Transformation of Na in an Australian high-sodium coal during pyrolysis

The volatility and transformation of Na in raw coals and washed coals by water and 0.1mol/L HCl during coal pyrolysis were investigated in a fixed bed from 400℃ to 700℃ and atmospheric pressure. The semichars were extracted by water and 0.1mol/L HCl, and the forms of Na were divided into three parts: water soluble, acid soluble but water insoluble and acid insoluble. The results show that Na in the raw coal is mostly water soluble NaCl. The Na volatility shows a maximum value between 500℃~550℃ because the organic Na as the carboxylic salt releases as atom Na. However, above 600℃ the Na in acid washed coal transforms into acid soluble but water insoluble, leading to the volatility of Na to increase again. It is found that at higher pyrolysis temperatures the volatile Na in the raw coal is transformed into water soluble; however, the Na in water washed coal may react with SiO2 to transform into acid insoluble Na.