Pyrolysis and combustion kinetics of thermally treated globe artichoke leaves

There are no data in the literature on the energy valorization of globe artichoke (GA) leaves. Thus, an extensive lab-scale experimental torrefaction, carbonization, and coking study was performed. Operative temperatures of 200 degrees C-1000 degrees C with 30-120 min residence times were considered. Nonisothermal thermogravimetric analysis was performed at 10, 20, and 40 degrees C/min heating rates. Pyrolysis and combustion kinetics of raw and thermally treated samples using the Ozawa-Flynn-Wall (OFW) isoconversional method were investigated. All samples exhibited three-stage thermal decomposition behavior: first, moisture and light volatiles evolution common under air and nitrogen; second, carbohydrate fraction decomposition under nitrogen and volatiles combustion; third, lignin decomposition under nitrogen and char combustion. Average activation energy ranges are 54-223 kJ/mol and 223-503 kJ/mol for combustion and pyrolysis, respectively. Some irregular trends appeared when carbonization exceeded 500 degrees C due to the occurrence of secondary reactions between residual char and evolved gas and the decomposition of some ash components at temperatures reaching 1000 degrees C. Negative temperature kinetic coefficient appeared at 800-1000 degrees C as the temperature approached ash softening/fusing temperatures. SEM images indicated amorphous nature and increased porosity from 600 degrees C, which explains the pyrolysis and oxidation behavior observed in biochar samples produced over this range. Samples pyrolyzed for 30 min showed better elemental and energy results compared to longer times.

Automated summary

This study investigated the energy valorization of globe artichoke (GA) leaves through extensive lab-scale experimental torrefaction, carbonization, and coking processes. The samples exhibited three-stage thermal decomposition behavior, with fluctuating activation energy ranges in different temperature ranges. Irregular trends were observed when carbonization exceeded 500 degrees C.