Microstructural evolution during pyrolysis of Shengli lignite and hydrochloric acid-demineralized lignite

A fixed-bed pyrolysis experiment was adopted to generate solid products of Shengli lignite (SL) and hydrochloric acid-demineralized lignite (SL⁺) at different temperatures. The structural properties of the chars were investigated by FT-IR, XPS, XRD, and Raman spectroscopy to correlate with the microstructural evolution of SL and SL⁺ during pyrolysis. The results indicated that the concentration of oxygen-containing structures in hydrochloric acid-demineralized lignite/chars was relatively high and decreased with increasing pyrolysis temperature. The mineral components demineralized by hydrochloric acid limited the orderly arrangement of aromatic rings, promoted the condensation of aromatic ring clusters, caused more crystalline defects in the chars, and was adverse to the development of side chains during pyrolysis.