Evolvement behavior of microstructure and H2O adsorption of lignite pyrolysis

The effect of pyrolysis on the microstructure and moisture adsorption of lignite was investigated with low field nuclear magnetic resonance spectroscopy. Changes in oxygen-containing groups were analyzed by Fourier transform infrared spectroscopy (FTIR), and H2O adsorption mechanism on the surface of lignite pyrolysis was inferred. Two major changes in the pore structure of lignite char were observed as temperature increased in 105–200 °C and 500–700 °C. Pyrolysis temperature is a significant factor in removing carboxyl and phenolic hydroxyl from lignite. Variation of ether bond content can be divided into three stages; the content initially increased, then decreased, and finally increased. The equilibrium adsorption ratio, content of oxygen-containing groups, and variation of pore volume below 700° were closely correlated with each other. The amount of adsorbed water on char pyrolyzed at 700 °C increased. Moreover, the adsorption capacity of the lignite decreased, and the adsorption state changed.

Graphical abstractThe effect of pyrolysis on the microstructure and moisture adsorption of lignite was investigated with 1H NMR` spectroscopy and FTIR. The two major changes of the pore structure of lignite char were discovered as temperature increased in 105–200 °C and 500–700 °C (a), and water adsorption decreased with the decomposition of oxygen functional groups before 700 °C (b). The amount of adsorbed water of pyrolysis char after 700 °C increased. Moreover, the adsorption state changed, the adsorption capacity decreased with the extended relaxation (b).Figure optionsDownload full-size imageDownload as PowerPoint slide