I have been working with a Linseis TGA. After the pyrolysis is over the gases exit the system into an exhaust. I tried to collect the exiting gases for analysis in GC but the amount of H2 and CO2 detected is way below expected amounts.
Sample: Woody biomass
Pyrolysis Temp: 800C
Heating rate: 50 K/min
Sample Mass: 20 mg
Expected Hydrogen (%): 1-2% and CO2: 50%
Obtained H2: 0.05% and CO2: 1 %
GC Detector: Thermal Conductivity Detector
GC Column: Porapak N (80/100 mesh)
Column Temp: 80C
Hold time: 1.8 min
Did you consider the possibility that the gases could be adsorbed onto silica bed? I'm not sure whether this is the right explanation... Maybe a molecular sieve or a cold trap (not sure about CO2 sublimation) would be more suitable options in this case.
As Tibor Dubaj notes and as I noted at https://engineering.stackexchange.com/questions/24700/causes-of-underestimation-in-pyrolysis-gases-exiting-a-thermogravimetric-analyze#comment45325_24700 , the suitability of your gas line capture system probably needs to be confirmed and its operation calibrated.
Tibor Dubaj I have analyzed the gases coming out of TGA directly i.e. without passing it through condenser and filter as well as and obtained similar results. There is no other point of exit for the gases.
Jeffrey J Weimer I will calibrate this system and if there's an improvement I will update this question.
Update: I had to ultimately abandon this set up and attach a portable gas analyzer, the type used in analysis of exhaust gases etc., and that seems to have solved my problem of carbon balance.
It is most likely that the problem was with the GC Column that was unsuitable to identify low quantity carbon dioxide.
Thank you for the follow up. I am glad to hear that you found a solution to your problem. This is often cause for a big celebration even though you may never know the exact reason why your initial setup did not work properly.
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