Study on sulfur transformation during the drying of Lignite and sulfur distribution in pyrolysis

Coal pyrolysis-based poly-generation technology has become a key area of scholarly inquiry. Nonetheless, reducing the sulfur content in coal pyrolysis products persists as a challenge. In order to reveal the complex behavior of sulfur evolution in lignite during drying and to elucidate the main mechanism, this work studied the sulfur transformation characteristics during drying and examined the effect of drying on the sulfur distribution in lignite pyrolysis products. The results indicated that drying temperature predominantly governs sulfur evolution. The sulfur content of coal decreased incrementally with escalating drying temperatures. Drying the coal at 210°C resulted in a 32.71% reduction in sulfur content. Sulfate and organic sulfur contents diminished by 57.3% and 23.9%. Drying caused sulfate removal and organic sulfur decomposition. Sulfate migrated to wastewater, while organic sulfur decomposition liberated sulfur-containing gases. Raw coal and dried coal were pyrolyzed, revealing a 90% reduction in sulfur mass in the tar after drying at 210°C. The evolution of organic sulfur during drying was simulated using model compounds containing sulfur. The results indicate that diphenyl sulfone and diphenyl disulfide convert to dibenzothiophene during drying. The formation of thiophene sulfur increases the thermal stability of organic sulfur. The phenomenon is attributed to the decreased sulfate content and enhanced thermal stability of organic sulfur in dried coal. •Soluble sulfate in coal was removed by water during the drying process.•The sulfur mass in tar from coal dried at 210°C decreased by 90% during pyrolysis.•The formation of thiophene during drying enhanced the thermal stability of organic sulfur in coal.