Sequential Thermal Dissolution Of Xiaolongtan Lignite

Xiaolongtan lignite(XL) was selected as the research object in this study. XL was thermally dissolved at 320 oC in cyclohexane, benzene, methanol, ethanol and isopropanol, respectively, to obtain soluble portions(SPs), XL and XL residues(XLRs), which were characterized by various modern analysis instruments. According to the dissolve rules and structural features of SPs and the differences between XL and XLRs, the chemical reactions which might occur during the thermal dissolution process were speculated and the differences of thermal dissolution effects of these reagents were studied. Besides, in the same experimental conditions, 0.1 mmol anthracene was added as the capture agent of active hydrogen to study the generating and transfer pathways of active hydrogen during thermal dissolution process, which provides a scientific basis for optimizing coal direct liquefaction process.Compared with XL, the composition and properties of XLRs are quite different. The C contents of XLRs increase, while the H contents decrease slightly and O contents decrease sharply. Through thermal dissolution process, the pyrolysis temperatures of XLRs are higher than that of XL, and the species of pyrolysis products of XLRs are far less than XL, indicating that the small molecular organic compounds were dissolved out thoroughly.The yields of SPs in cyclohexane and benzene(SPC and SPB) are comparatively low, due to the stable structures of cyclohexane and benzene, which can not react with the small molecular organic compounds in XL. The thermal dissolutions of cyclohexane and benzene are physical dissolution. Therefore, SPC and SPB could reflect the composition and structural features of XL factually. The O atom in methanol, ethanol and isopropanol has nucleophilicity and could attack oxygen-containing bridged bonds, leading to alcoholysis and alkylation reaction, so the yields of SPs in methanol, ethanol and isopropanol(SPM, SPE and SPI) are higher than those of SPC and SPB. The nucleophilicity of O atom in ethanol is stronger than that in methanol, and the steric hindrance of ethanol is smaller than that of isopropanol, so the yield of SPE is the highest and up to 52.58%.349 compounds were detected with GC/MS in all the SPs. They could be classified to arenes, alkanes, alkenes, phenols, esters, ketones, ethers, nitrogen-containing organic compounds(NCOCs), sulfur-containing organic compounds and other organic compounds, in which arenes, alkanes and phenols are the most abundant, and some esters only appear in SPM, SPE and SPI.According to FT-ICR MS analysis, in the positive-ion mode, the molecular mass(MM) of SPC is concentrated in 600-700 u, while the MM of other SPs is concentrated in 300-600 u. In the negative-ion mode, the MM of SPI ranges from 800 u to 1000 u with the relative content of over 50%. The species of SPI are far more than that of other SPs. The MM of other SPs is concentrated in 200-400 u. The double bond equivalent(DBE) of NCOCs is concentrated in 4-20, and carbon numbers(CN) is concentrated in 10-40. In the negative-ion mode, the DBE of SPs is concentrated in 1-9. Noteworthily, the relative content of organic compounds with DBE=1 is the highest.The blank tests indicate cyclohexane and benzene are inert solvents, and hydrogen transfer reaction occour in thermal dissolution in methanol, ethanol and isopropanol. The active hydrogen is mainly generated by pyrolysis reaction in thermal dissolution in cyclohexane and benzene. The relative content of 9,10-dihydroanthracene decreased with the experimental times increase, indicating the content of active hydrogen in XL decreases with the experimental times increase. The relative content of 9,10-dihydroanthracene was higher and increased in the order: SPM < SPE < SPI. Alcoholysis reaction during thermal dissolution in methanol, ethanol and isopropanol produces a large amount of active hydrogen, which can react with anthracene, leading to hydrogen transfer reaction.