CATALYTIC EFFECTS OF FE- AND CA-BASED ADDITIVES ON GAS EVOLUTION DURING PYROLYSIS OF DACHENGZI OIL SHALE OF CHINA

The pyrolysis of Dachengzi oil shale (OS), Huadian City, China, was carried out in a stainless-steel cylindrical retort at 520 degrees C both in the absence and presence of catalyst under argon atmosphere to evaluate the catalytic effects of Fe2O3 and CaCO3 additives on the products yield and characteristics of non-condensable gases. The results showed that the catalyst significantly affected the reactivity of OS kerogen pyrolysis. The shale oil yield increased after adding the catalyst, especially Fe2O3, but the shale char yield decreased in the presence of the catalyst. The non-condensable gases yield rose in the CaCO3-catalysed pyrolysis and declined upon the Fe2O3-catalysed process, indicating that CaCO3 had a more pronounced catalytic effect on the secondary reactions of oil vapors. In addition, the gaseous products obtained both with and without the catalyst had a higher volume content of CO2, CH4 and H-2, and a lower volume content of CO and C-2-C-4 hydrocarbons. The peak concentrations of CO2 and H-2 increased in the presence of the catalyst, especially Fe2O3, while that of CO enhanced with addition of CaCO3 as a catalyst. H-2 was generated at higher temperature compared to CO2 and CO. Furthermore, Fe2O3 and CaCO3 exhibited different effects on the evolution of C-1-C-4 hydrocarbons. COS and H2S evolved almost simultaneously, the amount of H2S released being higher than that of COS. The peak concentrations of the said gases decreased with adding the catalyst, especially Fe2O3. The non-condensable gases produced both before and after catalysis mainly consisted of CO2 and CH4, and some minor gases, in terms of mass distribution. The mass contents of ethane, butane, CO2 and H-2 increased after the use of the catalyst, while those of butane, H2S and COS decreased. Moreover, adding Fe2O3 and CaCO3 resulted in the decline in the ethene/ethane and propene/propane ratios, respectively, suggesting that different catalysts possibly led to different changes in the physical structure of oil shale and then caused the secondary reactions of pyrolysis products to proceed to different extents. CaCO3 was more efficient than Fe2O3 in producing non-condensable gases of high heating value.