Structural Analysis of Pyrolysis Tar from a Mongolian Brown Coal using GC/MS

Abstract

This study aims to structural analyses of the tar, one of the pyrolysis products, for the three different Mongolian brown coals (Baganuur, Shivee-Ovoo and Khuut). This pyrolysis coal tar (coal tar) were analysed by gas chromatography/mass spectrometer (GC/MS), at temperatures from 400 to 900°C in a horizontal fixed-bed reactor. From the results, we are to reveal the differences among coal samples by applying chemometrics of principal component analysis (PCA). The coal tar mainly contained long-chain aliphatic compounds, such as n-alkanes, n-alkenes and aliphatic ketone, and polycyclic aromatic hydrocarbons (PAHs). The peak intensity of the aliphatics in each coal tar increased with the increase of temperatures up to around 600°C, and decreased rapidly above 700°C, while the concentration of total PAHs in tar exponentially increases exceeds 700°C except for Baganuur coal. The total PAHs concentrations of coal tar of Shivee-Ovoo and Khuut at 900°C were 57.1 and 34.7 mg/g, respectively. At 900°C, the PAHs concentration of Baganuur coal tar had the lowest value of 8.85 mg/g among them. This is assumed to be because the O/C value was the lowest compared to the other two coal types, which made it difficult for the thermal decomposition to proceed. PCA analysis showed that there is a negative correlation between the aliphatic compound amounts and the PAHs concentrations at pyrolysis temperature above 800°C, implying that aliphatic compounds are converted to PAHs by the pyrolysis. It also demonstrated differences in tar components from pyrolysis, suggesting that this may be a useful indicator for evaluating lignite quality.