Solvent extraction of Chinese lignite and chemical structure changes of the residue during H2O2 oxidation

• Oxidation of extract residues by H2O2 is predominantly affected by temperature.
• Chemical structure of extract residues studied by FT-IR showed little differences.
• Aliphatic hydrocarbon was present in the extracts during all oxidation steps.
• The relative content of esters in all oxidation steps was high.

Solvent extraction and oxidation of coal under mild conditions can assist in understanding of coal chemical structure. It can also offer a potential for conversion of coal into useful chemicals, allowing more efficient use of coal resources. In this study, a Chinese lignite was extracted by different solvents including CS2, ethanol, and acetone. The composition of the extracts was analyzed by GC–MS method. It was found that the CS2 extracts contained high amounts of aliphatic hydrocarbon. The ethanol and acetone extracts mainly contained oxygen-containing compounds. The effects of reaction temperature and residence time on coal oxidation and composition of extract residues were also investigated. The results showed that lignite was readily oxidized in H2O2 aqueous solution at temperatures above 40 °C, and the oxidation behavior (oxidation rate, product distribution and yields) was strongly temperature dependent. Oxidation of extract residues in H2O2 solution was carried out at different temperatures. Water soluble products of oxidation were analyzed using the GC–MS. Aliphatic hydrocarbons were present in all oxidation steps. The relative content of esters in all oxidation steps was also high. The chemical structure changes of coal, the extract residues, and the oxidation residues were studied using FTIR technique. The results indicated that the extract residues had lower intensity of aliphatic hydrogen compared to raw coal. The aromatic carbon concentration remained relatively unchanged when oxidized at temperatures below 30 °C, then decreased slightly with increasing the oxidation temperature.