Transformation mechanism of sodium during pyrolysis of Zhundong coal

The modes in which Na occurs play an important role in its release and catalytic effects during thermal utilization of Zhundong coal. The modes of Na transform with increasing temperature during pyrolysis, but the transformation mechanism remains unclear. In this study, an acid-washed coal was used as a substrate to eliminate the influence of Na inherently present in the raw coal. Na2SO4, NaCl, NaHCO3, and sodium carboxylate were loaded onto the acid-washed coal by impregnation or ion exchange. Pyrolysis of the sodium-loaded coals was conducted in a fixed-bed reactor. Transformation of Na in chars was studied over the temperature range 300-900 degrees C. Interconversion of H2O- and CH3COONH4-soluble sodium occurred below 400 degrees C. CH3COONH4-soluble sodium mainly transformed to H2O-soluble sodium at 400-600 degrees C. The transformation of Na from the H2O-soluble to insoluble form occurred above 600 degrees C. The transformation of Na related to its initial form in the coal. Transformation routes and mechanisms of Na are proposed center dot H2O-soluble sodium can react with -COOH to form CH3COONH4-soluble sodium below 400 degrees C. The decomposition of CH3COONH4-soluble sodium occurred at temperatures lower than 600 degrees C. H2O-soluble sodium may combine with minerals or be coated by the carbon matrix to form insoluble sodium above 600 degrees C. Na that volatilized above 600 degrees C was mainly in the H2O-soluble form.