Functional Mechanism of Inorganic Sodium on the Structure and Reactivity of Zhundong Chars during Pyrolysis

The reactivity of Zhundong chars is remarkably affected by the high sodium content of their parent Zhundong coal. The functional mechanism of inorganic sodium (NaCl) on the structure and reactivity of Zhundong chars was investigated in this study. Chars were prepared in a single-bed reactor under different pyrolysis temperatures and durations. Preliminary experimental results showed that inorganic sodium has a dual effect on the char yield of pyrolyzed Zhundong coal: inorganic sodium can decrease char yield at high pyrolysis temperatures of >= 600 degrees C but increase char yield at the low pyrolysis temperature of 400 degrees C. Nitrogen adsorption technique and scanning electron microscopy were utilized to identify the effects of inorganic sodium on the physical structure of Zhundong chars. The results showed that inorganic sodium affects pore structure detrimentally, inhibits the growth of char vesicles, and enables the formation of smooth char surfaces. Fourier transform infrared spectroscopy and Raman spectroscopy were used to identify the effect of inorganic sodium on the chemical structure of Zhundong chars and to investigate the homogeneous and heterogeneous NaCl-char interactions that occur during pyrolysis. The results showed that homogeneous and heterogeneous NaCl-char interactions both can affect the char's chemical structure. Homogeneous NaCl(s)-char interactions accelerate the decomposition of O-containing functional groups and the formation of new Na-containing carboxylic groups. Heterogeneous NaCl(g)-char interactions accelerate the decomposition of functional groups and increase the ratio of small aromatic ring systems to large aromatic ring systems in the char. Thermogravimetric analysis revealed that inorganic sodium has a catalytic effect on the combustion reactivity of Zhundong chars. Finally, the catalytic mechanism of inorganic sodium on the reactivity of Zhundong chars was proposed.