In-situ infrared and kinetic characteristics analysis on pyrolysis of tar-rich coal and macerals

Abstract

Tar-rich coal is a high-quality coal-based oil and gas resource, pyrolysis of tar-rich coal is crucial to alleviate the world energy crisis and pressure on oil and gas resources. This paper analyzed pyrolysis characteristics of tar-rich coal and macerals and evolution mechanism of main functional groups by thermogravimetric analyzer and Fourier in-situ infrared spectrometer. The thermogravimetry results showed that when the heating rate was 10 ∼ 40 °C·min−1, inertinite's volatile yield was 25.21 %∼27.27 %, significantly lower than that of tar-rich coal and vitrinite, the average activation energy required for tar-rich coal pyrolysis was 185.63 kJ·mol−1, lower than 360.56 kJ·mol−1 of vitrinite, indicating that inertinite had more macromolecular structure and was not easy to be pyrolyzed and volatilized, volatile was more likely to be generated and liberated in tar-rich coal. The results of in-situ infrared analysis showed that coal mainly contained out-of-plane aromatic CH, C-O-C, aliphatic-CH3, –CH2, –CH, C = O, –OH and other major functional group structures. Vitrinite contained more aliphatic-CH2, –CH3, –CH and other aliphatic hydrocarbon structures. Tar-rich coal and vitrinite contained more hydrogen-rich structures such as aliphatic CH and active groups such as free-OH, inertinite contained more ether bonds, C = O and hydrogen bonds, almost no aliphatic hydrocarbons and oxygen-containing active groups, and had stronger structural stability. The results of structural parameter analysis showed that under the same conditions, for vitrinite, the aliphatic chain length and hydrocarbon potential were 1.14 and 2.37, greater than those of tar-rich coal and inertinite. The aromatic degree and aromatic condensation degree were 0.39 and 0.48, lower than those of tar-rich coal and inertinite. The pyrolysis characteristic indexes of tar-rich coal and vitrinite were 90.04 (10-8 %·min−1·°C−3) and 93.64 (10-8%·min−1·°C−3), significantly higher than 30.90 (10-8 %·min−1·°C−3) of inertinite. The above results showed that vitrinite had more aliphatic long chains and alkyl side chain, tar-rich coal and vitrinite had better pyrolysis reaction performance and strong volatilization ability, inertinite had less hydrogen-rich structure, poor pyrolysis reaction performance and stronger stability. Based on the discussion of the relationship between functional groups distribution and reaction performance of tar-rich coal and macerals, variation range of structural parameters with functional groups distribution was obtained.