Effect Of Minerals On The Pyrolysis Behavior Of Oil Shale

The effect of inherent minerals and additional pyrite on Longkou oil shale pyrolysis was investigated in a.fixed-bed reactor. The interaction between pyrite and oil shale during pyrolysis was studied, and the composition of oil was obtained by GC analysis.The mineral composition of oil shale was determined by washing the raw oil shale with HCl, HF and HNO3solutions in sequence. The results by XRD and FT-IR analyses indicate that the major minerals in oil shale are calcite, quartz and pyrite. TG-MS results show that inherent minerals have no effect on the release of CH4, while the release of H2S and SO2at510-550℃is related with the decomposition of pyrite. The oil and gas yields increase after the removal of calcite and quartz, which can be explained by the driving force for heat transfer since more heat was transferred towards the inside of the oil shale particles. Quartz inhibits the pyrolysis of oil shale, thus decreasing the oil yield. Inherent pyrite accelerates the pyrolysis of oil shale and has positive effect on the formation of oil, but has negative effect on gas yield. The increase of the oil yield accelerated by pyrite is related with the sulfur in pyrite.The effect of additional pyrite on oil shale pyrolysis was also investigated. The pyrolysis temperature, pyrite content and the interaction between oil shale and pyrite were examined. The results show that additional pyrite can promote the conversion of oil shale. Higher oil yield is obtained at500℃with the addition of8wt.%pyrite, and the oil and gas yields are41.7wt.%and14.4wt.%(all in dry and ash-free basis) respectively under this condition, increasing by4.5wt.%and3.3wt.%compared to those from pyrolysis of raw oil shale. However, pyrite has slightly effect on oil yield at the temperature of above500℃, but can enhance the gas yield, which may be related to the complete decomposition of pyrite and the predominant influence of temperature. It is thought that additional pyrite interacts with oil shale at high temperatures, which promotes the reduction of pyrite decomposition temperature and increases volatiles of oil shale pyrolysis. The effect of pyrite on oil shale pyrolysis is indirectly via sulfur produced during the conversion of pyrite to pyrrhotite.The FT-IR spectra indicate that the organic matters in oil shale are mainly composed of aliphatics, and GC results show the major compounds in oil are aliphatics, suggesting that the evolution of volatiles in oil shale pyrolysis is mostly produced from aliphatics in kerogen. Pyrite can promote the increase of the alkane compounds in oil by inhibiting the aromatization, condensation and cyclization reactions.