I am analyzing themogravimetric data (TGA) to determine kinetic parameters of thermal reaction of oil using Coats and Redfern method.

A plot of either ln{[(1-(1-a)1-n]/[T^{2}(1-n)]} against 1/T or for n= 1, In{-ln(1-a)]/T^{2}} against 1/T should yield a straight line with a slope ( -E/R) for the correct value of n.

Where a = fraction of the reactant decomposed at time t. Therefore, (1-a) = the remaining weight percent of the reactant.

The value of E obtained graphically is then used to calculate the pre-exponential factor.

I am validating my calculation using the data extracted from the work of Kamal N. Jha and Bela Verkoczy (The attached file "The Role of Thermal Analysis Techniques in the In-Situ Combustion Process". In the attached calculation file (.xls), the calculated slopes are from 765 to 1074 for the temperature range of 140~360 ^{o}C. By multiplying the slopes to R (8.314 J/mol.K), the activation energy are from 6360~8930 J/mol. The results are much smaller than the values in the study of Jha and Verkoczy. Please refer to the excel file for your review.

I would like to hear your opinions and suggestions on this topic.

Link files:

http://www.mediafire.com/file/za6jyirfyaoowzc/The_Role_of_Thermal_Analysis_Techniques_in_the_In-Situ_Combustion_Process_SPE-12677-PA.pdf/file

http://www.mediafire.com/file/6dqm08v464lxs2i/Calculate_Kinetic_Parameters_from_TG-DTG_Data.xlsx/file