New Insights into the Primary Reaction Products of Naomaohu Coal via Breaking Weak Bonds with Supercritical Ethanolysis

Coal is an important energy source in the world, and its chemical structure is the basis of its application, especially for its pyrolysis and liquefaction. Supercritical ethanolysis is a type of chemical extraction that can effectively depolymerize some weak bonds in organic matter. In this work, new insights into the primary products of Naomaohu coal were studied with supercritical ethanolysis. The non-covalent and weak covalent bonds (such as ether and ester bonds) in the coal were broken to yield small molecular compounds (SMCs) with a conversion of 70.3% (dry and ash-free basis) at 370 °C. SMCs, including esters, alcohols, aldehydes, ethers, ketones, hydrocarbons (aromatic and aliphatic hydrocarbons), acids, phenols, and heteroatom compounds, were identified quantitively through gas chromatography/mass spectrometry. Fourier transform infrared spectroscopy and 13 C nuclear magnetic resonance were used to characterize the structure of the coal and its ethanolysis residues. The structure characteristic of the coal was deduced through analyzing the SMCs and residues. Interestingly, the SMCs can reflect the primary reaction products of the coal during its pyrolysis or liquefaction.