In situ FT-IR analysis of coke formation mechanism during Co-pyrolysis of low-rank coal and direct coal liquefaction residue

In situ Fourier transform infrared spectroscopy and thermogravimetric analysis were conducted to characterise the co-pyrolysis of low-rank coal (SJC) and direct coal liquefaction residue (DCLR) as well as the evolution of the main functional groups of the pyrolysis products. This research is expected to further elucidate the reaction mechanism of co-pyrolysis. It was found that the co-pyrolysis of SJC and DCLR has synergistic effects and increases the hydrogen supply during co-pyrolysis. The chain breakage and thermal decomposition of functional groups during co-pyrolysis lead to the formation of solid, liquid, and gaseous products. The presence of DCLR promotes deep pyrolysis to produce numerous aromatic and aliphatic groups; many of these free-radical fragments rearrange and condense with hydrogen free radicals ([H]) to produce tar with a high molecular weight. When the [H] content is low, the free-radical fragments combine with each other to form solid coke. During co-pyrolysis, SJC and DCLR serve as both, hydrogen transmitters and donors. The catalysed hydrocraking of aromatic hydrocarbons and phenols in the tar product in the presence of hydrogen increases the content of the light component in the tar and produces alkanes, decreasing the aromatics and phenol contents.