Evolvement behavior of microstructure and H2O adsorption of lignite pyrolysis

Abstract

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 H 2 O 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.

Effect of -O- on Water Molecule Adsorption and Adsorption Mechanism of Lignite and Coke

“…e number of active sites or oxygen-containing functional groups was the highest [18]. e moisture was absorbed on the active sites, which led to increased water molecule absorption in lignite in this temperature range.…”

“…According to above analysis and previous research [18], the water molecule adsorption mechanisms of lignite and coke were determined, and they are shown in Figure 11.…”

“…With the removal of water in the pores, more pores were exposed, resulting in a significant increase in the pore content. When the heat-treatment temperature was higher than 200 °C, the heat-treatment process caused significant weight loss and gas escape [18]. In particular, condensation polymerization occurred at about 300 °C, resulting in ether bonds and pore contraction (Figure 10).…”

“…However, the maximum adsorption force was the weakest (Figure 6), because the functional groups were almost gone (Figure 8). rough comprehensive consideration of the pore changes [18], it was found that the cracks were larger (Figures 7(a) and 9) and the multilayer water was not easy to retain. e moisture state of the coal sample heated at 700 °C changed, and the amount of multilayer adsorption increased (Figure 7(b)).…”

“…In this study, the pore distribution, the effect of oxygencontaining functional groups on water molecule adsorption, and the relationship between the oxygen-containing functional groups, pores, and water molecule adsorption were examined [18]. Based on previous studies, the influence of ether bonds on the water molecule adsorption in lignite and coke (<950 °C) was investigated through proton nuclear magnetic resonance ( 1 H-NMR) and water molecule absorption and desorption experiments to lay a foundation for the inhibition of lignite reabsorption and spontaneous combustion.…”