Restudy on torrefaction of corn stalk from the point of view of deoxygenation and decarbonization

In this study, the torrefaction of corn stalk was performed at 200-290 degrees C for 30 min. The solid products (torrefied corn stalk), liquid products (water and tar), and gaseous products were collected and analyzed, and the migration of oxygen and carbon during torrefaction was discussed. Results showed that as the torrefaction temperature increased from 200 degrees C to 290 degrees C, the relative content of aromatic/aliphatic carbon (C-C, and C=H) in the torrefied corn stalk increased from 55.66% to 69.90%, while the content of ether or hydroxyl/phenol groups (C-OR) obviously decreased from 21.96% to 8.79%. This result was also confirmed by ultimate analysis, indicating that increasing in the torrefaction temperature resulted in a sharp decrease of the oxygen content and a gradual increase of carbon content of corn stalk. During the torrefaction process, oxygen of corn stalk was released in the form of CO2 and CO in the gaseous products, and H2O and oxygen-containing compounds like acids and phenols in the liquid products. In the temperature range of torrefaction experiments, 7.05%-57.25% of oxygen in raw corn stalk migrated into the liquid and gaseous products in the form of H2O, followed by CO2 and CO. Along with the deoxygenation process, a small amount of the carbon (3.31%-27.26%) from raw corn stalk was transferred into the gaseous products, followed by tar. These results indicated that the dehydration reactions and gas formation dominated the deoxygenation and decarbonization of corn stalk torrefaction, respectively.