Occurrence And Pyrolysis Transformation Of Organic Sulfur During Pyrolysis Of High Sulfur Coal From Weibei Coalfield

A better understanding of the occurrence and pyrolysis transformation of organic sulfur in coal at molecular level is of great significance. It is benefit to build molecular models of organic sulfur to realize the selective conversion by controlled reaction, the reduction of SO2 emissions and the clean, efficient utilization of coal. The main objective of this work is to study the occurrence and pyrolysis transformation of organic sulfur in Permo-Carboniferous high sulfur coal form Weibei coalfield and to build the molecular model of Vitrinite.By the experiments of sieve test and float-sink test, as well as XPS analysis, it was found that the main occurrence of organic sulfur in coal is thiophenes. A small amount of sulfoxides, sulfones and thiols are also existed.The pyrolysis experiments were carried out under different atmospheres to investigate pyrolysis transformation of organic sulfur in Vitrinite. Temperature is the significance factor.(1) With temperature rising, organic sulfur in semi-coke decreases during pyrolysis under CH4 and H2.(2) Organic sulfur in semi-coke decreases below 700 oC and dramatically decreases from 700 oC to 800 oC under N2 pyrolysis, due to the decomposition of unstable thiols and sulfoxides, thiophenes. It slightly increases higher than 700 oC due to new thiophenes have been generated by the polymerization of sulfur-containing radicals with carbon in coal and the polycondensation of thiophenes.(3) Organic sulfur in semi-coke increases below 500 oC under low temperature air oxidation pyrolysis, which causes by the conversion from thiols to sulfoxides.(4) With temperature rising, organic sulfur in semi-coke decreases and dramatically decreases from 600 oC to 800 oC under ethanol steam pyrolysis, due to more radicals have been generated by the decomposition of ethanol. Oxygen-containing radicals weaken the C-S bond and H radical react with S radical to generate H2 S.(5) Organic sulfur in semi-coke obtained under steam pyrolysis is lower than under N2 due to the gasification of carbon skeleton. With temperature rising, unstable organic sulfur decreases, and thiophenes decrease below 700 oC and increase higher than 700 oC. The number of aromatic rings of thiophenes increases. According to pyrolysis transformation of organic sulfur in Vitrinite, thiophenes with aromatic rings more than 3 are dominant, as well as thiophene and benzothiophene are low.The total weight loss of Vitrinite increases during pyrolysis, sulfur-containing gases in pyrolysis gas increase, as well as the contents of thiophenes in coal tar increase by the pretreatment of low temperature solvents, especially for propylene glycol refined coal tar, the content of thiophenes is up to 15.71%. The types of thiophenes in coal tar are mainly thiophene, benzothiophene, dibenzothiophene, naphthothiophene, phenanthrothiophene and benzonaphthothiophene. Dibenzothiophene and benzonaphthothiophene are relatively concentrated. The substituent of thiophenes is methyl and its numbers are 1 or 2.Based on the analysis of the occurrence, distribution and pyrolysis transformation of organic sulfur in gas, liquid and solid products during pyrolysis of high sulfur coal from Weibei coalfield, thiophenes with 1 to 6 aromatic rings are existed in high sulfur coal from Weibei coalfield. Dibenzo[b]thiophene and benzo[b]naphtha-[2,3-d]thiophene are dominant, and also a small amount of their isomers are existed.The parameters of coal molecular model and the occurrence and distribution of C, H, N, O and S were obtained by ultimate analysis, FTIR, XPS of Vitrinite. The molecular model of Permo-Carboniferous high sulfur coal form Weibei coalfield was built by Chem Draw /Chem3 D. The molecular structure and conformation analysis of model were simulated by molecular mechanics and molecular dynamics. The final molecular formula is C644H368N8O15S7, molecular mass is 8682, and aromaticity is 0.789. Organic sulfur in molecular model exists in the form of thiophenes with 3 to 4 rings.The occurrence and pyrolysis transformation of organic sulfur in coal will provide guiding significance for the removal of organic sulfur and the clean and efficient utilization of high sulfur coal. The molecular model construction of high sulfur coal form Weibei coalfield will be reference for similar applying.