Structural characterization and oxidation study of a Chinese lignite with the aid of ultrasonic extraction

• Structural characterization of a Chinese lignite was performed.
• The oxidation mechanisms of the lignite were modeled using Gaussian 09W.
• Theoretical results for coal oxidation were confirmed by in situ FTIR.

Chinese lignite coal from the Beizao mine which located in Shandong Province of China was studied using a combination of ultrasonic extraction under mild conditions (which generate minimal chemical changes) in conjunction with modern analytical instrumental techniques. This procedure allowed the development of a structural model. Calculations with the Gaussian 09W package generated an optimized structural geometry and also determined the activities of various functional groups. The initial stages of oxidation were found to consist of the oxidation of hydroxyl groups, the rupture of C–O and C–C bonds, and the dehydrogenation of carboxyl groups. In contrast, both the decarboxylation and decarbonylation reactions were determined to require significant energy inputs and thus occur only at high temperatures. In situ Fourier transform infrared analyses were used to confirm the results of the theoretical calculations.