Composition of soluble organic matter and its causes of No. 11 coal from Sangshuping Mine, Shaanxi Province

Eight samples of No.11 coal in Sangshuping Mine were used for organic geochemical study, Gas chromatography-mass spectrometry (GC-MS) and X-ray fluorescence spectrometry (XRF) were combined with the test results of proximate analysis, sulfur forms and random vitrinite reflectance, the organic matter sources and coal-forming environment of No.11 coal from the Sangshuping mine, Shaanxi Province were comprehensively analyzed. The results indicate that the total sulfur content of the coal sample is 3.29%, and the mean vitrinite oil-leaching reflectance is 2.01%, which is high-sulfur lean coal. The phase parameters of major elements indicate that the coal samples are mainly formed in reductive sedimentary environment. There are two types of carbon number distribution of n-alkanes in saturated hydrocarbon: the front peak type main carbon peak is C₁₆, and the back peak type is main carbon C₂₆; Combined with the distribution characteristics of ∑C₂₂⁻/∑C₂₃⁺、(C₂₁+C₂₂)/(C₂₈+C₂₉)、Pr/nC₁₇、Ph/nC₁₈ indicated that the parent material of organic matter come from aquatic organisms and higher plants. The OEP value was between 0.49 to 1.05,with an average value of 0.84, indicating that No.11 coal of Sangshuping has undergone different degrees of biodegradation. In the analysis of saturated hydrocarbon steroidal terpanes, the ratio of w(T_s)/w(T_m) is between 0.83-1.21 and w(T_s)/w(T_s)+w(T_m) is between 0.45-0.55, indicating that the thermal evolution degree of coal sample is high. In the analysis of aromatic compounds, the methyl rearrangement of trimethylnaphthalene and the distribution characteristics of methyl phenanthrene index are correlated with the high thermal evolution degree of coal samples. The aromatic hydrocarbons were dominated by naphthalene, phenanthrene and biphenyl series, and the sulfur-containing compounds in the trifluorene series (oxygen-fluorene, sulfur-fluorene, fluorene) are obviously higher than the oxygen-containing compounds, which also indicates the coal-forming environment under higher salinity partial reduction conditions.