Effect of CO₂ on pyrolysis behaviors of lignite

The pyrolysis of Huolinhe lignite under CO₂ atmosphere was carried out in a thermobalance and a fast heating-up fixed bed reactor. The distribution of gases, char yield and its property such as element, surface structure, FT-IR spectra were analyzed. By this, the effect of CO₂ on the pyrolysis behaviors was studied. The results show that CO₂ gasification of the nascent char, which destroys the hydrogen-containing char structure, not only promotes cracking of benzene ring and fracture of hydroxyl, methyl and methylene groups etc., but also weakens the interaction between H and char matrix and increases the H fluidity, leading to the increase in the generation of H radicals. These H radicals can combine with other free radical fragments generated from fracture of the coal macromolecules to produce more volatiles. This will produce the char with a high specific surface and high pore volume and porosity. The introduction of CO₂ promotes the coal pyrolysis and generation of volatile, resulting in decrease in char yield and increase in the evolution amount of H₂, CO, CH₄ and other small molecules hydrocarbons.