Up to me it appears that some organic material is burned away. Is the pyrolysis performed under inert gas or is there a risk for air leaking in into the reactor?

What is the ash content of the starting material compared to the final carbons, there should be an increase?

Can there be some pyrogenic metals present in the feedstock? Have seen some carbon be burned away if the reactor is opened too early or the feed of the inert gas ends att too high temperature.

But You are right assuming that carbon content should increase. But try to fins a method to measure total carbon, not only organic carbon.

Henrik Romar Thank you. I used a Muffle furnace to produce biochar. The biomass was fully protected with an aluminum tray and foil paper. I used the Black and Walkley method to determine total organic carbon as I have the facility in the lab. I used the technique to determine the TOC of soil as well. What could be the reasoning for decreasing the carbon with increasing temperature? I found that dissolved organic carbon (DOC) decreases with increasing temperature. So, in my MS thesis book, what should I conclude regarding the TOC determination of the biochar with the Black and Walkley method? And, I found very small (12-15%) percentage of carbon in the biochar with the method. How could I discuss it?

Or should the organic carbon of biochar part be removed from the thesis book as that is not my main experiment? I have incubation study of biochar and soil. I analyzed the TOC of the soil with Black and Walkley method and should I only discuss that?

You burn the carbons. You have to feed an inert gas like nitrogen to flush out any oxygen, continue the nitrogen feed during the whole process.

In fact the method used is close to the method used for ash determination. In that the sample is placed in a crucible covered with a lid and heated to 540C. All carbon based materials is burned away.

That is why we found a lower amount of carbon in the biochar (12-15%). But what could be the explanation for decreasing the carbon content with increasing temperatures? It should not be occured, right? I found in the literature that DOC can be decreased with increasing temperature.

What is the temperature span used? Normally the higher the temperature the higher is the burn off. Calculate the yield from the process,mass after pyrolysis/initial mass. This should be some 30-50% depending on temperature. If it is lower You have a burn-off. Normally yields are lower the higher temperature used.