Structural characteristics of char derived from acid-washed coal pyrolysis and its corrections with char reactivity

Acid-washed process can eliminate the effects of alkali and alkaline earth metallic species on the characteristics of char derived from pyrolysis.The evolution of char structure and its correction with char reactivity is thus to be investigated independently.Acid-washed coal is injected into a fluidized-bed reactor instantaneously to prepare the acid-washed char samples under different pyrolysis temperatures.The FT-Raman spectra of chars in this study is curve-fitted with six bands representing structural characteristics of chars.The results show that the ratio ofI(D)/I(S+D+A1+A2) representing the microcrystalline degree of char increases, and the ratio of I(A1+A2)/I(D) representing the degree of small aromatic ring and large aromatic ring system in char decreases gradually with increasing pyrolysis temperature.Taking the changes of I(D)/I(S+D+A1+A2) and I(A1+A2)/I(D) together into account, it indicates that the conversion of smaller aromatic rings to the large aromatic rings would mainly account for the growth in the carbon crystallites.The differences of the reactivity of char at various conversion levels under 600℃ and 700℃ pyrolysis are larger than that of the reactivity of char under 800℃ pyrolysis.It indicates that the char reactivity is dependent on the different structural characters of char at different pyrolysis temperatures.The relativity between the Raman structures and the char reactivity illustrates that the ratio of I(D)/I(S+D+A1+A2) could well correlate with char reactivity.