煤热解过程中噻吩类硫化物迁移转化机理研究进展

Progress in the migration and transformation mechanism of thiophene compounds during coal pyrolysis

  • 摘要: 噻吩类硫化物是煤炭中有机硫的重要赋存形式,在煤炭热解过程中,噻吩类硫化物会迁移至热解产物中进而影响产物品质或引发环境污染,因此明晰煤热解过程中噻吩类硫化物的迁移转化特性与机理对煤炭高效清洁利用以及国家双碳目标的实现具有重要意义。本文首先归纳了噻吩类硫化物在煤炭中的赋存和热解过程中的析出特性,噻吩类硫化物的含量随着煤阶升高而增多,热解过程中的噻吩类硫化物主要来源于煤中大分子结构热裂解释放,部分来源于无机硫和硫醚、硫醇等有机硫的转化。随后概述了噻吩类硫化物热解特性与反应机理的相关实验和计算研究结果,噻吩类硫化物的分解主要由C-S键均裂和氢迁移引发,裂解产生多种含硫自由基中间体进而生成H2S、SO2、COS和CS2等含硫气体,其他含硫基团相互聚合或与芳香环结合形成多环含硫芳烃迁移到焦油和焦炭中。然后总结了多种热解条件对噻吩类硫化物热解的影响,热解温度的升高通常能促进噻吩类硫化物的分解,升温速率越慢噻吩类硫化物的脱除越彻底;H2、水蒸气以及CO2气氛都对噻吩类硫化物的分解有促进作用,其中H2和水蒸气能够通过提供氢自由基攻击噻吩环上的硫原子,或者与不饱和的C=C键发生加成反应促进噻吩类硫化物热解;CO2的氧化性会降低C-S键断裂难度,促进噻吩类硫化物形成更多的SCO2、CHO和R-O自由基从而促进气相含硫产物的生成;煤中的高岭土能促进噻吩类硫化物的释放,钙质矿物则会与其反应向CaS转化;不同性质的添加剂能够作为反应物或催化剂影响噻吩类硫化物的热解反应。基于噻吩类硫化物的迁移机理,对煤热解过程的调控应从两方面入手,一方面定向促进氢迁移反应和C-S键断裂以促进噻吩类硫化物分解;另一方面提供热解环境缺少的氢自由基和含氧基团抑制多环含硫芳烃化合物生成。未来还需要在噻吩类硫化物向液相和固相迁移的反应机理、反应器型等多因素耦合作用下的噻吩类硫化物热解调控机制等方面深入开展研究。

     

    Abstract: Thiophene sulfide is an important organic sulfur form in coal. During coal pyrolysis,the thiophene sulfides will migrate into the pyrolytic products,affecting the quality of the products or causing environmental pollution. There⁃ fore,it is of great significance to clarify the migration and transformation mechanism of thiophene sulfide during coal pyrolysis,which is useful to the efficient and clean utilization of coal and the realization of carbon peaking and car⁃ bon neutrality goals. First,the presence of thiophene sulfide in coal and its formation characteristics during pyrolysis are summarized. The content of thiophene sulfide rises with the increase of coal rank. The thiophene sulfide in the py⁃ rolysis process mainly comes from the thermal cracking of macromolecular structure in coal,and partly originates from the transformation of inorganic sulfur and organic sulfur such as thioethers and thiols. Then,the relevant experi⁃ mental and computational results of the pyrolysis characteristics and mechanism of thiophene sulfide are reviewed. The decomposition of thiophene sulfide is mainly caused by C—S bond homolysis and hydrogen migration. Sulfur⁃containing gases of H2 S,SO2 ,COS,and CS2 are then produced from the sulfur⁃containing free radical intermedi⁃ ates. Other sulfur⁃containing groups will polymerize with each other or combine with the aromatic rings to generate sul⁃ fur⁃containing polycyclic aromatics which are retained in tar and coke. Afterward,the effects of various reaction condi⁃ tions on the pyrolysis of thiophene sulfides are summarized. The increase of pyrolysis temperature can generally pro⁃ mote the decomposition of thiophene compounds,and a slow heating rate is also beneficial for the thorough decomposi⁃ tion of thiophene compounds. H2 ,steam,and CO2 atmosphere can promote the decomposition of thiophene sulfides. H2 and steam promote the pyrolysis of thiophene sulfides by attacking the sulfur atom on the thiophene ring with hydrogen radicals,or reacting with C

     

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