Regulates the molecular structure of high-sulfur coal to achieve directional desulfurization during pyrolysis: An integrated TG-MS and ReaxFF-MD simulation approach

The unclear migration mechanism of organic sulfur during coal pyrolysis limits molecular-level understanding, hindering targeted desulfurization and clean utilization of high-sulfur coal. In this study, a "structural simplification" strategy was proposed, in which the thermal dissolution soluble fraction (TDSF) from Duizhen high-sulfur coking coal (DHSC) was employed as the research subject. This TDSF is characterized by its structural homogeneity and ash-free nature, thereby eliminating the interference caused by structural heterogeneity and ash. By combining TG-MS and ReaxFF-MD simulations, the abundant aliphatic structures in TDSF generate a strong "self-hydrogen supply" effect during the pyrolysis process. At 2800 K, the number of C-H bond cleavages in the DHSC/N 2 system is 167, whereas in the TDSF/N 2 system, it reaches as high as 258. The co-hydrogenation experiments of TDSF and DHSC with phenanthrene demonstrated that the hydrogen-donating capacity of TDSF was 1.64 times that of DHSC. The generated active hydrogen radicals selectively attack the C-S bonds in thiophene and sulfoxide, prompting a large amount of sulfur to migrate to the gas and liquid phases. The pyrolysis experiments showed that the sulfur removal rate of TSDF (37.39%) during pyrolysis was significantly higher than that of DHSC (30.08%). It was demonstrated that the desulfurization performance of DHSC can be further enhanced by the use of a hydrogen atmosphere and elevated pyrolysis temperatures. Based on these molecular-level insights, precise desulfurization strategies for high-sulfur coal pyrolysis can be formulated.