Study On The C-S Bond Cleavage And Sulfur Migration Of Coal-related Sulfur-containing Model Compounds

Efficient removal of sulfur from coal has been a research hotspot in the clean use of energy,in which the removal of organic sulfur in coal is the key to deep desulfurization of coal.However,it is very difficult to study the migration of sulfur in coal immediately,since the migration processes of different forms of sulfur are intertwined and making it difficult to clarify the fracture nature of chemical bonds and the migration rule of sulfur.In this work,on the basis of typical structure of sulfur in coal,suitable organic sulfur-containing model compounds were designed and selected to investigate the C-S bond cleavage and sulfur migration of coal-related sulfur model compounds.Firstly,the thermal fragmentation regularity and the sulfur thermal migration of 10 pyrenyl-based sulfide,sulfoxide,sulfone and thiophene compounds with larger molecular weight were studied under the environment of thermogravimetry.It was found that the sulfur atoms in different sulfur groups had a correlation with the chemical bonding energies of the surrounding environment,and establishing the thermal fragmentation regularity of C-S bond with different sulfur groups.In other words,the cleavage orders of C-S bond are determined as thiophene > diarylsulfide > diarylsulfone > arylalkylsulfone and diarylsulfoxide > dialkylsulfone > arylalkylsulfide > dialkylsulfide > arylalkylsulfoxide and dialkylsulfoxide.The thermal fracture of C-S bond depends on the electron conjugation effect between sulfur atom and the surrounding environment.Secondly,nine kinds of phenyl-based sulfur-containing compounds with smaller molecular weight including dialkyldisulfide and dialkylsulfide,arylalkylsulfide and arylthiophenol,diarylsulfide and diaryldisulfides,dibenzothiophene,dialkylsulfone and dialkylsulfoxide were studied to investigate the sulfur thermal migration and the fracture of S-S bond,Calkyl-S bond,Caryl-S and H-S bond in these compounds.The composition and structural characteristic of the reaction products were identified with gas chromatography/mass spectrometry detector(GC/MS).The results show that the thermal fracture of different sulfur groups depends on the environment in which the sulfur atom is in the molecule,and the leaving ability of sulfur atom depends on the strength of conjugation effect between sulfur and its attached groups.The cleavage degree of the compounds match with the thermo gravimetric regularity,and the reaction follows the free radical reaction mechanism.The cleavage of strong Caryl-S bond was promoted by the stable free radicals which produced by the cleavage of weak Calkyl-S,H-S and S-S bonds in thioethers,disulfides and thiophenols,and the sulfur in thioether compounds can effectively migrate in the form of hydrogen sulfide.The cleavage of the C-S bond depends on not only the conjugation effect between sulfur atom and its surrounding environment,but also the generation of free radicals on the sulfur substitution position with stable attacking.Finally,the sulfur migration and the cracking of C-S bond in coal and coal-related sulfur compounds were studied in the presence of adjuvants(NaBH4 and NiCl2·6H2O).The results show that the sulfur in all typical organic sulfur groups in coal can effectively separate out at room temperature and atmospheric pressure under the condition of active hydrogen source and metal Ni(II),but different sulfur-containing groups have different reactivity.The cleavage of the C-S bond mainly depends on the steric effect and electron effect of the environment in which the sulfur atom is located,which can be speculated that the removal of sulfur is mainly in the form of hydrogen sulfide.