Volatile-char interactions during biomass pyrolysis: Effects of functionalized graphitized carbon nanotubes on volatile distribution of cellulose and its model compounds

Volatile-char interactions are prevalent in biomass pyrolysis processes. To gain deeper insights into their impact on biomass pyrolysis volatile distribution, interactions between volatile compounds and char during flash pyrolysis of glucose, cellobiose, and cellulose were investigated using a pyrolysis–gas chromatography/mass spectrometry detection technique, by modifying both the chain lengths of the raw materials and the functional groups of graphitized multi-walled carbon nanotubes (CNTs). The results reveal that volatile-char interactions markedly influence the distribution of the final pyrolysis products derived from glucose-based compounds. In the presence of any type of CNTs, dehydrated saccharides in the primary products, particularly levoglucosan (LG), exhibit the highest sensitivity to the interactions. Consequently, primary products such as LG and 5-hydroxymethylfurfural (HMF) undergo secondary pyrolysis, yielding compounds such as levoglucosenone (LGO) and 5-methyl-2-furancarboxaldehyde (FCM). Additionally, CNTs without functional groups are advantageous for the production of expensive LGO (The relative abundance reached 9.65%), whereas the relative abundance of FCM increases significantly with hydroxyl-, carboxyl-, and amino-modified carbon nanotubes. Particularly, the relative abundance of FCM is highest in the presence of amino-modified carbon nanotubes, regardless of whether the feedstock is glucose, cellobiose, or cellulose, with values of 25.14%, 23.32%, and 4.23%, respectively. Furthermore, consistent changes in product distribution trends among different glucose-based compounds under identical CNT conditions suggest that glycosidic bonds have minimal impact on volatile-char interactions.