Solvent extraction of superfine pulverized coal. Part 3. Small angle X-ray scattering characterization

Because of the unique physicochemical textures induced by reduced particle size, superfine pulverized coal presents attractive characteristics in different utilization processes, including solvent extraction. In this work, the synchrotron radiation-based small angle X-ray scattering (SAXS) with high precision was used to quantitatively characterize all the products during the coal extraction process, including raw coal, extract, and residue. In addition, the evolutions of pore structures (solid state) and aggregate configurations (liquid state) were focused on. The results show that the fractal dimensions of pore surfaces are mainly related to the pore sizes and cor-responding quantity distributions. When the particle size is less than 14 jim, the comminution induced me-chanical effect on the pore surface gradually changes from impact to polish during the superfine grinding. Additionally, the fractal dimension decreases with the decline of particle size and ash content, whilst increases for the lower ranked coals. As for the extraction process, the extraction effect of tetrahydrofuran on anthracite coal is relatively better, while pyridine is more effective for bituminous coal. The diverse driving force caused by particle size effect leads to different radii of the gyration of the extracted aggregates, indicating the selected bituminous coal has active sites that are susceptible to reacting with aromatic compounds, while anthracite has a large number of active sites that accept electrons. Finally, the surface fractal dimension of the extraction residue declines about 2% and 4% for HN and NMG coal respectively, and the decreasing trend declines for larger coal particles. Interestingly, this decreasing trend of bituminous coal is more evident, which indicates the pore surface of bituminous coal is easier to react with solvent. The research sheds light on thoroughly depicting the pore structure of coal and residue at a molecular level, which promotes a better understanding of the solvent extraction mechanisms. The results also provide a new perspective for constructing more comprehensive coal molecular models in the future.

Automated summary

In this study, synchrotron radiation-based small angle X-ray scattering (SAXS) was used to characterize the products of superfine pulverized coal during solvent extraction, focusing on pore structure (solid state) and aggregate configurations (liquid state) evolution. The results revealed that the fractal dimensions of pore surfaces were closely related to pore sizes and corresponding quantity distributions. The research also showed the extraction effect of different solvents on anthracite coal and bituminous coal, as well as the impact of particle size on extracted aggregate radii. Overall, the study provides insights into the molecular-level characterization of coal and residue pore structures and enhances understanding of solvent extraction mechanisms.