-E/(RT):

Taking logarithm of Eq. (2) the linear dependence is found:

Where

If the points with the same degree of conversion (isoconversional points) will be taken from experiments performed at different heating rates then values ln[A(α)/F(α)]-ln(E(α)/R will be the same for all of them and Eq. (3) will look like the straight line

y=b+ax (4)

where

y=ln(β/T²)
b=ln[A(α)/F(α)]-ln(E(α)/R)
a=E/R
x=-1/T .

The Kissinger-Akahira-Sunose (KAS) plot y(x) looks as set of straight lines for different α values, where for each α the activation energy can be found from the slope and pre-exponent from the intercept for known(or assumed) f(α).

Advantages and disadvantages of this method and a comparison table with other methods..

Example

Decomposition of La(OH)₃:

Experimental data,
Kissinger-Akahira-Sunose plot,
Activation energy E(α),
Pre-exponent A(α) (for the assumption of first-order reaction),
Comparison between experiments and simulation for Kissinger-Akahira-Sunose dependences E(α) and A(α).

Fig.3 Kissinger-Akahira-Sunose Activation energy E(α).

Fig.5 Comparison between experiments(symbols) and simulation(solid lines) for Kissinger-Akahira-Sunose dependences E(α) and A(α).

Fig.2 Kissinger-Akahira-Sunose plot containing straight lines for different conversion values α.

Fig.4 Kissinger-Akahira-Sunose pre-exponent A(α) (for the assumption of first-order reaction).

Kinetics Neo

This method is used in Kinetics Neo software as model-free method Kissinger-Akahira-Sunose

Reference

H.E.Kissinger, J.Res. Nat. Bur. Stabd. 57 (1956) 217-221

https://nvlpubs.nist.gov/nistpubs/jres/057/jresv57n4p217_A1b.pdf