[A Quick Quantitative Analysis for Group Composition of Coal Liquefaction Oil by Ultraviolet Spectroscopy]

Gas chromatography is now the primary analysis method for the coal liquefaction oil. However, a simple and rapid quantification/qualification of the coal liquefaction oil can hardly be realized, because the coal liquefaction oil is in a heterogeneous state with a long boiling range. The aim of this study was to establish a rapid and accurate method for the quantification of phenolic compounds, aromatics and aliphatic hydrocarbons in coal liquefaction oil. A representative composition of coal liquefaction light oil, i.e., the distillate fractions of the boiling point range 180-200 degrees C, was chosen as the investigated object. The characteristic absorption peaks of the samples in the UV spectra (200-400 nm) were examined, using three kinds of solvents, cyclohexane, ethanol, 50 Wt% NaOH/ethanol mixture. Among them, the mixture solvent provided the best performance, where the aromatics interfered minimally with the quantification of phenolic compounds by avoiding the peak overlapping problem. By comparison of the UV absorption standard curves between the standard compounds (phenol, m-cresol, p-cresol and o-cresol) and the phenolic mixtures in coal liquefaction oil, m-cresol was selected for the quantification of phenolic compounds in coal liquefaction oil. The content of phenolic compounds was determined to be 32.14% according to the calibration curve of m-cresol at 290 nm, and this result is largely consistent with that determined by weighing after separation. Based on UV and GC analysis of the dephenolized oil, the standard curve of tetrahydronaphthalene at 266 nm was used for the quantification of aromatic hydrocarbons in coal liquefaction oil. The contents of aromatic and aliphatic hydrocarbons were determined to be 44.91% and 22.95%, respectively. To verify the accuracy of the method, recovery of added standards in the oil samples was determined and found to be 104.3%-110.75% and 84.3%-91.75% for phenolic compounds and aromatics, respectively. These results indicate that the contents of phenolic compounds and aromatics can be determined simultaneously with the UV standard curves of m-cresol and tetrahydronaphthalene, respectively, and the aliphatic compounds can be determined by difference.