I have a scenario where I used pelleted macroalage for pyrolysis. The heating rates were 20, 30 and 40 C/min. I had experience in using isoconversitional methods in the past were I have seen values as high as 350 kJ mol-1 for microalgae. But recently, with a type of macroalage, the activation energies were more than 1200 kJ mol-1 at few conversions and the average kinetic energy was around 600 kJ mol-1. Is this possible? If yes, what could be the possible reasons?
The macroalage is pelleted and stored for a long time before the experiments were done. I have used both integral and differential isoconversional (KAS and Friedman) methods and got the same range of activation energy.
Thanks for the valuable explanations.
What is the density of your pellets? I reckon the problem is that the volatiles cannot escape from your pellets and the tars are cracking internally and making char - your problem is that the heating rate is only a surface phenomena and not intraparticle. Variablility in density and algae will lead to variations in the activation energy. Use less material and not pelletised. You will get very different results.
Hi,
You need to reduced the density of the biomass (possibly powder ) which will help to removal of hot vapors and ultimately reduced the activation energy. Also, i was not aware of the composition of the biomass such as hemicellulose, cellulose etc, which have highly affect on the pyrolysis. On the other side what model you have adopted along with approximation may be other possible reason.
The pelletizing process can cause chemical modification in the particle and this could alter its activation energy. It may be the effect of temperature during pelletizing process of the particles.
Best Regards
Sample density and high heating rates could be responsible for the high values of Ea
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