The Effects of sodium and alkalinity on the microcrystalline structure and the steam gasification performance of Shengli lignite

•Sodium and alkalinity are the crucial factor on the char reactivity.•Sodium and alkalinity have an effect on microcrystalline structure in pyrolysis and steam gasification performance.•Reactivity and dynamics of char are analyzed in gasification.•The reaction evolution process about the effects of sodium and alkalinity on microcrystalline structure of char give a description of catalytic pyrolysis.

The pyrolysis of Shengli lignite (SL-Raw) and sodium-based anion doped into coal samples (SL-NaOH, SL-Na2CO3 and SL-NaNO3) was analyzed by investigating the effects of sodium and alkalinity on the differences in crystallite structure of chars by XRD, Raman, XPS and FT-IR. The steam gasification of chars was performed in a fixed-bed reactor. The char gasification results showed that sodium and alkalinity have a catalytic effect on the char reactivity, and the chars have better activity when the sodium compounds are more alkaline. The XRD and Raman results showed that NaNO3, Na2CO3 and NaOH inhibited the growth of the aromatic ring structure, and the carbon microcrystalline structure of the chars was destroyed due to sodium atoms during pyrolysis. The XPS and FT-IR results indicated that the phenolic hydroxyl (COH) was converted into sodium phenolate (CONa), and the reactivity of chars was better.